[TRNSYS-users] Type 56 Thermal Mass

[Devin Rohan]

It seems like Type 56 isn't taking into account the concrete floor I have in
a space I'm modeling.  What I have is

   - 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.

-- 
Devin M. Rohan, LEED Green Associate
Purdue University
Civil/Architectural Engineering
drohan at purdue.edu
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