Case Study of Shrewsbury Flaxmill Maltings Ground Source Heat Pump Project

00:00:00:12 - 00:00:21:12

Speaker 1

Thank you. And good afternoon, everyone, and welcome to this Technical Tuesday, which is going to be a case study of the Shrewsbury Flaxmill Maltings Ground Source Heat Pump project. And hopefully it will demonstrate how older buildings can be adapted to use sustainable energy sources and play their part in the efforts to tackle climate change. My name is Caroline Cattini-Dow

00:00:21:12 - 00:00:40:17

Speaker 1

as Matt said and I'm Historic England's building services team leader and principal engineer in the technical conservation team. And I am very pleased to welcome the two presenters today, Nick Hill and Hugh Griffiths. And I'm going to let them introduce themselves rather than I will. And Nick, if you would like to introduce yourself, please.

00:00:42:05 - 00:01:02:08

Speaker 2

Yes. Hello, everyone. Nick Hill national conservation projects manager with Historic England, chartered building surveyor. And my role on the Flaxmill Maltings project has been in charge of the delivery of the the construction works over the eight or nine years or so of my involvement on the project.

00:01:03:03 - 00:01:06:08

Speaker 1

That's great. Thank you, Nick. And to Hugh, if you would like to introduce yourself.

00:01:06:20 - 00:01:20:01

Speaker 3

Good afternoon, everyone. My name's Hugh Griffiths. I'm a partner E-3 Consulting Engineers. We were the M&E designers on the design team for the Flaxmill, so we were involved in specifying the heat pump, which I'm looking forward to sharing with you later.

00:01:20:21 - 00:01:37:24

Speaker 1

That's great. Thank you. So just as an overview on the topics that Nick and here are going to be covering today. So first of all, Nick's going to give us an overview of the history of the site and the project and then look at the site services masterplan and then go on to sort of look at some of the environmental analysis as well.

00:01:38:16 - 00:01:58:02

Speaker 1

And then Hugh, which is going good to be covering most of the presentations. We're going to look at some of the basics about how heat pumps work. So just refresh ourselves on how that works. If you've joined some of our other webinars, we're going to look at the heat pump system designed for Shrewsbury and the radiators, and then some control and optimization as well to conclude on that.

00:01:58:02 - 00:02:09:13

Speaker 1

And there'll be plenty of time at the end for questions. So as Matt said, make sure you get your questions in in the chapter. So first of all, without any ado, I will hand over to Nick.

00:02:11:04 - 00:02:40:04

Speaker 2

Thanks very much, Caroline. Yes. I'm just going to give a brief overview of the the project as a whole before handing over to Hugh, who is the mastermind of all things, on the on the heat pump and all the technical details. So here we're looking at a view of the the main mill, Shrewsbury Flaxmill Maltings. This has been Historic England's major rescue heritage led regeneration project on the site and through 2017 two just completed in 2023.

00:02:40:15 - 00:03:15:23

Speaker 2

It's in Shrewsbury in Shropshire, one mile outside of the the town centre. It's a grade one listed building and it's been the focus of a major project and a £20.7 million grant from the National Lottery Heritage Fund. So next slide, sorry, There we go. And so just an overview of its history. It was built as a flax mill in 1797 and it spent its first 90 years as that and its claim to fame.

00:03:15:23 - 00:03:47:11

Speaker 2

And the principal reason why historic England has been so involved in rescuing the site is that it has this amazing iron frame. It's the first iron framed building in the world, built in 1797, designed by Charles Bage and master iron founder William Hazeldine. This is a view of the third floor showing the iron frame at its best, and we often refer to it as the grandparent of the skyscraper, because this was the sort of generation really of that whole different way of building.

00:03:47:11 - 00:04:07:23

Speaker 2

And the details of the iron frame been much studied, do go in is open to the public. This wonderful exhibition there you can see a lot of it there if you want to it's open most days of the week, some details of the iron frame. It's really quite intricate the way it's put together. Extraordinary thing. Probably the first major use of nuts and bolts in constructing a major building.

00:04:09:06 - 00:04:36:21

Speaker 2

It was then converted. The flax industry making linen thread in particular was getting into difficulties and being supplanted by cotton. So at the end of the 19th century, in 1897, it was converted into a maltings and had a second use as a maltings right up to 1987. And for the maltings we have a whole historic record which has been gathered together by the volunteers.

