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In situ measurements of frame wall thermal resistance
N21d
I
no.
1075
(*
National Research
Conseil national
C. 2
Council Canada
de recherches Canada
BLDO
I
I N SlTU MEASUREMENTS OF FRAME WALL THERMAL RESISTANCE
by W.C. Brown and G.D. Schuyler
Reprinted from
ASH RAE Transactions
Vol. 88, Part 1,1982
p. 667
-
676
DBR Paper No. 1075
Division of Building Research
Price:. $1 .OO
OTTAWA
I
N R C-
C I S T IB L M .
RES.
J
Rwh.
BW&
C N R C-
1 a 1 1 7 'On a u t i l i s e d e s a p p a r e i l s de mesure de l a t r a n s m i s s i o n de c h a l e u r e t d e s c a l o r i d t r e s pour rechercher l e s f a c t e u r s q u i i n f l u e n t s u r l e s mesures de l a r e s i s t a n c e thermique e n p l a c e d e s murs 3 o s s a t u r e de b o i s . Ces f a c t e u r s s o n t :
l ' o r i e n t a t i o n d e s mrs, l a d u r h d e s meeures, l e dephasage thermique, l e s e f f e t s de l a temperature moyenne e t l ' h e u r e d e s mesures. On a 6galement u t i l i s e c e s r s u r e s pour determiner l a r e s i s t a n c e thermique e n p l a c e de l ' i s o l a n t e t l ' e f f e t d e s O l h e n t s de l ' o s s a t u r e s u r la r e s i s t a n c e thermique g l o b a l e du mr.
Une bonne connaissance d e s e f f e t s dynamtques s u r un mr d ' e s s a i e s t i n d i s p e n s a b l e pour o b t e n i r d e s r e s u l t a t s p r e c i s . On a obtenu d e s mesures de r e s i s t a n c e thermique p r e c i s e s pour d e s mrs B o s s a t u r e en b o i s a p a r t i r des v a l e u r s des d i f f g r e n c e s de temperature e t de l a transmission de c h a l e u r s u r une pgriode continue de 24 heures (des c o r r e c t i o n s a p p r o p r i h s o n t S t € e f f e c t u h s pour t e n i r c o m t e du dephasage d e l a transmission de c h a l e u r e t pour l ' e f f e t de l a temperature moyenne). Toutes l e s a u t r e s d t h o d e s de mesure o n t conduit a d e s r e s u l t a t s moins p r e c i s (-is acceptables) ou t o u t a f a i t inacceptables.
In Situ Measurements
of Frame Wall
Thermal Resistance
W.C. Brown
G.D.
Schuyler
INTRODUCTION
In p r e d i c t i n g t h e thermal performance of a w a l l , one of t h e most important c h a r a c t e r i s t i c s t o be determined i s t h e s t e a d y - s t a t e thermal r e s i s t a n c e o f t h e w a l l . For t h i s r e a s o n , measurement of thermal r e s i s t a n c e was chosen a s t h e s t a r t i n g p o i n t f o r a f i e l d i n v e s t i g a t i o n of w a l l
thermal performance. The i n v e s t i g a t i o n was designed:
1. t o determine t h e e f f e c t s of v a r i o u s f a c t o r s on t h e accuracy of t h e measurement o f wall thermal r e s i s t a n c e ,
2. t o compare measured r e s i s t a n c e w i t h t h a t p r e d i c t e d from t h e thermal p r o p e r t i e s o f t h e wall components,
3 . t o determine t h e e f f e c t s of framing members on o v e r a l l wall thermal r e s i s t a n c e .
F a c t o r s s t u d i e d t o meet t h e f i r s t o b j e c t i v e included wall o r i e n t a t i o n , l e n g t h of measurement p e r i o d , thermal l a g , mean temperature, and time of measurement.
