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Introduction 48
Building design/construction 48
Calculation of heating loads 48
Heat transfer theory 49
Heat loss calculations and 'U' values 49
Types of heating system 51
Heat sources 52
Alternative heat sources 53
Combustion air 54
Boiler sizing 54
Heater emitter selection 54
Piping system design and sizing 55
Pipe layout and sizing 56
Domestic hot water - types of system 57
Piping installation 59
Controls 59
Underfloor heating systems 60
Design considerations 62
Design criteria 63

47
 Heating Plumbing Engineering Services Design Guide

a. Increase insulation levels within roof Insulation

voids to 200mm thickness.
b. Ensure window and door openings Existing levels of insulation and draught
Modern central heating systems have to are adequately draught proofed and proofing (if any). Adequate, or do they
be capable of meeting the user’s un-used chimneys closed off. Ensure need improving?
expectations of providing an adequate that there is still adequate ventilation
level of heating in an efficient manner. An to prevent odour/moisture build-up
efficient system is one that provides the and if closing off a chimney, leave just Boiler
correct amount of heat at the correct sufficient ventilation to protect the Preferred type of boiler - combined
place at the correct time, burning the fuel internal fabric of the chimney from primary storage unit (cpsu), fuel (location
used in the most efficient way possible deterioration. of nearest supply - storage), floor/wall
Licensed copy from CIS: southbank, Southbank University, 27/05/2013, Uncontrolled Copy.

and switches off the boiler when the mounted, conventional/balancedflue.

demand is satisfied. Achieving this C. Insulate flat roofs by the application
of insulation on top of the existing Possible locations (including any ancillary
objective will require correct system equipment), taking into account possible
design, avoiding inefficient oversizing of roof waterproofing membrane.
pipe routes, flue requirements -
plant, and the use of appropriate d. Insulate external walls. There are conventional/ balanced and fan assisted
controls. However, the more sophisti- several types of material used for balanced flues - condensate drainage
cated the system the greater the potential cavity wall insulation and solid walls provision (condensing boilers).
for problems and so good design often can be insulated internally or
requires a compromise between what is externally, although the choice of
the ideal solution and what is advisable method needs careful evaluation. F & E cistern
in terms of operational and maintenance
considerations.The recommendations in e. Consider replacing window frames in Position for F & E cistern - routes for
this Guide relate primarily to domestic poor condition with sealed double- cold feed and safety vent pipes and
and small commercial installations with glazed units, possibly using low location of rising main for float valve
boiler input ratings not exceeding 60kW, emissivity glass where there are supply. Alternatively, space for sealed
although much of the content will also be potential solar radiation gains. It is not
system expansion vessel and
applicable to larger systems. For a cost effective to install double-glazing pressurisation set.
greater understanding of efficiency simply to reduce energy
requirements reference should be made consumption.
to the Resource efficient design section.
Source of electrical supply and position
for controller, thermostats, etc. Adequacy
of existing earthing. Position of socket
Building design/ With an existing building, the pre-
requisite of a successful heating system
outlets, etc. Equipmentllighting loads?

design is the carrying out of a detailed

survey, which should provide the Pipe routes
necessary information for the heat loss
New buildings calculations and for the system Possible/acceptable pipe routes
preliminary design. The following details (concealed/exposed?) including drops for
In designing a new building, there are the various aspects that should be between floor connections.
many considerations which will have a covered by the survey and could form the
direct impact on the design of the basis of a check list.
heating system and its operational Heaters
efficiency, such as fabric selection,
constructional details, orientation, Client preference for type of system/
internal layout, nature of occupancy/use,
Occupancy components and reasons?
domestic hot water loading and provision Details of pattern of occupancy -
for plant installation, access & preferred temperatures.
maintenance.
To maximise the desirable influences and
ameliorate those that have an Building layout Calculation of
undesirable effect on the building
operational efficiency, the heating
Orientation, positions of windows, doors
and major items of furniture - party and
heating loads
engineer should, ideally, have an early external walls (load bearing ?). For each
involvement in the design of the building. room, ceiling height, floor dimensions, The heating load of a building is
skirting and cill height, window size and dependant upon fabric heat loss and
type of glazing - wall and roof ventilation heat loss due to air infiltration.
Existing buildings construction. Floor construction - if In commercial installations there may be
suspended, direction and depth of floor offsetting internal gains from people,
With existing buildings, insulation levels equipment, lighting, etc., but this is only
may be far from satisfactory and the joists and position of any steel beams - if
solid, type of construction (e.g. reinforced taken into account if it is continuous
design engineer should determine what during the pre-heat and heating periods.
cost effective insulation measures can be concrete, beam and pot). Details of any
natural ventilation shafts (e.g. open Such gains are normally ignored in
taken in order to reduce heat losses and domestic situations, as are solar
therefore the size and capital cost of the chimneys) and/or ventilation fans.
Possible locations for any envisaged radiation gains.
installed heating system, such as :
equipment, taking access for installation/
maintenance into consideration.

48
 Plumbing Engineering Services Design Guide Heating

Emissivity Factor (E) the Kelvin scale, but they are not the
Heat transfer theory Emissivity Factor (E) is the ratio of heat
same for actual temperatures: 0°K is
-272"C!
emitted by a unit surface area of a
Heat is a form of energy and its transfer material to that emitted by a unit area of 'U' value
occurs through three basic processes - a perfect black surface at the same The 'U' value is a measurement of the
conduction and convection, which both temperature - most building materials rate of heat flow across one square
require a medium through which the heat have an emissivity of 0.9 - 0.95 - metre of the element of the structure in
is transmitted, and radiation which occurs shinyheflective surfaces have a low consideration, with a 1"C temperature
from one body to another and does not emissivity of around 0.05. differential across that element and
require a medium. All three processes assuming steady state heat transfer
require a temperature difference for heat conditions. It can be written as:
Licensed copy from CIS: southbank, Southbank University, 27/05/2013, Uncontrolled Copy.

transfer to occur.
I
Conduction is a process whereby heat is U=
transferred without an appreciable RSi+ L,-+-
t2 + . . . R, + R,
movement of the molecules within the h2
medium concerned. For a solid material, calculations h,
the rate of heat transfer is directly
proportional to the area (A) across which
and I UI values where RSiand R,, are the internal and
external surface resistances; R, is the
resistance of any airspace; t , , t2, etc. are
the heat is being conducted and the the thicknesses of each of the structural
temperature gradient (t, - t2). It is Calculation of the rate of heat loss (a) elements (in metres, not millimetres) and
inversely proportional to the thickness of from a building is straightforward. It h,, &, etc. are the conductivities of the
the material (I). involves calculating the area (A) of each respective materials.
constructional element of the building
The lower the 'U' value of a material, the
through which heat is going to flow, such
better its thermal insulating properties -
as the wall, roof, floor and windows -
Q = heat transfer rate in Watts do not confuse with electrical insulation.
different areas of the same element may
A = area in m2 be of different construction and so the Tabulated 'U' values for specific
heat loss across each area must be constructions, or Thermal Conductivities
t = thickness in metres separately calculated.The area is then for various materials can be found in a
t = temperature in "C (or Kelvin) multiplied by the temperature differential variety of sources including the CIBSE.
across each element (t, - t2) and the 'U' Guide, Building Regulations Section L1,
h = thermal conductivity in-
W value. Insulation Industry Handbook,
m"C HVCNCIBSEIloP Domestic Heating
Q = UA(t, - t2), Design guide, manufacturers' literature
The thermal conductivity for a material The constructional elements considered and many other sources.
can vary, depending upon its mean are usually those which form the
temperature, moisture content and boundary between the inside and outside
density. For liquids and gases, it will also of the building, with the temperature Building Regulations
depend upon pressure. Good insulators difference being that between the inside
have low thermal conductivity. and outside design temperatures. In The Building Regulations (reference
some cases it may also be necessary to Approved Documents L1 and L2), that
The reciprocal of the conductivity gives
calculate the heat loss from one internal apply to replacement and new systems
the resistivity of the material
space to another, if they are at stipulate that 'reasonable provision shall
Dividing the conductivity of a specific significantly different temperatures (say be made for the conservation of fuel and
material by its thickness gives its thermal 3°C or more) - an example would be a power in buildings. For domestic
conductance and its reciprocal gives the bathroom at 22°C with an adjacent dwelling designs, as covered by L1, this
thermal resistance W. bedroom or hallway at 18°C. requires:
h -- thermal conductance -
- Alternatively, the adjacent area may be Limiting heat loss through the building
t its reciprocal unheated, such as a garage beneath a fabric: from hot water pipes and hot
bedroom, and so the likely temperature air ducts and from hot water vessels
L of the unheated space has to be
- = thermal resistance 'R' Providing space heating and hot
a. determined. This can be calculated, but
in most instances it is sufficient to make water systems which are energy
Convection a reasoned 'guess'. The temperature in efficient
an unheated garage within the envelope Providing lighting systems with lamps
Convection is a process whereby heat is of a house is likely to be some 5°C to
transferred as a result of the actual and controls that use energy
8°C above outside design temperature - efficiently.
movement of the fluid molecules within if it has an exposed roof and walls, then
the medium. 2°C may be more appropriate. For buildings other than dwellings, as
covered by L2, in addition to the above,
Radiation Consideration must also be given to the there are requirements relating to the
additional heating load resulting from air provision of mechanical ventilation, air
Radiation is the transfer of heat between infiltration. conditioning, lighting systems and more.
two bodies at different temperatures due
to electromagnetic radiation waves It is worth noting that whilst temperatures
passing through the intervening space are usually quoted in degrees Centigrade
and the rate of radiant heat transfer ("C), temperature differences are often
depends upon their shape, orientation quoted in degrees Kelvin (OK). One
and their relative emissivities and degree difference in the Centigrade scale
absorptivities. is the same as one degree difference in

49
 ~~ ~~ ~ ~~

Heating Plumbing Engineering Services Design Guide

885449. In domestic situations it is

'U' value calculation necessary to consider whether designing
for adjacent areas to be at considerably
varying temperatures is reasonable. In
Thermal Conductivity (h) practice, communicating doors are
Plaster 0.16 W/mK frequently left open, and so to calculate
Celcon Solar 0.11 ,,
Rockwool 0.035 ,, on the basis of one room being at 21"C
Brick (outer) 0.84 ,, and an adjacent communicating room
Thermalite 0.19 ,, being at 16°C may be unrealistic -with
Wood 0.14 ,, the door open the adjacent room
Fibreglass 0.04 ,,
Polystyrene 0.035 ,, temperature is likely to stabilise at
Licensed copy from CIS: southbank, Southbank University, 27/05/2013, Uncontrolled Copy.

