Heat
pump
water heater
Energy efficient electric hot water heaters
Heat pump water heaters are one of the most
promising energy saving options in water heating. Although electric
powered, there significantly more energy efficient than
conventional electric storage tanks.
In most applications, electric heat pumps are
more efficient than conventional gas water heaters as well. In
appropriate applications, a heat pump hot water heater
consumes less electricity than a conventional storage tank,
and at an
equivalent or comparable first
hour rating.
Heat Pump Water Heating
vs. Conventional Electric Water Heating
Heat
pump water heating uses electricity to transfer heat from an
existing source (the surrounding air) to the domestic water.
Conventional electric water heating utilizes electric resistance to
heat
elements that are
immersed within the storage tank, along with the stored domestic water.
Heat pump
technology is a viable energy saving alternative to electric resistance
because redirecting existing heat to stored domestic water
requires less energy than directly generating or creating heat within a
water heating storage tank.
The past
Heat pumps have been used in space heating and
space cooling systems in both residential and commercial applications
for several decades. In fact this same heat redirecting technology is
utilized in refrigerators and storage freezers.
More recently heat pumps have been incorporated in
both domestic water heating systems as well as swimming pool water
heaters. This heat capturing and moving technology, while similar in
freezers and refrigerators, is designed to operate in reverse when
utilized in water heating systems.
Heat pump hot water heaters were first
introduced by electric utility companies as a means of
reducing peak hour demand. With the high initial cost, poor consumer
awareness, and a lack of production from large appliance manufacturers,
these systems failed to gain popularity with consumers and
professionals alike.
The present
While electric utility companies continue
to aggressively promote this technology, a few large appliance
manufacturers have introduced heat pump water heaters, with
other
large manufacturers developing and/or announcing plans to follow suit.
Some of the new generation heat pump models have
earned energy star ratings and energy factor ratings
of 2.0 and 2.5, which is significantly higher than most of the gas and
electric powered residential storage tanks currently available.
Today these models (as well as other models) are
eligible for federal and state water
heater tax credits, local electric utility
rebates, and most current models are featuring longer product
warranties.
A handful of reputable mid size companies (that
are U.S based) design, develop, manufacture and market electric heat
pump water heaters that are ideal for both residential and light
commercial applications.
Heat
Pump Water Heating; An Under Utilized
Technology
Unfortunately, heat pump water heating systems are
very much underutilized
in both residential and light commercial applications
throughout most of the
United States. Heat pump water heating is
underutilized for
several reasons;
- Many home owners and business owners remain
unaware of
the superior efficiency of these water heating systems.
- Many contractors are either unaware or
unfamiliar with heat pump water heaters and often times it's a
contractor who recommends a replacement system or a new system in the
case of new constructions.
- Compared to other technologies,
there's often a lack of availability. Only a handful of reputable
manufacturers are
active in the residential and light commercial heat pump water heater
market. For decades the industry's main focus has been on large
commercial
applications.
- The majority of heat pump water heaters are
unavailable at retailers and public whole sellers. Manufacturers often
utilize electric utility providers, independent
representatives and some contractor based whole sellers to promote
these
systems for residential and light commercial applications.
How
heat pump water heaters work
Air
Source Vapor Compression Cycle
These water heating systems use an air
source heat pump. A vapor compression cycle gathers heat from the
ambient (or surrounding) air and this gathered heat is then indirectly
transferred
to the stored domestic water.
The major internal components within the heat pump
vapor compression cycle are the compressor, the evaporator an the
expansion valve. A refrigerant is circulated throughout the major
components of the system.
When the temperature of the stored domestic water
falls below
the temperature setting, the evaporator absorbs heat from the
ambient air, with the assistance of an electric fan. The
compressor is then activated, extracting refrigerant vapor from the
evaporator
coil.
The systems' refrigerant vapor is then pressurized
and heated by the compressor. The pressure applied by the
compressor transforms the refrigerant into liquid.
The heated
liquid refrigerant then enters the condenser. In most instances, the
water is plumbed from the storage tank and through the condenser coils.
The condenser serves as a liquid to liquid heat
exchanger, transferring heat from the heated refrigerant to
the
stored domestic water. The liquid
refrigerant is then returned to the evaporator through the expansion
valve.
The expansion valve reduces the pressure of the
refrigerant, in effect returning it back to vapor. This water
heating vapor compression cycle is
reactivated when the stored domestic
water requires re heating.
Back
Up Power Source
In these systems, conventional heating
elements (either built in or existing) are designed to
serve as the
systems' back up power
source.
Heat
pump water heaters
are designed to work in conjunction with conventional electric
resistance
heating elements, and some units can operate in conjunction
with
conventional gas burners as well.
HPWH types
and system configurations
Although the technology involved is generally
universal, heat pump water heaters are available in distinctly
different configurations and system types. Which system type is more
suitable
will ultimately be determined by the particular application.
- Add
on HPWH; a retrofit unit, designed to
operate in
conjunction with an existing conventional storage tank water heater.
- Drop
in HPWH; often referred to as integral or
integrated. These units are standalone systems that incorporate both
the heat transfer and storage.
- Integrated
and Full Demand Systems; integrated water
heating,
space heating and space cooling systems.
More
on electric heat
pump water heaters
More on energy efficient water heating
Other energy efficient water heating options
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