[BLDG-SIM] How to model a soil covered earth roof in DOE2?

John Weale jweale at eskimo.com
Mon Sep 10 18:56:10 PDT 2001


I am trying to get an approximate energy savings from adding a 'green
roof' (6" soil with living grass) to a flat roofed building.  Currently, I
see how to define a 'soil' layer, which will account for the u-value and
thermal mass of the soil. I do not see how to account for the evaporative
cooling effects (the grass will be properly watered).  I expect the
cooling to be rather small since the roof would have R-19 insulation under
the grass, so I am leaning towards neglecting them.

The other issue I would appreciate comments on is modeling the roof
surface temperature.  Is there an option to give the roof surface a
maximum temperature (it should not get above the ambient wetbulb), or do I
need to just settle with the absorbance of green?  This is really another
aspect of the evaporative cooling question.

The building will be a two story, flat roofed building in a pretty cold
climate (near Denver, Colorado, USA).  The grass roof is desirable for
non-energy reasons (esthetics and process water disposal) so this
calculation doesn't need to be overly precise (I would not be using DOE2
for it except I already have a fair DOE2 model I can quickly tweak into
shape).  Any advice or experience on forcing DOE2 into doing this?


John Weale, P.E.

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