The Viability of Ground Source Heat Pumps in Historic Buildings

00:00:00:18 - 00:00:25:19

Speaker 1

Good afternoon, everyone, and welcome to our first Technical Tuesday webinar of 2024, which will share the findings of our latest work looking at ground source heat pumps in historic buildings. I'm Dan McNaughton, a senior building services engineer at Historic England. And I'm delighted to be joined today by Andrew McQuatt of Max Fordham, who has worked closely with us on this work and led the investigations.

00:00:26:04 - 00:00:58:18

Speaker 1

We looked at five ground source, heat pump installations, and I was fortunate to be able to join Andrew and his team on site visits to two of these case studies. Our regular audience may have seen Andrew and I talk about heat pumps at these webinars before, and this is actually the third historic England webinar on this subject. If you keep an eye on the chat today, I'll post some links to the recordings of our previous heat pump webinars and also some links to historic England's web pages and guidance on heat pumps.

00:00:59:02 - 00:01:18:16

Speaker 1

It'd be great if you could type any questions that you have in the Q&A area that Matt’s just explained, and we'll try and answer as many as possible at the end so that that's enough for me. I'll be available with Andrew for any questions that you may have, and I'm very pleased to hand over to Andrew.

00:01:19:08 - 00:01:41:20

Speaker 2

Thank you, Dan, and thank you, everyone, for tuning in. It's a privilege to be back and doing another webinar with Historic England. So this work today is about ground source heat pumps in historic buildings. And as Dan said, it's very much a continuation on some of the work that we've completed with Historic England before. And I think Dan will be dropping in these links.

00:01:41:20 - 00:02:03:10

Speaker 2

But if you want to see the report that has already been published, you can you can find that on Historic England website. And as Dan mentioned, and September last year, I presented a webinar on the on the second phase of the air source heat pump report and this the second phase isn't published yet, but we hope it will be it will be published soon.

00:02:04:10 - 00:02:29:05

Speaker 2

And so yeah, and what I would say is mostly the points made in that presentation are equally as valid, even with air source heat pumps, a lot of that is equally valid regarding ground source heat pumps and of trying not to duplicate information today. So if you're interested, please go and have a look at that. So as Dan said there, we looked at five ground source heat pump installations across the UK.

00:02:29:05 - 00:02:56:14

Speaker 2

And for this to this project and we tried to cover some larger, larger installations. But the report is it's finished and it's currently under review by the various different case study participants and so to respect the confidentiality until they're happy. And I'm not going to mention the individual case study by name today rather I'm going to focus on some of the most interesting considerations that that came out of the report.

00:02:57:13 - 00:03:19:20

Speaker 2

So the first thing I’m going to do is something a little bit differently. And I decided to take it right back to some really fundamental heat pump and heat pump basics. So I did that for a heat pump nerd. And I, I live and breathe heat pumps. I have a heap of at home when I'm not tinkering with the settings I'm out about on behalf of Historic England, looking at heat pumps and historic buildings.

00:03:20:01 - 00:03:37:14

Speaker 2

And when I'm not doing that, you probably find me at work talking to someone about heat pumps. And it's really easy for me to forget that not everyone lives and breathes this stuff. And it's maybe not the obvious to a lot of people how they work. So I’ve personally been thinking about heat pumps, a refrigeration cycle since about 2003.

00:03:37:14 - 00:03:58:16

Speaker 2

And I can think back to some practical lab sessions I had at university when we were when we were looking at the refrigeration cycle, which is what underpinned heat pumps. And back then I had no idea that that technology that is normally used for keeping things cold would play such a pivotal role in keeping us warm whilst moving us away from burning stuff.

00:03:59:13 - 00:04:19:20

Speaker 2

And I think it's really important to have a strong working model about how something works in your head because once you have a good model, I think you're much more likely to be able to make more informed decisions about how it might be best to use that and use that technology. And also, when we start talking about air source, ground source, water source, you really fundamentally understand what that means.

