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The Components Of Heating And Cooling Energy Loads

asked 2016-04-01 13:13:17 -0500

ngkhanh gravatar image

Hello, i would like to observe component load (monthly, daily, hourly) from internal load and HVAC system load in Energyplus like this load breakdown. I went through a lot different reports and variables but still did not fully get reasonable relation between the numbers.

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answered 2016-04-04 09:22:31 -0500

updated 2019-04-11 07:50:02 -0500

To report loads like this at different intervals, you will need to examine the RDD output file. This file contains a list of all possible output variables that can be reported to a CSV file and it changes depending upon what is included in your model (i.e. if there are no electric equipment objects, there can be no electric equipment outputs). Here are some outputs that you seem to be interested in:

Output:Variable,*,People Total Heating Energy,monthly; !- Zone Sum [J]   
  *Need to have **People** objects in model*
Output:Variable,*,Lights Total Heating Energy,monthly; !- Zone Sum [J]   
  *Need to have **Lights** objects in model*
Output:Variable,*,Electric Equipment Total Heating Energy,monthly; !- Zone Sum [J]   
  *Need to have **ElectricEquipment** objects in model*
Output:Variable,*,Surface Inside Face Conduction Heat Transfer Rate,monthly; !- Zone Average [W]   
  *Need to have **BuildingSurface:Detailed** or other opaque surface objects in model*
Output:Variable,*,Surface Window Heat Gain Rate,monthly; !- Zone Average [W]   
  *Need to have **FenestrationSurface:Detailed** or other transparent surface objects in model*
Output:Variable,*,Zone Infiltration Sensible Heat Loss Energy,monthly; !- HVAC Sum [J]   
  *Need to have **ZoneInfiltration:DesignFlowRate** objects in model*
Output:Variable,*,Air System Fan Air Heating Energy,monthly; !- HVAC Sum [J]   
  *Need to have fan object as part of air system in model*

For the ventilation sensible heat transfer, you should probably use the sensible heat gain output variable for the ventilation fan. This may require some more post-processing work if you have lots of zones or objects, as you'll need to add the outputs in the CSV output file to get a total value for each category in the model

The last input field before the semi-colon ";" in each output variable is the reporting frequency. They are currently all set to monthly, but you can change that or even have multiple instances of the same output variable with different reporting frequencies. If you want to examine what model objects these output variables correspond to, it's easy to do a Google Custom Search from the online E+ Input / Output Reference documentation.

image description


If you are only interested in seeing annual summaries of typical sensible load contributions in each zone, then add the Sensible Heat Gain Summary option to the Output:Table:SummaryReports object.

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@Aaron Boranian : Thank a lot for your suggest, I have some confuses about: 1/ As my understands, the energy means the sum in J while the "rate" is average intensive in W time (Wh, Wmonth, etc) and have same value in J as energy variable, is it right ? 2/How about the ventilation load (latent and load) ? i tried the Zone Mechanical Ventilation Cooling Load Increase Energy (formula??) to catch up cooling load but it's still not fulfill, may be Zone Air System Sensible Cooling Energy is ok but it's hard for me to separate the latent part of HVAC load system.

ngkhanh gravatar imagengkhanh ( 2016-04-04 13:37:12 -0500 )edit

@ngkhanh: Yes, kW-hr and J are both units of energy, while W is unit for power or energy/time. Energy is averaged over the reporting frequency (hourly, daily, monthly, etc.) in the output CSV file. The output variable for ventilation load depends upon your HVAC system. If it includes an air system, you will need air system ventilation output variables. If it includes zone-level HVAC (PTAC, window AC, etc.), you will need zone ventilation output variables.

Aaron Boranian gravatar imageAaron Boranian ( 2016-04-04 14:07:47 -0500 )edit

in case of zone-level HVAC, i still have question for breakdown ventilation load -Zone Mechanical Ventilation Cooling Load /Heating Load ...... what are their formulas ? is the sensible part of Zone Mechanical Ventilation Cooling Load ... included in Zone Air System Sensible Cooling Energy or Local system sensible Cooling Energy ? in general, i still did not clearly determine the relationship between the Zone Load and HVAC Load so i am not sure about my breakdown values.

ngkhanh gravatar imagengkhanh ( 2016-04-04 15:16:11 -0500 )edit

@ngkhanh: If you want to see equations, you'll need to examine the Engineering Reference. There is a section that covers the difference between zone and air system calculations and how they interact with each other ( From the Input/Output Ref, "Zone Mechanical Ventilation" output variables relate to OUTDOOR AIRintroduced in the central air system (

Aaron Boranian gravatar imageAaron Boranian ( 2016-04-04 17:05:21 -0500 )edit

answered 2016-04-05 07:02:02 -0500

You may want to look at the Zone Component Loads Summary which can be output when the Output:Table:SummaryReports, see:

Unfortunately, it only produces two of the twelve months that you are looking for. I suppose it could be repeated six times using different design day periods for six different simulations. A description of how the Zone Component Loads Summary is created is described in:

It also talks about the difference between space heat gains and loads. I would encourage you to review that section to see how the loads are estimated.

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Thanks i have reviewed them before load component summmary but it's for sizing not monthly or yearly. Moreover, it still requires me a lot efforts to definite likes the IntGainTypeOf_People due to lack of formula and explanation as my question in the mentioned thread

ngkhanh gravatar imagengkhanh ( 2016-04-05 07:48:28 -0500 )edit

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Asked: 2016-04-01 13:13:17 -0500

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Last updated: Apr 11 '19