If you’re minded to go ahead with a heat pump, as previously indicated, there are considerations. Ground Source Heat Pumps are more expensive and esoteric, and have space and installation hurdles that are likely to preclude them from most of Hammersmith.  But if you happen to live above the Central Line, there’s probably almost limitless heat to be had c/o TfL with the right installation !  Most of us though, would be considering Air Source Heat Pumps (ASHP).

Air Source Heat pump internals [Automated Home]

The picture, right, is important for several reasons.  Size and weight are obviously issues, but perhaps as much are the plumbing and complexity, not only of the unit and its controls, but the installation.  Figures mentioned in recent media reports indicate 2 people x 2 days to install, as opposed to 1 person x 1 day for a gas boiler. By our maths that’s 4x the time, so probably as much as 4x the install cost, this doesn’t include modifications which may be required to radiators, plumbing, tanks (if they exist… only 38% of homes now have them).  With a target install rate of 600,000 per year (starting now!), it’s unclear where all the installers are going to come from – the UK installs 1.7 million conventional boilers annually for comparison.

Looking at the local skyline [next tab], we can see how many homes there are (80,600 -Ed), and what a large percentage are terraced or semi-detached, often smallish, Victorian with the constraints we’ve listed before. There are some substantial estates too with different constraints (district heating schemes would make sense); neither fit heat pumps particularly well, though the previous article showed us that with unwavering faith and a good helping of design + cash, it can be done successfully.

Skyline / map c/o our 2021 Award winner : 245 Hammersmith Road

Better insulation has long been called for, and is mentioned in the new strategy as ‘fabric first’ and ‘whole building’ approaches. It’s unfortunately one of the most disruptive, expensive and difficult things to achieve at any measurable scale on existing buildings, especially with our preponderance of small Victorian homes. Small but effective wins can be achieved by weather-stripping sash windows and doors to eliminate draughts, but these are the kinds of things diligent homeowners should be doing anyway with £5-10 per window spent at a DIY shop and a spare Sunday afternoon. The government knows what more extensive measures cost to do professionally – they commissioned a BEIS report in 2017 – £5,000 to £10,400 for insulating the walls of a small semi for example.  Reading across these numbers, one rather suspects a some Yorkshire pricing has slipped in – in London one has to expect rather more.  Glazing replacements at £5000 – £7000 are couched in terms of uPVC – probably double if conservation grade wooden sashes are required.

Regardless of absolute numbers, and the obvious value of insulation in pure energy saving terms, the BEIS summary table shows just how relatively more expensive and laborious it is to insulate than it is to replace a boiler, helping to explain why our housing stock is where it is.  Equally, when the average internal temperature of a UK home in the winter months was 12°C as recently as the 1970’s did it matter so much ?

Clearly missing-in-action though, are the bang/buck ratios. How can one decide what’s worth prioritising without a yardstick of the relative merits of each intervention, especially the really messy and difficult ones ?  It’s essential to know the relative value of, say, wall insulation vs. floor insulation for your home – most won’t accept the disruption for all possible interventions – let alone afford them (grants only for low income households).  Of course experts will say “it depends…” but there must be better guidance available to the general population.

Energy assessors tot up an SAP score based on a number of parameters they check to create the mandatory Energy Performance Certificate (EPC) when you sell your home, and unless the government is protecting that industry which seems unlikely, it should be possible for a quick’n’dirty self-assessment via an online calculator to be able to make some better informed decisions.  In fact the Energy Saving Trust used to have such a calculator, but it now appears to involve joining an online community, which is likely to reduce uptake. Your correspondent has found no useful alternative, other than paying for a 3rd party EPC, and quizzing the assessor on the detail of the calculations.

LETI: Green Hydrogen vs heat pumps

Despite the government cogitating on it, some specialist groups such as LETI already discount hydrogen, whether blue – made from natural gas – or green – from renewable power, largely for the good engineering reason of end-end efficiency, and the energy multiplier effect in ASHP’s, as shown in the adjacent diagram (“green hydrogen” as shown, but “blue” not much different just in efficiency terms anyway). The argument is: why go through all the transformations (power generation + H₂ conversion +  storage + gas network distribution)  only to get 45-55% end-end efficiency, vs. 200% + with ASHP’s ? Comparisons are slightly oversimplified, but it’s an argument with plenty of merit.  Factors missing in the argument against H₂ are the set of storage tanks shown – energy storage is likely to become increasingly important as we rely more on renewables – and the capacity of your domestic supply and the grid to cope if we’re all on ASHP’s (ask a Californian about summer when all their A/C heat pumps are on full).