Heat Flow Meters (HFM, s e e Appendix A ) were i n s t a l l e d i n t h e w a l l s of a house t o measure h e a t flow, Q, through i n s u l a t i o n , and thermocouples were placed on t h e i n s i d e and o u t s i d e s u r f a c e s t o measure temperature d i f f e r e n c e , AT, a c r o s s i n s u l a t i o n . The r e s u l t s were used t o determine t h e r e s i s t a n c e of t h e i n s u l a t i o n and t h e e f f e c t s of v a r i o u s f a c t o r s on t h e accuracy of t h e measurement of r e s i s t a n c e . A c a l o r i m e t e r ( s e e Appendix B) and an IiFM were i i l s t a l l e d t o g e t h e r i n a second house t o measure h e a t flow Q i n a s i m i l a r wall s e c t i o n . ' These r e s u l t s were used t o determine t h e e f f e c t s of framing members on o v e r a l l h e a t flow and thermal r e s i s t a n c e through t h e w a l l .
The i n v e s t i g a t i o n was c a r r i e d out i n two of f o u r t e s t houses used by t h e D i v i s i o n of Building Research, National Research Council o f Canada (DBR/NRCC),in c o o p e r a t i o n with t h e Housing and Urban Development A s s o c i a t i o n of Canada f o r s t u d i e s of energy u s e i n s i n g l e - f a m i l y d w e l l i n g s . 2 B u i l t i n 1977, t h e houses a r e l o c a t e d i n t h e Ottawa a r e a (4674 O C d a y s ) . T'ne w a l l s
a r e wood frame 38 x 89 mm s t u d w a l l s a t 406 mm on c e n t e r (O.C.) (nominal 2 x 4 i n . , 16 i n . O.C.) and t h e s t u d space i s f i l l e d with mineral wool i n s u l a t i o n (RSI 2.1 [R 1 2 ] ) . * The o u t s i d e of t h e s t u d wall i s f i n i s h e d with 25 mm (1 i n . ) f i b e r b o a r d s h e a t h i n g , RSI 0.5 (R 3 ) , and
h o r i z o n t a l aluminum s i d i n g . The i n s i d e of t h e s t u d wall i s f i n i s h e d with 38 x 38 mm (nominal 2 x 2 i n . ) h o r i z o n t a l f u r r i n g and 12 mm ( 0 . 5 i n . ) gypsum board. The f u r r i n g i s a t 406 mrn
(16 i n . ) O . C . and i s f i l l e d with RSI 0 . 9 (R 5) mineral wool i n s u l a t i o n . The HFM's were b u i l t
2 2
*
Thermal r e s i s t a n c e , SI u n i t s , m K/:*:, and conventional u n i t s f t h°F/BtuW.C. Brown, Research O f f i c e r , D i v i s i o n of Building Research, National Research Council of Canada, Ottawa, Ontario,
G . D . Schuyler, P r o j e c t Engineer, Morrison, H e r s h f i e l d , Theakston and Rowan L t d . ,
Guelph, Ontario, Canada
around t h i s i n s u l a t i o n . A schematic drawing o f t h e w a l l i s shown i n F i g . 1. The thermal r e s i s t a n c e of t h e components through t h e i n s u l a t i o n i s RSI 3.78 a t 24OC (R 21.5 a t 75 F) mean t e m p e r a t u r e . Assuming p a r a l l e l h e a t flow and i g n o r i n g t h e e f f e c t s of f a s t e n e r s , t h e o v e r a l l thermal r e s i s t a n c e o f t h e w a l l i s c a l c u l a t e d t o be RSI 3.53 a t 24°C (R 20.0 a t 75 F ) mean t e m p e r a t u r e .
