The Viability of Water Source Heat Pumps

00:00:00:10 - 00:00:25:03

Speaker 1

Good afternoon, everyone, and welcome to this Technical Tuesday webinar which will share the findings of our latest work looking at water source heat pumps in historic buildings. I'm Dan MacNaughton, a senior building services engineer at Historic England, and I've designed a couple of successful new build projects that were heated by water source heat pumps. So I was very interested to learn more about how this technology works in older buildings.

00:00:25:03 - 00:00:47:01

Speaker 1

And as Matt has already said, I'm delighted to be joined today by Andrew McQuatt of Max Fordham, who has worked closely with us on this, on this and led the investigations. We looked at a good variety of water source, heat pump installations, which Andrew will explain five in total. And I really enjoyed visiting three these case studies with Andrew and his team.

00:00:47:09 - 00:01:14:23

Speaker 1

If you ever get the opportunity to see this or any heat pump technology installed in a historic building and someone is willing to explain the installation and how it all works, then I would highly recommend a visit. Some of you will likely have seen Andrew and I talk about heat pumps at these webinars before. This is actually the fourth Historic England webinar on this subject, and it'd be great to hear from you as much as possible, please, in the Q&A.

00:01:16:08 - 00:01:29:07

Speaker 1

So if you could type any questions in there and we'll try and answer as many of those as possible at the end. So I'll be available with Andrew for any questions that you may have. And I'm very pleased to hand over to Andrew.

00:01:29:07 - 00:01:51:06

Speaker 2

Thank you very much Dan. It's a pleasure to be back and I hope everyone enjoys the session today. So I think what I’ll do is I think I'll flip through some of my initial slides reasonably quickly because I think both Matthew and Dan kind of covered the fact that this is a continuation of other projects that we've been doing with Historic England.

00:01:51:15 - 00:02:08:07

Speaker 2

And really the best thing to do is if you want to look at the report that's been published or any of the webinars that we've already done is just to go over to the Historic England website and have a and have a search for those things and skip past those and please look at them if you're if you're interested.

00:02:08:18 - 00:02:35:15

Speaker 2

And so today is about the water source heat pump study that we we've been carrying out with Historic England. And so starting back in January 2023 and as Dan said, we went round and we looked at five and different water source heat pump installations around England. Now, the report that's been written on these are still in draft format.

00:02:35:15 - 00:02:58:23

Speaker 2

They haven't been they haven't been anonymized and approved by the people that took part in the study. So rather than speaking about the specifics of the studies today, I'm going to keep it broad and keep it to some more basic fundamentals. And then you can read about all the details and when the reports come out. And so the last heat pump and webinar that I gave, I started with some heat pump basics.

00:02:59:04 - 00:03:16:11

Speaker 2

And what I'm going to do is I'm going to go through the same information again. And if you were if you attended the ground source one, please bear with me. And there are new slides after this. But this will be a recap of of last time. And so hopefully it will act as a little revision as well, if you've already seen it.

00:03:16:11 - 00:03:37:08

Speaker 2

So the first thing to point out is that I'm a bit of a heat pump nerd and I kind of live and breathe heat pumps. I have a home when I'm not tinkering around with those settings I am out and about on behalf of Historic England looking at historic heat pumps. And when I’m not doing that you’ll probably find me at work talking to people about heat pumps.

00:03:37:15 - 00:04:00:18

Speaker 2

It's an easy to forget that not everyone lives and breathes this stuff, and not everyone has a really strong understanding of how they work. So I've been thinking about heat pumps and probably in high school, but I can remember doing practical lab sessions at university in 2003 and on the refrigeration cycle. And I never thought that this technology that was and is commonly used for keeping things cold.

00:04:01:01 - 00:04:27:10

Speaker 2

We play such an essential role in keeping us warm and allowing us to move away from burning stuff and for keeping our buildings warm. And I really believe it's important to have a strong working model of how things work in your head, because once you understand fundamentally how something is working and you can make the best decisions about how to apply that technology, and we're also going to understand the difference between an initial heat pump, a water pump and a ground source heat pump as well.

00:04:28:11 - 00:04:48:09

Speaker 2

So first of all, we're going to look at the big picture and we're going to ask, what does a heat pump do? Well, essentially, it makes heat flow in the wrong direction. And on the face of it, it looks like it's defying the laws of thermodynamics. Of course. Of course it's not. We can draw some analogies here with something else that we think that flows.

00:04:48:16 - 00:05:03:12

Speaker 2

We can think about water and we all know that water flows downhill and copious amounts of experimentation in your bathtub as a toddler taught you that if you wanted washed the floor to fill up your little bucket and you had to you had to lift it up. And it was this it was this lifting up of the water.

