Webinar on the Use of Heat Pumps in Historic Buildings

On this page you can find a recording and transcript of a webinar on 'the Use of Heat Pumps in Historic Buildings', recorded in December 2022 as part of our Technical Tuesdays series. You can also find the results of the subsequent Q and A session and links to other relevant resources.

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00:00:00:06 - 00:00:03:00
Speaker 1
And I'm joined today by Dan MacNaughton.

00:00:03:17 - 00:00:15:03
Speaker 2
Yes. Good afternoon, everyone. I'm a senior building services engineer at Historic England, and I'm really pleased to be joining you today to share what I know about heat pumps.

00:00:15:09 - 00:00:32:09
Speaker 1
So let's just give you an overview of what we're going to cover in this webinar. So first of all, we're going to look at actually what our heat pumps. They're moving on to some common misconceptions about the use of the particularly in older properties. We're going to look at how heat pumps work, the different types of heat pumps that are available.

00:00:32:24 - 00:00:50:12
Speaker 1
Then we're going to look at how they compare in terms of emissions in air pollution to other forms of heat generation. We're going to look at how you design a heating system, particularly in relationship to heat pumps. We're going to move on to flow temperatures, the water flow temperatures and why that is important to understand in relation to heat pumps.

00:00:50:22 - 00:01:11:19
Speaker 1
And also what that means in terms of your pipes, pumps and emitters. Then we're going to look at some practical considerations for both buildings and sites and where to go first. Good advice. And then we're going to finish off what is coming up in 2023 for historic England's building services engineering team relating to the decarbonization of heating in our buildings.

00:01:12:05 - 00:01:16:23
Speaker 1
And Dan is going to start us off on the first one of those of what a heat pump is.

00:01:17:21 - 00:01:48:11
Speaker 2
Yes, it's a good place to start. So at the simplest, non-technical level, it's just a box, really, that you put electricity into and get heat out. But of course, as an engineer, I'm not really happy with that definition. So without getting too complicated at the moment, I would explain. A heat pump is a device that uses a refrigeration cycle to transfer heat efficiently from an external source to provide useful heat for heating or domestic hot water.

00:01:48:20 - 00:02:11:10
Speaker 2
There is more to how this works and we'll come on to that in a little bit. And also to how the heat can be used. But this is the most common application, and unless something has gone horribly wrong, you'll get more heat output in kilowatts and the electricity that you input in kilowatts. So I'm going to get you involved quite early today with our first interactive poll.

00:02:11:10 - 00:02:33:14
Speaker 2
If we could have that, please. Matt. And the question is, when was the first large scale heat pump installed in the United Kingdom? And Caroline is going to give you a little bit of help with this question in a minute. But your options are the 1880s, the 1940s, the 1970s or the 1990s?

00:02:34:22 - 00:03:02:15
Speaker 1
Yes. So to help you this, I would describe the heat pump. So it was Bill in Norwich and it could deliver a peak output of 234 kilowatts, which probably means absolutely nothing to you. But to put this number into context, this is about enough heat to provide heating to around 30 average sized modern UK homes. And this heat pump was able to circulate heated water temperature between 50 and 55 degrees centigrade.

00:03:02:15 - 00:03:08:16
Speaker 2
See already Caroline got a clear runner at the moment. The 1946 looking like a popular choice.

00:03:08:16 - 00:03:09:23
Speaker 1
Do you think my clue is helped?

00:03:10:17 - 00:03:42:10
Speaker 2
I think it might have done. Okay, good. So that is nearly getting even more popular now. That's nearly 200 people going for the 1940s, about 100 to say in the 1880s, and then 100 again split between the seventies and the 1990s. So yeah, I think it's time to move on. So if you said the 1880s, this isn't a bad answer actually, because the world's first heat pump was built in Austria in the 1850s just before that.

00:03:44:00 - 00:04:12:15
Speaker 2
But the correct answer for the United Kingdom's first heat pumps the 1940s, and it was built in 1945 by John Sumner and yet is here. It's the UK's first heat pump. And the only reason that this technology wasn't developed further at that time was that we had a plentiful and relatively cheap supply of fossil fuels. With hindsight, this way of thinking has contributed to the climate emergency that we find ourselves in.

00:04:12:22 - 00:04:37:08
Speaker 2
And frustratingly, this pioneering heat pump work to be well. And it was very efficient. So there are many misconceptions surrounding heat pumps. And here it's just a selection of what I've heard people say this past year. You'll be pleased to know that this is the only slide that I'm going to read at what is written. But bear with us because it is really important.

00:04:37:08 - 00:04:41:00
Speaker 1
Let's just go back. So heat pumps don't work with historic buildings.

00:04:41:05 - 00:04:47:06
Speaker 2
Yeah, not true of design themselves in historic buildings. And I've also seen many examples of this.

00:04:48:16 - 00:04:53:02
Speaker 1
So I know this one is heat pumps don't work when the weather is cold.

00:04:53:05 - 00:05:09:09
Speaker 2
Yeah, again, not true. I mean, heat pumps are widely used in Scandinavia, which is a much colder climate than the UK. And if you need a good example close to home, then heat pumps have been widely used to heat buildings in the Orkney Islands, which is why I've included a photo of this location.

00:05:10:10 - 00:05:14:21
Speaker 1
And this next one we get asked a lot is heat pumps are a new technology.

00:05:15:04 - 00:05:23:10
Speaker 2
Yeah, well I think the last poll actually answered that ones we know from a discussion that this is tech, this technology's well developed now.

00:05:24:08 - 00:05:28:12
Speaker 1
And again another one we get an awful lot of suppose heat pumps don't work if you don't improve the fabric.

00:05:28:12 - 00:05:41:01
Speaker 2
Yeah, not true there. And sometimes the best option is to improve the fabric. But heat pump is just a device and it really doesn't know if you've installed secondary glazing or not.

