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Measured field performance of aluminium windows in Kuwait
Energy and Buildings, 17 (1991) 75-85
75
Measured field performance of aluminium windows in Kuwait Osama Daoud*, Gopal M a h e s h w a r i and H a k e m Al-Shami Engineering Division, Kuwait Institute f o r Scientific Research, P.O. Box 24885, Safat 13109 (Kuwait)
(Received February 18, 1990; accepted June 22, 1990; revised paper received July 27, 1990)
Abstract The air infiltration rate is determined for 154 aluminium windows installed in 25 buildings in Kuwait. The influence of window characteristics such as type, dimensions, source of profile, source of workmanship, building function, cost and age has been studied. Air-tightness is determined using portable equipment to pressurize a chamber created on each window and to measure the air flow and pressure increase. The results show that aluminium windows in Kuwait have a mean infiltration rate of 13.48 m3/h/m at 75 Pa, about 3.4 times higher than the ANSI/ AAMA maximum limit. The type of window is the main factor influencing performance, with horizontally hinged windows leaking the most, and tilt-and-turn and fixed windows the least. Newly installed windows and those installed in low-cost projects show marginally greater mean air-infiltration values than those in old or prestigious projects; however, the standard deviation is noticeably greater, indicating lower quality control. Windows installed in residential buildings produce lower leakage rates than ~hose in office or public buildings. The volume of air leakage remains the same for sliding windows with different areas, indicating that leakage occurs mostly at the corners; however, leakage increases with area for vertically hinged windows, showing that leakage occurs at the sash/window joint.
Introduction Aluminium w i n d o w s have g a i n e d p o p u l a r i t y in the Arabian Gulf r e g i o n in the p a s t 15 y e a r s b e c a u s e of their relatively low c o s t c o m p a r e d to t i m b e r or steel ones. Aluminium billets are locally p r o d u c e d in one f a c t o r y in Bahrain. I m p o r t e d billets f r o m n e i g h b o u r i n g c o u n t r i e s are also available at c o m p e t i t i v e prices. In Kuwait, a l u m i n i u m profiles are e x t r u d e d in two factories, w h e r e a s a l u m i n i u m w i n d o w s a n d d o o r s are f a b r i c a t e d u s i n g local a n d i m p o r t e d profiles in 45 w o r k s h o p s . Most o f the w i n d o w s f a b r i c a t e d are double sliders; since t h e s e do n o t o c c u p y s p a c e w h e n t h e y are open. Other types, s u c h as tilt-and-turn a n d vertically or horizontally h i n g e d windows, are gaining a c c e p t a n c e . However, the c h o i c e of w i n d o w type does n o t follow a n y f u n c t i o n a l or per*Present address: 34 Goal Gamal Street, Agooza Cairo, Egypt.
0378-7788/91/$3.50
f o r m a n c e criteria, b u t d e p e n d s mainly o n cost. A serious d r a w b a c k in f e n e s t r a t i o n w o r k s in Kuwait arises f r o m the w i n d o w s ' lack o f aira n d water-tightness. The c o n s e q u e n t high energy c o n s u m p t i o n for c o o l i n g s y s t e m s is a b u r d e n o n the total national c o n s u m p t i o n . T h e s e s h o r t c o m i n g s in w i n d o w p e r f o r m a n c e are a t t r i b u t e d to the following factors: (1) No c o d e o f p r a c t i c e or national s t a n d a r d for w i n d o w p e r f o r m a n c e is applied. Designers a n d c o n t r a c t o r s follow o w n e r s ' r e q u e s t s for m i n i m u m profile t h i c k n e s s a n d a n o d i z a t i o n colo u r only. No p e r f o r m a n c e criteria are p r o v i d e d in m o s t d e s i g n d o c u m e n t s . (2) In t h o s e rare c a s e s w h e r e p e r f o r m a n c e criteria are specified, t h e y are generally ignored, since n o testing facilities are available to verify c o m p l i a n c e . (3) There is little interest a m o n g building o w n e r s in the e n e r g y savings t h e y c a n achieve f r o m tighter windows, since the g o v e r n m e n t
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76 subsidizes up to 90% of the cost o f electricity. Thus, o w n e r s are m o r e i n t e r e s t e d in cutting down o n initial costs by using inferior c h e a p windows. Consequently, m a n y design, fabrication, installation and m a i n t e n a n c e defects are obs e r v e d in f e n e s t r a t i o n works [1]. Not only are air and heat allowed to p e n e t r a t e into the interior, causing a t e m p e r a t u r e increase and high c o n s u m p t i o n of e n e r g y to o p e r a t e the cooling systems, but also dust particles can enter, creating a n u i s a n c e for tenants. Fine dust is c o m m o n in Kuwait during high winds, especially in the summer; the annual dust fallout is 119 tA
o r a t o r y results with practical field e x p e r i e n c e . F u r t h e r m o r e , he s t r e s s e d the n e e d for inform a t i o n on the p e r f o r m a n c e of windows subj e c t e d to natural w e a t h e r i n g conditions. Literature, however, is s c a r c e on the perf o r m a n c e o f aluminium windows installed in old buildings in a h a r s h climate, s u c h as that of the Arabian Gulf States. Quality and perf o r m a n c e criteria for t h e s e e l e m e n t s have not b e e n well defined. Many c o n t r a c t o r s i m p o r t windows either r e a d y - a s s e m b l e d or k n o c k e d down, without giving m u c h c o n s i d e r a t i o n to their suitability. I m p o r t e d materials v a r y widely in quality, and, in the a b s e n c e o f controls, low g r a d e s are used. It is generally a c c e p t e d that the quality of w o r k m a n s h i p greatly influences w i n d o w perf o r m a n c e . D a o u d et al. [4] f o u n d that defects due to fabrication and installation p r o c e s s e s are the m o s t influential in degrading the perf o r m a n c e of aluminium windows installed in buildings of different ages in Kuwait. The quality o f w o r k m a n s h i p in the Gulf states is normally related to the size of c o n t r a c t o r . Large cont r a c t o r s have the r e s o u r c e s to c o n t r o l quality in o r d e r to maintain their reputations. Small c o n t r a c t o r s , o n the o t h e r hand, do not p a y m u c h a t t e n t i o n to this area. T h e y often d e p e n d on newly hired p e r s o n n e l with little or no e x p e r i e n c e , in o r d e r to minimize the cost. Also, small c o n t r a c t o r s are involved in small p r o j e c t s a c c o r d i n g to g o v e r n m e n t a l categorization. This applies to general c o n t r a c t o r s ; however, its application to specialized c o n t r a c t o r s , such as t h o s e involved in f e n e s t r a t i o n works, is n o t clear. Weidt and Weidt [5] f o u n d the cont r a c t o r ' s e x p e r i e n c e can greatly influence the air infiltration rate t h r o u g h newly installed windows. This, however, was d e d u c e d f r o m a limited n u m b e r of field tests. This s t u d y was directed towards evaluating the effect of w i n d o w type, s o u r c e of material and w o r k m a n s h i p , and the age, dimensions, function and cost of the building on air infiltration t h r o u g h aluminium windows. The data w e r e b a s e d o n field air-infiltration tests of windows installed in 25 buildings in Kuwait. The aim was to initiate national a w a r e n e s s of the n e e d for national specifications for w i n d o w p e r f o r m a n c e , and to s t u d y the effect of different w i n d o w characteristics o n p e r f o r m a n c e .
77 residential buildings was a l m o s t double that of office or public buildings. This is c o n s i s t e n t with their actual distribution. The care and m a i n t e n a n c e o f windows o f e a c h type is exp e c t e d to v a r y noticeably. V~rmdows in residential buildings are u s e d b y a limited n u m b e r o f people, and are c l e a n e d and c h e c k e d o n a m o r e regular basis t h a n t h o s e in office or public buildings. Since public buildings have m a n y m o r e users, their windows are s u b j e c t e d to m o r e abuse. W i n d o w s ranging in age f r o m newly installed to m o r e t h a n 10 y e a r s old w e r e t e s t e d (Fig. l ( c ) ) . Newly installed windows (less t h a n o r equal to two y e a r s old) d o m i n a t e d the sample, since t h e y r e p r e s e n t the m o s t r e c e n t p r a c t i c e in Kuwait, w h i c h t h e o r e t i c a l l y s h o u l d r e p r e s e n t the highest quality. Notably, haft o f t h e s e have b e e n installed in national h o u s i n g p r o j e c t s that are c u r r e n t l y u n d e r c o n s t r u c t i o n and are the highest quality g o v e r n m e n t a l h o u s i n g projects, since t h e y benefit f r o m the cumulative e x p e -
Sample selection The field s u r v e y was carried out o n 154 windows installed in 25 buildings l o c a t e d a r o u n d Kuwait City. Eight o p e r a t i o n a l t y p e s w e r e included: horizontal d o u b l e slider, vertical single slider, vertically h i n g e d single a n d d o u b l e leaf, horizontally h i n g e d single and d o u b l e leaf, tilt-and-turn and fixed (Fig. l ( a ) ) . H o r i z o n t a l d o u b l e sliders d o m i n a t e d the sample, r e p r e senting 45% of the total; this is in Line with the fact that d o u b l e sliders are the m o s t comm o n t y p e of w i n d o w in Kuwait. Vertically h i n g e d windows, at 29%, axe the s e c o n d m o s t c o m m o n type. Tilt-and-turn, vertical sliders and fixed windows are rare, and h e n c e w e r e the least n u m e r o u s in the sample. The s a m p l e i n c l u d e d windows installed in buildings with t h r e e different functions: residential, office and public. The total n u m b e r o f windows within e a c h type was k e p t a l m o s t c o n s t a n t (Fig. l ( b ) ) , h o w e v e r , the n u m b e r o f
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(d) (c) Fig. 1. Characteristics of windows included in the sample (a) W'mdow type; (b) building type; (c) window age; (d) building cost.