00:05:03:12 - 00:05:22:18

Speaker 2

It was where you put in the work to make the water do something that it didn't naturally want to do, which was go from a low place to a high place. And instinctively we all know which direction heat wants to flow. You know, you hold a hot cup of tea that the tea will cool down, your hands will warm up the air and the room will warm up a little bit as well.

00:05:22:18 - 00:05:49:05

Speaker 2

So he heat likes to flow from hot places to cold places. So in a building and winter heat is constantly flowing through the walls, the floors, the windows and the doors and and without any heat being added to the inside of this building will eventually reach equilibrium with outside. And this will happen quickly or slowly, depending on how well the building is insulated.

00:05:49:21 - 00:06:10:11

Speaker 2

But what we need to understand on our road to understanding how heat pumps work and where they get their energy from is, we have to understand that everything around us contains contained heat. Now we're quite sensitive little creatures. They like to exist within a band of between, when we're sedentary we like to be between 21 maybe and 24 and all to keep our core temperature at 37 degrees.

00:06:10:18 - 00:06:36:18

Speaker 2

So we really struggle to view the ground at ten degrees or our water at 12 degrees or even, and air at five or minus five is having any energy available in it at all. But it does. And we know the ice will start to melt outside soon as the temperature rises above one degree. And this is because energy is moving from the air or the ground into that ice.

00:06:36:23 - 00:07:05:15

Speaker 2

And so from the eighties point of view, the air is warm and it contains energy in the form of heat. And only when atoms stop moving at -273 degrees, if there are no more heat energy to be had. So by placing something cold outside, we can get heat to naturally want to flow into it. And so by the same measure, if we place something hotter than the surroundings inside a building, we can get heat flow out of that and into our building to heat it up.

00:07:06:16 - 00:07:34:05

Speaker 2

The first thing we need to do is we need to place something very cold, a colder than its surroundings outside to allow us to gather some free heat. So what heat pumps to use a refrigerant to gather heat from outside. And we carefully select that refrigerant to exhibit useful properties at specific temperatures. So in the case of heat pump for heating, we manipulate the pressure so that the boiling point of the liquid is lower than that of the temperature of the air, the ground, the water.

00:07:35:04 - 00:07:54:11

Speaker 2

So high school science and for you, the boiling point of water, as we all know, is 100 degrees at sea level. If we if we manipulate atmospheric pressure, for instance, if we climb to the top of Mount Everest, we would reduce the boiling point at which that water boils to 70 degrees. And we can do the same with the refrigerant.

00:07:54:12 - 00:08:21:15

Speaker 2

So we can we can manipulate pressures to make that refrigerant boil very cold temperatures like -50. And so this -50 degrees refrigerant begins to boil in the heat pump and it starts to absorb energy from its surroundings. And we will learn why that boiling is really important in a minute. So once the refrigerant has absorbed all the heat it can, we are left with a cold gas.

00:08:21:16 - 00:08:42:04

Speaker 2

So it's collected energy from its surroundings and that's the energy. But the temperature isn't useful. So how can we elevate the temperature of this of the cooled gas to a temperature that we could use to heat their building? And the key to this is why we were interested in manipulating the boiling point, because we can do something with a gas that we can't do with a liquid.

00:08:42:17 - 00:09:06:15

Speaker 2

We can compress the gas and we can raise its temperature. And the best everyday example of this is a bicycle pump. So if you pump up your tire, you're compressing the air and we'll just finish with that fuel, your body pump, you see that it's got significantly hotter. And so we can do the same with a compressor and a heat pump, and so we can compress that core gas and it's going to become hot gas again.

00:09:06:19 - 00:09:34:05

Speaker 2

The trick is to manipulate the pressures. So we're left with a hot gas, really useful temperature. So for heating and for heating a building, we probably want something like 60 degrees. So that gas gives up its energy, its surroundings, the refrigerant does the opposite of boiling. It's going to condense and as the refrigerant condenses, it's changing from a very energetic gas state into a less energetic, liquid state.

00:09:35:00 - 00:09:59:16

Speaker 2

But of course, to allow this cycle to continue, we must get back to our original cold, liquid state. So what we're going to do is going to place a restriction in the refrigeration pipe. This is called an expansion valve. The effect of this expansion valve is to create a change in pressure. So as the cool liquid passes through and it's a low pressure side, it gets colder and then we can connect it all up again, ready for the cycle and to start over.

00:10:00:22 - 00:10:31:05

Speaker 2

And the magic of the heat pump is that the everything that was collected and outside was with free energy. And then we have to elevate this to use the temperature mechanism compressor. That compressor is driven by an electric motor and sadly we have to pay for the electricity that we use to do that. But the great thing is that a modern well run heat pump and three quarters of the energy delivered into your into your building is basically free.

