Heating is a process of transferring heat from a heat source, such as a furnace, heat exchanger, radiant panel or electric coil, to any space within a building.
Ventilation is the process of supplying air to any space within a building, without noticeable odors and without an objectionable level of contaminants, such as dust or harmful gases, and removing polluted air. Outdoor, or fresh, air is a generally acceptable source for ventilation air. Often, however, a mixture of fresh air and air present in a building is also acceptable. In either case the air may or may not be conditioned; that is, filtered and adjusted in temperature and humidity.
Air conditioning is the process of treating air to control simultaneously its temperature,humidity, cleanliness and distribution to meet design criteria for any space within a building. Air conditioning may be applied to raise the temperature of the space by heating or to lower the temperature by cooling.
Cooling is a heat-removal process and may also be accomplished without air conditioning.
For maintenance of a desired temperature within a space, heat usually must be added to or removed from the space. This heat is considered a load on the heating, ventilation and air conditioning systems. The component of this heat supplied by any
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source is considered the heat load on the space from that source.