78 rience of the p a s t 10 years. The o t h e r a g e g r o u p s w e r e included to c o m p a r e old with n e w p r a c t i c e a n d to d e t e r m i n e the i m p a c t o f a g e on p e r f o r m a n c e . The c o s t of the building reflects the size of the c o n t r a c t o r involved in its c o n s t r u c t i o n . Figure l ( d ) s h o w s the p e r c e n t a g e o f w i n d o w s t e s t e d within e a c h c o s t g r o u p . T h r e e g r o u p s w e r e defined, r e p r e s e n t i n g the wide r a n g e of buildings in Kuwait. T h e s a m p l e i n c l u d e d buildings r a n g i n g in c o s t b e t w e e n U S $ 1 5 0 0 0 0 a n d US$ 25 0 0 0 000. Sixteen small villas, s u c h as t h o s e built in the national h o u s i n g s c h e m e , r e p r e s e n t e d the low-cost buildings, a n d w e r e m o r e n u m e r o u s in the s a m p l e ; s e v e n c o m m e r c i a l c o m p l e x e s or large public facilities r e p r e s e n t e d the o t h e r e n d of the scale. T h e w i n d o w s in the l o w - c o s t buildings n u m e r i c a l l y d o m i n a t e d the s a m p l e , w h i c h reflects the a c t u a l distribution t h a t exists. Since a large s h a r e of the m a r k e t in Kuwait d e p e n d s o n i m p o r t e d m a t e r i a l s a n d labour, the s o u r c e s of a l u m i n i u m profiles a n d w o r k m a n s h i p w e r e included as two p a r a m e t e r s so t h a t their i m p a c t on p e r f o r m a n c e c o u l d b e a s s e s s e d . The s a m p l e s e l e c t i o n w a s c o n t r o l l e d b y g e o m e t r i c a l factors, s u c h as the w i n d o w s h a p e , d i m e n s i o n s a n d accessibility, as well as b y the t e n a n t s ' r e s p o n s e to the t e s t i n g request. The w i n d o w h a d to h a v e either an e x t e r n a l or internal r e c e s s to e n a b l e the w o o d e n f r a m e t h a t f o r m e d (with the w i n d o w a n d the wall) the t e s t p r e s s u r e c h a m b e r to b e m o u n t e d . This arrangement eliminated any permanent damage to the wall finish n e a r the window. Also, w i n d o w d i m e n s i o n s w e r e limited to less t h a n 1.8 m in either direction for p r a c t i c a l r e a s o n s , particularly the t r a n s p o r t a n d m o u n t i n g o f c h a m b e r e l e m e n t s . W i n d o w s with e x t e r n a l r e c e s s e s h a d to be a c c e s s i b l e f r o m the outside to e n a b l e the f r a m e to be m o u n t e d . T h e r e f o r e , only g r o u n d - f l o o r w i n d o w s or t h o s e o v e r l o o k i n g terr a c e s c o u l d be tested.
u n d e r a p a r t i c u l a r p r e s s u r e , as specified in the ASTM E 2 8 3 s t a n d a r d . In this case, the air is infiltrating the w i n d o w t h r o u g h the j o i n t bet w e e n t h e s a s h a n d the f r a m e , w h o s e length is defined as the c r a c k length. In the field test, the c h a m b e r is built a r o u n d the window. In the c u r r e n t study, this w a s a c h i e v e d b y installing a w o o d e n f r a m e with p l e x i g l a s s s h e e t on either the interior or ext e r i o r o f the w i n d o w to f o r m the c h a m b e r (Fig. 2). T h e w o o d e n f r a m e ' s j o i n t with the wall w a s s e a l e d with silicon p a s t e , as w a s the p l e x i g l a s s / f r a m e joint. The t e s t is s t a n d a r d i z e d in ASTM E 7 8 3 . In the field test, air c o u l d infiltrate the w i n d o w t h r o u g h the s a s h / f r a m e j o i n t a n d / o r the window/wall joint. The m a i n c o n c e r n w a s the v o l u m e o f air infiltrating the window, reg a r d l e s s o f the r o u t e it took. T h e infiltration r a t e w a s r e p o r t e d p e r unit o f c r a c k length to facilitate c o m p a r i s o n with o t h e r w i n d o w s a n d with l a b o r a t o r y results. The field-test e q u i p m e n t c o n s i s t e d of a n air blower, an airflow m e t e r a n d a m a n o m e t e r . The b l o w e r w a s c a p a b l e of delivering 75 m3/ h at a m a x i m u m p r e s s u r e of 6 0 0 Pa. The airflow m e t e r c o m p l i e d with t h e r e q u i r e m e n t s of ASTM E 7 8 3 . T h e p r e s s u r e difference w a s m e a s u r e d using a m i c r o m a n o m e t e r with an acc u r a c y up to 0.01 m m o f liquid c o l u m n height;
Field test set-up Air-infiltration t e s t s are n o r m a l l y c a r r i e d out in the l a b o r a t o r y , w h e r e the w i n d o w is e n c l o s e d in a p r e s s u r e c h a m b e r a n d e x p o s e d to differential p r e s s u r e s . T h e airflow a n d p r e s s u r e diff e r e n c e a c r o s s the w i n d o w are u s e d to calculate the infiltration r a t e p e r unit of c r a c k length
Fig. 2. General arrangement of the pressure chamber on a double sliding window installed at a ground floor.
79 the liquid h a d a specific g r a v i t y of 0 . 7 9 3 at 20 °C. T h e t e s t w a s c a r r i e d out 24 h o u r s a f t e r the f r a m e w a s installed, to give e n o u g h t i m e for the silicon to set. The w i n d o w w a s l o c k e d p r i o r to the test. The airflow m e t e r a n d the mic r o m e t e r w e r e s e t to zero, a n d the liquid w a s c h e c k e d to e n s u r e t h a t it w a s free of air b u b b l e s . The air-supply hose and the pressure tubes w e r e c o n n e c t e d to nozzles fixed to t h e plexiglass s h e e t (Fig. 3). T h e w i n d o w w a s e x p o s e d to a p r e s s u r e o f 150 P a to c h e c k for air leaks t h r o u g h the f r a m e j o i n t s or the c o n n e c t i o n s b e t w e e n the c h a m b e r a n d the t e s t i n g a p p a r a t u s . Once t h e a p p a r a t u s w a s s e c u r e d , the t e s t w a s c a r r i e d out b y i n c r e m e n t a l i n c r e a s e s in t h e air flow in s t e p s o f 2 cm. The c o r r e s p o n d i n g p r e s s u r e w a s r e c o r d e d . At least o n e r e a d i n g w a s t a k e n close to a c h a m b e r p r e s s u r e o f 75 Pc, w h i c h is the s t a n d a r d p r e s s u r e r e q u i r e d b y the ANSI/AAMA 101-85 v o l u n t a r y specifications. In c a s e s w h e r e this p r e s s u r e w a s n o t a c h i e v a b l e , e.g., b a d l y leaking w i n d o w s , the airflow at 75 P a w a s e x t r a p o l a t e d b y
Q75 = (75/AP)l/2Q w h e r e Q=air loss at s t a n d a r d a t m o s p h e r i c t e m p e r a t u r e a n d p r e s s u r e c o n d i t i o n s (STP) (mS/h); Q75 = air loss at STP at c h a m b e r p r e s -
s u r e o f 75 P a (mS/h) a n d A P = p r e s s u r e loss a c r o s s t h e orifice m e a s u r e d in m e t e r s of w a t e r (Pc). T h e r e s u l t s w e r e r e p o r t e d in the following ways: Total v o l u m e o f air loss (Q) in m3/h. Air infiltration r a t e p e r unit c r a c k length in mS/him. Air infiltration r a t e p e r unit daylight a r e a in m 3 f n / m 2. Air infiltration r a t e p e r unit ventilation a r e a in m V h / m 2.
