- a 4 x 4 x 3 m detached test lab space expose to the outside on all sides.
- I'm modeling the all the walls and ceiling as resistance layers only
- have a concrete floor as a massive layer with thermal 6.12 kJ/hmK (i.e. 1.7 W/mK), specific heat as 1.4 kJ/kg K, and density of 2200 kg/m^3...pretty standard properties which gives me a capacitance of 7500 kJ/K.
- Infiltration is .5 ACH, no internal gains, no heating/cooling, and a south facing window 3.8 x 2.4 m.
I built a 1D finite difference model and wanted to see if my model agreed with TRNSYS. The problem is that I see a thermal lag and attenuation in the air temperature in my model, while in TRNSYS, the air temperature experiences no lag and varies wildly as it follows the ambient temperature. It's only when I increase the airnode capacitance to around what my floor capacitance is (7500 kJ/K) that I see good agreement between my model and TRNSYS.
Why do I have increase this airnode capacitance and is this reasonable? Thanks so much for any help or insight.
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Devin M. Rohan, LEED Green Associate
Purdue University
Civil/Architectural Engineering
drohan@purdue.edu