Indoor Temperature 10°C Above Outdoor and 16°C Above Setpoint in ASHRAE Climate Zone 7 – HB Ideal Air

[Alice2]

Hi everyone,

I’m currently running building energy simulations across all 19 ASHRAE climate zones using Ladybug Tools in Grasshopper. For each climate zone, I’m using the software’s built-in default constructions that correspond to that specific zone. Apart from the construction sets and the EPW weather files, every other input is identical – same geometry, internal loads, schedules, HB Ideal Air settings, etc.

The simulations for most climate zones behave as expected: the HB Ideal Air system is able to keep the indoor air temperature within the cooling setpoint range. However, I’m seeing a very strange result that occurs only in Climate Zone 7. I’ve tested this with three different city EPW files from that zone, and the pattern is consistent:

• Overall energy consumption is very low.
• During summer, the indoor air temperature is roughly 10°C higher than the outdoor air temperature, and about 16°C above the cooling setpoint.
• In all other climate zones, the indoor temperature stays comfortably within the setpoint range.

This doesn’t make sense to me. It looks like the cooling system is barely working, yet the indoor temperature is far above the setpoint. Could this be caused by the default constructions for Climate Zone 7? Or maybe an interaction between the very low outdoor temperatures in that zone and the sizing/control logic of the HB Ideal Air system? Has anyone encountered something similar or have any idea what might cause such severe overheating only in this one climate zone?

Any help or suggestions would be greatly appreciated. Thanks in advance!

[chris]

Hi @Alice2 ,

The issue is probably that the ddy file associated with your EPW file has sizing criteria that is not as hot as the conditions in your EPW file. This can cause the cooling system to get auto sized to something close to zero for cooling capacity. Either you can check the DDY and create your own with more rigours cooling sizing criteria. Or you could use the HB Ideal Air component to set the _cool_limit_ to No Limit to ensure that there is always cooling capacity availble for the room.

[Alice2]

Hi @chris ,

Thank you for the suggestion!

I had actually already set the cool_limit to a very large number (100000000) on the HB Ideal Air component to simulate “No Limit” capacity. But even with that huge cooling capacity, the indoor temperature in Climate Zone 7 still floats 10°C above outdoor and about 16°C above the cooling setpoint.
I also tried changing the construction to the Climate Zone 1 defaults. The indoor temperature came down, but it still couldn’t stay within the setpoint. Do you have any other ideas what might prevent the ideal cooling system from engaging in a super-insulated building like this? It behaves like an overheating thermos bottle.

Appreciate your help!

Best,
Alice2

[Alice2]

The specific simulation results are shown in the figure.