HEAT FLOW METER RESULTS
Thermal Lag and I n t e g r a t i n g P e r i o d
The s t e a d y - s t a t e thermal r e s i s t a n c e of a w a l l can be determined by i n t e g r a t i n g h e a t flow, Q, and s u r f a c e t e m p e r a t u r e d i f f e r e n c e , AT, measurements w i t h r e s p e c t t o time u n t i l t h e r a t i o of t h e i n t e g r a l s becomes c o n s t a n t . The v a l u e of t h e c o n s t a n t r a t i o i s t h e s t e a d y - s t a t e thermal r e s i s t a n c e . I f Q and AT were s i n u s o i d a l , t h e r a t i o of t h e i n t e g r a l s o f Q and AT o v e r one p e r i o d would g i v e t h e s t e a d y - s t a t e r e s i s t a n c e . In t h e f i e l d , however, AT i s n o t s i n u s o i d a l , and i s n o t , i n f a c t , s t a t i o n a r y ; The p e r i o d of i n t e g r a t i o n r e q u i r e d t o g i v e a c o n s t a n t r a t i o
i s t h e r e f o r e unknown. In a d d i t i o n , t h e s i g n a l i s n o t t r u l y p e r i o d i c and t h e wall i n t r o d u c e s a l a g between Q and AT, s o t h a t t h e i n t e g r a t i o n p e r i o d f o r Q should be lagged behind t h a t f o r AT by t h e d e l a y o f t h e w a l l i n o r d e r t o o b t a i n a c c u r a t e r e s u l t s .
The t e m p e r a t u r e d i f f e r e n c e a c r o s s a w a l l and t h e h e a t flow through a w a l l change p r i m a r i l y because of changes i n e x t e r i o r s u r f a c e t e m p e r a t u r e ; t h e s e changes a r e caused by t h e d a i l y c y c l e of t h e ambient a i r t e m p e r a t u r e and s o l a r r a d i a t i o n . Although t h e d i u r n a l t e m p e r a t u r e c y c l e h a s an equal e f f e c t on a l l wall o r i e n t a t i o n s , s o l a r r a d i a t i o n a f f e c t s t h e s o u t h w a l l t o t h e
g r e a t e s t e x t e n t and, t o a l e s s e r e x t e n t , t h e e a s t and west w a l l s . A s a consequence, t h e s o u t h w a l l e x p e r i e n c e s t h e most r a p i d changes i n e x t e r i o r s u r f a c e t e m p e r a t u r e , w i t h a corresponding i n c r e a s e i n t h e magnitude of t h e h i g h e r frequency components o f t h e s u r f a c e t e m p e r a t u r e . I n a d d i t i o n , t h e e f f e c t s v a r y from day t o day because of cloud cover v a r i a t i o n s . The s o u t h w a l l , t h e r e f o r e , e x p e r i e n c e s g r e a t e r v a r i a t i o n i n AT and Q t h a n t h e n o r t h w a l l and t h e a p p a r e n t v a l u e of thermal r e s i s t a n c e i s c o r r e s p o n d i n g l y a f f e c t e d .
A sample o f AT and Q d a t a c o l l e c t e d from t h e w a l l s under t e s t (Fig. 2) shows t h a t t h e r e i s
one dominant d e l a y p e r i o d between t h e two s e t s of d a t a . T h i s can be determined by f i n d i n g t h e d e l a y t h a t produces t h e maximum c r o s s - c o r r e l a t i o n between t e m p e r a t u r e d i f f e r e n c e and h e a t flow
(Fig. 3 ) . The d e l a y w i t h t h e maximum c r o s s - c o r r e l a t i o n i s 2.5 h. T h i s a g r e e s w e l l w i t h t h e d e l a y t h a t i s e v i d e n t from a v i s u a l i n s p e c t i o n of Fig. 2. S i g n i f i c a n t l y reduced s c a t t e r should be expected i n t h e c a l c u l a t e d thermal r e s i s t a n c e v a l u e s i f t h e Q d a t a a r e lagged by 2.5 h behind t h e AT d a t a .
Fig. 4 shows how t h e i n t e g r a t e d thermal r e s i s t a n c e , c a l c u l a t e d w i t h 2.5 h l a g i n Q, approaches a c o n s t a n t v a l u e a s t h e i n t e g r a t i o n p e r i o d l e n g t h e n s . In f a c t , f o r t h e s i x p e r i o d s shown, both n o r t h and s o u t h o r i e n t a t i o n s s e t t l e d t o w i t h i n '5% of t h e seven-day v a l u e a f t e r 24 h. In a d d i t i o n , it shows t h a t a d e l a y i n Q r e d u c e s t h e magnitude of t h e v a r i a t i o n s i n c a l c u l a t e d r e s i s t a n c e . I n t e g r a t i o n p e r i o d s s h o r t e r t h a n 2 4 h may a l s o produce a c c e p t a b l e r e s u l t s (55%) and w i l l be d i s c u s s e d l a t e r .