00:04:20:22 - 00:04:54:15

Speaker 2

So you can sit back looking at the big picture, what does a heat pump do? Well, essentially, we're trying to make it flow in the wrong direction and seemingly defying the laws of thermodynamics. Of course. Of course it doesn't. And but we can draw some we can draw some analogies. So if we think of something else that we know that flows through, we all know that water flows don't help the copious amounts of experimentation in your bathtub as a toddler taught you that you worked out that if you wanted more watched flow you’d fill up your little bucket and you had to lift and it was that it was that lifting that that's the bit where you put

00:04:54:15 - 00:05:14:12

Speaker 2

in a little bit extra work to make the water do something they didn't naturally want to do that. That is move from a low place to high place and we know which direction heat wants to flow. You know, if you hold a V a coffee in your hand, you will feel that heat moving from the hot tea into your cooler hands and also into the into the air around you.

00:05:14:12 - 00:05:43:23

Speaker 2

So this is what we're doing with heat pumps and we're trying to make heat flow in the wrong direction. We're trying to make flow from and cold too hot. So inside a building, winter heat is constantly moving to the walls, the floors, the roofs, the doors. And if we don't add any heat into that building and the building will cool down and it will reach an equilibrium with our site, and it doesn't matter if the building's insulated or not, and that will just affect the rate in which the cool down, the cool down happens.

00:05:44:24 - 00:06:01:17

Speaker 2

So the first thing we have to do on a road to understanding how a heat pump works is, is to understand where they're going to get their energy from. And we need we need to recognize something in the first thing we need to understand is that everything around us contains heat. And it's we are we're sensitive creatures.

00:06:01:23 - 00:06:21:21

Speaker 2

And when we're sedentary, we like to exist somewhere between 21 and 24 degrees and all keep our body temperature around 37 degrees. So to some things, we have a real problem in imagining that the ground at ten degrees or the air at five degrees or even minus five has any energy that we're having now. Of course it does.

00:06:22:02 - 00:06:44:10

Speaker 2

And we know the ice outside will start to melt and see the temperature gets above zero. And that's because from the ices point of view, the ground and the air are all are all warmer than two. And so it is energy. And that energy starts to move from the air in the ground into the into the ice and actually only when at and stop moving at -273 degrees is there no more heat energy

00:06:44:13 - 00:07:10:03

Speaker 2

to be had. So fundamentally by placing something very, very cold outside, we can get heat to flow into it. And that same measure, if we place something hotter than its surroundings inside, we can get that same heat, flew back everything and into our building. So the first thing we're going to do is we're going to place something colder than its surroundings outside and we're going to like that together some free heat.

00:07:10:20 - 00:07:32:11

Speaker 2

So if you pump, we use refrigerant to gather that heat from outside and we carefully select the refrigerant to exhibit some useful properties at specific temperatures. So in the case of a heat pump for heating, we're manipulating the pressure so that the boiling point of that liquid is lower than the temperature of the air or of the ground.

00:07:32:11 - 00:07:56:01

Speaker 2

It's a little high school science fact. So we all know what the boiling point of water is, 100 degrees. That's 100 degrees at sea level. And if we manipulate atmospheric pressure, I see it climbing to the top of Everest, we can reduce that boiler room temperature data about 70 degrees. So by manipulating the pressure of the refrigerant, we can make it boil at very low temperatures like -50.

00:07:56:15 - 00:08:18:14

Speaker 2

So this -50 refrigerant begins to boil and the heat pump absorbs energy from its surroundings. And we will learn other in a moment why that boiling is more important. Once it's absorbed all the energy it can, we're left with a cold gas. It's collected all the energy it can from the surroundings, and that is free energy. But the temperature itself is not useful to us.

00:08:19:04 - 00:08:36:10

Speaker 2

So how can we elevate the temperature of this cool gas to a temperature that we can use to heat our buildings? So the key here is why is this important to us? Why we decided to make it boil and become a gas? This is something we can do with a gas that we wouldn't have been able to do with liquid.

00:08:36:24 - 00:08:54:15

Speaker 2

We can compress the gas and it can raise its temperature and the best everyday example of this, it's when you pump up a bicycle tire at the end. If you if you feel the pump, you will feel the pump has got quite warm. And that's because if that's the gases being compressed and heating up so we can do the same with a compressor and a heat pump.

00:08:55:07 - 00:09:25:17

Speaker 2

So as the as the compressor compresses the cool gas, it becomes hot gas. And again, the trick is manipulating the pressures. So they were left with a useful temperature. So to hit a building, we're going to need something that's at least and a gas to be C 60 degrees. So the hot gas then begins to give up its energy surroundings and again manipulate it, the temperature, the pressures, so the fridge and as the opposite foil it starts to condense.

