30. Energy use during Winter
- suerowlands47
- Feb 19
- 3 min read
The EcoBungalow has been through the coldest quarter of the year. It’s far exceeded my expectations in how comfortable it has been. But how much energy has been used to achieve this comfort, and how much has it cost?
Energy use and carbon emissions: Third Quarter – Nov 2024 to Feb 2025
I had to double and triple check the table below to make sure I’d got the numbers right. They’re dramatic! The reduction in energy use is incredible: one sixth of 2021/22’s energy and less than a quarter of 2022/23.
Costs are less easy to compare, as energy prices have been volatile. However, this last quarter has cost about 25% less than the same period 3 years ago and a whopping 53% less than 2 years ago.
It goes without saying that the reduction in carbon emissions has also been huge: down 80% from 2021/22 and down 73% on 2022/23.
Comfort
In the last three months, I’ve never walked into a cold house after a weekend away or returning from holiday. I’ve never got up to a chilly bedroom. I’ve never felt the suffocating blast of radiators coming on in the evening, followed by the dip in temperature when they turn off for the night. Sometimes – when I’ve sat still for long periods of time – I’ve felt a little cool and put an extra layer on.
It's a phenomenal contrast to the same period in 2022-23. Energy bills had risen dramatically, so I was trying to be economical with my heating. The house was unpleasantly cold and uncomfortable a lot of the time. If I needed to sit still, I wore thermals and lots of layers. And I still felt cold!
Whilst the insulation and airtight construction are vital to the low energy use and comfort, the MVHR (Mechanical Ventilation with Heat Recovery) has performed an important role. I’ve been amazed at just how much it increases the temperature of incoming fresh air. One day in November, the outside temperature was – 3ºC and yet the incoming air was being warmed to 17ºC by the outgoing stale air. This has a huge impact on reducing heat loss.
I’ve maintained the target temperature for space heating at 21ºC when I’m at home. This gives a pretty steady maximum temperature of 20.5ºC, dipping down to 19.5ºC. There are no doubt some adjustments I could make to the heating curve to get the target and actual temperatures closer together. But I’m happy with the way the ASHP is operating and the internal comfort, so I’m not going to meddle just yet. The Coefficient of Performance (CoP) is the ratio between the amount of electricity consumed by the ASHP and the thermal energy it generates. For November to January, this has averaged 5.7. Over 3 is considered good, so the Viessman unit is operating very efficiently.
When I go away, I keep the Air Source Heat Pump running and reduce the target temperature to 18ºC. The internal temperature gradually drops when I’m away, settling at the target. The key thing to be aware of is that an ASHP works slowly, so I have to remember to increase the target temperature back to normal at least 24hours ahead of my return. What I avoid is turning the heating off completely so that the internal temperature gets really low. It would take ages (and a lot of energy) to get it back up to temperature.
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