Mean Temperature E f f e c t s
A s t h e thermal r e s i s t a n c e of i n s u l a t i n g m a t e r i a l s changes w i t h mean t e m p e r a t u r e , one should expect t o s e e v a r i a t i o n s i n t h e thermal r e s i s t a n c e caused by changes i n ambient temperature. The 24 h thermal r e s i s t a n c e s a r e p l o t t e d a s a f u n c t i o n of mean t e m p e r a t u r e
(Fig. 5 ) . These i n d i c a t e a l i n e a r r e l a t i o n between thermal r e s i s t a n c e and mean t e m p e r a t u r e .
A comparison of t h e mean t e m p e r a t u r e c o r r e c t e d and u n c o r r e c t e d r e s i s t a n c e s (Fig. 6) shows t h a t an a p p a r e n t s e a s o n a l v a r i a t i o n and s c a t t e r have been reduced by c o r r e c t i n g f o r mean
temperature.
One p o i n t t o n o t i c e i s t h e d i f f e r e n c e between t h e 0°C thermal r e s i s t a n c e s f o r n o r t h and s o u t h w a l l s (Fig. 5 ) . The n o r t h w a l l shows RSI 4.45 a t O'C (R 25.3 F a t 32 F) w h i l e t h e s o u t h w a l l shows RSI 4.28 (R 24.3), a 4% d i f f e r e n c e . I t i n c l u d e s t h e v a r i a b i l i t y of t h e i n s u l a t i o n a s manufactured, m o d i f i c a t i o n o f performance by exposure, and measurement e r r o r . The
normalized mean t e m p e r a t u r e c o e f f i c i e n t s f o r t h e n o r t h , 0.0059, and s o u t h , 0.0058, w a l l s a r e q u i t e c l o s e , i n d i c a t i n g t h a t t h e w a l l s have t h e same mean t e m p e r a t u r e dependence but s l i g h t l y d i f f e r e n t r e s i s t a n c e s .
Time o f Dav
f o r t h e s t a r t time of t h e i n t e g r a t i o n . Comparisons o f 24 h i n t e g r a t i o n s s t a r t i n g a t d i f f e r e n t t i m e s of t h e day showed t h a t s t a r t time had l i t t l e e f f e c t . I f one chooses t h e s t a r t t i m e c o r r e c t l y , however, a much s h o r t e r i n t e g r a t i o n p e r i o d may g i v e s a t i s f a c t o r y r e s u l t s (Fig. 4 ) ; w i t h a s t a r t time of midnight, an i n t e g r a t i o n p e r i o d of a few h o u r s i s adequate.
To i n v e s t i g a t e t h e s t a r t time of i n t e g r a t i o n , an i n t e g r a t i o n p e r i o d of 4 h was a p p l i e d t o t h e d a t a . Comparison of t h e means and o f t h e s t a n d a r d d e v i a t i o n s f o r 4 h r e s i s t a n c e c a l c u l a t e d from v a r i o u s s t a r t t i m e s (Tab. 1 ) shows t h a t unlagged d a t a g i v e g e n e r a l l y u n p r e d i c t a b l e r e s u l t s f o r both n o r t h and s o u t h o r i e n t a t i o n s and a l l s t a r t t i m e s . Lagged d a t a g i v e s a t i s f a c t o r y r e s u l t s f o r both o r i e n t a t i o n s i f i n t e g r a t i o n s t a r t s n e a r midnight, but t h e r e s u l t s become p r o g r e s s i v e l y worse, e s p e c i a l l y f o r t h e s o u t h w a l l , i f t h e s t a r t t i m e i s such t h a t t h e i n t e g r a t i o n p e r i o d approaches d a y l i g h t hours. I f d a y l i g h t hours a r e i n c l u d e d i n t h e i n t e g r a t i o n p e r i o d , t h e r e s u l t s a r e u n a c c e p t a b l e .
