Resilient building retrofit in a changing climate

Home Retrofit
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What should the design temperatures be for our retrofit, taking climate change into consideration?

It seems unlikely that humanity will keep global warming below 3 degrees, given the lack of incentive for the majority to compromise their present convenience, comfort and short-term economic position to reduce the risk to the planet and to ensure the safety of future generations. So it seems that I need to use a summer cooling design temperature of 35 degrees or more when planning our UK retrofithttps://www.metoffice.gov.uk/services/insights/future-weather-forecast-for-2050.

There is also a significant risk, for the UK, of the Gulf Stream stopping (correctly the Atlantic Meridional Overturning Current (AMOC), which drives the Gulf Stream), before long. If it doesn’t stop, then that 35 degree Celsius cooling design temperature applies. If it does stop, then our winter temperatures will drop by 12 degrees or so, so we need to use a design temperature of around -16 https://www.carbonbrief.org/ocean-current-collapse-could-trigger-profound-cooling-in-northern-europe-even-with-global-warming/. (In that case, there will be no summer cooling need, of course).

We could cover both possible scenarios by insulating to a high level. So should we be asking our retrofit designer to design to whichever of these two scenarios results in the greater level of insulation requirement and heat pump energy supply?

With that potential cooling need in mind, I imagine any retrofit designer we employ is likely to recommend that we give up our planned idea of a government grant under the Boiler Upgrade Scheme (BUS) for an air-to-water heat pump, and will recommend instead an air to air heat pump (or pumps), which can provide cooling in summer (as well as winter heating) in the event of no AMOC collapse (or in the mean time until it happens)? If so, is s/he likely to suggest a heat-pump water heater, for our hot water (DHW), which, after all, an air-to-air system cannot supply, I wonder?

Am I over-thinking resilience in the face of climate change? We don’t really want to find that we need to upgrade an inadequate retrofit in 30 years time, however, given its likely cost, and given that we hope we are in our ‘forever house’ now.

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Unfortunately you have misunderstood the effects of AMOC and its collapse. Currently the Gulf Stream has an ameliorating effect on the climate. Without it seasonal extremes will become exaggerated. Think of a New England climate. Bitterly cold in winter and hot in the summer. In other words your resiliency plan, which is a very good idea, needs to allow for both excessive cold and heat. To some extent this can be seen in Europe away from the maritime zone.

Your retrofitted home needs to cope with more than excessive heat and cold. It also needs to be able to cope with extremes of wind, water and draught. Think about how your solar panels are fixed down (and of course the rest of your roof). Get quality panels that withstand the weight of snow and impact of hail. Fit extra capacity guttering with extra downpipes to water stores rather than soak aways. If you live on a hill review how to deflect runoff from uphill away from your property and how to absorb what you don’t deflect.

Coming to your question:

There are air to air heat pumps that have a water heating capacity, a few of which may be available in the UK. I know that Daikin make one.

A2A is noisier inside than A2W but then British supplied A2W doesn’t cool. You can get ones that cool elsewhere but you need fan coils, which can be noisy, and a plan for removal of condensation.

The outside units of decent modern heat pumps are quieter than the roar from a boiler’s flue. My Daikin A2W is undetectable to me and various visitors. I can hear when my neighbours’ are using hot water by the noise from the flue.

If you can get away with minimal internal disruption I have no qualms in recommending A2W for heating. You might even get a grant.

For cooling you really need A2A, with the associated noise. That noise needn’t be very much if the system is correctly specified.

Even better that cooling is to avoid over heating in the first place, which means shading (as well as insulation). Think of the style of American farm houses. Deep verandas facing south. Unless your house is totally concealed from view your local planning department won’t be happy with such a change and something more compact will be needed, such as the blinds and shutters found on southern European buildings. Shutters can also help protect against the cold too. Something I discovered in Milan last winter. Another solution is a covered pergola. However pergolas don’t shade upstairs windows, so alternate arrangements need to be made for them. My pergola has solar panels for a roof.

Direct electric is easy to fit and there are now smart storage heaters that charge up the correct amount in off peak for you day time requirements but they don’t cool the house in summer. Heat pumps are generally more efficient when heating than cooling, so it is unlikely that you will need direct heating for anything more than top up.

