Mitsubishi Electric ecodan PUHZ-W50VHA2 User Manual page 10

How a heat pump works
The heat pump essentially works the same way as your refrigerator but in reverse.
The Ecodan is hermetically sealed (no refrigeration piping involved) with R410A
refrigerant. The cycle it completes to produce heat is known as the vapour-
compression refrigeration cycle:
The first phase begins with the refrigerant being cold and at low pressure.
The refrigerant within the circuit is compressed as it passes through the
compressor. It becomes a hot highly pressurised gas. The temperature also
rises typically to 60°C.
The refrigerant is then condensed as it passes across a plate heat
exchanger. Having a cooler side to the heat exchanger it decreases the
temperature, so it changes the property of the refrigerant from a gas to a
liquid.
The refrigerant as a cold liquid still has a high pressure. For expansion to
occur it passes through an expansion valve. The pressure drops but it is still
a cold liquid.
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
outside air is absorbed by the refrigerant.
It is only the refrigerant that is being passed through this cycle; the water is heated
up by the plate heat exchanger. The cooler water extracts energy from the hotter
refrigerant, i.e. the water is heated as it passes across the plate heat exchanger.
This water flows towards the heating system and hot water storage tank, where
its energy is used to provide domestic hot water and space heating.
Sealed Ecodan Unit
Outside Air
4 evaporates
Evaporator
8
INTRODUCTION
1 compressed
Compressor
Expansion Valve
3 expansion
7
Boiling points:
The refrigerant used within the
cycle has a different boiling point
to water, which boils (turns from
liquid to gas) at 100°C. This is
only true at atmospheric pressure.
When the pressure increases so
does the boiling temperature;
decrease the pressure and boiling
temperature drops. Liquid turns
to gas at a lower temperature.
The boiling point changes when
the pressure changes. Refrigerants
have different properties to water
and have much lower boiling
temperatures. During the fourth
stage of the cycle the outside
ambient temperature is much
hotter than the temperature of
the refrigerant and will heat it.
Hot water for heating
and hot water
2 condensed
Heat Exchanger
Fig. 1.3