Talking tech

Heat pump specialist Bob Long looks at ways to boost the uptake of heat pumps via improvements to economic performance

Back in 2010, with the imminent promise of the RHI, many of us decided to get involved in this emerging market with prospects of vibrant activity.

How wrong could we be? The delivery date kept moving with many companies teetering on the edge of bankruptcy, and some eventually succumbing.

Eventually the RHI arrived but the uptake of heat pump technology just does not seem to have been as dynamic as we had all hoped.

Growth in the heat pump market is challenged by the low price of other heating alternatives although, surprisingly, the comparative cost pence per kW appears to suggest otherwise.

Probably the greatest low-cost competitor is natural gas with a cost of heating at around 6p/KWh. Assuming electrical energy is costed at 12p/KWh, a heat pump of minimal permissible efficiency (SPF 2.5:1) should return an operating cost of 4.8p/kWh.

With a simple calculation it’s easy to explain to a potential customer how savings can be made. A 20 percent reduction on a heating bill makes for a compelling argument in favour of installing a heat pump.

With such calculable evidence, the heat pump market should have followed the solar epidemic, but sadly it didn’t!

To help growth in the market the value-for-money ratio must improve. But this can only in part be achieved by better performance from the heat pump, and improvements in system design will probably have the largest overall impact on operating costs.

A call from governing bodies for an improved SPF of perhaps 3.5:1 would deliver the energy at a cost of approximately 3.4p/KWh, which already indicates this is a fight we can win.

All this arithmetic looks good but, in surfing a number of online forums for both trade and consumer interest groups, I am not reading great results.

I regret to say that stories from a number of end users are not confirming the anticipated savings. Some heat pump owners are very pleased with their decision, and others are scared to receive the next electric bill.

Much of the solution can be found in ‘designing for lifestyle’, which I have discussed in a previous article.

The output of the boiler also plays an important role in heating economics, particularly one of short-time occupancy. A boiler’s ability to rapidly raise the working fluid temperature, deliver the energy and shut down, is not easily achieved with a heat pump.

A domestic ASHP is usually limited in output by the available electrical supply. 14kW output is probably closest to the industry-average size for a single phase supply, and is less than half the output of its strongest opponent, the natural gas combi boiler.

Generally the heat load calculations carried out during the quotation survey are calculated on the assumption of the building fabric temperature remaining fairly constant. Cold building fabric will absorb a significant portion of the heat pump’s output over a prolonged period of time, preventing the air temperature from reaching a comfortable level in an acceptable period of time.

The obvious remedy for this problem would be to advance the time at which the heat pump starts but, in doing so, the running hours and electrical consumption will also rise, leading to higher heating bills. Not an ideal remedy.

If the electrical supply limits the rate at which energy can be introduced, the system design may need to prioritise essential living areas, allowing them to achieve a comfortable temperature quickly and allow a low-time-occupancy home to benefit from the potentially good economics of heat pump technology.

Designing for lifestyle is a major consideration in heat pump system design and I have seen little evidence of this requirement detailed in training courses, manufacturers’ manuals or other heat pump-related publications.