We have been modelling a purely passive building for the past few months, for the UK Future climate.
What we are finding is that the honeybee tools can pretty much get us 90% of the way there, however, some key control strategies are holding us back.
The below graph shows two very hot days. The night purge works well, combined with thermal mass. However, you can see that the CO2 in the space is quite low during the hottest period of the day, since the vents are effectively fully open. What we would like is for the vents to optimize the space conditions, allowing the CO2 to rise, to say 1000ppm, keeping the windows shut to keep the heat out. The same for the winter, we need to allow the CO2 to rise on particularly cold days, and the windows partially shut so the air temperature is more finely controlled.
Is there any way to do this currently? We are of course taking CO2 ppm from E+, using a custom string, but were not sure how to establish control of apertures to CO2 levels and internal temperature.
Once you start getting into complex control logic, the EnergyPlus EMS is going to be your friend. You should be able to accomplish what you are after by putting sensors on your CO2 monitor (and maybe on the Room air temperature node) and actuators on the windows.
It’s possible to do this all with additional strings if that is what you have gotten comfortable with but, if this were me, I would implement this by postprocessing the OSM using the OpenStudio SDK as it will take less overall effort and be more reusable.
Hi Chris,
Thanks for you reply. I’ve been going around in circles trying to implement this with the SDK (admittedly using co-pilot) first, and then with additional strings, but both have failed. It seems to struggle with the EMS: Actuator Schedule, flipping between ‘Constant’ and ‘Userdefined’.
Before I actually try and learn the idf, has anyone else already done something similar to this?
For now, i’ve essentially baked the control i want over the top of the aperture schedules, which works perfectly when looking at a few days of the year.
If I can suggest a good place to start with the EMS, try exporting your model with an AFN using the HB Airflow Network component. When you use the AFN in Honeybee, you’ll see that the resulting OSM/IDF has an EMS program within it, which is used to open and close the windows of the AFN based on the logic that you specify with the HB Ventilation Control component.
So, if you can understand this basic EMS program that opens the windows based on the room air temperature and (optionally) the schedule you apply with HB Ventilation Control, you can edit the EMS program to also have logic based on the CO2 sensor that you place in the room.
Or, yea, if the schedule in the Ventilation Control already gives you what you need to model CO2/occupancy related phenomena, then use that.
