Handbook of air conditioning and refrigeration / Shan K

3.2 CHAPTER THREE
3.1 BUILDING ENVELOPE
Building envelope consists of the building components that enclose conditioned spaces. Heat,
moisture, and contaminants may be transferred to or from the outdoors or unconditioned spaces and
therefore affect the indoor environment of the conditioned space.
Building envelope used for air conditioned space in buildings consists of mainly walls, roofs,
windows, ceilings, and floors. There are two types of partitions: exterior partitions and demising
partitions. An exterior partition is an opaque, translucent, or transparent solid barrier that separates
conditioned space from outdoors or space which is not enclosed. A demising partition is a solid
barrier that separates conditioned space from enclosed unconditioned space.
● An exterior wall is a solid exterior partition which separates conditioned space from the outdoors.
Exterior walls are usually made from composite layers including any of the following: stucco,
bricks, concrete, concrete blocks, wood, thermal insulation, vapor barrier, airspace, and interior finish.
The gross exterior wall area is the sum of the window area, door area, and exterior wall area.
● A partition wall is an interior solid barrier which separates a conditioned space from others. Partition
walls are usually made from interior surface finishes on two sides, wooden studs and boards,
concrete blocks, concrete, bricks, and thermal insulation. A demising partition wall separates a
conditioned space from an enclosed unconditioned space.
● Wall below grade is a solid barrier below ground level which often separates a basement or a
crawl space from soil.
● A roof is an exterior partition that has a slope less than 60° from horizontal and has a conditioned
space below directly or through a ceiling indirectly. Roofs are usually made from clay tile, waterproof
membrane, concrete and lightweight concrete, wood, and thermal insulation.
● A ceiling is an interior partition that separates the conditioned space from a ceiling plenum. The
ceiling plenum may or may not be air conditioned. Ceilings are usually made from acoustic tile or
boards, thermal insulation, and interior surface finishes.
● An exterior floor is a horizontal exterior partition under conditioned space. A floor placed over a
ventilated basement or a parking space is an exterior floor. Exterior floors are usually made from
wood, concrete, thermal insulation, and face tiles.
● Slab on grade is a concrete floor slab on the ground. There is usually a vapor barrier, thermal
insulation, and gravel and sand fill between the concrete slab and the ground.
● A window is glazing of any transparent or translucent material plus sash, frame, mullions, and
dividers in the building envelope. Glazing is usually made from glass and transparent plastics.
Frames are often made from wood, aluminium, and steel. The window area is the area of the
surface of glazing plus the area of frame, sash, and mullions. A fenestration is any area on the
exterior building envelope which admits light indoors. Fenestrations include windows, glass
doors, and skylights.
● A skylight is glazing having a slope of less than 60° from the horizontal. There is often a conditioned
space below skylight(s).
3.2 HEAT-TRANSFER FUNDAMENTALS
Heat transfer between two bodies, two materials, or two regions is the result of temperature
difference. The science of heat transfer has provided calculations and analyses to predict rates of
heat transfer. The design of an air conditioning system must include estimates of heat transfer
between the conditioned space, its contents, and its surroundings, to determine cooling and heating
loads. Heat-transfer analysis can be described in three modes: conduction, convection, and
radiation.