the “cooling loads” as reported on the Read EP Results component is actually calculated based on the output variable
“Zone Ideal Loads Supply Air Total Cooling Energy J”
which is the sum of
“Zone Ideal Loads Supply Air Sensible Cooling Energy J”
and
“Zone Ideal Loads Supply Air Latent Cooling Energy J”
in the .csv result file.
However, I don’t know what “Zone Ideal Loads Zone Total Cooling Energy J” is as highlighted below in the csv file that is about 158kWh less than “Zone Ideal Loads Supply Air Total Cooling Energy J” …
Is it true that:
Zone Ideal Loads Supply Air Total Cooling Energy J
If it is the case, then how come Zone Ideal Loads Outdoor Air Total Cooling Energy is not reported in the .csv result file?
Another question is:
What is the output variable “Zone Ideal Loads Zone Total Heating Energy J” as shown in the csv file image above? Why does it have non-zero values, because the simulation result is for a building with no heating needs as indicated by the zero value for the output variable “Zone Ideal Loads Supply Air Total Heating Energy J”…?
As for your 1st question I guess the outdoor air is doing a little bit of pre-cooling this is why **Zone Ideal Loads Supply Air Total Cooling Energy **and **Zone Ideal Loads Zone Total Cooling Energy **are not equal.
As for your 2nd question I’m pretty certain that the following is true.
Zone Ideal Loads Supply Air Total Cooling Energy J
You can report **Zone Ideal Loads Outdoor Air Total Cooling Energy **as it is in the ZoneHVAC:IdealLoadsAirSystem Outputs you just need to add it to the IDF file and then run the simulation.
Do you have humidity control in your model? I would think that energy is being used to keep the supply air at a certain humidity.
I’m using the default apartment building program for the thermal zones, so I assume it may have a humidistat. Do you mean that the non-zero Zone Ideal Loads Zone Total Heating Energy is the one used to maintain the humidity level of the supply air?
I see that you are going through the crazy navigation of the E+ outputs for the ideal air system that took me over a year of trial and error to figure out (it is crazy how E+ has hundreds of outputs but lacks some of the really important ones). Hopefully, you can fet through this discovery faster then it took me. To go down the list:
The “supply air total coolng energy” is the energy removed by the ideal air “cooling coil” from the supply air stream (this supply air includes the outdoor air). As such, this output is the closest thing to the actual system cooling load that you can get from an ideal air loads model. The “zone total cooling energy” is the energy removed from the zone by the ideal air cooling system, which is fundamentally different than the energy removed by the cooling coil from the supply air stream (since the supply air stream includes outdoor air). The numerical difference that you see between these two outputs in your csv is the energy removed by outside air from the supply air stream.
Ironically, the statement that you have written is not true although it is what I thought when I first saw an ideal air output with “outdoor air” in it. The “zone outdoor air total cooling energy” is the energy removed from the ZONE by outdoor air coming through the ideal air system when it is in cooling mode. It is not energy removed from the SUPPLY AIR STREAM by the outdoor air, which is actually what we want to know most of the time to complete our energy balances. As such, I find the"zone outdoor air total cooling energy" to be a royally useless output. What is perhaps more frustrating is that EnergyPlus does not have an output for theergy removed from the SUPPLY AIR STREAM by the outdoor air and so I have to calculate this inside the readEPResult component by subtracting the zone cooling energy from supply air stream cooling energy.
We currently do not have humidity co trol but adding this should have a minimal effect as air based cooling systems already remove a lot of the humidity by having a low supply air temoerature. This said, humidity control is easy to implement if anyone wants to have a go at editing the ideal air system template that we use.
I was wondering if there was a simple explanation for a problem I have been having with getting surfaces to be evaluated. In the work that I was doing I was seeing surfaces that would not run, and when I changed the surface type in your sample file from “Ceiling” to “Roof” that surface does not display in the output.
I connected the Color Surfaces component to your model and all surfaces displayed. Changing nothing but the surface type of the ceiling to Roof, that surface disappears.
Is there something I am missing that is telling certain surfaces not to be included in the E+ calculation?
You are going to have to start your own discussion with a GH file that demonstrates the problem in order to be able to help you. I really can’t tell what is going on through your description.
Hi, @chris sorry for digging this old post, I have a query on your comment. I have no idea to understand the difference between “energy removed from zone by outdoor air” and “energy removed from supply air stream by outdoor air”. Is there any difference in these two value?
The Ideal Air System provides minimum outdoor air ventilation while also satisfying the thermal loads of the space. So you can conceptually think of the energy needed to heat/cool this minimum outdoor air as a separate term of the energy balance from the heating/cooling that the Ideal Air System does directly to the zone itself (eg. removing heat gains of people, lights, solar, etc).
In the case that a zone needs cooling and the outdoor air is cooler than the indoor air, the Ideal Air System system can also provide “free cooling” by just supplying the outdoor air directly to the zone (aka. an Air-Side Economizer). And this “free cooling” is “energy removed from zone by outdoor air”.
@chris Does it mean that two values are different only when oa has no need to be conditioned by hvac system, in this case system oa energy is 0 while zone oa energy still has value? Otherwise, two value is same?
@gogog ,
If you set the HB Zone ventilationPerArea and ventilationPerPerson to 0, then yes, these two outputs (supply air total and zone total) should be equal to one another. At that point, the Ideal Air system will only be satisfying the heating/cooling demands of the zone and not introducing any outdoor air into the zone.
Hi to all, new in the discussion but thinking on this IdealLoad system and its outputs since some days now. In order to understand clearly (and because I didn’t find it anywhere, so sorry if it exists) I made the following scheme to understand these outputs. Please, do you agree with the following scheme from your understanding ? It helped me to make the difference between the zone and the supply energy, the heat recovery and also by looking at the different mass flow rates.
Hi everyone,
I was just reading this post (which I find very interesting) and found information about some of the outputs that you were commenting. I leave you the link in case it is useful for you!