COMPARISON OF
0
FROM HFM AND CALORIMETERIn comparing t h e measurements o f Q made by t h e HFM w i t h t h o s e made by t h e c a l o r i m e t e r , t h e most obvious d i f f e r e n c e i s t h e q u a n t i t y being measured. The HFM measurement does n o t i n c l u d e h e a t flow through any framing members, while t h e c a l o r i m e t e r measurement i n c l u d e s h e a t flow through a l l but t h e t o p and bottom p l a t e s . A s t h e c a l o r i m e t e r measures h e a t flow a t t h e i n s i d e s u r f a c e of t h e gyproc and i n c l u d e s t h e l a g s of t h e framing members, i t should i n d i c a t e a l o n g e r l a g between Q and AT t h a n does t h e HFM, which measures h e a t flow a t a p l a n e w i t h i n t h e w a l l and does n o t i n c l u d e framing members. The c r o s s c o r r e l a t i o n of t h e measured h e a t flows (Fig. 7)
shows t h a t t h e c a l o r i m e t e r h e a t flow l a g s t h e HFM h e a t flow by approximately 0.5 h.
Fig. 8 shows t h a t t h e r a t i o of t h e whole w a l l h e a t flow, a s measured by t h e c a l o r i m e t e r , and h e a t flow through t h e p o r t i o n between t h e framing members, a s measured by t h e HEM, i s 0.78. That i s , t h e framing members and f a s t e n e r s reduce t h e o v e r a l l w a l l r e s i s t a n c e t o 0.78 of t h e i n s u l a t i o n r e s i s t a n c e . T h i s r a t i o i s lower t h a n t h e 0.93 r a t i o c a l c u l a t e d assuming p a r a l l e l h e a t flows and u s i n g e s t i m a t e s of t h e thermal r e s i s t a n c e of t h e components.3
Combining t h i s f a c t o r of 0.78 with t h e measured r e s i s t a n c e through t h e i n s u l a t e d p o r t i o n of t h e w a l l (Fig. 6 ) g i v e s an o v e r a l l wall r e s i s t a n c e of RSI 3.40 a t O°C (R 19.3 a t 32 F) mean t e m p e r a t u r e . T h i s compares w e l l with t h e measured r e s i s t a n c e of a s i m i l a r w a l l specimen
(2.4 x 2.4 m [8 x 8 f t ] ) t e s t e d i n t h e DBR/NRCC guarded h o t box f a c i l i t y . The r e s u l t from t h a t t e s t was RSI 3.61 a t - 7 O c (R 20.5 a t 19.4 F) mean t e m p e r a t u r e and 55 K (99 F ) t e m p e r a t u r e d i f f e r e n c e . The e s t i m a t e of t h e r e s i s t a n c e through t h e i n s u l a t i o n (RSI 3.78 a t 24OC mean t e m p e r a t u r e ) compares w e l l w i t h t h e measured r e s u l t from t h e HFM a t t h e same mean t e m p e r a t u r e
(RSI 3.68 s o u t h o r RSI 3.83 n o r t h ) .
A s t h e measured r e s i s t a n c e through t h e i n s u l a t i o n compares well w i t h t h a t p r e d i c t e d from t h e s e p a r a t e r e s i s t a n c e s of t h e components and t h e o v e r a l l r e s i s t a n c e v a l u e compares w e l l w i t h a l a b o r a t o r y measured v a l u e , t h e measured r a t i o of r e s i s t a n c e s ( h e a t f l o w s ) a p p e a r s t o be v a l i d . The d i f f e r e n c e between t h e measured (0.78) and p r e d i c t e d (0.93) r a t i o s i s probably due t o t h e f a s t e n e r s used t o hold t h e w a l l t o g e t h e r and t o n o n - p a r a l l e l h e a t flows i n t h e w a l l .
