August 1st, 2007

Ann Vole

Heat diode insulation for hot climates

Air gaps of 1/2 inch (12mm) or more that have at least on surface being reflective have an insulation value of about R1 for "heat flow down" (0.980 for 1 reflective surface 1.034 for both reflective) but less then 1/3 that for "heat flow up" (0.324/0.322 1/both reflective) This means for hot days, you can get R2 per inch for simple air gaps but that R value drops way down when the outside air is cooler then the house.

A study on how people feel in rooms with different temperatures for the different surfaces in a room found that a hot ceiling caused way more discomfort then a hot or cold wall or a cold ceiling. This means that the biggest improvement for the least cost for comfort in hot seasons is ceiling insulation and other means to make the SURFACE of the ceiling to be cool (this is based on sensations of hot and cold based on radiant energy reaching the person). I would like to try different ceiling configurations and in-ceiling air flows to keep the ceiling and the rest of the room as close to the desired temperature as possible... This might eliminate the need for air conditioning and humidity reduction simply by having cool surfaces (as long as those surfaces can handle condensed moisture which plastic or aluminum foil can handle quite well). One thing that brought this to my attention is the complaint by one of my tenants that the basement is real hot where as I find the basement quite cold... He is sensing the hot ceiling in the basement from the floor of the hot first floor instead of the actual temperature of the basement air.