HVAC
Heating Ventilation and Air Conditioning (HVAC) systems are the means to provide a an environment that is different from the outdoors. As humans we feel most comfortable within certain temperatures, humidity, air velocities (i.e. no draft) and require oxygen and little CO2 and other noxious gases. Even with a perfect envelope, we still need to have systems to create a good environment.
HVAC systems have to overcome these basic challenges:
- system must condition the space at very hot and very cold days; yet most of the operation will be on non-extreme days
- internal loads and usage can be unpredictable and fluctuate
- different parts of the building face different load patterns at different times. For example the west facade will gain more heat in the afternoon while the east facade will receive sunlight in the morning. Some spaces may be unoccupied during much of the time, requiring no conditioning, while other parts may require conditioning all the time.
- Heating and cooling may be required at the same time. For example core rooms may have a cooling load all year while perimeter areas require heating in winter.
- Moving large amounts of air costs energy. Many HVAC systems rely on moving air instead of water. but one unit of water can transport much much more energy than one unit of air.