I am running a simple EP (v8.3) simulation with ideal air loads and noticed that I was getting some latent cooling loads even though I have not set any humidity limits in the EPzonethresholds component.
Looking at the IDF, I noticed that all humidity settings under HVACTemplate:Zone:IdealLoadsAirSystem were left blank; which I took to mean no humidity controls were set up. I was wrong! EP was somewhat setting a maximum absolute humidity in the supply air, hence the latent cooling loads I got in the results.
I then went on to try and manually edit the IDF and put ‘None’ under Dehumidification Control Type. This resolved the issue and my supply air humidity is allowed to fluctuate to saturation (and only then there is some dehumidification)
Although I am not very familiar with coding, looking at the runEnergySimulation component, I think I small change in the code may resolve the issue to make sure that ‘None’ is specified if humidity limits are not set (see below). Hope this works!
original code
#Humidity Control
if zone.humidityMax != “”: dehumidCntrl = “Humidistat”
else: dehumidCntrl = “”
if zone.humidityMin != “”: humidCntrl = “Humidistat”
else: humidCntrl = “”
suggested change
#Humidity Control
if zone.humidityMax != “”: dehumidCntrl = “Humidistat”
else: dehumidCntrl = “None”
if zone.humidityMin != “”: humidCntrl = “Humidistat”
Thanks for realizing this and reporting. I added in the ability for humidity control with the ideal air system a couple of weeks ago. However, I failed to realize that the default humidity control when the field is left blank is not “None” as I would expect but “ConstantSensibleHeatRatio”. I agree that it should be none if no humidity setpoints are assigned.
I have changed this to now be “None” as you suggest:
I’ve the same problem. I’ve tried everything, but the latent cooling loads remain.
I tried to use the HVACTemplate:Xone:IdealLoadsAirSystem and the ZoneHVAC:IdealLoadsAirSystem and the problem is the same.
I put ‘None’ under Dehumidification Control Type, and as an alternative I changed the range of minimum and maximum air supply and I used the humidistat with a range from 0 to 100, but the problem remains.
You will always have some latent cooling as long as your cooling supply air temperature (usually ~13C) is below the dewpoint of the outdoor air.
Imagine that it is raining outside and it is 27C (so the dewpoint is also 27C). The indoor setpoint is 22C and the space needs to be cooled with air that is at a low temperature (13C) since the internal+solar gains in the space are high and you don’t want the flow rate and air velocity of your cooling supply air to be too high. To get the supply air to 13C, the cooling system will be cooling the incoming outdoor air far past its 27C dewpoint, meaning that some humidity will condense out of the incoming air. Accordingly, you will have latent cooling load even though you are not specifically trying to remove the humidity for “humidity control” purposes. Jute meeting the thermostat setpoint generated a latent load.
If you want to minimize the latent cooling load, you can raise your cooling supply air temperature above 13C with the Honeybee_Set Ideal Air Loads Parameters component like so:
Just bear in mind that you will have higher flow rates of cooling supply air because of this and higher velocities of supply air to the point that papers might blow around in some places. Also, your indoor air will have a higher humidity.
