The im­por­tance of glaz­ing

The Glengarry News - Glengarry Supplement - - News -

A key de­ter­mi­nant of a win­dow's en­ergy ef­fi­ciency is its glaz­ing.

With win­dows ac­count­ing for more than a quar­ter of the an­nual space heat­ing needs in a typ­i­cal new home, us­ing the most en­ergy ef­fi­cient glaz­ing is a key to con­serv­ing en­ergy and re­al­iz­ing cost sav­ings.

As there are more than 300,000 types of win­dow prod­ucts on the mar­ket, and the ar­eas and types can vary widely with the vin­tage of homes, mak­ing the right choice of glaz­ing can be a chal­lenge.

Low-emis­siv­ity (low-e) coated win­dows pro­vide im­proved ther­mal per­for­mance over clear glass, but the many types of low-e coat­ings vary greatly when it comes to so­lar per­for­mance.

There are many fac­tors to con­sider when choos­ing a glaz­ing, in­clud­ing ris­ing cool­ing loads, peak elec­tric de­mands, and heat loss co­ef­fi­cients (uvalue or u-fac­tor). But one of the most im­por­tant de­termi- nants of a win­dow's en­ergy ef­fi­ciency is its So­lar Heat Gain Co­ef­fi­cient (SHGC): The frac­tion of in­ci­dent so­lar ra­di­a­tion that the win­dow ad­mits.

The SHGC is a num­ber be­tween 0 and 1, with low so­lar gain prod­ucts hav­ing an SHGC of less than 0.30 and high so­lar gain prod­ucts an SHGC greater than 0.30.


To de­ter­mine the im­pact of us­ing high ver­sus low so­lar gain glaz­ing sys­tems, the Na­tional Re­search Coun­cil of Canada (NRC), Nat­u­ral Re­sources Canada ( NRCan), and Canada Mort­gage and Hous­ing Cor­po­ra­tion (CMHC), with con­tri­bu­tions from 37 com­pa­nies, used the Cana­dian Cen­tre for Hous­ing Tech­nol­ogy (CCHT) twin­house fa­cil­i­ties to com­pare high so­lar heat gain (HSG) win­dows and low so­lar heat gain (LSG) win­dows.

Thirty-one glaz­ing units were tested in four types of win­dows – case­ment, fixed case- ment, fixed, and pa­tio door – on north, south, east, and west­fac­ing walls. Both the high HSG and low HSG win­dows were dou­ble-glazed and low ecoated.

Re­sults for HSG and LSG win­dows were com­piled for lo­ca­tions through­out North Amer­ica and the re­sults for 10 Cana­dian lo­ca­tions in­di­cated that: - HSG of­fered 13% to 17% en­ergy cost sav­ings com­pared to con­ven­tional win­dows. - HSG of­fered an­nual en­ergy cost sav­ings of $117 to $354. - LSG of­fered 8% to 10% en­ergy cost sav­ings com­pared to con­ven­tional win­dows. - LSG of­fered an­nual en­ergy cost sav­ings from $71 to $203.

Lessons from the field in­clude the ob­ser­va­tion that en­ergy ef­fi­ciency ben­e­fits are de­pen­dent on the mode of op­er­a­tion, ori­en­ta­tion and cli­mate, and that com­bi­na­tions of glaz­ing (e.g., LSG on the north, HSG on the south) can gen­er­ate the best re­sults.

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