The VZC changeover logic requires the following conditions to switch the system operating mode between Heat and Cool. In all scenarios, the timer for minimum time before changeover must be expired (Changeover Min Time).
- The system changes from heat to cool when:
- The number of urgent cooling requests exceeds the minimum number of urgent requests to change modes (Min Urgent Requests to Change) or the number of cooling requests, including urgent requests, exceeds the minimum number of requests to change modes (Min Requests to Change) and all heating requests have been satisfied.
- The system changes from cool to heat when:
- The number of urgent heating requests exceeds the minimum number of urgent requests to change modes (Min Urgent Requests to Change) or the number of heating requests, including urgent requests, exceeds the minimum number of requests to change modes (Min Requests to Change) and all cooling requests have been satisfied.
The logic for cooling requests ignores one heating request when determining if all the current heating requests have been satisfied. By ignoring one heating request, the cooling request logic prevents a single zone from forcing the system to remain in heat mode when the current cooling requests exceed the minimum number of change modes. The heating request logic also ignores one cooling request for the same purpose.
Urgent requests do not require that all zones are satisfied before changing modes. The system changes modes even if requests or urgent requests of the opposite mode occur.