00:09:26:12 - 00:09:50:21

Speaker 2

And as the refrigerant condenses, it changes from an energetic gas to less energetic liquid. And then we need and now to get our cycle to continue, we're going to get back to that original cold liquid. So the way we do that is we place a restriction in the refrigerant pipe called expansion valve. And the effect this expansion valve has is to basically create a change in pressure.

00:09:50:22 - 00:10:14:14

Speaker 2

So as the two liquid passes through to the low pressure side, it drops right down in temperature. And that makes it very to start the cycle all over again. So the energy collected by the evaporator, we call it the evaporator, just that odd because actually the refrigerant in the evaporator is boiling. But I think for obvious reasons, it's probably best we don't we don't call them, we don't call them boilers.

00:10:15:00 - 00:10:45:15

Speaker 2

And but it's absorbing energy and that energy is coming for free. But we need to elevate that free energy to a usable temperature. And to do that being a compressor, the compressor is driven by an electric motor and sadly, we have to pay for the electricity to that electric motor uses. But the magic is that in a modern, well running heat pump, three quarters of the energy delivered into the building is free and one quarter comes from the electricity that drives that compressor.

00:10:46:02 - 00:11:04:09

Speaker 2

And we can improve these numbers and we can improve that ratio and make our heat pump even more efficient. And we can do that and in two ways. First, we may find a heat source that gets hotter. So, for example, we may decide to use ground water rather than air, which is going to be warmer and therefore improved efficiency for heat pump.

00:11:04:23 - 00:11:38:04

Speaker 2

And another thing we can do and we can do both of these things at the same time, we could try to reduce the temperature, which we're asking the heat pump to provide. And we might do this by insulating our building. We might install larger radiators or, as you will see later, in the case of conservation heating simply by heating our buildings to a lower temperature. All the things that help and improve efficiency. So that that is it that is the fundamentals of what's going on inside a heat pump and at its core, every type of heat pump and has very similar cycles to that.

00:11:38:16 - 00:12:00:13

Speaker 2

And so be that direct expansion heat pump also known as an air to air or a mono block heat pump, which maybe you've heard called water to air. So we're going to explore those two different types a little bit further here. So first of all, a direct expansion sometimes referred to as DX, VRF, VRV, air to air are all names given to a particular type of heat pump.

00:12:01:06 - 00:12:27:00

Speaker 2

And easiest way to identify one of these heat pumps is to look at how the heat is being distributed into the building. Here's your building. And it's a historic building. So basically, if the heat is distributed directly into the building using refrigerant rather than through an interface with water, that's a DX heat pump. And the difference between the DX and monoblack is discussed quite thoroughly

00:12:27:00 - 00:12:47:00

Speaker 2

in the air source heat pump report that we talked about earlier. So if you if you want to know more please go and have a look at that. And I'm not going to talk about this type of heat pump any farther in this condition because of all of the five key studies, none of them used DX heat pump technology. So the other type was called a mono block heat pump. So, the difference there

00:12:47:00 - 00:13:09:01

Speaker 2

is a mono block heat pump interacts with the hot refrigerant through a traditional and wet heating system. And old examples like to use this, use this type of the heat pump. So let's fix that right hand side and say that all the heat pumps we’re looking at interface with a wet heating system. So I’m going to think about the difference between the different types heat pump.

00:13:09:01 - 00:13:32:00

Speaker 2

So the difference between an air pump, ground source heat pump and water source heat pump it where free heat is collected from. So in an air source heat pump, we install a fan to blow air across the evaporator and energy is extracted directly from the air and most of the components of of air source heat pumps are located on the outside of the building.

00:13:33:06 - 00:14:02:08

Speaker 2

But rather than blowing air over the evaporator, we can also install water to refrigerant heat exchanger and we can gather the heat from either the ground or from surface water. And really, whether we call something a ground source heat pump or a water source heat pump just normally comes down to where we get the heat from. The actual heat pump itself is normally and usually exactly the same type of unit and in the case of water and ground source heat pumps, and they're normally installed in a plant room inside a building.

00:14:03:16 - 00:14:24:00

Speaker 2

If we if we connect that to a source of water and with a pump and we connect like this water directly, we call this an open loop water source heat pump. And there would normally be another heat exchanger and between the river of groundwater and the heat pump and to stop any biofilm or sediments forming.

