Heat output and window dressings
Heat output and window dressings
(OP)
I'm wondering if anyone has any good data or resources on heat output from sun hitting a) aluminum miniblinds, b) vinyl miniblinds, c) ____ other type of window dressing, etc.
E.g., direct sun impact on type x will be ballpark __BTU/hr-ft2 and type y will be about __BTU/hr-ft2.
Not looking for exacts-I realize all the variables, just comparatives. Assuming all the same color (say white). I've googled such but didn't get too far.
Thanks for any insight... CB
E.g., direct sun impact on type x will be ballpark __BTU/hr-ft2 and type y will be about __BTU/hr-ft2.
Not looking for exacts-I realize all the variables, just comparatives. Assuming all the same color (say white). I've googled such but didn't get too far.
Thanks for any insight... CB





RE: Heat output and window dressings
RE: Heat output and window dressings
Solar absorption by each element in a glazing/shading layer array.
ASHRAE Transactions | July 1, 2006| Wright, John L.; Kotey, Nathan A. |
ABSTRACT
Window solar gain can strongly influence building energy consumption and peak cooling load. Shading devices such as venetian blinds, roller blinds, and drapes are routinely used to control solar gain. There is a strong need for models that allow shading layers to be included in glazing system analysis. This paper presents methods by which existing solar optical models for systems of specular glazing layers can be extended to include the effect of layers that create scattered, specifically diffuse, radiation in reflection and/or transmission.
RE: Heat output and window dressings
I might try this question in the heat transfer forum also. It could be important for a job I'm trying to help with - a "glass box" building with an overheating south face. It could probably be calculable somehow, with radiation heat transfer and Stephan Boltzman's constant and all that stuff. I'm just not proficient in that.
This might end with me using an IR thermometer, a couple miniblind purchases and a real set of data...
Thanks again, CB
RE: Heat output and window dressings
I think you need to have reflective window coverings applied directly to the glass to make a big impact, or to have external louvers, or somesuch.
TTFN
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RE: Heat output and window dressings
Translate that into a radiant and convective heat load to the room, and that's the amount of solar gain that's now inside the space and has to be treated. The biggest comfort effect is from the radiant heat- at a delta of 20F-25F room temp to surface temp of the blinds, that's a good 30-35 Btuh/SF of radiant heating for the blind area The convective heated air isn't much of a factor to the room comfort, as that warmed air is drawn off by a ceiling return air path, but that does impact the return air temp and hence your main cooling coil in the AHU.
You can try to calculate the heat effect from the interior blinds, but it's a transient load and you can only really estimate the peak load. I just cut to the chase and beat up the Architects to get exterior shading, reduced window areas, tuned for the climate and exposure. Keep the solar gain outside in the first place- don't let it get inside the space, unless you are in a heating dominated climate and want to harvest a bit of winter passive solar heat.
RE: Heat output and window dressings
RE: Heat output and window dressings
RE: Heat output and window dressings
Additionally, most blinds are rarely designed to be constantly perpendicular to the sun, so only a tiny fraction of the day will have optimum retroreflectance, assuming the blind was even flat to start with. The blinds I have at home have a slight curvature, compounding the problem. But, even if the blind was perfectly flat, perfectly aligned in azimuth, the midday sun, in someplace like Los Angeles, is about 70 degrees high, so a large portion of what makes it through the glass will not escape due to the higher reflectance of the glass at high incidence angles.
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: Heat output and window dressings
RE: Heat output and window dressings
Nothing beats exterior shading devices, deciduous trees, eyebrows, exterior adjustable blinds, punched/recessed windows, etc.