Concrete Block 0.57 ,, around 18"C-I9"C.

The environmental temperature is
weighted in favour of the mean surface
temperature and is generally used in
13mm Plaster dynamic heat transfer calculations,
where the heat exchange between the
150mm Celcon surfaces and the enclosed space is
50mm Rockwool considered.

50mm Airspace
Air change rates
In a building of normal construction there
will be air infiltration occurring at various
Resistances Walls Roofs
Inner surface R,, 0.12 rn2Khv 0.10m2Khv points through the building structure (e.g.
Outer surface R, 0.06 ,, 0.04 ,, window and door frames) and this has to
Air space R, 0.18 ,, 0.18 ,, be allowed for in the heat loss
calculations. Actual infiltration rates may
0.013 0.15 0.050 0.18 0.105 o,06= 3,36
R=O.12- t t- t +-- +

vary considerably, depending upon the

0.16 0.11 0.035 0.84 age of the building, level of insulation and
exposure. Empirical values of air change
Therefore U = = 0.298 W/m2"C rates for various situations are given in
3.36
the HVCNCIBSE/loP Domestic Heating
Figure 1 'U' value calculation Guide. The procedure for calculation is
straightforward -the volume of the room
is calculated (V) and multiplied by the air
All new housing and conversions must temperature and variations in structural change rate (N), the specific heat of air
have an energy rating, calculated in thickness and/or density. If considering (0.33 W/m3"C) and the inside/outside
accordance with the Government's the dynamic performance of a structure temperature difference.
Standard Assessment Procedure (SAP) (normally in relation to heat gain
and which has to be declared for Building calculations) then it is necessary to take Modern buildings are increasingly being
Regulations approval. into account three factors in addition to constructed with higher standards of
the 'U' value: Surface Factor (F), insulation and draught proofing and as a
For domestic dwellings, the Building result, the air change rate can drop to
Admittance Factor (Y-value) and
Regulations (Section L1) details three considerably less than that required to
Decrement Factor (f).
methods of demonstrating that the adequately control moisture and odour
Regulations have been complied with in build-up. Under these circumstances,
respect to the building heat loss -the some form of mechanical extract and/or
Elemental method; Target U-value Design temperatures supply ventilation should be considered.
method and Carbon index method. Full The temperature sensed by a body
details of the methods of calculation are The provision of mechanical extract from
depends upon the surrounding air
given in Section L1, together with domestic kitchens, bathkhower rooms
temperature and the mean radiant
example calculations. and some toilets is now mandatory under
temperature (MRT) of all the surrounding
the Building Regulations (reference
For other buildings, the Building surfaces - a similar level of comfort can
Approved Document F) and literature
Regulations (Section L2) details three be achieved with a high air temperature
from domestic fan manufacturers gives
methods of demonstrating that the and low MRT, or with a lower air
guidance on requirements.
Regulations have been complied with in temperature and higher MRT.
respect to the building heat loss - the In commercial properties it is also
To only consider air temperature when
Elemental method; a Whole building necessary to take into account the
carrying out heat loss calculations may
method and Carbon emissions number of occupants and ensure that an
give unsatisfactory results, so either
calculation method. adequate supply of fresh air is available.
'environmental' or 'dry resultant'
The recommended fresh air supply rate
The calculated heat flow rate based on temperatures are normally used, which
in offices, where there is minimal or no
the 'U' value is for steady-state conditions take into account both air and mean
smoking, is 5-8 I/s per person.
and for the majority of situations, will give surface temperatures.
Installation of a fresh air ventilation
a perfectly adequate indication of the For normal situations, where air system may be required. Alternatively,
mean rate of heat loss from the structure. movement is IOW,the dry resultant the use of through-wall heat recovery
However, in reality the heat flow rate will temperature is used, and recommended ventilator units, could be considered.
vary in response to fluctuations in values for various situations are given in
internal temperature, external Wherever mechanical ventilation is used,
the CIBSE Guide. NHBC Guide and

50
 Plumbing Engineering Services Design Guide Heating

its effect on the heat loss must be located at least 1m above the top of the
considered and allowed for. Types of heating highest heater or section of circulating
pipework and connected to the system
by a cold feed and expansion pipe. The
Heat loss calculations purpose of the cistern is to keep the
system topped up with water and to
Accurate heat loss calculation is Heating systems generally fall into one of
accept the increase in system water
essential for efficient operation. Using four categories - wet, dry (warm air),
volume as it heats up. The F & E cistern
‘rule of thumb’ methods or a simple disc radiant and electric storage and a
capacity to waterline should be not less
calculator will invariably result in system building could have a combination of any
than 18 litres plus 1/20th of the water
oversizing, with increased capital and of these.
content of the system, and the cold feed
running costs. A number of radiator
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pipe should ideally be sized to contain

manufacturers now offer free of charge the expansion volume of the system
heat loss programmes which can be run Wet system (usually means 22mm minimum size)
on a PC, but it is essential to understand and connected to the circulating part of
In a wet system, the heat source is
the ‘manual’ method of calculation, if only the system with an anti-gravity loop.
invariably a boiler burning gas, (natural
to do ‘spot checks’. Terminating over the F & E cistern is the
or LPG), oil or solid fuel, or an electric I

Examples of design calculation storage boiler. Water is heated in the safety open vent pipe which must have
worksheets can be found in the boiler and then pumped via a piping an unobstructed path back to the heat
HVCA/CIBSE/loP Domestic Heating distribution system to the heat emitters, generator and the function of which is to
Design Guide. where the heat is given out. The cooled vent any air liberated from the heat
water then returns to the boiler for re- generator and provide a relief for any
It must be remembered that the steam produced as a result of a boiler
heating. Wet systems are adaptable,
calculation of heat losses is not an ‘exact’ thermostat failure.
extendable (subject to capacity) and fully
science, since there are many variables
controllable and in domestic situations With an open vented system the
involved, such as variations in standard
they usually also provide domestic hot positioning of the pump in relation to the
of construction and in the constructional
water heating via an indirect cylinder. safety open vent and cold feed
materials and their moisture content (e.g.
bricks) Heat emitters are usually radiators or connections is very important if problems
natural or fan assisted convectors, or of pumping over, open vent aeration or
The heat losses are calculated a room at suction leaks are to be avoided. As a
underfloor heating may be installed, in
a time and for rooms over 5m height a general rule, position the pump on the
which hot water is circulated through a
percentage addition is made to the flow after the safety open vent
network of underfloor pipes. This gives a
calculated heat loss, dependant upon the connection. In low head situations a
very even level of heating, with no
type of system (convectivehadiant). combined safety open vent and cold feed
heaters to occupy wall space and the
The calculated heat loss for each room maintenance requirement and potential is permitted, provided the boiler has a
forms the basis for the sizing of the heat leakage risk is reduced. Underfloor high limit safety thermostat. Always fit a
emitters and the total of all the calculated heating can be installed within new floors diaphragm type safety valve if there is a
heat losses forms the basis for sizing of and over all types of existing floors and risk of freezing.
the primary heat source. However, whilst offers proven energy consumption A sealed system has no F & E cistern,
the individual room heat losses all reductions in the order of 15-20%, cold feed or safety open vent pipe. The
include for the effect of air infiltration, the compared to normal wet heating system is usually filled direct from the
rooms into which air will be infiltrating at systems. The installation is usually mains via a filling loop incorporating a
any given time will depend upon the wind carried out by specialist contractors. double check valve, isolating valve and,
direction. Air will infiltrate into rooms on ideally, a pressure reducing valve, to a
Wet systems can be either open vented
the windward side, pass through the pressure of approximately 0.5 bar above
or sealed. With an open vented system a
building and exit the building from the the static head from the fill point to the
feed and expansion (F & E) cistern is
rooms on the leeward side, thus the air highest point in the system.
infiltrating into the leeward side rooms,
will have already been heated by its Figure 2 Typical open vented system
passage through the rooms on the
windward side. The fact that the air Cold feed and
entering the leeward side rooms has expansion pipe
been pre-heated cannot be taken into
account in the sizing of heat emitters for t- Safety open vent pipe
the rooms - a change in wind direction
may reverse the situation - but it can be
considered when sizing the primary heat

f
source. With a property having two or
more exposed elevations and internally Safety
partitioned, the primary heat source valve
basic load can be reduced by up to 50% HWS
of the calculated ventilation heat loss. cylinder
The actual reduction allowed will be by-pass valve-
dependant upon the building I I-
configuration - if a domestic property I
has a through lounge, exposed at both I
ends to the outside, then a 50%
reduction in respect of this room would
not be appropriate, but it may well be in
respect of bedrooms at first floor.

