Cooling Limit in Ideal Loads

#1

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
http://discourse.ladybug.tools/t/ideal-loads-outdoor-air-economizer/362/2

Many thanks,
Gustavo

1 Like
Issue in keeping temperature
Ideal Loads Cooling Limit [W]
#3

@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,
-Chris

#4

@chris

Hello together,

unfortunately I have a similar problem when trying to set a cooling limit for an Ideal Loads system.
My task is to investigate the temperatures in an office space with internal loads under extreme weather conditions. The space has a cooling system that was designed to cover a cooling load of 700 Watts (cooling set-point of 23°C). I would like to analyse if the cooling system/device with a capacity of 700 W is enough for the space and simulate the expected hourly temperatures for the given year/weather data.

Due to the fact that the actual cooling system isn’t clear yet, I would like to use the simplified Ideal Loads system in Honeybee. Matching with task described before I need to limit the system size/cooling capacity to 700 Watts. Within the actual Honeybee component the cooling capacity can only be limited by flowrate, which in this case I don’t know about. So I tried to adjust the inputs by making use of the relatively new Ironbug plugin, but my results are quite strange:

  • the air temperature for few hours can be maintained at 23°C, but that all of sudden is decreasing and reaching temperatures of approx. 29°C
  • the cooling load/power doesn’t go up to the previously defined 700 W and only reaches values around 500 W

My presumption is that there is some kind of mechanical ventilation that brings the hot outdoor air into the room (can also be seen when looking at the results for mech. vent. energy…)

My question now is

  1. if my approach to the given task is the right or if there is another, more elegant way (maybe without using ironbug) to investigate the problem?
  2. why do I have the outdoor air coming in even though I didn’t define that

I read all the other related posts about the Economizer, DDY etc., but all those hints didn’t lead to a solution.

Cheers,

/Tobi

Cooling_ideal_loads.gh (888.6 KB)