Three-deck Multizone Systems
The three-deck multizone system is a possible solution to overcome the energy inefficiency of the overlapping use of heating and cooling in a traditional multi- zone system.
The three-deck system is similar to the dual-duct and multizone systems, except that there is an additional (third) air stream that is neither heated nor cooled. Hot and cold air are never mixed in the three-deck system. Instead, thermal zones that require cooling receive a mixture of cold and neutral air, and thermal zones that require heating receive a mixture of hot and neutral air. The air flow control is shown in Figure 7.12. Thus, the three-deck system avoids the energy waste due to the mixing of hot and cold air streams.
The neutral air in the three-deck system is neither heated nor cooled and its temperature will change with the season. In summer, the neutral air will be warmer than the cold deck air. Consequently, the neutral air will take the place of the hot-deck air, eliminating the need for the heating coil in summer. In winter, the neutral air will be cooler than the hot deck, thus replacing the cold deck and the need for activating the cooling coil in winter. The net annual result is that there is no penalty for having heating and cooling coils operating simultaneously.