51
 Heating Plumbing Engineering Services Design Guide

charge and output controls and some

electricity supply companies have tariffs

fA
which provide a mid-afternoon boost, as
Safety well as radio controlled charging periods.
valve
-
)e
HWS
Boiler cylinder
Heat sources
With wet heating systems the heat
Licensed copy from CIS: southbank, Southbank University, 27/05/2013, Uncontrolled Copy.

A
source is invariably a gas or oil fired
Automatic by-pass valve (if required)
boiler, although solid fuel boilers may be
found in areas without a natural gas
SlJPPlY.
W Filling loop
Expansion vessel

Figure 3 Typical sealed system Solid fuel boilers

Solid fuel boilers can be quite
To accommodate the expanded water domestic) and ducted systems may be economical, especially the ‘smokeater’
volume as the system heats up, an difficult to extend without major building type units, which can burn bituminous
expansion vessel is connected to the works. coals in smokeless zones, but usually
system, which must also be fitted with a much more expensive to operate for
Commercially, ducted systems can be
non-adjustable safety valve (diaphragm heating the domestic hot water only
zoned, possibly with individually
type) set at 3 bar. All boilers connected during the summer - use electric heating
controlled heaters for each zone and/or
to sealed systems must have high limit for summer DHW, unless large quantities
motorised zone dampers and mixing
thermostats. All gas combination boilers required. They need frequent
boxes, but in domestic situations, due to
are of the sealed type, with the maintenance, plus fuel storage facilities
cost limitations, they only offer a limited
expansion vessel, safety valve and high and, since the heat cannot be turned on
degree of control and separate provision
limit thermostat all built into the unit and and off in the same way as with gas or
has to be made for domestic hot water
a number of ordinary boilers are now oil, they must have ‘heat-sink’. They are
heating.
available as ‘system boilers’ with all not suited to fully automatic control.
necessary sealed system components
built in. The suitability for use of an existing
Radiant heating chimney must be checked. Flue gas
A sealed system avoids the risk of temperatures from solid fuel boilers will
freezing of the F & E cistern and Radiant heating systems are suited to be considerably higher than with gas
associated pipework; overcomes situations with very high ceiling levels, or
boilers and flues must be capable of
problems associated with positioning of very high air change rates, with heaters withstanding these temperatures (around
the cold feed and open vent connection usually of the gas fired ‘radiant plaque’ or 1,200”C if any tar deposits catch fire) -
to the system - a particular problem with ‘tube’ type. suitable types are twin wall S/Sinsulated
low water content boilers - and Gas-fired radiant heating systems can be (some with additional ceramic lining) and
drastically reduces the corrosion highly efficient and economical, with refractory block flues. Existing chimneys
problems due to oxygenation of the running costs of between 20% and 40% must be checked for suitability for use -
system. lower than alternative types of system. can be lined with insulating refractory
With any wet heating system, the However, to realise these savings it is concrete liners of ‘cast-in-situ’ refractory
pipework requires protection from essential to correctly control the heaters liner - single skin flexible liners must not
damage/frost. (non-adjustable black bulb type be used. Consult a specialist if in doubt.
thermostat) and consideration of access
to the heaters for maintenance purposes
Dry (warm air) system must always be considered when Gas fired boilers
evaluating the economics. The potential
With a dry (warm air) system, air is savings in running costs could be Gas fired boilers, both natural gas and
heated by passing through a heater, negated by the cost of installing a tower LPG fired, are available as floor or wall
which can be directly heated (e.g. gas or to give access for maintenancehepair. mounted models with conventional or
oil fired) or indirectly heated by a heater balanced flues. Balanced flue boilers can
battery through which hot water is be located in any room, and fan assisted
circulating.The heated air is discharged, Electric storage balanced flue boilers do not have to be
either directly or via a ducting system, located on outside walls - some flues
into the areas requiring heating. Electric storage heating is possibly the can be extended by up to 30m. There are
Depending upon the application, the air cheapest to install, but lacks the inherent limitations in the siting of conventionally
having given up its heat, may pass back control flexibility of wet systems and is flued boilers, particularly in relation to
to the heater, via a ducting system or by therefore invariably less efficient, unless bathrooms, shower rooms and sleeping
natural ventilation paths, to be re-heated, used only for ‘background’ heating. They accommodation and reference must be
are suited to very well insulated made to the current Gas Safety
(Installation and Use) Regulations. There
are also restrictions on under stairs
installation of boilers, as there are in
relation to the manner and positioning of
flue terminations.

52
 Plumbing Engineering Services Design Guide Heating

For domestic and commercial boilers rising to at least 94% when fully
with atmospheric burners (flue gas condensing. Alternative heat
temperatures up to 260”C), flues can be The only major difference between a
of single wall or flexible stainless steel
condensing boiler and a fan assisted
type. To comply with the Gas Safety balanced flue boiler is that the
Regulations, one should never, generally, condensing boiler has a corrosion Three alternative primary heat sources
connect a new appliance to an existing which could be considered are: heat
resistant aluminium or stainless steel
flue liner - the liner should always be pumps, combined heat and power (CHP)
heat exchanger, with a very high heat
renewed at the same time. units and solar heating.
exchange surface area, and a
For solid fuel boilers, commercial boilers condensate collection and drain point.
with pressure jet burners and certain Installation is no more difficult than for a
Heat pump
Licensed copy from CIS: southbank, Southbank University, 27/05/2013, Uncontrolled Copy.

DFE fires, where flue gas temperatures conventional boiler, the only additional
can be up to 540°C flues must be twin requirement being a plastic drain pipe to
wall insulated or of refractory block/liner. a suitable drain connection. Do not run A heat pump operates in the same way
the condensate piping in copper, or as a domestic refrigerator, but in reverse
In commercial situations a ‘Monodraught’ - heat is removed from some
connect it to copper or lead piping, since
type flue or fan diluted flue system can ‘inexhaustible’source (e.g. outside air,
the condensate is mildly acidic and will
overcome problems of boiler location and ground water) and discharged into the
corrode copper and lead. When the
fluing. The choice of system depends on heating system, in the same way that
condensing boiler is working at its most
location and it is advisable to seek the heat is removed from the icebox and
efficient, ‘flue pluming’ is most prevalent.
manufacturers advice relating to given out at the condenser coil at the
design/installation requirements. System design is to normal parameters, back of the refrigerator cabinet.
as with a conventional boiler. Oversizing
of heat emitters is not economically
Oil fired boilers justified - 50% oversizing only improves CHP units
efficiency by 2.4%. Even without entering
Oil fired boilers are available as the condensing mode, the boiler will still CHP units are usually gas-fired and
conventional or balanced flue units, both achieve an efficiency of around 87% comprise of a gas driven internal
floor standing or wall mounted. They compared to around 77% for a modern combustion engine linked to an electrical
require the provision of an oil storage floor standing unit. With the cost of generator. A high percentage of the
tank (accessible for filling) plus boilers steadily reducing, the increased energy that would otherwise be wasted
connecting pipework to the boiler and capital cost can be quickly recovered as heat from the engine unit can be used
safety controls. For conventional flues, through reduced running costs. to power the heating system, giving an
check with boiler manufacturer for correct operational efficiency in excess of 85%.
type, as this will depend on flue gas Condensing boilers are also available for For a client with a fairly constant
temperature - aluminium/ceramic/ operation with LPG (Propane), and oil. electrical and heating demand, this can
clayware are not normally suitable. be an extremely efficient method of
See Building Regulations (Part J) and BS electrical generation.
5410 for detailed installation
Direct fired air heaters
requirements. Direct fired air heaters are available as
balanced flue gas fired room heaters; Solar heating
conventional or balanced flue gas fired Although fairly high levels of solar
Electric boilers unit heaters; oil fired conventionally flued radiation are available in the UK, even in
heaters and radiant gas heaters. There cloudy winter days, solar heating will only
Some electric boilers are similar to a are numerous variations to suit different
normal night storage heater, but provide what is generally termed a ‘low
applications and they are usually quite grade’ heat source, such as is suitable
incorporate a pump, heat exchanger and efficient, due to them being individually
pipework for connection to the central for pre-heating domestic hot water and
controlled. for heating of swimming pools.
heating distribution system. Since all the
heat is stored in one unit the distribution Note that in garages/workshops the All the above alternatives offer a variety
of the heat output is far more flexible combustion air supply to the burners of permutations and combinations, and it
than with individual storage heaters and, should be ducted from outside. is essential to obtain independent and
provided any ‘boost’ consumption at the Electric quartz radiant heaters, operating unbiased professional advice if any of
higher general tariff rate can be kept to on normal tariff rates, will be very these options are being considered.
an absolute minimum, although expensive to run, although they may be
economical to run, they can be quite the ideal solution in certain areas
bulky and heavy. requiring localised and intermittent
heating.
Condensing boilers
Conventional boiler efficiencies are
limited to around 80% to 83%, to keep
the flue gas temperatures around 220°C
and prevent condensation occurring in
the boiler or flue. The annual efficiency of
a conventional boiler will be around 67%
(with a badly controlled system this can
easily drop to well below 60%) compared
to 87% for a gas fired condensing boiler,

53
 Heating Plumbing Engineering Services Design Guide

if the appliance is located in a hot water heating margin is unnecessary.

