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Analysis of daylight responsive dimming system performance
\ PERGAMON
Building and Environment 23 "0888# 120Ð132
Analysis of daylight responsive dimming system performance A[!S[ Choia\ \ R[ G[ Mistrickb a
Institute of En`ineerin` + Construction Technolo`y\ Samsun` Co[\ 317!4\ Gon`se!Ri\ Giheun`!Eup\ Yon`in!City\ Kyun``i!Do\ Korea b Department of Architectural En`ineerin`\ Pennsylvania State University\ University Park\ PA 05792\ U[S[A[ Received 10 January 0887^ accepted 14 May 0887
Abstract A detail computer analysis model "DayDim# was developed to investigate the performance of daylight responsive dimming systems[ This computer model analyzes performance and lighting energy saving potential of the systems by modeling photosensor response[ System performance was quanti_ed and analysed through computer simulation using CIE and Perez daylight models for daylighting analysis[ In addition\ a large o.ce space employing an open!loop proportional control daylight responsive dimming system was monitored[ The results from simulation and _eld measurements show generally good agreement and issues which would a}ect system performance are discussed[ Þ 0887 Elsevier Science Ltd[ All rights reserved[
0[ Introduction To integrate daylight and electric light\ automatic lighting control systems have been developed to ful_ll the demand for energy savings and further environmental protection issues[ As a result\ using a daylight responsive dimming system becomes an appropriate option to reduce the electric lighting energy consumption in spaces where daylight can be a useful source of illumination[ The objective of such a system is to maintain the resulting workplane illuminance "daylight¦dimmed electric light# at least equal to the target illuminance level with mini! mum use of electric lighting[ How well this system can meet this objective is a}ected by the design components of the system[ Many constraints and variables can a}ect system performance[ However\ previous research did lit! tle to evaluate system performance\ but simply provided the optimum amount of saved lighting energy from such a system[ To investigate actual system performance\ a sophisticated performance model was needed[ A detailed computer analysis model "DayDim#\ using the _nite element technique for luminous ~ux transfer\ was developed to investigate the performance of daylight responsive dimming systems ð0Ł[ DayDim analyzes per! formance and lighting energy saving potential of daylight responsive dimming systems by modeling photosensor response[ DayDim considers the directional response of the photosensor\ which is determined through laboratory
Corresponding author[ Fax] ¦71!220!178!5656^ E!mail] pennaeÝ samsung[co[kr
measurement of a particular commercial photosensor[ DayDim also allows the analysis of accurate daylighting and electrical lighting calculations[ For daylighting analysis\ the CIE standard daylight model ð1Ł and the Perez daylight model ð2Ł were implemented[ The CIE standard daylight model\ consisting of three sky types "clear\ partly cloudy and overcast#\ portrays the long term average data\ whereas the Perez daylight model\ classifying eight discrete sky conditions from totally over! cast to very clear "sky clearness types 0Ð7#\ accounts for the dynamic nature of the sky from on!site measured weather data[ DayDim was validated through an existing lighting computer model "LumenÐMicro 5[9# for day! light:electric lighting workplane illuminance values and through _eld measurements in a small o.ce for pho! tosensor signal response ð3Ł[ In addition\ a large o.ce space employing an open! loop proportional control daylight responsive dimming system "The maximum response of the photosensor faces the window and electric light is dimmed proportionally according to the photosensor signals# was monitored[ The workplane illuminance and lighting power con! sumption were monitored in order to quantify system performance and saved lighting energy from a daylight responsive dimming system[ In this research\ computer simulations using both day! light models with two di}erent control algorithms "open! loop proportional and closed!loop proportional# and _eld measurements for a space employing an open!loop proportional control system\ were undertaken to inves! tigate system performance[ "Open!loop in this research means that the maximum response of the sensor faces the
S9259Ð0212:88 ,*see front matter Þ 0887 Elsevier Science Ltd[ All rights reserved PII] S 9 2 5 9 Ð 0 2 1 2 " 8 7 # 9 9 9 1 8 Ð 7
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window\ while closed!loop means that it faces the back wall[ The control governing equations of each algorithm can be found in ð4Ł[# 1[ Application of DayDim and _eld measurement 1[0[ Analysis space A large o.ce space "Fig[ 0# in Coopersburg "PA#\ U[S[A[ was monitored in order to investigate the per! formance of a daylight responsive dimming system[ This o.ce space was also simulated to determine how well predictions agree with actual system performance[ Twenty!four parabolic ~uorescent luminaires "0?×3?# were installed in this space and the _rst three rows of luminaires from the window were controlled with dimming[ A photosensor was installed on the ceiling 3[7 m from the window[ The critical workplane point was assumed to be the area directly below the photosensor so that an illuminance meter was installed at the workplane the same distance from the window[
value ð5Ł[ Sky clearness types 1Ð4 represent a partly cloudy sky\ while types 5Ð7 represent a clear sky[ Sky clearness types were generated hourly by the computer simulation of the Perez daylight model\ then the fre! quency of each sky clearness type at each hour and day over the bin month determines the proportion of sky types to apply to that month|s design day[ Table 0 shows the number of days for each sky type in a bin month throughout the year 0884[ The standard working period\ from 9799Ð0699 h\ was considered[ Conditions for each hour were analysed at 29 min past each hour[ Both open!loop proportional "maximum response of the photosensor toward window# and closed!loop proportional "maximum response of the photosensor toward back wall# control algorithm systems were simulated[ In this research\ a total of 213 simulations "01 months\ 8 h and 2 sky types# were performed to compute the annual simulation using the bin method[ The number of calculations could have been cut in half by considering only six months "combining summer\ fall\ spring and winter solar conditions#[ 1[3[ Predictions using the Perez daylight model
