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Why the building load is not constant even if the weather file/internal loads/thermostats are set constant? [closed]

I am interested in studying a simple building in which I would like to obtain contstant thermal loads. For this purpose I modified with Elements the weather file, setting 0 for the solar radiation and a constant drybulb/wetbulb temperature. I have also set to 0 the wind speed. This modifications have been made on an existing weather file, and only for the July month (the simulation will be run only in this custom-made month).

I deleted all the internal gains, except for the lighs, which are scheduled to be always on and with constant value. I also set up the internal thermostats to be 16°C and constant during the simulation period. The simulation should be for July only, so I have specified this in the simulation settings.

I have also selected the simulation to be run only for the weather file run period, I skipped zone sizing calculations, system sizing calculations, plant sizing calculations.

I was expecting to have constant building loads during the reported period. Unfortunately, analyzing the variables (with Data Viewer) "District Cooling:Facility" when the ideal loads are on, or the variable "Water to Water Heat Pump Load Side Heat transfer Rate" when I have a plant connected, I can see that there are 31 peaks, exactly the number of days that July is composed.

This suggested me that maybe there is still some kind of weather influence. Checking the external temperature and solar irradiation during the simulation periods, they are correctly set to the desired value, both in DViewer and in Elements chart viewer.

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Closed for the following reason the question is answered, right answer was accepted by FSilenzi close date 2019-01-30 06:26:34.096450

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Add output variables for Site Sky Temperature and all of the Surface Outside Face * variables (well, the key ones). That should reveal what is changing. If the Surface Outside Face Net Thermal Radiation Heat Gain Rate is changing, the simplest way to eliminate external radiant transfer is to use SurfaceConvectionAlgorithm:Outside,SimpleCombined; but that may defeat the purpose of you modeling. To get a constant sky temperature, I am fairly certain you need to make the epw "Horizontal Infrared Radiation Intensity from Sky" (HorzIRSky).

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