Staring at the data
With the EWI now complete and the MVHR humming away, it is time to see what effects these improvements have had on the indoor climate.
The Sensors
In 2016, we bought a Nest smart thermostat. Amongst other things, this device has a temperature (T) and relative humidity (RH) sensor built in, and somebody somewhere created a script that could poll the Nest for T and RH data at regular intervals. Unfortunately the script stopped working when Google (bought Nest and) updated their authentication protocols.
In 2019 I rigged up a modular system. It consists of low-power nodes that read out a factory calibrated SHT-31 sensor every 20 (or so) minutes, and transmit the T,RH data to a central receiving node that displays the data and logs it to SD card.
The State of the House, thermally
In 2016, the main thermal elements of the house still were pretty much as we bought it: 50mm mineral wool cavity wall insulation, uninsulated floors, no internal wall insulation. The original 100mm mineral wool in the loft was topped up to 150mm. Since, then, the following improvements were made:
- July 2017, building works for the extension commenced. The estimated heat loss would not change much because of this: the super-insulated extension would, as a whole, lose as much heat as the area of the external wall it covers. It did include replacing the kitchen floor with a super-insulated screed floor with underfloor heating (UFH)
- August 2018: 200mm polystyrene (EPS) external wall insulation (EWI) was added to the rear and side of the house, including 100mm from DPC level down to the footings. The basecoat and render finish took many more months to complete!
- December 2018: the living room was converted: back boiler removed, chimney flue blocked up, suspended timber floor replaced by super insulated screed floor. New condensing boiler installed with weather compensation controls, driving the ground floor UFH directly.
- April 2020: MVHR installation complete, switched on on 6/4/20. Final commissioning and fine tuning a month or two later. Chimney vents were blocked.
- October 2020: Finished adding 50mm PIR insulation between rafters in the loft. Chimney channels blocked off using stuffed bin bags and vents added just above. Roof space airtightness is still sub par as the party wall is not sealed.
- June 2021: Completed replacing the windows and door at the front of the house, and adding 200mm EPS EWI, including 150mm below DPC. Again, the finishing took many months more to complete.
The Data
First the temperature. The 2016-2020 (up to March 2020) data looked very similar and was averaged, and the same goes for the March 2020- December 2021 data.
I initially found it a bit surprising that the average temperatures in the winter months had not changed even though a lot of insulation was added over the years. Only when improvements to airtightness were made and the MVHR came online the average winter temperatures improved. It goes to show that if there is no provision for ventilation so that cold air has to be let in in winter, comfort cannot be improved: even well insulated homes need MVHR to increase comfort levels. What did change with the added insulation is the energy required for heating to the same temperatures as before:
It clearly shows the massive drop in energy consumption after adding the EWI, even when only partially applied. The still large drops thereafter are mostly due to the boiler replacement ('18-19) and MVHR ('20-'21).
Here again, the MVHR made the difference, notably when there is a big temperature difference between inside and outside, not so much otherwise.
With the front of the house now properly insulated, I expect another substantial drop in heating requirement for 2021-2022. After that, the gains are mainly to be had by improving airtightness: reducing infiltration and make the MVHR run more efficiently.
... to be continued ...