ERROR
Although 24 h d a t a with time l a g and mean t e m p e r a t u r e c o r r e c t i o n can produce good r e s u l t s ( + 5 % ) , t h e most a c c u r a t e way t o determine t h e r e q u i r e d c o r r e c t i o n s i s from d a t a c o l l e c t e d over an extended p e r i o d of time. A q u i c k e r and s t i l l a c c e p t a b l e way t o o b t a i n t h e a p p r o p r i a t e time l a g i s by v i s u a l i n s p e c t i o n of t h e AT and Q c u r v e s . In t h e example s t u d i e d , t h e time l a g from v i s u a l i n s p e c t i o n agreed w e l l w i t h t h a t o b t a i n e d from c r o s s c o r r e l a t i o n a n a l y s i s . There i s no q u i c k way t o o b t a i n t h e mean t e m p e r a t u r e c o r r e c t i o n . I t would be a p p r o p r i a t e , however, t o r e c o r d t h e mean t e m p e r a t u r e a t which each measurement was made.
I t may be advantageous i n some c a s e s t o i g n o r e one o r both o f t h e c o r r e c t i o n s and t o a c c e p t a l a r g e r s c a t t e r i n t h e r e s u l t s . Tab. 2 shows t h e mean, normalized by t h e 0°C mean t e m p e r a t u r e v a l u e of F i g . 5; t h e s t a n d a r d d e v i a t i o n ; and t h e 99% confidence i n t e r v a l f o r s e v e r a l c a s e s ranging from both c o r r e c t i o n s t o no corrections."he r e s u l t s f o r t h e s o u t h w a l l , which has l a r g e r v a r i a t i o n s i n Q and AT because of s o l a r r a d i a t i o n , a r e a s good a s t h o s e from t h e n o r t h w a l l . A s would be expected, l a r g e r e r r o r s e x i s t i f c o r r e c t i o n s a r e n o t made, but r e s u l t s can be expected w i t h i n 210% o f t h e c o r r e c t v a l u e , even i f no allowance i s made f o r time l a g and mean t e m p e r a t u r e e f f e c t s .
While a c c e p t a b l e r e s u l t s have been o b t a i n e d f o r t h e frame w a l l used i n t h i s s t u d y , o t h e r t y p e s of w a l l s may produce l e s s a c c u r a t e r e s u l t s . For example, b r i c k veneer w a l l s with a
vented a i r space would be l e s s amenable t o t h i s approach; e x t e r i o r t e m p e r a t u r e would have t o be measured a t t h e i n s i d e s u r f a c e o f t h e a i r space. S o l i d c o n c r e t e w a l l s , with l o n g e r dynamic e f f e c t s , might r e q u i r e longer i n t e g r a t i o n p e r i o d s t h a n t h o s e used f o r t h i s s t u d y . The r e s u l t s from such w a l l s should be a s s e s s e d v e r y c a r e f u l l y b e f o r e t h e y a r e a c c e p t e d .
CONCLUSIONS
Reasonably a c c u r a t e (210%) v a l u e s o f i n s i t u frame w a l l thermal r e s i s t a n c e can be o b t a i n e d from h e a t flow and t e m p e r a t u r e d i f f e r e n c e d a t a i n t e g r a t e d over a 24 h p e r i o d . Values a c c u r a t e t o
55% can be o b t a i n e d i f c o r r e c t i o n s a r e made f o r b o t h w a l l t i m e l a g and mean t e m p e r a t u r e dependence. These c o r r e c t i o n s can be determined from a n a l y s i s of s e v e r a l d a y s ' d a t a ; o r a r e a s o n a b l e c o r r e c t i o n f o r time l a g a l o n e can be determined from v i s u a l i n s p e c t i o n of 24 h h e a t flow and t e m p e r a t u r e d i f f e r e n c e c u r v e s . T r a d e o f f s between a c c u r a c y and t h e number of
c o r r e c t i o n s a p p l i e d a r e summarized i n Tab. 2.
