Carrier RTU OPEN 11-808-427-01 - Manual (Page 61)

RTU Open 55
If no heating or cooling is required or the current air source mode is satisfied, the VVT Master calculates the
weighted average of the occupied and unoccupied heating and cooling setpoints. It also calculates a zone
temperature that is midway between the setpoints (occupied or unoccupied based on the system’s current
occupancy status). This information, plus the occupancy status, is sent to the air source so that its current
mode is disabled and the unit ceases heating or cooling operation. If the system is occupied, the air source
fan and OA damper, if applicable, operate to maintain proper ventilation.
Linkage Air Source Modes
In a linked system, the air source determines its operating mode and qualifies that mode based on its own
Supply Air Temperature (SAT). The following modes can be sent by the air source depending on its
configuration:
•
Off – Air source fan is off
• Fan Only – Air source fan is on and providing ventilation (neutral SAT) without heating or cooling
• Economizer Cooling – Air source fan is on and providing cooling, using economizer only
• Cooling – Air source fan is on and cooling is provided by economizer and mechanical cooling
• Heating – Air source fan is on and heating is provided (gas or electric)
• Dehumidification – Air source fan is on and Humidi-MiZer™ is active
• Test – The RTU Open Service Test mode is active
• Shutdown – Air source fan is off due to Safety Chain, Fire Shutdown, or invalid SAT sensor
• Unocc Free Cooling – Air source fan is on, with the economizer providing cooling while unoccupied