00:10:31:15 - 00:10:52:05

Speaker 2

And one quarter comes from the electricity that drives that compressor. Now we can improve that free heat to electricity ratio in two ways. We can either find a heat source with the highest possible temperature. So and very, very applicable to what is your heat pumps. The water might be warmer than the air. So we might we might do that.

00:10:52:18 - 00:11:26:01

Speaker 2

And we can also reduce the temperature that we need to heat our building. So we could do this through things like insulating our insulating our building, maybe adding secondary glazing, sorting out draft proofing or indeed and installing larger radiators will help to make that some more efficient. So that is the fundamentals of how heat pumps work and at their core and almost every type of heat pump will have a similar cycle to that, be that direct expansion heat pump, also known as an air to air or a mono block heat pump, which is known as water to water.

00:11:26:04 - 00:11:45:05

Speaker 2

So we'll look at all of these a bit detail. So direct expansion, also known as DX, VRF VRV air to air are all names for a particular type of heat pump. And the easiest way to identify one of these heat pumps is to look at how it distributes heat or cooling even around the building. So here's our building.

00:11:45:18 - 00:12:09:18

Speaker 2

Here's our start building. Basically, if the heat is distributed directly into the building using refrigerant rather than water, it will be a DX heat pump. And so the differences between DX and mono blocks are discussed in quite a lot of detail in our in our reports. If you want to read more about that, please go to the Historic England website and look for the phase one air source heat pump report.

00:12:10:17 - 00:12:31:04

Speaker 2

And but none of our case study projects in the water source study had a heat pump like that so we're not going to look at this in any more any more detail. So the other type of heat pump, it's called a mono block heat pump. So the interface, the heating refrigerant with a wet traditional heating system and all the examples we looked at used this kind of model block and heat pump.

00:12:31:14 - 00:12:56:15

Speaker 2

So let's fix that right hand side and with an interface to a wet, wet heating system. And then we'll look at the difference between the difference between air source heat pump, ground source heat pump, a water source heat pump. It's all just to do with where that free heat is collected from. So in an air pump, we install a fan and we blow air directly across the evaporator and that's how the energy is extracted from the air.

00:12:57:13 - 00:13:15:19

Speaker 2

And most of components of air source heat pumps are located outside of the building, but rather than blowing air of the evaporator, what we can do is we can install a water to refrigerant heat exchanger and we can gather our heat from that, from the ground or from surface water. And so why do we call something what is a heat pump

00:13:16:03 - 00:13:44:20

Speaker 2

or a ground source heat pump normally just comes from where we're getting that free energy from the heat. The heat pump units themselves are often exactly the same type of unit and water and ground source heat pumps are often normally installed and inside a plant, inside a building. And if we go and connect a source of water and we pump that water directly through the heat pump, that's what's known as an open source

00:13:44:24 - 00:14:02:04

Speaker 2

water source heat pump. And if you want to avoid any issues with say biofouling or sediment going into your heat pump, you may wish to use a closed loop system. And we can also take a similar we can take a closed system like that and we can bury it in the ground rather than taking in water.

00:14:02:04 - 00:14:31:13

Speaker 2

And then we call that a ground source heat pump. Okay, so now we're onto some new slides. So thank you for being with me if you’ve heard all this before. So now we're going to look at water source heat pumps and the different collector types and that are that are available. So across our five case studies and we saw two different methods from extracting heat from surface water and four of the examples used a closed loop collector in lakes

00:14:31:13 - 00:15:07:15

Speaker 2

and one example used an open loop system and a river So we didn't actually observe. And in this study, anyone using boreholes, to take water from an aquifer, but I've included it. I'm going to include it here for complete next because it is also a really common way and that people get water for what is risky pumps. So we'll look at each of these in turn and it's interesting what makes water source heat pumps pretty unique is that if they're an option for you all will really depend heavily on your proximity to source of water.

00:15:08:03 - 00:15:28:02

Speaker 2

And so this is the water could be a lake, a pond, a river, a canal or even the sea. And if you want to use water from a below ground aquifer, and you're going to require the right type of geology beneath your feet, and most of the case study projects that we looked at were actually large, stately homes.

00:15:28:02 - 00:16:01:15

Speaker 2

So they were either positioned close to bodies of water or had had large bodies of water created close to them. And some are old and that landscaping works with the past, so it works great. Well, the first one is our closed loop pond mats. The pond mats are really popular and because if you're fortunate enough to be located next to a nice open body of water and that you own or you can get permission to use, then it's a relatively simple and low cost method of harvesting heat from the environment.

