Talk title: Assessing low temperature waste heat integration in 5th Generation district heating & cooling
Speaker: Dr Orestis Angelidis, Buro Happold
Event: CIBSE Scotland Conference 2026: Heating the Future, 27 May 2026
Video: https://youtu.be/a0EZtOm6AXg

[00:00] My name is Orestis Angelidis and I am going to be speaking to you about the last part which is around academic things. So we'll be presenting some findings from our PhD. So at the moment I'm an associate energy engineer with Buro Happold, but this is part of the work that I did during my PhD with the University of Glasgow and the University of Edinburgh. And it's also Alan Thompson is here, he gets a shout out for being my technical supervisor during the PhD from Rambo.

[00:31] So today is going to be talking about the low temperature waste heat integration and this is another thing we haven't talked about today as much, which is fifth generation district heating and cooling. It's going to be around a case study. We're going to be studying in Clyde Gateway and Clyde Gateway was also an organization that helped in the preparation of this work. So thanks for their support. And without further ado, let's get cracking.

[00:56] So I'm going to skip through some things because we've been here for the whole day. So we do know why decarbonized heat matters and I hope that you've been paying attention. So I'm just going to skip through some of these things. Yeah. Why decarbonized heat? Yeah. So we have a lot of CO2 emissions. We do need to move away from fossil fuels and finding pathways to interconnect the thermal and electrical grid is going to be key about how can we do this in a robust and economically feasible way.

[01:31] Now the question that we keep on hearing is like, what solution are we going for? If we're an urban center, if we're a rural community, we have different options. The key ones that I've summarized here and that I looked during my presentation are the things that we need to do. Hel defendant heat Pipel looks absolutely mes Mercel yes. Yes. ина or Simpson. This would be a more individualistic approach with Kendrick blackjulie up with some air conditioning for cooling.

[02:09] They cause we're seeing more and more cooling required. And could be also a fifth generation district heating and cooling where without competition in the morning. Basically phrasing it as and then Luke. Basically the same concept with some differentiations. In here where we're looking to individual booster heat pumps that are boosting the temperature room and let's see if we apply a little stuff into our options and trying to find out some modifications as well. Yep. Mm hmm. Okay. Yeah I'm very excited. For either heating or cooling in the building level and a shared ambient network or loop. And it would require a central balancing unit, which would provide both hydraulic and thermodynamic balancing. So these are our three key scenarios. Now, for this solution, I'm going to be focusing, as I mentioned, more on that fifth generation concept.

[02:38] The key element of it is reuse. So when we have heating and cooling, basically the waste heat that we have from cooling something down can be used for heating and vice versa. The economic viability of this thing still remains a bit of an unknown. We mention it a lot in most of the feasibility reports you will see out there. They'll say, what an ambient loop, but when does it actually make sense? So this is what I started to look a lot more in that PhD.

[03:05] The key thing that I want us to cover here, and that would be the key takeaway that I would like you to have from this talk, is this demand overflow. So what does that refer to? A lot of the times we just talk about energy. We say, right, if we have a lot of heating and a lot of cooling, that means great, we can share the two. The one thing we don't talk about as much is that we need the two to kind of coincide. We need to have them at the same time. Otherwise, how are we going to use that waste heat or that waste cooling?

[03:33] So the hourly profile dictate how much can we have of that overlap rather than just annual benchmarks. So let's say, if we have 50% of cooling demand for the 100% of heating, that only reflects around 20% of actual overlap. And if we have 10% overlap, that is still just 9%. And this is happening because during the winter we need heating, during the summer we need cooling.

[04:01] It's rare that we would have this flat profile between the two. Now, from that academic world, there were a few studies conducted and here's the key two elements, saying that around 20% to 30% of a demand overlap coefficient or like overlap of heating and cooling is needed for the thing to even start making sense economically. And from another kind of report, it was found that only 0.1% of the building stop in Europe actually hits that overlap.

[04:31] So the question is, how can we use this technology? When does it make sense? And is there anything else that we can do to start making that overlap come to life? Even though the demands might not be happening at the same time. An idea there is that we can use low temperature waste heat. That kind of acts as a heat sink or a heat source throughout the year. So basically, it can manually create that overlap between that heating and cooling.

[05:00] But if we think about this, what would be the system configuration and overall operational strategies for this to make sense? How could we do it? How does the techno-economic and environmental performance of these 5G systems actually compare to these other counterfactuals that we just mentioned? What is the impact of different 5G approaches to how to use this low temperature waste heat? And here's where we enter the idea of Clyde Gateway.

[05:26] So Clyde Gateway is very kind enough to basically allow us to use some of the work that they're doing in this PhD study to try and see what could be the opportunity with this specific case study. Clyde Gateway is basically looking into redeveloping an area near the River Clyde. And as you can see, it's very close to the Dalmarnock wastewater treatment plant.

[05:52] So therefore, it allows for some sort of low temperature waste heat utilization. This is kind of how it looks like in terms of when the, or at least an iteration of it, of how the buildings could come to life. And the question was, let's try and use this to see what could happen with 5G and utilizing that low temperature waste heat potential. So we're coming back to what we mentioned before, but this time a little bit more centered around our case study.

[06:21] We could have this fifth generation system, only that this time we also have this waste heat or waste heat, sorry, source or sink. And we could use fourth generation and individual air source heat pumps. But again, which, how do we use that wastewater treatment plant? We could use it in fourth G case as just the entrance for a sewer water source heat pump. But for the 5G, what do we do exactly?

