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Comparison of low and medium rise housing development in wind tunnel. Energy and wind climate aspects
Journal o[ Wind Engineering and Industrial Aerodynamics, 32 (1989) 111-120
111
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
COMPARISON OF LOW AND MEDIUM RISE HOUSING DEVELOPMENTS IN WIND TUNNEL. ENERGY AND WIND CLIMATE ASPECTS
KT~ROLY BAL~ZS Hungarian Institute for Building Science /~TI/, H-1113, Dgvid F.u.6.(Hungary)
ABSTRACT Con~arison of a low-rise and a n~diun~rise version of a new housing developmerit was n ~ e with the help of wind tunnel test at a scale of 1/500. Ground level wind speeds were measured and con~ared to criteria. Seasonal total filtration and ventilation heat loss of the buildings was estin~ted with conjurer model based on pressure coefficients from the wind tunnel test. The low rise version proved to be better from both aspects.
OBJECTIVE, METHOD AND TECHNIQUE In the prelin~inary design of a new housing development on a 0.7 knR empty land in a South-West district of Budapest two alternates were considered. The first was to consist of low rise, 3-4 story buildings with saddle roof of 45 degree pitch arranged into rectangular ensembles of corner and row elements, with low rise conmlunal and conmlercial buildings. The second version was to nmL1e up of medium rise, 10-storey block buildings, typical in recently built housing developments in Hungary, and the same conmlunal buildings were assumed (Fig.1. and 2.). Comparisons of several aspects lead to the decision that the first version would further be elaborated in the detailed design and actually constructed. However, some aspects were left for analysis, among which was the effect of the obviously different aerodyn~lical character of the two versions on the wind clin~te and on filtration and ventilation heat losses. The method of the comparison was wind tunnel testing combined with computer simulation based on experimental data from the tests. Suburban boundary layer was generated using a combination of a low toothed wall and 7.0 m fetch of 40x40 x20 nm~ wooden bricks in a diagonal array. This setup had been calibrated and checked with COOK's scaling method /I ./ and found to fit the 1/450-I/500 length scale range with acceptable accuracy. The 1/500 scaled model was mounted onto the turntable of the ~TI wind tunnel that has a 9.3 m long, 2.2xI .4 m working section. As the turntable was turned in 22.5 degree increments according to 16 n~in compass points a data acquisition system was used for sampling and processing signals from a DISA hot wire mounted on a 3-D traversing rig and from a Setra transducer that served the Scanivalve ports for pressure measurements°
0167-6105/89/$03.50
© 1989 Elsevier Science Publishers B.V.
112
'D 0
0 r-"
7
i-~ ~ ~ ~
m
$
~ 'i
m.c
® .g o3
. . . . . . .
"
®
~L
~ \ _ I ~~ L~ ~
~
I-I ~1 ®
u i
'
®
~I:IL---~-~ ...... i ~d ~ i~® @,,,, ,,,..,
-
f-
'''
u ',,, ~
I
-g
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rt .....~, .... ~:~" H
11
_q
0 m
/
0
~_.-m~ ~__/~__
®
',
I./
t.) ÷
~
L
0
Fig.1. Plan view of the two housing development versions. Left: low-rise, rich t: mediun~rise version.
113
LOW BUILDINGS pressure taps for
MEDIUM h 31
e i i
25
~ CP1 "
~ CHZ "
V(m3/h.mZ) 83 , 60
,
,,-
b4~
19
I
13 ?
_L._:~
~1
2(
o
12 ~
I--11
12
Li 'I
,! .ll
- x•
I i
® ®
10 15 4
•
50
, 100 200
86 (Pc)
• ~I-
i F i g . 2 . House types / l e f t / ,
and window leakage categories / r i g h t / ~/oof points where criteria-are exceeded
~-F(i)-annual 100 hours of exceedence
Blow-rise
Categ°rY~D
~ medium-ri_~ e Category. \D
~_,
.~:r~e~'+
tot medium rise Jl- low-rise
~\-b,, . . . . .
5
A~
~1_ ,
10
vebcity criteria (m/s)
15
5
0./
Fig,3. Con~parison o£ ground level wind clin~tes
10 15 velocity criteda (m/s)
114
The models of both versions were measured in the sanle way. The wind tunnel tests were followed by higher level processing of the data, including calculations of filtration and ventilation.