1[1[ Lighting control hardware Each luminaire has an electronic dimming ballast\ cap! able of dimming lamp output smoothly and uniformly[ The dimming range is speci_ed from 099) to 09) of light output[ The lighting output and input power have a linear relationship\ with the minimum 09) of lighting output equivalent to 20) of input power\ which was derived from the measurements[ A _xture mounted lighting controller was used in this research[ The daylight photosensor was designed with an open!loop proportional control system[ That is\ it is designed to detect the luminous ~ux from daylight primarily from the ~oor near the window and to minimize the detection of the luminous ~ux from the electric light! ing[ 1[2[ Predictions using the CIE daylight model In this research\ a bin method was employed to analyse the annual performance of the daylight responsive dim! ming system[ To use a bin method for lighting energy consumption\ the period of a bin month and design day were based on the solar noontime altitude angle ð3Ł[ Since the cloud cover code "9Ð7# measured from the National Weather Service "U[S[A[# is not relevant to determine the typical three sky types\ the proportion of sky types "clear\ partly cloudy\ overcast# to apply to each day was deter! mined by the sky clearness type and sky brightness value generated from the Perez daylight model[ Sky clearness type 0 indicates an overcast sky which has three ranges of sky conditions] dark overcast\ intermediate overcast and bright overcast\ determined by the sky brightness
Using the Perez daylight model\ a bin method of energy calculations was implemented for 0884 weather conditions[ In addition\ another hour!by!hour simulation for March 0885 was performed to compare in detail with the results of _eld measurements[ Using the Perez daylight model with 0884 hourly total solar irradiance data\ the sky types for each hour were determined from the sky clearness and sky brightness[ The same design days were applied as in the CIE standard daylight model[ In this research\ only two kinds of over! cast skies\ dark and intermediate overcast were generated so that two overcast sky clearness types and the other seven sky clearness types were simulated at each hour[ A total of 861 simulations over the entire year "01 months\ 8 h and 8 sky types# were performed[ The energy cal! culations using the CIE standard daylight model were accomplished on a day!by!day basis\ whereas for the Perez daylight model\ these were accomplished with an hour!by!hour basis[ Using the CIE daylight model\ it is assumed that each hour has the same sky type in one day[ Using the Perez daylight model\ however\ each hour may have di}erent sky types throughout the day[ Table 1 shows the hourly frequency for each sky clearness type and hour throughout the year 0884[ In performing the hour!by!hour simulations for March 0885\ the actual measured weather data for each hour were used as the input data[ 1[4[ Field measurements During 6 months\ from September 0884 to March 0885\ a large o.ce space with a daylight responsive
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Fig[ 0[ Analysis space[
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Table 0 The number of days for each sky type "Coopersburg "PA#\ U[S[A[# Period of bin months
Clear
P!cloudy
Overcast
01Ð12 ½ 0Ð11 0Ð12 ½ 1Ð11 1Ð12 ½ 2Ð11 2Ð12 ½ 3Ð11 3Ð12 ½ 4Ð11 4Ð12 ½ 5Ð11 5Ð12 ½ 6Ð11 6Ð12 ½ 7Ð11 7Ð12 ½ 8Ð11 8Ð12 ½ 09Ð11 09Ð12 ½ 00Ð11 00Ð12 ½ 01Ð11
0 04 00 02 02 00 8 09 06 03 4 5
02 8 6 00 7 03 01 19 00 7 00 02
06 6 09 6 8 5 8 0 2 8 04 00
Table 1 The frequency of each sky clearness type across each bin month "Perez daylight model# Month Hour Sky clearness type
dimming system was monitored[ The illumination levels and lighting power consumed were recorded using a data acquisition system[ Three illuminance meters\ for hori! zontal workplane illuminance\ vertical window illu! minance and total horizontal exterior illuminance\ were installed[ These three illuminance values\ along with the current\ voltage and wattage supplied to the dimmed luminaires\ were recorded every 4 min from 9599Ð1999 h\ everyday[
1
2
3
4
5
6
7
0
8 09 00 01 02 03 04 05 06
5 2 0 1 2 3 2 3 3
04 01 04 03 03 00 02 05 5
7 2 0 1 0 1 1 0 8
9 9 0 9 9 1 1 7 9
1 8 1 2 1 0 6 9 1
9 9 09 7 5 5 1 9 1
9 1 9 0 3 2 0 1 0
9 1 0 0 0 1 0 9 9
9 9 9 9 9 9 9 9 1
1
8 09 00 01 02 03 04 05 06
1 9 9 9 9 0 0 1 1
5 6 6 5 4 4 4 3 3
9 0 1 1 2 0 4 4 4
3 3 0 3 1 3 1 1 1
1 2 4 9 2 0 2 1 6
00 1 1 5 1 4 0 3 4
5 02 01 6 6 6 4 4 4
9 0 1 5 8 6 8 6 0
9 9 9 9 9 9 9 9 9
2
8 09 00 01 02 03 04 05 06
2 2 0 0 1 1 2 3 2
7 7 6 5 7 5 5 3 6
2 1 3 3 2 1 1 1 3
1 9 1 0 9 1 2 3 1
1 2 9 0 1 3 1 1 0
2 1 0 2 0 1 9 0 0
6 8 7 4 3 2 4 7 8
9 0 4 6 7 6 6 2 0
9 9 9 9 9 9 9 9 9
3
8 09 00 01 02 03 04 05 06
1 1 1 2 1 0 0 1 1
5 5 6 5 4 3 4 6 02
2 2 1 1 0 4 3 4 0
9 0 1 1 1 3 2 3 0
1 0 9 0 3 2 5 9 0
0 0 0 1 0 0 9 2 3
05 4 4 5 3 1 1 3 2
0 01 01 8 01 00 09 5 5
9 9 9 9 9 9 9 9 9
4
8 09 00 01 02 03 04 05 06
3 3 2 3 0 1 2 0 2
4 4 5 3 09 3 3 6 4
1 0 2 2 9 3 2 2 5
1 0 0 0 0 2 0 3 3
9 1 0 1 0 2 2 1 0
2 1 1 0 4 2 1 1 0
09 7 3 4 1 4 8 6 8
3 6 09 09 09 5 4 3 0
9 9 9 9 9 9 9 9 9
5
8 09 00 01 02 03 04 05 06
1 1 1 9 9 0 1 2 2
8 4 4 5 6 3 4 5 8
1 0 0 2 2 1 2 3 3
9 4 3 3 1 3 3 2 3
2 0 3 1 3 3 1 0 1
3 1 0 2 2 2 2 5 4
09 7 5 2 2 6 7 7 2
0 9 6 9 7 9 09 9 8 9 5 9 3 9 9 9 0 9 continued