There i s v i r t u a l l y no d i f f e r e n c e i n measurement accuracy f o r a n o r t h f a c i n g o r shaded w a l l and a s o u t h f a c i n g o r sunny w a l l f o r 24 h i n t e g r a t e d d a t a . S i m i l a r l y , t h e r e i s l i t t l e
d i f f e r e n c e i n accuracy between 24 h i n t e g r a t e d d a t a , c o r r e c t e d f o r l a g and mean t e m p e r a t u r e , and c o r r e c t e d 4 h i n t e g r a t e d d a t a a s long a s t h e 4 h i n t e g r a t i o n p e r i o d o c c u r s around midnight. The accuracy of 4 h d a t a becomes p r o g r e s s i v e l y worse a s t h e i n t e g r a t i o n p e r i o d approaches d a y l i g h t hours and becomes u n a c c e p t a b l e i f d a y l i g h t hours a r e i n c l u d e d .
Thermal r e s i s t a n c e measured through i n s u l a t i o n i n s t a l l e d i n t h e f i e l d a g r e e s v e r y well w i t h v a l u e s p r e d i c t e d from r e s i s t a n c e s of i n d i v i d u a l components. The r a t i o of r e s i s t a n c e f o r t h e w a l l t o t h a t of t h e i n s u l a t i o n between t h e framing members (0.78) i s l e s s t h a n t h a t p r e d i c t e d by a simple p a r a l l e l h e a t flow c a l c u l a t i o n ( 0 . 9 3 ) . T h i s may be p a r t i a l l y e x p l a i n e d by a r e d u c t i o n i n t h e thermal r e s i s t a n c e o f t h e wall components due t o n a i l s , e s p e c i a l l y t h e r e d u c t i o n i n t h e r e s i s t a n c e of t h e i n s u l a t i n g s h e a t h i n g board by t h e l a r g e number of aluminum n a i l s used t o f a s t e n t h e s i d i n g .
REFERENCES
1. Brown, W.C. and S c h u y l e r , G.D., "A C a l o r i m e t e r f o r Measuring Heat Flow Through Walls," Proceedings o f t h e ASHRAE/DOE Conference on Thermal Performance of t h e E x t e r i o r Envelopes of B u i l d i n g s , Kissimmee, FL, December 1979.
2. Q u i r o u e t t e , R . L . , "The Mark X I Energy Research P r o j e c t - Design and C o n s t r u c t i o n , " N a t i o n a l Research Council of Canada, D i v i s i o n of Building Research, Building Research Note 131, October 1978.
3. ASHRAE Handbook
-
1977 Fundamentals Volume, American S o c i e t y of Heating, R e f r i g e r a t i n g and A i r - c o n d i t i o n i n g E n g i n e e r s , New York, NY.4. Hays, W.L., S t a t i s t i c s , H o l t , R i n e h a r t and Winston, I n c . , 1963. ACKNOWLEDGMENTS
The a u t h o r s wish t o acknowledge t h e t e c h n i c a l a s s i s t a n c e of J.A. Richardson and D . L . Logan, of t h e D i v i s i o n of Building Research, i n conducting t h e s t u d y .
T h i s paper i s a c o n t r i b u t i o n from t h e D i v i s i o n o f Building Research, N a t i o n a l Research Council of Canada, and i s p u b l i s h e d w i t h t h e approval of t h e D i r e c t o r of t h e D i v i s i o n .
TABLE
1
4 Hour Resistances for Various Integration Start Times
South North
Start
h
Without Lag in Q
With Lag in Q
NOTE: All RSI values adjusted for Tm as per Fig. 5
KSI, mean 2 4 h resistance as per Fig. 5
u standard deviation
TABLE 2
Comparison of Measurement Precision for Various HFM Measurements
Computation Plan South North
NOTE: All integration periods start at midnight
P integration period
d 2.5 h delay in Q (Y
-
Q delayed, N-
Q not delayed)Tm mean temperature correction (Y
-
corrected, N-
not corrected)RS I mean resistance
RS I,, mean 2 4 h resistance with corrections for d and Tm
RSIms = 4.28 m2.~/w, RSImn = 4.45 m2.~/w
a standard deviation
99% CI 99% confidence interval
-
99 readings out of a 100 should fallAPPENDIX A
HEAT FLOW
METERThe meters used in the investigation were constructed from the same materials as make up the section of the wall they replace. Figure A-1 shows their construction and placement within the wall. The meters were made with a 12-junction thermopile across the insulation layer as well as a separate thermocouple on each surface for temperature measurement.