Discussion of results T h e m e a n air infiltration r a t e p e r unit o f c r a c k length o v e r the entire s a m p l e w a s 13.48 m3/h/m, w h i c h is 3 4 0 % h i g h e r t h a n the m a x i m u m a l l o w e d b y ANSI/AAMA 101-85 for field tests. T h e f r e q u e n c y o f o c c u r r e n c e for t h e r e s u l t s is p l o t t e d a g a i n s t t h e u p p e r limit o f the air-infiltration r a t e within e a c h strip in Fig. 4. Nine w i n d o w s (five fixed a n d f o u r tilt-andt u r n ) satisfied the ANSI/AAMA limit, r e p r e s e n t i n g 6% of t h e t o t a l s a m p l e . In c o n t r a s t , W e i d t a n d W e i d t [5] r e p o r t e d t h a t 60% of n e w l y installed w i n d o w s in the U.S.A. h a v e s a t i s f a c t o r y air-infiltration rates. F i f t e e n wind o w s h a d air infiltration r a t e s r a n g i n g f r o m 3 . 0 7 to 6 . 1 4 m S / h / m ( 1 0 0 - 2 0 0 % o f the limit). This i n c r e a s e d to 30 f o r t h e n e x t g r o u p , w h e r e the a i r - l e a k a g e r a t e r a n g e d f r o m 2 0 0 to 3 0 0 % of the ANSI/AAMA limit. Accordingly, 54 windows, i.e., 3 5 % of the t o t a l s a m p l e , allowed an a m o u n t o f air infiltration less t h a n or e q u a l 40 [] R I I Windows o
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Fig. 3. Attachment connection between air hose and test chamber.
Fig. 4. Frequency distribution for air infiltration rates of all windows, double sliders and vertically hinged windows.
80 to three times the ANSI/AAMA limit. The remaining 65% had an air-infiltration rate higher than 9.27 ma/h/m. Plotting the same diagram for the double sliders (Fig. 4) indicates that nine of the 72 in the sample had air-leakage rates ranging from 3.07 and 6.14 mS/h/m, and 17 had rates between 6.14 and 9.27 ma/h/m. Thus, 36% of sliding windows had air-leakage rates below 9.27 mS/h/m, almost the same ratio as in the entire population. The frequency diagram for vertically hinged windows (single and double leaves combined) indicates that 15 windows out of 44 had air-leakage rates below 9.27 mS/ h/m. This represents the same percentage as for the entire population.
Effect of w i n d o w type on p e r f o r m a n c e The effect of window operational type was studied by evaluating the air-infiltration rate per unit of crack length, unit area of daylight and unit area of ventilation opening. Figure 5 shows the variation in air-infiltration rate per unit of crack length with different window types. Vertical sliders were not plotted due to lack of results. All types of openable windows had mean air-infiltration rates per unit of crack length exceeding the ANSI/AAMA limit. Horizontally hinged single-leaf (hopper) windows produced the highest mean (33.16 mS/h/m), and the vertically hinged double-leaf the lowest (11.10 mS/h/m). The means for tilt-and-turn
and double sliders were close to the lower limit, and those for double hopper and singleleaf vertically hinged windows came in midrange. Only four tilt-and-turn windows rated below the limit for the entire population of openable windows. Five fixed windows complied with the ANSI/AAMA limit for fixed windows (4.06 ma/h/m2). Weidt and Weidt [5] found that window type is a dominant factor controlling air leakage. Their mean values for casement, double sliders, vertically hinged double-leaf, single slider and vertically hinged single-leaf windows were 1.28, 3.41, 4.02, 4.41 and 5.36 mS/h/m, respectively. These are 30-40% of the values obtained for corresponding windows (double sliders and vertically hinged) in this study. It must be noted that Weidt and Weidt's sample contained wood, wood-cladded and aluminium windows. The method of reporting air-infiltration rate can slightly modify the position of each type with respect to the others. Figure 6 shows the types in descending order for each method of reporting, starting with the most airtight. The hopper and double hopper windows performed badly, regardless of the method of reporting the air-leakage rate. Tilt-and-turn and fixed windows consistently ranked among the types with least leakage. Double sliders and vertically hinged windows interchanged positions, depending on the method of reporting. However, the most noticeable change in rank occurred
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Per Unit Ventilation Area
Fig. 6. A i r i n f i l t r a t i o n rates o f v a r i o u s w L n d o w types.
when the double slider was r e p o r t e d per unit area of ventilation. This is mainly because the ventilation area of such windows is almost half the daylight area, thus doubling the deduced rate. Clearly, the m e t h o d of reporting air infiltration does not play an important role in judging window pe r f or m a nc e in Kuwait, possibly because the types of window tested are not sensitive to the m e t h o d of reporting airleakage rates. Weidt and Weidt [5], however, observed that the m et hod of reporting significantly affected the p e r f o r m a n c e evaluation of their sample, which included single and double sliders and single- and double-hung windows. In single-slider and single-hung types, the crack length is almost half that of the double-slider and double-hung ones, whereas the ventilation area and daylight area remain almost the same for both types. As a result, double sliders and double-hung windows always p r o d u c e d lower rates when the air infiltration was r e p o r t e d per linear crack length. When air leakage was r e p o r ted by either unit area of daylight or of ventilation, the single-slider and single-hung types p e r f o r m e d better than the double windows. In this study, the areas and crack lengths of vertically hinged double-leaf and doubleh o p p e r windows were almost double those of single-leaf windows. Thus, the double-leaf type always p er f o r med better than the single-leaf, regardless of reporting method. One except i on
is the vertically hinged group report ed by dayfight area, where the double-leaf type p r o d u c e d slightly higher rates than the single-leaf. This was attributed to the fixed daylight area in some double-leaf windows, which did not contribute to either the crack length or ventilation area data, being unopenable. However, this effect showed only when the rate was r e p o r t e d per daylight area. The standard deviation and range were more consistent than the m ean values of air infiltration for different types. Eliminating fixed windows and vertical sliders, the standard deviation ranged from 5.48 to 9.69 for doubleleaf windows and hoppers, respectively, whereas the m ean value of air infiltration per unit crack length varied from 11.10 to 33.16 ma/h/m (i.e., threefold). The range of results for all windows e x c e p t fixed and vertical sliders was also consistent, indicating that the quality of workmanship was consistent regardless of window type. However, the high standard deviation and range indicate that quality control over fabrication activities was poor. It is important to improve quality control to reduce the variability, and hence the standard deviation, in the results. This should be in parallel to reducing the mean value, in order to upgrade performance. Tilt-and-turn windows p e r f o r m e d better than the single-leaf vertically hinged ones. Both types have essentially the same function, except
82 that the tilt-and-turn windows can swing o p e n horizontally to act as a h o p p e r for ventilation. The tilt-and-turn type p r o d u c e d an air-leakage rate per unit c r a c k length a p p r o x i m a t e l y 50% that of the single-leaf and 33% that of the h o p p e r . T h e s e ratios i m p r o v e d w h e n the unit areas of daylight w e r e c o m p a r e d , with the tiltand-turn p r o d u c i n g 40% and 25% of the leakage rates for vertically hinged single-leaf windows and h o p p e r s , respectively. This significant superiority m a y be due to the m o r e r u g g e d construction and s u p e r i o r materials used to acc o m m o d a t e the s o p h i s t i c a t e d m e c h a n i s m for the dual operation.
Effect of w i n d o w age F o r windows up to 10 years old, age had no effect on the m e a n values of air infiltration, w h e r e a s older windows s h o w e d a 2 0 - 4 0 % imp r o v e m e n t in p e r f o r m a n c e . The s t a n d a r d deviation for newly installed windows was m o r e than double that for older windows, indicating that the level of quality control has declined in the past five to ten years. D e t e r i o r a t i o n of w e a t h e r strips and o t h e r e l e m e n t s over time a p p e a r e d to have little or no effect on w i n d o w p e r f o r m a n c e . This m a y reflect the v e r y high air-infiltration rates o b t a i n e d in this study, w h e r e b y the effects of aging were m a s k e d by serious defects in window construction. Weidt and Weidt [5] f o u n d that windows 2 5 - 5 0 years old p r o d u c e d h i g h e r air-leakage rates t h a n newly installed windows. Their sample was limited ( 6 - 9 cases), but t h e y a t t r i b u t e d this decline in p e r f o r m a n c e to the loss of w e a t h e r strips in old windows.
Effect of building type Slight variations in p e r f o r m a n c e w e r e obtained a m o n g windows installed in residential, office or public buildings. Residential buildings yielded air-infiltration rates 28% and 17% lower t h a n t h o s e for office and public buildings, respectively. This m a y reflect the e x t r a care t a k e n in selecting and maintaining windows in residential buildings. Since all t h r e e types had air-infiltration rates m o r e t h a n t h r e e times the ANSI/AAMA limit, this c o m p a r i s o n is spurious.
Effect of building cost The cost f a c t o r had no influence on the m e a n value for air infiltration. However, the s t a n d a r d deviation for low-cost buildings was the highest,
indicating that quality control was p o o r for this group. The m o s t e x p e n s i v e buildings prod u c e d the lowest s t a n d a r d deviation, indicating b e t t e r quality control. F o r all categories, however, b o t h the s t a n d a r d deviation and the airinfiltration rates w e r e quite high.
