Passive Hause Concept part 1
- Irene Ludovic
- Feb 9, 2023
- 3 min read
Updated: May 29, 2023
With the first plan draft of the house, I made a simple estimation of the passive character of the house. First, I determined the insulation of the house using the very useful app from the ubakus website [1]. For our original design, I obtained a heat transmission through the walls of 225 W/K. The heat losses or gains then depend on the average outdoor temperature (T(t)), which I took from the weather station of the Kanti Glarus [3].
The inside average temperature Tin was allowed to vary between 19°C and 26°C and adjusted each month to reduce the difference between input and output heat transfer.
For the heat gain through the south-facing windows, I used a simple vector geometry with the x-axis pointing east, the y-axis pointing north, and the z-axis pointing up. The idea is to calculate the heat gains and losses for a typical day in each month. For the position of the sun, I used the value of the 21st of the month.
The vector of solar radiation is given by:
The elevation angle epsilon and the azimuthal angle alpha were determined using data from the suncalc website [2]. For the intensity of solar radiation, I used data from the weather station of the Kanti Glarus [3], averaged over 2 years and over the days of each month. The data were fitted with a sinusoidal function. The reason for such a function is to reflect the expected attenuation by the Earth's atmosphere (proportional to path length) of the incoming radiation. The effect of the different shadow given by the Glarner mountains between the Kanti Glarus and the position of our new building is eliminated by using the fitted function and the no-shadow time for the integration.
The vector of the window is directed inward perpendicular to its surface and has the glass surface as its norm. For example, for a south-facing window with width b and height h, this gives:
The shading of the roof canopy and balcony of length d on the south side was then considered as a multiplication factor
A negative scalar product means that the window is in shadow, so we define:
The g-factor indicates the solar energy transmittance of the glass. Then we sum the contribution of each window and integrate it over the sunny part of the day. The sunrise and sunset considering the nearby mountains were taken from [4]:
For each month, I then obtained an average heat gain and loss through the wall and windows. In addition heat produced by the electrical equipment (~5.4 kWh/day) and the people living in the house (100 W per person over 12 hours per day) as well as the losses through ventilation (1/3 ) must be considered.
The shading effect causes the heat gains to be relatively constant throughout the year. Missing heat is observed in December-January, as expected, but also in April-May, probably due to the bad weather conditions in the reference years. The model allowed to optimize the protrusion of the roof and balcony for maximum heat gain in winter without overheating in summer. We obtain the optimal value of d=~1.35 m.
The missing heat can be partly compensated by the heat gained by the solar collector stored in the boiler. This can be simulated using the excel datasheet of jenni [5]. We obtain a solar coverage of a bit more than 100%, meaning that in average the solar energy gained directly through the windows or through the thermal solar panel covers all our heat needs (Heating and warm water). However due to weather fluctuations (typically a week without sun is possible in Schwändi) we will need a small auxiliary heater.
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