00:14:24:00 - 00:14:46:03

Speaker 2

And the heat exchanger having shown here just for just the clarity and to avoid any of those issues with the biofilms sediments, we could choose to sink a closed loop heat exchanger into that body of water. And these pipes are filled with a thermal transfer of the transfer fluid, often referred to as brine. And this is what we call a closed loop system.

00:14:46:03 - 00:15:05:04

Speaker 2

So if we call something a ground loop, ground source heat pump sorry, if we buried that that same loop of thermal transfer fluid and in pipes into the ground and we use it to collect energy from the ground that it's just as a note here, the energy that we're collecting from the ground, the vast majority of it has come from the sun's energy.

00:15:05:04 - 00:15:31:10

Speaker 2

And you have to go a lot deeper. And to start collecting geothermal energy. So from this point on, I'll just be talking about ground source heat pumps. So across the five case studies, there were three different methods of extracting heat from the ground. So what do we see? We saw vertical boreholes, we saw an boreholes drilled in a radial configuration, a variant, and we saw some horizontal ground loops.

00:15:31:15 - 00:15:55:08

Speaker 2

So we're going to see we're going to we're going to work through these and talk about the pros and cons of them. So the vertical boreholes, as the name suggests, are drills vertically down into the ground and with a pipe loop fixed in it. And that's fixed with a highly thermal and conductive grout. So the thermal transfer fluid is circulated from the heat pump through the loops.

00:15:55:14 - 00:16:17:09

Speaker 2

And then it's that energy that's basically collecting the heat and sending it back to the heat pump. As I said before, it's often referred to as a brine loop and this is just referring to the fact that there's usually, well there would be, antifreeze in these loops to stop them from freezing and in the old days, they might have been brine salty water and they would produce other types of hopefully environmentally friendly antifreeze in there.

00:16:18:20 - 00:16:41:11

Speaker 2

So the total length of borehole that you're going to require depends on on quite a lot of things. It depends on the heat load of the building. It depends whether you're going to use the system, if you going to install a reversible system, if you're going to have any cooling in the summer because any cooling could put heat back in the ground and that can reduce the number of boreholes you need.

00:16:42:01 - 00:17:07:14

Speaker 2

But more than that, it really depends on the geography and the geology, sorry, of your site. In Britain we have some of the most complex geology in the world. It can change from it can change from town to town. And so it's incredibly complicated. And because of the differences in geology, a single borehole maybe could yield anything between 5 to 35 kilowatts.

00:17:07:23 - 00:17:31:10

Speaker 2

So, that's what, that's what I'm trying to show there is, there's a huge range. And so if you just try to use a rule of thumb, it doesn't really work because you do really need specialist help to understand the fundamentals of your site. And there's quite a quite a wide range there for what one borehole might be able to produce. But once we worked out what the total length of borehole is and then we can work out what the optimal number of boreholes would be for your site.

00:17:31:10 - 00:18:05:16

Speaker 2

So boreholes range and between 50 and 200 meters deep and you use that space around seven meters, seven meters apart. And multiple boreholes can be used for a borehole array serving single or multiple and multiple heat pumps. And as I said, the ground source heat pumps are normally located inside a building. So rather than bringing all the borehole, all the individual borehole pipes back to your plant in one go, what we normally do is we gather them all together in a manifold housing located outside the building.

00:18:06:00 - 00:18:28:21

Speaker 2

And from here you can monitor and isolate the separate loops. And, you know, we should we should definitely design a manageable chambers for safe access and given them and give them an adequate drainage. So boreholes require specialist drilling equipment and that's going to result in quite a high cost. And boreholes are often used where there is limited space available.

00:18:29:03 - 00:18:58:23

Speaker 2

But for for big installations, they normally are quite an economic choice and for your ground loop. Now radial boreholes can be used when you can imagine the planned area that you have. Looking down isn't very large, but perhaps you do have access to a large site that might come, come, come about when, for example, in a church. And if you are, you might be need to drill, but you have to avoid graves and archaeological layers, sort of this type of thing might work better for you.

00:18:59:01 - 00:19:23:10

Speaker 2

So the array starts with a single borehole which goes vertically down and then separate boreholes have been drilled, branching off from the main access chamber and around the circumference. So and each branch is as a separate brine loop which can be isolated from that from the access chamber. And again, this stuff requires specialist drilling equipment, which is going to lead, which is going to be reasonably expensive to do.