COMPARISON OF GROUND LEVEL WIND CLIMATE As nmrked on Fig.9. 30 locations were selected on both versions for n~asuremerit of the ground level wind speed. All the locations had the same usage function, that is typical activity and exposure of people there. MELBOURNE's /2./ criteria were used for the acceptable limits of the hourly wind speed as deduced from the acceptable peek gust speeds averaged over 2 sec by asstm~ing Gaussian distributions of a suburban 6v=0.2 standard deviation of the velocity fluctuations. The criteria are shown in Table 9.
TABLE I Acceptable limits of the hourly wind speed
Category Activity Exposure Limit 2 sec gust speed (n~s) Acceptable hourly mean speed (m/s)
A Steady Long
B Steady Short
C Walk Short
D Danger of accident
90.0
13.0
96.0
23.0
6.2
8.0
9.8
~4.9
A local reference m e a n wind speed was measured at each wind directions at a height corresponding to 900 m in full scale over the windward leading edge of the turntable in the centre line of the tunnel. Since the surroundings of the area tested was quite flat and homogeniously suburban in surface roughness there was no need to change roughness configuration. While the tunnel speed were kept constant a vertical hot wire was traversed from location to location and the local mean wind speed was measured at 2 m full scale height. Local to reference velocity ratios were sinmltaneously calculated and stored for further analysis. This was repeated for all wind directions. The meteorologic~l data base for the analysis of the measured data was fortunately exceptionally good due to the fact that one of Budapest's two n~in stations is situated within 2 km reach and that a large flat area including this station and our site is of the same type of terrain roughness. Thus it was simple to transform the station's wind statistics into the local reference point using the gradient wind method described by LAWSON /3./. The local joint probabilities of the hourly wind speed exceeding a certain value at a wind direction and the measured velocity ratios were then used to calculate the exceedence of the local acceptable limits in annual hours at each location.
115
F(i) =ZP(d)~ exp (~U@/ (C~V)) k ) ~ 8760 (h/year) d
/I./
where F(i) is the nun~er of annual hours in location i while the wind speed exceeds U@, V=V(i,d) is the measured velocity ratio, d is the index of wind direction, P(d) is the probability of d direction, and C and k are directional dependent constants of the Raleigh-type distribution fitted to the annual probability statistics of the hourly n~an wind speed for each wind direction. As shown in Fig.3. the n~dium rise version was found to be nmch more windy in terms of annual hours of exceeding acceptability limits. Part a./ of the figure shows the relative fraction of locations Ntot where acceptability linits of Table I. are exceeded for all locations, and for groups of locations corresponding to criteria A-C(D) assigned as Ncat and plotted with dotted line. Part b./ shows the totals of annual hours of exceedence for the groups of locations corresponding to the different criteria for both versions. It can he seen that the A-C functional criteria are exceeded in 429 hours for the low rise housing and in 1783 hours for the medium rise version. The accident liner is exceeded in , and 18 hours respectively.
PRESSURE MEASUREMENTS For the estinmte of the filtration and ventilation heat losses of the buildings simplified computer simulations can be used. Though other design data were mostly known or reasonably assumed for the analysis, wind pressure data n~ght not be assumed in an analysis that targeted the comparison of the effect of aerodynan
supposing the area of the surface is in the order
of his I and I/2 storey single family houses. This finding and his own experiences encouraged the author to use pressure taps in an arrangement shown on Fig.2., using pneun~tic averaging for 2-3 story high, n~ax 16 m wide facade and roof elements. The time factor heavily restr~cted the total number of pressure taps to be used though the laboratory has 4 pcs of 48-port Scanivalves, that would have facilitated almost 600 taps if every 3 had been pneumatically averaged. The instrumentation and measuring process as well as the running time of the filtration program restricted the pressure measurements to 11 buildings of the two versions. corner and 4 row house elements of the low rise version, as shown on Fig.1. and 2., were measured and 3 sections of the 100-odd sin~lar ones of the medium
116
rise housing. These were asstm~d to be representative in size, shape and posi tion, and with an approxin~tion the whole housing might be ragarded as ensen~les of n~itiples of these buildings. Besides, there was no wimd direction of outstanding frequency of occurence, that n~de the estin~te more reliable. Some results of the pressure measurements are presented on Fig.4., where CPI and CP2 are assigned to parts of building envelops as shown on Fig.2.. These are in fairly good agreement with WIR~N's /3./ data as regards the low rise version. Fig.5. shows the variation of the n~gnitude of pressure difference as a function of the wind direction in the foml of ABS(CPI-CP2) for the three most exposed and sheltered buildings, at the perimeter and in the core of the new housing respectively. All pressure coefficients were non-din~nsionalized by the d y m a ~ c head at an elevation of ~0 m in full scale, value of which were gained from log-law profiles measured over the en~tly modell section with the whole boundary layer generating setup in the working section.