00:05:41:01 - 00:05:42:14
Speaker 1
Heat pumps are too noisy.

00:05:43:07 - 00:06:02:04
Speaker 2
And I'm not true. I mean, sometimes I have to design acoustic enclosures for our source heat pumps. But in all ten case studies from a recent investigation looking at those heat pumps, it was found that noise was not a concern in any of these installation gardens.

00:06:02:04 - 00:06:07:11
Speaker 1
So heat pumps need to be concealed or screened for aesthetic reasons in all applications.

00:06:07:22 - 00:06:18:24
Speaker 2
Yeah, you can see see why this one comes up a lot, but it's not always true. This is going to depend a lot on the significance of the historic building on the site.

00:06:18:24 - 00:06:21:24
Speaker 1
And heat pumps. Heat building slower than gas boilers.

00:06:22:08 - 00:06:43:12
Speaker 2
Yeah, definitely not true. A seven kilowatt heat pump will provide the same amount of heat as a seven kilowatt gas boiler, but the heating system will only heat the building slower if the designer does not consider the heat emitters, pumps and distribution pipe. What? Even then, some heat pumps will work perfectly fine with the existing heating system.

00:06:45:02 - 00:06:48:21
Speaker 1
And heat pumps can only provide a low flow temperature.

00:06:48:21 - 00:07:06:24
Speaker 2
Well, yeah, you guessed it. Not true. So some heat pumps can easily provide a 90 degrees C flow temperature, but these can be expensive and a bit more challenging to control. And then there are also high temperature heat pumps which are less efficient, but which can fight a flow temperature of 80 degrees C, which is the same as a gas boiler.

00:07:07:21 - 00:07:12:02
Speaker 1
And we got another fabric cooling here. So heat pumps are less efficient if you do not improve the fabric.

00:07:12:10 - 00:07:28:00
Speaker 2
Yeah, not true. The efficiency of the heat pump depends on a few factors and that is the external temperature, the system flow temperature and the choice of refrigerant and even the manufacturer. You go to.

00:07:28:00 - 00:07:33:00
Speaker 1
And finally, heat pumps are too expensive and they can't achieve financial payback.

00:07:33:10 - 00:08:00:10
Speaker 2
Yeah, not always true, Caroline. I mean, in some feasibility studies that I've carried out, this technology does achieve financial payback within the expected lifetime of the heat pump. So moving on, I want to give you a fairly simple introduction to how heat pumps work. And for this, I'm going to describe a vapor compression cycle for an air to water air source heat pump, which heats a building.

00:08:00:10 - 00:08:23:08
Speaker 2
If we start on the left hand side of the diagram, the heat pump uses the heat energy that is available from an external heat source. We are so used to the physical properties of water in the freeze is at zero degrees C and it boils at 100 degrees C that a lot of people find it difficult to recognize that there's heat energy in the external air when it's minus three degrees C.

00:08:23:23 - 00:08:51:01
Speaker 2
This is where the usefulness of a refrigerant becomes apparent and the commonly used refrigerant in heat pumps boils at -52 degrees C. And hopefully this will help some of you to visualize that the external air is warm enough, even in the winter, to evaporate the refrigerant into what we call a low pressure vapor. Now, unfortunately, this refrigerant in vapor form does not have sufficient energy yet to heat the building.

00:08:51:15 - 00:09:16:11
Speaker 2
So the next step is to use a compressor to turn this refrigerant from a low pressure vapor to a high pressure vapor. The electricity you use to operate the compressor is where the electricity is consumed by the heat pump. And this high pressure vapor now has sufficient energy to be useful in this useful heat. What we're really interested in is shown on the right hand side of the diagram.

00:09:16:23 - 00:09:40:23
Speaker 2
What happens is that the heating system uses the energy from the high pressure vapor and transfers this energy to the heat emitters throughout the building. In this heat transfer process, the energy that is removed from the refrigerant causes it to condense into a high pressure liquid. And there is more we could discuss about the vapor compression cycle. But I think this is about as much as I want to explain for the purpose of this webinar.

00:09:41:23 - 00:10:07:21
Speaker 2
So I want to show you some of the key benefits of heat pumps. If we first consider a direct electric heating and every manufacturer of electric heat is will always tell you that this type of heating is 100% efficient. That is, for every kilowatt of electricity you put into the heater, you get one kilowatt of heat output. So in other words, they are 100% efficient.

00:10:08:07 - 00:10:41:17
Speaker 2
This is also known as the coefficient of performance or copy of one. Now if we compare that 100% efficiency for direct electric heating with what a heat can achieve, using the same kilowatt of electricity put into a heat pump, you will get between 1.5 to 4 kilowatts of heat output, which is an efficiency of between 150 and 400%, or in other words, a copy of between 1.5 and four.

00:10:42:05 - 00:11:09:03
Speaker 2
As far as heating cooling goes, the higher the scope, the better. So this example illustrates that heat pumps will be between one and a half to four times more efficient than direct electric heating. And this is possible because you getting the free heat from the external heat source will have a big advantage when comparing heat pumps to direct electric heating is that the size of the electrical supply will be at least one and a half times smaller.

00:11:09:08 - 00:11:21:14
Speaker 2
And this has huge benefits when considering the available electrical capacity, particularly where expensive upgrades are required.

00:11:21:14 - 00:11:39:10
Speaker 1
So let's move on to look at the types of heat pumps that we have. So essentially, there are three types of heat pumps, and the difference between them is where they get their free heat from. So we've got ground water and air source heat pumps. So let's take a look at these in the in turn. And we're going to start with the air source heat pump, first of all.

00:11:39:10 - 00:11:57:20
Speaker 1
So air source comes in two types. You have mono block and direct expansion. And if you remember back to Diane slides, I think Slide eight where there was that illustration of a heat pump showing how it works. The evaporator extracts heat from the outside air and then condenser is the part of the heat pump that delivers the heat into the building.

