Thermodynamics – Explanation 

How Thermodynamics Work

The thermodynamic system is similar to a heat pump, in that it uses a refrigerant liquid, However, unlike a heat pump the system uses a solar plate collector to maximise the use of the air temperature.

The panel is 190 cm X 80 cm and utilises both sides to absorb the heat. This means one panel has a collective area of about 3.2 metres.

The liquid refrigerant runs through the panel at -26 and is heated by the atmospheric temperature. The bigger the differential the faster the system works. Not only does the panel absorb heat from the sun but also from the wind, rain and snow. This is how it can produce hot water even through the night.

The system will work down to about -10 degrees Celsius but of course the warmer the temperature the faster the recovery will be.

There are four stages to the process

Step One

The environmentally friendly refrigerant liquid is fed into the veins of the solar collector

The liquid absorbs the heat and it vaporises into a gas which increases the pressure.

Step Two

The hot gas is then passed through a compressor where the pressure causes it to heat further.

Step Three

The heated gas is then passed into the heat exchanger where the heat is transferred into the water cylinder.

Step Four

The cooling gas then passes through a valve reverting back into a liquid where it runs back into the panel where the process begins again.

Thermodynamic Diagram

The system is a solar domestic hot water system in which the solar loop operates on a similar principle of a heat pump.

It is composed of:-

  • An unglazed heat absorber  (1) with 3.20 m2 total aperture area.
  • An insulated,  hot water thermal store (200 l) (2)
  • A  thermoblock, which comprises the electrical powered compressor (5), the thermostatic expansion valve (7), the electrical heating element (4) and the controller.
  • Heat transfer fluid (refrigerant R134a)

The heat transfer fluid in the solar loop is the refrigerant R134a.

The refrigerant is passing through the absorber and evaporates while collecting energy from the surroundings.

The evaporated refrigerant is sucked by the compressor which raises the pressure.

In the condenser, which is integrated as an immersed solar-loop heat exchanger in the lower part of the store, the refrigerant condenses while transferring its condensing heat to the domestic water in the store.

Before the refrigerant is returning to the absorber, a thermostatic expansion valve is reducing the pressure.

An electrical heating element is located in the lower part of the store at the height of the solar-loop heat for use in emergencies and for the anti-legionnaires system.

The magnesium anode (8) or sacrificial anode will extend the life of the tank.

For more information on the thermodynamic systems click here