[06:48] So in here we have two possible scenarios. One, which I'm just going to refer to as 5G one, is that we just use a heat exchanger and we directly use whatever the temperature profile was in the wastewater treatment plant. We use that to feed into the 5G network or we put a water source heat pump at the place. So at the wastewater treatment plant to fuel the balancing unit.

[07:16] So how this looks is exactly like that. So either we go with just a direct heat exchanger or we put a sewer water source heat pump at the space. And that is what's feeding into that ambient network on the left. So to look into it and understand it, we had to understand what we have to play with. The first thing is understanding what the wastewater treatment plant is looking like. So we had to look at the temperatures and the final influence from there, categorize them as to what percentage of the year we're exceeding a certain temperature.

[07:48] And from that, understand what would be the temperature profile on that ambient network. So not just say we're going to put temperature a or temperature B, actually make it based on whatever information we had. So in this case, we just split it between winter and summer so that we would have a profile that would match the temperatures that we were seeing. So above seven degrees or below 16 degrees. And what this looks like is some sort of an operation for the ambient temperature network profile split between the heating season and the cooling season, depending on again, when is it more making sense to use the plant as a heat sink or a heat source?

[08:29] Now, this is a heavy slide, and for this, we're going to just allow it to have a look. You can always use the QR to see a lot more in detail with a paper explaining the different elements. But how we approached it was to look into a demand modeling, supply analysis, the network simulation, the hydraulics and the overall techno-economics. We used a variety of models. And again, I'm not going to spoil the fun.

[08:54] I'm going to allow you to read through it and you can have all the info answered for you. And let's go to the key results, which might be of interest. So if we didn't use the wastewater treatment plant and we just had the buildings, we would only have 3.4% or 114 MWh. Of overlap. That's nothing, just to put it in perspective. So if we, however, start using the wastewater treatment plant in that way, as either a heat source or a heat sink, it rises to 38%.

[09:25] That is over that 20% or 30% that I mentioned earlier, that 5G starts making sense economically. And just for it to look a little bit better, purple is what it would look without. The blue is what it looks with. So there is a start, like a very clear difference there and something that is happening. Throughout the year. If you were to have a data center, this would look even more with just kind of like a flat curve, since you would just have that flat waste heat coming in.

[09:50] Now, in terms of electricity use, and once again, we don't discuss about this as much, but this is very interesting, there is a key thing to discriminate between what's the capacity required and what's the energy use. The energy use was higher for 5G because we have more basically stages that were updating the heat. We have one centralized and then we have the booster heat pumps rather than the 4G, but because we needed a lot of air conditioning units, we had a very high capacity requirement.

[10:19] So when you have individual units, you're going to have a larger capacity because you can diversify your demand and your supply. And that's what we found. And it's the same with the air source heat pumps, which performed horribly when it came to what would be the electrical capacity requirements for the installation. The costs as well, where we looked into it ended up that 5G was the cheapest of the options.

[10:45] Now, because of that is because we had all of them, as you can see, quite high cost. And when I say quite high, I mean very high cost compared to other technologies that we saw before. And the reason for this, and this is just food for thought, is that we have with new buildings less demand. When you have less demand, you have less supply. So the cost is spread over less demand. And this is something that we don't talk about as much, but it's a key thing to consider that when you don't need as much energy in your buildings, your costs, your relative costs are higher.

[11:15] And then we also conducted a sensitivity analysis, which was to see if we were to have more capacity, what would happen. And again, when we were using the wastewater treatment plant with the heat exchanger, we went all the way up to 40, sorry to. Where are we? Increased by 50, we go to 41.8, so we increase slightly. The overlap coefficient and when we drop it is also dropping by 28.

[11:46] So it has an effect, but not as much. So again, to round it up with the discussions. There is a high levelized cost of energy in the new buildings due to low demands. These are, again, the points that I would like you to keep from this. The seasonality of heating and cooling demands plays a massive role and we shouldn't just treat it energy in, energy out, what's happening on an hourly basis. There could be flexibility, as we mentioned, with phasing, because like booster heat pumps don't all have to come at the same time as maybe with the network or with the energy center as a 4G network.

[12:18] But once again, this is one element to look into. The low demand co-currents could be tackled by utilizing low temperature weight heat sources, which is what we saw here. But it's important to understand when that makes sense. However, there are several limitations that we need to take into consideration. Hydraulics are a lot more complicated. If we look into bi-directional load, it's not something to just take lightly.

[12:43] Things can get very messy. It can be done, but it's messy. So there needs to be a strong case as to why we're looking into it. The more control, kind of more complex control regimes can also be a bit difficult. And what's happening with the booster heat pumps, the asset ownership, there is a whole different kind of business case there to unravel that people need to look into and not just use old kind of paradigms into a new system.

[13:09] The incorporation of an equipment free balancing unit would be an amazing thing. So basically, instead of having an air source heat pump to match the thermodynamics of whatever the ambient temperature network needs, if we have an open source, for example, well, or we can use geothermal, that would significantly reduce the amount of energy that we would use, but we would not look into this into this case. And it would be interesting to check a wider technology mix.

[13:37] So overall, the proposal here was that we can look into that 5G because it starts to make sense in this specific case and it showcases how important waste heat utilization can be when we try to overlap this heating and cooling. We had more electricity use, but at the same time, less capacity requirement, because even though we had more of a staged uplift of the temperatures, we had more centralized units because we didn't have the individual air conditioning units.

[14:06] If we had district cooling, for example, instead of individual air conditioning units for the district heating case, that would be an entirely different story. And the best economic for 5G, more complicated controls. I'm reiterating myself because I really want you to keep these things. And this output of kind of this research is to try and quantify the benefits. Like when does it make sense and when it doesn't.