00:11:58:06 - 00:12:17:10
Speaker 1
Now all air source heat pumps house the evaporator in the outdoor unit. So the difference between the two types of air source heat pump is the location of the condenser. So the part that delivers heat into the building. So if we first look at the mono block, so a mono block, heat pump or air to water heat pump.

00:12:17:17 - 00:12:39:21
Speaker 1
Now this takes F outside air and then uses water to circulate the heat in the building. The condenser is located with the evaporation throughout our unit. So if you look at that photo on the left hand side, that piece of equipment there, the condenser and the evaporator are both housed within that unit. Now, the mono block heat pump connects directly to the building's heating system.

00:12:39:21 - 00:13:02:07
Speaker 1
So from that external unit on the left hand side, you have insulated pipes, fills with heat and system water going into the building, inside the building, the heating system, it could be a traditional heat emitters such as radiators, or could be an underfloor heating that heats the internal space. Now it's important to note that no refrigeration pipework is taken into the building.

00:13:02:12 - 00:13:25:09
Speaker 1
It is all contained within that heat pump outside and is only the heating system. Water pipes that go to and from the building, from the heat pump. So let's look at our next type of air source. Heat pump, which is the direct expansion or air to air. Now, in this type of air source heat pump, the condenser is not in the outside unit like our previous one.

00:13:26:00 - 00:13:51:04
Speaker 1
And the heat pump transfers heat into the building using refrigerant rather than water. The remote condenser in the dock system can interface with a warm, wet heating system. So if you have radiators or underfloor heating, heating, you could use that. But you would require heat exchanger to make that work or commonly see as in the photo on the right hand side, it connects directly into individual room units.

00:13:52:15 - 00:14:14:03
Speaker 1
So that's our source. The next type we're going to look at is ground source. And they take heat, as the name suggests, from the ground. So below 1.5 meters, the ground temperature remains pretty much constant between eight and 12 degrees centigrade all year round. And they extract heat from the ground using buried pipes known as ground collectors and the ground collectors.

00:14:14:03 - 00:14:36:14
Speaker 1
They could be borehole or trench collectors. Boreholes could be anything from 15 to over 100 meters deep and need to be correctly spaced if you don't get the spacing correct and they're too close together, there can be a net cooling effect on the ground and this will reduce the efficiency of the system. And you can also experience local freezing of the ground as well as boreholes.

00:14:36:14 - 00:15:01:20
Speaker 1
I mentioned you also have horizontal trench collectors. These are commonly laid in trenches, 1.2 to 2.5 meters deep. And horizontal collectors, they're going to require much larger land area than if you had the equivalent borehole collectors. If you have the land, they can be considerably cheaper than vertical boreholes. As the ground works tend to be less intensive, they are slightly less efficient than boreholes.

00:15:01:20 - 00:15:20:05
Speaker 1
As you get more fluctuation in the ground temperature near the surface. Now, if you were to compare ground source with air source heat pumps, they are more expensive and this is basically down to the ground works in both, but they are slightly more efficient. So let's move on to look at our last type, which is the water source, heat pump.

00:15:21:15 - 00:15:40:11
Speaker 1
And these can extract heat from lakes, rivers and ours or the sea. And for anyone who swims outside or does water sports over the winter, you'll be well aware that the water temperature in the winter is often higher than the ambient air temperature. So there's that free heat available from water sources that can be upgraded using a heat pump to heat our buildings.

00:15:41:07 - 00:16:04:20
Speaker 1
The water body does need to be close to the building to be heated, as should be running flow and return pipework from the water source back to the building. So water together with antifreeze is pumped around a loop located in the water source and the heat is transferred by the heat pump into the heating system with water source heat pumps care must be taken as to the suitability of the water source and feasibility stage.

00:16:04:20 - 00:16:26:18
Speaker 1
This there's quite a lot to consider your need to be looking at the specific characteristics of the water across all of the seasons. So such as how deep and how wide it is. What is that turnover rate? So how frequently is the water replaced? You'll be looking at temperature profile of the water flow rates. You'll do analysis of the ecosystem and also the quality of the water.

00:16:27:21 - 00:16:50:07
Speaker 1
Now, if a body of water is not large enough to be a net cooling effect, so a bit like with ground source heat pumps lowering the average temperature of the water and reducing the efficiency of the heat pump. But more importantly, this could impact on the floor and fauna that is dependent on that water source. So that's why care must be taken.

00:16:50:07 - 00:17:13:22
Speaker 2
So there are two things that I want to highlight regarding the use of heat pumps and the environmental benefits. The first thing is about the carbon dioxide emissions, which most of you would recognize as the main greenhouse gas in the United Kingdom, which is having a significant impact on climate change. We know that heat pumps use electricity and the national grid is on a path to be net zero carbon by 2050.

00:17:15:02 - 00:17:49:01
Speaker 2
The carbon emissions of electricity we generate have been improving and in 2020, renewables accounted for more than 43% of the UK's total electricity generated in recent weeks. When the web hasn't been as good. I've observed wind power alone generating more than half of the United Kingdom's electricity load. Now, if we compare the current energy mix for the National Grid in 2022, there are at least half as many carbon dioxide emissions for an air source heat pump when compared with a natural gas boiler for every kilowatt of heat that is used.

00:17:49:09 - 00:18:10:01
Speaker 2
And if we carry out a similar comparison with oil, the improvements are even greater with around a third as many carbon dioxide emissions for an air source heat pump when compared with an oil fired boiler for every kilowatt of heat that is used. The other thing to consider are the particulate, which are produced from the combustion of fossil fuels.

00:18:10:17 - 00:18:45:22
Speaker 2
It really isn't the brightest idea to be burning things in densely populated urban areas. Particulate matter of size PM 2.5, which is becoming recognized as the particulate size which can pass through our lungs and potentially into our bloodstream and cause health issues, has a diameter of 2.5 micrometers. Looking at the chart on the right hand side of this slide, which may or may not be able to read and we can consider how many PM 2.5 emissions are produced for different fuels when one gigajoule of heat energy is used.

