Preventing simultaneous heating and cooling in OpenStudio

asked 2021-06-22 14:46:16 -0500

bchoi gravatar image

updated 2021-07-09 16:33:01 -0500

Hello. I am working on a residential home with two HVAC units - a gas furnace for heating and a whole house fan for cooling. The heating setpoint is 69 deg and the cooling setpoint is 78 deg. For their HVAC operation schedules, I selected "Always Off" and set night cycle to be "Cycle on Full System if Heating or Cooling Required" - I did this to activate the units only when the zone setpoints are not met. image description

However, I noticed in the results that both heating and cooling were activated at the same time. It looks like heating would also turn on when cooling is needed and vice-versa. I concluded this by seeing that 1) zone conditions were worse than when there was no unit at all, 2) gas consumption was higher during the summer. I am guessing OpenStudio does not separate heating and cooling requirements. Also, I don't think OS realizes that the gas furnace unit is heating only and the house fan is cooling only. I have the unit screenshots below along with their setpoint managers - maybe I am using wrong setpoint managers? I took the min and max values as desired zone temperature ranges.

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Would there be a good strategy to prevent simultaneous heating and cooling in my model? There is no set unit on/off schedule as the operations solely depend on meeting the temperature setpoints. Also the home occupancy is 100%.

Thank you so much!

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@bchoi have you reviewed time series outputs to make sure that cooling and heating are provided simultaneously? You will need to generate outputs at a "Timestep" frequency, anything longer would be an average of multiple timesteps and be misleading.

Aaron Boranian gravatar image Aaron Boranian  ( 2021-06-23 08:38:17 -0500 )edit

@Aaron Boranian I saw that both heating and cooling HVAC unit fans are operating at the same time in Data Viewer time series plots. It looks like the "Cycle on Full System if Heating or Cooling Required" setting is prompting both units to turn on at the same time when zone temps are not met.

bchoi gravatar image bchoi  ( 2021-06-23 18:05:16 -0500 )edit