00:19:23:19 - 00:20:07:18

Speaker 2

However they can be particularly useful where you do have this unique situation where you have to avoid certain ground features. And the last one we saw was horizontal ground loops. The thing about these is that they require significantly more area to be available than their, than their vertical cousins. So you'll likely see these technologies utilized in places that have large open fields maybe for grazing next to, the next buildings. so horizontal grain loops are typically placed within a trench one to two metres deep by one metre wide and spaced three to four metres apart, and then they're dug into the ground and then they're backfilled with the soil that was used, that was

00:20:07:18 - 00:20:30:05

Speaker 2

removed from them. So the pipe containing the thermal transfer fluid is usually laid in a in a linear pipe configuration. And it's something that is laid in a coil often called a slinky. The more up to date thinking as the linear configuration is the preferred method because localised ground freezing can occur where the coils overlap each other.

00:20:30:05 - 00:20:57:11

Speaker 2

So just like the vertical collectors, the design, the total pipeline really does depend on the ground conditions and, and, but, but they can be installed without particularly specialized equipment. So there's a reason that the trenches are about and a metre wide because this is the width of a big excavation bucket so often it doesn't need any more than just an excavator working its way around a field.

00:20:57:17 - 00:21:20:18

Speaker 2

But it does require a lot of space and potentially a lot of time to install. Another thing to say is because they don't go as deep and the ground and maybe is a little bit less stable and temperature at that point and you maybe get a lower temperature of your thermal pressure fluid back, which means you may not be quite as efficient as it would have been if you'd gone vertical.

00:21:21:21 - 00:21:46:08

Speaker 2

And of course, you can use multiple loops for large and large installations. So whatever ground collector style you decide to use, the total install cost is likely to be at the very least, double that of comparable air source heat pump installation. So I want to ask the question why, why choose to install a ground source heat pump? There obviously must be more issues than just cost.

00:21:48:01 - 00:22:13:23

Speaker 2

So the first thing to say is a modern ground source heat pump, good controls, a correctly sized ground rate, will be more efficient and therefore cheaper to run than an equivalent air source heat pump. And this is because when we need to heat buildings in the winter, the ground is on average warmer than air. So what we've done there is the heat source temperature is higher, which improves our heat source efficiency.

00:22:15:03 - 00:22:38:03

Speaker 2

And another reason ground source heat pumps can be more efficient than air source heat pumps is because of the density of the thermal transfer fluid. So to extract the required amount of heat using a pump and thermal transfer fluid, you’ve only got to move a small amount of that thermal transfer fluid around. When you compare that to an air source, heat pump and air is very, not very dense,

00:22:38:08 - 00:23:05:10

Speaker 2

therefore, you've got to move a lot of air across that heat exchanger and that fan energy uses a lot of energy. So this is this pumping energy in relation to the fan energy, that creates a little bit of a difference in efficiency between ground source and air source. But however, even with these improved payback costs and all else equal, it may still be quite difficult to justify against this heat pump over an air over an air source in terms of payback.

00:23:05:15 - 00:23:32:01

Speaker 2

So again, there must be more to it than that. Ground source heat pumps can often be installed internally in existing internal plant rooms while air source heat pumps are normally installed outside. So if you just simply do not have external space for an initial heat pump, then this might be all the justification and that's required to spend that initial capital cost and go for a ground source.

00:23:33:01 - 00:24:02:14

Speaker 2

And although externally, it can be, as I’ve shown before, it can be very disruptive, but actually once the work is done and the ground has been re-established and so settled down, it's basically not noticeable after that. And the ground can then be used for other functions such as farming or car parking. And so the last thing I think that may and depending on your situation may take and take the balance in favour of ground source is of course noise.

00:24:04:00 - 00:24:25:05

Speaker 2

So the components that create noise in a ground source heat pump are all, are the compressor and the pumps and they're located generally inside the heat pump casing and then that heat pump casing is all inside an internal plant room. And addressing noise and an internal plant room is much, much easier than when you have to do outside like for any air source heat pump, for example.

00:24:26:01 - 00:24:45:17

Speaker 2

So the noise generated by the heat pump itself is often very similar to other heating system components such as the boilers and circulation pumps. So I think you do have to consider acoustics and it may be not maybe it doesn't have to be considered over and above what you would have already have to consider for a plant room that contains pumps.

