Republic of the Philippines

NUEVA ECIJA UNIVERSITY OF SCIENCE AND TECHNOLOGY

College of Engineering
Sumacab Campus

DOMESTIC WATER
HEATING
Engineering Utilities 2 (Basic Mechanical Engineering)
ME 223

BSCE 2H

Bautista, Marylei Honey R.

Santos, Abigail Lyca L.
Felipe, Rosemarie V.
Agustin, J-ann-Riel V.
Dela Cruz, Marifher Kate F.
De Jesus, Emmanuel D.G.
Salonga, Albert Claude D.
Sagun, Brian Paul Albert A.
Flores, Regine B.
Water Heating
A water heater is an appliance or system that heats water for domestic or building service hot
water use. There are three types of water heaters: storage tank water heaters, instantaneous on-
demand (tankless) water heaters, and circulating water.

Types of Water Heaters

1. Storage Tank Water Heater
Storage Tank Water Heater is the most popular and familiar style for homes. In fact in United
States, storage tank water heaters remain the most popular type for residential heating. A
storage tank water heater consists of a storage tank and a heating medium. The tank holds the
water that should be heated. The tank is insulated so that when the water heats up, it remains
warm until it needed. The fuel sources of storage tank water heaters include natural gas,
propane (LP), fuel oil, and electricity

The tank features two valves:

 Temperature Control Valve opens to release heat and moderate temperature when the
water reaches over 120 degrees Fahrenheit.
 Pressure Control Valve opens to lower the pressure when it reaches about 150 psi.

Electric water heaters have coil-like elements that extend into the tank, which heat water as
electric current passes through the elements.

Gas and fuel oil fired water heaters have burners located on the bottom of the tank and a vent
that passes up through the center of the tank.

Gas and Fuel Oil Storage Tank Electric Storage Tank Water Heater
Water Heater
 ADVANTAGES DISADVANTAGES
 Tank sizes have increased with the
National Appliance Energy
 Available in a wide range of sizes Conservation Act (NAECA)
(tank options usually ranging from standards; so, these systems tend to
20 to 80 gallons) require more space.
 Most affordable style and easy to  Offers a limited supply of hot water
install. when used for extended periods.
 Have an average energy factor (EF)  Can waste up to 15% of energy
rating of 0.67. through radiant heat loss.
 Typically have a life expectancy of
10 to 15 years.

Types of storage tank water heaters include the following:

 Residential storage tank water heaters are designed for the residential market, but can
be appropriate for many small commercial facilities. They are relatively inexpensive
and widely available.
 Commercial storage tank water heaters are available with much higher gas input
ratings (1 000 000 Btu/hr or more) and larger storage tanks (up to 250 gal). They also
feature larger pipe connections, more rugged controls, and a few features, such as flue
dampers and electronic ignition.
 Ultraefficient water heaters use power burners and enhanced heat exchangers to force
hot combustion gasses into chambers and tubes that are submerged in the stored water.
Ultraefficient water heaters are vented with plastic pipes that go directly through an
outside wall. Because they draw combustion air directly from outside, through one of
those pipes, their combustion processes are sealed off from the occupied space

Classification of Storage tank water heaters based on their method of venting:

 Nonventing (electric)
 Naturally aspirated water heaters have a flue that runs vertically through the center of
the tank. Products of combustion are vented by relying on the natural buoyancy of the
flue gases.
 Power-vented water heaters use a fan to exhaust flue gases.
 Sealed-combustion water heaters have supply air and exhaust air connections to the
outdoors. These units do not require any indoor air to operate.

Two types of sealed-combustion water heaters:

 Some units have a flue up the center of the tank (similar to the power-vented
water heaters).
 The second type of unit has a heat exchanger that wraps around the tank.

Water Heater Type Maintenance Activity Frequency

  Recommended every 6
 Draining and flushing months to annually (will
storage tanks. vary depending on local
water quality conditions)
 Inspection of burner,
Storage Tank Water thermostat (operation
 Recommended every 3
Heater of), venting system,
months to annually
temperature and
pressure relief valve.
 Recommended every 1 to 2
 Inspection of the anode
years or more frequently in
rod.
areas with soft water.

2. Instantaneous (Tankless) Water Heaters

Instantaneous water heaters also called as tankless water heaters or demand water
heaters. This water heater has no tank and it features the modern technology. There are super-
heated coils that fill with water and heat water in a flash as you need it, that why it is also
called as the demand water heater.

They have a heating device that is activated by the flow of water when a hot water
valve is opened. Instantaneous water heaters are available in natural gas, LP, and electric
models. Gas-fired models have a higher hot water output than electric models. Examples:
home heating system, bathroom, booster for dishwasher and washing machines.

