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# E+ vs. IES: Loads Results comparison

I am trying to do a comprehensive analysis between the two software, IES VE and E+ (Grasshopper), regarding the Zone Loads. I know that a diffrent method is used for IES (CIBSE) while E+ uses other standards. So far I managed to model and simulate a test building, with the same inputs in both. The results I am getting are diffrent by 9%. I am trying to compare the inputs/outputs and for that I need to get from E+ the following:

-Air temperature (°C)

-Dry resultant temperature (°C)

-External conduction gain (kW)

-Internal conduction gain (kW)

-Air system input sensible (kW)

-Aux vent gain (kW)

-Infiltration gain (kW)

-Natural vent gain (kW)

-Space conditioning sensible (kW)

-DHW heating demand (kW)

I am guessing that:

-Air temperature (°C) --> Setpoint

-Aux vent gain (kW) --> Heatgain rate from DOAS

-Infiltration gain (kW) --> Infiltration Heat addition (IES has negative values for certain rooms while E+ has zeros)

But I am missing the rest ..

Hope this makes sense :/

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Keep in mind that the goal here shouldn't be to determine that software X calculates loads that are 10% lower than software Y. It should be to understand how they are different. You say the inputs in your two models are the same. I guarantee there are differences, whether they're obvious or not. I'm not sure of your ultimate goal with this information, but I've seen students comparing different modeling tools as an experiment, and end up drawing the conclusion in my first sentence, which missed the point of the activity, in my opinion. Best of luck to you though.

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Hello Greg, Firsto of all sorry for the late reply, I must have missed your post somehow. Anyway thanks for taking the time to respond. My ultimate goal was to gain a better understanding between the two software and try to align the two models as much as possible, in terms of inputs.The process of translating the inputs appropriatetly for each case was quite difficult indeed. I did discover though a few things that are foundementaly different between the two methods of calculation. I am planning on sharing a few comments at some point.

( 2019-07-30 05:41:39 -0500 )edit

You can change IESVE calculation methodology to ASHRAE to check so. As I know, CIBES is more on steady state methode, ASHRAE is true dynamic simulation, so it's different. IES also suggests that after sizing with CIBSE methodology, users need to check unmet hours to ensure heating capacity is enough, no need this checking with ASHRAE.

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First of all thank you for taking the time to reply! Yes, I know that I can do the calculation using IES VE, but the purpose of this exercise is to identify the main diffrences between the two software (IES vs. EnergyPlus (using OS for GH)). I know they use a diffrent method to calculate (IES using both ASHRAE and CIBSE) while OS only ASHRAE but according to CIBSE Guide A: This is essentially only an issue of computational efficiency and does not affect validity. Among other things I want to estimate the margin between the two, should I decide to only OS for/and GH, from now on.

( 2019-01-07 11:31:53 -0500 )edit

Hi @lutinfr, can you please elaborate how I can change my calculation method to ASHRAE in IESVE?

( 2019-07-17 07:58:12 -0500 )edit

Sorry for the late reply.

Click on 'Apache' from the left column and then from the top ribbon select 'Settings' the thrird option from the dropdown should be 'Loads Methodology'.

Hope this helps!

( 2019-07-30 05:35:34 -0500 )edit

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