Many government and institutional buildings have older multizone air handling units in operation but often lack sufficient resources for full system upgrades to more efficient modern designs such as variable air volume systems.

A controls retrofit that converts a multizone system into a variable volume system is a significantly lower-cost alternative to a complete system change out. It can be an interim solution to meeting energy efficiency and resiliency requirements within currently limited budgets while incorporating retro-commissioning efforts.

The retrofit occurs primarily in the mechanical room and on the building control system, making it less disruptive to occupants than a system changeout requiring vacating building areas during construction. The retrofit was demonstrated on five air handling units in two different climate zones over one year. The multizone types included the conventional 2-deck (hot deck/cold deck) and a neutral deck unit (i.e., three decks). The controls sequences of operation turn heating or cooling down or off when not needed. The fan speed is modulated based on both the most open zone damper position and ventilation requirements, The deck heating (or cooling) coil valves are closed when no zone calls for heating (or cooling).

Sequences were developed for both a fixed ventilation rate and demand-controlled ventilation. The measured energy savings were impressive at 24-60%.

This presentation describes the retrofit design, demonstration methodology, performance analysis, applicability insights, and a suite of technology transfer support tools.