My current work is testing solar thermal collectors, I have to think about the design of solar thermal collection a lot. The angle of a collecting surface and it thermal effects tend to average out. In this case, especially with a car, it is moving around relative to the sun, and the sun is moving around a lot as well. I am thinking everywhere the glass is vertical there is larger roof or other surface. It is true when the incident angle is high that more energy is reflected than absorbed, but sometimes it just hits another surface square on and heats it instead.
People are always trying to bend surfaces (absorbers and mirrors both), and add them in an effort to improve heat collection (the opposite - collecting less - heat is pretty similar), but when a surface is square to the sun at one time it is father away at another. It always tends to average out as a function of the gross exposed area. The differences end up being a quibble. On Sat, Aug 2, 2014 at 10:56 AM, Peri Hartman via EV <[email protected]> wrote: > I think Dennis was speaking more of the angle of the glass relative to > the sun rather than the type of glass. Certainly, if a pane of glass was > parallel to the rays of sunlight, it would transfer virtually no heat or > light (only that reflected from other surfaces). > > But they type of glass does make a difference. In residential and > commercial glass, there's a rating called Solar Heat Gain Coefficient > (SHGC) and there are treatments that have quite a spread of effects - > without tinting. I have no idea if any of these are allowed for > windshields. Or, perhaps, they are already used. > > Second, insulation makes a huge difference. True, nothing will stop heat > from entering over time. But slowing down the rate of energy absorbed > directly relates to the energy needed for cooling. If you slow the heat > absorption down by 50%, you would need 50% less cooling capacity (for the > heat coming through non glass areas). > > Peri > > ------ Original Message ------ > From: "Michael Ross via EV" <[email protected]> > To: "EVDL Administrator" <[email protected]>; "Electric Vehicle Discussion > List" <[email protected]> > Sent: 02-Aug-14 7:41:47 AM > Subject: Re: [EVDL] Hybrid Mustang: AC or DC? > > I think the solar gain has less to do with the glass than the small cabin >> size. >> >> While involved with designing climate controlled cabins (at Caterpillar) I >> learned that that any glass you have - whatever tint level - re-radiates >> the absorbed energy into the cabin. The main effect of tint is to reduce >> the heat felt on the skin - the AC load remains the same. Likewise, the >> roof, walls, everything basically sinks heat until equilibrium. No amount >> of insulation mitigates this when you are just out in the sun for long >> periods. Insulation slows the conduction, it can't really stop it. >> Convection from motion helps, but absorption and conduction carry on as >> always. If you could make the cab into a vacuum bottle... >> >> The load on the AC ends up being pretty simple to estimate - how much area >> is in the sun. It is hard to win this game. >> >> Reflecting light back out when not moving is always effective. Reflective >> tints (not generally legal in US) don't actually reflect much energy - the >> glass still absorbs the bulk of it, and it is radiated in as IR. >> >> >> On Sat, Aug 2, 2014 at 3:26 AM, EVDL Administrator via EV < >> [email protected] >> >>> wrote: >>> >> >> On 2 Aug 2014 at 2:03, Dennis Miles via EV wrote: >>> >>> > On the other hand a friend in St Petersburg, FL. uses a 7,500 BTU ac >>> in >>> his >>> > S-10 Pickup (About a 400 watt load) and runs it from a 1,000 Watt >>> 110v. >>> > inverter... >>> >>> I can absolutely believe that. Pickup cabs are typically fairly small. >>> They also usually have relatively vertical glass, for less solar gain >>> than >>> most cars. >>> >>> Besides ... >>> >>> http://evdl.org/images/aircon-daewoo.jpg >>> >>> ;-) >>> >>> > Your 25000 to 30000 btu/hr are two to two and a half tons (Same as HP >>> > or similar to Kw. ) and that is as much a a small house. >>> >>> Exactly! A passenger car with lots of glass area and poor insulation can >>> easily take that much capacity to cool. >>> >>> However, now that I think about it, I'd guess that much of that >>> capacity is >>> there so the car cools down quickly after it's been sitting in the hot >>> sun. >>> You could no doubt use a much lower capacity aircon unit if you allowed >>> plenty of time to pre-cool it. (Or always parked in the shade. ;-) >>> >>> David Roden - Akron, Ohio, USA >>> EVDL Administrator >>> >>> = = = = = = = = = = = = = = = = = = = = = = = = = = = = = >>> EVDL Information: http://www.evdl.org/help/ >>> = = = = = = = = = = = = = = = = = = = = = = = = = = = = = >>> Note: mail sent to "evpost" and "etpost" addresses will not >>> reach me. To send a private message, please obtain my >>> email address from the webpage http://www.evdl.org/help/ . >>> = = = = = = = = = = = = = = = = = = = = = = = = = = = = = >>> >>> >>> _______________________________________________ >>> UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub >>> http://lists.evdl.org/listinfo.cgi/ev-evdl.org >>> For EV drag racing discussion, please use NEDRA ( >>> http://groups.yahoo.com/group/NEDRA) >>> >>> >>> >> >> -- >> Put this question to yourself: should I use everyone else to attain >> happiness, or should I help others gain happiness? >> *Dalai Lama * >> >> Tell me what it is you plan to do >> With your one wild and precious life? >> Mary Oliver, "The summer day." >> >> To invent, you need a good imagination and a pile of junk. >> Thomas A. Edison >> <http://www.brainyquote.com/quotes/quotes/t/thomasaed125362.html> >> >> A public-opinion poll is no substitute for thought. >> *Warren Buffet* >> >> Michael E. Ross >> (919) 550-2430 Land >> (919) 576-0824 <https://www.google.com/voice/b/0?pli=1#phones> Google >> Phone >> (919) 631-1451 Cell >> (919) 513-0418 Desk >> >> [email protected] >> <[email protected]> >> -------------- next part -------------- >> An HTML attachment was scrubbed... >> URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/ >> attachments/20140802/72277c31/attachment.htm> >> _______________________________________________ >> UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub >> http://lists.evdl.org/listinfo.cgi/ev-evdl.org >> For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/ >> group/NEDRA) >> >> >> >> > _______________________________________________ > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub > http://lists.evdl.org/listinfo.cgi/ev-evdl.org > For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/ > group/NEDRA) > > -- Put this question to yourself: should I use everyone else to attain happiness, or should I help others gain happiness? *Dalai Lama * Tell me what it is you plan to do With your one wild and precious life? Mary Oliver, "The summer day." To invent, you need a good imagination and a pile of junk. Thomas A. Edison <http://www.brainyquote.com/quotes/quotes/t/thomasaed125362.html> A public-opinion poll is no substitute for thought. *Warren Buffet* Michael E. Ross (919) 550-2430 Land (919) 576-0824 <https://www.google.com/voice/b/0?pli=1#phones> Google Phone (919) 631-1451 Cell (919) 513-0418 Desk [email protected] <[email protected]> -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20140802/2ef9f12e/attachment.htm> _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
