Peak Load Calc - Interpreting Results

Hello HB/LB Community,

I’m looking into creating a baseline peak load calculation that I can compare to results from other software and eventually look at the effect of shading. To do so, I’ve created a box with heat transfer just through the south wall / window.

I’ve seen Chris M’s shading study hydrashare file. However, one of the functionalities I’d like is to look at the design day and hr of the peak load per the “ReadEio” output component and the load breakdown (e.g. solar, conduction) from this component. At the moment, I only see how to read out the clg and htg peak loads and not the associated date/hr or breakdown.

Also, I’m curious as to how the design day file (ddy) is specified. Is it connected to the selected epw file? For example, Id like to confirm that the calculation is running through all possible hours, to capture a fall high solar load case) and not just the hottest dry bulb days, when looking at peak cooling load.

I’d be happy to hear your input if you have experience in these areas.

CAL 2017-1226 Shaded Box Load (596.1 KB)


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@victorbrac ,

Here’s an example file that shows you how to extract the load breakdown over the design day:,0
It relies on excel and TTToolbox but it should serve your purposes.

That particular example file is looking at the loads on the high outdoor temperature design day but all 7 of the types of design days in the ddy file next to the epw are being run (high humidity, high solar, sensible heating, high wind, etc.). You can see that the loads on these other design days are imported next to the high outdoor temperature day.

I’ll also add that the timestep breakdown of the air load on the design day is available on the latest Honeybee_Read HVAC Sizing component:

This air load will show you the actual amount of heat that must be removed from / added to the air at each timestep on the cooling / heating design days. The data is taken from the inZsz.csv file that is output in OpenStudio simulations. This air load is lower than the peak instantaneous load in the space because the thermal mass of your space will dampen the transfer of heat from the surfaces of the zone to the air.

Hope that helps!

Hey Chris,

Thank you for taking the time to respond.

To comment on your response, I opened the hydrashare file and ran the simulation. I did not see where the loads for the other design days are “imported next to the high outdoor temperature day”. I just see the hourly breakdown for one day in the excel readout. Could you clarify?

In my .gh, I’m still finding that the EIO component peak load result is not accurate in my analysis of a simplified building in Chicago.

When I open the ddy file for my project I see two dates called out, one in January and one in July (corresponding to 99.6% db in January and various cooling design psychrometric conditions in July).

Now when I run the simulation, I find the inZsz.csv file that holds the peak load results only seems to look at the July date for cooling. While there’s no date called out, I found the same peak load in the in.csv under the column “Zone Ideal Loads Supply Air Sensible Cooling Energy” for the date of July 21st.

This tells me that the E+ peak load calc / EIO component do not look at all possible peak load days e.g. high solar day. When I continued to investigate the in.csv file, I found that the actual peak load is in September (higher load than the EIO result). This is supported by my results from IES and Trane Trace.

How would one update the EIO component or the ddy file such that the EIO component will yield the actual zone peak cooling load?

On a side note, I believe I found an example of what you were saying in terms of dampening of heat transfer. In the in.csv file, I find that the sum of the surface and solar heat transfer is greater than the “Zone Ideal Loads Supply Air Sensible Cooling Energy”.

CAL 2018-0106 Box Load (604.5 KB)