00:18:46:00 - 00:19:14:23
Speaker 2
Now that's not an easy amount of energy to consider. So I will tell you that this is approximately the amount of heat energy that the average UK home uses every week. So considering this energy consumption, a natural gas fired boiler will produce less than 0.1 grams of PM. 2.5, which is very low. However, an oil fired boiler will produce six grams of PM 2.5, which is at least 60 times more than the natural gas equivalent.

00:19:15:18 - 00:19:39:23
Speaker 2
Oil is often considered a dirty fuel, however, burning an equivalent amount of wood produce is 375 grams of PM 2.5, which is almost 4000 times more than the natural gas equivalent. This is the reason why many urban areas are only permitting the combustion of authorized fuels within smoke controlled zones. And to give you an idea of the scale of this.

00:19:40:08 - 00:20:03:16
Speaker 2
The blue area on the map is the smoke control area for the city of London. So we now going to talk through some of the basics of how to design a heating system when installing a heat pump. The first thing, which is particularly important with historic buildings, is to establish the design heat loss. Unlike boilers, heat pumps do not work well if they are oversize.

00:20:03:24 - 00:20:33:13
Speaker 2
So please never assume that an existing boiler is correctly sized. Rushing to a project proposing to swap a 30 kilowatt gas boiler for a 30 kilowatt heat pump in determining the peak design heat loss. So you need the technical input of a building services engineer who will use software or manual calculation methods to determine how much he is lost through the fabric, how much is lost by a controlled ventilation, and how much fire infiltration which is uncontrolled.

00:20:33:21 - 00:21:01:08
Speaker 2
And for those of you who are unfamiliar with infiltration, this is the air leakage through cracks and gaps in the building envelope. Once you've established the design, heat loss is easy to skip the next steps and rush into a choice of heating technology, whether it be a boiler, a heat pump or something else. And this is where you should appoint a building services engineer to carry out a detailed feasibility study to explore all available options.

00:21:01:14 - 00:21:28:23
Speaker 2
This should consider the environmental and financial performance in addition to any practical considerations. We going to talk about the importance of considering the existing heating system in a retrofit project. Within the next few slides. And another crucial consideration is to understand when the building is occupied and how it is used. And this would always be considered within a good quality feasibility study.

00:21:32:09 - 00:21:58:24
Speaker 1
So first of all, I just want to show you this slide from the latest CPC guidance. I am 16, which hopefully will demonstrate the relationship between what flow temperature you operate, a heat pump up to what impact this will have on the emitter sizes, its efficiency and running cost. So first of all, if we look at the left hand side there with the blue box roll around, this is where a heat pump is running at a lower flow temperature.

00:21:59:15 - 00:22:21:13
Speaker 1
So at the low flow temperature, yes, you'll need larger heat emitters, typically radiators or if you have an underfloor heating system, the output will be lower for me. So it will take longer to reach the conditions required, but it will be operating at a higher efficiency and therefore the running costs will be lower. So let's look at the other side now.

00:22:21:14 - 00:22:43:18
Speaker 1
So this is one with the red box around there. So if you look at running a heat pump, a higher flow temperature, yes, you're going to have smaller emitters and you achieve a higher output if you have underfloor heating system. But the system will be operating at a lower efficiency as the compressor is having to work a lot harder and therefore the running costs will be higher.

00:22:45:00 - 00:23:07:01
Speaker 1
Now, as we're talking about, older buildings are not newbuilds. There is likely to be an existing heating system. And a major part of the design of any heating system is the heat emitters. Now, that could be radiators, underfloor heating or even phone call units. So it's really important that these are sized correctly. So comfort conditions can be achieved in all spaces.

00:23:07:23 - 00:23:29:07
Speaker 2
Yeah. And I should note, before we move on, I want to ask the audience another question. Actually, if you could bring in the second pole. So having seen the previous slide and do you always think that you need to replace the heat emitters when using a heat pump so you can find out if you think yes, no. Or sometimes there.

00:23:32:14 - 00:23:42:11
Speaker 1
No. Interesting.

00:23:42:11 - 00:23:44:05
Speaker 2
Lots of people going for sometimes.

00:23:44:22 - 00:23:46:14
Speaker 1
I think we got clear from one of the.

00:23:54:18 - 00:24:25:08
Speaker 2
And we've got 100 now saying no don't always have to replace the heat as well and I think that's about so got 4% saying yes, 26% say no and 70% saying sometimes. Now, I would say the correct answer is really no, because sometimes a building services engineer will be able to determine that the existing heat emitters are already oversize.

00:24:26:04 - 00:24:39:19
Speaker 2
But to be fair, you can see we've got a lot of people that are saying sometimes and I think that's a pretty good answer to because often heat emitters will need to be larger. Or you can supplement existing heat emitters with additional emitters to meet any shortfall in heat.

00:24:40:19 - 00:24:44:04
Speaker 1
So, Dan, how much larger would you say the heat emitters have to be?

00:24:45:20 - 00:24:53:13
Speaker 2
Could I have the presentation to back that? Thank you.

00:24:55:23 - 00:25:23:21
Speaker 2
So this is a useful illustration of how much larger one particular form of radiator needs to be to provide an equivalent amount of heat. So in this example, the radiator on the right hand side is 750 millimeters in width and it provides one kilowatt of heat output for the same form of radiator. And I do need to stress that is the same form being used with the heat pump, the overall which is more than double the 800 millimeters.

00:25:24:04 - 00:25:50:13
Speaker 2
However, I've been a bit more fortunate in my own home when renovating rooms, I have been able to replace single panel radiators with double panel radiators that have very similar face dimensions. So that is the width and the height and underfloor heating is worth a mention as well, where a building is frequently occupied as this type of heating works on lower system temperatures which can maximize the efficiency of heat pumps.