Effect of source o f material Most of the windows had locally p r o d u c e d profiles, but the s o u r c e of profile had little or no effect on the results. The i m p o r t e d profiles p r o d u c e d an air-infiltration rate 13% b e l o w t h o s e locally p r o d u c e d , and 9% below the overall average ( 1 3 . 4 8 ma/h/m). The double-slider windows yielded c o n s i s t e n t air-infiltration rates r e g a r d l e s s of the material source. A m o n g horizontally hinged ( h o p p e r and d o u b l e - h o p p e r c o m b i n e d ) windows, the local material allowed a b o u t 50% h i g h e r infiltration t h a n i m p o r t e d materials installed by foreign c o n t r a c t o r s . Although b o t h significantly exc e e d e d the s t a n d a r d limit, the windows that w e r e m a n u f a c t u r e d and installed b y local cont r a c t o r s were of significantly lower quality. This m a y have r e s u l t e d f r o m a lack o f local exp e r i e n c e with aluminium h o p p e r and doubleh o p p e r windows, since these t y p e s are relatively new.
Effect of source of w o r k m a n s h i p Since only 24 of the 154 windows t e s t e d involved i m p o r t e d w o r k m a n s h i p , it would be statistically u n s o u n d to c o m p a r e t h e m with the entire sample. However, since the i m p o r t e d g r o u p c o n s i s t e d mainly o f two t y p e s of window, double sliders and d o u b l e h o p p e r s , a reasonable c o m p a r i s o n could be m a d e with the corr e s p o n d i n g local groups. Since no double hoppers w e r e m a n u f a c t u r e d locally, they w e r e r e p l a c e d b y locally p r o d u c e d h o p p e r s . The sliders installed using i m p o r t e d w o r k m a n s h i p p r o d u c e d slightly h i g h e r infiltration rates t h a n local windows. This m a y be b e c a u s e t h e y w e r e mainly installed in public buildings, which generally yielded h i g h e r rates t h a n o t h e r buildings. Nevertheless, b o t h g r o u p s w e r e well a b o v e the ANSI/AAMA limit.
Effect of w i n d o w dimensions The effect of w i n d o w width (L) and a r e a (A) was studied to d e t e r m i n e if t h e r e are o p t i m u m dimensions at which air infiltration is minimized. Table 1 p r e s e n t s the air infiltration by total volume, v o l u m e p e r linear c r a c k length
83 TABLE 1. Air infiltration rates for different window widths Window width (m)
Number
Mean value
Standard deviation
Lower limit
Upper limit
34.64 33.36 44.33
0.00 18.68 0.00
164.73 155.70 166.47
0.00 3.56 0.00
46.75 28.11 29.94
0.00 12.00 0.00
191.89 116.00 149.55
Total v o l u m e of air infiltration (m3/h) L < 1.0 1.0 < L < 1.5 L > 1.5
75 58 21
66.09 68.57 68.90
Air infiltration per unit crack length (mS/h/m) L < 1.0 1.0 < L < 1.5 L > 1.5
75 58 21
14.77 12.51 11.59
10.02 6.28 8.04
Air infiltration per unit daylight area (ma/h/m2) L < 1.0 1.0 < L < 1.5 L > 1.5
75 58 21
65.25 47.65 46.36
and volume per unit daylight area for different window widths across the total sample. Table 2 presents the same data for different window areas. The results show the following: (1) Whereas the air-infiltration rate per unit crack length or daylight area decreases with increasing L and A, the total volume of air infiltration remains almost unchanged. This is explained by the increased crack length and daylight area in larger windows, which result
43.56 26.27 42.50
in decreased infiltration rates. However, the air-infiltration volume depends on the size and location of the defects. Since most of the defects found in the sample were basically independent of size, e.g., gaps between the vertical sections of double sliders, missing hardware or missing hole caps, the insensitivity of total volume of air to window size is explicable. (2) Infiltration rates for double sliders and double-leaf windows in different width and area
TABLE 2. Air infiltration for different window areas Area (m 2)
Number
Mean value
Standard deviation
Total v o l u m e (mS/h) A < 1.0 1.0 < A < 1.5 1.5 < A < 1.8 1.8 < A < 2.0 A>2.0
A < 1.0 1.0 < A < 1.5 1.5 < A < 1.8 1.8 < A < 2.0 A > 2.0
45 59 22 23 5
45 59 22 23 5
69.60 72.59 63.67 53.93 64.91
Mean value
Standard deviation
Per crack length (m3/h/m) 35.38 40.57 34.63 19.77 16.79
17.64 13.24 11.70 8.65 8.95
10.73 7.78 6.35 3.57 2.53
Per daylight area (mS/h/m 2)
Per vent. a r e a (ma/h/m2)
82.47 55.18 40.26 28.62 24.17
126.76 106.08 92.84 62.67 66.76
44.90 33.87 23.27 10.12 6.29
63.66 64.72 67.16 27.74 32.94
84
groups were analysed separately. For the same length or area group, most double sliders leaked less air than vertically hinged windows. In terms of total volume, the larger the area of the vertically hinged windows, the lower the volume of air leakage. This indicates that per f or m ance was influenced by factors other than dimensions, since this result was not expected. For double sliders, the air volume was independent of window size. This may be because double sliders leak mainly from corners and gaps, which are independent of window size, whereas hinged windows leak along the sash perimeter, which depends on the dimensions. It is therefore ex p ected that, the larger the window, the larger the perimeter and the higher the volume of air infiltration.
Conclusions The study showed that only 6% of windows in the sample complied with the ANSI/AAMA 101-85 limit. The majority yielded air-infiltration rates well above this limit, indicating grave shortcomings in window construction in Kuwait when judged by American or E u r o p e a n standards. Furthermore, the deviation in the results was high, showing p o o r quality control over production activities. Horizontally hinged windows p r o d u c e d the highest air-infiltration rate, whereas fixed windows and tilt-and-turn windows allowed the least leakage. Double sliders and vertically hinged windows were midway between the extremes. Tilt-and-turn windows provided air leakage rates approximately one-half those of vertically hinged windows. Age had a negligible effect on window performance. Old windows per f or m ed better than the new ones, mainly due to a decline in construction practice and quality control in the local market. Windows in residential buildings yielded airinfiltration rates 28% and 17% lower than those in office and public buildings, respectively. Building cost, and hence contractor grade, seemed to have no influence on the mean values of air infiltration; however, low-cost buildings yielded higher standard deviations, indicating p o o r quality control among small contractors. The source of the aluminium profile had little or no effect on the air-infiltration rate. Windows
made from imported profiles produced an airleakage rate 9% below the overall average, and 11% below that of the locally p r o d u c e d profiles. Similarly, the source of workmanship (i.e., local or imported) had only a minor effect on performance. This, however, may change when perform ance limits are imposed by the national code of practice. The total volume of air infiltration seem ed to be independent of window size, since size is largely irrelevant to those defects allowing air leakage. However, double sliders leaked mostly from corners, whereas vertically hinged windows leaked from the sash/window joint. These conclusions are greatly influenced by the p o o r perform ance of windows in Kuwait, and may not necessarily be applicable to windows installed in regions where perform ance criteria are imposed on window production. Hence the output of the study has created public concern about the need to impose such limitations on window fabrication in Kuwait. A revised Kuwaiti specification incorporating performance requirements is currently under preparation.
Acknowledgements This study was sponsored by the Kuwait Foundation for the Advancement of Sciences (KFAS), the Arabian Light Metal Co. and the Kuwait Institute for Scientific Research (KISR). The authors are grateful to Dr Mozammal Khan for his help in analysing the data, and to Mr Hamdy Hussain for his assistance during the field test.
References 1 0 . Daoud, H. A1-Shami and G. Maheshwari, Field survey and performance assessment of aluminium windows in Kuwait, Kuwait Institute f o r Scientific Research, Rep. No. KISR3072, Kuwait, 1989. 2 Annual StatisticalAbstract, Central Statistical Office, Ministry of Planning, Kuwait, 1985. 3 J. F. S. Carruthers, The performance assessment of windows, Proc. Windows in Building Design and Maintenance, Gothenburg, Sweden, Swedish Council of Building Research, 1987, pp. 34--40. 4 O. Daoud, G. Maheshwari and H. A1-Shami, Defects in aluminum windows and their impact on dust and air infiltration, in preparation.
85 5 J. Weidt and J. Weidt, Air leakage of newly installed residential windows, Lawrence Berkeley Laboratories, Rep. LBL 11111, National Technical Information Service, Springfield, VA, U.S.A., 1980. 6 AAMA, Voluntary Specifications f o r A l u m i n u m Architectural Windows, GS-O01, American Architectural Manufacturers Association, IL, U.S.A., 1984.
7 ANSI/AAMA, VoluntarySpecificationsforAluminum Prime Windows and Sliding Doors, ANSI/AAMA 101-85, American Architectural Manufacturers Association, IL, U.S.A., 1985. 8 J. Nevander, Closing remarks, Proc. Windows in Building Design and Maintenance, Gothenburg, Sweden, Swedish Council of Building Research, 1987, pp. 133-134.
