TECHNICAL FEATURE FIGURE 1 Example zone damper sequencing (proportional-only control). Conventional MZ Open Cold Deck Damper Hot Deck Damper Closed -4 -2 Setpoint 2 Zone Temperature (°F from Setpoint) 4 Closed Open Closed Open Bypass (Texas Style) MZ Neutral MZ Cold Deck Damper Bypass Damper Reheat Valve Open Hot Deck Damper Closed -4 -2 Setpoint 2 Zone Temperature (°F from Setpoint) conditioning will have a damper control signal that calls for the greatest damper opening to either heating or to cooling. The fan adjusts speed until this most needy zone damper is near full open to its needed coil (i.e., heating or cooling). The control scheme also disables the heating or cooling coil (closing the respective control valve) when not needed as indicated by the zone damper commands. The retrofi t is noninvasive in that it takes place primarily in the mechanical room and on the building control system, so is less disruptive to building occupants than a complete system replacement that requires vacating building areas during construction. The purpose of the retrofi t control scheme is to turn components down or off when not needed and may be applied to different types of multizone units. This results in both electric savings at the fan(s) and thermal load savings at the coils (i.e., a reduction in the energy FIGURE 2 Basic retrofit schematic with added items marked in red. Exhaust Air Airfl ow Measurement Array Outside Air AF MA Damper Actuator MA Digital Control Supply Fan SF VFD Variable Frequency Drive V Return Air Digital Control V T H C Hot Deck Cold Deck C C T Temperature Sensor Digital Control Typical Damper Actuator Digital Control Typ. Zone Stat N.C. N.O. To Each Zone Temperature Sensor 4 -4 -2 Setpoint 2 Zone Temperature (°F from Setpoint) transfer at the coils, which translates into fuel savings for the supplying heating and cooling equipment such as boilers or chillers). Fan Capacity Control The control scheme adjusts fan speed based on both space conditioning requirements and outside air ventilation requirements. Space Conditioning Requirements are dictated by the most open (to any deck) zone damper, where fan speed is decreased until one of the (multiple) zone dampers is at full or near-full open position. The zone dampers open and close based on deviation from the space temperature setpoint (Figure 1). The scheme reduces fan capacity until one of the zone dampers is near full open (by tracking the damper signal and targeting 95% as indication of near full open). The objective is to let the dampers open wide so the fan speed can be lower while 4 Neutral Deck Damper Cold Deck Damper 36 ASHRAE JOURNAL ashrae.o rg S E P T E M B E R 2 0 2 2 Damper Position Damper Position Damper Positionhttps://ashrae.org/