2[ Results The correlation between daylight illuminance at a workplane point directly below the photosensor "ED\ 3[7 m from the window# and the photosensor signal "SD# was used as a measure of the performance of the daylight responsive dimming systems[ Rubinstein et al[ ð4Ł ana! lysed these correlations with daylight illuminances and photosensor illuminances using scale model measure! ments[ They considered variables such as window orien! tation\ photosensor con_guration and the use of blinds in the analysis of small and semi!in_nite rooms[ In this research\ the varied parameters include control algo! rithms\ seasonal changes and sky types[ In addition to computing the ratios of ED:SD\ cali! bration and performance of a daylight responsive dim! ming system were simulated in order to investigate system performance for the workplane analysis point[ The design objective of such a system is to maintain the resulting workplane illuminances at a target level[ In the real world\ however\ the resulting workplane illuminances are some! times higher or lower than the target level due to the di}erent ratios of ED:SD across sky types and lighting systems[ The calibration setting will also a}ect the degree to which it is higher or lower[ In this research\ the com! puter model was used to compute photosensor signals and then the resulting workplane illuminances to show
0D 0M
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whether these illuminances were maintained at a target level or not[
Month Hour Sky clearness type
6
7
8
09
00
01
0D 0M
1
2
3
4
8 09 00 01 02 03 04 05 06
1 2 0 0 0 0 0 9 0
01 5 6 4 6 6 3 6 7
3 4 1 6 3 9 3 2 5
2 2 1 0 1 4 2 5 1
0 1 3 2 3 0 4 1 1
1 4 2 2 2 4 2 6 6
8 09 00 01 02 03 04 05 06
9 9 9 9 9 9 9 9 0
5 1 0 1 3 1 1 1 3
0 4 0 1 0 0 4 0 3
2 2 3 1 1 3 0 1 5
0 3 4 3 5 4 2 8 9
8 09 00 01 02 03 04 05 06
0 0 0 0 0 0 0 0 1
2 2 3 0 1 3 4 2 6
9 9 0 1 1 1 1 3 3
2 0 0 1 1 0 9 4 4
8 09 00 01 02 03 04 05 06
3 3 1 2 1 2 2 2 3
3 2 5 3 6 4 3 7 5
1 1 0 0 9 1 2 1 1
8 09 00 01 02 03 04 05 06
3 1 1 3 1 0 2 8 7
5 00 00 8 01 03 03 8 3
8 09 00 01 02 03 04 05 06
5 3 0 0 9 0 2 4 9
4 3 7 5 09 00 09 01 9
5
6
7
5 2 7 7 6 4 7 4 3
9 2 2 1 1 5 1 9 09
9 9 9 9 9 9 9 9 9
7 2 0 1 4 5 7 00 1
00 09 00 01 7 6 6 5 3
0 3 7 6 4 5 4 9 9
9 9 9 9 9 9 9 9 9
4 2 0 1 2 1 5 5 3
1 2 1 4 3 1 4 2 5
2 01 8 7 2 00 5 8 2
3 7 01 09 03 7 5 9 9
9 9 9 9 9 9 9 9 9
0 0 9 3 3 1 4 2 7
0 1 0 9 0 1 1 0 6
1 9 2 0 0 3 1 09 2
02 01 01 8 09 8 00 2 9
2 5 4 7 4 2 9 9 9
9 9 9 9 9 9 9 9 9
1 2 2 0 2 2 1 5 4
2 0 0 1 2 3 1 3 3
1 2 9 3 3 0 4 1 2
4 2 3 3 1 1 2 0 1
8 7 5 4 3 5 1 9 9
9 9 3 1 0 9 9 9 0
9 9 9 9 9 9 9 9 1
5 4 0 0 9 3 2 3 9
1 9 0 3 2 1 0 3 9
2 5 1 2 2 0 4 4 9
0 1 5 2 3 3 6 9 9
1 4 5 6 5 4 9 9 9
3 3 4 4 3 1 0 9 9
0 9 9 9 9 9 9 9 9
2[0[ Using the CIE daylight model The results in Table 2 show that the ratios of daylight illuminances at the workplane point to the photosensor signals "ED:SD# from open!loop proportional control vary monthly by small amounts for clear and partly cloudy skies[ Because an overcast sky distribution changes only in magnitude across di}erent solar positions\ this ratio is a constant for this model sky[ December has the highest ratio for a clear sky and a partly cloudy sky\ whereas
Table 2 Correlation between ED and SD Sky type "CIE#
Month
Open!loop
Closed!loop
ED:SD ratio
R1
ED:SD ratio
R1
Clear "9899Ð0299#
0 1 2 3 4 5 6 7 8 09 00 01
9[5481 9[4758 9[4072 9[3617 9[3381 9[3303 9[3319 9[3404 9[3669 9[4295 9[4888 9[5550
9[5851 9[5671 9[6429 9[7186 9[7627 9[7706 9[7552 9[7386 9[7270 9[7435 9[7183 9[6587
0[7416 0[6093 0[4545 0[3594 0[3949 0[2760 0[2802 0[3030 0[3577 0[4576 0[6949 0[7303
9[7314 9[7075 9[7354 9[7832 9[8189 9[8208 9[8000 9[8910 9[8947 9[8114 9[8019 9[7673
P!cloudy "9899Ð0399#
0 1 2 3 4 5 6 7 8 09 00 01
0[9336 9[8287 9[7239 9[6531 9[6151 9[6984 9[6953 9[6112 9[6610 9[7696 9[8702 0[9560
9[8394 9[8221 9[8021 9[7080 9[7425 9[7447 9[7463 9[7688 9[7601 9[7570 9[7795 9[8013
1[2167 1[1990 1[9277 0[8164 0[7543 0[7283 0[7370 0[7502 0[8235 1[9690 1[1076 1[2257
9[8826 9[8809 9[8786 9[8756 9[8726 9[8730 9[8656 9[8761 9[8754 9[8785 9[8803 9[8825
Overcast "9899Ð0699#
0 1 2 3 4 5 6 7 8 09 00 01
9[7750 9[7741 9[7748 9[7744 9[7755 9[7750 9[7745 9[7752 9[7759 9[7756 9[7741 9[7756
9[8888 0[9999 9[8888 0[9999 0[9999 9[8888 9[8888 0[9999 9[8888 0[9999 9[8888 9[8888
0[8855 0[8820 0[8803 0[8890 0[8843 0[8828 0[8806 0[8815 0[8839 0[8850 0[8801 0[8880
9[8887 9[8888 9[8887 9[8888 9[8887 9[8886 9[8887 9[8888 9[8888 9[8888 9[8888 9[8887
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June has the lowest values of ED:SD for a clear sky and July has the lowest ratio for a partly cloudy sky[ Considering di}erences between sky types\ a clear sky has the lowest values of ED:SD throughout the year\ while a partly cloudy sky and overcast sky have relatively simi! lar values[ Through March to October\ an overcast sky has higher ratios\ whereas a partly cloudy sky has higher ratios from November to February[ Figure 1 shows that each sky type across the year has di}erent ED:SD ratios for open!loop proportional control[ Closed!loop proportional control also provides di}er! ent ratios of ED:SD for each sky type across the year[ The ratios of ED:SD increase for a clear sky and for a partly cloudy sky from June to January\ while an overcast sky provides a constant ratio as in open!loop control "Table 2#[ Closed!loop control has slightly higher R1 values and smaller seasonal changes compared to the open!loop con! trol case[ Across di}erent sky types\ the results are similar to those for open!loop control[ A clear sky has the lowest values of ED:SD through the entire year\ while a partly cloudy sky and overcast sky have similar values[ The ratios are more similar in the closed!loop case[ Figure 2 shows that closed!loop control has di}erent ratios of ED:SD for each sky type across the year[ The calibration procedure which initially determines the relationship between daylight illuminance at the workplane and the photosensor signal would likely be accomplished in the morning on a clear day[ It is assumed that this relationship for a clear sky represents all other
