Proceedings of Clima 2007 WellBeing Indoors
New European standards for design, dimensioning and testing embedded radiant
heating and cooling systems.
Bjarne W. Olesen, Ph.D.
International Centre for Indoor Environment and Energy, Department of Mechanical
Engineering, Technical University of Denmark.
Corresponding email: bwo@mek.dtu.dk
SUMMARY
Due to the increasing use of embedded, hydronic systems for heating and now also cooling of
buildings there has been a need to revise the existing European standard EN1264-part2 for floor
heating. At the same time a new set of standards EN15377 for these systems has been developed
in relation to the many CEN-standards developed for implementing the Energy performance of
Buildings directive.
The EN1264 standard series [1,2,3,4,5] have been revised as testing and prove standards for
floor heating. A new part is now included for other surfaces (ceiling, walls) and also for cooling.
The standard presents a test method either by calculation or by experimental testing. In this way
the heating-cooling capacity can be tested under standardized conditions and used for
certification.
The new standard EN15377 [6,7,8] includes calculation method for design and dimensioning of
embedded radiant heating and cooling systems. For some systems the same calculation methods
as in EN1264 is used for design and dimensioning. For other system types not covered by
EN1264 new calculation methods are included. A separate part is dealing with systems (TABS)
embedded directly in the building mass (slabs). This part shows how to take into account the
dynamic behavior of the system.
INTRODUCTION Formatted: Bullets and
Numbering
The new standard for embedded, water based surface heating and cooling systems, EN15377
consists of the following parts:
⎯ Part 1: Determination of heating and cooling capacity
⎯ Part 2: Design, dimensioning and installation
⎯ Part 3: Optimizing for use of renewable energy sources and dynamic considerations
In Part 1 the steady state heating and cooling capacity is determined calculation in accordance
with design documents and a model. The calculation models are listed in prEN1264 part 2 and 5
and in EN15377-1. In the case of special constructions and if necessary, the determination of
thermal performance by calculation is combined with a test method according to EN1264-2.
The heating-cooling capacity is given as a function of the temperature difference between room
and mean water temperature.
The surface temperature and the temperature uniformity of the heated/cooled surface, nominal
heat flow intensity between water and space, the associated nominal medium differential
temperature and the field of characteristic curves for the relationship between heat flow intensity
and the determining variables are given as the result.
The standard include several methods like general Finite Difference or Finite Element methods,
simplified calculation methods depending on position of pipes and type of building structure.
The simplified calculation methods are specific for the type of system. The standard is for
Proceedings of Clima 2007 WellBeing Indoors
systems which are calculable in accordance with EN1264 part 2 and part 5. The simplified
methods include certain boundary conditions, which must be met before the given method is
applied.
CONCEPT OF THE METHOD TO DETERMINE THE HEATING AND COOLING
CAPACITY
A given type of surface (floor, wall, and ceiling) delivers, at a given average surface temperature
and room temperature (operative temperature θi), the same heat flow intensity in any space
independent of the type of embedded system. It is therefore possible to establish a basic formula
or characteristic curve for cooling and a basic formula or characteristic curve for heating, for
each of the type of surfaces (floor, wall, and ceiling), independent of the type of embedded
system, which is applicable to all heating and cooling surfaces.
Two methods are included in this standard:
Different simplified calculation methods are included in for calculation of the surface
temperature (average, maximum and minimum temperature) depending on the system
construction (type of pipe, pipe diameter, pipe distance, mounting of pipe, heat conducting
devices, distribution layer) and construction of the floor/wall/ceiling (covering, insulation layer,
trapped air layer, etc). The simplified calculation methods are specific for the given type of
system, and the boundary conditions listed in the standard must be met. In case a simplified
calculation method is not available for a given type of system, either a basic calculation using
two or three dimensional finite element or finite difference method can be applied or a
laboratory testing in combination with a calculation may be applied according to EN1264
Based on the calculated average surface temperature at given combinations of medium (water)
temperature and space temperature, it is possible to determine the steady state heating and
cooling capacity. If proved certificated values for the specific thermal output shall be used,
generally EN 1264 part 2 and/or Part 5 apply.
