Cooling Limit in Ideal Loads


Hi all,

I noticed that the Ideal Loads Air System object generated by honeybee always have the Cooling Limit set to ‘LimitFlowRate’ with the flow rate set to ‘autosize’. I understand that is necessary if i have an outdoor air economizer. But in one of my models (without economizer) that was limiting my cooling capacity and preventing me from achieving the temperature setpoint during certain periods. This was resolved once I manually edited the idf to set the cooling limit to ‘NoLimit’ and rerun.

Is there a way to change the cooling limit in Honeybee without needing to go into the IDF? I want to automate a series of parametric runs and having to manually change the idf will make that impossible.

BTW I found this old discussion that deals with it, but it relates to the older components

Many thanks,

Issue in keeping temperature

@GustavoB ,

Very good question and the best way that you can fix this issue is by making sure that your design day schedules actually reflect the worst-case scenario of the year. The reason why E+'s autosize feature is under-sizing your ideal air system is probably that the cooling design day schedules do not have the maximum equipment/people/lighting loads applied.

This said, I can see that it’s better to air on the side of usability, particularly for the ideal air system, which is the first HVAC template that many people will use. You are correct that the only reason why the LimitFlowRate input is set by default is to support the outdoor air economizer. So, when there is no economizer, we might as well set the system to have no limit. Accordingly, I have changed the default condition to put no limit on the size of the ideal air load system when there’s no economizer requested:

For the vast majority of cases, this will produce no change in results. But, for rare cases like yours where the autosized capacity from the design day was not enough to meet the thermostat during the annual simulation, it will fix it to meet the thermostat by default.

To help those people who may still want to limit the size of the ideal air load system, I have made the ‘airSystemHardSize’ input on the air details relevant to the ideal air loads system. So you can now hard size the ideal air loads system if you so desire.

I hope this helps,