sky conditions[ The lower ratio of ED:SD in open!loop control for a clear sky would result in higher resulting illuminance than the target level during overcast or partly cloudy days[ This is because daylight illuminances at the workplane for overcast or partly cloudy skies are higher than those for a clear sky with the same photosensor signal[ The seasonal changes in the ratio of ED:SD also cause the resulting illuminance to vary from the target level[ For resulting workplane illuminance and dimming level\ the January results are shown as examples[ The illuminance ranges from the target level are −8[6Ð7[9) "clear#\ 9[0Ð02[2) "partly cloudy# and −02[7Ð−7[7) "overcast# for the open!loop control case[ In the cases of partly cloudy and clear sky conditions\ the dimming levels are not at minimum "9[09# around sunset when daylight illuminances are higher than the target level[ This is because the direct sun component from lower solar alti! tude angle reaches the back wall which results in higher point illuminance\ but does not have a corresponding e}ect on the photosensor[ The results of closed!loop control across the year show similar trends to the open!loop control case\ but overall\ the closed!loop control tracks the daylight levels slightly better than does open!loop control[ 2[1[ Using the Perez daylight model with weather data For seasonal changes of the ED:SD ratio\ an overcast sky condition was investigated[ Table 3 shows variations
Fig[ 1[ Correlation between daylight point illuminance at the workplane and photosensor signal for open!loop[
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Fig[ 2[ Correlation between daylight point illuminance at the workplane and photosensor signal for closed!loop[
Table 3 Correlations between EDand SDfrom the Perez daylight model "seasons# Sky type 0 "overcast# Month
2 5 8
Open!Loop
Closed!Loop
ED:SD ratio
R1
ED:SD ratio
R1
0[0039 0[9401 0[9750
9[8896 9[8625 9[8815
1[2327 1[1570 1[2433
9[8878 9[8818 9[8874
Note] 9899Ð0399 for sky type 1Ð6 and 9899Ð0699 for sky type 0[
in the ED:SD ratios from a bin method for sky clearness type 0 "overcast#[ Under an overcast sky condition\ the ED:SD ratio increases by 5[9) from June to March[ This is most likely due to the fact that an overcast sky varies azimuthally and provides di}erent relative luminance gradations at di}erent solar altitude positions in this day! light model[ To further examine correlations of ED:SD for di}erent sky types\ the entire year was simulated with a bin method[ Figure 3 and Table 4 shows that each sky type across the year has di}erent ED:SD ratios for open!loop proportional control[ As the sky condition changes from a dense partly cloudy sky "sky clearness type 1# to a totally clear sky "sky clearness type 6#\ the ratios of ED:SD decrease continuously[ The ratio for an overcast sky "sky clearness type 0# is higher than for type 1[ Under a partly cloudy sky condition\ the di}erence in ED:SD between the
lowest value "sky clearness type 4# and the highest value "sky clearness type 1# is a 08[4) increase[ In comparing all sky clearness types\ the di}erence in ED:SD between the lowest one "sky clearness type 6# and the highest one "sky clearness type 0# is a 71[0) increase[ Closed!loop proportional control also provides di}er! ent ratios of daylight illuminance at the workplane point to the photosensor signals "ED:SD# for sky clearness type 0 "Fig[ 4 and Table 4#[ The trends in correlations of ED:SD for closed!loop proportional control are relatively similar to those of an open!loop proportional control system[ Seasonal changes are reduced compared to the open!loop control case and across all sky clearness types\ the ratios are more similar in the closed!loop case[ For resulting workplane illuminance and dimming level\ the larger di}erences in partly cloudy and clear sky conditions occur around sunset due to rear wall re~ection as in the CIE daylight model case[ The largest di}erence in those conditions are 21[9) "clear\ open!loop# and 30[1) "partly cloudy\ open!loop#\ and 12[6) "clear\ closed!loop# and 18[9) "partly cloudy\ closed!loop# in January[ 2[2[ Field measurements The results of the dimming level from _eld measure! ments on each day during September 0884 to January 0885 are shown in Table 5[ In Table 5\ the dimming level for the open!loop proportional control indicates lighting input power\ not lighting levels[ Since _eld measurement
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Fig[ 3[ Correlation between daylight point illuminance at the workplane and photosensor signal for open!loop[
Table 4 Correlations between ED and SD from the Perez daylight model "sky types# Sky type
0 1 2 3 4 5 6
Open!Loop
Closed!Loop
Relative ED:SD ratio
R1
Relative ED:SD ratio
R1
0[9582 9[8851 9[7805 9[7950 9[7224 9[5422 9[4762
9[8683 9[3319 9[6013 9[6991 9[6142 9[7307 9[7534
1[2152 1[1814 1[0920 0[8641 0[7450 0[6317 0[5134
9[8265 9[7547 9[8179 9[8971 9[8522 9[8534 9[8219
the minimum level during a portion of any partly cloudy sky and clear sky day[ 3[ Discussion
Note] 9899Ð0399 for sky type 1Ð6 and 9899Ð0699 for sky type 0[
was sometimes interrupted in the analysis space being used\ the results are shown on a daily basis rather than monthly[ The dimming level "lighting power# was averaged hourly and then daily from 4 min interval data[ These dimming levels result from a measured low end light output of 03)\ which was the limit of the electronic ballasts and lighting controller[ Due to the large window on the west side\ daylight illuminance alone exceeded the target illuminance level and dimming was maintained at
In this section\ the following are compared] "0# ED:SD ratios of the CIE daylight model and the Perez daylight model^ "1# Dimming levels of the CIE daylight model and the Perez daylight model^ "2# Dimming levels of DayDim and _eld measurements^ and "3# Open!loop and closed! loop proportional systems[ The ED:SD ratios from the CIE daylight model and Perez daylight model show similar trends across di}erent sky types and seasons[ A partly cloudy sky has higher ratios than a clear sky and the ratios during winter are higher than during summer for the same sky conditions[ Since an overcast sky has an almost constant ratio throughout the year "the Perez model showed little vari! ations#\ the ratios are the highest among di}erent sky types during summer[ For partly cloudy sky conditions\ the average ED:SD ratios from the Perez model are similar to the ED:SD ratios from the CIE model[ However\ the ED:SD ratios for overcast sky conditions are di}erent between the two daylight models[ The monthly average dimming levels for the CIE day! light model and Perez daylight model are shown in Table 6[ The di}erences are caused by two factors[ The _rst
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Fig[ 4[ Correlation between daylight point illuminance at the workplane and photosensor signal for closed!loop[
