District energy systems and CHP can work but need to be updated in line with a modern energy strategy, writes Ground Source Consult’s Andy Howley
Decisions used to be easy. When I was a child you had coal, oil or gas heating and, for most people, it came from a single supplier. You had electricity from the electricity board, gas from the gas board and water from the water board. You had little or no choice about who your supplier was, you just moaned and accepted it; there were no decisions to make apart from turning it on and off. It all just came out of the tap, pipe, bunker or cables having burnt or about to burn something.
Only during the miners’ strikes of the early 1970s (yes, I am that old) did anybody start to appreciate just how vulnerable power supplies could be after trying to put a mantel into a tilley lamp and huddling around candles.
Fast forward to the fuel tanker strikes in the 1990s and, although it was petrol and diesel for road transport being disrupted, it still caused havoc at the time, to a fuel that must be extracted, refined, stored and burnt.
Since these times, and with the ever increasing awareness of energy security and the global need to reduce carbon emissions, the move towards low carbon power for heating and cooling has now started to become a topic of conversation in the pub, alongside the age-old gripe of the way the price of chips always seems to go up while the price of potatoes comes down.
A host of low carbon technologies
It gets confusing though. Solar photovoltaic cells, solar thermal, ground source, air source, biomass, combined heat and power (CHP), district heating, fuel cells – and I am sure there are others just waiting to line up and jockey for position in the race to be first. But why should any of these solutions be the winner? Do we need an outright winner? Is this what is best for us? I’m not so sure…
They all have their merits, but all too often, we see energy strategies produced by building services consultants which discount renewable or low carbon technologies x, y and z because technology a is ‘better’. Rarely do we see an energy strategy produced that concludes that a mix of renewable and low carbon technologies x, z and a would be the most appropriate for a particular facility. Decisions seem to be made based on generic high-level rule of thumb information and little or no real life operational characteristics to support the findings one way or another.
However, worse than that (and I would love to be corrected here) what we are yet to see is an energy strategy that looks to the future. We still see the race where there has to be a winner when perhaps we should be seeing the race where it’s the taking part that counts!
A non-static energy strategy
To further compound the impact of the single technology race to be the winner, the odds are stacked, the cards are marked and the winning horse is knobbled. The strategy always seems to be based on the conditions at the start of the race rather than throughout the duration. I am sure if Lewis Hamilton went to the grid with his super-soft tyres without the opportunity to change them he would initially disappear into the lead only to be caught after a few laps, easily passed, and go on to lose miserably – if indeed he finished the race at all.
Why then do we see energy strategies based on today’s fuel carbon intensities – for some technologies the equivalent to the super-soft tyre – when this is a fast and ever changing number which should probably be based upon the medium tyre that will last the race well into the future.
The government has published papers on future carbon reduction targets with predictions to reach 50 g/kWh for grid-supplied electricity, so why are we not putting these decreasing figures, as we work towards this target, into the race for the most appropriate technologies? Obviously one cannot start the race with 50 g/kWh but using industry agreed reducing values within feasibilities and energy strategies to show the impact of grid decarbonisation and the various tipping points where one technology might become obsolete, we might actually get to the end of the race and that is where the prize awaits. We have values now in Part L which already are out-of-date and probably were when they were first put in, but worse is the fact that these values do not reflect the future or even an estimate of it.
New systems becoming obsolete
An energy strategy producing a ‘winner’ such as CHP, for example, based only on today’s grid intensity figures, in our opinion, does our clients a huge disservice and may railroad them into adopting a technology that may be obsolete and frowned upon in as little as 10 years’ time or even sooner. This, of course, is a situation that could be avoided with suitable guidelines for future grid and other technology carbon intensities as opposed to the standard Part L values.
On the face of it, the economics of CHP can be quite compelling based upon the current rules of the race. However, this could result in organisations such as hospitals, district network operators or campus style situations simply opting for a CHP unit with good payback of perhaps 2-5 years rather than actually looking at the building infrastructure and fabric as a first step and looking to the future and what may be required in not so many years.
Furthermore, if the entire system is designed initially for high-temperature operation then, in all likelihood, high-temperature systems would always follow on and be installed at the end of life of the CHP in perhaps 10-15 years. This rather limits the choice of a replacement technology. A good carbon saving now for a CHP will almost certainly lead to an undesirably poor one in the future as the grid is decarbonised. Designing only for today does little more than simply kick the can down the road to future generations who may well find it very difficult to bat the can back!
Room for fossil fuels (for now)
Using any type of fossil fuel technology should be afforded a far greater thought process and be viewed as an interim measure. CHP on its own does tick a lot of boxes so long as there is a near constant demand for heat and electricity. Even gas boilers, if they are used as part of a peak energy strategy with other suitable equipment, can tick the box for an energy and carbon efficient building. However, as outlined, these technologies should be viewed as interim measures and the entire heating and cooling system designed with this in mind for when the grid is suitably decarbonised.