00:25:51:12 - 00:26:14:22
Speaker 2
So wherever possible, we should always consider reusing radiators and pipework as the embodied carbon originally used to manufacture the equipment can be considerable. Some of the existing systems may also have historical significance or be part of the character of the building's interior. As you can see in the example, shown the radiators and pipework needs being good work in order.

00:26:15:00 - 00:26:45:16
Speaker 2
You don't want that to be corroded or any risk of failure. And now existing radiators that can be pressure tested, cleaned and repainted and the heating system firm return temperatures on the previous slide showed a temperature difference of ten degrees C, but in practice, most air source heat pumps are designed for a maximum temperature difference of between five and seven degrees c and boiler systems are designed for a temperature difference of between 11 and 20 degrees C.

00:26:45:23 - 00:27:09:07
Speaker 2
What that means is that the flow rate that needs to be provided by pumps and it needs to travel through pipes could be up to four times greater to provide the same amount of heat. This can often result in larger pumps and larger pipework being required. And again, this is why a building service engineer should always consider the suitability of the existing pipes, pumps and heat emitters.

00:27:09:07 - 00:27:39:08
Speaker 2
The actual heat source. The boiler may have come to the end of its life, but it should not be assumed that the rest of the system, the heat emitters in the pipe work also needs to be replaced. But looking at the previous slide, you may think that if we re-use the radiators, they won't be able to deliver the conditions we require as they are too small, as they were designed to use in a gas or oil boiler working at a higher water flow temperature of cool or so we can supplement the existing heat emitters with additional emitters.

00:27:39:15 - 00:28:03:18
Speaker 2
Or we could operate the heat pump at a high temperature. But this is disadvantages in that the heat pump will be less efficient and more costly to run. Sometimes with historic buildings, there is a compromise that needs to be made between system efficiencies and the size and style of heat emitters that would be suitable. Caroline is now going to show real examples that would demonstrate some of what I've just described.

00:28:05:16 - 00:28:25:08
Speaker 1
Okay. So this is Tom Pool we're going to be looking at now is our Swindon office. And some of you may be may have and this would be a familiar image to you on the screen. Now, our office is a grade two listed building and date back to the 1840s and it does have an existing heating system with radiators and much of the gas boilers.

00:28:26:04 - 00:28:30:00
Speaker 1
I suspect you might be less familiar with our boiler room.

00:28:30:18 - 00:28:43:20
Speaker 2
Well, to be honest, Caroline, the boiler room is one of my favourite areas that this is an office as well as the rooms in the archive, I've got to say. So isn't that uncommon to find me in one of those areas?

00:28:43:20 - 00:29:15:10
Speaker 1
Thanks for that, Dan. So this is the inside of Dan's favorite place, the boiler room and much of the gas boilers in there that you can see in the photo. Now, they've come to the end of their economic life and is proving hard to get parts. So it's time that we replace the heating system. Part of the decision making in what to replace the system with is that historic England has set a target to achieve net zero by 2040, and in order to achieve this target, we need to look at our emissions from the energy usage associated with our office estate.

00:29:16:09 - 00:29:42:12
Speaker 1
So this is an opportunity where we could replace the existing system with a low carbon heating solution to reduce our scope on emissions. Now there is no doubt that the boilers need to be replaced, but the radiators of work have been reasonably well looked after, so there's been regular maintenance and a good water treatment strategy. So the point worker radiators are in good condition and not at the end of their useful life.

00:29:42:12 - 00:30:07:13
Speaker 1
Also, you can see from this image on the right hand side there that the radiators work well with the window design. And I know someone's mentioned this in the chat about how you work with radiators. We have a building design now. In the initial design work that we had done, we were told that for a heat to work and deliver the comfort conditions required in all spaces, we would need to replace or supplement all the radiators in our office.

00:30:07:13 - 00:30:40:16
Speaker 1
We have larger versions now. We weren't keen on this as it would be obviously more expensive for us and a huge amount of disruption to the internal space. So what we did is we looked at what the current system with the gas boilers was delivering and what a heat pump would. So the existing gas boilers and radiators run in 82 degree flow temperature from those radiators inside, we were getting 640 kilowatts of hate into that building now keeping with exactly the same radiators, not adding to them.

00:30:40:16 - 00:31:05:07
Speaker 1
No additions, no changes. I'm running with a new heat pump at 55 degrees centigrade. We were getting 281 kilowatts of heat in that space. So you can see that difference there. But under half the amount of heat energy than with a air source heat pumps than we would get with an existing gas boiler. So maybe what we were told was correct, we need to replace or supplement all the radiators in the building.

00:31:05:07 - 00:31:26:16
Speaker 1
If we were going to change from a gas boiler to a heat pump. So before I give you the answers or Dan does, we're going to do another poll. I want to ask you, do you think using a heat pump, think about our Swindon office with our current radiators. So no additions, no supplement is enough to provide the comfort conditions in our office.

00:31:27:07 - 00:31:36:00
Speaker 1
So you've got four choices here? No, none of the time. Yes, all the time. Now you've got three most of the time or you're not sure. Are you sitting on the fence or bit.

00:31:37:05 - 00:31:39:09
Speaker 2
Near the cogs turning with the telly?

00:31:40:22 - 00:32:01:20
Speaker 1
Yeah, most people, 70%, most of the time. Okay, interesting. I still call people voting in surveys. Give it a bit more time. Yeah.

00:32:02:23 - 00:32:04:16
Speaker 2
I mean, very good today the audience haven't.

00:32:04:20 - 00:32:30:24
Speaker 1
I think as I got your spot on you've got answer three though. So yes, you're quite right most of the time. But so let's go and see why that is the case. Okay. Let's just move that slide on. So we've got a scary graph now. So this graph is from our building management system for Swindon office, and this graph is of the actual gas usage for the heating plant.

