High heating energy use during summer

grasshopper honeybee
1

Hello! I am a student who just started working with rhino/grasshopper, and now I have encountered my first problem, which is very high energy usage for heating during summer. I made a geometry for an apartment complex with three floors, and windows to the north and south. There is no internal walls, as the geometry is supposed to be as general as possible. The goal is to keep the amount of hours above cooling setpoint (26 degrees celsius) within a year to 50 at max. There is no active cooling in the building, so I have added window opening control. My ventilation system is ideal, and all heating is happening through there. I have set the values for window opening as seen in the picture, but despite windows closing at 23.9 degrees indoors, it looks like heating is starting (setpoint 21 degrees). Previously, I tried to add an economizer to the ideal HVAC system, but got warnings about overheated surfaces. The same happened when I tried to add a schedule for availability for heating, so it would not be available during summer.
I have also tried to increase the minimum outdoor air temperature, but then the hours exceed 50, and I will have to increase the operable fraction area for the windows, which again leads to more heating.

Right now the input to the IdealAir component is NoEconomizer, 0.8 for sensible heatrecovery, heat limit = no limit, cooling limit = 0, cooling available = always off.

windowopeningcontrol
windowopeningcontrol1270×591 124 KB

I have checked my U-values and everything seems fine. The values pictured above are the ones that are needed to reach the goal of less than 50 hours above cooling setpoint. The energy demand for heating at these values is simulated to be 42.7 kWh/m^2.
If there are any questions about any other values please don’t hesitate to ask!

If anyone has any advice on what to try, it would be greatly appreciated!

2

Hi @Emma15

Could you please let us know which climate you are simulating in, and provide a load balance graph for the model?

You haven’t specified a maximum indoor temperature or a maximum outdoor temperature at the moment… what are the defaults loaded in at the moment?

When I have had trouble with excess heating during summer when adding natural ventilation to my model, the cause has usually been that my HVAC setpoints and natural ventilation setpoints haven’t been well aligned, or that the minimum outdoor temperature has been too low.

I find that low minimum outdoor temperatures often result in unwanted heating in my results - even with granular timesteps in the simulation. -10 degrees is very low, I usually start to encounter problems when going below 15 degrees. I think this has something to do with way more cold air coming into the building than you would expect and then the building has to heat it back up, so the natural ventilation and heating systems end up fighting each other in the model, even though that seems pretty unrealistic to me.

It’s really strange that adding a heating availability schedule didn’t remove the heating - I’m guessing this could be because you are using ideal air, which doesn’t simulate an actual HVAC system but instead works out the energy flows in and out of the zones due to environmental conditions, and then how the building must respond to keep the net energy flow in/out balanced across the months and the year. But that’s just a hunch - what happens if you use a non-ideal air HVAC system and template with your heating availability schedule?

Anthony