VC-21-C009 -- Multizone Air Handler Controls Retrofit for Energy Efficiency

The DoD has thousands of older multizone units in operation, but often lacks sufficient resources for full system upgrades to more efficient modern designs such as variable air volume systems. A novel controls retrofit, presented here, is a significantly lower cost alternative to a complete system change out and can be an interim solution to meeting energy efficiency and DoD resiliency requirements within current limited budgets. The retrofit takes place primarily in the mechanical room and on the building control system, so is less disruptive to building occupants than a system changeout that requires vacating building areas during construction. The retrofit was demonstrated on five air handling units in 2 different climate zones over a one year period. The multizone types included the conventional 2-deck (hot deck/cold deck) and a neutral deck unit (i.e. with three decks). The controls sequences of operation turn heating or cooling down or off when not needed, modulate fan speed based on both most open zone damper position and ventilation requirements, and also close deck heating (or cooling) coil valves when no heating (or cooling) is called for by any zone. Sequences for both a fixed ventilation rate and for demand controlled ventilation were developed. The measured energy savings were impressive at 24-60%, but economic performance is mixed which indicates careful selection of retrofit candidates is required. This paper describes the retrofit design, demonstration methodology, performance analysis, applicability insights, and a suite of technology transfer support tools.