MODEL OF FILTRATION AND VENTILATION After studying different simple filtration models of LYBERG /4./ it was decided that simple single-cell model would be used for filtration calculations. Since the target was a con~arison of the seasonal heat den~nd necessary to cover losses due to filtration and ventilation a great number of runs bec~mle necessary. The meteorological input data were split into two parts. The frequency of wind directions and the joint probability of wind speed and outdoor ten~erature were separately treated. The resolution of this later was 3 m/s increments from 0.5 m/s to 9.5 m/s and 8°C increments from -14°C %o +I0°C respectively. As paranleters of the analysis 3 classes of airtightness of the windows, as shown on Fig.2., and 4 ventilation alternates were assumed. The four ventilation modes were the following: a./ filtration only * occassional intensive aeration through windows to nminrain the mininml air change of 0.5 ACH if filtration is not sufficient to do that; b./ filtration + pern~nent slight opening of a fraction of windows, as observed, analysed and described by LYBERG /5./ + occassional aeration to 0.5 ACH; c./ filtration + controllable vents below each window as described by PE~ZES et al. /6./ + occasional aeration to
0.5 ACH;
d./ filtration + pern~nent and steady exhaust ventilation with a capacity of 0.5 ACH. For modes a.-c. one individual venting duct leading up over the roof was assumed to each flat and substituted with an equivalent opening on the roof. This approach did not counted for other lea~kages that n~ght and certainly would, occur in the actual buildings. Therefore it is reasonable to present the
117 CPI-CP2 2
HOUSE 1 - -
1
3 .............
......
'.. ............ i:::........
5,1
-1 -2
oc
45
1"
90
135
A\
180 225. 270 315 360
.HOUSE 4 8 ...... -6 --10 ............ (3- 4 storey, row)
, . % - . . .
...........~ ~ / ~
0
.
-I
.
.
45
I
.
.
.
90.
.
.
.
13S
o
~j'
. . . . . . . . . . .
150
225
270
OC
315
360
HOUSE 5 9 ....... 7 .... 11 (3-4storey, corner.) .-.---: ......
~\
--.-.--.
0
-.1 0
45
90
;.~-.c ::'~
c,c 135 180 225 270 315 360
Fig.4. Variation of CPI-CP2 with the wind direction 2 ABS(CPI-CP2) HOUSES: e=4,
b.=l,
c.= 5, (EXPOSEOHOUSES)
C,
0 O
45
90
135
180
225
270 3]5
360 IX,
2 HOUSES d.=7.,
e.=3.,
[=10.
(SH~LTEEEOhOUSES}
0 0
45
90
135
180 225 270 315 350 ~
F i g . 5 . V a r i a t i o n o f ABS (CP1-CP2) "~ith t h e w i n d d i r e c t i o n f o r m o s t e x p o s e d and s h e l t e r e d h o u s e s o f ~che two v e r s i o n s . / H o u s e s 1. , 3 . , a r e ~ 0 - s ~ c o r e y _ _ t h e o t h e r s a r e 3 - 4 s t o r e y c o r n e r o r row e l e m e n t s i n ~che .ow-rlse versz0n/
118
assumed overall air-tightness of the buildings in te~is of N(50), that is the ACH at 50 Pa pressurization to enable a wider comparison of the results. This i~ shown in Table 2.
TABLE 2. Assumed overall air-tightness of the sin~lated buildings in N(50) as function of window tightness class and ventilation modes
Vent.mode
Air-tightness class of the windows I.
a., d.
