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HVAC Systems
Published in Kathleen Hess-Kosa, Indoor Air Quality, 2018
To further complicate and confuse, some level of awareness and knowledge is prudent when assessing an HVAC system. A single HVAC system may have one or several zones, each of which has its own temperature control (e.g., thermostat), and each zone will have its own dedicated air distribution box. The distribution boxes are sites where dust, air contaminants, and moisture can and do collect. Distribution boxes are briefly described as follows: Constant air volume (CAV)—varies temperature of the air delivered to the occupied spaces; temperature is regulated by controlling delivery of heated and cooled air to a mixing box for each zone according to its requirements; and mixing box may collect, retain, and distribute air contaminants.Variable air volume (VAV)—varies air volume delivered to the occupied spaces as demand needs vary by zone; possible failure to receive adequate makeup air as required by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) Standard for Ventilation for Acceptable Indoor Air Quality.Hybrid systems—the best and the worst of both CAV and VAV.
Heating, Ventilating and Air Conditioning Systems
Published in Stephen A. Roosa, Steve Doty, Wayne C. Turner, Energy Management Handbook, 2020
The air handling system may have been designed to provide a constant amount of air to each zone as dictated by cooling and heating load, space temperature, and ventilation requirements. This type of system is known as a constant air volume (CAV) system. A CAV system will then modify the temperature of the air to each space to maintain space temperature setpoint as loads and occupancy vary. Heating may be from a central heating coil (single zone) or individual heating coils in zone branch ducts.
HVAC Control Systems
Published in T. Agami Reddy, Jan F. Kreider, Peter S. Curtiss, Ari Rabl, Heating and Cooling of Buildings, 2016
T. Agami Reddy, Jan F. Kreider, Peter S. Curtiss, Ari Rabl
The preceding five example systems are actually control subsystems that must be integrated into a single control system for the HVAC system’s primary and secondary systems. In the remainder of this section, we briefly describe two complete HVAC control systems widely used in commercial buildings. The first is a fixed-volume or constant air volume (CAV) system, and the second is a variable air volume (VAV) system.
A fast building demand response method based on supply–demand coordination for urgent responses to smart grids
Published in Science and Technology for the Built Environment, 2019
Chen Jin, Chengchu Yan, Rui Tang, Hao Cai, Ruixuan Zeng
Significant power savings can be achieved by controlling the power consumption of distribution equipment, including air distribution fans and water distribution pumps. For variable air volume (VAV) systems, the power consumption of variable-speed fans can be reduced during DR events by reducing the duct static pressure set-point (Rotger-Griful et al. 2016). For instance, using this static pressure resetting strategy, fan power and cooling energy during DR events can be reduced (Motegi et al. 2007; Wang and Tang 2017). Limiting the speed of fans with variable frequency drives (VFDs) can also be used for fan power demand. Hao et al. (2014) proposed a DR method using a fan speed limiting strategy and showed that up to 15% of fan power capacity can be deployed for DR purposes. For constant air volume (CAV) fan systems, the only way to reduce fan energy is by shutting off multiple fans or package units (Goddard et al. 2014). For implementing DR in pumps, similar approaches (such as resetting the pressure of the pump head and limiting the pump speed) can be applied to chilled water distribution pumps. For instance, Tang et al. (2016) proposed a demand response strategy by limiting the speed of pumps for power reduction.
Computational psychrometric analysis as a control problem: case of cooling and dehumidification systems
Published in Journal of Building Performance Simulation, 2022
A constant air volume (CAV) mixed-air system supplies a fixed mass flow rate of air, , usually to a single space or thermal zone (Stanke 2000; TRANE 2002). The aim of sizing is to find the thermal load of the cooling coil and its Apparatus Dew-Point ADP (Eppelheimer 2002), and the thermal load of the reheating coil (if supply air tempering is used).