Overview
A ground source heat pump is only as good as the ground loop feeding it. The heat pump itself is a manufactured unit with a published performance curve. The array buried outside is site built, and how well it is purged, charged and balanced determines whether the installation ever reaches the efficiency the design promised.
Air is the main enemy. A ground loop is filled with water that carries entrained air and construction debris, and unless that air is physically driven out at velocity it collects at high points and in individual circuits. The result is reduced flow through affected loops, uneven heat extraction across the array, noisy circulation and a heat pump working harder for less. None of it registers as a fault. It registers as a running cost, year after year.
ProMech delivers ground loop purging and conditioning across Northern Ireland, Dublin and London, on new arrays at commissioning and on existing arrays that have never performed as designed.
Our Process
- 1
Loop survey and circuit schedule
We record every circuit: borehole or horizontal array, loop lengths, pipe diameters, manifold arrangement and header configuration. Purging is done circuit by circuit, so knowing what is out there comes first.
- 2
Pressure test before purge
Each loop is pressure tested and held to confirm integrity before anything else happens. Finding a damaged loop after the array is charged with glycol is an expensive way to find it.
- 3
High velocity purge
A purge rig circulates water through each circuit individually at a velocity high enough to carry air and installation debris out of the loop rather than pushing it round it. Low flow purging simply relocates the air.
- 4
Air separation and verification
Purging continues until the return runs clear and free of entrained air, verified visually at the sight glass and by stable flow, not by elapsed time.
- 5
Antifreeze mixing and charging
Glycol is pre mixed to the concentration the design requires for the freeze protection specified, then charged and circulated. Concentration is confirmed by refractometer rather than assumed from the volume added.
- 6
Flow balancing across circuits
Individual loops are regulated so each takes its share of flow. An unbalanced array leaves some loops over pumped and others barely circulating, which degrades the thermal yield of the whole field.
- 7
Performance verification and records
Flow rates, pressure differentials, glycol concentration and inlet and outlet temperatures recorded per circuit and issued as the commissioning record for the array.
Symptoms of a Poorly Purged Array
Heat pump short cycling
Insufficient flow through the ground loop trips the unit on low source temperature, so it stops and restarts repeatedly instead of running a full cycle.
Coefficient of performance below design
The unit runs, the building is warm, and the electricity bill is well above what the design predicted, because the source side is not delivering.
Uneven circuit temperatures
Return temperatures differing markedly between loops on the same manifold, indicating some circuits are carrying the array and others are contributing little.
Audible air in the system
Gurgling or trickling in the manifold and pipework, the most obvious sign that air was never fully driven out at commissioning.
Pump running at maximum
The circulator sitting at full speed to achieve design flow, consuming more power and wearing faster than it should.
Freeze protection unproven
No recorded glycol concentration, so nobody knows the actual protection temperature until the winter that tests it.
Standards & Compliance
- MCS MIS 3005, heat pump systems installation standard
- CIBSE CP1, heat networks code of practice
- BSRIA BG 50/2021, water treatment for closed heating and cooling systems
- CIBSE Commissioning Code W, water distribution systems
- CDM 2015 site safety protocols
Where We Work
- District and heat networks, shared ground arrays
- Public sector estates, schools and civic buildings
- Commercial developments, offices and mixed use schemes
- Large residential, apartment blocks and housing schemes