Ground temperature at 1m deep is typically around 130C in the South of England – it does lower slightly towards the north of Scotland.
The Ground Loop
A series of pipes are buried at this depth and are filled with water – glycol (anti-freeze) fluid. This is what is known as the ground loop. They can be laid in a number of ways depending on the site requirements. If space permits, a horizontal ground-loop is generally specified either as a ‘slinky’ loop or as a straight run. Where space is limited, compact collectors laid either horizontally or vertically can be used or more commonly boreholes (vertical loops) are specified. Typically boreholes are up to 100m deep.
Where a series of ground-loops are used, they are connected together through an underground manifold which often will incorporate isolation valves which are used to isolate the individual ground-loops.
The fluid (approx -30C) exits the Evaporator and travels the full length of the ground loop, slowly warming from the surrounding ‘heat’. The warmed fluid returns to the Evaporator.
The Evaporator is the first component part of the heat pump and consists of a heat exchanger the function of which is to take the collected ‘heat’ out of the ground loop liquid and then return it in readiness for its’ next journey through the ground loop.
On the opposite side of the evaporator is a refrigerant which enters as a very cold liquid, but when warmed by the ground-loop fluid in the heat exchanger turns to a gas boiling at approximately -100C.
The refrigerant gas exits the evaporator and travels to the heat pump Compressor.
The heat pump Compressor is an electrically driven pump used to rapidly raise the pressure of the refrigerant gas.
Compressing the refrigerant gas raises its’ temperature dramatically with up to 1250C achievable.
This high temperature gas is fed to the heat pump Condenser.
The heat pump Condenser is another heat exchanger where its function is to draw the heat from the refrigerant gas out and into the domestic plumbing system where it heats the water circulating in the under-floor heating or radiators as well as that in the hot water tank. The now cooler but still pressurised gas now passes through the Expansion valve.
The Expansion Valves’ function is to release the pressure the gas is currently under and as a result returns the gas to a cold (below -100C) liquid state in readiness for entering the Evaporator and for the cycle to start once more.