The chart below is from DECC’s 2015 Assessment of the Costs, Performance, and Characteristics of UK Heat Networks. The same report states that CHP will still be a winning race car until 2032, and I am not entirely sure why!
The clear advantage of a CHP engine driven by gas is the grid carbon that it offsets and obviously its ability to provide heat, too. However, as the carbon it offsets for electricity generation falls, the carbon use in the CHP itself remains constant and so this offset gets smaller and smaller and the relative carbon intensity of the engine gets higher and higher compared to other technology.
The purple lines added to the graph below shows that, with a grid CO2 intensity of 300 g/kWh, even a poor performing heat pump will already be at the first corner before CHP leaves the grid in terms of the CO2 content of the heat they produce; when we do finally get to the target area of 50 g/kWh even poor performing heat pumps and direct electric CO2 content is reduced by an order of magnitude.
Charting grid carbon intensity
So how long have we got to wait until grid power CO2 intensity is at just 300 g/kWh? Not that long, it seems, because as I write this paragraph, grid carbon intensity is currently reported as being 293 g/kWh (source: Ecotricity live data) and during the summer has been in the 100s too. Clearly this live value changes and goes up as well as down, however, the value to be used in an energy strategy is still an unrealistic 519 g/kWh and even this seems to occasionally vary upwards as well.
It would appear CHP CO2 savings have already hit the buffers – it’s just that benchmarking numbers have not yet caught up! Yet, there continues to be a huge push to implement this technology, and indeed other technologies, into district heating systems.
In this publication, there have been various articles written about the merits, or not, of high-temperature district heating systems. Some have focused on the efficiency of the primary input to output but this may overlook the inefficiencies of the distribution network. District heating can be used, in some cases, as a bargaining tool by planning authorities to ensure new buildings are hooked up to the district heat network as a revenue generating tool, but is that always the best thing to do for a property or the client?
Again, recent focus in the UK has been towards hot district heating networks at least in part driven by having seen what the Scandinavians have done and how ‘wonderful’ this must be. However, when doing this, we may in fact be looking through rose-tinted spectacles as there is increasing hostility towards district heating operators in Sweden; costs are increasing, maintenance has been increasing and customers are far from happy at the monopoly situation of a single supplier.
Can we in the UK now reverse the choices that we currently have with our energy providers and head back to the 1970s, to a single supplier who has total control over the costs and supply of the heat into a building? It seems all is not perfect in Sweden and according to many Swedes, the cracks are starting to appear, just as we begin to gain traction towards copying what they thought best 10-15 years ago or more.
In theory, hot district networks can be a good idea. However, in practice, and with the advent of more choice in what we buy and who we buy it from, the undeniable energy losses involved and the widespread use of gas as the primary energy source, perhaps this theory needs to be challenged.
From district heat to district energy networks
What if there were a district heating scheme that needed no insulated pipe work, made simply with polyethylene pipe, and where undesirable energy loss into the surrounding ground was not realised? What if that district heating system could also provide cooling highly efficiently? What if there was a district system that could share energy between buildings on its network? What if there were a district system that could be used as a heat sink for industrial processes rather than wastefully discharge it to the atmosphere losing it forever?
Welcome to low-temperature ground source district networks, or less of a mouthful, Cold District Energy Networks; not a heat network but an energy network.
Picture a single loop (water filled energy pipe) with various sources and loads attached to it, in effect being used to keep the district network within its desired temperature range. An ‘almost living’ and ‘nearly breathing’ energy system that simply moves the stuff around rather than burning to supply heat and possibly some inefficient absorption cooling and making people adopt it from a single supplier.
Does this sound the death knell for CHP or boilers as an interim? Absolutely not. As the energy network can accept rejected heat, the CHP engines react to it and then this CHP heat energy is passed around to wherever it is needed. Boilers can still be used for peak periods to keep the energy network in tune.
Creating adaptable systems for the future
What about flushing money down the drain? In terms of energy, that is exactly what is being done each time a tap runs or a toilet flushes. Hook up a sewage heat recovery and rejection system to the energy networks and you simply capture and pop the energy back into the district energy network.
The point is this: District systems are a good idea and have worked well, but we need a 2016-2050 version of a district energy network. With some design thought, systems could be designed with all of the current technology mix, including CHP, oil, gas, etc. so long as the design recognises their limited time frame for inclusion and the system is capable of operating without them in the future. They also need to be easily adaptable for the inclusion of the new low carbon technologies of the day.
A cold district heating network using harvested energy, ground energy, solar energy, energy from sewage or industrial processes, plus some electricity to push it all around would appear to fit very nicely into this future if only we would look to it. Surely it is better to move around the energy we have before we start to generate more of it?
Andy Howley
Technical Director
Ground Source Consult Ltd
+ 44 (0) 2476 629762
andy.howley@gscltd.co.uk
www.gscltd.co.uk
Twitter @gscltd1
