I have a model with 4 VRF terminal units on the same system that serve an entire floor. I zoned the floor by space usage since there are bathrooms, corridors, electrical/utility rooms, stairs, and a lobby. I do not wish to combine the zones. Is there a way to model 11 zones on 4 VRF terminals in OpenStudio 1.8?
No not really, each zone will need its own VRF terminal. It should be okay to model with 11 VRF terminals. It is common to do some abstraction where the modeled number of terminals is different than the actual number in the real building (though usually it works out to be fewer modeled units rather than more units the idea is the same).
As an advanced approach it would be possible to choose 4 of the largest zones and consider them "master zones" that get the VRF terminals (and good control). Then couple the remaining slave zones to a master zone with simple airflows using balanced pairs of ZoneMixing objects. The slave zones won't be under good control but their loads will get mixed into the master zone by movement of air between the spaces. The larger the airflow, the more tightly coupled the spaces will be.
Thanks @Archmage, I grouped the spaces together based on the terminal unit serving them. The terminal with 3 thermostats has vent fans in the electrical and restroom so I set 1 thermostat for the zone. I will see if I can add the vent fans with their own thermostat. Otherwise I can just add the fans to the spaces as plug loads.
Comments
Do you have 11 zones each with their own thermostat/control? Or have you got 11 spaces, which you could then group into 4 zones as you can have multiple spaces in a zone?
Here is a breakdown of my terminal units, rooms, and zones:
Terminal unit 1 - 3 rooms (lobby, stair, elevator); 4 thermal zones (lobby exterior, lobby interior, stair, elevator); 1 thermostat (lobby)
Terminal unit 2 - 4 rooms (corridor, stair, electrical, restroom) 4 thermal zones (corridor, stair, electrical, restroom) 3 thermostats (corridor, electrical, restroom)
Terminal unit 3 - 1 room (storage) 1 thermal zone (storage) 1 thermostat (storage)
Terminal Unit 4 - 1 room (utility) 1 thermal zone (utility) 1 thermostat (utility)
It strikes me as highly unlikely that a single VRF terminal unit would have 3 thermostats. I have never seen an installation with more than one stat per terminal unit.