Warsaw, Poland (Latitude 52°N): Average winter temperature: Around -2°C to -6°C. Warsaw, while also benefiting from some moderating influences, tends to experience colder winters than the UK Midlands, illustrating the protective role of the jet stream over the British Isles.

Warsaw gets colder winters because it's further in land. From living in Spain which is 80% mountains I saw how in the summer it is so much hotter inland than the coasts and so much colder in the winter.

We could go snow boarding in Granada on a winter morning and the same day go lie on an Andalucían beach in a bikini in the afternoon. Germany, Romania Poland and Ukraine are good examples of really cold winters and hot summers. 

That's not to deny the impact of the gulf stream on the UK of course but a Spanish meteorologist once told me that the biggest impact on British weather was being a little rock in the sea alongside the major landmass of Europe. He drew me charts of Atlantic weather patterns and how they hit our little rock. 😁

@derek-m Could you be a little more precise please, is that a.m or p.m.?😉 Toodles.

Massive global events usually happen in the morning. 😆 

…but in this case you’ll be fine for a bit of lunch but it’ll ruin your barbecue. You’ll need a rib-sticking hearty slow-cooked stew instead but if you time it right you can cook it for free from the solar leccy generated in the morning.

Massive global events usually happen in the morning. 😆 

One other factor I hadn't thought of while writing the article is that given the typical lifespan of heat pumps there is room for ongoing assessment of the risks and potential recalibration as our understanding of climate change and its impacts evolves. So, for example, if winters get dramatically colder over say a decade, then installation guidelines surrounding sizing of heat pumps would have to adapt and change to accommodate for these vacations. 

Your concern about overwhelming the workforce with too many variables is also valid. The challenge is to ensure that discussions about future-proofing heating systems remain measured and practical, without causing undue alarm or complicating the already complex task of transitioning away from fossil fuels. 

However, oversizing also brings inefficiencies and higher running costs in the short term, which we must weigh against the potential long-term benefits. This is what makes this so complicated

In some ways it's a major advance that we are actually talking about design.  Most fossil fuel central heating systems aren't designed so far as I can make out!

PS I wasn't for a moment suggesting you article was intended to help the fossil fuel industry.  However it will do anything to preserve itself so far as I can tell, so if it can use a spin on the gulf stream to sow fear it will.

Realistically any system design can only be optimised for a certain range of conditions.  If the conditions change then the system may perform sub optimally but often still acceptably, or may need adaption.  On rare occasions it will need replacing in toto, but usually only in response to large changes.  This is true for heating systems and many other systems.  

Also just because a system is 'designed' for say -3 at 45C doesn't mean it won't (automatically) increase the flow temp above 45 when the temperature is even colder.  Many, perhaps most, will, so will just work or may simply need a tweak to the WC curve.

I did think about the gulf stream issue a year or two ago in relation to my own system and concluded that ignoring it was both a safe way forward and probably the best given the timing uncertainty.  If it happens in 2025 then various adaptions can deal with it (from a heating point of view).  However I suspect heating might be the least of the problems this effect of climate change triggers.

My concern about introducing yet another variable (climate change at an uncertain date) into the design process (other than for geeks like us) is that it overwhelms an already strained workforce which, frankly, is struggling with the current design requirements.  If it is to be introduced then it needs to be done through some simple change to the target design temp or similar.  Asking installers to cope with the uncertainties is asking for trouble.  So I do agree it needs to be discussed, but in a relatively closed group that reaches and implements a conclusion not the general public domain and certainly not in the telegraph or daily mail.  Otherwise the almost inevitable result is further to delay the move away from fossil fuels.

It’s clear from your description that effective system design, including proper sizing and volume management, plays a crucial role in ensuring that heat pumps can perform reliably even in colder conditions. Your approach of using a well-insulated, airtight house with MVHR and a well-sized heat pump system is a great example of how thoughtful design can enhance performance and efficiency.

The fact that your system performs well at -9°C despite being initially undersized speaks to the resilience of a well-designed heat pump setup. This is the question that I wanted answered, and that many seasoned installer are still grappling with.

Your experience also underscores an important point made in the article: while heat pumps are designed to cope with a range of temperatures, the specifics of their performance can depend significantly on how they are installed and managed. Systems that are well-designed, with sufficient volume and appropriate control settings, can indeed handle colder conditions more effectively than those that are not.

However, oversizing also brings inefficiencies and higher running costs in the short term, which we must weigh against the potential long-term benefits. This is what makes this so complicated

With good system design it need not be the case. Our house is new well insulated and pretty airtight with MVHR. Heat pump sizing was done my me on a self install. I chose the heat pump being close enough and it was a really good prices - but it kicks out 6kW at -3 when my heat load is around 3kW. And at an average outside temperature of 10 degs I don't need heating. Getting a suitable heat pump not that easy and at the time none on the shelf. So not really by design I have a heat pump that's still ticking over at -9. But I needed to work smart to get it all to work. So no zones, no additional pumps just simple and open. And about 60-70L of system volume.

To support a given kW and not suffer short cycling you need a defined volume of water of 10 to 15L per kW output. Then a bit of fine tuning the running parameters.

I am currently running cooling via UFH - have been for the past month, the heat pump runs for 10 to 13 mins then compressor stops, for an hour or so based on floor return temperature (dictated mostly solar gain) and so overnight there is 3 or 4 hrs between runs.  When the compressor runs it has a starting spike of about 1kW and quickly settle down to about 6-700W. The pattern is pretty similar when I start to need heating. As it gets colder the compressor runs longer.

Low flow temperature is key to flexibility for falling temperature, you need headroom to increase flow temps as needed.

You can live with a perceived oversized heat pump. But you need big volumes of water with large heat pumps. So a 12kW heat pump is needing 120 to 180L. So a big system and/or volumiser or a big 2 port buffer, with hydraulic separation, suitably controlled.