HEAT EXCHANGE COEFFICIENT BETWEEN SURFACE AND SPACE
The relationship between heat flow intensity and the temperature difference between room and
average surface temperature (θi - θS,m ) is given by equations (1) to (4)) depending on the type of
surface (floor, wall, ceiling) and whether the temperature of the surface is lower (cooling) or
higher (heating) than the space temperature.
Table 1 - Total heat exchange coefficient (combined convection + radiation) between surface and space,
recommended max/min surface temperatures and heating capacity by 20 °C room temperature and
cooling capacity by 26 °C room temperature for cooling (EN15377-1, Olesen et. al. 2000 [10]).
Total heat exchange Acceptable surface Maximum capacity
coefficient temperature W/m²
W/m².K °C
Heating Cooling Max. Min. Heating Cooling
Heating Cooling
Floor Perimeter 11 7 35 19 165 42
Occupied
11 7 29 19 99 42
Zone
Wall 8 8 ∼40 17 160 72
Ceiling 6 11 ∼27 17 42 99
Floor Heating and Ceiling Cooling q = 8,92 (θi - θS,m )1,1 (1)
Proceedings of Clima 2007 WellBeing Indoors
For other types of situations the following relations shall be used:
Wall heating and Wall cooling: q = 8 (| θi - θS,m |) (2)
Ceiling Heating: q = 6 (| θi - θS,m |) (3)
Floor cooling: q = 7 (| θi - θS,m |) (4)
SIMPLIFIED CALCULATION METHODS FOR DETERMINING HEATING AND
COOLING CAPACITY OR SURFACE TEMPERATURE
Two types of calculation methods can be applied according to the type of system:
One method is based on a single power function product of all relevant parameters developed
from the finite element method (FEM). Another method is based on calculation of equivalent
thermal resistance between the temperature of the heating or cooling medium and the surface
temperature (or room temperature).
A given system construction can only be calculated with one of the simplified methods. The
correct method to apply depends on the type of system, A to G (position of pipes, concrete or
wooden construction) and the boundary conditions listed in the standards.
Universal single power function according to EN1264-2.
The heat flux between embedded pipes (temperature of heating or cooling medium) and the
space is calculated by the general equation:
q = B ⋅ ∏ (aimi ) ⋅ ΔθH (W/m2) (5)
i
where:
B a system-dependent coefficient in W/(m2⋅K). This depends on the type of system and
on the heat exchange coefficient
∏ (aimi ) the power product, which links the parameters of the structure (surface covering, pipe
i
spacing, pipe diameter and pipe covering).
The heat flow density is proportional to ΔθH where the heating /cooling medium differential temperature
is:
θV − θ R
Δθ H = °C (6)
θ − θi
ln V
θ R − θi
Where: θi = Room operative temperature, °C
ΘV = Supply water temperature, °C
θR = Return water temperature, °C
Type D
1-Floor covering; 2-Screed; 3-PE foil; 1-Floor covering; 2-Screed; 3-PE foil; Floor covering, load distribution
4-pipes; 5-Insulation; 6-Structure slab; 4-Scred; 5-pipes; 6-vapour barrier; Plane floor section, insulation,
- 7-insulation; 8-structure slab. Structure slab
Figure 1: System type A, C and D covered by the calculation method in EN1264-2 and 5.
Proceedings of Clima 2007 WellBeing Indoors
This calculation method is given in EN1264 part 2 for the system types A, B, C, and D (see
figures 1 and 2)
1-Floor covering; 2-Screed; 3-PE foil
1-Floor covering; 2-Screed; 3-PE foil
4-Heat conducting plate (device); 5-Pipes
4-Heat conducting plate (device); 5-Pipes
6-Insulation; 7-Structure slab 6-Insulation; 7-Structure slab
Figure 2: System type B covered by the calculation method in EN1264-2 and 5.
Thermal resistance methods
The heat flux between embedded pipes (temperature of heating or cooling medium) and the
space or surface is calculated using thermal resistances. The concept is shown in Figure 3.
