This blog was originally posted on networks.online.
Any heat network operator or customer will tell you that heat losses matter – a lot.
Losses that go unchecked can easily double the cost of heat on the network. But while everyone agrees it’s hugely important to limit losses, the way we talk about heat loss is all wrong. And heat network performance is suffering as a result.
Industry players and government policies talk about losses from networks as percentages. Open almost any project specification or government consultation relating to district heat and you’ll find losses defined as the percentage of heat that leaves the plant room, but isn’t consumed as useful heat by the customers.
There are two big problems with defining losses in this way.
First, because it’s calculated as a percentage of plant room output, the losses figure will depend on heat demand – if customers require more heat, output from the plant room will be higher. If they require less, it will be lower. So even if the amount of heat that’s lost stays the same, the percentage changes depending on demand.
Second, because percentage heat losses can only be defined relative to demand, it’s impossible to measure it until you’ve got customers. And their presence isn’t enough – you can’t calculate a percentage loss on move-in day. Instead, you’ve got to measure consumption over time, say across several seasons, to ensure you capture an accurate picture of how much people use.
Framing heat loss as a percentage leads to perverse outcomes that are doing real damage to heat network performance.
Because percentages are dependent on consumption, the measured losses can vary even though the actual (kWh) heat loss is unchanged. As an illustration, consider two identical heat networks, one with heat-hungry customers and the other with thrifty customers. The percentage losses on the heat-hungry network will appear lower than its neighbour.
Or imagine I’m a maintenance contractor or facilities manager tasked with keeping percentage losses low. I want customers to consume as much as possible to keep percentages down. The last thing I want to see is energy efficiency improvements like solid wall insulation – they’ll cause the percentage loss figure to rise dramatically, potentially making me miss my contract KPIs.
Arguably the most dangerous side-effect of using percentages is that they’re impossible to measure before practical completion (when the building is handed over by the contractor to the client). As a result, it’s impossible to prove whether the contractor and project team have done their jobs properly and should get paid.
Let that sink in for a second: using percentage heat loss in a contract makes it impossible to determine whether you’re getting what you’re paying for. Who on earth would define their contract requirements in a way that’s impossible to verify? The answer: almost everyone.
In this situation, clients have little option but to write a cheque, cross their fingers and let the network go into operation without knowing whether it’s been commissioned properly. Usually it hasn’t. And the customers bear the brunt of poor performance, high heat cost and repeat visits from engineers trying to retrospectively sort out the root causes.
Instead of using percentages, we should define heat loss from networks in absolute terms, such as watts per dwelling or kWh per customer per year.
This would have several important advantages over the current practice, for example:
- Designers and project teams know exactly what performance targets they’d be held to.
- Losses are independent of consumption, so two identical networks would appear as such, regardless of how much the customers use. An energy performance contract defined in this way sits happily alongside energy efficiency works.
- Most importantly, performance could be verified at commissioning and before practical completion. With an absolute metric, the project team can be held to account before they collect the cheque.
In summary, the way the industry currently defines losses is all wrong. I’d go so far as to say that we won’t consistently deliver high efficiency (low loss) networks until we change how we talk about heat loss.
Casey, you can’t make the topography of systems nor the proportion of different ambient temperature zones around pipework the same on different schemes. We cannot have heat network design dictate over building function? I believe the way forwards is simply to to define the correct criteria for the best reasonably achievable heat loss outcomes and then put that in building regulations.
Regards,
Steve
Hi Steve. Aren’t you meant to be skiing rather than commenting on blogs?!
To respond to your point, I don’t think that will sort the problem. The key point is that metrics (like heat loss) have to be put in the contract and then verified before practical completion. Even if we could rely on building inspectors to do a thorough check of, say, insulation levels (which in my view we can’t), it wouldn’t prove that the network was working well. It would just prove the insulation level was as specified.
I agree that fixed heat loss targets are more useful than percentages in a contract and ensure that the appropriate incentives for good design are in place.
I disagree with this though:
“because percentage heat losses can only be defined relative to demand, it’s impossible to measure it until you’ve got customers. And their presence isn’t enough – you can’t calculate a percentage loss on move-in day. Instead, you’ve got to measure consumption over time, say across several seasons, to ensure you capture an accurate picture of how much people use.”
“Losses are independent of consumption, so two identical networks would appear as such, regardless of how much the customers use. An energy performance contract defined in this way sits happily alongside energy efficiency works.”
“Most importantly, performance could be verified at commissioning and before practical completion. With an absolute metric, the project team can be held to account before they collect the cheque.”
Heat losses vary according to occupancy and heat use because these affect:
-How often pipes that are allowed to cool between uses (HIUs, HIU branches, laterals) are actually cool
-How much heat is being delivered and therefore the temperatures required to deliver this
-What the temperatures in the communal/services areas are and the losses from the pipework into these
It is untrue and completely wrong for engineering reasons to say that heat losses are independent of consumption.
The real solution to this problem:
“In this situation, clients have little option but to write a cheque, cross their fingers and let the network go into operation without knowing whether it’s been commissioned properly. Usually it hasn’t. And the customers bear the brunt of poor performance, high heat cost and repeat visits from engineers trying to retrospectively sort out the root causes.”
Is a contract that guarantees the in-use efficiency of the system. The easiest option here is a full-service ESCo with a price cap on the heat supplied and therefore an enormous commercial incentive to make it work.