Measurements taken at each HFM location were:
Tao outside air temperature (150 mm from the surface) T a . inside air temperature (150 mm from the surface)
1
Tso outside surface temperature Tsi inside surface temperature
T. temperature of outer surface of
HFM
1
E thermopile output
The output from each meter was calibrated at one mean temperature, using an ASTM C518 HFM apparatus, at DBR/NRCC. In addition, the dependence of the output upon mean temperature was measured for one HFM and applied to all others.
APPENDIX B CALORIMETER
The calorimeter used in the investigation was constructed of two layers of foil-backed rigid glass fibre insu1ation.l The total wall thickness was 10 cm, with a thermal resistance of RSI 2.8 (R 16). It was 1.2 m wide by 2.1 m high (4 x 7 ft) and contained a 150
W
heating cable. The heater was controlled to maintain zero temperature difference across the calorimeter walls, and temperature difference was sensed by an 18-junction thermopile. The calorimeter was mounted on the inside surface of the wall for which heat flow was to be measured. Measurementsincluded :
To outside air temperature T. room air temperature
1
E energy supplied to the calorimeter
Figure 1. Schematic of test wall 50 I V l l t NORTH WALL
8
Y 45---
W I- 5 - - 0 l i l l l3
339 345 341 342 35P 540 1 ' 341 1 . 342DAY FROM 1 JAN. 1980 DAY FROM 1 JAN. 1980
W
0
0.0-
G
LLL
/
\
W 0 0 0.8- Z-
-
N 0-
---
E-
-
3
0.7-L
W We
0: 07
0.6-- V) V) 0e
- s
-
-
-
0 0 5 1 1 1 1 1 a 0 1 2 3 4 5 6HEAT FLOW DELAY, h
Figure 3. Cross-correlation coefficients for differect orientations
...--...--.
" NO DELAY INQ
DAY FROM 1 JAN. 1980
Figure 4. Cumulative HFM resistance
I I I I I 1 1 1 I I
,-
NORTH WALL-
RS I = 4.45*(1.0-0.0059*TM) (r2=0.821) 6-
-
5-
d-
4-
-
J-
-
-
2-
-
I-
1-
-
I I I I I I I I I I w- 0 zs
I I 1 I I 1 I I I 1'"
V) W 7 - SOUTH WALL-
K RS I = 4.28*(1.0-0.0058*TM) (r2=0.607) C 6-
-
*
N-
5-
-
-
4-
I =-
-
3-
-
-
2-
-
C 1-
-
-
-4 -2 0 2 4 6 B 10 12 14 1B 20 MEAN TEMPERATURE. "CFigure 5. 24h resistance vs mean temperature (delay 2.5h)
NORTH WALL AVERAGE RSI 4.45
W 0
0 0 9 - - 0
z *
8
o NOT ADJUSTED FOR T,2
-
-
V) ADJUSTED FOR T,k.2
0.a I I 1 I I I I I I I L SOUTH WALL AVERAGE RSI 4.28 - 0.
..
a..
-.
.
.
.
0-...:..:-.-.
.
.o .* O. 0 e 00 000 0 Onm-
0 0 0 0 oO 0 0 0 0-
-
0 NOT ADJUSTED FOR T,
-
ADJUSTED FOR T, DAY FROM 1 JAN. 1980
CALORIMETER HEAT FLOW DELAY, h
Figure 7. Cross-correlation coefficient for
calorimeter and HFM heat flow
12 mm GYPSUM BOARD RSI 0.9 INSULATION 3 mm PLYWOOD
CALOR I METER HEAT FLOW, w/m2
Figure 8. 24h HFM heat flow vs calorimeter heat flow (delay 0.5h)
+ THERMOPILE JUNCTION X THERMOCOUPLE STUDS FURRING
JY[{
1
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