Summer may not be a time when we want to remember cold winter weather, but it’s certainly the best season to service heating systems, explains heat pump specialist Bob Long in the first of two parts
Heat pumps must maintain a high level of performance to deliver their economic saving. Defects that will reduce performance can invisibly occur, while outward signs appear normal. Annual examination is therefore essential, and starts with a few visual checks, after turning the power off and safely isolating the unit of course!
A visual examination begins with particular focus on the overall condition of the unit’s enclosure, and surfaces showing evidence of corrosion. The fins should be tightly fitting to the horizontal tubes. Corrosion of the fin material can eventually cause the fins to come loose from the pipes resulting in reduced thermal conductivity between the fin and the refrigerant pipe, and compromised efficiency
An ASHP is usually designed to draw air through the fin/coil block and in doing so, garden debris such as leaves and grass cuttings can attach to the outer surface and cause a severe fall in efficiency. This fault is common so it’s important to suggest to owners that they make periodic checks throughout the year.
The evaporator fan should be checked for corrosion and treated as necessary. Examine the fan blades for evidence of metal fatigue cracks and try to move the fan-motor drive shaft from side to side, checking the motor bearing for any excessive movement up, down and laterally. If available, the correct lubricant should be applied. Check the insulation on all interior and exterior pipes, water and refrigerant, and repair any places where the insulation is suspect.
GSHPs also have a number of essential checks to carry out regarding the cold-side of the system comprising the ground-loop, header tank or expansion diaphragm, working fluid circulating pump, flow filter and evaporator.
If leakage is suspected, the cause must be found and remedied before continuing any further. The working fluid is probably going to contain a freezing point depressant such as glycol, and the concentration should be checked to meet with the manufacturer’s recommendation. Hand held refractometers are quite reasonably priced and a great way to obtain an accurate reading.
To complete the testing for the low temperature side of the system, the flow rate of the working fluid circulation pump should be measured and compared with manufacturer’s requirements. Centrifugal pumps do ware out and this is evidenced by a reduced pumping efficiency, causing a reduction in flow rate. If there is evidence of this, and the pump shows signs of ware, it should be replaced.
The flow and return temperature of the ground loop should be noted and compared with the previous year’s reading. This will provide a good indication as to the ground’s ability to yield energy without a fall in operating temperature. If an annual reduction in operating temperature is noted, it is possible that the system is in fact mining energy rather than collecting from a renewable resource.