Hot gas reheatuses refrigerant leaving the compressor to reheat the air leaving the evaporator. This is done by channeling high-temperature, high-pressure air from the compressor through a hot gas reheat coil using hot gas reheat valves. Hot gas reheat is typically used in the dehumidification cycle to meet the required sensible temperature setpoint. Electric reheat can be also used for this purpose but it is energy-consuming.
Modulating hot gas reheat can precisely control the leaving air temperature of the air handler.
The following diagram is a schematic representation of a hot gas reheat system.
Hot gas bypass is used to provide a false load on the evaporator coil to keep the HVAC system running in low-load conditions. It prevents coil frosting during system operation at low load levels. A hot gas bypass valve reroutes the hot refrigerant from the compressor to the inlet of the evaporator. The use of hot gas bypass technology results in energy wastage. The problem of coil frosting can now be resolved with the help of variable capacity compressors or modulating compressors. Figure following is a schematic representation of a hot gas bypass system.
2018 Virginia Energy Conservation Code limits the usage of hot gas bypass systems in cooling systems. According to section C403.3.3 of 2018 VECC, It is not allowed to use hot gas bypass or any other evaporator pressure control system in cooling systems designed without multiple steps of unloading or continuous capacity modulation.