00:24:46:05 - 00:25:16:19

Speaker 2

And I'm not saying here that the air source heat pumps are particularly noisy. And of course, there are things you can do with air source heat pumps to combat the noise they make but this is definitely much, much easier to do than the ground source. So in this project we looked at and we looked at key pumps and they were providing thermal comfort to a medieval church, medieval hall and a Georgian manor and all of these buildings had very, very limited fabric improvements done to them.

00:25:17:23 - 00:25:47:07

Speaker 2

So this hammer, this home, again, the efficiency of a heat pump improves as the temperature of the of the water, which we require to heat the building, reduces. So for every one degree drop in flow temperature the efficiency of your heat pump goes up by about two and a half per cent. And so if you can improve the thermal performance and the existing heating system effectively becomes oversized which means you can run it cooler which means the heat pump efficiency is improved.

00:25:47:24 - 00:26:12:03

Speaker 2

Of course, a lot of historic buildings may have limited options for fabric improvements and that might be due to listed building consent or issues with moisture. But there are various things you can do and often such as draft lobbies, secondary glazing, additional insulation and all of these things are utilized in the picture here. This is an example from the phase one air source heat pump report.

00:26:12:03 - 00:26:39:19

Speaker 2

But another question we have to consider when we're designing these heating systems is to think about what we're heating, what we're trying to achieve. Are we trying to achieve conservation or we are trying to achieve comfort. Historic buildings are incredibly vulnerable to damage from the environmental conditions, particularly humidity. So conservation heating increases the temperature in a building to reduce the relative humidity to prevent damage to building fabric

00:26:39:21 - 00:27:02:15

Speaker 2

and it's contents. And so we use humidistats and temperature sensors around the building to bring the heating system on when certain targets are exceeded. So the heating system is not driven by thermal comfort, but is driven by conservation needs. And as I said, it's to protect the fabric of the building and its contents.

00:27:03:03 - 00:27:29:10

Speaker 2

And the thing is, the internal temperatures required to control humidity are generally much, much lower than the temperatures that you would require to provide comfort. And this has an implication. So the existing heat emitters and maybe in your building, these may be from a previously installed fossil fuel heating system and they will likely be sized to generally comfort conditions within the within the space.

00:27:29:10 - 00:28:00:11

Speaker 2

So when we come along with the ground source heat pump, which like to operate at a much lower temperatures, the output of the radiators and also drops but because and because of the internal the lower internal temperatures you're looking for with conservation heating and often works out that these radiators can provide enough heating at the lower temperatures without anything having to change and actually swings and internal temperature and RH are the worst thing for historic fabric and context stress.

00:28:00:12 - 00:28:22:17

Speaker 2

It's really important that we that we have slow changes in temperature in RH and actually the flow temperatures of heat pumps being lower, mean they are they're much more able to provide a gentle consist heat rather than pulsing on and off with maybe an older fossil fuel system. So they may actually be an improvement over being over operating a fossil fuel boiler temperature.

00:28:22:20 - 00:28:45:20

Speaker 2

And actually what was quite interesting is a lot of the properties that were being heated for conservation and reasons for the heat up. So the air temperatures were low. But even then, staff and volunteers often reported that they found the building more comfortable and they would say this is because the swings in temperature were less, so it was very consistent. And instead it was, it's actually, despite the average temperature probably being the same,

00:28:46:03 - 00:29:14:13

Speaker 2

they reported it being much more comfortable once the heat pumps had been installed. So the final aspect I want to look at today is what to do when you have a conflicting requirements of providing both comfort and conservation alongside each other. So this happens when you might have residential apartments or office accommodation inside a historic building where much of the historic building actually requires conservation, heating.

00:29:16:01 - 00:29:50:08

Speaker 2

And so a heating system designed for thermal comfort is going to have different flow temperatures, probably higher, may have larger heat emitters, and they also might have to operate at different times of the day. So you have two options are available. The first option is to install a single heat pump and to serve conservation, heating and the comfort spaces or you can install two heat pumps: one for the conservation area and one for the comfort area. And those two heat pumps can share a ground loop together.

00:29:51:10 - 00:30:31:11

Speaker 2

So if you do decide to go down the route of a single heat pump, which is what we saw, which is what we saw in quite a lot of the case studies, the heat pump would be required to always be producing heat to satisfy the most demanding load. So in this case, we might need 55 degree water to satisfy the internal comfort conditions, even though the rest of the building might only require 25 degrees and to satisfy the conservation heating. Now, the heat pump would have to produce all the water at 55 degrees and then at 55 degree water would be blended down to 25 degrees for some circuits.