2.8-3.2
2.
3.
3.6-3.8
5.6-6.2
b. (x)
3.0-(5.6)
3.7-(6.6)
5.9-(9.0)
c.
3.8-4.1
4.7-5.1
6.7-7.4
(x)
weather dependent aeration habits gave varying values The following set of fundamental equations were used for the calculation of
n~ss flows of air into and from the building. ~ P = 9 ~ U(10)2/2 ~ (CPe-CPi) - 9 * g ~ AT/Ti ~ z
/2./
for the total pressure difference driving the leakage flow n1~a . ~ p b
/3./
for the n~ss flows, with b varying from 0.5 to I depending on the type of opening, and for n~ss conservation: ~in
+~1out = 0
/4./
The results of the calculations were extrapolated for the whole housing develop ment by n~itiplying the results gained for the individual representative houses by the number of the similar houses and sun~ling up. The total internal volume of the houses was the s~le for the two versions as well as the total leakage area. The comparison of the heat losses due to air change are presented in bar charts on Fig.6.
CONCLUSIONS Of the two housing alternates the low rise version aerodym~m~ically better matched the suburban envirormlent. The lower houses at the perimeter create a harmonic transition to the surroundings. The pitched roofs also contribute to this. Even if the ground level wind speeds may be regarded as acceptable for both versions, that is, the degree of exceedence would not n~nke architectural modifications necessary, the conditions over the low rise version are by far better. Some suggestion were made to the garden architect as to vegetation shelterbelts.
119
Ventilation mode d./
Ventilation mode a./
QFplant total(TJ)
QFplant total (TJ) 35
35
3O
30
25 20 0.5AC 15 I0
oHI m,j iMM 25
20
_
0.5 A~ 15 10
n|
5 0
1
2
1
3
QPplant total(TJ)
QFplant t o t a l (TJ)
5O
5O
45
45
4O
4O
35
35
25 2O 0.5 ACH 15 10 5 0
m
,
nl nl
30
2
I
--
0.5 ACH
IMi
I
3
Ventilation mode c./
Ventilation mode b./
30
2 ~dow l e a k ~
3
~ low rise version
15
3
:::::::::::::::::::medium ::::::::::: rise version
Fig.6. Comparison of the plant total seasonal heat losses due to air change in buildings for different ventilation modes and window leakage categories
120
The analysis of the filtration gave sonmwhat unexpected results.
In cases
where the total heat losses coincided with that of the 0.5 ACH, the filtration air change had never exceeded that rate, for no house, no meteorological situation. This means that either the air leakage was underestinmted or, if the building turned out to be really as tight as that, the necessary minimum of ACH can not be achieved without uncontrolled opening of the windows by the habitant~ that, in turn, would certainly increase the ACH above the necessary. It is likely that those con~inations of the assumed airtightness and ventilation mode are realistic, where N(50) is higher. For these cases it was found that the total filtration and ventilation heat loss is 20-40 % higher in the medium rise version than in the low one.
REFERENCES
/I ./ COOK,N J: De%erndnation of the model scale factor in wind tunnel simulations of the adiabatic atmospheric boundary layer, Journ, of Ind.Aerodyn. 2 ( 1 9 7 7 / 7 8 ) pp. : 3 1 1 - 3 2 1 . /2./ MELBOURNE,W: Criteria for envirormlental wind conditions, Journ of Wind Eng. and Ind. Aerodyn. 3 (1978) pp. : 241-249 /3./ WIR~N,B G: Effects of Surrounding Buildings on Wind Pressure Distributions and Ventilation Losses of Single-Family Houses. part I. : 1 I/2-Storey De%ached Houses. Bulletin of S.I.B., M85: 19, G~vle,Sweden, 1985. /4./ LYBERG, M D: Models of Infiltration and Natural Ventilation. Bulletin of S.I.B. , M83 : 23, Ggvle,Sweden, 1983. /5./ LYBERG, M D: Use of Windows by Residents. Proc. of Conf. Windows in Building Design and Maintainance, GSteborg, Sweden, 1984., pp.: 344-349 /6./ P~NZES, GY; SZALAY, Z: Complementary venting structure. Proc. of Conf. Windows in Building Design and Maintainance, GSteborg, Sweden 1984., pp. : 473-478.
