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RE: [EnergyPlus_Support] Further Insight : Skylight / Radiant Cooling Strange Behavior
Ian,
I believe this is a known bug (CR6897). But unfortunately it isn't a
quick job and I don't think it was fixed in V1.4 (which is already out).
brent
________________________________
From: EnergyPlus_Support@xxxxxxxxxxxxxxx
[mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Ian Doebber
Sent: Friday, October 13, 2006 4:15 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Further Insight : Skylight / Radiant
Cooling Strange Behavior
Looking into the problem further today, this problem only occurs when
the radiant cooling system is on. When I turn the radiant system off
during peak hours (5-7 pm), the Window Heat Gain is ~10% greater than
the solar energy transmission. The radiant energy exchange calculation
between the glazing and a radiant floor surface should be evaluated to
make sure that it is not over calculating the exchange by a factor of
10. If this is a quick change, if it were possible to include the fix
for v1.4 great but I'd imagine that it would be too late for that. Any
recommendations on how to trick the program avoiding this issue would be
appreciated.
Ian Doebber
Graduate Mechanical Engineer
Arup
901 Market Street Suite 260 San Francisco CA 94103
tel: 415-946-0292
fax: 415-957-9096
cell: 415-613-4314
ian.doebber@xxxxxxxx <mailto:ian.doebber%40arup.com>
www.arup.com
________________________________
From: EnergyPlus_Support@xxxxxxxxxxxxxxx
<mailto:EnergyPlus_Support%40yahoogroups.com>
[mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx
<mailto:EnergyPlus_Support%40yahoogroups.com> ] On Behalf Of Ian Doebber
Sent: Friday, October 13, 2006 1:46 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
<mailto:EnergyPlus_Support%40yahoogroups.com>
Subject: [EnergyPlus_Support] Skylight / Radiant Cooling Strange
Behavior
I'm modeling a single retail space with 100 sky lights and a radiant
cooled slab. I modeled the skylights as prismatic glass (Diffusing=Yes)
with SHGC~.40.
When I modeled the space using purchased air to validate the loads etc,
the sky light transmitted solar was ~10% less than the total sky light
heat gain which makes sense.
Yet, when I model the space using radiant cooling, the sky light
transmitted solar remains the same as expected but the total sky light
heat gain is 10x what it should be which is impossible. For example, at
peak summer noon, with 1000 W/m2 of incident solar radiant, 360 W/m2 is
transmitted which is correct but the total heat gain is 3400 W/m2 which
doesn't make any sense.
I've side stepped the problem by having only 10 sky lights so the gain
is roughly correct but this adds too much convective heat gain to the
space increasing my internal temperature with minimal solar radiation
component reducing the effectiveness of the radiant floor, the very
reason I'm doing the analysis.
I've tried many combinations of changing the diffusing option to No,
changing the reflectance calculation under the Building heading,
changing the internal emmissivity of the glazing all to no avail. I
would imagine there is something quirky with the radiative heat exchange
between the skylights and the floor that is throwing everything off.
Any assistance would be greatly appreciated.
Thanks
Ian
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