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Heating and Cooling availability based on OA temp

asked 2017-10-31 16:48:17 -0500

nalassek's avatar

updated 2017-11-01 12:28:20 -0500

I'm running an energy model on an existing building built in the 1960's. The building is heating and cooling change over system that is manually changed over to heating or cooling mode based on space temperatures. However the control sequence says to change over to heating when OA temp is below 67 and Cooling with OA temperature is over 67.

I feel like it should be an availability schedule but i can not figure out how to implement it.

Would it be on each individual coil availability? (There are 9 AHU's with both heating and cooling coils and obviously the system only does heating or cooling at a given time)

Or would it be on the boiler/ chiller availability?


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answered 2017-11-01 12:27:33 -0500

There are a group of Availability Manager objects that turn loops off according to min or max temperature bounds. One example is the AvailabilityManager:HighTemperatureTurnOff, which you can apply to the boiler loop to turn off whenever the outdoor air temperature is above 67F. Likewise, you can also apply the AvailabilityManager:LowTemperatureTurnOff object to the chiller loop to turn off whenever the outdoor air temperature is below 67F.

Controlling the AHU's is tricky. Ideally, you would want the AHU supply fan to operate when the space temperature and outdoor air temperature both align i.e. (space temperature requires heating and outdoor air temperature is below 67F) or (space temperature requires cooling and outdoor air temperature is above 67F). Otherwise, the AHU supply fan may operate while the boiler or chiller loop is shutoff, so energy is wasted from supplying unconditioned air. To properly apply this control strategy for the AHU supply fan to operate according to both space temperature and outdoor air temperature, you will need to use EMS objects because there isn't a great Availability Manager that will work (AvailabilityManager:DifferentialThermostat comes close, but it will be difficult to control correctly).

If you are working in OpenStudio, you cannot define Availability Managers or EMS objects within the application. However, there are OpenStudio SDK objects that allow you to write an OpenStudio measure to add Availability Managers and EMS objects to the OSM.

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Asked: 2017-10-31 16:48:17 -0500

Seen: 4,729 times

Last updated: Nov 01 '17