111
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
COMPARISON OF LOW AND MEDIUM RISE HOUSING DEVELOPMENTS IN WIND TUNNEL. ENERGY AND WIND CLIMATE ASPECTS
KT~ROLY BAL~ZS Hungarian Institute for Building Science /~TI/, H-1113, Dgvid F.u.6.(Hungary)
ABSTRACT Con~arison of a low-rise and a n~diun~rise version of a new housing developmerit was n ~ e with the help of wind tunnel test at a scale of 1/500. Ground level wind speeds were measured and con~ared to criteria. Seasonal total filtration and ventilation heat loss of the buildings was estin~ted with conjurer model based on pressure coefficients from the wind tunnel test. The low rise version proved to be better from both aspects.
OBJECTIVE, METHOD AND TECHNIQUE In the prelin~inary design of a new housing development on a 0.7 knR empty land in a South-West district of Budapest two alternates were considered. The first was to consist of low rise, 3-4 story buildings with saddle roof of 45 degree pitch arranged into rectangular ensembles of corner and row elements, with low rise conmlunal and conmlercial buildings. The second version was to nmL1e up of medium rise, 10-storey block buildings, typical in recently built housing developments in Hungary, and the same conmlunal buildings were assumed (Fig.1. and 2.). Comparisons of several aspects lead to the decision that the first version would further be elaborated in the detailed design and actually constructed. However, some aspects were left for analysis, among which was the effect of the obviously different aerodyn~lical character of the two versions on the wind clin~te and on filtration and ventilation heat losses. The method of the comparison was wind tunnel testing combined with computer simulation based on experimental data from the tests. Suburban boundary layer was generated using a combination of a low toothed wall and 7.0 m fetch of 40x40 x20 nm~ wooden bricks in a diagonal array. This setup had been calibrated and checked with COOK's scaling method /I ./ and found to fit the 1/450-I/500 length scale range with acceptable accuracy. The 1/500 scaled model was mounted onto the turntable of the ~TI wind tunnel that has a 9.3 m long, 2.2xI .4 m working section. As the turntable was turned in 22.5 degree increments according to 16 n~in compass points a data acquisition system was used for sampling and processing signals from a DISA hot wire mounted on a 3-D traversing rig and from a Setra transducer that served the Scanivalve ports for pressure measurements°
0167-6105/89/$03.50
© 1989 Elsevier Science Publishers B.V.
112
'D 0
0 r-"
7
i-~ ~ ~ ~
m
$
~ 'i
m.c
® .g o3
. . . . . . .
"
®
~L
~ \ _ I ~~ L~ ~
~
I-I ~1 ®
u i
'
®
~I:IL---~-~ ...... i ~d ~ i~® @,,,, ,,,..,
-
f-
'''
u ',,, ~
I
-g
~ iN li
rt .....~, .... ~:~" H
11
_q
0 m
/
0
~_.-m~ ~__/~__
®
',
I./
t.) ÷
~
L
0
Fig.1. Plan view of the two housing development versions. Left: low-rise, rich t: mediun~rise version.
113
LOW BUILDINGS pressure taps for
MEDIUM h 31
e i i
25
~ CP1 "
~ CHZ "
V(m3/h.mZ) 83 , 60
,
,,-
b4~
19
I
13 ?
_L._:~
~1
2(
o
12 ~
I--11
12
Li 'I
,! .ll
- x•
I i
® ®
10 15 4
•
50
, 100 200
86 (Pc)
• ~I-
i F i g . 2 . House types / l e f t / ,
and window leakage categories / r i g h t / ~/oof points where criteria-are exceeded
~-F(i)-annual 100 hours of exceedence
Blow-rise
Categ°rY~D
~ medium-ri_~ e Category. \D
~_,
.~:r~e~'+
tot medium rise Jl- low-rise
~\-b,, . . . . .
5
A~
~1_ ,
10
vebcity criteria (m/s)
15
5
0./
Fig,3. Con~parison o£ ground level wind clin~tes
10 15 velocity criteda (m/s)
114
The models of both versions were measured in the sanle way. The wind tunnel tests were followed by higher level processing of the data, including calculations of filtration and ventilation.
