Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
Your CAV air system with constant supply air temperature (SAT) isn't able to modulate cooling or heating provided to the space, since it's always at the same flow and temperature. This will make it very hard and inefficient to control your zone within specific temperature ranges. I would change the system configuration, unless you're trying to match an existing system.
With that said, the CAV air system does "turn on" and provide air when the zone's temperature is above the cooling setpoint or below the heating setpoint specified by the Zone Thermostat object. You CANNOT assign multiple thermostats to one zone in EnergyPlus (one to control the CAV and another to control the climate ceiling). To override the thermostat signal used by the CAV air system, you may have to use EMS Controls, which are complicated but allow you to do pretty much anything in EnergyPlus.
As a side note, using Ideal Load Air System is similar to connecting a zone to a black box that will meet heating and cooling loads with 100% efficiency. The object should really be used for sizing calculations so that you can assign better capacity values to zone HVAC components and avoid unmet hours.
| | 2 | No.2 Revision |
Someone has asked a similar question here.
Your CAV air system with constant supply air temperature (SAT) isn't able to modulate cooling or heating provided to the space, since it's always at the same flow and temperature. This will make it very hard and inefficient to control your zone within specific temperature ranges. I would change the system configuration, unless you're trying to match an existing system.
With that said, the CAV air system does "turn on" and provide air when the zone's temperature is above the cooling setpoint or below the heating setpoint specified by the Zone Thermostat object. You CANNOT assign multiple thermostats to one zone in EnergyPlus (one to control the CAV and another to control the climate ceiling). To override the thermostat signal used by the CAV air system, you may have to use EMS Controls, which are complicated but allow you to do pretty much anything in EnergyPlus.
As a side note, using Ideal Load Air System is similar to connecting a zone to a black box that will meet heating and cooling loads with 100% efficiency. The object should really be used for sizing calculations so that you can assign better capacity values to zone HVAC components and avoid unmet hours.