00:16:01:17 - 00:16:25:07

Speaker 2

So the idea is very simple. You take a manifold at a convenient location close to the water's edge. You connect the main floor and return pipes back to the plant room with water. So heat pump is located. You flow as many coils of pipe out onto the surface of the leak as you need and you need to weigh them down with enough and weight to counteract the natural buoyancy of the plant material.

00:16:25:07 - 00:16:50:09

Speaker 2

Because most modern plastic pipes are actually less dense than water. So they're naturally going to want to fill float. Sorry. Even when they're full of water, you connect the ends of the pipes to the manifold and you carefully fill your system with thermal transfer fluid. And and as the paints fill the water, they're going to it's going to displace the air and the pipes are going to start to sink down to the bottom of the leak.

00:16:51:00 - 00:17:13:11

Speaker 2

So the extent to which the pond mat will need to be physically locked in place will really depend on how much and movement there is in the water. So if you're in a reasonably fast flowing river or if it's exposed to the tides, you're going to require more secured fastening than you would in a nice, gentle and leak environment.

00:17:13:11 - 00:17:35:00

Speaker 2

What if the water in the lake freezes? so the pipes themselves will be filled with thermal transfer fluid, which is a water glycol mixed, so the water inside the pipes won't freeze and because of the oddity that solid water is less dense than liquid water, ice always floats up and forms on the surface of a lake or pond.

00:17:35:13 - 00:17:54:06

Speaker 2

And so this is, this is quite nice feature because it means that, as long as our pond mat is deep enough, we're always going to have nice liquid water with a good heat transfer rate going on and the bottom of the pond, even when even when the surface is frozen. And that is essential. Why? To make sure that the pond is fully submerged.

00:17:54:15 - 00:18:27:06

Speaker 2

So and also locating upon the bottom of the of the lake will keep it protected from physical damage. So normally you're looking at least 1.2 meters off of cover to make sure they don't freeze and to protect them from accidental damage. So in some sites where the lake is used for recreation, such as boating or fishing, the management teams have decided to mark out the location of the pond mats with buoys and ask people to avoid using that area to avoid any any damage.

00:18:28:11 - 00:18:47:24

Speaker 2

So one question might be how big does my lake need to be? Well, that's going to depend on on the following. So you're going to have to ask yourself and how much heat is going to need to be extracted. Well, that's going to depend on how large a building is and how much and how well-insulated your building is.

00:18:48:18 - 00:19:05:04

Speaker 2

We also have to look at whether there's anything topping up heat into the lake. You know, is there is there a big stream or river flowing into it? Because this this this water inflow will help to replace and heat that we are taking out, which will all have an effect on the size of the body of water that's required.

00:19:06:15 - 00:19:35:16

Speaker 2

Now, one of the key study projects we looked at was fed by a stream that had just emerged from its journey through an underground and river network. And it had a really nice effect that the water that was replenishing the way the heat was been taken from remained lovely. Ten degrees all the way around, even in the depths of winter, you had a lovely ten degree water and extracted heat from making for it the potential for an extremely efficient system, if you like.

00:19:35:16 - 00:19:57:03

Speaker 2

It doesn't have much of a flow through it or you're not fortunate enough to be located. Makes an underground river network and your pond or lake will be will get heat from from the sun and from rain falls into the earth. And so, of course, a balance needs to be struck between the heat going into your body of water and the heat that you're taking to avoid over or extraction.

00:19:58:02 - 00:20:26:07

Speaker 2

And like always, look for a specialist with experience in these and these systems to carry out full system design for you. If there is a good flow of water across the mats and you can actually they can actually be designed to have quite a wide pipe spacing so they don't nest in a way. They can be quite close together, so they don't actually take up much of surface area if the water is stagnant, some of you don't have you don't have much of an inflow.

00:20:26:18 - 00:20:49:23

Speaker 2

Then you'd have to look at the mats and you'd have to space them further apart to avoid any local over extraction of water. So the danger is you create cold spots and then the heat pump and efficiency and it declines. One consideration would be what if what if we have an antifreeze leak into our river? So our bodies of water in this country

00:20:49:23 - 00:21:19:08

Speaker 2

be that lakes or rivers is an absolute haven for our wildlife. And the quality of water and in our lakes and rivers is in the constant pressure from things like and agricultural runoff and stormwater runoff and industrial discharges. And of course, climate change is causing temperature rise. It's also causing more frequent intense flooding. And that all washes more pollutants into our into our and into our rivers.

00:21:19:08 - 00:21:46:16

Speaker 2

And, of course, said it starts at the point of all of this stop burning stuff to heat our buildings. You know, we're trying to do something and we're trying to do something to stop contributing to climate change. The last thing we want to do by our actions is to have an unintended impact on on biodiversity and another way so and one of the main unintended consequences would be of the accidental discharge of thermal transfer fluid into our watercourses.