COMPARISON OF GROUND LEVEL WIND CLIMATE As nmrked on Fig.9. 30 locations were selected on both versions for n~asuremerit of the ground level wind speed. All the locations had the same usage function, that is typical activity and exposure of people there. MELBOURNE's /2./ criteria were used for the acceptable limits of the hourly wind speed as deduced from the acceptable peek gust speeds averaged over 2 sec by asstm~ing Gaussian distributions of a suburban 6v=0.2 standard deviation of the velocity fluctuations. The criteria are shown in Table 9.
TABLE I Acceptable limits of the hourly wind speed
Category Activity Exposure Limit 2 sec gust speed (n~s) Acceptable hourly mean speed (m/s)
A Steady Long
B Steady Short
C Walk Short
D Danger of accident
90.0
13.0
96.0
23.0
6.2
8.0
9.8
~4.9
A local reference m e a n wind speed was measured at each wind directions at a height corresponding to 900 m in full scale over the windward leading edge of the turntable in the centre line of the tunnel. Since the surroundings of the area tested was quite flat and homogeniously suburban in surface roughness there was no need to change roughness configuration. While the tunnel speed were kept constant a vertical hot wire was traversed from location to location and the local mean wind speed was measured at 2 m full scale height. Local to reference velocity ratios were sinmltaneously calculated and stored for further analysis. This was repeated for all wind directions. The meteorologic~l data base for the analysis of the measured data was fortunately exceptionally good due to the fact that one of Budapest's two n~in stations is situated within 2 km reach and that a large flat area including this station and our site is of the same type of terrain roughness. Thus it was simple to transform the station's wind statistics into the local reference point using the gradient wind method described by LAWSON /3./. The local joint probabilities of the hourly wind speed exceeding a certain value at a wind direction and the measured velocity ratios were then used to calculate the exceedence of the local acceptable limits in annual hours at each location.
115
F(i) =ZP(d)~ exp (~U@/ (C~V)) k ) ~ 8760 (h/year) d
/I./
where F(i) is the nun~er of annual hours in location i while the wind speed exceeds U@, V=V(i,d) is the measured velocity ratio, d is the index of wind direction, P(d) is the probability of d direction, and C and k are directional dependent constants of the Raleigh-type distribution fitted to the annual probability statistics of the hourly n~an wind speed for each wind direction. As shown in Fig.3. the n~dium rise version was found to be nmch more windy in terms of annual hours of exceeding acceptability limits. Part a./ of the figure shows the relative fraction of locations Ntot where acceptability linits of Table I. are exceeded for all locations, and for groups of locations corresponding to criteria A-C(D) assigned as Ncat and plotted with dotted line. Part b./ shows the totals of annual hours of exceedence for the groups of locations corresponding to the different criteria for both versions. It can he seen that the A-C functional criteria are exceeded in 429 hours for the low rise housing and in 1783 hours for the medium rise version. The accident liner is exceeded in , and 18 hours respectively.
PRESSURE MEASUREMENTS For the estinmte of the filtration and ventilation heat losses of the buildings simplified computer simulations can be used. Though other design data were mostly known or reasonably assumed for the analysis, wind pressure data n~ght not be assumed in an analysis that targeted the comparison of the effect of aerodynan
supposing the area of the surface is in the order
of his I and I/2 storey single family houses. This finding and his own experiences encouraged the author to use pressure taps in an arrangement shown on Fig.2., using pneun~tic averaging for 2-3 story high, n~ax 16 m wide facade and roof elements. The time factor heavily restr~cted the total number of pressure taps to be used though the laboratory has 4 pcs of 48-port Scanivalves, that would have facilitated almost 600 taps if every 3 had been pneumatically averaged. The instrumentation and measuring process as well as the running time of the filtration program restricted the pressure measurements to 11 buildings of the two versions. corner and 4 row house elements of the low rise version, as shown on Fig.1. and 2., were measured and 3 sections of the 100-odd sin~lar ones of the medium
116
rise housing. These were asstm~d to be representative in size, shape and posi tion, and with an approxin~tion the whole housing might be ragarded as ensen~les of n~itiples of these buildings. Besides, there was no wimd direction of outstanding frequency of occurence, that n~de the estin~te more reliable. Some results of the pressure measurements are presented on Fig.4., where CPI and CP2 are assigned to parts of building envelops as shown on Fig.2.. These are in fairly good agreement with WIR~N's /3./ data as regards the low rise version. Fig.5. shows the variation of the n~gnitude of pressure difference as a function of the wind direction in the foml of ABS(CPI-CP2) for the three most exposed and sheltered buildings, at the perimeter and in the core of the new housing respectively. All pressure coefficients were non-din~nsionalized by the d y m a ~ c head at an elevation of ~0 m in full scale, value of which were gained from log-law profiles measured over the en~tly modell section with the whole boundary layer generating setup in the working section.
