RTU
In occupied mode, the RTU controls and adjusts the supply air temperature (SAT) to meet the SAT setpoint. The supply fan controls and adjusts the duct static pressure (SP) to meet the current duct SP setpoint.
The Verasys system supports an RTU-based occupied heating operation, in which the individual zones use their local heating first. The zone controllers use local heating if they are equipped with local supplemental or box heating.
VAV box
The zone controller uses hot water or electric box heat to maintain the zone temperature value within the cooling and heating setpoints. The zone controller does this with the VAV box. If the VAV box uses hot water heat, the building must provide hot water. If the VAV box uses electric box heat, the system initiates a user-set flow-based heating lockout according to the flow (Staged Reheat Min Flow). For example, if the user-set heating lockout flow is set to 200 cfm, the staged electric heating does not turn on if the flow drops below this value. When the zone temperature is above the cooling setpoint, the zone controller uses a pressure-independent strategy, or cascaded flow loop to adjust the zone temperature. When this strategy is used, the VAV box adjusts the supply flow to meet a flow setpoint. The zone temperature resets the flow setpoint. When the zone temperature drops below the occupied heating setpoint, the zone controller adjusts to meet the setpoint. This occurs when the zone damper is equipped with local supplemental or box reheat. Stage the optional box reheat or supplemental heating as needed to accomplish the zone temperature control. Supplemental heat is used before box reheat when both are present, unless the dual maximum strategy is used. The zone damper adjusts the supply flow to the occupied cooling minimum flow, when the zone controller uses supplemental heat. If the box heat is on, or if both box reheat and supplemental heat are on, the zone damper adjusts the supply flow to the occupied heating minimum flow. If the zone controller is not equipped with either supplemental or box reheat, the control modulates box flow to the occupied cooling minimum flow position. VAV boxes equipped with hot water reheat and a SAT sensor, use a dual maximum control strategy. When the zone temperature drops below the heating setpoint, the flow remains at the cooling minimum flow. The zone controller then resets the SAT from the current setpoint to the maximum setpoint. When the maximum SAT setpoint is reached, the flow setpoint resets from the cooling minimum flow to a heating maximum flow. On boxes equipped with both supplemental and box reheat, supplemental heat is used after box reheat.