HVAC systems control buildings

Indoor air contaminants can originate within the building or be drawn in from outdoors. If contaminant sources are not controlled, problems can arise, even if the HVAC system is properly designed and well-maintained. Sources can be from outside the building from operating equipment, from human activities, and other or miscellaneous sources. Sources outside a building include contaminated outdoor air, emissions from nearby sources, soil gas, or moisture or standing water. 

When local or central computers are used for controlling the operation of HVAC installations in buildings, they are described as building automation systems. In the control station, operators communicate with control installations, which are connected through the computer plant. Computers for individual use are called personal computers (PCs). The use of PCs for technical and economic tasks in the past few years has increased considerably. The business overflows with PCs, which get greater data power and memory at lower prices. 

To save energy, many HVAC systems employ a mechanism for regulating the flow of outdoor air called an economizer cycle. An economizer cycle takes advantage of milder outdoor conditions to increase the outside air intake and in the process reduces the cooling load on the system. Controlling the rate of flow of outdoor air appears simple, in theory, but often works poorly m practice. The small pressure drop required to control the flow rate of outdoor air is rarely controlled and monitored. Quite often, the damper system used to regulate the airflow is nonfunctional, disconnected from the damper actuators, or casually adjusted by building operators (Institute of Medicine, 2000). 

At all intakes for fresh air or HVAC systems to buildings in an electrically classified area according to the National Electrical Code (NEC) or subject to ingestion of combustible vapors. Especially if they are considered inhabited, critical or of a high value. Typically control rooms, critical electrical switchgear, or main process area power sources are provided with gas detection. 

Where it is possible for flammable or toxic gas or vapor released within a hazardous area to migrate to the inlets for HVAC systems serving nonhazardous enclosed areas such as control rooms, detection systems should be installed in those HVAC inlets or connecting ductwork. Detection should be provided in HVAC system intakes if the building, room, or enclosure served is not electrically classified and a flammable (or toxic) gas or vapor could feasibly be drawn into the area, either by mechanical ventilation systems or by differential pressures. The detection system should alarm and automatically shutdown the HVAC to prevent gas or vapor concentration in the protected space from reaching the flammable or toxic range. 

In the control and optimization of renewable energy processes, ambient humidity is one of the important parameters. Humidity also plays an important role in building controls and in minimizing the energy use of HVAC systems. Leonardo da Vinci was the first to attempt the measurement of humidity by weighing a ball of wool. Today, as shown in Figure 3.24, a wide range of humidity sensors is available. 

A temporary haven can be a room or building that, because of its design and construction, can provide protection to a few people for the expected duration of a toxic release. Usually control rooms in plants are set up as safe havens for operators, to enable them to effect an orderly and safe shutdown of the facility and isolate the source of the release. These control rooms are usually fitted out with special HVAC systems that can be shut down quickly, air intakes that close tightly, and a separate supply of breathing air capable of supporting the necessary personnel for an extended period of time. 

This hierarchical structure provides the foundation for information access that is, the information search capabilities that enable rapid access of, say, the calibration records for the Heating, Ventilation, and Air Conditioning (HVAC) system controlling zone 1 within the biochemistry building. 

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