00:30:31:20 - 00:30:56:04

Speaker 2

But remember that the heat pump really benefits from running as cool as possible. And if we locked the systems together this way, we are basically locking the heat pump into always producing water at not very efficient and not efficient temperature. So our remedy for this would be to install two separate heat pumps, one for the conservation area and one for that for the area

00:30:56:04 - 00:31:22:00

Speaker 2

requiring thermal comfort. And this would allow both pumps to be sized directly. It would allow them to run independently and also both heat pumps could be fine tuned to run at the optimum temperatures to satisfy the load. So that one at bottom would be running 25 when it thought about 55. And the key question for all of these projects as well is this is this worth the effort?

00:31:22:01 - 00:31:45:09

Speaker 2

Well, as always, the answer is maybe. So, the drawback of using separate heat pumps is that the system will likely have a higher capital cost, because all else equal, two half sized heat pumps are going to cost you more upfront the one full sized heat pump. But as always, the correct answer will really depend on the balance of loads that are going on within a building.

00:31:45:18 - 00:32:13:08

Speaker 2

And this I think this is definitely something that's worth considering, with a system design say when you're looking at the looking at options. So lastly, I'm run through some of the and some of the conclusions that we that we drew in the phase one report and then we can take some questions. So, the closed loop ground source heat pumps are definitely a viable option for decarbonizing heating systems in historic buildings, and that is for both comfort and conservation

00:32:13:08 - 00:32:54:21

Speaker 2

and heating applications. The ground source heat pumps we've seen are being deployed to decarbonize heating without actually major works going on to the existing heating systems and this is particularly true when there’s conservation heating in the heating strategy. And then in future you could you could build up and improve the efficiency of the heat pump by improving the building or changing the radiators or something like that. Where we saw performances and performance issues with the heat pumps and it was often due to that heat pump and design not being considered rather than the fundamentals of heat pump and pump technology.

00:32:54:21 - 00:33:17:00

Speaker 2

The installation of ground collectors is disruptive while the ground work is going on, but after the ground is restored and the ground collector has a really minimum visual impact and really it's in their small number of manhole covers that can be seen. And lastly, ground source heat pumps have a noise level similar to that of other components such as large circulation pumps.

00:33:17:10 - 00:33:33:24

Speaker 2

And so if they're installed inside a plant room the noise they make can be can be easily, easily handled, which may give them that edge over an air source heat pump installation in particular situations. So thank you very much.

Question: With borehole approach to what extent does recharging the borehole, running the heat pump in reverse, have to be considered to avoid long term energy depletion particularly with closed-loop GSHP solutions?

Andrew: When designing a borehole array, it's important to ensure that the amount of heat taken out of the ground is balanced with the amount of heat replenished by the sun over a year. If you extract more heat from the ground than what can be replenished by the sun, the ground will start to cool down year after year, which will ultimately reduce the efficiency of your heat pump system. However, if you add heat back into the ground using a cooling system, you can help to balance the annual heat input and output cycle. This means that you will likely need fewer boreholes for your system.

As a follow I didn't see an open-loop GSHP in the diagrams - are there challenges with aquifer based heat pumps - e.g. licences?

Dan: Mentioned in webinar that we will cover water source heat pumps in the next webinar on 20.2.24

Question: Will HE be publishing any reports on the recent installation of GHP at Farnborough Abbey?

Dan: No plans to do this. If you think that there is something unique about this installation and you know who to contact then please feel free to email me at: [email protected]

Question: Would for an average domestic dwelling would you normally expect to use a single phase or a 3 phase heat pump

Dan: single phase

Question: How would the internal target temperature be known  for a particular RH target when in conservation heating mode?

Dan: It is part of the design criteria and can be programmed by either a Building Energy Management System or by using a purpose made conservation heating control system. If you are interested in the specifics of the design criteria then have a read of this: https://www.getty.edu/conservation/our_projects/science/climate/paper_staniforth.pdf

Question: Setting aside environmental considerations, have you compared running costs of heat pumps compared to fossil fuel heat sources such as gas boilers?

Dan: The running costs are comparable if the heat pump system is well designed and installed.

Question: For the separate heat pump configuration to provide comfort and conservation heating. Would the radiators in the comfort heating side need to be resized? Additionally, is it always suitable to leave radiators in the conservation heating areas as is?