Fig[ 5[ Comparison of measured dimming levels with hour!by!hour simulation using the Perez sky models in a large o.ce space[
factor results from the di}erent assumptions used for calculating the average dimming levels[ The same sky type was assumed throughout one day in application of the CIE model\ while each hour had di}erent sky types for the analysis with the Perez model[ The second factor is due to the di}erent daylight illuminances calculated
from both sky models[ The CIE model represents the annual average\ but the Perez model utilizes a particular year of actual measured weather data[ The actual performance of a daylight responsive dim! ming system employing open!loop proportional control was compared to the computer simulation results[ The
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Table 5 The dimming levels "lighting power# from _eld measurements
Table 5 The dimming levels "lighting power# from _eld measurements
Month
Day
Watt
Avg dim
Month
8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8
0 1 2 3 4 5 6 7 8 09 00 01 02 03 04 05 06 07 08 19 10 11 12 13 14 15 16 17 18 29
9[264 9[285 9[273 9[273 9[274 9[272 9[285 9[310 9[443 9[257 9[263 9[258 9[370 9[392 9[263 9[359 9[256 9[264 9[399 9[340 9[567 9[275 9[257 9[604 9[276 9[256 9[261
9[257 9[277 9[265 9[265 9[266 9[264 9[277 9[302 9[432 9[250 9[256 9[251 9[361 9[284 9[256 9[340 9[259 9[257 9[281 9[331 9[554 9[267 9[250 9[690 9[268 9[259 9[254
Month average
9[310
9[302
9[263 9[270 9[273 9[472 0[905 0[998 0[900 0[997 0[997 0[904 9[614 9[855 9[267 9[305 9[267 9[261 9[268 9[279 9[400 9[256 9[265 9[325 9[390 9[317 9[381 9[484 9[347 9[320 9[522
9[256 9[263 9[265 9[461 9[885 9[878 9[880 9[877 9[877 9[884 9[600 9[836 9[260 9[397 9[260 9[254 9[261 9[262 9[490 9[259 9[258 9[316 9[282 9[319 9[371 9[472 9[338 9[312 9[510
Month average 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09
0 1 2 3 4 5 6 7 8 09 00 01 02 03 04 05 06 07 08 19 10 11 12 13 14 15 16 17 18 29 20
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
Day
0 1 2 3 4 5 6 7 8 09 00 01 02 03 04 05 06 07 08 19 10 11 12 13 14 15 16 17 18 29
Month average 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01
0 1 2 3 4 5 6 7 8 09 00 01 02 03 04 05 06 07 08 19 10 11 12 13 14 15 16 17
Watt
Avg dim
9[472
9[461
9[796 9[517 9[332 9[333 9[343 9[597 9[362 9[348 9[604 9[422 9[631 9[778 9[695 9[446 9[364 9[377 9[388 9[411 9[659 9[408 9[371 9[431 9[679 9[414
9[680 9[505 9[323 9[324 9[334 9[485 9[353 9[349 9[690 9[412 9[616 9[761 9[581 9[435 9[355 9[367 9[378 9[401 9[634 9[498 9[362 9[420 9[654 9[404
9[474
9[463
9[577 9[593 9[331 9[359 9[457 9[368 9[319 9[396 9[394 9[270 9[390 9[416 9[332 9[513 9[337 9[272 9[274 9[306 9[268 9[306 9[304
9[564 9[481 9[322 9[340 9[446 9[369 9[301 9[288 9[286 9[263 9[282 9[406 9[323 9[501 9[328 9[264 9[266 9[398 9[261 9[398 9[396 continued
A[!S[ Choi\ R[G[ Mistrick:Buildin` and Environment 23 "0888# 120Ð132 Table 5*continued The dimming levels "lighting power# from _eld measurements Month
Day
Watt
Avg dim
01 18 01 29 01 20 Month average
9[329 9[361 9[350
9[311 9[352 9[341
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Month average
9[429 9[467 9[380 9[300 9[359 9[441 9[396 9[347 9[423 9[356 9[335 9[354 9[790 9[459 9[529 9[682 9[339 9[331 9[519 9[493 9[418
9[419 9[456 9[370 9[392 9[340 9[430 9[288 9[338 9[413 9[347 9[326 9[345 9[674 9[438 9[507 9[666 9[320 9[322 9[597 9[383 9[408
0 1 2 3 4 5 6 7 8 09 00 01 02 03 04 05 06 07 08 19 10 11 12 13 14 15 16 17 18 29 20
Note] The numbers in bold type indicate days when measurement was interrupted during some hours[
results of the dimming level and resulting illuminance from _eld measurements for March 0885 are compared to values from computer simulations using the Perez day! light model[ The results of the dimming levels from the computer simulation of the Perez daylight model and _eld measurements show a similar trend\ but not identical dimming levels or illuminances "Fig[ 5#[ The results from _eld measurements show that the minimum dimming level is sometimes not achieved when the resulting illu! minance is much higher than the target level[ Variations of the maximum and minimum wattages in lighting power and a selected control algorithm slope MOP "open!loop slope\ ð4Ł# from pre!determined slopes of the lighting con! troller at the calibration time a}ect the dimming levels in _eld measurements[ In addition\ the dimming levels in computer simulations are a}ected by the system cali! bration[ If the information input at the time of system
130
calibration is di}erent\ di}erent dimming levels will result[ Under open!loop proportional control\ the results show that the magnitudes of ED and SD as well as the varying ratio of ED:SD a}ect system performance[ Target illuminance was not achieved with the same ED:SD ratio as at the calibration time "Table 7#[ This is caused by a non!zero value of SEM "signal produced for d "dimming level# 0 without daylight\ ð4Ł# in the open!loop pro! portional control governing equations[ The results from the simulations of the CIE daylight model showed that the di}erences were reduced as daylight illuminance increased\ with the same ED:SD ratio[ The results from the simulations of the Perez daylight model showed that low daylight illuminances in early morning or late after! noon resulted in lower illuminances than the target level\ whereas high daylight illuminances around noon resulted in higher illuminances than the target level[ If SEM is zero\ the target illuminance is achieved with di}erent magnitudes of ED and SD\ which is an inherent objective of open!loop control[ In the results of this research\ full electric light "0[99!computer simulation dimming level\ 0[91 kW!