Dear TRNSYS users, I think there is also a less physical explanation to the sudden change in Tsky at sunrise. If you use Type69 in mode 0, it calculates a "cloudiness factor" based on the solar radiation. Obviously, that value cannot be computed at night so Type69 just keeps a constant sky cover until the sun rises again (actually Type69 only uses radiation values higher than 150 kJ/h/m2). This probably explains some of the "bumps" you see at sunrise. Type69 also allows you to use the sky cover from your weather file if it is available. TMY2 (for the US) and IWEC (World) data both include the "Total Sky Cover" and the "Opaque Sky Cover". I attached an IIsiBat project showing the difference between the computed value and the two values from the weather file. If you look carefully to the values obtained with the Sky cover from the weather file, you will still see some sudden changes at sunrise. I assume that those ones are explained by the phenomenon mentioned by Bengt. I would personally use the "Total Sky Cover" rather than the "opaque sky cover"... I hope someone will correct me if I am wrong! Regards, Michaël Kummert _________________________________________________________ Michaël Kummert Solar Energy Laboratory - University of Wisconsin-Madison 1303 Engr Res Bldg, 1500 Engineering Drive Madison, WI 53706 Tel: +1 (608) 263-1589 Fax: +1 (608) 262-8464 E-mail: kummert@engr.wisc.edu SEL Web Site: http://sel.me.wisc.edu TRNSYS Web Site: http://sel.me.wisc.edu/trnsys > -----Original Message----- > From: owner-trnsys@relay.doit.wisc.edu > [mailto:owner-trnsys@relay.doit.wisc.edu] On Behalf Of Bengt Perers > Sent: Wednesday, February 26, 2003 06:18 > To: trnsys@relay.doit.wisc.edu > Subject: Re: about the sky temperature > > > To mee the data seems reasonable at a quick glance. > > I have experience from some years with infrared thermografy > and image processing + Poolheating. As rule of thumb for > northern Europe at least the effective sky temperature is > about 10-20 degrees below the ambient temperature at ground > level at clear sky condtions and close to and just below (1-2 > deg) the ambient temperature during cloudy conditions. This > is independent on season. The low sky temperature is cause by > radiation in the artmospheric window at 8-14 um and is where > all the discussion on greeenhouse gasses have their main real effect. > > There is a very nice text book on these radiation subjects > for the atmospehere and earth surface in the Infrared > Handbook by W.L.Wolfe and G.J. Zissis ISBN 0.9603590-1-X. > > The shift at sunrise may correspond to that the realtive > humidity and fog content is decreasing rapidly at synrise > when the moisture in the air is heated by the sun again. We > often not a dip in ambient temperture just after the sunrise > which you should not expect otherwise. > > I am still an observer more than an expert but please tell me > if you find out something more. >
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Type69.zip
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