Heat Pumps (blame the small print)
(Image: SEE Monster)
Stories of heat pump disaffection abound – ‘it’s cold, my energy bills have increased.’ Assuming it is not damaged it is not the fault of the technology but a product of incentivisation. The UK is purported to have the worst housing stock in Europe a fact we in the main would need to endorse. It also has (or did have) some fairly bold decarbonisation pledges.
These facts do not sit well together and go some way in explaining dissatisfaction. I would add that retrofitting to any effective standard is difficult, intrusive and costly. Manufacturers are soon to be penalised for not achieving government roll-out targets and the ads that claim lower bills and better performance do not always reflect reality; these efficiencies can be achieved but often will not be. We boil it down to three variables:
Flowrate, Expectation of Comfort and Fabric. In terms of performance these need to be delivered in the range low, moderate and high, respectively. Take three client installations.
The first, onboard with the environmental agenda, live in a well-built and well -loved house perhaps now a little dated. They have the money and the wherefore all to get the builders in to do a full retro fit. There is a plant room and PV on the roof serving an orthodox if enhanced wet heating system. Not sure of the bills but they appear content and warm.
Installation two is the conversion of an outbuilding that already supports an extensive PV array that helps offset energy bills in the main house which is old. We have gone to some effort to improve thermal performance and airtightness and the building appears to be working well though we as yet have no data on running costs. Heating and hot water is provided by ASHP (ground source was preferred but proved too costly) and is delivered by continuous underfloor heating at ground level and upstairs by large twinned vertical radiators. Openings on the upper level are few and a large south facing glazed wall below is triple glazed. There is also a high-performance Swedish stove with a heat sink flue.
The energy efficiency targets of the third installation have been a little diluted by stylistic considerations and a very, very idiosyncratic building such that heat loss is both difficult to predict and mitigate. A high performance ASHP with booster set has been sourced capable of high flowrates to offset these variables and ensure that peak lows can be accommodated. Given potentially damp conditions (an historic flint wall encloses one side of the building and solid masonry the remainder) comfort may come at a cost. Some form of humidity control is envisaged and the strategy otherwise is to provide constant low-level heat using the exposed hard stuff as a heat sink.
As an aside we are aware that manufacturers such as Vattenfall (a Swedish state-owned energy company) has been trialling a high temperature heat pump that does not require the same degree of retro fit as other pumps. It relies on carbon dioxide as a refrigerant and uses a buffer (water) tank to mitigate high return flow temperatures.