Simulated Indoor Temperatures are too High - DesignBuilder

asked 2025-08-11 21:46:23 -0500

updated 2025-08-13 10:01:31 -0500

14460 ●91 ●25 http://bigladdersoftware.com/

I'm attempting to calibrate my model of a simple single-storey residential fibro home with measured indoor temperatures and have been stuck for a while trying to get them close to matching.

I'm experiencing these crazy spikes where some days it peaks to 40°C, which is unrealistic. The measured performance is horrible and may be lucky to be 5°C higher than the outdoor temperature. There is no HVAC in the whole house. I've tried making variations of the occupancy and activity schedules, but I still get the same results.

Has anyone dealt with this before and has solutions for this?

Here is a graph of the measured indoor temperature and a photo of the simulated indoor temperature with the simulated outdoor temperature.

image description

I've only shown one zone in the screenshot as that was the same place where the indoor temperature was taken.

George

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answered 2025-08-12 11:42:54 -0500

Reza Basafa
31 ●1 ●1

updated 2025-08-13 10:01:16 -0500

Aaron Boranian

14460 ●91 ●25 http://bigladdersoftware.com/

1) Use the correct variable for calibration

1-a- For matching with measured data from a standard room sensor, use Air Temperature (Zone Mean Air Temperature), not Operative Temperature. Operative Temp includes mean radiant effects and is mainly for thermal comfort metrics (PMV/PPD), not for calibration.

1-b- Increase your simulation timestep to 6–12 per hour — this often removes unrealistic spikes caused by numerical oscillations.

2) Ventilation & Infiltration

Default infiltration rates are often too low, especially for older fibro-type houses. You might want to try 0.7–1.5 ACH as an average baseline. Use wind- and temperature-driven infiltration, and apply realistic day/night schedules (e.g., windows slightly open at night) to capture natural cooling.

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