Combustion air compartment - some appliances do not With the full boiler output switched to hot
require compartment ventilation - see water heating, the short period of loss of
With any fuel burning appliance it is vital manufacturers' requirements. space heating will not be noticed.
that there is an adequate provision for Inadequate ventilation can be lethal, Where there is a requirement for a high
combustion, cooling and flue dilution air. particularly with gas fired appliances. performance shower, the domestic hot
Full details of requirements are given in it is the installer's responsibility to water heating load will be greater and is
the Building Regulations, Gas Safety ensure that the complete gas likely to constitute the largest element of
(Installation and Use) Regulations and installation and connected appliances the total boiler heating load. Calculation of
relevant British Standards - the following are safe to use. A contractor working DHW storage capacity is therefore a
summarises the basic requirements. on a gas installation would be matter of achieving an economic balance
Licensed copy from CIS: southbank, Southbank University, 27/05/2013, Uncontrolled Copy.

committing a criminal offence if he between storage capacity and boiler re-

does not belong to a class of persons heat capacity, assuming a very high
Unflued appliances approved for the time being by the recovery cylinder with heat transfer
Health and Safety Executive. capacity >boiler output capacity.
The concentration of carbon dioxide must
not exceed 2800ppm where people may Carbon monoxide poisoning causes The following can be used to evaluate
be present and ventilation must be cherry red appearance in victims face - requirements:
provided by natural ventilation via remove victim from contaminated area
and ensure continued breathing - Specific heat of water = 4.18kJIkg"K.
permanent openings at high and low
level, or by mechanical ventilation with administer oxygen if possible. See Table 1. 1 Joule = 1 Watt for 1 sec.
airflow safety interlock.
1kW/h = 3,600kJ.
Assumed cold water supply at 10°C and
Open flued appliances mixed water temperature at 40°C.
These require permanent ventilation
Boiler sizing Useful energy stored in cylinder (H1 kJ.):
openings, either directly to outside or via H1 = storage volume (litre = kg.) x
adjacent room(s).Vents must be non- Boiler size is normally based upon the (storage temp. - 40)"C x 4.1 8kJ/kg"K.
closeable; must not incorporate any calculated heat loss plus 10% (or 15%),
screens that could be blocked by dirt, but with intermittently occupied buildings a Re-heat potential from boiler (H2kJ.):
insects, etc. and must not be positioned margin of 20425% may be more H2 = boiler output (kW) x
where they could be blocked by leaves, appropriate. If there is a great amount of
snow, etc. Vents through cavity walls pipework which is not giving off useful heat draw off duration (min.)
x 3,600kJ.
must be sleeved. Always check effect of (e.g. beneath suspended or intermediate 60 min
any extract ventilation fans on the floors or passing through unheated voids
or cupboards) an additional allowance Required energy (H3 kJ.) :
operation of the flue. To correctly size the
grilles, check the manufacturers' must be included. H3= Draw off volume (litre = kg.) x
information on the percentage of 'free In domestic situations an additional 2 or (40 - l0)"C x 4.18kJIkg"K.
area'. 3kW is often added to the boiler load for
domestic hot water heating, but with a well To meet load, H3 = H1 + H2
insulated domestic dwelling this could
Balanced flue (room sealed) represent around 30% of the total load and
appliances seriously reduce the boiler efficiency.

The design of these appliances places In the average domestic situation, with a
well controlled system and with a low
Heat emitter
the air inlet and flue discharge in the
same pressure zone. The only ventilation capacity very high recovery cylinder (at
requirement may be for cooling purposes least 20kW heat transfer capacity) and hot
water priority, the inclusion of an additional

Table 1 Types of heat emitters

~ ~~

% Saturation
of haemoglobin Symptoms The common steel panel radiators are
with carbon monoxide available with single or double panels
and with fins welded to them to further
0.005 Threshold value increase output. Radiators manufactured
0.01 I Sliaht headache in 2-3 hours from steel are also available in a variety
0.02 Mild headache, dizziness, nausea and sleepiness after 2-3 hours of shapes and designs, as are ones
0.04 Frontal headache and nausea after 1-2 hours; risk of death manufactured from aluminium, copper,
after 3 hours cast iron and even plastic, but they are
0.08 Severe headache, dizziness, convulsions after 45 minutes; more expensive than the steel panel
unconsciousnesswithin one hour; risk of death after 2-3 hours type. In certain circumstances, such as
with the elderly, infirm or young children,
0.16 Headache, dizziness and nausea within 20 minutes; unconsciousness,
risk of death after 1-2 hours
it is necessary to use low surface
temperature radiators. Radiators give
0.32 Headache, dizziness and nausea in 5-10 minutes; risk of death after approx. 80% of their output by convection
15 minutes
and 20% by radiation.
0.64 Severe svmDtoms after 1 to 2 minutes: death within 10-15 minutes
1.28 I Immediate symptoms; death within 1 to 3 minutes
There should be at least 100mm
clearance from the top of the radiator to

54
 Plumbing Engineering Services Design Guide Heating

any cill above and 150mm clearance From 1-7-97, radiator outputs have had
below for the pipework and connections.
Heat emitter sizing to comply with EN-442 which requires
A long, low radiator will give better heat To size a heater it is first of all necessary that quoted outputs are based on a
distribution than a tall one (note emission to decide on the system flow and return mean water to room temperature
penalty) and avoid locations covered by water temperatures. The 'conventional' difference of 50°C -this will result in the
furnishings. Natural convectors will give a temperatures for low pressure systems quoted outputs being reduced by around
quicker heat-up than a radiator and can are 82°C flow and 71"C return 20%. Also, testing has to be carried out,
be either wall mounted or of the skirting (18O0F/160°F) giving a mean water or quoted outputs adjusted, to equate to
or under floor type. temperature of 76.5"C for heaters on a pipe connections at top and bottom
two-pipe system, it is worth considering same ends (TBSE), thus requiring a
Fan convectors will give an even faster deduction of 8-9% from quoted outputs
basing the design on 82"C/68"C flow and
heat up and can be timehemperature
Licensed copy from CIS: southbank, Southbank University, 27/05/2013, Uncontrolled Copy.

return, in order to reduce pipe sizes and to allow for bottom opposite end
controlled. They are very compact and connections -the normal in the UK.
flow rates. There is no reason why the
can be built into fitted units, bench seats Virtually all UK radiator manufacturers
temperature differential cannot be even
or stairways; mounted at high level or still quote outputs based upon 60°C
higher, but attention must be given to any
recessed into floors. Significant savings temperature difference, the figures
can result if the operation of the fan limitations imposed by the boiler
manufacturer, and the saving in pipe shown in their catalogues being adjusted
convector can be linked to a touch from the 50°C difference at which testing
sizing may be offset by the necessary
activated timer control or occupancy is carried out.
increase in radiator size.
detector. Ensure the path of the airflow is
not obstructed by any furniture. The generally accepted method of sizing Oversizing will result in reduced system
radiators is to add 10% to the calculated efficiency due to temperature overshoot.
room heat loss and select the nearest As a general guide one heater will
Choice and positioning sized radiator. With the variations in the satisfactorily cover up to 20sq. metres.
UK Winter climate during recent years, a
of heaters 15% margin may be considered more
Heat is given out in two ways - by appropriate., especially if heating is very
radiation and by convection. With radiant intermittent. It is not normal in domestic
heating, the heat rays given out strike situations to consider internal heat gains Piping system
any surfaces in their path, such as from people and equipment, since these
people, furniture, and walls, and warm can be intermittent. design
them up -these surfaces then in turn Prior to 1-7-97, radiator outputs were
heat the surrounding air. With convective
heating the heat warms the air which in
based on BS 3528:1977 which specified and sizing
a mean water to room temperature
turn heats the surfaces it comes into difference Of 60°C and pipe Connections
contact with, as it circulates around the The most common type of heating
at top and bottom opposite ends (TBOE). distribution system is a two-pipe system,
room. Occupancy patternhse of area will With normal system flow and return
influence selection of emitter type. although there are many older single-
temperatures of 82/71"C the Outputs will pipe systems still in existence.
Comfort depends not only on the air therefore be lower. Table 2 gives the
temperature but also the average radiant correction factors with which the
temperature (Mean Radiant Temperature manufacturers figures must be multiplied Two-pipe system
- MRT) of all the surrounding surfaces - for 82/71"C flow and return temeratures
the lower this average temperature the and varying room temperatures: plus The two-pipe system will have separate
higher the air temperature must be to other correction factors for varying flow and return pipes with the flow and
give comfortable conditions. Around 20% methods of installation. return connections to each heater
of the heat output from a radiator is by connected to the respective flow and
All the correction factors below are return pipes.
radiation and the remaining 80% is given cumulative, so for a radiator with a rated
out by convection - a reasonable output of 1500W installed in an open Two-pipe systems are always pumped
balance for most domestic situations, recess in a room at 20°C with BOE and have the advantage of a positive
where the radiant level will balance the connections, its output will reduce to (pumped) flow of water through each
effect of colder external wall surfaces. 1500 x 0.9 x 0.85 x 0.90 = 1032W. heater. Copper piping systems of
With highly insulated buildings, a faster 15-28mm size are referred to as 'small-
responding convective heater may be
more appropriate.
Table 2 Correction factor for radiator outputs
If radiators are positioned on outside
walls, significant savings (5-1 OY0)can be Room temperature I Correction factor for radiator outputs
achieved by putting reflective foil faced 16 1 .oo
insulation behind the radiators.
Avoid obstructing any electrical socket 20 I 0.90
outlets. If using a fan convector, ensure 22 I 0.87
the path of the airflow is not obstructed
by any furniture. Connections top bottom same ends (TBSE) 1.04
Connections bottom opposite ends (BOE) 0.85
Radiator lenath areater than 5 x its heiaht 0.93
Radiator in oDen fronted recess I 0.90
Radiator in recess with front grille 0.80 and lower
Radiator shelf above down to 0.90
Metallic Daint finish from 0.9 to 0.8

