New Heat Pump Charter is welcome
Many householders are very aware of the challenge created by global warming, and understandably want to do their best to minimise their own personal contribution to climate change.
One of the most difficult areas to reduce greenhouse gas emissions is from the heating of our own homes. Ofgem (the government body responsible for the regulation of the energy sector) has observed that there is a “range of possible different pathways to decarbonise” heating our homes, and that “electric heat pumps (including hybrid variations) and replacing natural gas with hydrogen are two of the alternative low carbon technologies to heat our buildings”. 
We believe that the best approach, in the interests of both people seeking an affordable way of heating their homes, and for the environment, is to keep the current gas grid, and increasingly move to sourcing the gas within it from renewables, either biomethane, which is chemically the same as the natural gas we are already using but manufactured from renewable sources like municipal waste; or from zero carbon hydrogen.
In the meantime, domestic consumers should remember that natural gas is the lowest carbon emitting of all the fossil fuels, and gas central heating systems make extremely efficient use of that energy.
However, some climate change campaigners prefer the option of shifting all of our heating to electricity, and replacing our current gas central heating systems with electric powered heat pumps. Although it is quite well established technology, most people in the UK haven’t come across heat pumps, so this needs some explanation.
Normally heat energy flows from a hotter source to a cooler destination, but heat pumps operate by transferring heat against the natural direction of energy flow, from a lower temperature source to a higher temperature destination. In the same way that a pump can move water uphill.
A heat pump is conceptually similar to a refrigerator, which cools the temperature inside the heated cabinet, and lets the warmth sucked out of the interior radiate from the coils at the back of your fridge as waste heat.
By a similar process, a heat pump reduces the temperature of the lower temperature source outside your home ( by pipes to air, ground or water sources), and then transfers the energy sucked into the pipes into your home to be used as heating. 
The government has been encouraging the roll out of heat pumps through a subsidy called the Renewable Heat Initiative (RHI), and by January 2020, a whopping £141.9 million in subsidies has been paid under the Domestic Renewable Heat Initiative (RHI) scheme towards 5812 ground source heat pumps.  An average subsidy of £24,415 per installation, with further subsidies towards air sourced heat pumps. 
The RHI is coming to the end of its life, and will be replaced by the proposed Clean Heat Grant of £4000 per installation, which would still be a significant public subsidy, although advocates of heat pumps are unhappy about what they see as a reduction in government support.  
Unfortunately, the experience of customers who use heat pumps is often reported to be less satisfactory than the experience of domestic gas consumers. The Heating and Hotwater Industry Council (HHIC), has recently produced a produced a “Heat Pump Charter”, in recognition that while many heat pump installations follow industry best practice, some consumers have heat pump solutions fitted that provide a poor heating solution, which in turn damages the reputation of the industry. 
The Heat Pump Charter is a guide to best practice, and when followed can result in a well performing system. However, it points out that the fabric of the building needs to be addressed before fitting a heat pump, including fitting loft and cavity wall insulation. Heat pumps should not be considered in homes without double glazing, or that have solid walls, and it is necessary to fit either underfloor heating or larger radiators, (it may also be necessary to fit a water tank). There is also a need for a full heat loss calculation to be undertaken for the property, to ensure that the correctly sized system is fitted.
Energy Saving Trust  produced a report based upon a comprehensive heat pump field trial that tested 83 heat installations in the UK: 29 air source and 54 ground source, for 12 months from 2008 until 2010. This field trial measured the Coefficient of Performance (COP) for operational systems (this is the boost that heat pumps give compared to simple electric heating) and found that it varied between 1.3 to 3.6 for ground source heat pumps and from 1.2 to 3.3 for air source, in most cases lower that manufacturer claims.
A subsequent phase 2 field trial programme tested 44 installations, and following system design improvements, the average COP was 2.82 for ground source, and 2.45 for air sourced installations. In most cases the COP was lower in a real-life deployment than in the ideal conditions that the manufacturers assume.
One reason was poor installation, through both errors in system commissioning, but also through incorrect rating specifications. If a heat pump is too big, then it will always be operating inefficiently, but if it is too small, then the heat pump component will not be adequate, and additional electric heating, or a gas boiler will be required to contribute more frequently than anticipated to top the heat up.
System commissioning errors, for Ground Source Heat Pump systems in particular, can dramatically increase operational costs, where, for example, there is insufficient ground array of pipes, or the pipes are too close together.
A second phase of field tests were conducted by Energy Savings Trust to retest 44 sites out of the original 83 test sites. This was to remedy design failures found in the phase one testing, and retest to judge the efficiency of the improvements. Of these remedial works, 12 were major interventions requiring the input of heat pump experts and manufacturers, where, for example, the original systems had been wrongly sized and needed to be replaced. Nine systems required medium scale interventions by a qualified plumber, but these were still non-trivial and expensive to rectify, for example, installing buffer tanks, or high efficiency circulation pumps.
Industry practitioner experts observe that it is essential that the hydronic systems are accurately designed, and will not work efficiently without very careful planning of both primary and circuitry pipework and emitters. Heat Pump installations are much less forgiving than domestic gas heating systems and require a higher skill level for design. 
Even after the introduction of the current Microgeneration Certification Scheme (MSC) qualification, there are examples of poorly designed systems, with consequently high running costs; furthermore building controls may have become more lax, and buildings are not always performance tested to ensure compliance with regulations. 