00:04:36:21 - 00:05:09:20

Speaker 2

The Friends of Flaxmill Maltings over many years. Here’s one of the maltsters using one of those floors. Great! Grain laid out to germinate before it goes into the kiln to turn into malt. This is a very nice old photograph from around 1900 showing it. Earliest photograph we have showing it has converted. I think you'll notice in particular here is that as part of that conversion, two out of every three of the large windows were blocked up, bricked up.

00:05:09:20 - 00:05:57:05

Speaker 2

You can see the blocked openings there. And that was something that we had to then address as part of the project. You've got the canal just to the right there as well, which was built in the same year 1797 as the Flaxmill. And here's an aerial view of the site. Around 2000 and the time when historic England with support from Shropshire Council as they now are, took it over and to rescue the site in 2005 and it's a very extensive industrial complex and quite a large redevelopment site as a former bus depot, just around the bit to the right of the slide there in the town, you'll see, which was cleared away from industrial

00:05:57:05 - 00:06:25:02

Speaker 2

sheds. So it's really a brownfield site ready for regeneration and the focus has been on the main mill and the adjoining kiln as the first major phase of the project and the most important building. And that's the kiln over there on the on the right there. And it's obviously been through a major program of structural repairs. The iron frame in particular needed major work to make it viable.

00:06:25:11 - 00:06:48:12

Speaker 2

So building for occupation and this is a view from our architects. Our lead consultants Feilden, Clegg, Bradley Studio and shows the uses of the building is the main mill. The big building here on the ground floor is open to the public with an exhibition and cafe. It's quite a large building, four floors of commercial offices for rent above.

00:06:48:20 - 00:07:12:02

Speaker 2

We've got, as you'll be seeing from Hugh later on, we've got plant room and service cores at both ends in blue, and then a circulation hub, with lifts and so on, and the kiln here. There's quite a number of other buildings around the site as well. So that's current views as completed in 2023 of the cafe and some of the exhibition on the ground floor.

00:07:12:24 - 00:07:38:21

Speaker 2

Now this is up on the first floor which we fully fitted out and divided into compartmented offices on this with a quite a generous corridor. So you still get the feeling of the amazing iron frame and that's now all tenanted and occupied. This is the the third floor and the upper floors are still waiting fit out an occupation and we're talking to a number of prospective tenants about that.

00:07:40:05 - 00:08:10:23

Speaker 2

But we're hoping in particular on the third floor to keep that open plan arrangement, which, as you said, has a different impact on the heating regime. And then this is just a brief view into the kiln. The end of the kiln was part of the 1897 Maltings conversion. It's grade two listed and we've created an extraordinary entrance atrium with lifts going up to the upper floors and it's quite a large development site altogether.

00:08:11:07 - 00:08:41:03

Speaker 2

So that's the main mill. And the kiln here has got a number of other major grade one, two star buildings around. We've put in a new roadway to open up the site. This is it as it currently stands, aerial view showing that as it stands this this green stripe here is the line of the former canal, which we've retained as part of the sort of historic landscape feature in this car, parking at the back new service road coming in as well as the main entrance over here.

00:08:43:04 - 00:09:06:19

Speaker 2

And there is then a large amount now of brownfield site which we've decontaminated opened up access for. And this is the current masterplan vision for creating 120 housing units on that, some of that brownfield land around that and that's he'll talk briefly about that and sort of how it impacts on the design of the site wide services installed.

00:09:07:08 - 00:09:32:13

Speaker 2

And then that's the final view from me about and the the main mill itself with a wonderful stormy sky behind. And I'll hand over now to Hugh, who will introduce himself a bit more. But as Caroline said, he's been a key person in terms of the M&E services and in particular the heat pump all the way through this project.

00:09:32:13 - 00:09:59:17

Speaker 3

Okay. Thanks very much indeed, Nick. And yeah, the first slide of my presentation, which you should be able to see. And so I'll talk through, as Caroline said, I’ll talk through a little bit about the main mill and the the project overview before moving on to details of the heat pump itself. So just to introduce E3 quickly to begin with. We're a building services design consultancy established in 2010.

00:10:00:00 - 00:10:40:17

Speaker 3

We're based in Bristol and Bath, and we serve projects across the country. Our focus has always been on low energy buildings, both existing and new build, and increasingly projects involving decarbonization of both existing and historic buildings. So a few examples of our historic buildings over the years. The bottom right hand corner of that, Dyrham Park is an example of one of my current projects with the National Trust, and we've delivered a series of enhancements over the last few years in the Mansion House, and we're now working on a new build welcome building within the historic parkland, and then some examples of our more contemporary low energy work.

