Schematic diagram in HVAC
The air-conditioning system considered so far provides a single source of air with uniform temperature to the entire space, controlled by one space thermostat and one space humidistat. However, in many buildings there is a variety of spaces with different users and varying thermal loads.
These varying loads may be due to different inside uses of the spaces, or due to changes in cooling loads because the sun shines into some spaces and not others. Thus our simple system, which supplies a single source of heating or cooling, must be modified to provide independent, variable cooling or heating to each space.
When a system is designed to provide independent control in different spaces, each space is called a “zone.”
A zone may be a separate room. A zone may also be part of a large space. For example, a theatre stage may be a zone, while the audience seating area is a second zone in the same big space.
Each has a different requirement for heating and cooling. This need for zoning leads us to the four broad categories of air-conditioning systems, and consideration of how each can provide zoned cooling and heating.
The four systems are
1. All-air systems
2. Air-and-water systems
3. All-water systems
4. Unitary, refrigeration-based systems
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