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The Changing Jet Stream Could Challenge UK Air Source Heat Pumps

Mars · 2024-08-10T13:48:37Z

Climate change is not just an abstract, distant threat; it is an ongoing process with tangible impacts on our weather systems. One crucial element of our atmospheric dynamics that climate change is influencing is the jet stream, a fast-flowing ribbon of air high in the atmosphere that plays a pivotal role in shaping weather patterns. Recent studies indicate that the jet stream is becoming more erratic due to climate change. This shift has profound implications, particularly for regions like the UK, where the jet stream’s behaviour directly affects temperature and precipitation patterns. The Jet Stream, AMOC & Climate Change The jet stream is driven by the temperature difference between the polar regions and the equator. As the Arctic warms at an accelerated rate (a phenomenon known as Arctic amplification) the temperature gradient that powers the jet stream weakens. This can cause the jet stream to slow down and become more wavy, leading to prolonged weather patterns, whether they be cold spells, heatwaves or storms. In the UK, this altered jet stream behaviour can result in more extreme and unpredictable weather conditions. A related and critical component of this climatic interaction is the Atlantic Meridional Overturning Circulation (AMOC). The AMOC is a system of ocean currents, including the Gulf Stream, that circulates warm water from the tropics to the North Atlantic. This circulation plays a significant role in regulating the climate of the North Atlantic region, including the UK. As the planet warms, there is concern that the AMOC could slow down due to an influx of freshwater from melting ice caps and increased rainfall, which disrupts the salinity-driven component of this circulation. A slowdown of the AMOC could further destabilise the jet stream, exacerbating the climatic impacts on the UK. Multiple studies have shown the link between climate change and alterations in the jet stream. Research published in Nature Climate Change has demonstrated that the jet stream is becoming more wavy, which can lead to prolonged periods of extreme weather. Another study in Science indicated that a weakening AMOC contributes to these disruptions by reducing the thermal gradient between the equator and the poles, a crucial driver of the jet stream’s strength and stability. The jet stream has traditionally acted as a protective barrier for the UK, moderating its climate by steering severe cold and hot air masses away from the region. The UK’s relatively mild winters are, in part, due to this influence. For example, the jet stream helps to keep the frigid Arctic air at bay, ensuring that the UK’s winter temperatures remain relatively moderate compared to other locations at similar latitudes. Comparison with Other Regions on the Same Latitude To understand the jet stream’s protective effect on the UK, it’s insightful to compare it with other regions on similar latitudes: Midlands, UK (Latitude 52°N): Average winter temperature: Around 3C to -3C. Calgary, Canada (Latitude 51°N): Average winter temperature: Around -9C to -15C. Calgary experiences significantly colder winters compared to the Midlands due to its continental climate, which is not moderated by the Atlantic Ocean or the jet stream to the same extent as the UK. Warsaw, Poland (Latitude 52°N): Average winter temperature: Around -2C to -6C. 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. Minneapolis, USA (Latitude 45°N): Average winter temperature: Around -10C to -15C. Despite being at a lower latitude, Minneapolis experiences much harsher winters than the Midlands. This further emphasises the unique moderating effect the jet stream has on the UK. Challenges with Colder Spells & Their Impact on Air Source Heat Pumps Given that most heat pumps in the UK are designed and sized based on the national average winter temperature of around -3C (colder as you head north into Scotland), if the UK were to experience a month of -10C or -15C, would many air source heat pump systems struggle to reach and maintain target temperatures? To explore this, we asked several heat pump installers whether this was a fair assessment. Here’s what they had to say: David Alston explains that some high-quality ASHPs can maintain their output even at very low temperatures, such as -17C, by artificially running the compressor at higher frequencies through the inverter. However, he points out, “the colder it gets, the more kilowatts the house will need, often requiring built-in immersion heaters to supplement the heat.” Alston notes that during the cold snap in 2011, while many boilers failed, ASHPs continued to operate. “Customers did understand they would have to wait a little longer for domestic hot water as a lot of the energy was focused on the heating circuit a lot of the time, but it was an interesting experiment,” he says. He al...

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Air Source Heat Pumps (ASHPs)

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SusannaSaunders

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26/10/2026 7:21 pm

@rob-of-york Thanks Rob!

A LOT to digest here!

Please give me a day or two to work through this and it's implications!

That table of Flow Temp vs radiator output factor... 😬 🤯 Does this mean you need to increase the radiator surface area by 5 times to operate at a flow temp of 40 [Rad temp of 35C]! Even achieving 45C/40C with a factor of 0.3 so aka about 0.35 or roughly 1/3rd 'rule of thumb' of the radiator nominal power output. It seems that operating below this threshold, while theoretically plausible is practically unfeasible because the radiators would need to be enormous...

The Vaillant Aerotherm Plus installer manual graphs are very counter-intuitive as well as power output falls as the flow temperature increases... 🙃 How does that even happen??? 😲

The heat pump efficiency tables are very interesting too. Very Alarming! But very interesting too! To maintain any kind of half decent SCOP you need a fairly good amount of headroom to enable you to run the system at a low flow temp... Above 45C becomes punishingly low SCOP. Increase the HP capacity up to 7 or 10kW gives more head room but presumably higher running costs too. It would be interesting to know by what percentage increase across the size options (a complicated question I know because of the shorter cycling times and increased wear and tear issues). The 'sweet spot' is a complicated zone!

Thank you for all of this very valuable info!! 😘 🍻 you have increased my knowledge a fair bit so thank you for this! I'll come back to you once I've had some thinking time.

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