75
Measured field performance of aluminium windows in Kuwait Osama Daoud*, Gopal M a h e s h w a r i and H a k e m Al-Shami Engineering Division, Kuwait Institute f o r Scientific Research, P.O. Box 24885, Safat 13109 (Kuwait)
(Received February 18, 1990; accepted June 22, 1990; revised paper received July 27, 1990)
Abstract The air infiltration rate is determined for 154 aluminium windows installed in 25 buildings in Kuwait. The influence of window characteristics such as type, dimensions, source of profile, source of workmanship, building function, cost and age has been studied. Air-tightness is determined using portable equipment to pressurize a chamber created on each window and to measure the air flow and pressure increase. The results show that aluminium windows in Kuwait have a mean infiltration rate of 13.48 m3/h/m at 75 Pa, about 3.4 times higher than the ANSI/ AAMA maximum limit. The type of window is the main factor influencing performance, with horizontally hinged windows leaking the most, and tilt-and-turn and fixed windows the least. Newly installed windows and those installed in low-cost projects show marginally greater mean air-infiltration values than those in old or prestigious projects; however, the standard deviation is noticeably greater, indicating lower quality control. Windows installed in residential buildings produce lower leakage rates than ~hose in office or public buildings. The volume of air leakage remains the same for sliding windows with different areas, indicating that leakage occurs mostly at the corners; however, leakage increases with area for vertically hinged windows, showing that leakage occurs at the sash/window joint.
Introduction Aluminium w i n d o w s have g a i n e d p o p u l a r i t y in the Arabian Gulf r e g i o n in the p a s t 15 y e a r s b e c a u s e of their relatively low c o s t c o m p a r e d to t i m b e r or steel ones. Aluminium billets are locally p r o d u c e d in one f a c t o r y in Bahrain. I m p o r t e d billets f r o m n e i g h b o u r i n g c o u n t r i e s are also available at c o m p e t i t i v e prices. In Kuwait, a l u m i n i u m profiles are e x t r u d e d in two factories, w h e r e a s a l u m i n i u m w i n d o w s a n d d o o r s are f a b r i c a t e d u s i n g local a n d i m p o r t e d profiles in 45 w o r k s h o p s . Most o f the w i n d o w s f a b r i c a t e d are double sliders; since t h e s e do n o t o c c u p y s p a c e w h e n t h e y are open. Other types, s u c h as tilt-and-turn a n d vertically or horizontally h i n g e d windows, are gaining a c c e p t a n c e . However, the c h o i c e of w i n d o w type does n o t follow a n y f u n c t i o n a l or per*Present address: 34 Goal Gamal Street, Agooza Cairo, Egypt.
0378-7788/91/$3.50
f o r m a n c e criteria, b u t d e p e n d s mainly o n cost. A serious d r a w b a c k in f e n e s t r a t i o n w o r k s in Kuwait arises f r o m the w i n d o w s ' lack o f aira n d water-tightness. The c o n s e q u e n t high energy c o n s u m p t i o n for c o o l i n g s y s t e m s is a b u r d e n o n the total national c o n s u m p t i o n . T h e s e s h o r t c o m i n g s in w i n d o w p e r f o r m a n c e are a t t r i b u t e d to the following factors: (1) No c o d e o f p r a c t i c e or national s t a n d a r d for w i n d o w p e r f o r m a n c e is applied. Designers a n d c o n t r a c t o r s follow o w n e r s ' r e q u e s t s for m i n i m u m profile t h i c k n e s s a n d a n o d i z a t i o n colo u r only. No p e r f o r m a n c e criteria are p r o v i d e d in m o s t d e s i g n d o c u m e n t s . (2) In t h o s e rare c a s e s w h e r e p e r f o r m a n c e criteria are specified, t h e y are generally ignored, since n o testing facilities are available to verify c o m p l i a n c e . (3) There is little interest a m o n g building o w n e r s in the e n e r g y savings t h e y c a n achieve f r o m tighter windows, since the g o v e r n m e n t
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76 subsidizes up to 90% of the cost o f electricity. Thus, o w n e r s are m o r e i n t e r e s t e d in cutting down o n initial costs by using inferior c h e a p windows. Consequently, m a n y design, fabrication, installation and m a i n t e n a n c e defects are obs e r v e d in f e n e s t r a t i o n works [1]. Not only are air and heat allowed to p e n e t r a t e into the interior, causing a t e m p e r a t u r e increase and high c o n s u m p t i o n of e n e r g y to o p e r a t e the cooling systems, but also dust particles can enter, creating a n u i s a n c e for tenants. Fine dust is c o m m o n in Kuwait during high winds, especially in the summer; the annual dust fallout is 119 tA
o r a t o r y results with practical field e x p e r i e n c e . F u r t h e r m o r e , he s t r e s s e d the n e e d for inform a t i o n on the p e r f o r m a n c e of windows subj e c t e d to natural w e a t h e r i n g conditions. Literature, however, is s c a r c e on the perf o r m a n c e o f aluminium windows installed in old buildings in a h a r s h climate, s u c h as that of the Arabian Gulf States. Quality and perf o r m a n c e criteria for t h e s e e l e m e n t s have not b e e n well defined. Many c o n t r a c t o r s i m p o r t windows either r e a d y - a s s e m b l e d or k n o c k e d down, without giving m u c h c o n s i d e r a t i o n to their suitability. I m p o r t e d materials v a r y widely in quality, and, in the a b s e n c e o f controls, low g r a d e s are used. It is generally a c c e p t e d that the quality of w o r k m a n s h i p greatly influences w i n d o w perf o r m a n c e . D a o u d et al. [4] f o u n d that defects due to fabrication and installation p r o c e s s e s are the m o s t influential in degrading the perf o r m a n c e of aluminium windows installed in buildings of different ages in Kuwait. The quality o f w o r k m a n s h i p in the Gulf states is normally related to the size of c o n t r a c t o r . Large cont r a c t o r s have the r e s o u r c e s to c o n t r o l quality in o r d e r to maintain their reputations. Small c o n t r a c t o r s , o n the o t h e r hand, do not p a y m u c h a t t e n t i o n to this area. T h e y often d e p e n d on newly hired p e r s o n n e l with little or no e x p e r i e n c e , in o r d e r to minimize the cost. Also, small c o n t r a c t o r s are involved in small p r o j e c t s a c c o r d i n g to g o v e r n m e n t a l categorization. This applies to general c o n t r a c t o r s ; however, its application to specialized c o n t r a c t o r s , such as t h o s e involved in f e n e s t r a t i o n works, is n o t clear. Weidt and Weidt [5] f o u n d the cont r a c t o r ' s e x p e r i e n c e can greatly influence the air infiltration rate t h r o u g h newly installed windows. This, however, was d e d u c e d f r o m a limited n u m b e r of field tests. This s t u d y was directed towards evaluating the effect of w i n d o w type, s o u r c e of material and w o r k m a n s h i p , and the age, dimensions, function and cost of the building on air infiltration t h r o u g h aluminium windows. The data w e r e b a s e d o n field air-infiltration tests of windows installed in 25 buildings in Kuwait. The aim was to initiate national a w a r e n e s s of the n e e d for national specifications for w i n d o w p e r f o r m a n c e , and to s t u d y the effect of different w i n d o w characteristics o n p e r f o r m a n c e .
77 residential buildings was a l m o s t double that of office or public buildings. This is c o n s i s t e n t with their actual distribution. The care and m a i n t e n a n c e o f windows o f e a c h type is exp e c t e d to v a r y noticeably. V~rmdows in residential buildings are u s e d b y a limited n u m b e r o f people, and are c l e a n e d and c h e c k e d o n a m o r e regular basis t h a n t h o s e in office or public buildings. Since public buildings have m a n y m o r e users, their windows are s u b j e c t e d to m o r e abuse. W i n d o w s ranging in age f r o m newly installed to m o r e t h a n 10 y e a r s old w e r e t e s t e d (Fig. l ( c ) ) . Newly installed windows (less t h a n o r equal to two y e a r s old) d o m i n a t e d the sample, since t h e y r e p r e s e n t the m o s t r e c e n t p r a c t i c e in Kuwait, w h i c h t h e o r e t i c a l l y s h o u l d r e p r e s e n t the highest quality. Notably, haft o f t h e s e have b e e n installed in national h o u s i n g p r o j e c t s that are c u r r e n t l y u n d e r c o n s t r u c t i o n and are the highest quality g o v e r n m e n t a l h o u s i n g projects, since t h e y benefit f r o m the cumulative e x p e -
Sample selection The field s u r v e y was carried out o n 154 windows installed in 25 buildings l o c a t e d a r o u n d Kuwait City. Eight o p e r a t i o n a l t y p e s w e r e included: horizontal d o u b l e slider, vertical single slider, vertically h i n g e d single a n d d o u b l e leaf, horizontally h i n g e d single and d o u b l e leaf, tilt-and-turn and fixed (Fig. l ( a ) ) . H o r i z o n t a l d o u b l e sliders d o m i n a t e d the sample, r e p r e senting 45% of the total; this is in Line with the fact that d o u b l e sliders are the m o s t comm o n t y p e of w i n d o w in Kuwait. Vertically h i n g e d windows, at 29%, axe the s e c o n d m o s t c o m m o n type. Tilt-and-turn, vertical sliders and fixed windows are rare, and h e n c e w e r e the least n u m e r o u s in the sample. The s a m p l e i n c l u d e d windows installed in buildings with t h r e e different functions: residential, office and public. The total n u m b e r o f windows within e a c h type was k e p t a l m o s t c o n s t a n t (Fig. l ( b ) ) , h o w e v e r , the n u m b e r o f
V.Slider Fixed
(a)
(b)
$150,000
\
6 bldg] (> 10 yrs)
----'---/
\ 11.7__% 3 6/ . . US$ 150,000--6 m
)
\
/
.3% > US $ 6 m
/ /
[2 bldg]
(d) (c) Fig. 1. Characteristics of windows included in the sample (a) W'mdow type; (b) building type; (c) window age; (d) building cost.