MODEL OF FILTRATION AND VENTILATION After studying different simple filtration models of LYBERG /4./ it was decided that simple single-cell model would be used for filtration calculations. Since the target was a con~arison of the seasonal heat den~nd necessary to cover losses due to filtration and ventilation a great number of runs bec~mle necessary. The meteorological input data were split into two parts. The frequency of wind directions and the joint probability of wind speed and outdoor ten~erature were separately treated. The resolution of this later was 3 m/s increments from 0.5 m/s to 9.5 m/s and 8°C increments from -14°C %o +I0°C respectively. As paranleters of the analysis 3 classes of airtightness of the windows, as shown on Fig.2., and 4 ventilation alternates were assumed. The four ventilation modes were the following: a./ filtration only * occassional intensive aeration through windows to nminrain the mininml air change of 0.5 ACH if filtration is not sufficient to do that; b./ filtration + pern~nent slight opening of a fraction of windows, as observed, analysed and described by LYBERG /5./ + occassional aeration to 0.5 ACH; c./ filtration + controllable vents below each window as described by PE~ZES et al. /6./ + occasional aeration to
0.5 ACH;
d./ filtration + pern~nent and steady exhaust ventilation with a capacity of 0.5 ACH. For modes a.-c. one individual venting duct leading up over the roof was assumed to each flat and substituted with an equivalent opening on the roof. This approach did not counted for other lea~kages that n~ght and certainly would, occur in the actual buildings. Therefore it is reasonable to present the
117 CPI-CP2 2
HOUSE 1 - -
1
3 .............
......
'.. ............ i:::........
5,1
-1 -2
oc
45
1"
90
135
A\
180 225. 270 315 360
.HOUSE 4 8 ...... -6 --10 ............ (3- 4 storey, row)
, . % - . . .
...........~ ~ / ~
0
.
-I
.
.
45
I
.
.
.
90.
.
.
.
13S
o
~j'
. . . . . . . . . . .
150
225
270
OC
315
360
HOUSE 5 9 ....... 7 .... 11 (3-4storey, corner.) .-.---: ......
~\
--.-.--.
0
-.1 0
45
90
;.~-.c ::'~
c,c 135 180 225 270 315 360
Fig.4. Variation of CPI-CP2 with the wind direction 2 ABS(CPI-CP2) HOUSES: e=4,
b.=l,
c.= 5, (EXPOSEOHOUSES)
C,
0 O
45
90
135
180
225
270 3]5
360 IX,
2 HOUSES d.=7.,
e.=3.,
[=10.
(SH~LTEEEOhOUSES}
0 0
45
90
135
180 225 270 315 350 ~
F i g . 5 . V a r i a t i o n o f ABS (CP1-CP2) "~ith t h e w i n d d i r e c t i o n f o r m o s t e x p o s e d and s h e l t e r e d h o u s e s o f ~che two v e r s i o n s . / H o u s e s 1. , 3 . , a r e ~ 0 - s ~ c o r e y _ _ t h e o t h e r s a r e 3 - 4 s t o r e y c o r n e r o r row e l e m e n t s i n ~che .ow-rlse versz0n/
118
assumed overall air-tightness of the buildings in te~is of N(50), that is the ACH at 50 Pa pressurization to enable a wider comparison of the results. This i~ shown in Table 2.
TABLE 2. Assumed overall air-tightness of the sin~lated buildings in N(50) as function of window tightness class and ventilation modes
Vent.mode
Air-tightness class of the windows I.
a., d.
2.8-3.2
2.
3.
