Re: [GBlist] low E glass

[Sarah Holland/David Foley <hollandfoley@acadia.net>]

on 01/03/2002 4:46 PM, Richard Kadulski at kadulski@direct.ca wrote:

> What is more important, and more difficult to define simply, is the Mean
> Radiant Temperature.  Heat transfer from a body to its surroundings
> happens when the surface of the body is at a higher temperature than its
> surroundings. That is why surface temperatures of a room have a big
> impact on comfort. A room has several surfaces, each of which can be at
> different temperatures, depending on the room's finish and thermal
> insulation. Windows are usually the coolest surfaces.

Thanks, Richard - good explanation and insights.

Years ago, I worked at the Building Energy Analysis division of the Lawrence
Berkeley Laboratory.  We were investigating low-energy strategies for hot,
humid climates, and part of my work was to make a "Human Comfort Model",
which was just a lot of FORTRAN code based on the work of P.O. Fanger and
other researchers.  The model looked at a lot of variables, like wet and dry
bulb temperatures, air movement, clothing, activity level, mean radiant
temperature, etc., and would predict how comfortable the "average" person
would be under different circumstances.  I think it was a pretty good model
- it gave results consistent with actual data from real people.  When we
tested the model for sensitivity, we found that Mean Radiant Temperature
affected comfort more than any other single variable.

That may be the single most important reason to use low-e glass.  By
increasing Mean Radiant Temperature, it may be possible to lower air
temperature.  That, combined with the superior R-value of low-e  glazings,
promises significant energy savings.

That said, it is really too bad that U.S. Window manufacturers offer so few
low-e glass types.  The typical choices cut out so much potential solar gain
that they diminish the potential energy performance of buildings in
heating-dominated climates.  Our Canadian friends have done much better with
their windows, and we have turned to Stephen Thwaites and his colleagues at
Thermotech for windows with glazings "tuned" to different faces of a
building.

- David Foley
-- 
Holland & Foley Building Design L.L.C.
232 Beech Hill Rd.
Northport, Maine 04849 USA
p: (207) 338-9869 f: (207) 338-9859 e: hollandfoley@acadia.net


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