55
 Heating Plumbing Engineering Services Design Guide

Pipe layout and

Before sizing a piping system, it is

necessary to decide upon the position of
heaters etc. in order that pipe routes can
be decided, with due regard to the
constructional details of the building and
any client requirements. If installing a
Licensed copy from CIS: southbank, Southbank University, 27/05/2013, Uncontrolled Copy.

heater in a bathroom, it is a good idea to

connect it from the outlet side of the
pump before any control valves. It will
then heat up whenever the boiler comes
on and not be dependant on the
remainder of the house requiring heating.
Figure 4 Two pipe circuit circulating temperatures “C If installing a solid fuel boiler, at least one
heater must be connected on a separate
gravity circuit from the boiler to provide a
‘heat sink‘. If most of the heaters can be
picked up on one or two pipe loops, then
it may be worth considering a single pipe
system. Heaters will have to be sized to
take account of the reducing water
temperature, and they must be

82 I 76 I connected top bottom opposite ends and

always with the return connection
downstream of the flow. Convectors and
hot water cylinders cannot be put on a
single pipe circuit. Mixing microbore and
smallbore is quite permissible, provided
the pipework and pump are correctly
sized.
Always connect a hot water cylinder
Figure 5 Single pipe circuit circulating temperatures “C primary return to the combined heating
and DHW return pipe downstream of the
last heating return connection, to avoid
bore’. An option (usually for domestic connections must be top/bottom opposite
possible reverse circulation problems.
situations) is a ‘microbore’ system in ends (TBOE). Although there is less
which the main flow and return from the pipework to install, a single-pipe system Correct pipe sizing is essential if
boiler, connect to manifolds from which must be carefully designed and it cannot problems of insufficient water flow to the
the radiators are individually connected be used with convectors, which must farthest radiators on the system are to be
by 8mm or 10mm pipes. Being flexible, have a pumped flow of water through avoided. Having determined the piping
the pipes can be ‘threaded’ between floor them to achieve the rated output. layout, the heating load on each section
joists etc. in much the same way as can be calculated and the provisional
Since the water temperature around the
electrical cables, so avoiding having to pipe loop(s) will progressively drop as it
pipe size can be determined from Table
use fittings. Installation is simplified, but 3, which is based on a flow rate
passes each radiator, the radiators
the system has to be very carefully corresponding to an 11“C. system
towards the end of the circuit will have to
designed and a more powerful pump is temperature drop and also shows the
be larger than they would be for the
needed to circulate the water through the heat loss from uninsulated and insulated
same output on a two-pipe system,
small pipes as well as specially designed where there would be little variation in pipe.
‘twin- entry’ radiator valves.
flow temperature from one end of the For domestic systems it is generally
There are several variations for system to the other. unnecessary to carry out a detailed pipe
commercial installations, including sizing, with proportioning of mains
A variation on the basic single pipe
‘ladder’ or ‘reverse return’ configurations. system is the ‘loop-in’ system whereby
losses, etc., as one would do for a
commercial situation. However, it is a
the pipework loops in and out of a single
good idea to carry out an accurate
two connection valve on each radiator -
Single pipe systems the valve incorporates a by-pass so that
pressure drop calculation, in order to
check the adequacy of the pipe sizing
With single pipe systems, water some of the water enters the radiator
and check the pump duty.
circulates around one or more single whilst the remainder goes through the
pipe loops with the radiator flow and by-pass and is joined by the cooler water The procedure for this can be
return connections connected from the leaving the radiator - and the mixed summarised as follows:
same pipe loop, the return connection water leaves the valve through the
1. Total heating loads in each pipe
being downstream of the flow. Whilst second connection and passes to the
section and convert to flow rate in I/s
circulation is usually pump assisted, the next radiator on the circuit. This gives a
(same as kg/s). The following
circulation of water through each radiator more positive flow through each radiator.
conversion formula can be used:
is primarily by gravity, although it can be
aided by the use of diverter tees, and

56
 Plumbing Engineering Services Design Guide Heating

uninsulated, even lower efficiency will

Pipe Maximum Heat losslm result. The efficiency will improve with the
diameter load Bare Insulated addition of full thermostatic control.
(mm) (watts) (watts) (watts (9mm thick)) The efficiency of a fully pumped system
6 650 20 4 can be considerably increased by
installing a cylinder with a low storage
8 1300 27 6
capacity which has a very high recovery
10 2100 32 7 rated coil cylinder, far in excess of a
15 5500 46 10 normal BS cylinder.
22 11000 63 12 With low storage capacity and very high
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28 18000 78 14 heating coil surface area (heat exchange

capacity up to 30kW or more), heat is
35 28000 95 15 transferred to the stored water as fast as
the boiler can provide it. The boiler does
not cycle ‘on’ and ‘off’ during the heating
0.23825 Gas and oil piping period and a hot water only system
Load in kW x
Design temp drop K efficiency of well in excess of 75% can
= flow in I/s
installations be achieved.The use of a high recovery
Gas piping systems must be designed cylinder enables the boiler input to be
2. Measure length of each section of taken into account when calculating
pipe and add allowance for equivalent and installed in accordance with the
requirements of either BS 6891:1998 domestic hot water storage requirements,
length of fittings. since it will be re-heating the water to a
‘Installation of low pressure gas pipework
up to 28mm. in domestic premises’ or significant extent, even during a relatively
NOTE: short draw-off period.
This is a simplification of the procedure of Institution of Gas Engineers publication
multiplying the pipe equivalent length at a IGE/UP/2 ‘Gas installation Pipework, With a typical 60 litre cylinder and a gas
particular flow rate by the fining velocity Boosters and Compressors on Industrial fired boiler of 17kW output, the entire
pressure loss factor. and Commercial premises’.The contents will be heated from cold to 60°C
3. Determine pressure drop in Pa/m for requirements for LPG is covered in the in around 15 minutes if the boiler is hot
the flow rate in the pipe size ClTB Study Notes Publication ME 210. to start with, and 18 minutes if starting
concerned and multiply by the total Oil supply systems should be in from cold. With a 22kW boiler, these
length from 2 x 2 (flow & return) - accordance with BS 5410:Part 1:1977 - times reduce to 10 minutes and 17
this gives the pressure drop in that COPfor Oil fired installations up to 44 kW minutes The very fast recovery means
section of pipe. If the resultant output or Part 2 for above 44kW. baths can be run at around 10-15mins.
velocity >1m/s or pressure drop intervals, but use with a ‘hot water
>400Pa/m, then increase pipe size. priority’ control system. The inclusion of a
pump over-run thermostat to transfer
4. Total all calculated pressure drops residual boiler heat to the cylinder, will
from the boiler to the radiator at the
end of each of the distribution Domestic hot further increase the system efficiency, by
around 1/2-1%.
circuits, adding the resistance of the
boiler and any control valve - some
circuits may have common sections
-
water types of Advantages
of piping. The circuit with the highest i. Large quantities of hot water available
resistance is the Index Circuit and quickly
gives the required pump head at the ii. Once heated, availability of water
system flow rate -the pump unaffected by gas or electric supply
selection can then be made. Vented (storage) systems failure.
A reduction can be made in the heater In domestic premises with a heating
sizing for each metre run of exposed system, the normal method of providing Disadvantages
copper pipe, based on the outputs in the domestic hot water is via an indirect hot i. Water pressure may be inadequate
preceding table. These figures will vary water storage cylinder, with the cold for a good shower
depending upon room and water water supply from a cold water storage
temperatures, etc. but are sufficiently cistern. The efficiency of such a system ii. Considerable re-heat time once hot
accurate to be used with the normal will vary considerably - it is essential that water drawn off (unless a high
range of water and room temperatures. If the cylinder is very well insulated . recovery cylinder)
the pipe emission is too high, the Building Regulations require the use of iii. Requires cold water storage cistern,
efficiency of the system control could be factory applied insulation. Primary with consequent frost protection
adversely affected. heating pipework between the boiler and problems if located in a roof void
cylinder must also be insulated.
iv. Wasteful heat loss from stored hot
A very basic system, with time switch water when no demand
control, gravity circulation to the cylinder
coil, and no controlling thermostat on the v. Space required for storage cylinder.
cylinder to’shut off the boiler when the
temperature of the stored water is hot
enough, may have an efficiency as low
as 30% during ‘hot water only’ heating. If
the primary heating pipes are

