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TOM FOSTER’S ARCHITECTURE COLUMN (May/June 2022)

Fri 1 Jul 2022

By Tom Foster - Architecture Column

TOM FOSTER’S ARCHITECTURE COLUMN                                                                              

01647 24436   www.TomFosterArchitecture.co.uk   info@space-and-light.co.uk

Since I started this column in The Cottage, we’ve passed from old ‘normalcy’; via Windrush/Grenfell; Floyd and BLM; climate, youth-quake, G7 and CoP26; into Covid, lockdown, recession and social change; now war, inflation and shortages - but still people’s home- and workspace-improving dreams continue.

Providing initial Planning feasibility and cost advice and verbally contributing a bit of my architectural vision to such dreams is a large part of what I do. That is, distinct and separate from my ‘other’ business of actual architectural commissions – designing; drawing up and making Planning and Listed Buildings Applications; doing working drawings and making Building Regs Applications; supervising building works and administering building contracts.

As my initial advice sessions are not ‘free quotation’ visits hoping to sell a product (like say replacement windows); but my professional advice (like a lawyer’s or doctor’s) is itself the product, I make a per-hour charge for such initial sessions and any agreed associated desk-work. Once paid, my client has acquired and is free to use all my advice and any design ideas given, as s/he pleases, even to take to a competitor if appropriate. That way, I feel free to give my very best, including design vision (the core of my skills) rather than holding back until I ‘get the job’.

 In summary, as I advertise elsewhere,

“…. or perhaps you’d just like some can-do advice. Talk to Tom to bring your vision closer.”

Heat pumps

Ukranian horror has ironically done the rest of humanity (and all life on earth) a great favour. Governments all over are suddenly prioritising ‘energy self-sufficiency’, which in most places means kicking the carbon-fossil fuel (coal, oil, gas) import habit. Even for countries that produce their own carbon-fossil, the cheapest and quickest way by far to ramp up homegrown energy supply is now renewable (solar, wind) energy, though Boris characteristically pretends to favour (non-starter, 20yr timescale) nuclear.

This welcome acceleration of replacement of carbon-fossil energy by renewable is already well under way. Already the ‘carbon intensity’ of electricity is greatly reduced. Traditionally 1kWh of electricity required at least 3.5kWh of coal to generate it (2.5kWh wasted to atmosphere) – a carbon intensity ratio of 3.5. Nowadays, so much of that coal (or gas) is replaced by renewable generation (in UK mainly offshore wind), that electricity’s average carbon intensity is down to 1, on par with modern gas central heating – and falling. So from now on, electricity is already, and ever more so, the environmental ‘fuel’ of choice, even when directly used in fan or convector heaters.

But it's still expensive per kWh! So here are heat pumps – mainly air-source heat pumps (ASHP). They use electricity to suck in air, even cold winter air, and blow it out even colder, saving the extracted heat and ‘pumping’ it up to useful temperature. Current ASHPs produce about 3x as much useful heat as they consume in electricity - a ‘Coefficient of Performance’ of 3 (COP – nothing to do with the CoP26 conference!). So passing your electricity (carbon intensity 1) through a ASHP gives the resultant useful heat a carbon intensity of 1 divided by 3 = 0.33 – unbeatable! and improving. What’s more, the electricity’s effective cost is also divided by 3, compared with using it in a fan or convector heater.

Good for the environment and good for the pocket – governments are promoting heat pumps; in UK new gas boiler installations are banned from 2025. However two snags – the capital cost of a heat pump installation, and their relative unsuitability for hard-to-insulate buildings.

On capital cost, the UK government makes a habit of introducing one inadequate short-run subsidy scheme after another – check what’s available at the future time you read this.

More fundamental is the degradation of heat pumps’ great virtue – their COP – when used in hard-to-insulate houses. More precisely, a heat pump’s COP is related to the uplift that it has to ‘pump’ its output temperature. If winter ‘source’ temperature (outside air) is say 5oC, and the delivery temperature that the house’s radiators require is 40oC, that’s an uplift of 35oC, at which a ASHP will typically deliver a COP of 3. Increase that output temperature to 65oC, as required by a typical central heating radiator system, that’s an uplift of 60oC, at which COP will have fallen to 2 or lower. Going the other way, if output temperature is as low as 25oC, as required by underfloor heating, that’s an uplift of only 20oC, on which ASHPs thrive, giving a COP of 4.5 or even higher.

A building insulated to high standard is likely to have underfloor heating, or radiators requiring only moderate delivery temperature, for which a ASHP is ideal. A building to Passive House standard won’t even need a heating system at all! For buildings poorly insulated, or with best will in the world hard to insulate, such as many Listed Buildings, the required delivery temperature is likely to be high, at which heat pumps need to be both more-than pro-rata larger, and won’t give good COP.

Unfortunately this describes very many UK houses, so current heat pumps aren’t the universal answer. But there’s hope! A new breed of ASHPs is arriving, which maintain their COP much better when required to run hot. Make sure your heat pump supplier is up to speed on this issue, and willing to discuss it. The key indicator is use of R290 or R774 refrigerant fluid rather than standard R32 or R410A. One of the new breed is the Vaillant Arotherm.



Other columns by Tom Foster - Architecture Column

TOM FOSTER’S ARCHITECTURE COLUMN (November/December 2021) - Tue 9 Nov 2021
TOM FOSTER’S ARCHITECTURE COLUMN (July/August 2021) - Mon 2 Aug 2021
TOM FOSTER’S ARCHITECTURE COLUMN (March/April 2021) - Mon 1 Mar 2021
TOM FOSTER’S ARCHITECTURE COLUMN (November/December 2020) - Sun 1 Nov 2020
TOM FOSTER’S ARCHITECTURE COLUMN (July/August 2020) - Wed 1 Jul 2020
TOM FOSTER’S ARCHITECTURE COLUMN (January/February 2020) - Wed 1 Jan 2020


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