Dan: the size of all heat emitters for both heating modes should always be checked by a building services engineer with experience of these systems.

Andrew: The radiator sizes should always be calculated. However, don’t assume they will always need to be increased in size. For example, in one property we visited, the existing radiators were installed under each window, presumably to counteract drafts, rather than being based on a heat loss calculation. The result was that the existing radiators had enough capacity for comfort heating when they were run at heat pump-friendly temperatures.

Question: Could you please elaborate on your findings about not needing building upgrades? This seems to be a common recommendation in relation to heat pump installation?

Dan: Some of the case studies did improve the fabric of the building and others didn’t. All fabric options should be appraised along with all heating options in a feasibility study carried out by someone with technical competence.

Question: Could a GSHP or ASHP with conservation heating settings/infrastructure be 'topped up' with electric heaters, e.g. under-pew electric heaters in a church, or is this worse for carbon footprint overall?

Dan: Any electric heater will be less efficient than a heat pump system however it can be more cost effective overall to heat some areas with direct electric heating if their use is not extensive. It all depends on the specific building and how it is used.

Question: Have you tested ASHPs with propane as the refrigerant to provide higher flow temperature?

Andrew: Propane heat pumps are capable of functioning at temperatures of up to 70 °C. However, it is important to note that they are subject to the same laws of thermodynamics as other heat pump types. This implies that their efficiency will decrease at these higher temperatures, making them more expensive to operate at higher temperatures. A balance needs to be struck between upgrading the heating system/fabric and improving heat pump efficiency.

Question: Is there a procedure for determining the conservation temperature? 8deg shown in the example sounds very low.

Dan: It is part of the design criteria and if you are interested in the specifics of this then have a read of: https://www.getty.edu/conservation/our_projects/science/climate/paper_staniforth.pdf

Question: Moisture in buildings is regularly and rightly raised as an issue in historic buildings .although it may not work for comfort, to what extent are dehumidifiers part of the solution alongside temperature control?

Dan: I’ve not heard of dehumidifiers being used in conservation heating. They can be required when there are specific environmental conditions (high moisture) and sometimes high levels of moisture can indicate problems elsewhere such as damp, weather ingress or leaking services.

Question: What if you want to raise the temperature in the conservation part of the building for occasional usage? This would need to be part of the design?

Dan: Yes that is correct. A system where the emitters are sized for conservation heating would not be able to provide comfort conditions in the winter.

Question: Can the plant room be in an exterior building (e.g. shed/ barn)?

Andrew: It's important to keep in mind that heat will always be lost from pipework, thermal stores, hot water cylinders, and any other equipment in a plant room. If the plant room is located within the heated thermal envelope, then the heat loss is not really wasteful. However, if the plant room is situated in an outbuilding, the lost heat will not be of any benefit to you.

Question: Is there a minimum size of building that would be recommended for heat pump usage? Is it not worth the installation for e.g. a small cottage?

Andrew: Even a single room can be heated with a heat pump. I could not discount the option based on building size.

Question: To protect fabric in conservation building in e.g. offices occupied Mon-Fri 9-5, what is the best strategy? Heat to 21oC for when it is occupied and set back to 8oC at other times?  Or would these changes cause problems?

Dan: It depends on the sensitivity of the building/collection to being heated for prolonged periods. Short term temperature boosts can sometimes be tolerated but regular comfort heating for office design criteria may not be suitable.

Question: Can you add supplementary heating to the water loop in the distribution system e.g. an electric boiler?

Andrew: Yes, it is possible to combine heat pumps with other heat sources, such as electric boilers. However, careful integration is necessary to ensure that you get the most out of your heat pump. Electric boilers are capable of generating much higher temperatures than a heat pump, and if they activate without careful control, the heat pump could turn off. Additionally, it is essential to remember that every unit of heat provided by a heat pump will cost you between two and four times less than heat from an electric boiler.

Question: Would the GSHPs work for something like underfloor heating in historic churches?

Dan: Yes one of the case studies is a Cathedral with underfloor heating.

Question: I am a conservation officer. The size of ASHPs/noise barriers are often bulky and visual intrusive. Is there likelihood that the technology will get smaller to become less aesthetically intrusive?

Dan: I don’t anticipate it becoming smaller. Please note that in 14 case studies of ASHP installations in historic buildings, none of them had aesthetic or noise issues.