57
 Heating Plumbing Engineering Services Design Guide

Unvented (mains in conjunction with a suitable

thermostatic mixer. In hard water areas a
Alternatives and design
pressure) systems water treatment unit should always be considerations
installed on the mains supply to the
All cold water outlets and the hot water Where the points of demand are a
heater. It is also advisable to insulate any
storage system are fed directly from the considerable distance apart, or demand
long runs of hot water supply pipework to
mains, giving very good outlet pressures, is of a low level, consideration should be
reduce heat loss between the heater and
suitable for high resistance terminal given to the installation of individual ‘point
taps.
fittings, such as single lever operation of use’ heaters. In a large dwelling, with
taps - balanced hot and cold pressures an en-suite bathroom remote from the
will result in improved mixing and less Thermal storage system
main area of demand at the kitchen and
wastage of water, with consequent A thermal storage system provides main bathroom, consideration could be
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reduced running costs. mains pressure hot water to all points of given to the installation of two
Water is heated directly or indirectly in a use, in the same way as a multipoint independent low storagethigh recovery
purpose designed insulated storage heater. Heating water from the boiler is cylinders.
cylinder, either of copper or lined steel. passed through the shell side of the
Another option would be to install a
Expansion is accommodated in a small cylinder and the mains water is passed
single cylinder with a self-regulating
expansion tank and a number of special through the coil to supply all the taps -
electric trace heating cable on the very
safety controls are fitted. Suitable the volume of heated water is small, so
long dead-legs.
cylinders with expansion tank and safety all the safety devices of an ‘unvented
controls are available as packaged units system’ can be omitted, although the In the majority of small commercial
to serve just a few basin taps or a installation of a small expansion vessel to situations demand is low, and can be met
complete dwelling. Direct gas fired units act as a ‘shock arrestor’ is advisable, as by local point-of-use heaters, but
are also available, although these would is a thermostatic mixing valve. The occasionally one is involved in a project
normally be used for larger installations. heating circuit is separately pumped, requiring large quantities of water. Under
either from the shell side, or via the these circumstances, a dedicated gas
Mains pressure hot water can also be second coil. See below. Such a system fired water heater may be the answer,
provided by combination boilers, may give improved boiler part load which can be cistern or mains fed. If the
multipoint water heaters (gas or electric) efficiency and the thermal store provides high demand is on a very intermittent
and point-of-use electric heaters. If rapid response to both hot water and basis (e.g. showering) and there is a
installing a combination boiler, ensure heating system demand. The primary heating system installed, then another
the gas supply is adequate - input can circuit pump will be of a low head type option would be to install a non-storage
be >35kW for DHW heating. When and the potential for system aeration system with a plate heat exchanger,
comparing different makes, ensure you problems will be reduced. The inclusion which is heated on a priority basis by the
compare like with like - DHW output of a pump over-run thermostat will boiler plant.
claims may be based on 25”C, 30°C or further increase the system efficiency.
35°C temperature rise. The heating circuit could be a completely Advantages
separate sealed system with its own
Advantages expansion vessel and safety valve, whilst i. Cold water storage cistern not
the boiler remains on a low head open required (unless for clw outlets)
I. Cold watei storage cistern not
vented system. The latest packaged units ii. No space required for hot water
required
combine both a condensing boiler and storage (except thermal storage)
ii. Possible cheaper installation cost thermal store in one insulated unit,
together with purpose designed controls, iii. Hot water always available at the turn
iii. Removes problems of freezing of roof of a tap
and have a resultant energy saving
pipework etc potential. iv Possibly cheaper installation cost
iv. Reduced running costs than a storage system (except
V. Very good water pressure at outlets Electric water heaters thermal storage)
and better shower performance. Electric mains fed instantaneous water v No wasteful heat loss from stored hot
heaters are generally restricted to water
Disadvantages supplying a single outlet and small
vi High water pressure available at
electrically heated ‘point of use’ storage
i. Requires annual maintenance check outlets.
units of 7 litre capacity. capacity can be
of all safety controls by qualified
installed above or below a working
plumber Disadvantages
surface -they require special taps to
ii. May show up defect in existing piping provide a vent and prevent pressure i. For a gas multipoint heater an
installations when converted to the build-up. They avoid having to heat a adjacent outside wall and a gas
higher pressure un-vented operation. large quantity of stored water at a time supply is required
when only a small amount is required.
Inlet water treatment should be ii. Slower delivery rate of hot water than
with a storage system
Mains fed instantaneous considered in hard water areas, although
the majority of electric heater elements iii. Electric heaters are expensive to run
systems are easily removed for de-scaling. if quantities of water are required -
Usually supplied by a wall mounted they need a separate electrical
multipoint gas fired water heater or supply.
combination gas fired boiler. Some When designing any mains-fed system,
multipoint units have fan assisted flues storage or instantaneous, it is essential
and can be located up to 3m from the that the adequacy of the cold water main
outside wall. Outputs can be up to 35kW supply is checked for maintenance of
and most units will also supply a shower,
 Plumbing Engineering Services Design Guide Heating

adequate flowlpressure under periods of leakage are not positioned over any gate valves for ease of future
high demandldrought. electrical equipment. maintenance.
Water Regulations are very explicit in 7. Do not use softened water to fill a 20. Install temporary equipotential
their requirements to avoid wastage or system (or add washing-up liquid !!) bonds if breaking electrical
contamination of water supplies and -the high salt content can result in continuity of existing pipework, to
everyone who is involved with the design, serious corrosion problems. protect operatives and third parties.
specification, installation and
8. Only use the very minimum 21. Use non-dezincifiablefittings on
maintenance of domestic water systems
amounts of flux when making domestic water services.
must ensure that they comply with the
soldered joints and use a pre-
requirements of the various legislative
commissioning cleanser.
documents relating to the prevention of
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Legionella. 9. If there is a risk of the installation By-pass connection

being left switched off during For boilers fitted with pump over-run
freezing conditions, use an anti- thermostats it is essential that there is
freeze as well as a corrosion always an open circuit for the water to be
proofer or provide frost protection pumped around. If all circuits can be
Piping installation controls. closed off by motorised or thermostatic
10. Always connect the DHW cylinder valves, a by-pass is required - use an
1. Avoid placing bends or other fittings primary return as the last automatic pressure operated by-pass
close to the inlet or outlet of pumps, connection on the return pipe to the valve to avoid loss of boiler operating
as this can cause cavitation under boiler, after any heating return efficiency. If the system has a three-port
certain conditions. If possible, aim connections to avoid reverse motorised control valve, or if there is
for a 450mm length of straight pipe circulation problems. some other permanently open circuit,
both sides of the pump. such as via a bathroom radiator (without
11. Install pumps vertically, to self- hand-wheel valve), there is generally no
2. Fittings which offer a high purge of air, and with the shafts requirement for a by-pass connection,
resistance to the flow of water can horizontal (not below) to reduce but check with boiler manufacturer.
give rise to noise generation and bearing load and wear. Fit valves
problems of inadequate flow. each side and do not position at
Generally, compression elbows and system low point.
end feed elbows have a far tighter 12. If installing a combined cold feed
radius than integral solder ring and open vent, in order to comply
elbows, and therefore offer a higher with British Standard
resistance to flow. Note that 5449:Pt1:1990 the boiler must be
microbore pipes are vulnerable to However well designed a system, its
fitted with a high limit safety ultimate efficiency will depend upon the
damage and blockage and there thermostat.
may also be noise problems due to method of control. The basic requirement
high water velocities at any 13. Do not install a new boiler or of any control system is to provide the
restrictions. equipment into an existing system correct amount of heat in the right place
without cleansing it thoroughly. at the required time, and to ensure that
3. Always consider requirements for Avoid fabricated or aluminium heat the boiler is switched off when there is no
venting and pre-commissioning exchangers if the system is not system demand for heat.
cleansing and maintenance, and chemically cleaned. Consider the
include adequate provision for The main components of a control
requirement for a strainer on the system will usually be a programmer to
drainage. At least two 15mm valved return to the boiler.
full bore drain points should be enable selection of system operating
provided at low points in the 14. Use reflective radiator film over times; thermostats to control the space
system to enable it to be pipes which are immediately below and, where applicable, domestic hot
adequately flushed through, floor boards to avoid degradation of water storage temperature and motorised
positioning with regard to flushing floor covering. valve(s) to control the circulation of
paths, avoiding short circuiting. heating water to the different circuits (e.g.
15. Always fuse the control system at space heating and domestic hot water
4. Generally, the maximum safe depth 3A and mark the plug/connection heating).
for notching a floor joist is 0.15 x unit accordingly.
the joist depth, with a maximum Modern programmers are of the
16. The electrical supply to an electronic type (rather than electro-
width of 1.5 x the pipe width, and a immersion heater must be run
maximum of two pipes in a single mechanical) and either battery operated
directly from the distribution board, or mains operated with a battery reserve
notch. The maximum diameter for a and must not feed any other
hole drilled through a joist is 0.25 x (alkaline or rechargeable). Some are very
equipment. basic in operation, whilst others offer
the joist depth, with the centre line
between 0.25 and 0.4 of the joist 17. When an existing system cannot be three or more switching cycles a day,
depth down from the top. drained, a self cutting tee can be with separate times for heating and hot
used to provide a drain point. water plus separate programming for
5. Indicate on the floorboards with a each day of the week or weekdays and
felt marker pen the route of pipes 18. Use pipe clips that completely weekends. Such flexibility offers greater
under suspended floors. enclose the pipe and metal potential for energy saving, but
strapping for suspending pipes consideration of the occupants ability to
6. Ensure all high points are below floor joists.
adequately vented and that air vent operate the unit must be taken into
points, compression joists and any 19. Use good quality lever operated account.
other potential sources of water quarter turn ball valves rather than