00:10:40:24 - 00:11:04:04

Speaker 3

We've delivered a number of passive house certified buildings, most recently the Bicester Eco Business Centre, which is a community co-working hub and an eco town on the edge of Bicester. It was the UK's first non-domestic building to achieve the Passive House Trust Certificate. Okay, that's enough about E3. Let's talk about the flax mill. And Nick, thanks for your overview.

00:11:04:04 - 00:11:29:23

Speaker 3

That was an excellent introduction, I think for everybody listening and I hope you've all now got a basic overview of the Maine Mill Project and its context among the future master plan. This photo shows our first view of the site. When we first saw the buildings back in 2009, you can see the main mill still has its structural scaffolding and the concrete south silo on the left hand side is still standing.

00:11:31:17 - 00:12:05:16

Speaker 3

And the views inside were pretty ominous. The left hand side of view of the main, main mill itself, you can see the structural bracing spanning the building from left to right and an ominously large hole above your head there. But there were also some spaces with some really intriguing potential, such as the ground floor of the south silo that you can see on the right hand side there. Now back in 2010, the intention was to deliver the master plan of mixed use, commercial and residential development as one large project, one of those development.

00:12:06:03 - 00:12:30:09

Speaker 3

And so that brought an opportunity for us to consider a site wide energy strategy and a potential for a district heating network. We were looking at an energy center in the south silo. If I just use the cursor, it sits down here and with biomass as a low carbon heat source and then buried district heating pipework indicated in red there around the site.

00:12:30:18 - 00:13:02:13

Speaker 3

And then other ingredients included PVs on the roof of the main mill and air source heat pump providing heating and cooling to intensively used areas of the main mill. We also looked at other options for this site wide energy strategy. So on the left hand side that you can see an option with with groups of buildings served with smaller energy centres and on the right hand side, more of a building by building approach.

00:13:03:02 - 00:13:30:14

Speaker 3

And as the project has progressed since 2010, it's eventually been delivered on a phased basis, which meant the building by building approach was definitely the most logical strategy. The first project we delivered was the Office and Stables, so these two buildings down here, and we then moved on to the main mill and kiln, as well as the site services infrastructure to allow the other historic buildings to be developed in the future.

00:13:30:14 - 00:13:54:12

Speaker 3

When Feilden, Clegg Bradley, the architects, were first developing the glazing options for the main mill, we carried out a series of environmental analysis to optimize, optimize the design of the windows. We use software called IES Virtual Environment for this. It's a platform that allows us to carry out a range of analysis, such as daylight thermal and energy analysis using a common 3D model.

00:13:54:24 - 00:14:29:01

Speaker 3

And so you can see a view of our 3D model here. The main mill is highlighted in blue viewed from a couple of angles. So just to summarize some of the analysis we did, this is the daylight analysis. And here we're looking at the average daylight factor. And just to put this in context, we generally look for a number between two and 5%, and that was achieved throughout the project with good uniformity due to the relatively narrow floor plates with windows on both sides.

00:14:29:01 - 00:14:55:06

Speaker 3

This slide shows the strategy for natural cross ventilation of the building using opening windows. And here we have to consider a range of options both the open plan case and also fit out options with partitioned offices and meeting rooms. And our analysis was showing that we needed to maximize the free area of the windows. And so we came up with a design together with Feilden Clegg of two outward opening casement.

00:14:55:06 - 00:15:17:22

Speaker 3

So this is outward opening and that's outward opening either side of a central fixed pane. And that gives a really good free area for only a small opening distance of the window. For the partner partitioned offices we found it was necessary to allow the building to breathe in and ventilate across the floor plate. So we needed to introduce sound attenuated air paths.

00:15:18:06 - 00:15:44:08

Speaker 3

So this grill here above, above the partition allows that to pass across the building, but it restricts noise transfer from the office into the corridor. And this shows you a view from actually within the conference room. And you can see up here the sound attenuates opening windows to the right hand side so it allows two to cross the floor plate.

