This chapter is not concerned with the theoretical aspects of heat loss or gain, or with heating and cooling calculations per se. This information is covered in Chapter 2 (“Heating Fundamentals”) and Chapter 4 (“Sizing Residential Heating and Air Conditioning Systems”). The purpose of this chapter is to describe the various types of insulation used in construction, the methods of applying insulation, and the thermal properties of building materials.
Insulating Structures
An uninsulated structure or one that is poorly insulated will experience a heat gain in the summer (or a heat loss in the winter) as high as 50 percent. The exact percentage will depend upon the materials used in its construction, because all construction material will have some insulating effect. In any event, it has been observed that approximately 30 percent of heat gain (or loss) is experienced through ceilings and about 70 percent occurs through walls, glass, and window and door cracks or as a result of air ventilation.
Any attempt to heat or cool an uninsulated structure will be terribly inefficient and expensive. Obviously, the possibility of anyone being so shortsighted as to attempt to install a heating or cooling system in such a structure is fairly remote, but inadequate insulation in existing structures or the failure to provide for proper insulation in proposed construction is a common occurrence. The provision for some form of barrier to reduce the rate of heat flow to an acceptable level is therefore of prime importance. Insulation materials serve this purpose with varying degrees of effectiveness. As much as 80 to 90 percent of heat loss (or gain) through ceilings and 60 percent of heat loss (or gain) through walls can be prevented by properly insulating these areas.
The inefficiency of ordinary building materials in resisting the passage of heat brought about the need for the development of materials specifically designed for insulation. A good insulating material should be lightweight, contain numerous air pockets, and exhibit a high degree of resistance to heat transmission. The material should also be specifically treated to resist fire and the attacks of rodents and insects. Finally, a good insulating material should react well to excess moisture by drying out and retaining its resistance to heat flow, instead of disintegrating.
Many inexperienced workers seem to feel that the more insula- tion one uses, the better the insulating effect. Unfortunately, this does not hold true on a one-to-one basis. For example, twice as much insulation does not insulate twice as well. Apparently a law of diminishing returns operates here. The first layer of insulation is the most effective, with successive layers decreasing in the effective- ness to impede the rate of heat flow.
The capacity of a heating or cooling system is determined by the amount of heat that must be supplied (heating applications) or removed (cooling applications) to maintain the desired temperature within the structure or space. In heating applications, the amount of heat supplied to a space at constant temperature should roughly equal the amount of heat lost. In cooling applications, the heat removed from a space should be roughly equal to the amount of heat gained. Both heat loss and heat gain will be controlled by the way in which the structure is insulated. Good insulation will reduce the rate of heat flow through construction materials to an accept- able level, and this will mean that a heating or cooling system will be able to operate much less expensively and with greater efficiency. It will also mean that the capacity of the heating or cooling unit you wish to install will be less than the one required for a poorly insulated structure. This, in turn, will reduce the initial equipment and installation costs. As you can see, this type and quality of insulation in a structure is an important factor to be considered when designing a heating or a cooling system.
The roof or attic floor of any structure can be insulated, as can the walls of any frame building, whether of stucco, clapboard, shingles, brick, or stone veneer. The form in which the insulation is applied depends on whether the structure is already built or is being constructed.