Heatwave performance charts

From the data that we have collected from the Silverton Passivhaus since May, the most interesting period, in terms of the house’s performance, was during the heatwave in July. We saw temperatures in excess of 32 degrees which is a good test for the Passivhaus principle but also for the design input that we as a company have had on the building. If you want to download a drawing of the house, please click here for the PDF or click here for the data.

The house contains around 120 tonnes of concrete and steel that are fully within the insulation envelope. There are also around 20 tonnes of clay boards and around 6 tonnes of Fermacell boards which also add to the mass. The house uses a lot of wood fibre insulation wool and wood fibre boards for insulation. These have high thermal mass and should help keep the house cool in a heatwave.

The charts below, apart from looking like my 2 year old daughter has had a go with some colouring pens, show how the temperature varied with time during the heatwave in July this year.

This chart shows the South elevation. You can see from sensors 3 and 4 that the outer wood fibre boards are absorbing a lot of the heat from the direct sunlight with variations of around 15 degrees at sensor 4 (40mm below wall outer surface), 5 degrees at sensor 3 (140mm below wall outer surface) but buffering it so effectively that on the interior the variation is down to around 2 – 2.5 degrees. The exterior variation was up to 20 degrees between day and night and even during the day it is likely that there was at least a 20 degree difference between the inside and outside surfaces during the day.

The East and West face data set show relatively similar behaviour but that missing data from sensors 3 and 4 on the East face makes it difficult to see clearly how the wall behaved.

This data from the North wall shows the variations well but the temperatures experienced by sensors 1 and 2 is a couple of degrees higher that the interior temperature because there is a fridge nearby heating the area. Internal temperatures tended to peak when cooking happened in the evenings as the internal sensor was located near the kitchen area.

Overall the wood fibre insulation has performed well and done what is was supposed to have by keeping the building at a comfortable temperature inspite of high external temperatures. It would be great to be able to compare this to other Passivhaus buildings built with different materials to see how much is material dependent and how much is design dependent.

For more information on the Unger-Diffutherm wood fibre products see http://www.backtoearth.co.uk/products/unger-diffutherm-woodfibre-insulation-systems.

Chris Brookman
Chris Brookman