_eld measurement full load# does not happen at night because the photosensor still detects some ~ux from the electric light\ which causes the controller to dim the electric light[ In this research\ the night time dimming level was 9[80 in the computer simulation "CIE model# and therefore full load power rarely occurred at night in the _eld measurements[ In closed!loop proportional control\ however\ only the ratio of ED:SD a}ects system performance[ The target illuminance was achieved with di}erent magnitudes of ED and SD\ but with the same ED:SD ratio as at the calibration time "Table 7#[ 4[ Conclusions The following are the major _ndings from the appli! cation of DayDim and _eld measurements of a space employing a daylight responsive dimming system[ "0# The correlation between daylight illuminance at a critical workplane point "ED# and the photosensor signal "SD# is an important factor a}ecting the per! formance of daylight responsive dimming systems[ Choosing an appropriate calibration time and a pro! per location and con_guration of the photosensor are critical in order to reduce the di}erences among di}erent sky types and seasons[ "1# The ratio of ED:SD across the year depends on sky conditions\ season and photosensor orientation[ Di}erent ratios of ED:SD produce variations from the target lighting level for di}erent sky types through the seasons of the year[ "2# Closed!loop proportional control shows slightly bet! ter system performance than open!loop proportional control in this particular study[ The non!zero value of
131
A[!S[ Choi\ R[G[ Mistrick:Buildin` and Environment 23 "0888# 120Ð132 Table 6 Comparison of the average dimming levels from di}erent computer simulations Month
Min[ dim 9[0 Open
Min[ dim 9[90 Closed
Open
Closed
CIE
Perez
CIE
Perez
CIE
Perez
CIE
Perez
0 1 2 3 4 5 6 7 8 09 00 01
9[382 9[138 9[130 9[054 9[054 9[024 9[043 9[096 9[017 9[116 9[286 9[252
9[322 9[114 9[114 9[069 9[059 9[028 9[015 9[098 9[031 9[114 9[251 9[230
9[377 9[126 9[114 9[037 9[028 9[008 9[018 9[093 9[010 9[198 9[273 9[249
9[271 9[074 9[081 9[030 9[030 9[013 9[008 9[092 9[021 9[085 9[201 9[188
9[363 9[082 9[075 9[984 9[091 9[952 9[980 9[919 9[936 9[057 9[254 9[214
9[397 9[051 9[056 9[090 9[977 9[952 9[936 9[913 9[950 9[055 9[218 9[293
9[350 9[079 9[069 9[968 9[962 9[931 9[948 9[906 9[939 9[035 9[236 9[185
9[249 9[007 9[017 9[955 9[952 9[930 9[921 9[905 9[940 9[017 9[162 9[142
Annual
9[124
9[110
9[110
9[083
9[032
9[059
9[048
9[016
Table 7 The percentage di}erence of resulting illuminances from the target level with the same ED:SD ratio Open!loop Point E
Senser "O#
ED:SD "O#
)Dim "O#
Ele[ E "O#
Total E "O#
)Di}[ "O#
207[4 230[2 258[6 287[0 315[5 344[9
22[5 25[9 28[9 31[9 34[9 37[9
8[37 8[37 8[37 8[37 8[37 8[37
9[17 9[12 9[07 9[01 9[95 9[90
011[6 091[8 67[0 42[3 17[5 2[7
330[1 333[0 336[7 340[4 344[1 347[7
9[9 9[6 0[4 1[2 2[1 3[9
Point E
Senser "C#
ED:SD "C#
)Dim "C#
Ele[ E "C#
Total E "C#
)Di}[ "C#
207[4 232[9 256[4 281[9 305[4 330[9
02[9 03[9 04[9 05[9 06[9 07[9
13[49 13[49 13[49 13[49 13[49 13[49
9[17 9[11 9[06 9[00 9[95 9[99
011[6 87[1 62[6 38[1 13[6 9[1
330[1 330[1 330[1 330[1 330[1 330[1
9[9 9[9 9[9 9[9 9[9 9[9
Closed!loop
SEM in the open!loop proportional control governing equations causes a problem in achieving the target illuminance level on the workplane[ The magnitude of ED\ as well as the ratio of ED:SD\ a}ects the resulting workplane illuminances in open!loop proportional control[ "3# The lighting controller should be improved to account for the dynamic nature of the sky[ MOP and
MCL "closed!loop slope\ ð4Ł# should be computed at a calibration condition instead of pre!determined[
Acknowledgments This work was generously supported by Lutron Elec! tronics Co[\ Inc[ The authors would like to thank Dr
A[!S[ Choi\ R[G[ Mistrick:Buildin` and Environment 23 "0888# 120Ð132
Richard Perez "SUNY# for advice in applying his daylight model[
References ð0Ł Choi A\ Mistrick RG[ On the prediction of energy savings for a daylight dimming system[ Journal of the Illuminating Engineering Society 0886^15"1#]66Ð89[ ð1Ł IESNA\ IES lighting handbook\ 0883[
132
ð2Ł Perez R\ Ineichen P\ Reals R\ Michalsky J\ Stewart R[ Modeling daylight availability and irradiance component from direct and global irradiance[ Solar Energy 0889^33"4#]160Ð78[ ð3Ł Choi A\ Mistrick RG[ Application of the Perez model in daylight dimming system analysis[ IESNA Annual Conference Proceedings 0886^634Ð56[ ð4Ł Rubinstein F\ Ward G\ Verderber R[ Improving the performance of photo!electrically controlled lighting system[ Journal of the Illuminating Engineering Society 0875^04"0#]69Ð83[ ð5Ł Perez R\ Reals R\ Michalsky J[ Modeling sky angular luminance distribution from routine irradiance measurements[ Journal of the Illuminating Engineering Society\ 0882^12"0#]09Ð06[
Building and Environment 23 "0888# 120Ð132
Analysis of daylight responsive dimming system performance A[!S[ Choia\ \ R[ G[ Mistrickb a
Institute of En`ineerin` + Construction Technolo`y\ Samsun` Co[\ 317!4\ Gon`se!Ri\ Giheun`!Eup\ Yon`in!City\ Kyun``i!Do\ Korea b Department of Architectural En`ineerin`\ Pennsylvania State University\ University Park\ PA 05792\ U[S[A[ Received 10 January 0887^ accepted 14 May 0887
Abstract A detail computer analysis model "DayDim# was developed to investigate the performance of daylight responsive dimming systems[ This computer model analyzes performance and lighting energy saving potential of the systems by modeling photosensor response[ System performance was quanti_ed and analysed through computer simulation using CIE and Perez daylight models for daylighting analysis[ In addition\ a large o.ce space employing an open!loop proportional control daylight responsive dimming system was monitored[ The results from simulation and _eld measurements show generally good agreement and issues which would a}ect system performance are discussed[ Þ 0887 Elsevier Science Ltd[ All rights reserved[
0[ Introduction To integrate daylight and electric light\ automatic lighting control systems have been developed to ful_ll the demand for energy savings and further environmental protection issues[ As a result\ using a daylight responsive dimming system becomes an appropriate option to reduce the electric lighting energy consumption in spaces where daylight can be a useful source of illumination[ The objective of such a system is to maintain the resulting workplane illuminance "daylight¦dimmed electric light# at least equal to the target illuminance level with mini! mum use of electric lighting[ How well this system can meet this objective is a}ected by the design components of the system[ Many constraints and variables can a}ect system performance[ However\ previous research did lit! tle to evaluate system performance\ but simply provided the optimum amount of saved lighting energy from such a system[ To investigate actual system performance\ a sophisticated performance model was needed[ A detailed computer analysis model "DayDim#\ using the _nite element technique for luminous ~ux transfer\ was developed to investigate the performance of daylight responsive dimming systems ð0Ł[ DayDim analyzes per! formance and lighting energy saving potential of daylight responsive dimming systems by modeling photosensor response[ DayDim considers the directional response of the photosensor\ which is determined through laboratory
