(Vaillant preferred heat pump installer partner)


After the ground worker completed the final pressure test of the ground loop collector and I had connected the pipes to the heat pump, only the filling of the ground loop collector was left.

As a filling fluid, a mixture of glycol and water is recommended. This achieves good thermal conductivity and an efficient level of frost protection. Vaillant provides different sizes of canister of glycol concentrate which contain up to 30 litres. I used a water butt as mixing vessel and produced a mixture of 1 part glycol to 2 parts water.

I connected a filling pump between the mixing vessel and the filling station in the ground loop circuit. This proprietary filling station provides a neat and convenient way of filling the system and eliminates the hassle of having to assemble a suitable means of adding the fluid to the system.

The glycol-water mixture was pumped into, and circulated through, the ground loop collector for around 45 minutes to ensure that most of the air came out of the system. Once satisfied that as much air as possible had been removed from the collector, I pressurised the system to 1.5 bars. At this pressure, I was able to ensure that the expansion vessel for the ground loop collector was correctly filled. The expansion vessel must be adequately sized to ensure there is sufficient volume to accept the change in volume that the fluid undergoes as its temperature changes.


What we learnt: It is not always possible to completely remove all the air from the system during the filling stage. This must be explained to the customer who should periodically check the level of fluid within the system and its operating pressure during the first few weeks that the heat pump is operating.