This paper presents an overview of the solar boosted
heat pump water heater technology. The tests made on direct
expansion solar assisted heat pumps have shown that good
COP can be attained while using working fluids that do not
cause any harm to the environ ment. Modifications to the
condenser in the heat pump can be made in order to improve
and distribute evenly the heat transferred to the water.
HPWH – Heat Pump Water Heater
SBHPWH – Solar Boosted Heat Pump Water Heater
SBHP – Solar Boosted Heat Pump
COP – Coefficient Of Performance
SAHP – Solar Assisted Heat Pump
DX-SAHP – Direct Expansion Solar Assisted Heat Pump
Qw – Heat transfer to water
Wc – Electricity consumed by the compressor
CFC – Chlorofluorocarbon
ODP – Ozone Depletion Potential
GWP – Global Warming Potential
transformed into higher grade heat and transferred to the
An improved type of heat pump has been developed
and is known as the Solar Booster Heat Pump Water Heater
(SBHPWH). The principle behind this device is similar to the one described above. The difference lies in the energy source. Air is still providing energy to the system; however, the
evaporator also plays the role of the collector to absorb the radiations emitted by the sun.
There are several advantages to this type of heat
pump. The radiation emitted by the sun provides a good source of energy except during the night and on cloudy days. The
SBHP can still operate as it also uses the ambient air as an energy source. Using a refrigerant as the working fluid also prevents the system from rusting and it enables the SHBP to
function in low temperature environments where water, which
has a higher freezing point, would solidify and not flow in the structure. The refrigerant is usually at a temperature lower or equal to the ambient air which minimizes or even eliminates
the heat loss by convection to the surroundings.
2. BRIEF HISTORY AND WORKING PRINCIPLES
Heat pump water heaters are devices that extract
energy in the form of heat to transfer it to a fluid. The different type of sources used for heat pumps are: air, ground and
ground water. Each of these sources has energy stored in them and the role of the heat pump is to take that energy at low
pressure and temperature and raise those two properties of the fluid.
This paper will mainly focus on air as the one of the
sources of low-grade energy. Air is drawn into the heat pump by means of a fan. The air then flows through an evaporator
which contains a refrigerant. The fluid in the evaporator,
which is at a lower temperature than the air, absorbs its heat. A compressor is then used to increase the temperature a nd
pressure of the refrigerant. The hot refrigerant then flows
through a condenser which transfers the heat to the water
stored in a tank.
This system works in most of the places around the
world since air contains energy that can be absorbed,
Heat pumps have been developed to reduce the use of
fossil fuels for heating purposes in households.
The first concept of the heat pump has been awarded to
Sadi Carnot, a French officer, in 1824 but it is only in 1927 that an English engineer T.G.N. Haldane, patented this
invention for the first time. 
The first large scale uses of the heat pump water heaters
(HPWH) have been recorded in the 1950’s in the United States. The following decade, their unreliability caused a severe drop in their commercialization. The rise of the prices of fossil fuels in the 1970’s induced an increase in the cost of electricity. Greater efforts were made to develop technol ogies that would suppress or minimize the consumption of oil and gas. [1,2] . Heat pumps were then
The following figure illustrates how heat pump water heaters function.
exchanger [5,6]. The evaporator and solar collector were then combined in a single element to produce a new solar...