00:21:46:23 - 00:22:12:13

Speaker 2

And but the good news is collecting loops and can be can use nontoxic glycol as antifreeze. And there are several types of vegetable based glycols which are biodegradable and on the market today. So without the influence of external factors such as outboard motors, slicing right through your pipe and the heat collector pipe has an expected lifetime of between 50 and 70 years.

00:22:12:23 - 00:22:44:23

Speaker 2

And so there are some things we can do to help and help make sure our pipes last as long as possible and we protect against any accidental leakage. So the first thing is we've already mentioned is to make sure the pipes are deep enough, make sure there are at least 1.2 meters and below the surface. And if you if it is used for boating a lot, perhaps you decide and not to let boats use the area and just in case the pipes flow up and get damaged, it's also a good idea to design a pressure monitoring system.

00:22:45:05 - 00:23:10:20

Speaker 2

And so something that will automatically alert you if there's any sign of a pressure drop inside the inside the closed loop network. And so it's worth noting here that you often see automatic top up systems on heating systems, and they're really not recommended for closed loop heat collectors because this may automatically top up and in fact mask any evidence of of a leak. In a multi loop system

00:23:10:20 - 00:23:32:11

Speaker 2

you've got your you've got your manifold and you're able to isolate your loops from your manifold. So this is really good because if there was a problem and you probably isolate the affected loop and you could keep using your heat pump on the on the remaining loops until you got that you got that fixed. Okay. So now we're going to speak about open source surface water heat pumps.

00:23:32:11 - 00:24:04:01

Speaker 2

So this was one of the case studies and the project had a system such as this. So open loop systems, they promise to achieve even higher performance than both air source and ground source and closed loop and water source. And they don't take up space that the closed loop mat would take up. And so this essentially would be a really good opportunity if you have a small but fast flowing body of water that you wanted to use, perhaps or even you perhaps you own the body of water.

00:24:04:08 - 00:24:24:22

Speaker 2

It's unlikely you get the permission for a pond map, but perhaps you get permission to extract some water so it could open up the possibilities. So in the closed loop system used to manage your pipes. It's the thermal transfer fluid that is circulated, and so you never physically move the water that contains the heat that you want.

00:24:25:17 - 00:24:46:24

Speaker 2

And an open loop system. You're actually bringing the water that contains the heat you want. You're bringing it from the river. You're extracting the heat that you want from it, and you're sending it back to the lake or river. And so then this water is either pumped directly to heat pump like this and or are probably more common.

00:24:47:05 - 00:25:21:08

Speaker 2

You would use an intermediate heat exchanger. And so this this approach, if you're going to use this approach, also requires a second. Second pump to circulate the thermal transfer fluid between the secondary heat exchanger and your heat pump. Now, whether you choose to install a secondary heat exchanger or not primarily is probably due to what the manufacturer of the heat pump wants because lakes, salt water in lakes and rivers, they could be contained sand, salt, insects, bacteria to name just a few.

00:25:22:09 - 00:25:44:12

Speaker 2

So the larger particles can be filtered out really early to stop them getting into your pumps. But debris will build up over time on these filters and they need to be cleaned and in a safe manner. So right from the earliest feasibility stages, you've got to be asking yourself, these filters are located on pumps that are submerged in the water.

00:25:44:19 - 00:26:04:17

Speaker 2

How am I going to get to those pumps to clean them out safely? And if the answer to that is there is no safe way, then that just means that this type of heat pump isn't feasible for your for your project. But filters and how good they are, they're not going to be able to filter out bacteria and nutrients that that bacteria feed on.

00:26:05:19 - 00:26:24:11

Speaker 2

So these are going to enter your system and they're going to start to grow on any surface they can take a root on. So this growth is known as biofouling and when this accumulates on the surfaces of your heat exchanger, it's going to reduce their effectiveness and that's going to result in a system and a reduction in system performance.

00:26:25:00 - 00:26:50:20

Speaker 2

So understandably, heat pump manufacturers usually don't want river water or even sea water circulating directly around the internal and heat exchangers of their heat pumps. As I said, there's  two main reasons for that and the first one is that the internal heat exchanger is not normally designed to be demountable. It's a refrigeration, water and heat pump.

00:26:50:20 - 00:27:14:22

Speaker 2

So it can be it can be taken apart. And the second reason is, as we've seen, the refrigerant in a heat pump often get well below freezing. And so the raw river water from lakes doesn't contain antifreeze and so there's a possibility that that water could freeze in the heat exchanger. And if it froze, it expands, it could burst the heat exchanger leading to refrigeration leak.

