Heat pump
water heaters
Electric heat pump water heaters; application guidelines
Electric heat pump water heaters are
significantly more efficient than conventional electric water
heaters. With that said, certain considerations should be made prior to
installation in order to determine if application is both
viable and cost effective.
Hot Water Loads
and Heat Pump Water Heating
In order to maximize the potential energy savings,
heat pump water heating is best suited in sites with moderate to high
annual hot water loads. The systems' efficiency and the overall cost
effectiveness is compromised in applications with low hot water demand
and/or frequent vacancy.
In fact, the U.S Department of Energy has set a first hour rating of
50 gallons or higher in order for a residential heat pump water heater
to meet the energy star performance criteria and qualify for program
certification.
Adequate
Ambient Temperatures and Air Circulation
With both add on and drop in electric heat pump
water heaters, the ambient air temperature can have a significant
impact on the overall energy efficiency of the system. Manufacturers
often specify adequate
inlet or air
source temperatures or provide temperature ranges.
With
recent industry advancements, some add on and drop in heat
pump water heaters
can operate
efficiently with inlet air source temperatures as low as 35�.
An application that fails to adequately support
the specified inlet air temperature range will compromise the systems'
overall efficiency, resulting
in the extended operation of the back up electric resistance heating
elements, and/or resulting in a decreased hot water output, and/or resulting in a
decreased temperature
rise.
Add on and drop in heat
pump water heaters also require adequate amounts of
air
circulation in order for the system to operate efficiently. Proper air
circulation is required for both the systems' inlet air
and the systems' exhaust air.
Air
conditioning and dehumidification
The air
source refrigerant vapor compression cycle of an electric
heat
pump water heater not only efficiently heats stored domestic
water,
this process also expels cool and dry air through the
heat pumps' evaporator. So with add on and drop in units, cooler and
dehumidified surrounding air is a by product of operation.
It's important to note that both the cooling and
dehumidification of the ambient air is generally modest. With that
said, it's equally important to note that application in a conditioned
living space can have an adverse effect on space heating loads, albeit
modest.
With the by product of modestly cooler and
dryer air, the potential effect the add on or drop in unit may
have on annual space
heating and cooling loads must be considered by both consumers and
professionals prior to
determining application.
Condensate
drainage
The systems' vapor compression cycle also
produces moisture build up. This liquid build up is commonly
referred to as condensate. Both add on and drop in electric heat pump
water heaters come equipped with designated
connections and fittings for condensate drainage.
Some applications may require slight
modifications during the installation process in order to adequately
address condensate drainage. The drainage connection, more
times than not, can be fitted with a tube, and this tube can be
directed to a floor drain, a collection pan or container,
or directed outdoors.
The amount of condensate produced will
vary from model to model as well as from application to application.
With all models and applications, condensate drainage should
be considered prior to purchase and/or during installation. When in
doubt, consult with a local
water heating professional prior to purchase and
installation.
Heat
Pump Water
Heaters are Best Suited...
- in sites with moderate to high hot
water
loads, requiring a system with the capability of providing a moderate
to high first hour rating.
- in
applications that annually provide mild to warm inlet air temperatures.
Most manufacturers and professionals recommend inlet air
temperatures between 35� F and 100� F. An ideal location for unit
installation
can be an attic, crawlspace, garage, basement and/or furnace room.
- in
applications with a large air source. Most
manufacturers and industry professionals recommend installation in
spaces with at least 1,000 cubic feet of accessible ambient air for
proper system circulation.
- in
existing homes and/or businesses with an existing conventional
electric powered water heater. With the addition of an add
on HPWH, the
overall efficiency of the existing unit can
be significantly improved.
- in
existing homes and/or businesses that require an efficient
replacement
water heater that's electric powered. In such applications, a drop
in HPWH is most
ideal.
- in
new constructions that lack access to inexpensive natural gas and/or
new constructions that lack an adequate solar resource, eliminating the
possibility of installing a solar
hot water heater.
- in applications with unconditioned spaces that
can benefit from the year round by product of modestly air conditioned
and dehumidified air.
Heat
pump water heating in cold climates
With the
importance of warm intake air temperatures and with
the by product of cooler exhaust air, most industry professionals
generally agree that electric heat pump water heaters are better suited
in mild climate regions.
In any
climate, the overall efficiency of the system will be determined not
just by annual ambient air temperatures, or by the effect (or lack of)
that
the cool exhaust air has on annual space heating loads, efficiency will
be determined by the amount of annual heat pump operation as well.
After all
the constant operation of the back up electric resistance
heating elements will reduce
the overall efficiency of the system significantly.
With that
said, in many applications heat pump water heating can provide
energy savings in even the coldest of climate regions within the United
States, especially when
compared to conventional electric storage tanks.
Air
Source Ducting and Exhaust Air Venting
In some
applications (especially new constructions) the cool
exhaust air can be vented and redirected to an alternate location other
than the indoor ambient air surrounding the unit. An
alternate air source can be utilized as the units' intake air
source well.
The cool
and dry exhaust air can be vented to an unconditioned space such as a
garage or attic, or even outdoors. In some applications, the exhaust
air
can be vented directly to the central space cooling
systems' ductwork. This will
provide modest assistance during the space cooling
season.
The units'
air source can be gathered from a warmer and unconditioned space, such
as a crawlspace, utility room or even a furnace room, provided the
space in question has an
adequate amount of air source and the annual air temperature of the
ambient air is
adequate as well.
Both air
source ducting and exhaust venting can be achieved with duct flanges,
collars, dampers and other common ductwork connections.
In most
applications (especially new constructions) air source
ducting combined with exhaust
venting can provide the additional flexibility of locating the
electric heat pump water heater in either a conditioned or
unconditioned space.
In most
applications (especially in cold climate regions) the addition of
ductwork and vents can
significantly improve the efficiency of a heat pump
water heater by eliminating the potential adverse effects the cool
exhaust
air may have on space heating loads, while utilizing an air
source
that annually is warmer than the air source of a
conditioned space, while ensuring an adequate hot
water output.
Ducting
and venting, while especially ideal in cold climates, can boost
the energy efficiency and the output of the system in
any
climate region. With some HPWH, relatively inexpensive duckwork kits are available. Consult with a local water
heating professional before determining if ducting and
venting is viable.
More
on electric heat
pump water heaters
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