78 rience of the p a s t 10 years. The o t h e r a g e g r o u p s w e r e included to c o m p a r e old with n e w p r a c t i c e a n d to d e t e r m i n e the i m p a c t o f a g e on p e r f o r m a n c e . The c o s t of the building reflects the size of the c o n t r a c t o r involved in its c o n s t r u c t i o n . Figure l ( d ) s h o w s the p e r c e n t a g e o f w i n d o w s t e s t e d within e a c h c o s t g r o u p . T h r e e g r o u p s w e r e defined, r e p r e s e n t i n g the wide r a n g e of buildings in Kuwait. T h e s a m p l e i n c l u d e d buildings r a n g i n g in c o s t b e t w e e n U S $ 1 5 0 0 0 0 a n d US$ 25 0 0 0 000. Sixteen small villas, s u c h as t h o s e built in the national h o u s i n g s c h e m e , r e p r e s e n t e d the low-cost buildings, a n d w e r e m o r e n u m e r o u s in the s a m p l e ; s e v e n c o m m e r c i a l c o m p l e x e s or large public facilities r e p r e s e n t e d the o t h e r e n d of the scale. T h e w i n d o w s in the l o w - c o s t buildings n u m e r i c a l l y d o m i n a t e d the s a m p l e , w h i c h reflects the a c t u a l distribution t h a t exists. Since a large s h a r e of the m a r k e t in Kuwait d e p e n d s o n i m p o r t e d m a t e r i a l s a n d labour, the s o u r c e s of a l u m i n i u m profiles a n d w o r k m a n s h i p w e r e included as two p a r a m e t e r s so t h a t their i m p a c t on p e r f o r m a n c e c o u l d b e a s s e s s e d . The s a m p l e s e l e c t i o n w a s c o n t r o l l e d b y g e o m e t r i c a l factors, s u c h as the w i n d o w s h a p e , d i m e n s i o n s a n d accessibility, as well as b y the t e n a n t s ' r e s p o n s e to the t e s t i n g request. The w i n d o w h a d to h a v e either an e x t e r n a l or internal r e c e s s to e n a b l e the w o o d e n f r a m e t h a t f o r m e d (with the w i n d o w a n d the wall) the t e s t p r e s s u r e c h a m b e r to b e m o u n t e d . This arrangement eliminated any permanent damage to the wall finish n e a r the window. Also, w i n d o w d i m e n s i o n s w e r e limited to less t h a n 1.8 m in either direction for p r a c t i c a l r e a s o n s , particularly the t r a n s p o r t a n d m o u n t i n g o f c h a m b e r e l e m e n t s . W i n d o w s with e x t e r n a l r e c e s s e s h a d to be a c c e s s i b l e f r o m the outside to e n a b l e the f r a m e to be m o u n t e d . T h e r e f o r e , only g r o u n d - f l o o r w i n d o w s or t h o s e o v e r l o o k i n g terr a c e s c o u l d be tested.
u n d e r a p a r t i c u l a r p r e s s u r e , as specified in the ASTM E 2 8 3 s t a n d a r d . In this case, the air is infiltrating the w i n d o w t h r o u g h the j o i n t bet w e e n t h e s a s h a n d the f r a m e , w h o s e length is defined as the c r a c k length. In the field test, the c h a m b e r is built a r o u n d the window. In the c u r r e n t study, this w a s a c h i e v e d b y installing a w o o d e n f r a m e with p l e x i g l a s s s h e e t on either the interior or ext e r i o r o f the w i n d o w to f o r m the c h a m b e r (Fig. 2). T h e w o o d e n f r a m e ' s j o i n t with the wall w a s s e a l e d with silicon p a s t e , as w a s the p l e x i g l a s s / f r a m e joint. The t e s t is s t a n d a r d i z e d in ASTM E 7 8 3 . In the field test, air c o u l d infiltrate the w i n d o w t h r o u g h the s a s h / f r a m e j o i n t a n d / o r the window/wall joint. The m a i n c o n c e r n w a s the v o l u m e o f air infiltrating the window, reg a r d l e s s o f the r o u t e it took. T h e infiltration r a t e w a s r e p o r t e d p e r unit o f c r a c k length to facilitate c o m p a r i s o n with o t h e r w i n d o w s a n d with l a b o r a t o r y results. The field-test e q u i p m e n t c o n s i s t e d of a n air blower, an airflow m e t e r a n d a m a n o m e t e r . The b l o w e r w a s c a p a b l e of delivering 75 m3/ h at a m a x i m u m p r e s s u r e of 6 0 0 Pa. The airflow m e t e r c o m p l i e d with t h e r e q u i r e m e n t s of ASTM E 7 8 3 . T h e p r e s s u r e difference w a s m e a s u r e d using a m i c r o m a n o m e t e r with an acc u r a c y up to 0.01 m m o f liquid c o l u m n height;
Field test set-up Air-infiltration t e s t s are n o r m a l l y c a r r i e d out in the l a b o r a t o r y , w h e r e the w i n d o w is e n c l o s e d in a p r e s s u r e c h a m b e r a n d e x p o s e d to differential p r e s s u r e s . T h e airflow a n d p r e s s u r e diff e r e n c e a c r o s s the w i n d o w are u s e d to calculate the infiltration r a t e p e r unit of c r a c k length
Fig. 2. General arrangement of the pressure chamber on a double sliding window installed at a ground floor.
79 the liquid h a d a specific g r a v i t y of 0 . 7 9 3 at 20 °C. T h e t e s t w a s c a r r i e d out 24 h o u r s a f t e r the f r a m e w a s installed, to give e n o u g h t i m e for the silicon to set. The w i n d o w w a s l o c k e d p r i o r to the test. The airflow m e t e r a n d the mic r o m e t e r w e r e s e t to zero, a n d the liquid w a s c h e c k e d to e n s u r e t h a t it w a s free of air b u b b l e s . The air-supply hose and the pressure tubes w e r e c o n n e c t e d to nozzles fixed to t h e plexiglass s h e e t (Fig. 3). T h e w i n d o w w a s e x p o s e d to a p r e s s u r e o f 150 P a to c h e c k for air leaks t h r o u g h the f r a m e j o i n t s or the c o n n e c t i o n s b e t w e e n the c h a m b e r a n d the t e s t i n g a p p a r a t u s . Once t h e a p p a r a t u s w a s s e c u r e d , the t e s t w a s c a r r i e d out b y i n c r e m e n t a l i n c r e a s e s in t h e air flow in s t e p s o f 2 cm. The c o r r e s p o n d i n g p r e s s u r e w a s r e c o r d e d . At least o n e r e a d i n g w a s t a k e n close to a c h a m b e r p r e s s u r e o f 75 Pc, w h i c h is the s t a n d a r d p r e s s u r e r e q u i r e d b y the ANSI/AAMA 101-85 v o l u n t a r y specifications. In c a s e s w h e r e this p r e s s u r e w a s n o t a c h i e v a b l e , e.g., b a d l y leaking w i n d o w s , the airflow at 75 P a w a s e x t r a p o l a t e d b y
Q75 = (75/AP)l/2Q w h e r e Q=air loss at s t a n d a r d a t m o s p h e r i c t e m p e r a t u r e a n d p r e s s u r e c o n d i t i o n s (STP) (mS/h); Q75 = air loss at STP at c h a m b e r p r e s -
s u r e o f 75 P a (mS/h) a n d A P = p r e s s u r e loss a c r o s s t h e orifice m e a s u r e d in m e t e r s of w a t e r (Pc). T h e r e s u l t s w e r e r e p o r t e d in the following ways: Total v o l u m e o f air loss (Q) in m3/h. Air infiltration r a t e p e r unit c r a c k length in mS/him. Air infiltration r a t e p e r unit daylight a r e a in m 3 f n / m 2. Air infiltration r a t e p e r unit ventilation a r e a in m V h / m 2.