00:27:16:02 - 00:27:38:23

Speaker 2

So for this reason, manufacturers normally insist on a second heat exchanger to act as an interface between the thermal transfer fluid that contains the antifreeze and the raw river water or lake water. So this secondary heat exchanger can be can be a different type. Obviously, it's going to be a water, water heat exchanger. It can be it can be designed to be dismantled for cleaning.

00:27:39:13 - 00:28:10:14

Speaker 2

But you might be thinking to yourself, well, haven't we just moved the freezing problem to a different location? Well, yes, we absolutely have. And there we've just stumbled upon a fundamental limitation of this type of system. So large bodies of water will tend to tend towards the average air temperature for that season. So in England, that means about seven degrees, but smaller bodies of water, they're going to go a lot lower and get very, very cold.

00:28:10:14 - 00:28:34:23

Speaker 2

And the depth of winter, if they don't freeze completely to make it into just a couple of degrees. And that's going to be a problem because the heat pump is going to reduce the temperature of the water source by somewhere, anywhere between three and five degrees each pass through that heat exchanger. Therefore, to avoid freezing and the minimum surface water temperature that's permitted is usually about five degrees.

00:28:35:07 - 00:28:56:09

Speaker 2

So when the temperature of the surface water drops below five degrees, the heat pump needs to shut down to protect that heat exchanger from freezing. So at this point, you'd have to rely on a backup heat source. Now, if that backup heat was coming from a fossil fuel system, you've probably just undone any carbon savings that you were trying to make by purchasing that super efficient

00:28:56:09 - 00:29:18:10

Speaker 2

water source heat pump. So you do, you do have to be careful and there is another option that we could look at and which we will look at that keeps the water above five degrees all year. If you're interested to know more about surface water heat pumps I thoroughly recommend the CIBSE Guide CP2 Surface Water Source Heat Pumps.

00:29:18:18 - 00:29:42:16

Speaker 2

If you are a member of CIBSE you can get that for free and if you're not and it costs £100, buy it from their website. And I think it's a really, really good guide. Okay. So that's brought us on to the last type of collector and this is the open source and taking water from an aquifer or a flooded, flooded mine.

00:29:42:16 - 00:30:02:16

Speaker 2

So as I said, this wasn't actually, we didn't actually see this on any of the case study projects. But I've included it here because it is quite a common and common type. And if water source, like all water source heat pumps is very, very dependent on location. So you're either going to have an aquifer beneath your feet or you don't.

00:30:02:23 - 00:30:28:05

Speaker 2

Likewise, either have an abandoned, flooded mineshaft or you don't. But if you do, they can make an excellent source of water that well will remain in excess of ten degrees all year round. Your only problem is going to be getting your hands on that water. So in an aquifer system, the water flows under our feet through a layer of permeable rock.

00:30:28:14 - 00:30:47:23

Speaker 2

What we're going to have to do is going to have to drill an abstraction borehole sufficiently deep so that the natural inflow of water is equal or greater than the amount of water we want to take out and to heat our building through the heat pump. The water is going to flow into our into this borehole, through the through the walls of the borehole

00:30:48:08 - 00:31:12:00

Speaker 2

and it all comes down to the geology that will dictate how many cracks are in that and in that rock and how fast the water is going to flow in so it’s all, you have to you basically have to hire geologists and to do that to do that appropriate sizing for you. But once you've got your borehole, simply drop a submersible pump into your borehole and you start pumping that water you want to your heat pump.

00:31:13:10 - 00:31:36:06

Speaker 2

So in most instances, you'll be required to return to water into the same aquifer as you took it from. So the only thing you've taken is heat. The net effect on the amount of water in the aquifer would be zero, and this would require a second borehole known as a re injection borehole. And there are some instances where you will be allowed to return the water to a nearby water course.

00:31:36:15 - 00:32:10:20

Speaker 2

And this, of course, save you the expense of drilling that re injection borehole. I think with climate change and the constant pressure we're placing on our aquifer systems and it probably less and less likely all the time that you would get permission and you get permission to do that. So over time water from your re injection borehole is going to make its way through the rock and back to your abstraction borehole and what that will have the effect of its lowering the temperature that your extraction and borehole sees.

00:32:10:23 - 00:32:32:22

Speaker 2

Now don't worry too much about the temperatures after just there they were just they're just actually quite made up. But just to illustrate the point and it will decrease over time but any well-designed system which would take all that into account, maybe thinking that surely that pump at the sort of bottom or midway down that abstraction borehole and surely it's not very accessible.

00:32:33:09 - 00:32:54:18

Speaker 2

And why not just place the pump and connect it to a pipe and suck up the water that that we need? Well, this is because you can't suck water up more than ten meters. If you if you try to do that, you simply create a vacuum at the top of the pump once the once the water has risen ten meters.