00:15:44:08 - 00:16:07:14

Speaker 3

Okay. And then moving on to the analysis, which is most relevant to the talk today. We were we were able to enhance the thermal performance of the building in a number of areas. The windows are all double glazed. We've got an average u-value of 1.8 including the frame. The roof has sheep’s wool insulation in a void between the brick arches, between the brick vaults and the roof timbers.

00:16:08:20 - 00:16:38:19

Speaker 3

The ground floor has got a new structural slab, and below that, there's a 90 millimetres of rigid insulation. The main mil walls themselves are actually uninsulated. After quite long debate about the benefits of insulation weighed against the conservation impact of concealing the original 18th century fabric. But in the South Engine House, which is this block here, we actually introduce 60 millimetres of wood fibre insulation lining the walls.

00:16:39:13 - 00:17:01:08

Speaker 3

And that was because it was considered less historically sensitive. And this is actually an area that we think a bit of audience participation would be interesting. We were debating before and hopefully you can see hopefully you can see a poll coming out. Yeah. Thank you. There we go. So we were debating just before the session what the audience view was.

00:17:01:08 - 00:17:11:11

Speaker 3

And I can see a very interesting trend already emerging. Up to 85% of you thinking that we did the right thing by leaving the brickwork.

00:17:11:19 - 00:17:13:20

Speaker 1

I think Matt was more correct than we were.

00:17:14:14 - 00:17:22:05

Speaker 3

Yes, I thought it would be about 65% of people choosing to insulate the building. But clearly the audience.

00:17:22:11 - 00:17:23:03

Speaker 1

Which I think.

00:17:23:11 - 00:17:55:01

Speaker 3

Has a strong conservation focus, that's very interesting. So only 18 of you choosing to insulate. Okay, thanks very much. So it's great. Okay. So moving on to some numbers, we calculated the heat loss of the main mill at around 324 kilowatts at an outdoor temperature of minus four degrees. And if you look at the breakdown here on the right hand side, you can see that conduction and infiltration.

00:17:55:01 - 00:18:22:04

Speaker 3

These two are driven by the basic physics of the temperature difference between the inside and outside. So having decided on the thermal upgrades to the fabric, these a numbers of effects, we can't do anything about them. The other numbers are all actually variable. So the allowance for ventilation is based on a fully occupied building with windows opened in the winter by occupants to provide fresh air. The load for the kitchen, hot water and kitchen ventilation,

00:18:22:11 - 00:18:43:11

Speaker 3

they are also variable depending on how busy the cafe kitchen is. And so the total load will vary not just based on the outside temperature, but also the occupancy pattern of the building. Okay, let's talk about heat pumps work and start with the basics. And this may be a recap for many of you as Caroline mentioned earlier.

00:18:43:11 - 00:18:43:13

Speaker 2

00:18:44:16 - 00:19:09:24

Speaker 3

Heat pump is a device which uses power or work here to drive heat from a colder area to a hotter area. And it works against the natural temperature gradient. Your domestic fridge is the most common example which uses electricity to move heat from inside your fridge to the warm kitchen outside. And so how is that achieved in practice?

00:19:10:11 - 00:19:42:23

Speaker 3

Well, a ground source, heat pump uses the refrigeration cycle in exactly the same way as a fridge. It moves heat from a colder place, in this case, the ground to a warmer place. In this case, the water circulating through the radiators in the building. And there are three circuits involved. The first one is a pumped circuit, sending water down into a series of boreholes at about five degrees, absorbing heat from the ground and returning back up to to the surface at about ten degrees.

00:19:42:23 - 00:20:09:21

Speaker 3

The Second Circuit is the refrigeration cycle. And so just to take that step by step, we start at this point here with a cold liquid. And as it absorbs energy from the ground circuit, it evaporates to a cold gas. We then compress the gas through a compressor to a high pressure. And as the pressure increases, so does the temperature.

00:20:09:21 - 00:20:32:17

Speaker 3

The gas then releases heat into the radiator circuit and it condenses back down to a liquid and then finally it passes through an expansion valve here as the pressure reduces and the temperature drops back to a cold liquid. So if you followed that, the refrigerant is going through quite a cycle, being boiled and condense, then compress, then expand it.

00:20:33:09 - 00:21:01:17

Speaker 3

But through this process it absorbs heat from the left hand side, from the ground and passes it to the right hand side. The majority of the power into the system is into the compressor here. And for every unit of electrical energy used, about three units of heat is passed into the radiators. And this means that the heat pump has a coefficient of performance or COP of three, and this is a value that varies depending on the conditions.

