Overheating problems.

I have previously written about the importance of designing for the weather with the climate in mind. A sensible approach is to deal with both winter heating and summer cooling conditions.

For all the knowledge, technology and computer simulations having been conducted throughout the world over the last 20 years, we have still been getting it wrong. The decision that a winter heating dominated climate needs only to be designed for heating is a bad idea. The decision that massive amounts of solar heat gain for winter is good is also a bad idea. The recent change to the NCC to nominate a maximum cooling load is a direct result of having designed for winter only.

For a bit of an insight of how the rest of the world has been getting it wrong too, read the following articles, the first one from England:

Too many modern buildings are built with too much glass and poor ventilation, leaving them at risk of overheating in summer.

“More than 90 per cent of our population live in urban areas and as we have all been experiencing, heat is a significant problem,” said Baroness Brown of Cambridge, deputy chair of the committee.“We know it’s bad for productivity, we know it’s bad for wellbeing and we know it’s bad for health, yet building regulations don’t cover heat and the management of high temperatures.”

Buildings should be designed “not only to be well-insulated for cold weather but also to address management of high temperatures”, Baroness Brown said.

On my recent trip to America I had discussions along these lines with building Scientist, Justin Wilson. Justin raised the issue of unrestrained window solar heat gain and the effect that it has on a modern, well insulated and airtight building. He also mentioned his personal experience of living as a child in a 1970’s passive solar house in the North of America. “The house had so much *south facing glass that it overheated to the point where we had to open windows. At the same time the rest of the house was freezing. When the sun wasn’t shining the glass just acted as a big heat loss”. Justin’s parents still live in the house but it has since been renovated to decrease the glazing area, increase the insulation and improve the air tightness.

Building science aficionado, Professor Mark Bomberg has also written papers addressing this issue. The following excerpts are from his paper titled, A concept of integrated environmental approach for building upgrades and new construction, II: introducing the passive house plus1 concept.

1.2 The art of forgetting the lessons of past

The term “passive building” has now become the readily used and even fashionable slogan. Yet, a few people remember that this name was originally related to passive solar systems and was introduced by Shurcliff (1982,1988). Passive solar system is present in each building, if there is a glazed area. Unless adequate measures are provided in design excessive solar gains may result in unbearable overheating. While the passive solar energy use strategy is nowadays better understood, protection of the building against overheating is usually left to the final stage of the design process or even completely disregarded. To achieve a balance between solar gains and overheating and in the same time ensure high quality of indoor environment (Kisilewicz, 2015) becomes a part of the environmental control design.

3. Buildings must be designed for both heating and cooling

Cold climate design is often limited to the heating period. In doing so an architect places large areas of south-oriented windows to supply solar energy and thus minimizing the demand for heating. But in fact air temperature and thermal comfort in a highly insulated building are very sensitive to the local conditions. Optimum glazing area for heating may contradict optimum for cooling and the cooling load may even exceed the demand on heating. Results, presented prove that rational window sizing decision must be based on the technical characteristics of the building shell and climate conditions for both summer and winter. Large energy gains that are not absorbed with thermal capacity create unbearable conditions or big cooling load in living spaces (Cooper, 1997; Pfafferot et al., 2007).

So, what’s the upshot of all this? Well, we need to design for both winter and summer. We need to carefully address the solar heat gain through windows and be careful when we talk about passive solar. We can entertain and employ the passive solar concept but not treat it in isolation. As professor Bomberg says, “The more optimized for energy and comfort the building system is the more holistic must its design process be”.

The good news is that we don’t need endless computer simulations and WUFI analyses to determine a good holistic solution. Common sense and a decent knowledge of building physics goes a long way.


*south facing glass in the northern hemisphere = north facing glass in the southern hemisphere.