00:32:54:18 - 00:33:15:22

Speaker 2

And that's all to do with the weight of the atmosphere above our heads, where we're at when we're at sea level. So if you want to lift water more than ten meters, you can't suck and you must push. And also the quality of water in a borehole aquifer system tends to be much, much higher than a surface water system.

00:33:15:22 - 00:33:32:13

Speaker 2

And if at some point in its life, the pump is either going to fail or it's going to need cleaning, and actually that's not too difficult. And the same equipment that we used to lower the pump and the pipe into the into the borehole can be used to extract it, do the work, and then drop it, biting to it.

00:33:32:19 - 00:33:55:11

Speaker 2

It's not the end of the world or too difficult if you have the right equipment to any open. That system that abstracts or discharges into the environment is going to require you to have appropriate environmental permissions. Now, I'm not going to go into excruciating detail, firstly, because we've written about this in the report. Secondly, actually, there's excellent information.

00:33:55:11 - 00:34:16:23

Speaker 2

All you need to know is really on the GOV.UK website. It actually takes you through it all. But it's probably worth noting that any process like this that requires third party approval and is always going to be a danger in any project. And if you if you start your design based on the assumption that you're going to get approval and then you're doing it can set your design back a bit.

00:34:16:23 - 00:34:40:19

Speaker 2

So like anything like, you know, applying for utility connections or anything like this and it always gets done very, very early and in a project to make sure that all those licenses and things can be obtained on time and again CIBSE have produced this Guide CP3 which is really, really good to read. And again it's free to members of CIBSE and it's £100 to non members.

00:34:40:19 - 00:35:05:10

Speaker 2

If you're interested, please go and have a look at that. So water source heat pumps then? They offer the potential to be to operate at the highest efficiencies of both air and ground source heat pumps. And so if you're fortunate enough to be located next to a suitable body of water, a pond mat may be considerably cheaper and cause less disruption than the equivalent ground source heat pump.

00:35:06:09 - 00:35:29:12

Speaker 2

However, it probably still going to cost you more money than the comparable air source heat pump option. So why would you choose to install a water source heat pump over an air source? Well, that's because a modern water source heat pump with good controls, correctly sized heat collector is going to be more efficient and therefore costs less to run than a air source heat pump.

00:35:29:22 - 00:35:52:24

Speaker 2

And so the obvious reason for this is that in the heating season and the surface water temperature is higher than and is higher than the air temperature. And, of course, we need water for heating in the depths of winter. And so you get an extra efficiency there. The other reason water source and ground source pumps tend to be higher efficiency than air source

00:35:52:24 - 00:36:17:14

Speaker 2

heat pumps is that air isn't very energy dense. And so we have to move a lot of air through your through your evaporator in order to collect the energy that you want. And moving that air comes at a cost. We have to drive, we have to drive fans with electricity and we have to move a lot of that air. And in a water source or ground to keep up, you have thermal transfer fluid that use a pump to to circulate.

00:36:17:20 - 00:36:45:24

Speaker 2

And that sound and that energy exchange is a lot more dense. You have to secure a lot of a lower volume of water than the equivalent volume of air. Again, that all just factors in to make and water source and ground source a little bit more efficient than that air source. But seeing that the efficiencies aren't so staggering that it completely overrides the initial capital cost spend, so often other factors come into play.

00:36:45:24 - 00:37:06:23

Speaker 2

So a really important thing is that water source heat pumps are usually installed internally in existing plant rooms while air source heat pumps require external space to be found. So if you simply don't have and you don't have the external space or indeed the external space that you do have is too valuable for you and you're not willing to give it up.

00:37:07:07 - 00:37:39:17

Speaker 2

And this might be the only reason you need to go for a water source heat pump rather than an air source heat pump. So the initial groundwork can be quite destructive, quite messy. So these are pipes going in between the boiler room and the manifold. And obviously before the pipe loops are sunk, they're visible. But once, once the trenches have been backfilled and the loops sunk, the only thing that you're going to see is a manifold cover and often very, very visually not obtrusive at all.

00:37:39:24 - 00:38:06:17

Speaker 2

And you could basically and not see any evidence of that installation. But another factor that may just tip the balance in favour of a of a water source for your particular installation. Is that is that of noise. Now, I'm not saying that air source heat pumps are too noisy to be dealt with. And you can always, depending on the interventions you take, you're going to deal with the noise an air source heat pump makes,

00:38:07:05 - 00:38:29:16

Speaker 2

but the great thing about a water source or ground source is that you can put those pieces of equipment inside and the amount of noise they make aren't really any different to the amount of noise that big circulation pumps or other heating equipment makes. And once something's indoors, it just becomes an order of magnitude easier to deal with that noise than it does something sitting outside.