3.6-3.8
5.6-6.2
b. (x)
3.0-(5.6)
3.7-(6.6)
5.9-(9.0)
c.
3.8-4.1
4.7-5.1
6.7-7.4
(x)
weather dependent aeration habits gave varying values The following set of fundamental equations were used for the calculation of
n~ss flows of air into and from the building. ~ P = 9 ~ U(10)2/2 ~ (CPe-CPi) - 9 * g ~ AT/Ti ~ z
/2./
for the total pressure difference driving the leakage flow n1~a . ~ p b
/3./
for the n~ss flows, with b varying from 0.5 to I depending on the type of opening, and for n~ss conservation: ~in
+~1out = 0
/4./
The results of the calculations were extrapolated for the whole housing develop ment by n~itiplying the results gained for the individual representative houses by the number of the similar houses and sun~ling up. The total internal volume of the houses was the s~le for the two versions as well as the total leakage area. The comparison of the heat losses due to air change are presented in bar charts on Fig.6.
CONCLUSIONS Of the two housing alternates the low rise version aerodym~m~ically better matched the suburban envirormlent. The lower houses at the perimeter create a harmonic transition to the surroundings. The pitched roofs also contribute to this. Even if the ground level wind speeds may be regarded as acceptable for both versions, that is, the degree of exceedence would not n~nke architectural modifications necessary, the conditions over the low rise version are by far better. Some suggestion were made to the garden architect as to vegetation shelterbelts.
119
Ventilation mode d./
Ventilation mode a./
QFplant total(TJ)
QFplant total (TJ) 35
35
3O
30
25 20 0.5AC 15 I0
oHI m,j iMM 25
20
_
0.5 A~ 15 10
n|
5 0
1
2
1
3
QPplant total(TJ)
QFplant t o t a l (TJ)
5O
5O
45
45
4O
4O
35
35
25 2O 0.5 ACH 15 10 5 0
m
,
nl nl
30
2
I
--
0.5 ACH
IMi
I
3
Ventilation mode c./
Ventilation mode b./
30
2 ~dow l e a k ~
3
~ low rise version
15
3
:::::::::::::::::::medium ::::::::::: rise version
Fig.6. Comparison of the plant total seasonal heat losses due to air change in buildings for different ventilation modes and window leakage categories
120
The analysis of the filtration gave sonmwhat unexpected results.
In cases
where the total heat losses coincided with that of the 0.5 ACH, the filtration air change had never exceeded that rate, for no house, no meteorological situation. This means that either the air leakage was underestinmted or, if the building turned out to be really as tight as that, the necessary minimum of ACH can not be achieved without uncontrolled opening of the windows by the habitant~ that, in turn, would certainly increase the ACH above the necessary. It is likely that those con~inations of the assumed airtightness and ventilation mode are realistic, where N(50) is higher. For these cases it was found that the total filtration and ventilation heat loss is 20-40 % higher in the medium rise version than in the low one.
REFERENCES
/I ./ COOK,N J: De%erndnation of the model scale factor in wind tunnel simulations of the adiabatic atmospheric boundary layer, Journ, of Ind.Aerodyn. 2 ( 1 9 7 7 / 7 8 ) pp. : 3 1 1 - 3 2 1 . /2./ MELBOURNE,W: Criteria for envirormlental wind conditions, Journ of Wind Eng. and Ind. Aerodyn. 3 (1978) pp. : 241-249 /3./ WIR~N,B G: Effects of Surrounding Buildings on Wind Pressure Distributions and Ventilation Losses of Single-Family Houses. part I. : 1 I/2-Storey De%ached Houses. Bulletin of S.I.B., M85: 19, G~vle,Sweden, 1985. /4./ LYBERG, M D: Models of Infiltration and Natural Ventilation. Bulletin of S.I.B. , M83 : 23, Ggvle,Sweden, 1983. /5./ LYBERG, M D: Use of Windows by Residents. Proc. of Conf. Windows in Building Design and Maintainance, GSteborg, Sweden, 1984., pp.: 344-349 /6./ P~NZES, GY; SZALAY, Z: Complementary venting structure. Proc. of Conf. Windows in Building Design and Maintainance, GSteborg, Sweden 1984., pp. : 473-478.