What is a VAV reheat system?

System Description Variable air volume (VAV) with reheat systems provide conditioned air to each zone at a constant temperature, typically 55°F. The amount of air varies to match the heat gain from equipment, lights- exterior and people.

What is VAV in refrigeration?

Variable air volume (VAV) systems enable energy-efficient HVAC system distribution by optimizing the amount and temperature of distributed air.

Why VAV system is efficient?

VAV systems are very cost effective from a chilled-water and heating-water-pumping perspective. Because the unit transfers heat to the space using forced convection, the coil heat transfer area required is reduced as compared to a chilled beam.

When should I heat up my VAV?

Reheat is used sometimes for humidity control, and sometimes for occupant comfort. The latter use happens when zone cooling loads are low and too much cold air is supplied to a space. In a VAV system, a damper modulates the amount of cool air supplied to the zone.

What is VCD in HVAC?

Volume control dampers (or VCDs) are specifically intended for heating, ventilation, and air conditioning systems to regulate the volume, flow, and pressure of air within the ducts.

What is VAV electrical?

Variable Air Volume (VAV) is a type of heating, ventilating, and/or air-conditioning (HVAC) system. The simplest VAV system incorporates one supply duct that, when in cooling mode, distributes approximately 55 °F (13 °C) supply air.

What do VAV boxes do?

The VAV regulates the volume of the air to the zone by opening or closing the damper, thus controlling the amount of conditioned air directed to the zone. Each zone in a building has a thermostat that controls the VAV, telling it when to open or shut the damper based upon the needs of the zone.

Do VAV boxes have condensation?

More moisture condenses on the coils, dehumidifying the air. Thus, although a constant-volume and a single-zone VAV unit maintain the same room temperature, the VAV unit provides more passive dehumidification and more comfortable space conditions.

What control strategy saves energy in a VAV system?

The optimal start strategy reduces the number of system operating hours and saves energy by avoiding the need to maintain the indoor temperature at occupied setpoint even though the building is unoccupied. A related strategy is optimal stop.

Where is reheat/recool allowed in ASHRAE?

Figure courtesy ASHRAE 90.1, 2013 Users Manual SIMULTANEOUSHEATING ANDCOOLING EXCEPTIONS(6.5.2) From 2010, reheat/recool is allowed in: VAV Lab Systems Where 75% of reheat energy is from site- recovered or renewable energy

Is reheat/recool allowed with DDC?

With DDC reheat/recool allowed provided: Deadband flow less than the max of 20% of the max SA flow Flow require for code ventilation Higher SA flow that reduce OA flow Higher flow to maintain pressure relationships Reheated/recooled flow ≤50% of max SA flow

What are the simultaneousheating andcooling exceptions?

SIMULTANEOUSHEATING ANDCOOLING EXCEPTIONS(6.5.2) With DDC reheat/recool allowed provided: Deadband flow less than the max of 20% of the max SA flow Flow require for code ventilation Higher SA flow that reduce OA flow Higher flow to maintain pressure relationships Reheated/recooled flow ≤50% of max SA flow