00:38:30:00 - 00:38:53:04

Speaker 2

So acoustics does need to be considered. It's just it may not require significantly much more attention than an equivalent fossil fuel system. So this is the final section before I go through the conclusions of the report. And so the last webinar I did almost just about a month ago and there was a question raised about using heat pumps in series to elevate temperatures.

00:38:53:04 - 00:39:11:15

Speaker 2

And I thought it was quite interesting and I thought I could do a small section on, on looking at that. So as we all know, heat pump efficiency is governed by the difference in temperature between the source, that’s where the free heat is coming from and the sink, that's where you're delivering the heat. So into our into our building or process.

00:39:12:01 - 00:39:33:09

Speaker 2

And the closer you can get these two temperatures together, the more efficient a heat pump is going to be. So in the past, it was common for the maximum output at the maximum temperature output of a heat pump to be around 55 degrees. And if you wanted any higher temperatures in that you had, use an immersion heater and to boost that temperature further.

00:39:33:18 - 00:40:04:00

Speaker 2

So if you're running a commercial property and you have to store your domestic hot water at 60 degrees, you're going to need heating water from your heat pump in excess of 60 degrees to heat that water up. So that always requires some sort of top up. So people often ask, why don't you just generate heat, say generate heat for the heating system at say 40 degrees and then slap on a second heat pump to boost that temperature up to something like 65 degrees.

00:40:04:11 - 00:40:28:12

Speaker 2

And what we're interested in is just look at the performance of those pumps. So When we view those heat pumps individually, the performance appears to be pretty amazing. So our first heat pump, they're taking heat from water. We're taking four units of heat from the water. We are delivering one unit of heat through a compressor. And we do a lot of COP calculation.

00:40:28:12 - 00:40:48:16

Speaker 2

We find out this coefficient of performance of five. So then we are second heat pump. So we take that five units of heat and we feed it into the heat pump. We also feed in one more unit of electricity, we do our same COP calculation and that comes out with a COP of six. So it looks and it's pretty, pretty fantastic.

00:40:49:18 - 00:41:08:08

Speaker 2

But the keen eyed among you will notice that only the first heat pump was actually taking free heat from the environment and the second one wasn't. It was just taking heat from the first. So it's really important that we look at these systems as a whole and not individually. So we can combine those diagrams into a single one and we can look at the energy.

00:41:08:08 - 00:41:36:04

Speaker 2

So we can see that we still have that original four units of heat coming from the environment. We've got two units of heat coming from a compressor. They're delivering us six units of heat, so we do our little calculation. And we work a COP of three, which is still pretty respectable. But what we can what we can look at now is you notice earlier I said it was common for older heat pumps to have a maximum temperature of 55 degrees.

00:41:36:05 - 00:41:56:23

Speaker 2

So a modern heat pump and R2 90 or a propane heat pump, they can produce water on their own up to about 75 degrees without requiring any additional internal immersion heaters. But the same laws of physics still apply to those heat pumps. So if you try to create 75 degree water, they're not they're not super efficient at doing it.

00:41:56:23 - 00:42:36:03

Speaker 2

They just they just can. And have a look at this little example. We make 4.1 units of heat in, 1.95 units of electricity in via the compressor, giving us that same six units and we get a COP of around 3.1. And I have I have rounded up slightly there. And so the point wasn't to say that using one heat pump is significantly more efficient than two, but obviously buying one heat pump is going to probably cost you much less than buying two other heat pumps.

00:42:36:09 - 00:43:03:09

Speaker 2

So as long as you can select a single heat pump that's capable of satisfying the temperatures you require, it's often best to choose an individual heat pump and maybe share that common water source and just make sure you're extracting the maximum amount of them free heat available from the environment as possible. So it's becoming less and less and less and less common to see I think, all the time as heat pumps are more and more capable of pushing off a lot.

00:43:04:13 - 00:43:40:05

Speaker 2

Okay. So finally, I'm going to go through the conclusions that we took from the report. So firstly, what is to keep pumps can discreetly decarbonize heating systems in historic buildings. Water source heat pumps are typically well suited to historic stately homes because they're often and constructed next to large bodies of water. The heating performance issues are usually down to the actual heating system configuration in that interface rather than the actual water source heat pump technology itself.

00:43:41:14 - 00:44:07:09

Speaker 2

Water source heat pumps have noise levels similar to that of other system components, making them much more easier to deal with acoustically. But any lack in understanding of system controls can really have a limit on a system's efficiency. And we're in desperate need of skilled contractors and for both the installation and maintenance of these systems.

00:44:08:24 - 00:44:23:02

Speaker 2

And if you're considering an open loop system it’s so, so important to think about safe access and how are you going to clean those filters in a river or a lake otherwise it's basically just not an option. So thank you.