RE: [EnergyPlus_Support] Re: Modifying a weather file to reflect "real" weather

Dear Chris (and others),

I am bogging down a bit because it sounds as though (to paraphrase) "You can't give E+ a data set that simply and reasonably represents the solar impact that actually occurred for a specific time period."

Since sky cover is reported in many weather data sets, what if I just gave the actual % sky cover to E+ in a custom data set? As mentioned in my first post, my (perhaps simplistic) assumption is that the sun does the same thing every day, but the clouds vary a lot. How can we represent that factor simply to E+? If I did that, is there some other factor that renders it meaningless?

Since the sun has a big impact on many building designs, I want to reflect it's impact on HVAC and overall energy use. I'm trying to get a "reasonable and defensible" approach, not "precise to several decimal places".

Thanks again!

The Building Performance Team
James V. Dirkes II, P.E., LEED AP
1631 Acacia Drive NW
Grand Rapids, MI 49504
616 450 8653

From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Chris
Sent: Tuesday, June 02, 2009 6:36 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] Re: Modifying a weather file to reflect "real" weather

I know at least 100 papers that have been devoted to this question, most
of them proposing a simple empirical formula to obtain either the IR
(aka thermal or longwave) irradiance, or equivalently the sky
temperature or the sky emittance. Most of them, however, are for clear
skies only (when the sky temperature is significantly lower than the the
air temperature). Still. some offer models for overcast and
partly-cloudy conditions.

Chris

> Adding to the discussion, the weather file needs solar radiation data which could be estimated based on the total horizontal solar radiation which could be "cheaply" recorded, but eplus also requires the horizontal IR radiation, for which I have yet to find a method to estimate it using normally reported weather data (like temp, humidity, wind speed and direction, rain).
>
>
>

--
Chris A. Gueymard, PhD
Solar Consulting Services
P.O. Box 392
Colebrook, NH 03576, USA
Tel. (603) 237-8550
Fax (603) 237-5314
http://www.SolarConsultingServices.com

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