00:21:01:17 - 00:21:26:21

Speaker 3

So the lower the temperature difference between the ground and the heating water, the higher COP of the heat pump, the ground temperature itself is actually variable throughout the year. By the end of the heating season, after we've been extracting heat for a few months, the water might rise from the ground. It's about five degrees. The temperature of the ground then recovers over the summer when we're not heating the building.

00:21:27:03 - 00:21:51:18

Speaker 3

And so by the autumn it might come up around ten degrees. And so the COP of the system actually varies with it being highest in the autumn and then lowest in the spring. Okay. And then the analogy of fridge and heat pump keeps on giving here because in terms of what the two devices look like, they actually look surprisingly similar.

00:21:51:24 - 00:22:26:08

Speaker 3

So the heat pumps that the flats smell are floor standing. They're about 1.6 meters high and 700 by 700 in plan. So just to show this in in pictures at the Flaxmill, we have what's called a bivalent system. And that means that the building is heated partly by heat pumps and partly by gas boilers. So starting with the heat pumps, the plant room is at the second floor level and it contains the heat pumps and other ancillary plant that we'll examine in a bit more detail later.

00:22:27:04 - 00:22:54:21

Speaker 3

There are two heat pumps, each rated at 59 kilowatts. The pumped groundwater circuit passes water through pipework in ten and in ten boreholes. Each of them 170, sorry, 187 meters deep. The image on the right here shows the drilling rig on the site of the flax mill back in March 2021. The gas boilers are in the plant room on the first floor of the building.

00:22:55:05 - 00:23:25:03

Speaker 3

There are three boilers, each rated at 84 kilowatts. And finally, so that you can see the heating emitters, the upper four floors of the main mill are all heated with radiators, which you can see underneath the windows on either side of the building. The ground floor is heated with underfloor heating, and this view shows the heating pipework tied to the reinforcement bars before the concrete slab was poured.

00:23:27:00 - 00:23:51:17

Speaker 3

This diagram shows the distribution principles of the building. The blue areas are the core and landlord areas and we actually decided not to provide space heating in the kiln because this is used only as a circulation space, both horizontally and vertically between levels and areas of the building. So as a transient use, we chose not to heat it. The green areas of the tenant areas

00:23:52:02 - 00:24:12:17

Speaker 3

and the red areas are where are the plant and riser zones. The plant rooms, as I explained earlier, are in the south end of the building and then we have risers at both the south and north end of the main mill. There wasn't a feasible route to to bring the primary pipe heating pipework from the south to the north.

00:24:12:17 - 00:24:41:19

Speaker 3

So we actually chose a below ground tree, as you can see here. So the next few slides, I am going to show a few heating schematics and I promise not to go through every detail of every pump and valve, but instead use them just to explain to you and the design principles. And one interesting aspect of the design was that the decision to install the heat pumps was actually made after the projects had been tendered and the main contractor was already on site.

00:24:42:09 - 00:25:10:05

Speaker 3

So this was the heating schematic drawing when the design was for heating only using gas boilers. We had four 84 kilowatt boilers designed to operate as a flow temperature of 80 degrees and a return temperature of 60 degrees. And there are three pumps circuits, one serving the north riser, one serving the south riser, and then there's one serving the kitchen handling units and space heating systems.

00:25:11:07 - 00:25:34:17

Speaker 3

And then there was a fourth circuit over on the right hand side here, which was serving the kitchen, domestic hot water cylinder. So this next slide shows you what we did when we decided to introduce heat pumps and what changes we made to that schematic. And there were four primary moves. The first one was to get rid of that fourth gas boiler.

00:25:36:05 - 00:26:01:00

Speaker 3

The second move was to reduce the design temperature of the system. So you can see we're now operating at 70 degrees flow and 50 degrees return. The third move was to add in the ground source heat pump. We chose an arrangement that intercepts the return water at a temperature of 50 degrees here, elevates that to 57 and puts it back into the return header.

00:26:02:08 - 00:26:34:20

Speaker 3

And that means that the gas boilers just do the top up from 57 up to 70 degrees. And finally, we removed the domestic hot water circuit from the system as this is now served directly from the heat pump. And I'll show you that a bit later on. Now, before I do that, for those watching who may be building services, design engineers and designing a bivalent heating system from scratch, I just wanted to draw attention to an excellent article in the CIBSE Journal from last October.