59
 Heating Plumbing Engineering Services Design Guide

Thermostats keeping at reduced temperature for long commerciaVindustriaI sector, and now
periods (e.g. spare bedrooms). coming into the domestic sector. The
Modern room thermostats can be either basic principle of operation is that you
of the electro-mechanical type, (with programme the occupancy period and
either a bi-metallic strip or vapour- filled Motorised valves required temperature and the controller
bellows) or electronic type. Electro- then calculates the latest switch ‘on’ time,
mechanical type thermostats often Motorised valves will either be of the two- based on the preceding ambient
incorporate accelerator heaters (requiring port or three-port type. Two-port valves temperature. Can also provide optimum
a neutral connection) to reduce the are also called ‘zone valves’ and can be ‘off’ control.
temperature overshoot with radiator used to control the flow of water around
systems and some also have a night set- individual circuits (space heating or Boiler short cycling
domestic hot water heating). There may
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back facility. Modern electronic room

thermostats achieve much better control, be a boiler requirement for by-pass, Boiler short cycling controls operate in
with a differential of around 0.5”C. Since particularly where it has a pump-over-run conjunction with a normal room
each 1“C rise in temperature above that thermostat, to ensure that there is always thermostat controlled system, and delays
required will increase fuel consumption an open path for water circulation. the boiler firing for a timed period. Some
by about 7%, the energy saving potential are simply electronic delay timers which
Three-port valves have one inlet port, delay boiler firing for a timed period,
of the electronic thermostat is readily connected from the boiler flow (usually
apparent. Cylinder thermostats are regardless of level or frequency of
via the pump) and two outlet ports. The demand, whilst others take into account
invariably of the electro-mechanical type outlet ports will, typically, connect to the
with a differential of around 6-10°C to demand frequency. They have little
hot water cylinder heating flow and the energy saving potential and their use
prevent excessive boiler cycling. radiator circuit flow, although they could with certain types of systems may
both connect to two different zone actually increase energy consumption.
Programmable thermostats heating circuits. The valves are either of
Programmable room thermostats the diverting (two position) or mid-
comprise a single channel electronic position type. A diverting valve is driven
programmer and a room thermostat in by its motor to allow water to flow to one
one casing. They are often used where
the boiler does not provide domestic hot
or other of the two outlet ports, as
required by the controlling
Underfloor heating
water storage (e.g. the ‘combi’ type), or programmer/thermostat- usually give
for zone control. Being of the electronic priority to the hot water cylinder heating.
type, they give close temperature control A mid-positionvalve allows the water to
and offer programming on a daily basis flow to either of the outlet ports, or both There is available a complete range of
with as many as six timed periods a day, at the same time. Use of a three-port low pressure hot water underfloor
each at a different temperature setting. valve ensures that one port will always heating systems suitable for all types of
They all have battery back-up, or are be open to maintain a flow path for the buildings.This includes different floor
battery operated. The ‘off’ periods are water and may avoid the need for a constructions such as screed, concrete
determined by selecting a timed period at boiler by-pass. and timber suspended.
a reduced temperature (e.g. 14”C), Systems are also available for the
effectively giving frost protection. refurbishment market using special thin
Electronic controllers screeds and dry construction techniques.
There is an increasing use of more The design principles, however, are
Thermostatic radiator valves sophisticated electronic controllers in common to all systems and need to be
Thermostatic radiator valves are simple domestic systems and these fall into understood.
to install, requiring no electrical supply, three categories: compensated control;
optimising time control, and boiler short- Underfloor systems operate by means of
and can be installed to give temperature
cycling control. embedded loops of pipe connected via a
control in individual rooms. They should
manifold to the flow and return sides of
not be installed on all radiators as there
Compensated control the heat source. See Figure 6.
would be no means of automatically
stopping the boiler and pump when the Compensated control is a method Each loop or circuit can usually be
demand in all areas is satisfied, with the whereby the amount of heat that is put controlled and/or isolated on both the
valves having closed. The energy saving into the building is automatically varied, flow and return.
potential of the valves can be completely depending upon the outside temperature Systems will normally be designed to
lost due to the continued operation of the and therefore the rate of heat loss from operate at low water temperatures of
pump, with water circulating via a the building. This is achieved by either between 40°C and 60°C and a
continuously open or automatic by-pass varying the temperature of the water temperature drop of between 5 and 10°K
valve controlled by-pass loop, and flowing around the heating circuit, over- across the system.
inefficient cycling of the boiler under the riding the boiler thermostat, or by varying
control of its thermostat. The Building the length of the boiler ‘on’ periods. This Virtually all systems today use non-
Regulations require the installation of a method of control is more efficient than a ferrous plastic pipe instead of ferrous or
room thermostat, to shut the boiler off simple room thermostat control, and copper material. By laying modern
when demand is satisfied. The overcomes the problem of siting the polymer plastic pipe in continuous coils
thermostat must be located in an area room thermostat in a position that is truly without joints it is possible to avoid many
that is representative of the temperatures representative of the average conditions of the problems associated with systems
in the property and there must be no in the house. in the past. Modern polymers do not
thermostatic radiator valves in that area. corrode or attract scale and are in many
Optimising time control cases capable of outliving the useful life
Their use should be limited to selected of the building.
locations which are subject to external Optimising control is well proven in the
heat gains, or areas which require

60
 Plumbing Engineering Services Design Guide Heating

Solid floor construction

Typical floor make up:
a. Oversite
b. Concrete slab
c. Insulation
d. Underfloor heating pipes
e. Floor screed
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f. Final floor finish.

On some buildings, the insulation will be
fitted below the slab in which case the
pipes can be installed within the concrete
slab. See Figure 7.
The above construction is used for both
ground bearing and suspended slabs.

Floating floor construction

Typical floor make up:
Figure 6 Typical manifold
a. Oversite
b. Concrete slab
c. Pre-grooved insulation fitted with heat
emission plates
d. Underfloor heating pipes
e. Floor boarding
f. ' Final floor finish.
This design is often used on pot and
beam construction where the finished
floor is flooring grade chipboard laid over
the underfloor heating system.
The specially adapted insulation, which
is usually pre-grooved to accept the pipe
and heat emission plates, is designed for
full floor loading. The use of heat
emission plates ensures that the floor
temperature will be even across the
whole floor area. See Figure 8.

1 I
I
Figure 7 Solid floor construction

The most common materials in use rapid corrosion of any steel components
today are: within the heating system can occur.
PEX: Cross linked Polyethylene Better insulation standards in our
buildings have meant that most floors are
PP: Co-Polymer of Polypropylene
now insulated as standard. This means
PB: Polybutylene that for most buildings the installation of
the underfloor heating will be no more
All pipes should ideally incorporate a
difficult than any other form of heating.
diffusion barrier, which can be either
integral or applied to the outside of the The basic form of floor construction in
pipe as a coating. The purpose of the most buildings is solid concrete, floating
barrier is to reduce the amount of or suspended. There are many different
oxygen that can migrate through the pipe ways in which various underfloor heating
wall. Pipes without a diffusion barrier will manufacturers design their systems and
pass much higher rates of oxygen it is only possible to deal with some of Figure 8 Floating floors construction
thereby providing a highly oxygenated the standard methods of construction in
water circulation around the heating this publication.
system. If the heating system is not fully
The following are typical floor sections of
protected by a corrosion inhibitor then
the three most common types.

61
 Heating Plumbing Engineering Services Design Guide

The human foot is a highly effective

thermostat for the whole body. In the
colder areas of the world human kind
has been keen to 'take the chill off the
floor' since ancient times. The techniques
used to achieve this range from the
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simplest rugs and skins to the more

sophisticated hypocaust system of the
Greeks and Romans.
Research shows that a basic
temperature of 21"C on the floor surface
will give an ideal sensation of comfort.
International Standards indicate that the
comfortable range is between 19-26°C
Ygore 9 Suspended floors and dependant upon the required air
temperature, floor heating systems
By using the above formula, the 'U' value should stay within this band.
Suspended floor construction of the un-insulated slab can be Most areas are permitted with design
Typical floor make up: calculated. Once this value is known the floor temperatures up to 29°C.
amount of insulation required to bring the Temperatures up to 35°C are acceptable
1. Timber joists or battening
floor up to the standard required can be for specific areas such as pool
2. Insulation between joists calculated. surrounds, changing rooms, bathrooms
3. Cross battens For an insulated slab the formula would and the first metre of space adjacent to
be: walls with high fabric losses. This may
4. Heat emission plates fitted to occur where you have for instance
cross battens extensive floor to ceiling glazing where it
5. Underfloor heating pipes is necessary to offset as much as
possible the cold down draught that
6. Floor boarding occurs.
Where:
7. Final floor finish. The sensitivity of the human foot will
= U value of an insulated
Uinsulated perceive a temperature above 29°C as
This design is suitable for most types of slab W/m2 K
joisted or battened floors. The cross 'uncomfortable' at normal room
battening fitted at 90" to the joists means Uslab = U value of un-insulated temperatures of 18-22°C and should be
that a consistent pipe centre can be slab W/m2K avoided.
maintained irrespective of the joist RinSulation
= The thermal resistance of the Other limiting factors to the surface
centres. This particular system also insulation W/m2K temperature may be the particular floor
avoids any notching of the joists. covering and for some materials such as
The selection of a suitable insulation timer the maximum manufacturers
There are many variations on all the material will normally be made in
standard floor sections and there are temperature should be observed.
conjunction with the architect to ensure
systems available today which can be the material will meet the floor loading Modern well insulated buildings no
adapted in a variety of ways to meet the requirements in addition to the level of longer need high surface temperature in
building design. insulation required. order to provide sufficient output to meet
Insulation would be fitted to most floors the heat losses of a typical building.
For suspended floor slabs, the Average floor emissions of between 50
irrespective of the construction method calculations are more complex since an
and this would need to meet the and 75 watts per m2 will often be more
enclosed air space is introduced below than sufficient. Low temperature floor
requirements of the Building Regulations. the slab, which can often have a high
The downward heat transmission can be systems provide inherent, passive self
infiltration rate. regulation. Floor temperatures generally
calculated in several ways. For ground
bearing slabs the most common formulae It must be remembered that with need only be 3 4 ° K higher than room air.
underfloor heating a solid screed or Any rise in air temperature due to solar

z}
used is:
gain or increased occupancy means the
Uslab= (0.05+ (1.65 X :)] - (0.6 X
concrete floor will have a higher mean
temperature than a floor constructed
without underfloor heating. For this
air will begin to approach the floor
temperature. As this temperature
reason most floors will require a degree difference decreases the heat emission
Where: of insulation to be fitted to offset any from the floor reduces. This process is
downward losses. rapid and precise. Heat emission from
Uslab = U value of un-insulated slab the floor will begin to decrease as soon
W/m2K as air temperature rises. Given an air
P = External Perimeter of temperature of 20°C and a floor
Building m temperature of 23"C, heat emission from
the floor will decrease by about a third for
A = Total Area of Floor m2 each degree of temperature that the air
temperature rises. A three degree rise in