The answer is It’s the economy, stupid! as someone once famously said. Set aside the engineering and technical efficiency for a moment and do the financial, time, people and risk calculations, and avoid the great getting in the way of the merely good. Oh, and do those bang-for-buck calculations too.

To spell out the numbers – 30 million buildings to convert with only enough people to do a fraction of that number, or use a different engineering argument : would you/could you build a handful of clever industrial plants + 50% more wind turbines than you might otherwise need in a perfect world, OR have thousands of white-van-men running around for 20+ years making substantial changes to most homes – each one a prototype – a significant number with marginal insulation – finding sites for big white boxes outside (remembering that half of this borough comprises conservation areas, limiting positioning) – likely change radiators and hot water cylinders, for a heating system that’s significantly more complicated and capital intensive on a PER HOUSEHOLD basis, and potentially little or no cheaper to run ?

It’s the PER HOUSHELD unique and difficult interventions that mean a way has to be found to square the hydrogen circle, to decouple other building upgrades from a heating system which has enough headroom, so they don’t all have to be done at the same time. This is what HMG would do well to invest £ billions in – a risk/engineered approach that a lifetime of project experience says is the most pragmatic way to get the job done with available resources and a good amount of public acceptance, while minimising the risk of bodged “upgrades”.

Your correspondent’s mind is where government boosterism meets engineering reality. Heat pumps have been around a long time, and are actually a mature technology. The “Carnot Cycle” on which they are based is a well-understood piece of physical chemistry, meaning that they’re fundamentally limited in efficiency terms, and won’t get significantly smaller or more efficient.  They may be new as central heating units in the UK, but as air conditioners (which are largely the same tech – some even offer heating as an option) have been produced in huge numbers for decades all over the world. Indeed some ASHP’s can also do cooling, and that might be a consideration.  So it’s unclear why a small (in world terms) increase in demand will make the price fall by a factor of 5 as the government suggests.  But set against this, a 6kW fan-coil unit air conditioner kit “complete with Wi-Fi control” can be had today for less than £1000 in the UK.  It may be that this is just a volume market, or perhaps their efficiency is more limited, or the air-air incarnation is a lot cheaper to make than air-water, as a central heating system would be. More research needed – Ed

If you’ve had a recent boiler quote, you’ll know that it can be as much as £3000 around here. But you can buy a respected brand name boiler from a high-street supplier for less than £600, and a top brand name one for less than £800.  That benchmarks the person-day cost – we’ll be generous and call it ‘only’ £1250, which in turn means we can approximate the £5k government grant to cover the install cost.  But not the pump cost, these seem to hover around £6000 or so, so we’ll guess that you’ll need to find that £6000 as the starting point on your green journey, as long as your insulation and radiators etc are up to it.  If you have a combi boiler – as many do – bad luck, you’ll now need a tank and the space to house and plumb it, which will run another £1000+.  Not a hair-shirt in sight so far.  Until March 2022 you might check the tail-end of the Renewable Heat Incentive that may be advantageous.

COP (Daikin)

You’d also do well to get a little familiar with COP.  No, not COP26, but “Coefficient of Performance” – AKA efficiency – which varies depending on both outside temperature and the temperature you want from your “boiler”. If you’re super-keen you could delve into BS EN 14511 and BSIRA publications too!

Let’s cut to the chase, here’s one we found earlier. Not the latest, but scientifically researched, you can assume figures are in the right ballpark (Carnot cycle etc…).  What does this mean?  Essentially if it’s 5C outside – not a bad working assumption for an average chilly winter day here – and you need 50C from your “boiler”, you’ll get an efficiency around 2.5, meaning at current capped electricity prices, at the coldest time of year, your current heating cost would be around 8p/unit compared to gas currently capped at around 4p, though this would change if government moves green levies from electricity to gas as they say they may.  If you need 75C, hmm, you’re in the wrong place.  A Hybrid Heat pump is needed (boiler + pump – we touched on last time).

The industry headline COP figures vary around 3-5 but look deeper, and you’ll find a myriad of graphs and figures depending on the exact circumstances and UK location  Manufacturers simplify much of this using “SCOP”, or seasonally adjusted COP to smooth things out over the season, rather than present worrying raw COP values. These SCOP values are averaged over the whole of Europe too, here in London that’s OK, but not so in Newcastle. They’ve been averaging boiler efficiencies for years too, with SEDBUK figures, it’s just that with smaller margins for error, and higher costs all round, you really need this stuff to be right, or you could be cold in January.