Discussion of results T h e m e a n air infiltration r a t e p e r unit o f c r a c k length o v e r the entire s a m p l e w a s 13.48 m3/h/m, w h i c h is 3 4 0 % h i g h e r t h a n the m a x i m u m a l l o w e d b y ANSI/AAMA 101-85 for field tests. T h e f r e q u e n c y o f o c c u r r e n c e for t h e r e s u l t s is p l o t t e d a g a i n s t t h e u p p e r limit o f the air-infiltration r a t e within e a c h strip in Fig. 4. Nine w i n d o w s (five fixed a n d f o u r tilt-andt u r n ) satisfied the ANSI/AAMA limit, r e p r e s e n t i n g 6% of t h e t o t a l s a m p l e . In c o n t r a s t , W e i d t a n d W e i d t [5] r e p o r t e d t h a t 60% of n e w l y installed w i n d o w s in the U.S.A. h a v e s a t i s f a c t o r y air-infiltration rates. F i f t e e n wind o w s h a d air infiltration r a t e s r a n g i n g f r o m 3 . 0 7 to 6 . 1 4 m S / h / m ( 1 0 0 - 2 0 0 % o f the limit). This i n c r e a s e d to 30 f o r t h e n e x t g r o u p , w h e r e the a i r - l e a k a g e r a t e r a n g e d f r o m 2 0 0 to 3 0 0 % of the ANSI/AAMA limit. Accordingly, 54 windows, i.e., 3 5 % of the t o t a l s a m p l e , allowed an a m o u n t o f air infiltration less t h a n or e q u a l 40 [] R I I Windows o
•O.Sliders
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30
's S z
15.4 ~f .5 27.6 33.8 39.9 46 3 " a 7 . 149"21T2.3 18.4 24.6 30.7 36.8 4 2 . g 49.1 NQx i mum Fli r L e ~ Q g e ( c u . m / h / r n )
Fig. 3. Attachment connection between air hose and test chamber.
Fig. 4. Frequency distribution for air infiltration rates of all windows, double sliders and vertically hinged windows.
80 to three times the ANSI/AAMA limit. The remaining 65% had an air-infiltration rate higher than 9.27 ma/h/m. Plotting the same diagram for the double sliders (Fig. 4) indicates that nine of the 72 in the sample had air-leakage rates ranging from 3.07 and 6.14 mS/h/m, and 17 had rates between 6.14 and 9.27 ma/h/m. Thus, 36% of sliding windows had air-leakage rates below 9.27 mS/h/m, almost the same ratio as in the entire population. The frequency diagram for vertically hinged windows (single and double leaves combined) indicates that 15 windows out of 44 had air-leakage rates below 9.27 mS/ h/m. This represents the same percentage as for the entire population.
Effect of w i n d o w type on p e r f o r m a n c e The effect of window operational type was studied by evaluating the air-infiltration rate per unit of crack length, unit area of daylight and unit area of ventilation opening. Figure 5 shows the variation in air-infiltration rate per unit of crack length with different window types. Vertical sliders were not plotted due to lack of results. All types of openable windows had mean air-infiltration rates per unit of crack length exceeding the ANSI/AAMA limit. Horizontally hinged single-leaf (hopper) windows produced the highest mean (33.16 mS/h/m), and the vertically hinged double-leaf the lowest (11.10 mS/h/m). The means for tilt-and-turn
and double sliders were close to the lower limit, and those for double hopper and singleleaf vertically hinged windows came in midrange. Only four tilt-and-turn windows rated below the limit for the entire population of openable windows. Five fixed windows complied with the ANSI/AAMA limit for fixed windows (4.06 ma/h/m2). Weidt and Weidt [5] found that window type is a dominant factor controlling air leakage. Their mean values for casement, double sliders, vertically hinged double-leaf, single slider and vertically hinged single-leaf windows were 1.28, 3.41, 4.02, 4.41 and 5.36 mS/h/m, respectively. These are 30-40% of the values obtained for corresponding windows (double sliders and vertically hinged) in this study. It must be noted that Weidt and Weidt's sample contained wood, wood-cladded and aluminium windows. The method of reporting air-infiltration rate can slightly modify the position of each type with respect to the others. Figure 6 shows the types in descending order for each method of reporting, starting with the most airtight. The hopper and double hopper windows performed badly, regardless of the method of reporting the air-leakage rate. Tilt-and-turn and fixed windows consistently ranked among the types with least leakage. Double sliders and vertically hinged windows interchanged positions, depending on the method of reporting. However, the most noticeable change in rank occurred
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Air Infiltration Rate per Crack Length (m3 hr/m)
Fig. 5. Air infiltration rates per crack length for openable window types.
81 -350
35 F T DS DL SL H DH
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Fixed Tilt and Turn Double Slider Double Leaf- V. Hinged Single Leaf -V. Hinged Hopper Double Hopper
-300 e~~ -250
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Fig. 6. A i r i n f i l t r a t i o n rates o f v a r i o u s w L n d o w types.
when the double slider was r e p o r t e d per unit area of ventilation. This is mainly because the ventilation area of such windows is almost half the daylight area, thus doubling the deduced rate. Clearly, the m e t h o d of reporting air infiltration does not play an important role in judging window pe r f or m a nc e in Kuwait, possibly because the types of window tested are not sensitive to the m e t h o d of reporting airleakage rates. Weidt and Weidt [5], however, observed that the m et hod of reporting significantly affected the p e r f o r m a n c e evaluation of their sample, which included single and double sliders and single- and double-hung windows. In single-slider and single-hung types, the crack length is almost half that of the double-slider and double-hung ones, whereas the ventilation area and daylight area remain almost the same for both types. As a result, double sliders and double-hung windows always p r o d u c e d lower rates when the air infiltration was r e p o r t e d per linear crack length. When air leakage was r e p o r ted by either unit area of daylight or of ventilation, the single-slider and single-hung types p e r f o r m e d better than the double windows. In this study, the areas and crack lengths of vertically hinged double-leaf and doubleh o p p e r windows were almost double those of single-leaf windows. Thus, the double-leaf type always p er f o r med better than the single-leaf, regardless of reporting method. One except i on
is the vertically hinged group report ed by dayfight area, where the double-leaf type p r o d u c e d slightly higher rates than the single-leaf. This was attributed to the fixed daylight area in some double-leaf windows, which did not contribute to either the crack length or ventilation area data, being unopenable. However, this effect showed only when the rate was r e p o r t e d per daylight area. The standard deviation and range were more consistent than the m ean values of air infiltration for different types. Eliminating fixed windows and vertical sliders, the standard deviation ranged from 5.48 to 9.69 for doubleleaf windows and hoppers, respectively, whereas the m ean value of air infiltration per unit crack length varied from 11.10 to 33.16 ma/h/m (i.e., threefold). The range of results for all windows e x c e p t fixed and vertical sliders was also consistent, indicating that the quality of workmanship was consistent regardless of window type. However, the high standard deviation and range indicate that quality control over fabrication activities was poor. It is important to improve quality control to reduce the variability, and hence the standard deviation, in the results. This should be in parallel to reducing the mean value, in order to upgrade performance. Tilt-and-turn windows p e r f o r m e d better than the single-leaf vertically hinged ones. Both types have essentially the same function, except
82 that the tilt-and-turn windows can swing o p e n horizontally to act as a h o p p e r for ventilation. The tilt-and-turn type p r o d u c e d an air-leakage rate per unit c r a c k length a p p r o x i m a t e l y 50% that of the single-leaf and 33% that of the h o p p e r . T h e s e ratios i m p r o v e d w h e n the unit areas of daylight w e r e c o m p a r e d , with the tiltand-turn p r o d u c i n g 40% and 25% of the leakage rates for vertically hinged single-leaf windows and h o p p e r s , respectively. This significant superiority m a y be due to the m o r e r u g g e d construction and s u p e r i o r materials used to acc o m m o d a t e the s o p h i s t i c a t e d m e c h a n i s m for the dual operation.
Effect of w i n d o w age F o r windows up to 10 years old, age had no effect on the m e a n values of air infiltration, w h e r e a s older windows s h o w e d a 2 0 - 4 0 % imp r o v e m e n t in p e r f o r m a n c e . The s t a n d a r d deviation for newly installed windows was m o r e than double that for older windows, indicating that the level of quality control has declined in the past five to ten years. D e t e r i o r a t i o n of w e a t h e r strips and o t h e r e l e m e n t s over time a p p e a r e d to have little or no effect on w i n d o w p e r f o r m a n c e . This m a y reflect the v e r y high air-infiltration rates o b t a i n e d in this study, w h e r e b y the effects of aging were m a s k e d by serious defects in window construction. Weidt and Weidt [5] f o u n d that windows 2 5 - 5 0 years old p r o d u c e d h i g h e r air-leakage rates t h a n newly installed windows. Their sample was limited ( 6 - 9 cases), but t h e y a t t r i b u t e d this decline in p e r f o r m a n c e to the loss of w e a t h e r strips in old windows.
Effect of building type Slight variations in p e r f o r m a n c e w e r e obtained a m o n g windows installed in residential, office or public buildings. Residential buildings yielded air-infiltration rates 28% and 17% lower t h a n t h o s e for office and public buildings, respectively. This m a y reflect the e x t r a care t a k e n in selecting and maintaining windows in residential buildings. Since all t h r e e types had air-infiltration rates m o r e t h a n t h r e e times the ANSI/AAMA limit, this c o m p a r i s o n is spurious.
Effect of building cost The cost f a c t o r had no influence on the m e a n value for air infiltration. However, the s t a n d a r d deviation for low-cost buildings was the highest,
indicating that quality control was p o o r for this group. The m o s t e x p e n s i v e buildings prod u c e d the lowest s t a n d a r d deviation, indicating b e t t e r quality control. F o r all categories, however, b o t h the s t a n d a r d deviation and the airinfiltration rates w e r e quite high.
