So, the EcoBungalow is complete and I’ve been living in it since May 2024. My aim is to keep this blog going for at least a calendar year from moving in, to answer the two questions I’m most frequently asked:
How much energy does the EcoBungalow use, and how does this compare to the house before the retrofit?
What’s it like to live in? Is it comfortable?
Energy use and carbon emissions: First Quarter – May to August 2024
The table below shows energy use in the first quarter since moving back home. It includes a direct comparison with the same period (mid May to mid August) from 2021 and 2022. I haven’t included 2023 as building works started at the end of this period, meaning that comparisons aren’t like-for-like.
It’s been a terrible summer – a couple of short periods of hot, sunny weather but much wetter and colder than usual. Not much climbing this year! Despite the terrible weather, I haven’t needed to have the heating on so this quarter isn’t the most interesting.
Key observations:
The overall amount of energy used is significantly less, at about half the amount in total kWh.
Direct cost comparisons aren't very helpful as prices have increased so much in the last few years. However, the cost per kWh is greater than previously as the house is all-electric, with no gas. But, as the amount used is so significantly less, bills are lower than in 2022 and almost identical to 2021.
This second table shows the carbon emissions for energy use. I’ve used two sources to calculate these: the World Land Trust and Carbon Footprint. These two gave very slightly different figures, so I’ve used an average. Emissions are 40% lower for the same period than 2021, and 25% lower than 2022.
Comfort
I’m the sort of person that likes gadgets. So – on the recommendation of other Passive House dwellers - I bought a Netatmo Weather Station. This is a great way of monitoring inside and outside temperature and humidity, along with indoor air quality and noise. Not only does it tell you what’s happening now, it provides historic data and handy comparative graphs.
Unscientifically, I can report that the house is really comfortable to live in. The Netatmo confirms this: the internal temperature and humidity are steady, the air quality is great, and it’s really quiet.
The one issue I’ve had during this quarter is some overheating during the few days of really warm, sunny weather. The living room has large west-facing windows and solar gain can lead to temperatures rising. This was a problem with the house before the retrofit, particularly as the openable window area was very small so it was difficult to get any cross ventilation. I’m on a steep learning curve on understanding how the building behaves in different conditions, but I began to find ways of managing the overheating:
drawing curtains to minimise solar gain;
dumping heat morning and evening by opening windows to provide cross ventilation; and
fine tuning the Mechanical Ventilation with Heat Recovery (MVHR) controls.
Two Netatmo graphs from the very warm period in the summer provide a useful illustration.
July 31st: I was at home during the very warm weather on this day, and drew the curtains as the sun came round. Although the house got warm, it was still well below the outside temperature of 30ºC. I was surprised, however, that the house only cooled by around 1ºC overnight. Of course, the MVHR provides ventilation and not cooling. But I’d thought that there would be more of a drop overnight as cooler air circulated through the house. However, on reflection, this is perhaps not so surprising:
the increased thermal mass of the building retains more heat than the 'old' building;
the ventilation provided by the MVHR is quite gentle - you can't feel any air movement unless you put your hand right next to a vent. So it's asking a lot for the ventilation to create a significant temperature drop; and
I didn't open windows overnight during this warm period, relying solely on the MVHR for ventilation as my expectations were that this would have been enough. In retrospect, I should have left windows open overnight to cool the building.
August 1st: Given the slow rate of cooling overnight, the next morning I opened windows to dump some heat – you can see the drop in the graph on August 1st between 8am and 10am. Then I went climbing for the day and forgot to draw the curtains. The house was an uncomfortably warm 26ºC when I got home at 10:30pm. Again, I opened windows. The cross ventilation rapidly reduced the internal temperature by 2.5 degrees.
I noticed during this period that the MVHR wasn’t consistently switching to summer bypass. This bypass of the heat exchanger ensures that the incoming air isn’t being warmed by the outgoing air. Combing through the instruction manual, I realised that there was a simple adjustment I needed to make to ensure the bypass operated consistently at 100% open – adjust the temperature profile to ‘cool’ from ‘normal’. This tells the unit that I’d like a lower room temperature. (I’m writing this in October, and it seems that I now need to set the unit to ‘warm’ to prevent it deciding that it doesn’t need to warm the incoming air. So - despite being advised I shouldn't need to touch the unit - it seems that some fine-tuning is needed in response to the changing external temperatures)
Overall – apart from a short period of overheating – the house has performed well and is very comfortable. I’m looking forward to the next heatwave to see if I can manage it better next time around – but we’re going to have to wait until next summer!
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