00:26:35:10 - 00:26:58:18

Speaker 3

It's got a summary of the three typical methods of integrating heat pumps and boilers, and it describes the considerations and the control strategies for each method. The first one here is called the ‘Load Assist’ method, where the boiler and the heat pumps are working together in parallel and providing heat to a common low loss header. So that's the header there. In this situation

00:26:59:14 - 00:27:23:01

Speaker 3

they're working in parallel and they're working at the same temperature but with the heat pump controlled as the lead heat source. And this second method, which is called the ‘Thermal Store’ method, we have one large thermal store with a heat pump providing energy into the lower half of the store and then the boilers into the upper half here.

00:27:23:01 - 00:27:55:23

Speaker 3

And because of the stratification of heat within the thermal store, which means that water is warmer at the top and cooler at the bottom, it means that the heat pump can operate at a lower temperature and therefore a higher, higher efficiency. And the boilers operates as a higher temperature. And this is the final method. It's called the ‘Injection’ method, where the heat pump intercepts the return water from the heating circuits, elevates the temperature, puts it back into the return header, and then the boilers do the rest of the work.

00:27:56:07 - 00:28:19:08

Speaker 3

And this is the approach that we use at the Flaxmill. And I won't go into much more detail on the advantages and disadvantages, but for those who are interested, then there's a link there on your screen that you can screengrab or maybe I think Matt might be posting one in the chat. Okay. So back to the heat, to the Flaxmill and also just the promise

00:28:19:09 - 00:28:48:04

Speaker 3

this is the final heating schematic that I'll show you now. This is the arrangement of the equipment in the heat pump plant room at the Flaxmill. That just to briefly explain down here, we've got the first circuit, circuit one from the diagram area, earlier to the boreholes, the heat pumps here and they're configured in a parallel arrangement and they're working together to charge the buffer vessel here.

00:28:49:03 - 00:29:16:19

Speaker 3

The buffer vessel acts as a thermal store and it prevents the heat pumps from short cycling, which means that they switch on and off regularly in periods of low load, and which is a very inefficient way of operating. And finally, there's a pair of circuits serving the kitchen, domestic hot water cylinder directly from heat pump one. You'll see the three meters at the top of the diagram here.

00:29:17:08 - 00:29:49:00

Speaker 3

These are used for the renewable heat incentive. We managed to get the system registered for the RHI before the scheme was closed, and so the system is going to be eligible for payments based on metered energy consumption over the next 20 years. Here you can see a 3D drawing of the equipment within the plant room of the South Engine House with the heat pumps on the right hand side here, the buffer vessel here and the kitchen, domestic hot water here.

00:29:50:00 - 00:30:20:17

Speaker 3

We also decided to build a bund either side of the central access corridor so that if there's a leak from the vessels or the heat pumps, then any water is contained and discharged to drain. Considering where on the second floor with the kitchen and plant rooms below. This is the record drawing produced by the borehole contractor. And just to orientate you, orange up here is the main mill and we've got the kiln on the right hand side.

00:30:21:14 - 00:30:51:16

Speaker 3

Yeah, the purple area here is the zone for future residential development in the master plan. And then this green area is the former canal, which Nick explained earlier, and the canal towpath, which is now a cycle path along here. So we've got a pair of 110 millimetre plastic pipes emanating from the building below ground to a manifold chamber which is located here on the towpath.

00:30:52:11 - 00:31:20:13

Speaker 3

And from there there are ten separate paths of flow and return pipes to each of the ten boreholes which you can just make out number two, one, two, three, etc. here. They're separated by ten meters and arranged in a U-shape, and we deliberately left space on the right hand side here for potentially future boreholes systems serving either the future housing or some of the historic buildings.

00:31:21:22 - 00:31:51:04

Speaker 3

We decided to use vertical boreholes rather than the alternative approach of horizontal trenches with slinkys. And the reason for that was simply land take. We didn't have enough enough space for the slinky solution. So just to touch briefly on the radiator design. In the original design, before the heat pump was introduced, we had selected these fine tube radiators that you can see here.

00:31:52:01 - 00:32:30:19

Speaker 3

When we reduce the temperature to 70 degrees, we needed to increase the size of the heating emitters. And so we decided to change to these rectangular floor standing radiators. And the main constraint was the height of the original maltings window sills, which meant that we had to keep the radiators as low as possible. Now, one really important aspect to the design for the heat pump is that we don't have excessive flow of water through the radiators because otherwise the return temperature will be too high and the heat pump was either operate inefficiently or worse still not operating at all.

