Passive solar: insulated exterior shell

The better the insulation in the

• walls,
• roof,
• foundation,
• floors,
• doors,
• and windows,

(the shell of the house), the slower the leakage rate of heat or cold from the inside of the house to the outside, and vice versa.  To be more specific, heat always flows from the higher temperature to the lower temperature — so we don’t say that the cold escapes the house during hot summer days, but the hot flows to the house. Often it is initial cost considerations that determine the amount of insulation that gets added to a structure.  Even when the rest of the house as well insulated, it is often difficult (or even impossible) to insulate doors and windows to the same degree.  Therefore, these can cause one of the biggest heat loss or heat gain areas in a house.  A super-insulated, well-sealed structure with few or no openings would be extremely energy — efficient in that it would effectively conserve whatever heat or cold is inside the building.

Window openings for light and ventilation will decrease the amount of heat conserved, but can allow for solar gain — a free source of heating.  A building capable of collecting and storing heat in the colder months through passive solar absorption can balance out any loss in areas of lower insulation.  Furthermore, heat gain can be limited during the summer months when extra heat is a desirable if the house is properly oriented in order to work with the natural cyclic movement of the sun, receiving heat from some light in winter and excluding hot sunlight depreciating summer. You’ll read more about it in one of future posts about passive solar systems that is going to be posted here.

The exterior shell is insulated mostly with materials that have low thermal conductivity and therefore, high thermal resistance. For example, styrofoam and mineral wool have thermal resistances much higher than solid concrete block. It means that two walls of equal area and equal thickness would lose heat differently — heat losses would be much higher for the solid concrete wall than for styrofoam wall.