Central system air is usually supplied to a zone through a terminal unit such as a single duct VAV reheat box. Sometimes, however, it is desirable to supply central system air directly to a zone without any zone level control or tempering, e.g. when used in conjunction with a unitary packaged system.
The CAV No Reheat ADU allows central system air to be supplied directly to a zone without any reheat. The data required for the unit consists of the unit name, availability (on/off) schedule, and a maximum flow rate. Settings to control outdoor air provision can also be made.
For the units to work correctly, it is important in any systems including CAV No Reheat ADUs for the sum of the maximum zone air flow rates to be equal to the maximum central system flow rate. The central air system flow rate is specified in the air loop AHU data.
Important Note: In spite of its name, the CAV No Reheat ADU can be used in HVAC zones connected to either constant or variable air volume air loops. When used in a VAV loop the supply flow provided by the unit will be fixed at the value of the Maximum air flow rate setting.
This is a read-only label that is automatically generated by the software and which incorporates the name of the zone in which the ADU is located.
The design maximum volume flow rate (in m3/s or ft3/min) specified for the Direct Air ADU. This field may be auto-sized.
If this option is selected, the terminal unit will increase flow as needed to meet the outdoor air requirement specified on the HVAC zone dialog. If Outdoor air flow per person is non-zero, then the outdoor air requirement will be calculated by the software based on the current number of occupants in the zone. At no time will the supply air flow rate exceed the value for Maximum air flow rate. If this option is not selected, then the terminal unit will not be controlled for outdoor air flow.
When the above Control on outdoor air flow checkbox is checked, this option is used to select how outdoor air ventilation rates are calculated when based on a rate per person. It can be either based on the current number of people as affected by time-varying occupancy schedules, or on the constant value for the maximum number of people. Choose one of:
Note: this setting is only used when outdoor air ventilation rates are calculated when based on a per person rate.
This is the schedule that determines whether or not the unit is available for each timestep of the simulation. A schedule value greater than 0 (usually 1 is used) indicates that the unit can be on during the timestep . A value less than or equal to 0 (usually 0 is used) denotes that the unit must be off for the timestep .