This is a rambling answer to your post. I may have missed something out so I won’t be offended if you ask for any clarification or you point out anything I’ve missed.

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Thanks for your most prompt, informative and full reply, Tim.

The Carbon Brief paper, which I quoted and beleiev to be prettty authoritative, says of the UK situation after AMOC collapse plus global warming: “Summer temperatures, on the other hand, would be expected to remain just slightly cooler than they would in a pre-industrial climate”. But if you have other sources, it would be interesting to hear.

Currently, we have no solar panels, due to shading from a huge nearby ash tree to the south east and trees on high ground to the south. But its days may be numbered due to ash dieback and, even if it survives, we are considering having a pergola style solar panel shade roof to the south as you have built yourself.

And yes, external bamboo roller shades for our east and west facing windows, such as you and I discussed in some recent posts here, are in the plan. But even with shading I imagine that significant cooling will be needed if we have 3 degrees of warming and no AMOC collapse.

Our surface water drainage is all into small the perennial stream which runs within a couple of metres of the south wall of our property, so will not be a significant problem, I hope.

What you say about cooling by air-to-water heat pumps is interesting, and is another subject to which you and I (briefly) have both contributed in this forum in the past. (I am not sure how to refer to those other threads from here, or I would do so).

We have just had an air-to-water heat pump assessment from Heat Geek using the voucher code provided by @sianrichards55 to whom many thanks for that, saving us £200 or so. So we have been sold on A2W for some time, but until recently had been devoted to fabric first. It is having the Heat Geek surveyor round last week which has concentrated our minds on the whole issue of design temperature. Until now we have been ‘fabric first’, then wavered, swaying towards the ‘fabric fifth’ argument, hence commissioning the Heat Geek survey (especially with the voucher value). I have no concerns about noise from modern A2W pumps and we had been planning on one until the possibly very significant future cooling need dawned on me.

The two aspects of our potential, stepwise, whole-house plan for a deep energy retrofit which therefore exercise us now are 1. whether to go wholeheartedly for air-to-air heat pumps, with the cooling need due to global warming in mind, and 2. how tricky installing MVHR in an existing 1950s house will be. (Oh, and 3. the cost of all this. We have some budget but want to spend it well!)

Anyway, many thanks again, and we will see what proposals Heat Geek come up with. Given our currently leaky and largely single-glazed detached house, I fear that both the up-front and the running costs will be high, the latter especially until we have undertaken some major fabric upgrades. EWI and triple-glazing would be in the eventual plan, we hope, as funds may permit.

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You mention MVHR. I retrofitted that when we had an extension fitted. If you have no major works planned it will be relatively disruptive. The best place for vertical ducts is through fitted wardrobes. Unless one lives in a mansion the natural place for a retrofit heat MVHR is in the loft. With that in mind I fitted an extra large loft hatch and winch in my loft!

The AECB produced a report saying that MVHR is beneficial in any house but the better the airtightness the better it performed.

Make sure you but one that conserves coolth in the summer and doesn’t just try to warm the house, otherwise any air conditioning will be wasted. My Zehnder unit does that.

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My comments on AMOC were based on an article I read many years ago and may need updating. Unfortunately I do not remember the source. A quick search agrees with your summary. It also implies that we should begin an evacuation of all low lying land before panic sets in.

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I don’t think I would install an A2A heat pump now, if the only reason was to cater for AMOC collapse, because even if that happens you’ll have gone through several cycles of equipment replacement and technology evolution and wider availability in the UK of things which are mainly available elsewhere.

Of course, it’s still worth thinking about what that future retrofit might look like. Some folk do A2A simply by having a single main room at the receiving end of the warm or cool air, and relying on open doors to spread it around. In that case, a future switch from A2W to A2A might be straightforward.

Some folk prefer to use one heat pump for space heating and another for hot water, with an A2W integrated with the hot water tank. I have heard of installations where the supply air for this is taken from within the house, so that your summer hot water generation also cools your house air.

Anyway, as you and Tim say: form and fabric lead in considering future overheating.

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