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2
Introduction
How the Heat Pump Works
Space heating
Heat pumps take electric energy and low grade heat energy from the outdoor air
to heat refrigerant which in turn heats water for space heating. The efficiency of a
heat pump is known as the Coefficient of Performance or COP this is the ratio of
heat delivered to power consumed.
The operation of a heat pump is similar to a refrigerator in reverse. This process
is known as the vapour-compression cycle and the following is a more detailed
explanation.
Low temperature renewable heat
energy taken from the environment
Electrical energy
input
en
1 kW
Economical Best Practice
Air source heat pumps can provide space heating all year. The system is different
to a conventional fossil fuel heating system. The efficiency of a heat pump is
shown by its coefficient of performance as explained in the introduction. The fol-
lowing points should be noted to achieve the most efficient and economical opera-
tion of your heating system.
Overview of Controls
Built into the hydrobox is the Flow Temperature Controller(FTC). This device
controls the function of both the outdoor heat pump unit and the hydrobox. The
advanced technology means that by using an FTC controlled heat pump you can
not only make savings compared to traditional fossil fuel type heating systems
but also compared to many other heat pumps on the market.
As explained in the earlier section, 'How the Heat Pump Works,' heat pumps are
most efficient when providing low flow temperature water. The FTC advanced
technology enables the room temperature to be kept at the desired level whilst
utilising the lowest possible flow temperature from the heat pump.
In room temp. (Auto adaptation) mode the controller uses temperature sensors
around the heating system to monitor space and flow temperatures. This data
is regularly updated and compared to previous data by the controller to predict
changes in room temperature and adjust the temperature of water flowing to the
space heating circuit accordingly. By monitoring not only the outdoor ambient, but
the room and heating circuit water temperatures, the heating is more consistent
and sudden spikes in required heat output are reduced. This results in a lower
overall flow temperature being required.
3
2 kW
Heat energy output
3 kW
2. Condenser
(Plate heat exchanger)
3. Expansion valve
4. Evaporator
(Outdoor unit air heat exchanger)
The first phase begins with the refrigerant being cold and low pressure.
1. The refrigerant within the circuit is compressed as it passes through the com-
pressor. It becomes a hot highly pressurised gas. The temperature also rises
typically to 60°C.
2. The hot refrigerant gas is then condensed as it passes across one side of a
plate heat exchanger. Heat from the refrigerant gas is transferred to the cooler
side (water side) of the heat exchanger. As the temperature of the refrigerant
decreases its state changes from a gas to a liquid.
3. Now as a cold liquid it still has a high pressure. To reduce the pressure the liq-
uid passes through an expansion valve. The pressure drops but the refrigerant
remains a cold liquid.
4. The final stage of the cycle is when the refrigerant passes into the evaporator
and evaporates. It is at this point when some of the free heat energy in the out-
side air is absorbed by the refrigerant.
It is only the refrigerant that passes through this cycle; the water is heated as it
travels through the plate heat exchanger. The heat energy from the refrigerant
passes through the plate heat exchanger to the cooler water which increases in
temperature. This heated water enters the primary circuit and is circulated and
used to serve the space heating system.
• In most situations space heating is best performed using the room tempera-
ture mode. This enables the heat pump to analyse current room temperature
and react to changes in a controlled manner utilising the specialised Mitsubi-
shi Electric controls.
• Using the SCHEDULE and HOLIDAY functions prevent unnecessary Space
heating when the property is known to be unoccupied for instance during the
working day.
• Due to lower flow temperatures, heat pump heating systems should be used
with large surface area under-floor heating. This will provide a steady heat to
the room whilst improving efficiency and so lowering running costs of the
system as the heat pump does not have to produce water at very high flow
temperatures.
Ambient
temp.
sensor
Flow temp. sensor
Return temp. sensor
1. Compressor
FTC
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