00:32:31:04 - 00:32:50:07
Speaker 1
And we've got a whole year here. So this was for 2020. Now just to note for go on is really useful for your own projects. If there's any existing systems there, you may be able to get hold of some of their mistakes or there might be other data available that shows daily or annual usage patterns. And this will be invaluable to your building services engineer when they're doing the design.

00:32:50:16 - 00:33:18:03
Speaker 1
So always make sure you ask. It's always worth asking that question. Okay, so let's put some of the information we had on the previous slide. So our existing combination of Gasparilla and Radiators running at the 82 degrees flow temperature, so we've got our 640 kilowatts out there. So we know that. And then when we did the calculations for the source heat pump with the existing radiators, no additions, we got 281 kilowatts there.

00:33:19:04 - 00:33:43:17
Speaker 1
So if you look at that graph, you can see that well actually you have, I guess, use we're meeting most of those peaks. It's just sort of maybe three incidents where it just peaks above the. But interesting to note that the much of the gas was that boilers that were installed have a capacity of 600 kilowatts, which when you look at our graph of our building load is much slower than these two boiler capacity.

00:33:44:16 - 00:34:09:09
Speaker 1
Now hopefully looking at this, it demonstrates like what Diana said before, not to assume that the boiler installed was sized correctly and that the heat pump would need to be the same size. And it's important to ensure these correctly sized. Now, in this example, if we had not done that, if we just said, okay, we need a 600 kilowatt heat pump as well, we would have had an oversize heat pump and replaced all the radiator when it was not required.

00:34:09:09 - 00:34:34:02
Speaker 1
So all that disruption, all that expense as well. Now I suppose as to why that gas boiler was oversize, maybe they didn't take into account, you know, like sunlight, occupancy and equipment and that can make a significant contribution to heat in the buildings. But Dan, now I know you wasn't involved in the original boiler design at the Swindon office, but we do see this on other buildings.

00:34:34:02 - 00:34:37:08
Speaker 1
Can you suggest why the system may have been so oversize?

00:34:37:21 - 00:35:02:19
Speaker 2
It was scarily Caroline. I could have been involved in the original boiler design because I started designing heating systems over 20 years ago, so I'm very familiar with how the systems were designed. Now, the first factor be that it is common to include an oversize, in fact, to provide a boost to the heating system, to reduce the time it takes to warm up the building to a comfortable temperature.

00:35:02:19 - 00:35:32:03
Speaker 2
This provides a margin which was up to 10% oversize in according to the CDC guidance at the time. I know that in practice a more conservative approach was taken and a 20% margin was common to reduce warmup times and also to allow a bit of contingency for small future modification stations and extension ins. Now the second factor is that the heat loss from the distribution point would be accounted for in the plant sizing, and this could typically be in over 12%.

00:35:32:03 - 00:36:02:10
Speaker 2
So already we could be talking about oversize in plan by a margin of over 30%. And the third factor is that there could be an element of resilience or redundancy involved in the original plant design. So I know that the Swindon boiler is actually a large number of smaller 50 kilowatt modular gas boilers and therefore it is possible though that the system was designed to operate at full design load with between 33 and 50% of the modules not in operation.

00:36:02:24 - 00:36:23:04
Speaker 2
This approach is very common and shows business continuity and it also allows you to to enable maintenance and repairs to be carried out at any time of the heating season. In practice, the real reason for the boiler siting at the Swindon office is likely a combination of all three of these factors. It isn't really that surprising.

00:36:23:14 - 00:36:49:11
Speaker 1
I think it's just swing thought. So quick question in the chat while this slides up is that graph is typical for previous summers? Asked if it's hybrid or working from home, that graph is typical for previous years and it is 100% occupation. So it's very strong. But I think from what Dan said and just looking at this graph, this really again stresses why it's so important not to just take what the size of the existing boiler resources and assume that what is required for the heat pump as you wouldn't do that, would you done?

00:36:50:01 - 00:37:12:14
Speaker 2
No, definitely not. I think we're really drumming that message home today. You know, oversighting heat pumps is going to cause your heat pump to cycle on and off more free can, really, which in turn reduces the lifespan of your heat pump and the efficiency. So your heat pump won't last as long and the running costs will be greater.

00:37:12:14 - 00:37:38:17
Speaker 2
Now, when it comes to the practical considerations relating to a heat pump system, I want to emphasize the importance of good quality design, good quality installation and good quality commissioning to include optimization both pre and post handover. So we're going to need to think about where the heat pump is located and the details of the groundwater collective where applicable.

00:37:38:20 - 00:38:00:23
Speaker 2
I also saw a question in the chat as well. It was asking Do we always need plant rooms for source heat pumps? And I suppose in a lot of projects and the answers, you won't need as much plant space because most of the time the air source heat pumps are going to be located outside. You might have a buffer vessel in there, some pipework and some pumps.

00:38:01:05 - 00:38:24:04
Speaker 2
So plenty of space might be that bit smaller, but actually in quite a lot of sensitive buildings and not just historic buildings and you can install heat pumps in internal enclosures and leave them to atmospheres so they can reject that heat to outside. So there's all sorts of things you can do there and it will really depend on the specific project.

00:38:25:05 - 00:38:58:07
Speaker 2
And now heat pumps. We talked a bit about noise and they are going to generate noise from the compressor, the fans and the valves. If they're cited correctly, then often that's not a problem in our study. So we looked at ten case studies there. When we interviewed the owners and residents of the properties, noise was not considered an issue in any of them, which is, I'll be honest, was a bit of a surprise for me because, you know, on the other hand, you've designed heat pumps in areas with very strict planning conditions.