An equivalent resistance, RHC, between the heating or cooling medium to a fictive core (or heat
conduction layer) at the position of the pipes is determined. This resistance includes the
influence of type of pipe, pipe distance and method of pipe installation (in concrete, wooden
construction, etc). In this way a fictive core temperature is calculated. The heat transfer between
this fictive layer and the surfaces, Ri and Re (or space and neighbor space) is calculated using
linear resistances (adding of resistance of the layers above and below the heat conductive layer).
The equivalent resistance of the heat conductive layer is calculated in different ways depending
on the type of system. This calculation method, using the general resistance concept, is given in
for the following two types of systems shown in figure4 (Type E and F) and figure 5(Type G).
The equivalent resistance of the conductive layer may also be determined either by calculation
using Finite Element Analysis (FEA) or Finite Difference Methods (FDM) or by laboratory
testing according to prEN1264-2.
The heating and cooling capacity are in some of the described calculation methods determined
directly (see EN1264 part 5).
In other calculation methods, the average surface temperature is determined and the heating and
cooling capacity is calculated according to:
qdes = ht (⎢θs,m - θi ⎢)
For evaluation of the performance of the system – and when calculating the total heating and
cooling power needed from the energy generation system (boiler, heat exchanger, chiller, etc.) –
the heat transfer at the outward (back) side shall also be considered. This heat transfer shall be
regarded as a loss if the outward side is facing the outside, an un-conditioned space or another
Proceedings of Clima 2007 WellBeing Indoors
building entity, and it depends on the temperature difference between the pipe-layer as well as
the heat transfer resistance to and the temperature in the neighbor space or outside.
Figure 3 Basic networks of thermal resistances
Figure 4a Pipes embedded in a massive Figure 4b Capillary pipes embedded in a
concrete layer, Type E (EN15377-1) layer at the inner surface, Type F
(EN15377-1)
Figure 5 Pipes embedded in a wooden floor construction, Type G (15377-1, [11]
Proceedings of Clima 2007 WellBeing Indoors
EN15377- PART 3: OPTIMIZING FOR USE OF RENEWABLE ENERGY SOURCES
The aim of this standard is to give a guide for the design of water based embedded heating and
cooling systems to promote the use of renewable energy sources and to provide a method for
actively integrating the building mass to reduce peak loads, transfer heating/cooling loads to off-
peak times and to decrease systems size. A section in the standard describes how the design and
dimensioning can be improved to facilitate renewable energy sources. Peak loads can be reduced
by activating the building mass using pipes embedded in the main concrete structure of the
building (Thermo-Active-Building-Systems, TABS). For this type of systems, the steady state
calculation of heating and cooling capacity (part 1 of this standard) is not sufficient. Thus,
several sections of this standard describe methods for taken into account the dynamic behavior.
The proposed methods are used to calculate and verify that the cooling capacity of the system is
sufficient and to calculate the cooling requirements on the water side for sizing the cooling
system.
Thermo Active Building Systems (TABS)
A Thermo-Active-Building-System (TABS) is a water based heating and cooling system, where
the pipes are embedded in the central concrete core of a building construction. The heat transfer
takes place between the water (pipes) and the concrete, between the concrete core and the
surfaces to the room (ceiling, floor) and between the surfaces and the room.
