Cooling is also being included because today's construction standards have sufficiently reduced loads so that year-round cooling and heating systems can be installed at comparable costs to systems that only providing heating and ventilating. Load variations are dramatic and require automatic controls that can switch quickly from heating to cooling. For example, a typical classroom will switch from heating during the morning warm-up to cooling due to the heat from lights and occupants. In fact, it is not unusual for classrooms to cycle between heating and cooling several times a day during shoulder seasons. Control of temperature is more significant than humidity, assuming humidity is kept within acceptable levels.
Proper ventilation is necessary to control odors and reduce the spread of respiratory diseases.
Due to the diverse loads and space use, individual room control is important to a successful installation. Equipment should be capable of efficient operation at low and variable load conditions. Provision should also be made to shut outdoor air dampers when the space is unoccupied. School facilities must serve for 20 to 40 or more years of use, so high quality construction should be emphasized. Since schools do not pay taxes, system design economics should reflect life cycle cost analysis for the best taxpayer value.