What if we could all heat our buildings with renewable technologies?
On the third of NailsworthCAN’s ‘In Conversation …’ series on 13th January 2021, Chris Wilde, Managing Director of Yorkshire Energy Systems (YES), gave an entertaining and informative talk on the topic of ‘Domestic Heating and Renewables: Dispelling the Myths’. This was rooted in practical experience from his many domestic and commercial clients over the years.
He was in conversation with Dr Richard Erskine, Secretary of NailsworthCAN. Over 60 people signed up for this event, reflecting a great deal of interest, and this was demonstrated in the wide range of questions raised by participants.
The video of the talk and Q&A session is available here:
Chris was an historian of science and was in education for many years. Ten years ago he joined a company doing solar energy, and did very well, but he wanted to diversify into heat pumps and other technologies and - finding resistance from the company he had joined - decided to set up his own company to pursue these broader interests. He said that “he has never looked back”, and they are currently doing very well.
In his talk, Chris addressed 8 of the most common myths he hears time and again in relation to heat pumps:
My house is an older property and not very well insulated, so a heat pump is not suitable.
Because my house in not well insulated my bills will be very high if I fit a heat pump.
Heat pumps only work well with underfloor heating.
A heat pump will not be able to heat my house in winter.
I will need to install huge radiators for a heat pump to work.
I will not be able to have water hot enough for a bath.
Ground source heat pumps are much more efficient than air source so should always be preferred
Air Source Heat Pumps are too noisy.
Chris explained how a heat pump works [Note 1].
One of the myths is that heat pumps cannot heat older buildings, and this arises from cases where there has been a failure to properly size the elements of the system, and to set the right flow temperature. As Chris said:
If a gas boiler can heat a house, then so can a heat pump
That is, so long as the heat pump is sized correctly and radiators are also sized correctly [Note 2].
Chris showed a typical Yorkshire house: an early 18th century solid stone built semi-detached house, in an exposed location, in a conservation area (so no question of external wall insulation), that had good loft insulation (a “no brainer”) and modern double glazed windows, which was to be heated by an Air Source Heat Pump (ASHP).
He summarised the process that is gone through using the MCS calculation methods (Microgeneration Certification Scheme). The input data includes the height above sea level, target indoor temperature, floor area, glazing-to-wall-ratio, level of loft insulation, and much more.
The algorithms then calculate the projected total peak heat loss of the building, and also the expected overall annual heat energy required. The projected electrical demand is then typically a third of the heat demand or less, because of the harvested energy from the environment. That means that a heat pump will have a third of the running costs or less than direct electrical heating (e.g. using electrical bar heaters) [6]
And as the electricity grid gets greener and greener (as fossil fuel generation is progressively displaced), the carbon footprint of heating the home gets lower and lower, as time goes on.
It is crucial that the heat loss of every room is assessed, to ensure that radiators are sized correctly. If they are sized too small, then they will keep calling for heat from the heat pump, which can result in high bills and cold rooms. This is the origin behind several of the myths surrounding heat pumps. The answer is to do proper design, using professional tools to do the sizing, and of course, to install the system accordingly.
He mentioned that often not all radiators need to be replaced, but usually at least half will have to, to meet the heat demands of each room. Often the radiator profile (width and height) may not need to change but may need to be a bit fatter to include an extra panel and associated fins. This increases the effective surface area without the radiators having too much visual impact.
Chris has never had an issue satisfying the heating needs for older homes.
Yes, it can take longer to heat a home but for that reason, heat pumps tend to be run for longer, maintaining a comfortable temperature.
Chris then showed another example house where a Ground Source Heat Pump (GSHP) was used, where heat is drawn from the ground using slinkies buried in trenches [Note 3].
His customers often remark on the fact that their homes are warm and comfy all the time. Instead of driving an oil or gas system hard for 3 hours, twice a day, with big swings in the level of comfort experienced.
In addition to space heating, Chris talked about hot water. One of the myths is that heat pumps cannot get the water hot enough. He mentioned a customer who rang him in a panic half way through an installation, because their plumber said he’d never be able to have a bath again, because the water would never be hot enough!
Chris explained that the heat pump, when in space heating mode, will target the flow temperature needed to meet the heating demand, and over the year this can range from 35°C to as high as 55°C. But when it is heating the water required for bathing and kitchen use, in the cylinder, it targets 55°C [Note 4]. Most people shower with a water temperature no higher than 40°C, and no one would lie in a bath as hot as 55°C without being scolded. In fact, with modern building regulations, the output at a bath shouldn’t be higher than 48°C, to avoid scolding. You will still have to add cold water when running a bath.
Chris chose older properties deliberately in the talk to illustrate that heat pumps can cope with any situation, assuming a proper assessment, design and installation is done.
He finally dealt with the myth that ASHPs are noisy. He said that even at full load, new models only have a noise level equivalent to a kitchen microwave oven. With windows closed you hear nothing. He did caution against placing them on the wall outside a bedroom window. He said he is always asked about noise levels before installation, but has never had any issues afterwards.
He challenged the received wisdom that GSHPs are much more efficient than ASHPs over the year. His company has fitted about 40 GSHPs and 200 ASHPs, and the results show that over the whole year, they are all getting more than 3 to 1 as a performance ratio (of heat output to electrical input). It is very difficult to make comparisons because every house is different, but based on this practical experience, he suspects GSHPs are a little more efficient (between 10 and 15%), but not enough to justify the large extra costs involved which are typically at least 100% more [Note 5].
