HVAC systems system control

Thermal expansion valve (TXV) The component in the HVAC system that controls the amount of refrigerant that goes into the evaporator. 

DQ is performed by the supplier of the equipment or system at the supplier s factory as part of factory acceptance test. IQ (based on site acceptance test), OQ and PQ are performed on-site at the GMP facility. For a GMP manufacturing facility, the validation activities include the facility design, HVAC system, environment control, laboratory and production equipment, water system, gases and utilities, cleaning and analytical methods. Validation protocols (IQ, OQ and PQ) are prepared for each item, listing all critical steps and acceptance criteria. Deviations are reviewed and resolved before the validation activity proceeds to the next phase. 

Replacement parts for most HVAC controls are available directly from the manufacturers or their authorized distributors. The decision regarding repair versus replacement of the device is easier for controls than it is for mechanical equipment in an HVAC system because controls usually are much less expensive—and the troubleshooting process often recommends replacement. In general, there are three scenarios for inoperable or damaged equipment ... 

EM-20 Periodically Recommission HVAC Systems and Control Systems... 

Periodically Recommission HVAC Systems and Control Systems Energy Management 60 1,080 100,000 92.6 m m... 

HVAC the HVAC system is not able to control existing air contaminants and ensure thermal comfort (temperature and humidity conditions that are comfortable for most occupants). 

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. 

The elements of a PM plan include periodic inspection, cleaning, and service as warranted, adjustment and calibration of control system components, maintenance equipment and replacement parts that are of good quality and properly selected for the intended function. Critical HVAC system components that require PM in order to maintain comfort and deliver adequate ventilation air include a outdoor air intake opening, damper controls, air filters, drip pans, cooling and heating coils, fan belts, humidification equipment and controls, distribution systems, exhaust fans. 

These sensors can be programmed to record data and to control multiple elements of the HVAC system. 

Air-handling units equipped with heat recovery and sophisticated control of the key parameters of HVAC systems, such as temperature, airflow rate, and pressure difference... 

In the current review, the term effectiveness of air distribution will be used to describe the ratio of the occupied zone area (where thermal comfort and contaminant concentration are within ranges required by standards and codes) to the total occupied zone area. This hygienic criterion allows one to judge how well the HVAC system fulfills its main task—creating thermal comfort conditions and controlling contaminants in the occupied zone. 

The actual noise levels produced by HVAC systems can var) considerably, and it is not possible to generalize the problems that may be encountered. From a safety point of view, it is advisable to start hearing conservation programs for workers. Permanent hearing damage will result when the noise levels exceed 80 dB(A) for a given time period. Whenever possible, it is desirable to control noise pressure levels to meet the requirements of speech communication in this case noise should not exceed 65-70 dB(A). 

Many HVAC system engineering problems focus on the operation and the control of the system. In many cases, the optimization of the system s control and operation is the objective of the simulation. Therefore, the appropriate modeling of the controllers and the selected control strategies are of crucial importance in the simulation. Once the system is correctly set up, the use of simulation tools is very helpful when dealing with such problems. Dynamic system operation is often approximated by series of quasi-steady-state operating conditions, provided that the time step of the simulation is large compared to the dynamic response time of the HVAC equipment. However, for dynamic systems and plant simulation and, most important, for the realistic simulation... 

The HVAC system is quite often not simulated but dimensioned on the space load results of the simulation by using simpler tools. However, aspects of control and the related potential for optimization are then neglected. 

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). 

In terminal areas, the air volumes are much greater, and typical HVAC filtration systems do not remove aerosol particles from the air as efficiently as do aircraft Environmental Control Systems (see Chapter 2). Thus, the costs and benefits of various enhanced filtration and air-cleaning strategies would have to be carefully assessed. An ancillary benefit to be considered would be the reduction of the transmission of common ills such as cold and flu viruses (or more serious viruses, such as the severe acute respiratory syndrome [SARS] virus) among airport patrons. 

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. 

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