Passive House
Overheating in a passive house? This a design concept that is not just for housing but also for commercial buildings. The objective is to create a building that creates the energy it needs and uses virtually no external energy. That demands sustainable solutions.
However, several post-occupancy studies of these high performance buildings report high temperatures when shading has been overlooked as the most frequent problem. So why is that and how do you solve it?
As the cheapest energy is the energy that you do not need, the design maximises the insulation and seals it to prevent heat loss.
To minimise the energy need for heating the system utilises free energy from the sun on bright winter days. That is done by having large areas of south facing glazing designed with low U values that allow the gain in and then trap it inside the building.
That is fine in winter but in summer the glass still acts as a heat collector and without shading overheating is inevitable and not just in summer, on bright winter days the design can be so efficient it can overheat then as well.
Shading has to be external and dynamic.
External as it has to be intercepted before it reaches the glass and moveable so that it will allow the heat gain when it is needed and prevent it when it is not. For internal comfort the Gtot value needs to be a minimum of 0.15 and preferably better than 0.10. (Gtot is the measure of the solar gain of the shading and glazing system combined.)
In the UK with decades of cheap energy we have not had to consider external shading or even how the sun actually works as we have solved the problem with air-conditioning or fans but think back to the days before mechanical cooling every shop in those old photos of the High Street had a shop blind to keep their produce cool. So external shading is up to date technology but a traditional solution utilising basic science.
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Trojan