Chris made the point that currently, both ASHPs and GSHPs are heavily subsidised by a Government scheme known as the Renewable Heat Incentive (RHI). Under this scheme, the householder has to pay the project costs up front, but then receives 28 equal quarterly payments. The maximum total paid under RHI for an ASHP is £11,000, whereas for a GSHP is £31,000.
Chris asked: if these subsidies are taken away, who is going to install a GSHP as opposed to an ASHP?
And if there is insufficient land area for trenches, an alternative is to use boreholes with a GSHP. This would be even more expensive, adding another £10,000 to the costs. He noted that boreholes only make sense for multiple dwellings or blocks of flats, where the extra costs can be shared.
Chris believes that once these subsidies are gone, GSHP installations will become quite rare.
The talk then moved on to consider how best to reduce the carbon footprint of heating.
Using a graphic that had been prepared by Richard (and is discussed here), Chris made the point that while several retrofit measures such as loft insulation were “low hanging fruit”, the heat pump (in this case an ASHP) can make the largest single contribution of any single intervention.
Unsurprisingly, stopping burning gas (or oil) is key to reducing the carbon footprint of buildings!
Chris said:
“… insulation, yes, it’s low hanging fruit, it’s very important, if you insulate well you need a smaller pump and your bills will be lower - the same would be true of a gas boiler or any other form of heating - but if you are living in an old house where solid wall insulation would be impractical and so would floor insulation, it’s not a no go area for a heat pump, you can still have a heat pump …”
Chris restated the important point that as the electricity grid gets greener and greener, so does the heat pump, without the householder having to change anything!
A householder can also benefit from domestic Solar PV (PhotoVoltaic), because some of this electricity can be used to run the heat pump, reducing reliance on the grid and thereby reducing running costs.
Now, while the greatest demand for heat is in winter when the solar energy generated is at its lowest, we still need space heating in Spring and Autumn, when there is a significant contribution from solar, and of course, hot water is required all year round. Chris has found that for an average house, heating bills can be reduced by 25% by combining a 4kW solar PV system with the heat pump.
Solar panels have become 50% more efficient than 8 years ago, and are only one third of the price! That is a 6 fold improvement in price-performance. Even without subsidies, solar PV is a “no brainer” because of the reduction in electricity bills they deliver, for general use, as well as in combination with a heat pump.
Chris then took questions from the attendees. These have been written up and assembled into a separate document, which also includes answers to questions which were not covered on the night due to time constraints.
The feedback received about the talk afterwards was very positive.
Richard’s concluding remarks were that there was still a lot of misunderstanding and out of date information around, about heat pumps, and particularly Air Source Heat Pumps, and he hoped this talk will help to dispel many of the most persistent myths.
The event concluded with a well deserved round of applause.
. . . o o O o o . . .
Notes
1. In simple terms, it is like a fridge (which extracts heat inside the fridge and dumps it out of the back), but in reverse, taking ambient heat from the environment and concentrating it (which raises the temperature) and moving that to inside the house. Heat pumps are so efficient that for every unit of electrical energy put in they will give out at least 3 units of heat energy (so an efficiency of at least 300% on average through the year). Heat pumps can be ‘air source’, ‘ground source’ or ‘water source’ but in all cases the energy harvested ultimately comes from the sun which warms the ground, and water, and air. Even where bore holes are used for ground source (because of a lack of land area) this is true, and should not be confused with geothermal energy (getting energy from the Earth’s core) which requires much deeper boreholes than for ground source heat pumps.
Plumbers and others curious about learning more about the nuts and bolts of installing heat pumps, from an engineers perspective, take a look at these training resources.
2. One key feature of the overall design is the need to have radiators that are sized correctly, because the flow temperature for heat pumps is less than for gas boilers. This is not a problem as the target temperature is typically 21°C plus or minus a few degrees, so it does not matter that the flow temperature of the system is in the range 45-55°C (or even lower in mild conditions), but it is important that the total effective surface area of radiators is enlarged to compensate for the reduced temperature.
3. Each trench needs to be 1.2m deep and 5m apart from centres. In the example he showed there were four 50m long trenches. This equates to about 800 square metres for an average house (plus or minus 200 square metres). It is important to not pack the slinkies tighter than the design guidelines. Unlike with an ASHP - which has an effectively infinite source of heat energy in the atmosphere - it is possible for the ground’s heat to be exhausted if the GSHP system is designed incorrectly.
4. For dealing with legionella, the hot water will be boosted to over 60°C for short periods to kill the organisms.
5. Indicative project costs for a typical semi-detached house: £11,250 for an ASHP and £27,500 for a GSHP. This includes the cost of parts (heat pump, cylinder, valves, etc.) and labour [1-11-22 note: worth noting that since this talk, the RHI is no longer available, and the new up front grant of £5,000 for ASHP and £6.000 for GSHP largely removes the bias in favour of GSHP. There remains EPC related eligibility requirements. See https://www.gov.uk/guidance/check-if-you-may-be-eligible-for-the-boiler-upgrade-scheme-from-april-2022#eligibility ]
6. [new point assed 1st Nov 22: In talk point was made that a ASHP would have running costs similar to those of boiler, if replacing an old one. To understand the simple maths on this, given the Autumn 2022 unit price caps for gas and electricity. see this https://essaysconcerning.com/2022/10/25/will-my-heating-bill-increase-if-we-get-a-heat-pump/ ]