Corresponding author[ Fax] ¦71!220!178!5656^ E!mail] pennaeÝ samsung[co[kr
measurement of a particular commercial photosensor[ DayDim also allows the analysis of accurate daylighting and electrical lighting calculations[ For daylighting analysis\ the CIE standard daylight model ð1Ł and the Perez daylight model ð2Ł were implemented[ The CIE standard daylight model\ consisting of three sky types "clear\ partly cloudy and overcast#\ portrays the long term average data\ whereas the Perez daylight model\ classifying eight discrete sky conditions from totally over! cast to very clear "sky clearness types 0Ð7#\ accounts for the dynamic nature of the sky from on!site measured weather data[ DayDim was validated through an existing lighting computer model "LumenÐMicro 5[9# for day! light:electric lighting workplane illuminance values and through _eld measurements in a small o.ce for pho! tosensor signal response ð3Ł[ In addition\ a large o.ce space employing an open! loop proportional control daylight responsive dimming system "The maximum response of the photosensor faces the window and electric light is dimmed proportionally according to the photosensor signals# was monitored[ The workplane illuminance and lighting power con! sumption were monitored in order to quantify system performance and saved lighting energy from a daylight responsive dimming system[ In this research\ computer simulations using both day! light models with two di}erent control algorithms "open! loop proportional and closed!loop proportional# and _eld measurements for a space employing an open!loop proportional control system\ were undertaken to inves! tigate system performance[ "Open!loop in this research means that the maximum response of the sensor faces the
S9259Ð0212:88 ,*see front matter Þ 0887 Elsevier Science Ltd[ All rights reserved PII] S 9 2 5 9 Ð 0 2 1 2 " 8 7 # 9 9 9 1 8 Ð 7
121
A[!S[ Choi\ R[G[ Mistrick:Buildin` and Environment 23 "0888# 120Ð132
window\ while closed!loop means that it faces the back wall[ The control governing equations of each algorithm can be found in ð4Ł[# 1[ Application of DayDim and _eld measurement 1[0[ Analysis space A large o.ce space "Fig[ 0# in Coopersburg "PA#\ U[S[A[ was monitored in order to investigate the per! formance of a daylight responsive dimming system[ This o.ce space was also simulated to determine how well predictions agree with actual system performance[ Twenty!four parabolic ~uorescent luminaires "0?×3?# were installed in this space and the _rst three rows of luminaires from the window were controlled with dimming[ A photosensor was installed on the ceiling 3[7 m from the window[ The critical workplane point was assumed to be the area directly below the photosensor so that an illuminance meter was installed at the workplane the same distance from the window[
value ð5Ł[ Sky clearness types 1Ð4 represent a partly cloudy sky\ while types 5Ð7 represent a clear sky[ Sky clearness types were generated hourly by the computer simulation of the Perez daylight model\ then the fre! quency of each sky clearness type at each hour and day over the bin month determines the proportion of sky types to apply to that month|s design day[ Table 0 shows the number of days for each sky type in a bin month throughout the year 0884[ The standard working period\ from 9799Ð0699 h\ was considered[ Conditions for each hour were analysed at 29 min past each hour[ Both open!loop proportional "maximum response of the photosensor toward window# and closed!loop proportional "maximum response of the photosensor toward back wall# control algorithm systems were simulated[ In this research\ a total of 213 simulations "01 months\ 8 h and 2 sky types# were performed to compute the annual simulation using the bin method[ The number of calculations could have been cut in half by considering only six months "combining summer\ fall\ spring and winter solar conditions#[ 1[3[ Predictions using the Perez daylight model
1[1[ Lighting control hardware Each luminaire has an electronic dimming ballast\ cap! able of dimming lamp output smoothly and uniformly[ The dimming range is speci_ed from 099) to 09) of light output[ The lighting output and input power have a linear relationship\ with the minimum 09) of lighting output equivalent to 20) of input power\ which was derived from the measurements[ A _xture mounted lighting controller was used in this research[ The daylight photosensor was designed with an open!loop proportional control system[ That is\ it is designed to detect the luminous ~ux from daylight primarily from the ~oor near the window and to minimize the detection of the luminous ~ux from the electric light! ing[ 1[2[ Predictions using the CIE daylight model In this research\ a bin method was employed to analyse the annual performance of the daylight responsive dim! ming system[ To use a bin method for lighting energy consumption\ the period of a bin month and design day were based on the solar noontime altitude angle ð3Ł[ Since the cloud cover code "9Ð7# measured from the National Weather Service "U[S[A[# is not relevant to determine the typical three sky types\ the proportion of sky types "clear\ partly cloudy\ overcast# to apply to each day was deter! mined by the sky clearness type and sky brightness value generated from the Perez daylight model[ Sky clearness type 0 indicates an overcast sky which has three ranges of sky conditions] dark overcast\ intermediate overcast and bright overcast\ determined by the sky brightness