Some types of instantaneous water heaters are thermostatically controlled. They can
modulate (vary) their output temperature according to the water flow rate and the inlet water
temperature. Instantaneous point-of-use water heaters fit compactly under a fixture (example:
sink or lavatory) and heat water at the location where it is used.

ADVANTAGES DISADVANTAGES
 Consume 20% to 30% less energy
than storage tank models.
 They meet NAECA standards while
taking up minimal space and without
increasing installation costs.  The hot water flow rate is limited by
 Can be mounted on a wall. the size of the unit.
 Produce minimal standby energy  Typically, tankless systems can be
waste. more complicated and expensive to
 Provide a virtually endless supply of install.
hot water.
 Have an average life expectancy of
20 or more years.
 Have an average EF rating of 0.75.
 Instantaneous water heater

Water Heater Type Maintenance Activity Frequency

 Recommended every 2 to 4
 Draining and flushing years. (will vary depending
heat exchanger. on local water quality
conditions)
Instantaneous Water
Heaters  Inspection of burner,
temperature and
pressure relief valve, air  Recommended annually
intake filter, water filter,
and venting system

3. Circulating Water Heaters

Circulating water heaters consist of a separate storage tank that stores water heated by
a heat exchanger. The heat exchanger may be a separate unit that is heated by stream or hot
water from a boiler or may be contained in a boiler. The boiler may be designed to exclusively
heat water for DHW or BSHW use or may be used for other purposes.

ADVANTAGES DISADVANTAGES
 Noise.
 Convenience  Using too much power.
 Save money  Potential heat losses.
 Eco-friendly  Corrosion.
 Sensor valve costs.
Types of Circulating Water Heaters
 Standard: A circulation pump was designed to run continuously to keep the water hot at all
times. Examples are commercial buildings such as restaurants and hotels.
 On-Demand: A demand or on-demand water circulation system only starts circulating the hot
water when you want it. This system will also save you both water and money.
 Time and Temperature: These systems allow you to preset times and even specific
temperatures at which you would like your hot water.

Two types of water heaters that use space heating boiler:

 Tankless coil water heater. No separate storage tank is needed in the tankless coil water
heater because water is heated directly inside the boiler in a hydronic (hot water) heating
system. The water flows through a heating coil or heat exchanger in the boiler whenever a hot
water faucet is opened.
 Indirect water heater. A separate storage tank is required with an indirect water heater. The
indirect water heater circulates water through a heat exchanger in the boiler. But this heated
water then flows to an insulated storage tank. Indirect systems can be fired by gas, oil,
propane, electric, solar energy, or a combination of any of these.

Indirect water heater

WATER HEATER
ADVANTAGES DISADVANTAGES
TYPE
Tankless coil water  It’s easily fitted to most  Less efficient during
heater boilers. (Example: steam warmer months and in
boilers) warmer climates.
 More cost-efficient in the  Due to the reduced need
winter months than a and frequency for hot water
typical water heater. on demand.
 Much cheaper to install
 Can only last about 10
and maintain.
years.
 Easier to replace.
 Saving on heating costs  Not compatible with a
furnace.
 If the household is on hard
 water supply, it will require
a water softener to run
smoothly and efficiently.
 High mineral water areas
foul up heat exchanger.
Indirect water  Saves money and energy  Sometimes the need to over
heater  Furnace compatible. size boiler for hot water
load.

Heat Pump Water Heaters

Heat pump water heaters extract energy from outdoor air and use it to produce hot water very
efficiently. Heat pump water heaters use an electric motor to run a compressor. The compressor
draws a gaseous refrigerant through an evaporator, raising its pressure until it liquefies in the
condenser. This heat pumping process heats the condenser and cools the evaporator. In removing heat
from air, the heat pump both cools and dehumidifies the air, thus helping to also meet cooling needs.
The heat pump water heater makes economic sense in hot humid regions where natural gas in
unavailable (e.g., tropical islands like Hawaii), electric energy cost is high, and the need for
dehumidification is virtually constant. In most cases, the extra costs of heat pump water heaters over
standard electric water heaters are paid back in a few years.

ADVANTAGES DISADVANTAGES
 Efficient (Energy and Cost)  Expensive
 Safe and Environmentally Friendly  It might not keep up when demand is
 Save money and energy high

Water Heater Type Maintenance Activity Frequency

Heat Pump Water  Recommended to clean
 Cleaning of water tank.
Heaters regularly.

Solar Water Heaters

Solar water heater draws energy from the sun. Typically includes collectors mounted on the
roof or in a clear area of the yard, a separate storage tank near the conventional heater in the home,
connecting pipes, and an electronic controller. This system also needs a backup plan (such as natural
gas or electricity) so that the water heater can continue to run on cloudy days.
 Solar water heater

ADVANTAGES DISADVANTAGES
 Energy efficient
 High upfront installation costs
 Water heating bill savings
 Dependent on climate
 Low maintenance
 Only heats water
 Environmentally friendly

Desuperheaters
Desuperheaters in known as a secondary heat exchanger device. It is an attachment to an air
conditioner or heat pump that allows waste heat from that device to assist in heating domestic water.
In hot climates, a desuperheater can provide most of a home’s hot water needs.