00:32:31:15 - 00:33:02:20

Speaker 3

And so in order to have good control of the radiator, we chose a pre-setable radiator valves so that the flow through each radiator can be carefully controlled. For the final few slides, I'm going to talk about the control and operation of the system when it's not operating in its peak design condition in milder weather. So as I mentioned earlier, the coefficient of performance of the heat pump varies with the flow temperature of the water from the heat pump.

00:33:02:20 - 00:33:25:21

Speaker 3

And this graph shows the COP as it varies with flow temperature. So our design condition at 57 is around here and the COP is just under three, but the COP ramps up to a level of over 4.5 when the flow temperature is 35 degrees. So it's really important to reduce the temperature of the water in the radiators in mild weather.

00:33:27:21 - 00:33:57:16

Speaker 3

As I mentioned earlier, the COP also varies with ground temperature. So in fact, there's actually a family of curves depending on the temperature of the water in the ground circuit. These figures are for a groundwater circuit, temperature of zero degrees. So in reality, the COP should be higher than what you see here. This graph shows how we vary the temperature of the system as the outside air temperature varies, which is a technique called weather compensation.

00:33:59:09 - 00:34:28:24

Speaker 3

We've got outside air temperature from minus ten up to 25 on the X of here and system temperature on the Y. The blue line here is the boiler flow temperature. The green line is the return temperature of the water from the radiators. And then the yellow line, you can see the heat pump control conditions. So if you remember back to our design condition, minus four degrees outside air temperature, the return temperature was 50.

00:34:29:15 - 00:34:57:01

Speaker 3

The heat pump then elevates the water to 57 and then the boiler tops up to 70 degrees. But as the outside air temperature increases, we then reduce the flow temperature of the system, which means that, for example, five degrees, the heat pump is now able to maintain the full flow temperature of the system in isolation. And we then continue to reduce the temperature of the system as the outside air temperature increases.

00:34:58:04 - 00:35:25:07

Speaker 3

So not only is the heat pump doing all the work, but it's also operating more efficiently. And with the higher COP. So let's have a look at the weather now. This chart shows the frequency distribution of daytime external temperatures during the heating season. It shows that our designed condition minus four that's down here, only occurs for about 20 hours each year.

00:35:25:07 - 00:35:54:23

Speaker 3

For the majority of the time, the temperature is much milder and the peak occurring between about six and eight degrees. This red line here is, the temperature above which the heat pump can deliver the flow temperature by itself. And then below that temperature, the boilers gradually assist contributing about a third by the time you are at zero and then two thirds at minus four.

00:35:54:23 - 00:36:23:10

Speaker 3

So right now we're moving into the first heating season since the building was commissioned and handed over in April this year. And so we're starting a seasonal commissioning program, and it's likely that in reality the building may actually remain comfortable to occupants with the system operating at lower temperatures than the design figures. The basic heat loss counts are conservative because they ignore internal heat gain, such as lighting, equipment, people and also heat gains from solar radiation.

00:36:24:15 - 00:36:53:07

Speaker 3

So what we're planning to do is experiment with that flow temperature and reduce it during this winter. So if, for example, we could reduce the flow temperature from 70 down towards 60 it results in the heat pump, doing a larger proportion of the work at a lower outdoor air temperature. And then additionally, the slope of the heat pump is going to be higher generating savings in the electricity consumption.

00:36:54:22 - 00:37:12:05

Speaker 3

So it's just a case of watching this space. We're going to carry on monitoring the building over the next six months and hopefully be able to report back with some interesting findings next spring. Okay. I think that's all I've got time to share with you now. And I'm going to hand over to Caroline to host the Q&A.

00:37:13:04 - 00:37:37:09

Speaker 1

That's great. Thank you. Thank you, Nick as well. That's really interesting. I'm just going to finish before we come to some questions and we have got questions and that's great from everyone. I just wanted to share with you where you can find some further information. So this is the historic England Heat Pumps Web page. So there's all sorts of information on heat pumps, groundwater source, most source heat pumps on here, and you'll find links to our webinars as well.

00:37:37:09 - 00:37:43:13

Speaker 1

But you can always go to the Technical Tuesday's pages to find those. So just going to finish there.