00:38:58:15 - 00:39:23:17
Speaker 2
So I've had to design acoustic covers for the heat pumps and also put those heat pumps within acoustic enclosures. Now, that level of acoustic mitigation is unlikely to be required for most projects. And this again is why noise to be considered as part of the feasibility study at the early stages of a project. So we can we can avoid these issues and we can mitigate them.

00:39:24:20 - 00:39:47:20
Speaker 2
We also need to know the fabric performs to ensure the heat pump is sized, to provide the conditions required. And we must make sure that questions are asked about how and when the building is used. As this will often the recommendations from the feasibility study. In our study, some of the units have been concealed behind panelling and that is all right.

00:39:47:20 - 00:40:10:00
Speaker 2
We must make sure that any enclosures are not too close to the heat pump and that they don't affect the air pass into and from our source heat pumps. We need to make allowance within the project program and also the contract to ensure that there's time for the contractor to provide training for the client so they are confident in how to operate and adjust the system.

00:40:10:09 - 00:40:31:23
Speaker 2
It really needs to be understood that the radiators may not feel as warm as when they may have had a gas or oil boiler supplying the heat and the end user will need to understand the increase in the to them flow temperature will impact the efficiency and running costs. Now, of course, heat pumps use electricity to generate heat and they require a power supply.

00:40:32:07 - 00:41:01:18
Speaker 2
So on a domestic sized installation that normally only going to need a single phase supply, but larger installations will require a free face supply and an engagement with the energy provider. It's essential to check if the existing supply is the capacity or if a new supply is required. In some rural communities. This may be challenging where there's not been a rates to the electricity network yet to support the electrification of heating.

00:41:01:18 - 00:41:19:13
Speaker 1
So we're just going to go on to phones where you can find good advice. I mean, we could cover an awful lot more this weapon up. It's important to provide some time at the end to answer some of your questions in the chat. So just so that you can see on the screen here, we do have some new historic England pages on heat pumps and a lot of what we've copied is in them.

00:41:19:20 - 00:41:45:14
Speaker 1
So you can go and have a look at those as well as how to find professional help for your project and a link to our future. The heating conference that we did in June this year, and there's some talks on there about the decarbonization of heat and then what's coming up. So what's coming up in 2023. So the team have another technical Tue weapon on the 17th of January at 1 p.m. and this will cover the decarbonization of heating.

00:41:45:14 - 00:42:13:10
Speaker 1
I will present the results of a study looking at specifically looking at rural properties currently using oil for heating and what their options would be. We also have some studies that we're going to be publishing, so hopefully in January we will publish the first of our Source Heat Pumps study, which looks at the ten properties which don't it mentioned in in his presentation that was a mixture of domestic retail and there was two churches in there as well looking at how they perform and lessons learned as well.

00:42:13:10 - 00:42:30:13
Speaker 1
I will do a webinar on that one to cover that and we've already started on the second part, which is of the source heat pump study, which is looking at all non-domestic installations. So that would also be published next year and we'll be starting to more grant to more studies, one on ground source heat pumps and the other on water source heat pumps.

00:42:31:08 - 00:42:49:24
Speaker 1
And again, there will be a document from that will generate more information on our web pages from the findings from those. So in the next six months, these pages are going to be populate with a lot more information in some case studies as well. And also the technical tuesday which will deliver from those.

Q and A results

Question1 Are heat pumps less 'effective' if you don't improve the fabric?

Answer 1Try and distinguish between the heat pump as the heating plant and the overall design strategy. The latter will often include a heating strategy and proposals to improve the fabric.

Then it is important to be clear about what is meant by ‘effective’. For many projects this will mean capital costs, running costs and operational carbon. For retrofits in historic buildings, ‘effective’ can also mean that it does not impact the historical significance or moisture performance of the building.

Question 2 Are heat pumps 'stealable'? i.e. If you install a boiler on the outside wall of a house, I’d argue it would get stolen. If installing heat pumps to terrace houses in deprived areas, will they go missing without a security cage?

Answer 2 I’m not aware of this being an issue. The weight of the heat pump will vary (depending on the output) but the smaller ones are typically around 100kg. It would be best to carry out a risk assessment with specific site knowledge and access considered along with any known security issues and existing CCTV coverage.

Question 3 Our heating engineer advised that other means of heating would be more effective in our uninsulated mediaeval church - so does anyone have an example of a medieval church which successfully uses air source heat pump please (ground source not an option because of archaeology)?

Answer 3 There are 32 known ASHP installations in listed churches. 
I don’t know how successful each project is but it is useful to know how many installations have been carried out and their locations.

Question 4 What is the environmental impact of the refrigerant that is used (both in production and in disposal after the heat pump's useful life)?

Answer 4 It varies depending on the refrigerant. Key things to consider are the embodied carbon (in manufacture), the Global Warming Potential and the Ozone Depleting Potential. These should all be considered within the feasibility study.

Question 5 Are you able to comment on the Global Warming Potential of the refrigerants used by the heat pumps on the market, system leakage to atmosphere etc?

Answer 5 The GWP for each refrigerant is known and estimates on system leakage vary within industry. The chair of the Heat Pump Association stated in December 2022 that data from other countries suggests a leakage rate of around 1.5-2%. Professionals are calling for quality auditing including records of refrigerant charging during maintenance. This means that actual refrigerant recharge volumes will be known for specific systems and I would support this.

Question 6 What is the ideal flow temperature in winter that still means a heat pump is efficient?

Answer 6 Typical design temperatures for heat pumps are up to 55°C but the lower you can go, the more efficient the heat pump will be. A building services engineer will be able to estimate the energy consumption of all options at the feasibility stage.

Question 7 We are regularly told that buildings have to be upgraded to make them more energy efficient before installing a heat pump. What sources can you identify to counter this argument?

Answer 7 Upgrading the fabric where possible, will reduce the energy consumption so there is no argument to counter. Prior to working at Historic England, I have designed a large air to air heat pump in a listed building where no fabric improvements were made.

Question 8 Are plant rooms needed for air source heat pumps?