Types of desuperheater
 Unlagged Section Pipe – It is the simpliest type of desuperheater, where heat can be
radiated to the environment.
 Indirect Contact Desuperheaters – Example: Tube Bundle Type Desuperheaters.
This type of desuperheater consists of a heat exchanger, typically a shell and tube,
with superheated steam on the other.
 Direct Contact Desuperheaters – Example: Water Bath Type Desuperheater. The
superheated system is injected into bath. This additional heat will cause saturated
steam to evaporate from the surface of the bath.
 Water Spray Desuperheaters – Superheated steam is passed through a section of
pipe fitted with one or more spray nozzles. These inject a fine spray of cooling water
into the superheated steam, which cause water to be converted into steam.

Water Spray Desuperheaters are affected by the following factors:

 Particle Size
 Turbulence
 Pressure drop across the nozzle
 Velocity
 Cooling water flowrate
Desuperheater Process
Most common way of lowering the temperature of superheated steam or gas is direct addition of
water or relational gas. With the help of desuperheating process the temperature of this superheated
steam can be used for some other applications such as:
1. sanitary hot water
2. room heating
3. hot water for processes
4. cleaning water

ADVANTAGES DISADVANTAGES
 Reduction in condenser pumps power  Required a very high rated and
consumption. expensive equipments.
 Minimal pressure drop  The temperature of superheated
 Compact designs steam can damage sensitive
 Design code compliant equipments of the system.
 Range of outlet superheat capabilities
 Variety of standard materials
 Horizontal or vertical orientation with
upward flow

Energy Efficiency
The energy factor (EF) is a standardized measure used to express the efficiency of residential
heaters. It was developed by the U.S. Department of Energy. Energy efficiency simply means using
less energy to perform the same task – eliminating energy waste.

Benefits of Energy Efficiency:

 Reducing greenhouse gas emission.
 Reducing demand for energy imports.
 Lowering our cost on a household and economy wide level.

It represents the amount of heat required to warm up hot water for a typical home in a year,
divided by the amount of energy input into the heater to warm that water. A water heater with an EF
of 0.60 transfers 60% of the energy it consumes to the hot water; the remaining energy is vented
outdoors as waste heat. The higher the EF, the more energy efficient the water heater and the less
energy consumed.
High Efficiency (HE) Water Heater
High efficiency water heaters extract heat energy out of the exhaust gases to heat the water,
but they include a secondary heat exchanger that maximize the heat transfer process to extract as
much heat as possible. It use 10 to 50 percent less energy than standard models, saving homeowners
money on their utility bills. Actual energy savings from high efficiency water heaters depend on
family size, heater location, and the size and placement of water pipes.
Type of water heater that is most energy efficient:
Tankless heaters can be 24-34% more energy-efficient than regular water heaters for
households that use 41 gallons or fewer of hot water daily. Tankless heaters can be 8-14% more
energy-efficient for households that use around 86 gallons daily.

ADVANTAGES DISADVANTAGES
 More expensive equipment.
 Reduced operating costs.
 Higher maintenance costs.
 Creates hot water fairly quick
 Certain installation limitations can
 Does not require fire rated room
get expensive.
 Safer
 Accurate installation is crucial.

Hot Water Recirculating System

A hot water recirculating system continuously circulates hot water from the water-heating unit
through the hot water supply piping and back to the water heater through hot water recirculating
piping. This ensures that hot water is always available at the taps, thus avoiding the need to run water
for a long time to obtain water at the desired temperature.

Three types of hot water recirculating strategies:

 Continuous Recirculating - water is constantly recirculated from the water heater through the
piping. This type of system is best suited for buildings having round-the-clock occupancy.
Examples: Hospitals and multiunit residential buildings
 Timed Recirculating- involves use of an electronic or electromechanical timer to shut off
circulation of hot water when the building is not occupied. Nighttime housekeeping and
maintenance operations should not be neglected when considering shutdown periods.
Example: Commercial, institutional, and industrial buildings that are closed at night and/or on
weekends.
 Thermostatically Controlled Recirculating- relies on a sensor located at a remote location in
the recirculating line, which senses water temperature and activates the recirculating pump
when water temperature drops below a predetermined setting.
References

Wujek, J.B. & Dagostino, F.R. (1978) MECHANICAL AND ELECTRICAL SYSTEMS in
Architecture, Engineering, and Construction Pearson Prentice Hall

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