There is no magic metric that allows you to test an unoccupied heat network.
Procure the networks piecemeal and you’re that ESCo who has to get it right. Do a good job. Have somebody else put their balls on the table and they’ll get it right. Or go bust.
It’s that simple, no?
I think we can all agree that percentage losses are incorrect and that fixed heat network losses are a better approach.
“There is no magic metric that allows you to test an unoccupied heat network.” Maybe not a “magic metric” but one that allows both designers and contractors to be held to account much more easily.
Yes, it isn’t a perfect metric (I’m sure there isn’t one) but it would represent a huge improvement over what we currently have and a step in the right direction regarding holding everyone in the contract chain to account (somethign long overdue in this industry). It also helps to separate the sins of the designer and the contractor as it provides transparency as to whether the poor performance is due to design, install or commissioning.
The alternative approach, which is setting out stringent design guidance, stipulating parameters tightly in specs and then assuring that it is delivered precisely in line with the specs, doesn’t work. We’ve been down that line for the last decade and we’re left with a country full of heat networks that don’t work.
ESCo can’t solve the problem as they are usually too late to the party once the heat network has been designed. No amount of insulation will save a network that has oversized pipes, relies on bypasses, etc – you know how long this list could be 😉 and, traditionally at least, there aren’t any ESCos that are interested in providing this service to thousands of residential schemes in the 30 to 300 dwelling range that dominate new build in the UK. The fact that they are designed and built so poorly due to lack of contractural requirement is probably a major reason why ESCos keep these networks at arms length.
If it was that simple, it would have happened by now.
I absolutely agree that it’s much more useful and it definitely helps align incentives.
It absolutely cannot be tested prior to move-in though and I think it’s a bad idea to promote it as such.
I don’t think that the alternative approach (the client writing a thorough spec or an industry body such as CIBSE writing a thorough spec) has been attempted yet. The published specifications, designs, and guidance are nonexistent to thoroughly outdated to poor and that’s why we have a so many shady networks. I’d therefore like to go down this line as I feel we haven’t given it a decent go yet…
Procuring from an ESCo on a turnkey basis is very different to asking an ESCo to [bid for the right to] adopt a pile of crap designed and built by others. We’re seeing some decent performance on those networks that were specified by the ESCO that was to operate them subsequently. I agree that the 20-250 or 30-300 home networks are neglected though.
The main reason ESCo won’t touch these, in my view, isn’t that they’re materially better/worse designed/operated than the larger ones, but (1) the transaction cost of agreeing to do anything with one is high and (2) there’s no CHP to make enough money selling electricity to cover the costs of administration and heat losses.
Taking the summary:
“1) Designers and project teams know exactly what performance targets they’d be held to.
2) Losses are independent of consumption, so two identical networks would appear as such, regardless of how much the customers use. An energy performance contract defined in this way sits happily alongside energy efficiency works.
3) Most importantly, performance could be verified at commissioning and before practical completion. With an absolute metric, the project team can be held to account before they collect the cheque.”
1 – yes
2 – yes, within reason
3 – no, not on all sites anyhow
A) You can get close to (3) on a site with mechanical HIUs that have constant trickle keep-hot. Flip that site on and the standing losses will be about average under no-load. Return temps will drop (briefly) under DHW load and mean flow temps will rise (for an extended period) under space heat load. Nobody home = about the same losses as everybody home.
B) You’ll nail (3) on a site with HIUs that don’t have keep-hot, where they’re mounted extremely close to (multiple) risers, and where you use riser keep-hot. Nobody home = same losses as everybody home. Good luck finding such a network.
C) You’ll massively under-report (3) on a site that doesn’t use HIU keep-hot and has long laterals/branches. Or perhaps over-report if the space heating is on everywhere at the time. These layouts are the norm, this type of HIU and allowing peripheries to cool off is becoming increasingly accepted, and the only way you’ll get close to measuring the in-use losses is to put it in use. (3) doesn’t hold true.
D) Maybe with fancy eHIUs and a lot of operating data you can simulate a year in a week. (simulate DHW draw offs and space heating loads across the site by making the eHIUs dance remotely in order to establish the losses from the distribution network) The industry is some way off having the capacity to deliver this.
So for (A) it works but you shouldn’t designed that way. If you get (B) the problem is already solved and you won’t care much. It doesn’t work for mainstream (C) and (D) is future-gazing.
Steve’s suggestion of a recipe, that if followed, meant that it was impossible to fuck up the specification and installation of a heat network, is also good.
People like being taught rather than examined. Wouldn’t most clients rather blindly copy a worked example that works well than write an exam paper and spend all their time marking?
Pareto principle works on this. To over complicate the solution is to spend endless amounts of money on things that achieve very little. Decide on a suitable enhanced pipe insulation standard (could vary by a few system types) It needs to be tested on economics, carbon outcome and against all the usual impact assessment stuff. It’s DCLG that should be doing this and now before the new push to further implement DH is started.
Casey, Skiing was good, couldn’t resist commenting….
The existing system uses BS5422 and I’m not aware of many issues with non-compliance with that. The insulation suppliers offer loads of advice to contractors to sell their product and the Insulation contractors have a vested interest in getting the correct thicknesses in as that’s more revenue for them. It’s self-policing pretty much. Of course get a combo of a useless contractor and insulation contractor it can go wrong but not often in my experience.