Answer 8 You will need plant room space for the buffer vessel (where required), pumps, pipework and controls. With water and ground source systems, the heat pumps are also installed internally.

Question 9 My medieval church has a heat loss of 50-75kW, and I've been quoted for an ASHP/UFH system which consumes 20.8kW (output 40-50kW). I've been told it is best to keep the heat pump on 24h/day over the winter, but if it's going to draw 20.8kWh, this works out to over £10,000 a month to run (EDF want 80p/kWh). Would I expect it to draw the full 20.8kW all the time it's on?

Answer 9 No – unless the system is undersized. If we assume that the peak design temperature is -3°C then for this amount of electricity consumed, the external temperature would need to stay at -3°C for 24 hours every day for a month. A building services engineer needs to carry out a dynamic energy consumption calculation for you. Is it possible to get a more competitive tariff than 80p/kWh? This seems very high.

Question 10 Will heat pumps work with storage radiators?

Answer 10 Night storage heaters are electric heaters, so no (heat pumps don’t produce electricity).

Question 11 In heritage and listed buildings, how do you square off needing a larger emitter(s) with maintaining historic integrity?

Answer 11 It is a balance and in my experience the building services engineer will often be guided by the conservation architect during the initial design proposals. With experience, you get a feel for what aesthetic will be suitable but it is always worth highlighting the details of any proposals clearly and early in the project to avoid disappointment and misunderstanding.

Question 12 Presumably you're saying you'll need a larger emitter surface with ASHP? Why is this?

Answer 12 Usually but not always. When it is necessary to increase the output of the existing emitters, this can be achieved by higher output emitters or by installing more emitters. It is necessary because the emitter output depends on the system flow and return temperature which will typically be lower for a heat pump.

Question 13 Have you some direct comparisons with larger historic building, without significant insulation upgrade, that shows us running costs from previous oil/gas boilers to use of heat pumps. it seems common thought that the heat pump WILL cost more, not less?

Answer 13 Running costs are important but capital costs also impact the viability of the proposals. Just in terms of running costs for every kWh of heat output, oil will cost about 9.1p, gas about 10.5 p and a heat pump about 13.7p (obviously this all depends on what tariff is used).

Question 14 When working out the heat loss for a building (to assess the size of the heat pump and type of emitters), how do we get over the fact that 'standard' software often provides much poorer heat loss values for traditional wall build ups (or doesn't include the type of wall build up many vernacular buildings have) - meaning you might oversize the heat pump (or equally install more insulation than actually needed if improving fabric)?. Physical testing of fabric would provide more accurate heat loss info but is not feasible for lots of owners.

Answer 14 A building services engineer should not rely on software default values. I always input my own information into software where it is known to best reflect the actual building and avoid the risk and cost of oversizing plant. In a larger project it could be feasible and holistically more cost effective to determine the U value of some fabric elements by physical testing.

Question 15 What are your thoughts on using an air source heat pump to heat a water buffer tank to pre heat the water circulating in the radiators? Effectively, like pouring hot water in the kettle before boiling it.

Answer 15 Buffer vessels are often used in heat pump installations and some projects do use heat pumps as a primary heat source to raise system temperatures to a base level. The secondary heat source can then be heat pumps or boilers to raise the base temperature to the system temperature.

Question 16 The usage pattern graph of the Swindon office - is this with some form of hybrid WFH occupation or is it 100% full time occupation?

Answer 16 I believe this was pre-pandemic data.

Question 17 Is it correct that heat pumps have to be close to boilers / hot water cylinders? This is what I have been told, which can be a factor in deciding on locations for external heat pumps.

Answer 17 Not all heat pumps installations will have boilers or hot water cylinders. Air to air heat pumps have maximum refrigerant pipework lengths which are part of the design process. Air to water heat pumps will lose less heat with shorter pipe lengths. Ground and water source heat pumps can have extensive external pipework from the collectors to the heat pump.

Question 18 Is there any way to remove a GS borehole at the end of its life - or are they a completely irreversible intervention? Unlike an ASHP which can more simply be removed...

Answer 18 Not that I’m aware of; it would be more cost effective to drain and leave redundant boreholes installed which can be 80m to 100m+ in depth and isolate it at the manifold chamber.

Question 19 What about consents - especially in settings which are Registered Parks & Gardens?

Answer 19 The design proposals are an important part of the planning and listed building consent process. Early engagement is recommended.

Question 20 Completely understand the issues around increased Temp = lower COP & more cost but there are difficulties around client expectation management about having cooler radiators. They don't feel warm enough!

Answer 20 I would challenge this quite firmly and positively with the client. In my experience, most clients understand the benefits and are demanding more from their design team. Present the financial and environmental benefits of a lower temperature system (preferably with the bursar, environmental manager or equivalent in attendance) and then ask the client how important it is for the radiators to be too hot to touch, which in itself can be a safety concern for vulnerable occupants.

Question 21 Will your research look at the running costs of heat pumps in historic buildings?

Answer 21 It’s a concern in the cost of living crisis, particularly for low income households.
Yes, in the decarbonisation project the running costs for all options are included. It is worth noting that this research is for places of worship so the outcomes for dwellings and social housing will likely be different. In the viability of air source heat pumps project, it was found that not all of the energy bills were available from the installations. I know that some case studies resulted in lower running costs but I don’t have the full data to report for all of the installations.

Question 22. Are heat pumps better to be left on low level, rather than turned on and off daily as with gas/oil boilers?

Answer 22 The mode of operation should be part of the feasibility study to determine if the lowest energy consumption is achieved by continuous or intermittent operation.

Question 23. How much user intervention/tweaking do we need to do throughout the year to make sure we're getting the most out of the heat pump?

Answer 23 If you have the correct controls installed including weather compensation then very little. I would recommend a post-handover commissioning visit to check that everything is operating as the design intended.

Further resources