Effect of source o f material Most of the windows had locally p r o d u c e d profiles, but the s o u r c e of profile had little or no effect on the results. The i m p o r t e d profiles p r o d u c e d an air-infiltration rate 13% b e l o w t h o s e locally p r o d u c e d , and 9% below the overall average ( 1 3 . 4 8 ma/h/m). The double-slider windows yielded c o n s i s t e n t air-infiltration rates r e g a r d l e s s of the material source. A m o n g horizontally hinged ( h o p p e r and d o u b l e - h o p p e r c o m b i n e d ) windows, the local material allowed a b o u t 50% h i g h e r infiltration t h a n i m p o r t e d materials installed by foreign c o n t r a c t o r s . Although b o t h significantly exc e e d e d the s t a n d a r d limit, the windows that w e r e m a n u f a c t u r e d and installed b y local cont r a c t o r s were of significantly lower quality. This m a y have r e s u l t e d f r o m a lack o f local exp e r i e n c e with aluminium h o p p e r and doubleh o p p e r windows, since these t y p e s are relatively new.
Effect of source of w o r k m a n s h i p Since only 24 of the 154 windows t e s t e d involved i m p o r t e d w o r k m a n s h i p , it would be statistically u n s o u n d to c o m p a r e t h e m with the entire sample. However, since the i m p o r t e d g r o u p c o n s i s t e d mainly o f two t y p e s of window, double sliders and d o u b l e h o p p e r s , a reasonable c o m p a r i s o n could be m a d e with the corr e s p o n d i n g local groups. Since no double hoppers w e r e m a n u f a c t u r e d locally, they w e r e r e p l a c e d b y locally p r o d u c e d h o p p e r s . The sliders installed using i m p o r t e d w o r k m a n s h i p p r o d u c e d slightly h i g h e r infiltration rates t h a n local windows. This m a y be b e c a u s e t h e y w e r e mainly installed in public buildings, which generally yielded h i g h e r rates t h a n o t h e r buildings. Nevertheless, b o t h g r o u p s w e r e well a b o v e the ANSI/AAMA limit.
Effect of w i n d o w dimensions The effect of w i n d o w width (L) and a r e a (A) was studied to d e t e r m i n e if t h e r e are o p t i m u m dimensions at which air infiltration is minimized. Table 1 p r e s e n t s the air infiltration by total volume, v o l u m e p e r linear c r a c k length
83 TABLE 1. Air infiltration rates for different window widths Window width (m)
Number
Mean value
Standard deviation
Lower limit
Upper limit
34.64 33.36 44.33
0.00 18.68 0.00
164.73 155.70 166.47
0.00 3.56 0.00
46.75 28.11 29.94
0.00 12.00 0.00
191.89 116.00 149.55
Total v o l u m e of air infiltration (m3/h) L < 1.0 1.0 < L < 1.5 L > 1.5
75 58 21
66.09 68.57 68.90
Air infiltration per unit crack length (mS/h/m) L < 1.0 1.0 < L < 1.5 L > 1.5
75 58 21
14.77 12.51 11.59
10.02 6.28 8.04
Air infiltration per unit daylight area (ma/h/m2) L < 1.0 1.0 < L < 1.5 L > 1.5
75 58 21
65.25 47.65 46.36
and volume per unit daylight area for different window widths across the total sample. Table 2 presents the same data for different window areas. The results show the following: (1) Whereas the air-infiltration rate per unit crack length or daylight area decreases with increasing L and A, the total volume of air infiltration remains almost unchanged. This is explained by the increased crack length and daylight area in larger windows, which result
43.56 26.27 42.50
in decreased infiltration rates. However, the air-infiltration volume depends on the size and location of the defects. Since most of the defects found in the sample were basically independent of size, e.g., gaps between the vertical sections of double sliders, missing hardware or missing hole caps, the insensitivity of total volume of air to window size is explicable. (2) Infiltration rates for double sliders and double-leaf windows in different width and area
TABLE 2. Air infiltration for different window areas Area (m 2)
Number
Mean value
Standard deviation
Total v o l u m e (mS/h) A < 1.0 1.0 < A < 1.5 1.5 < A < 1.8 1.8 < A < 2.0 A>2.0
A < 1.0 1.0 < A < 1.5 1.5 < A < 1.8 1.8 < A < 2.0 A > 2.0
45 59 22 23 5
45 59 22 23 5
69.60 72.59 63.67 53.93 64.91
Mean value
Standard deviation
Per crack length (m3/h/m) 35.38 40.57 34.63 19.77 16.79
17.64 13.24 11.70 8.65 8.95
10.73 7.78 6.35 3.57 2.53
Per daylight area (mS/h/m 2)
Per vent. a r e a (ma/h/m2)
82.47 55.18 40.26 28.62 24.17
126.76 106.08 92.84 62.67 66.76
44.90 33.87 23.27 10.12 6.29
63.66 64.72 67.16 27.74 32.94
84
groups were analysed separately. For the same length or area group, most double sliders leaked less air than vertically hinged windows. In terms of total volume, the larger the area of the vertically hinged windows, the lower the volume of air leakage. This indicates that per f or m ance was influenced by factors other than dimensions, since this result was not expected. For double sliders, the air volume was independent of window size. This may be because double sliders leak mainly from corners and gaps, which are independent of window size, whereas hinged windows leak along the sash perimeter, which depends on the dimensions. It is therefore ex p ected that, the larger the window, the larger the perimeter and the higher the volume of air infiltration.
Conclusions The study showed that only 6% of windows in the sample complied with the ANSI/AAMA 101-85 limit. The majority yielded air-infiltration rates well above this limit, indicating grave shortcomings in window construction in Kuwait when judged by American or E u r o p e a n standards. Furthermore, the deviation in the results was high, showing p o o r quality control over production activities. Horizontally hinged windows p r o d u c e d the highest air-infiltration rate, whereas fixed windows and tilt-and-turn windows allowed the least leakage. Double sliders and vertically hinged windows were midway between the extremes. Tilt-and-turn windows provided air leakage rates approximately one-half those of vertically hinged windows. Age had a negligible effect on window performance. Old windows per f or m ed better than the new ones, mainly due to a decline in construction practice and quality control in the local market. Windows in residential buildings yielded airinfiltration rates 28% and 17% lower than those in office and public buildings, respectively. Building cost, and hence contractor grade, seemed to have no influence on the mean values of air infiltration; however, low-cost buildings yielded higher standard deviations, indicating p o o r quality control among small contractors. The source of the aluminium profile had little or no effect on the air-infiltration rate. Windows
made from imported profiles produced an airleakage rate 9% below the overall average, and 11% below that of the locally p r o d u c e d profiles. Similarly, the source of workmanship (i.e., local or imported) had only a minor effect on performance. This, however, may change when perform ance limits are imposed by the national code of practice. The total volume of air infiltration seem ed to be independent of window size, since size is largely irrelevant to those defects allowing air leakage. However, double sliders leaked mostly from corners, whereas vertically hinged windows leaked from the sash/window joint. These conclusions are greatly influenced by the p o o r perform ance of windows in Kuwait, and may not necessarily be applicable to windows installed in regions where perform ance criteria are imposed on window production. Hence the output of the study has created public concern about the need to impose such limitations on window fabrication in Kuwait. A revised Kuwaiti specification incorporating performance requirements is currently under preparation.
Acknowledgements This study was sponsored by the Kuwait Foundation for the Advancement of Sciences (KFAS), the Arabian Light Metal Co. and the Kuwait Institute for Scientific Research (KISR). The authors are grateful to Dr Mozammal Khan for his help in analysing the data, and to Mr Hamdy Hussain for his assistance during the field test.
References 1 0 . Daoud, H. A1-Shami and G. Maheshwari, Field survey and performance assessment of aluminium windows in Kuwait, Kuwait Institute f o r Scientific Research, Rep. No. KISR3072, Kuwait, 1989. 2 Annual StatisticalAbstract, Central Statistical Office, Ministry of Planning, Kuwait, 1985. 3 J. F. S. Carruthers, The performance assessment of windows, Proc. Windows in Building Design and Maintenance, Gothenburg, Sweden, Swedish Council of Building Research, 1987, pp. 34--40. 4 O. Daoud, G. Maheshwari and H. A1-Shami, Defects in aluminum windows and their impact on dust and air infiltration, in preparation.
85 5 J. Weidt and J. Weidt, Air leakage of newly installed residential windows, Lawrence Berkeley Laboratories, Rep. LBL 11111, National Technical Information Service, Springfield, VA, U.S.A., 1980. 6 AAMA, Voluntary Specifications f o r A l u m i n u m Architectural Windows, GS-O01, American Architectural Manufacturers Association, IL, U.S.A., 1984.
7 ANSI/AAMA, VoluntarySpecificationsforAluminum Prime Windows and Sliding Doors, ANSI/AAMA 101-85, American Architectural Manufacturers Association, IL, U.S.A., 1985. 8 J. Nevander, Closing remarks, Proc. Windows in Building Design and Maintenance, Gothenburg, Sweden, Swedish Council of Building Research, 1987, pp. 133-134.