Knowledgebase
Why do I get heat transfer through adiabatic partition/floor/ceiling surfaces?
Posted by Andy Tindale on 08-Jun-11 02:22 PM

It may not be immediately clear why there are heat gains through partition/floor/ceiling surfaces when they have been defined as adiabatic, i.e. no heat transfer. The reason is that the adiabatic boundary is on the outside of the surface and so heat can still flow into and out of the thermal mass. Over the course of a hour/day/week timescale there can be net positive or negative heat flow into the structure. Over a year though the heat flow should be very small compared to other heat flows in the zone.

Note that the surface heat transfer data displayed at building, block and zone levels for floors, ceilings and partitions is based on heat flow at the interior surface of the structure. So in short the heat flow associated with adiabatic surfaces in the DesignBuilder results represents the heat flow into/out of thermal mass.

So while adiabatic boundaries don't conduct heat, surfaces defined with adiabatic boundaries will always affect the the building thermal dynamics due to additional thermal mass and surface area exchanging heat with the rest of the zone.