62
 Plumbing Engineering Services Design Guide Heating

air temperature will thus be sufficient to the dry resultant temperature and is not All of these determine the total thermal
neutralise the system. Theoretically, this so affected by the rate of fabric loss. resistance above the pipe, which will
inherent self regulation makes it possible determine the drop in temperature
This means that the floor radiant systems
to design an underfloor heating system between the pipe and the surface of the
lower dry resultant temperature can
with no other form of room temperature floor.
safely be used for the calculation of heat
control.
losses. To achieve a set output from a floor
means that we can either vary the pitch
This difference can account for a
of the pipe and operate at a set water
reduction of 5-10% for most types of
temperature or we can fix the pipe pitch
buildings.
Design criteria In addition, it is not necessary to allow
and operate at different water
temperatures.
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any margins for height factors in

Constant water temperature is
To evaluate comfort purely in terms of buildings when considering the use of
sometimes introduced into the design by
temperature requires consideration of the radiant floor heating systems.
choice but more often is a function of
following: In order to prepare a design for a only 'one' water temperature being
1. Wet Bulb temperature building it is necessary to calculate the available regardless of different floor
heat losses in an acceptable form. constructions.The main disadvantage of
2. Dry Bulb temperature this approach will be encountered during
Many of the modern computer programs
3. Rate of air movement installation when the installer will have to
allow for the use of resultant
create different pipe pitches. Many
4. Mean radiant temperature. temperatures in conjunction with floor
projects - especially domestic ones -
radiant systems. These will give a more
There are various accepted methods for feature different floor structures with, for
accurate reflection of the steady state
the measurement of temperature example, the ground floor being concrete
heat losses.
including globe, equivalent, effective, and the upper storeys wooden
radiant, environmental, dry and wet bulb. Once the heat losses are known and suspended floors. Water temperature
tabulated then the underfloor heating required can differ by more than 15°C
The most commonly used measure of system can be designed. Since there is between the floors and such a
comfort for heating systems is the dry an upper limit on the surface temperature temperature difference is difficult to meet
resultant temperature which in the the maximum output from the floor is using constant water temperature.
absence of high rates of convection can restricted. Altering the pitch of pipes to meet
give accurate indications as to the level requirements from area to area also
of comfort that can be anticipated. For general purposes, a figure of 11
presents potential future problems when
Watts/m2 K can be used to determine the
The dry resultant temperature is defined floor covering materials are replaced e.g.
maximum floor emission. Where K is the
as: switched from tiles to wall-to-wall carpet.
difference between surface and air
In such circumstances, the pipe pitch
t, + TaidlOv temperature.
cannot be altered retrospectively and
tres =
1 +dlOv For example: heat transfer may not be sufficient to
Where the internal rate of air movement achieve design temperatures.
Room area 1Om2
v is less than 0.1m/s then the above If the pipe pitch is kept constant, it will
equation can be simplified as follows. Heat loss 540 Watts
result in varying water temperatures. This
,,t = 0.5tai + 0.5tr Heat required 54 Watts/m2 method leads to easier design and
installation. It must be borne in mind that
where: Air temperature 20°C
there is always an upper limit to the
,,t = dry resultant temperature "C Floor temperature 26°C desirable water temperature and in
extreme cases different pipe pitches and
Output required 54/(26-20)
tai = inside air temperature "C loop configurations may need to be
= 9 Watts/m2K
considered. Clearly there are an
t, = mean radiant temperature "C
In the above example, the heat required unlimited number of combinations of
The inside air temperature can be is within the design parameter of 11 construction methods and floor finishes,
assumed to be the dry bulb temperature Watts/m*K. each of which will give a different overall
with the mean radiant temperature as a thermal resistance.
calculation derived from the shape of the The calculation should be repeated for
room, it's area, surface emmisivity and each of the rooms or areas to determine The temperature drop across the pipe
temperature. whether there are any areas, which loops should be kept low i.e.
cannot be, heated within the permitted approximately 5-1 0°K in order to
The radiant temperature is significant to design limits of the maximum floor maintain even floor temperatures.
a feeling of comfort since it is the surface temperature.
exchange of radiation with our Different pipe sizes also require
surrounding that has the most effect on The water flow temperature required to equivalent adjustments to water
our perception of 'thermal comfort'. achieve a given surface temperature is temperatures however this adjustment is
dependant upon the following: very small. The difference between a
With convective systems, the air 15mm and a 20mm pipe result in only a
temperature will always be higher than 1. Surface temperature required
2% increase in flow temperature for the
the dry resultant temperature and this 2. Type of floor construction 15mm pipe.
difference can be as much as 5°K in
buildings with high fabric losses such as 3. Depth of pipe below floor surface Three main types of loop configuration
glass walled structures. are used for underfloor heating. The
4. Floor covering.
construction techniques used for the
Conversely in floor radiant systems the building will effect selection of the most
air temperature will always be lower than
 Heating Plumbing Engineering Services Design Guide

suitable type for the individual project. In

general when pipe layout plans are
formulated, attention should be paid to
routing the supply flow to the external
wall or other potentially cold areas.

Serpentine coil layout

Temperature variations within local areas
are kept to a minimum. The main
advantage of this configuration is that it
Licensed copy from CIS: southbank, Southbank University, 27/05/2013, Uncontrolled Copy.

is adaptable to all kinds of floor

structures and can be easily modified for
different energy requirements by altering
the pitch of the pipes. This configuration
is the most suitable for underfloor
heating installations serving domestic
premises. However, a flexible pipe is
required.

Double coil layout

The characteristic of this configuration is Figure 70 Serpentine coil layout
that supply and return pipes inthe layout as a function of outdoor temperature.
run in parallel. One of the main advantages using
This provides an even mean outdoor temperature compensation is the
temperature, but will result in a higher shorter reaction time particularly for
variation of temperature within small systems installed in concrete floors. The
areas. It is suitable for heating larger lower the water temperature is in the
areas with higher heat demands e.g. system the smaller the heat sink effect of
churches, hangers, or even for external the floor and the quicker the response, a
use under paths and driveways. disadvantage being the possible rapid
changes in the outside air temperatures.
Maximum comfort requires room
Spiral coil layout temperature control. Different areas of
the building will have differing heat
Supply and return pipes are run parallel,
requirements depending upon external
but in the form of a spiral in this
factors, including the orientation of the
variation. This approach is suitable for
building, wind direction etc. or internal
buildings with a higher heat demand, but
influences including open fires, number
is less suitable for installation in
of occupants etc. Underfloor heating
association with wooden floor structures.
installations can, with the right controls,
Studies show that a naked human foot meet all of these requirements. Water
cannot detect a temperature variation of circulation in each loop of the underfloor
less than 2°C. A serpentine layout with a system can be controlled individually by
pipe pitch of 250-300mm keeps the means of actuators and room
temperature comfortably within this Figure 7 7 Double coil layout
range, so that no variation in floor Figure 72 Spiral coil layout
temperature can be detected.
A number of different approaches may
be applied to the control of water
temperature in underfloor heating
systems.
One of the simplest means of control is
to maintain a constant supply water
temperature from the boiler to the
system by means of self-regulating
control valve and mixing circuit.
This type of circuit works by mixing some
of the return water from the underfloor
heating with the water from the boiler to
maintain a fixed supply water
temperature.
Whilst this is satisfactory for small
building such as domestic housing heat
demand for a building will vary principally

64
 Plumbing Engineering Services Design Guide Heating

I Alternative pump position Clock Programmer Room stat

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Figure 13 Control circuit for fixed supply temperature

thermostats. This gives the end user

individual control over each room or
area.
The U value of a building directly relates
to the performance of the underfloor
heating system, which serves it. If the
building is poorly insulated energy will be
wasted and response times will be
affected by the undesirable heat losses.
Floor structure also affects response
time. In buildings with concrete screeded
floors, the screed will serve as an energy
store, however by comparison a wooden
suspended floor has little thermal store
potential and therefore reacts much
quicker.
Careful consideration should be given to
the location of the manifolds at the outset
of the project. They should be located as
centrally as possible within the building
so that the length of pipe routing
between manifolds and the individual
heating zones is kept to a minimum. This
will help to balance the system and
improve the temperature control of
individual rooms. The manifolds can be
concealed in cupboards, or suitable
voids, so aesthetics are not a major
issue.
Care should be taken however, to ensure
that the manifolds are located in such a
way as to provide easy access for further
maintenance. Underfloor heating
systems, with an oxygen diffusion barrier,
can be used safely in association with
other heating systems and air
conditioning.
Complementary heating systems should
be set up in such a way that they do not
interfere with temperature control of the
underfloor heating system.

65