What Is a Hot & Cold Deck HVAC System?

Function

• HVAC deck systems use hot and cold decks to manage the intake of outside air and the output of indoor, conditioned air. For large HVAC systems, hot and cold decks are an efficient way for handling and conditioning hot and cold air according to the needs of each building zone. Generally, air traveling over cooling coils is pushed into one duct holding cool air. Air traveling over heating coils is pushed into another duct storing hot air for ventilation. A mixture of cool and hot air can also be supplied as the hot deck damper opens and the cold deck damper closes.

Types

• HVAC systems can be set up with different duct systems for conditioning and distributing hot and cool air. Single-duct or multizone systems use one duct for each building zone or area. Air handlers in multizone systems typically supply air temperatures for multiple zones simultaneously. Dual duct systems use parallel ducts to direct hot and cold air into separate mixing boxes. Similar to one-duct systems, each mixing box customizes the air temperature according to each zone’s needs. Variable hot and cold deck systems modify the volume of air supplied to zones based on heating and cooling loads in the building. Whereas air volume in traditional duct and multizone systems is constant, variable air volume (VAV) systems can adjust air volume levels constantly.

Benefits

• Hot and cold deck systems offer significant flexibility and control for regulating air temperatures for different rooms and areas of a building. Unlike single-zone systems, multizone and dual-duct HVAC systems supply varying temperatures for more than one zone simultaneously. VAV hot and cold deck systems are particularly energy-efficient since hot and cold decks are linked to thermostats. As the temperature increases and decreases, air volume is adjusted. This allows the system to respond easily to heating and cooling changes in the building and avoid wasting unnecessary energy.

Disadvantages

• Though hot and cold deck HVAC systems are more versatile than simpler, single-zone units, they are also more complex. Most air handlers in hot and cold decks in HVAC systems are limited to 12 zones, according to the UC Berkeley publication “Vital Signs: HVAC Components and Systems.” Buildings requiring HVAC systems servicing over 12 zones must install additional air handlers, which can increase operational costs. Moreover, VAV units are considered energy-efficient, but they can also degrade indoor air quality. Reducing fan power results in poor air circulation between zones. Check your manufacturer’s recommended minimum airflow settings for VAV units to maintain indoor quality and benefit from energy savings.