What Is A Hot Deck Cold Deck System

The hot deck is halfway open and the fan ramps up to maintain pressure in the unit.

What is a hot deck cold deck system.

This application note is relevant when using an ahu to control a multi zone air handler. Hot cold deck systems are found in older office buildings and in institutional buildings but are largely indistinguishable from other ahu based systems to the non technical observer. The hot deck cold deck. Some multizone units control one deck or the other in a multipoint arrangement such that the nearest to full heating controls hot deck temperature.

The ahu had both a cold deck cd and a hot deck hd where both maintained a constant leaving air temperature maybe 55 f and 95 f respectively with mixing dampers mounted on the front or top of the ahu. Temperature reset program is applied to dual duct systems and multizone hvac systems. Refer to photo 3 which illustrates damper actuators on a smaller mz system. In other systems the signal may.

Hot air and 55 degree f. Water and supply 100 degree f. Cold decks for providing heating and cooling capabilities simultaneously. As hot gas bypass will be required.

Therefore one actuator may operate the cold deck and hot deck simultaneously. Cool air through duct work to a terminal box. Up of two dampers one for the cold deck and one for the hot deck. Systems utilize a parallel arrangement of heating and cooling surfaces commonly referred to as hot and.

Typically the ahu controller also resets the hot deck and cold deck setpoints and controls the zone mixing dampers. Each zone requires an actuator application. The dual duct air handlers take 180 degree f. As the damper opens one deck it closes the other and vice versa.

As the signal approaches 0 the bypass deck is closed the hot deck is fully open and the fan is at full speed. In some systems this control may remain for example where the signal is a function of the thermostat branch line pressure. The cold deck is always closed during heating. As the call for heating reduces from full heat the hot deck starts to close the bypass.

And 42 degree f. The hot deck is reset based on the zone. Maintenance or operational staff will be able to advise whether a system is a hot deck cold deck type.