Another reason found for unsatisfactory performance was unsuitable usage, especially where a heat pump is employed without underfloor heating, and without legacy radiators being replaced by larger units suitable for lower temperature operation, i.e., so called Tlow emitters (either underfloor heating, or significantly larger radiators). Heat Pump systems installed into poorly insulated and draughty properties require a higher flow temperature.
Customer behaviour also contributed to poor performance, for example, using inefficient heating cycles. Element Energy observed that 73% of UK households use a scheduled heating cycle, for example bringing the heating on twice a day. The report concludes that this is the worst heating cycle for a heat pump, while the optimal performance is continuous heating.
There is also a strong evidence base that compared to domestic gas boilers, heat pumps do not provide competitive whole life costs for most consumers. The Department for Business, Energy & Industrial Strategy (BEIS) commissioned Element Energy  to produce a detailed report on Heat Pumps. This report models different assumptions for system installation costs in three scenarios:
Where heat pump installation costs fall by 30% by 2030 due to increased volume,
where installation costs fall by 30% by 2050 due to less increased volume,
where installation remain static due to very modest increased volume.
They then compared the lifetime costs of a conventional gas heating system, a heat pump system and a Hybrid heat pump system (which uses an auxiliary gas supply for peak demand and hot water), based on installation today, installation in 2030, and installation in 2050. Their report concludes that in all 9 of these scenarios, “gas heating remains lower in cost than electrical heating using the HP over the whole time period 2017-2050 and in all scenarios considered” Even assuming a 30% reduction of installation costs for heat pump systems due to increased volume, then gas heating systems offer considerably cheaper installations and lifetime costs. Comparing end user prices for heat pumps compared to individual gas boilers is more complex than might be expected, due to the UK’s very varied housing stock, differing energy efficiencies of households, different usage patterns;  and the fact that heat pump solutions differ in their use of heat source, and whether or not they contribute to domestic hot water.  For some households, heat pumps will be an efficient and cost effective solution, but for most properties, it would be expected that annual running costs would be higher than for gas. So, for those considering heat pumps, there is plenty to think about. While they can provide a good heating solution, they will typically require disruptive work to your home and an expensive installation; the systems are much less forgiving of any design and commissioning errors than a gas boiler system, and whole life costs are likely to be higher. Some systems may offer lower annual fuel bills, but many will not. It is also overoptimistic to assume that the electricity used to power heat pump systems would come primarily from renewables. it is estimated that shifting even 20% of domestic heating from individual natural gas boilers to electric powered heat pumps would also require additional electricity generating capacity, estimated at £28 billion, because the electricity generating system would need to be expanded to have enough capacity to heat all the homes at peak demand in the cold winter months. If electric heating in your homes is produced by sources that themselves create greenhouse gas emissions, then there is no gain.
 “Ofgem decarbonisation programme action plan”, Ofgem, February 2020.  Where a refrigerant gas is passed through an evaporator on its way to the heat source, where it expands to become a vapour accompanied by its temperature falling to below the temperature of the heat source, such that it draws heat in from the environment; the now warmer and lower-pressure working fluid is then pumped in gaseous form through a compressor, where its pressure is boosted transitioning it back to a liquid, simultaneously causing its temperature to rise, and this raised heat is then used for space heating. “Cogeneration and District Energy Systems”, p90, Marc A. Rosen and Seama Koohi-Fayegh. The Institute of Engineering and Technology, 2016  “Public reports and data: Domestic RHI”, https://www.ofgem.gov.uk/environmental-programmes/domestic-rhi/contacts-guidance-and-resources/public-reports-and-data-domestic-rhi , Ofgem, retrieved May 2020.  We are sceptical that this was good use of public money, given that off-grid properties isolated from the gas network could use biopropane (bioLPG) instead. This is already commercially available from Calor, who offer offer a green energy plan, whereby 40% home energy is renewable (40% BioLPG / 60% LPG), which the manufactures state can reduce the carbon footprint by up to 38% when compared to heating oil. https://www.calor.co.uk/biolpg (retrieved June 2020)  “Future support for low carbon heat”, BEIS, April 2020. https://www.gov.uk/government/consultations/future-support-for-low-carbon-heat  https://www.pumpitup.today (retrieved July 2020)  “Heat Pump Charter”, Heating and Hotwater Industry Council (HHIC), https://www.hhic.org.uk/uploads/5F045E39A69FB.pdf , July 2020.  “The heat is on, heat pump field trials, phase 2” Energy Savings Trust, August 2013, https://energysavingtrust.org.uk/policy-research/heat-heat-pump-field-trials-phase-2  “Has Gas had its day”, Berridge R. Installer Online, May 2020. https://www.installeronline.co.uk/gas-day-rob-berridge-takes-look/?fbclid=IwAR2Po_FO8WOmO4A0Ygo5XVX-sxUpv9SaUNqL9rkn6VGKS8-QOAESG32Wl9o#  Berridge, ibid.  “Hybrid heat pumps study”, Element Energy, for Department for Business, Energy & Industrial Strategy https://www.gov.uk/government/publications/hybrid-heat-pumps-study (April 2018)  “United Kingdom housing energy fact file”, Palmer J and Cooper I, Department of Energy and Climate Change, 2013  “Hybrid heat pumps study”, Element Energy, for Department for Business, Energy & Industrial Strategy https://www.gov.uk/government/publications/hybrid-heat-pumps-study (April 2018)