49
FEATURES
A corporate office-sized heat pump.
insulation to avoid energy losses. All this influences the
performance of a heat pump and the efficiency you can get
out of the system.”
Grant Spires, maintenance manager at GMC Aircon outlines
some other factors that can affect the performance of a heat
pump. “Lime scale build up in the shell tube heat exchanger
can reduce heat transfer into the water, which in turn will
have a negative effect on the COP of the heat pump unit.”
Certain processes can be undertaken in the manufacturing
or installation process to extend the life of the equipment.
“Stainless steel sheet metal can be used in the
manufacturing of heat pumps, and evaporator coils can be
chemically treated to extend the life span of heat pumps
placed along coastal areas. Servicing of heat pumps is very
similar to that of an air conditioner’s condenser (outdoor unit).
Coils and drain pans need to be kept clean and the usual
electrical and refrigerant checks need to be carried out. The
system is self-contained (such as with a fridge) so one should
never really have to adjust gas pressure unless there has
been a gas leak. Most of the maintenance and repairs would
be carried out by an air conditioning technician,” says Spires.
Altmann adds, “For heat pump manufacturers it´s important
to take the wide range of temperature difference in South
Africa into consideration. Heat pumps must be able to work in
conditions between -10°C and +42°C outdoor temperature,
otherwise the system will keep tripping or running purely on
the element. Furthermore it´s important that the heat pumps
are protected against corrosion in the coastal regions, as the
salty air is very aggressive and can cause corrosion. As we
have a high demand for cooling in summer, the heat pump
should also be able to cool, so that the client can use one
device for his domestic hot water heating, space cooling and
pool heating.”
In addition, ambient air temperatures also affect the COP of
the unit, says Vermeulen. “The higher the air temperature, the
better the performance will be. When the system gets tested
at SABS and test laboratires they test it over a spectrum of
August 2019 Volume 25 I Number 6
-0.5°C to 40°C to get an average COP of the system. Where
a heat pump is deployed in an extremely hot location it has
a safety feature whereby when the combined temperature
of the water and the system gets above a limit of 90°C, it
automatically switches off to protect the compressor from
overheating, until it cools down.”
Altmann adds, “To install a heat pump system, the building
must have a central plant room where the storage water
tanks as well as accessories like circulation pumps can be
placed. The heat pump can be placed in this plant room.
It can be connected with air ducts to the outside, so that
the system will get enough fresh air as energy source and
can blow the exhaust air out again. Another possibility is to
place the heat pump installation outside, in which instance
the building has to offer enough space for such an outdoor
installation. To supply the hot water to the different points
of use, it´s recommended to run a ring main through the
building, to serve the client with immediate hot water and
avoid waste of water.
“A heat pump would typically mainly be recommended by
consulting engineers, but is also picking up on the contractor
side of the industry. For a domestic application, a consultant
is not necessary, but with industrial or commercial I would
say consultants are needed and both consultants and
contractors should work closely together to make sure that
both understand the hot water design and also the function
of the heat pump. Examples of common pitfalls are: not
understanding the application and its hot water demands and
then undersizing the hot water storage (vessel); the sizing
of the heat pump according to size of storage; and recovery
times of the water for the next draw of hot water.”
Vermeulen says the architect and consulting engineer should
jointly be involved from the beginning in designing the service
ducts to accommodate the system, “especially if the heat
pump is to be located in the basement of a large commercial
building, to ensure adequate ventilation.” Wet services
engineers need to be involved to ensure the correct pipe
sizing and installation is correct, he adds.
“Heat pumps
must be able
to work in
conditions
between
-10°C and
+42°C outdoor
temperature,
otherwise the
system will
keep tripping
or running
purely on the
element. ”
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