Most outside walls are insulated between the exterior sheathing and the interior drywall. In the middle of such a wall, the temperature will be somewhat cool to touch in the early morning. However, if you go to the corner of such a wall, where two outside walls meet, you will likely find the corner to be noticeably colder. This is not just your imagination playing tricks on you, and it is not random. It is geometry performing mathematics on your heating bill.
The reason why corners of buildings are weak spots is because of thermal bridging. Every structural element (corners, junctions, lintels) is a thermal bridge: they connect inside of a building to the outside air. Heat always travels from warm to cold, so inside of the building to the outside air. In the case of a flat wall, the heat travels in one direction. But in the case of a corner of a building, where two outside walls meet, the heat travels in two directions. So the same volume of inside air is spread over a much smaller area. The same is true for the junctions between floors and ceilings. The Energy Saving Trust explains how heat escapes through junctions and corners in more detail than you could possibly want. It’s dire reading, especially the numbers. It shows that even though these weak spots only take up a tiny percentage of the surface area of a building, they can account for a large proportion of a building’s total heat loss.
The amount by which heat is transferred through a structural link is measured by the building scientist and expressed as a psi value (psi is the Greek letter ‘sigh’). Psi values express the amount by which the heat transfer through a structural link exceeds that through the surrounding building envelope, on a per meter basis. The worst of these values were in the mid 20th Century discovered by engineers who were measuring the heat loss from building envelopes. They found that the worst heat loss occurred at the corners of the building and were amazed at the amount of mould and mildew that grew at these locations. The building scientists found that the surface temperature at these locations were so low that the moisture in the air was condensed at these locations even when the rest of the building was at a comfortable temperature.
It is important to note that a duct work layout that does not account for the corner(s) of a building can cause those areas to be starved of conditioned air. A well placed supply register can be used to force air into these areas where it is needed to counteract the effects of thermal bridging.
More on HVAC Williamsport PA can be found at qualityairmechanical.com/hvac.
The cold corner is not a mystery – it is the building revealing its weakest spots.
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