The peak-shaving is the possibility to heat and cool the structures of the building during a period
in which the occupants may be absent (during night time), reducing also the peak in the required
power (Figure 6). In this way energy consumption may be reduced and lower night time
electricity rate can be used. At the same time a reduction of the size of cooling system including
chillier is possible
Figure 3 – Example of peak-shaving effect (X-axes: time; y-axes: cooling power W )
1) heat gain, 2) power needed for conditioning the ventilation air, 3) power needed on the water
side, 4) peak of the required power reduction
The performance and dimensioning of TABS can be done by full dynamic building simulations
with commercial programs including calculation models for embedded pipes. (Olesen and Dossi,
[9]). The standard includes a more simplified calculation method. Besides the standard includes
Proceedings of Clima 2007 WellBeing Indoors
diagrams like the one shown in Figure 7 [12]. This simplified diagram give the relation between
internal heat gains, water supply temperature, heat transfer on the room side, hours of operation
and heat transfer on the water side. The diagrams correspond to a concrete slab with
Figure 5 – Working principle of TABS (Koschenz and Lehmann [12]
raised floor (R=0.45 m2K/W ) and a permissible room temperature range of 21 °C to 26 °C. The
upper diagram shows on the y-axis the maximum permissible total heat gain in space (internal
gains plus solar gains) W/m2 , and on the x-axis the required water supply temperature. The
lines in the diagram correspond to different hours of operation (8h, 12h, 16h, and 24h) and
different maximum amount of energy supplied per day Wh/m2 d . The lower diagram shows the
Proceedings of Clima 2007 WellBeing Indoors
cooling power W/m2 required on the water side (for dimensioning of chiller) for thermally
activated slabs as a function of supply water temperature and operation time. Further, the amount
of energy rejected per day is indicated Wh/(m2 d). The example shows, that by a maximum
internal heat gain of 38 W/m2 and 8 hour operation, a supply water temperature of 18,2 °C is
required. If, instead, the system is in operation for 12 hours, a supply water temperature of 19,3
°C is required. In total, the amount of energy rejected from the room is app. 335 Wh/m2 per day.
The required cooling power on the water side is by 8 hours operation 37 W/m2 and by 12 hours
operation only 25 W/m2. Thus, by 12 hours operation, the chiller can be much smaller. The total
heat rejection on the water side is app. 300 Wh/m2 per day.
SUMMARY AND DISCUSSION
This paper presents a new and a revised European standard for the calculation of heating and
cooling capacity for hydraulic, radiant surface heating and cooling systems. Different
“simplified” calculation methods, depending on the type of construction, have been presented. In
contrast to radiant heating and cooling panels, where the heating/cooling capacity must be
determined by testing in a standardized test room, the determination for embedded systems is
based on calculations. Besides the included “simplified calculation methods,” the standard also
allows the use of finite difference and finite element methods. The manufacturers of radiant
heating and cooling systems can use the standardized calculation methods to develop diagrams
relating water temperature and space temperature to the cooling-heating capacity. This will
avoid unnecessary testing of systems.
Besides the new standard includes a part describing methods to take into account the dynamic
effects of thermally activated building systems (TABS), where the pipes are embedded in the
main building structure (concrete slabs or walls), to activate the building mass.
REFERENCES
1. EN 1264-1, 1999: Floor heating: Systems and components - Part 1 : Definitions and symbols
2. prEN 1264-2, 2007: Prove methods for the determination of the thermal output of floor eating
systems using calculation and test methods
3. EN 1264-3, 1999: Floor heating: Systems and components - Part 3 : Dimensioning
4. EN 1264-4, 2001: Floor heating: Systems and components - Part 4: Installation
5. prEN 1264-5, 2007: Heating and cooling surfaces embedded in floors, ceilings and walls —
Determination of thermal output and cooling output
6. EN15377-1, 2007: Design of embedded water based surface heating and cooling systems:
Determination of the design heating and cooling capacity
7. EN15377-2, 2007: Design of embedded water based surface heating and cooling systems:
Design, Dimensioning and Installation
8. EN15377-3, 2007: Design of embedded water based surface heating and cooling systems: - Part
3: Optimizing for use of renewable energy sources
9. Olesen, B.W. and Dossi, F.C. Operation and control of activated slab heating and ooling
Systems, CIB World Building Congress 2004,
10. Olesen B. W. E. Michel, F. Bonnefoi, M. De Carli, Heat Exchange Coefficient Between Floor
Surface and Space by Floor Cooling: Theory or a Question of Definition. ASHRAE Trans. 2000
Part 1.
11. NordTest NT VVS 127 (2001): Floor Heating Systems: Design and Type Testing of Waterborne
Heat Systems for Lightweight Structures
12. Koschenz, M und Lehmann,B : Thermoaktive Bauteilsysteme, tabs . EMPA, Switzerland, 2000