Using the Perez daylight model\ a bin method of energy calculations was implemented for 0884 weather conditions[ In addition\ another hour!by!hour simulation for March 0885 was performed to compare in detail with the results of _eld measurements[ Using the Perez daylight model with 0884 hourly total solar irradiance data\ the sky types for each hour were determined from the sky clearness and sky brightness[ The same design days were applied as in the CIE standard daylight model[ In this research\ only two kinds of over! cast skies\ dark and intermediate overcast were generated so that two overcast sky clearness types and the other seven sky clearness types were simulated at each hour[ A total of 861 simulations over the entire year "01 months\ 8 h and 8 sky types# were performed[ The energy cal! culations using the CIE standard daylight model were accomplished on a day!by!day basis\ whereas for the Perez daylight model\ these were accomplished with an hour!by!hour basis[ Using the CIE daylight model\ it is assumed that each hour has the same sky type in one day[ Using the Perez daylight model\ however\ each hour may have di}erent sky types throughout the day[ Table 1 shows the hourly frequency for each sky clearness type and hour throughout the year 0884[ In performing the hour!by!hour simulations for March 0885\ the actual measured weather data for each hour were used as the input data[ 1[4[ Field measurements During 6 months\ from September 0884 to March 0885\ a large o.ce space with a daylight responsive
A[!S[ Choi\ R[G[ Mistrick:Buildin` and Environment 23 "0888# 120Ð132
Fig[ 0[ Analysis space[
122
123
A[!S[ Choi\ R[G[ Mistrick:Buildin` and Environment 23 "0888# 120Ð132
Table 0 The number of days for each sky type "Coopersburg "PA#\ U[S[A[# Period of bin months
Clear
P!cloudy
Overcast
01Ð12 ½ 0Ð11 0Ð12 ½ 1Ð11 1Ð12 ½ 2Ð11 2Ð12 ½ 3Ð11 3Ð12 ½ 4Ð11 4Ð12 ½ 5Ð11 5Ð12 ½ 6Ð11 6Ð12 ½ 7Ð11 7Ð12 ½ 8Ð11 8Ð12 ½ 09Ð11 09Ð12 ½ 00Ð11 00Ð12 ½ 01Ð11
0 04 00 02 02 00 8 09 06 03 4 5
02 8 6 00 7 03 01 19 00 7 00 02
06 6 09 6 8 5 8 0 2 8 04 00
Table 1 The frequency of each sky clearness type across each bin month "Perez daylight model# Month Hour Sky clearness type
dimming system was monitored[ The illumination levels and lighting power consumed were recorded using a data acquisition system[ Three illuminance meters\ for hori! zontal workplane illuminance\ vertical window illu! minance and total horizontal exterior illuminance\ were installed[ These three illuminance values\ along with the current\ voltage and wattage supplied to the dimmed luminaires\ were recorded every 4 min from 9599Ð1999 h\ everyday[
1
2
3
4
5
6
7
0
8 09 00 01 02 03 04 05 06
5 2 0 1 2 3 2 3 3
04 01 04 03 03 00 02 05 5
7 2 0 1 0 1 1 0 8
9 9 0 9 9 1 1 7 9
1 8 1 2 1 0 6 9 1
9 9 09 7 5 5 1 9 1
9 1 9 0 3 2 0 1 0
9 1 0 0 0 1 0 9 9
9 9 9 9 9 9 9 9 1
1
8 09 00 01 02 03 04 05 06
1 9 9 9 9 0 0 1 1
5 6 6 5 4 4 4 3 3
9 0 1 1 2 0 4 4 4
3 3 0 3 1 3 1 1 1
1 2 4 9 2 0 2 1 6
00 1 1 5 1 4 0 3 4
5 02 01 6 6 6 4 4 4
9 0 1 5 8 6 8 6 0
9 9 9 9 9 9 9 9 9
2
8 09 00 01 02 03 04 05 06
2 2 0 0 1 1 2 3 2
7 7 6 5 7 5 5 3 6
2 1 3 3 2 1 1 1 3
1 9 1 0 9 1 2 3 1
1 2 9 0 1 3 1 1 0
2 1 0 2 0 1 9 0 0
6 8 7 4 3 2 4 7 8
9 0 4 6 7 6 6 2 0
9 9 9 9 9 9 9 9 9
3
8 09 00 01 02 03 04 05 06
1 1 1 2 1 0 0 1 1
5 5 6 5 4 3 4 6 02
2 2 1 1 0 4 3 4 0
9 0 1 1 1 3 2 3 0
1 0 9 0 3 2 5 9 0
0 0 0 1 0 0 9 2 3
05 4 4 5 3 1 1 3 2
0 01 01 8 01 00 09 5 5
9 9 9 9 9 9 9 9 9
4
8 09 00 01 02 03 04 05 06
3 3 2 3 0 1 2 0 2
4 4 5 3 09 3 3 6 4
1 0 2 2 9 3 2 2 5
1 0 0 0 0 2 0 3 3
9 1 0 1 0 2 2 1 0
2 1 1 0 4 2 1 1 0
09 7 3 4 1 4 8 6 8
3 6 09 09 09 5 4 3 0
9 9 9 9 9 9 9 9 9
5
8 09 00 01 02 03 04 05 06
1 1 1 9 9 0 1 2 2
8 4 4 5 6 3 4 5 8
1 0 0 2 2 1 2 3 3
9 4 3 3 1 3 3 2 3
2 0 3 1 3 3 1 0 1
3 1 0 2 2 2 2 5 4
09 7 5 2 2 6 7 7 2
0 9 6 9 7 9 09 9 8 9 5 9 3 9 9 9 0 9 continued
2[ Results The correlation between daylight illuminance at a workplane point directly below the photosensor "ED\ 3[7 m from the window# and the photosensor signal "SD# was used as a measure of the performance of the daylight responsive dimming systems[ Rubinstein et al[ ð4Ł ana! lysed these correlations with daylight illuminances and photosensor illuminances using scale model measure! ments[ They considered variables such as window orien! tation\ photosensor con_guration and the use of blinds in the analysis of small and semi!in_nite rooms[ In this research\ the varied parameters include control algo! rithms\ seasonal changes and sky types[ In addition to computing the ratios of ED:SD\ cali! bration and performance of a daylight responsive dim! ming system were simulated in order to investigate system performance for the workplane analysis point[ The design objective of such a system is to maintain the resulting workplane illuminances at a target level[ In the real world\ however\ the resulting workplane illuminances are some! times higher or lower than the target level due to the di}erent ratios of ED:SD across sky types and lighting systems[ The calibration setting will also a}ect the degree to which it is higher or lower[ In this research\ the com! puter model was used to compute photosensor signals and then the resulting workplane illuminances to show
0D 0M
124
A[!S[ Choi\ R[G[ Mistrick:Buildin` and Environment 23 "0888# 120Ð132 Table 1*continued
whether these illuminances were maintained at a target level or not[
Month Hour Sky clearness type
6
7
8
09
00
01
0D 0M
1
2
3
4
8 09 00 01 02 03 04 05 06
1 2 0 0 0 0 0 9 0
01 5 6 4 6 6 3 6 7
3 4 1 6 3 9 3 2 5
2 2 1 0 1 4 2 5 1
0 1 3 2 3 0 4 1 1
1 4 2 2 2 4 2 6 6
8 09 00 01 02 03 04 05 06
9 9 9 9 9 9 9 9 0
5 1 0 1 3 1 1 1 3
0 4 0 1 0 0 4 0 3
2 2 3 1 1 3 0 1 5
0 3 4 3 5 4 2 8 9
8 09 00 01 02 03 04 05 06
0 0 0 0 0 0 0 0 1
2 2 3 0 1 3 4 2 6
9 9 0 1 1 1 1 3 3
2 0 0 1 1 0 9 4 4
8 09 00 01 02 03 04 05 06
3 3 1 2 1 2 2 2 3
3 2 5 3 6 4 3 7 5
1 1 0 0 9 1 2 1 1
8 09 00 01 02 03 04 05 06
3 1 1 3 1 0 2 8 7
5 00 00 8 01 03 03 8 3
8 09 00 01 02 03 04 05 06
5 3 0 0 9 0 2 4 9
4 3 7 5 09 00 09 01 9
5
6
7
5 2 7 7 6 4 7 4 3
9 2 2 1 1 5 1 9 09
9 9 9 9 9 9 9 9 9
7 2 0 1 4 5 7 00 1
00 09 00 01 7 6 6 5 3
0 3 7 6 4 5 4 9 9
9 9 9 9 9 9 9 9 9
4 2 0 1 2 1 5 5 3
1 2 1 4 3 1 4 2 5
2 01 8 7 2 00 5 8 2
3 7 01 09 03 7 5 9 9
9 9 9 9 9 9 9 9 9
0 0 9 3 3 1 4 2 7
0 1 0 9 0 1 1 0 6
1 9 2 0 0 3 1 09 2
02 01 01 8 09 8 00 2 9
2 5 4 7 4 2 9 9 9
9 9 9 9 9 9 9 9 9
1 2 2 0 2 2 1 5 4
2 0 0 1 2 3 1 3 3
1 2 9 3 3 0 4 1 2
4 2 3 3 1 1 2 0 1
8 7 5 4 3 5 1 9 9
9 9 3 1 0 9 9 9 0
9 9 9 9 9 9 9 9 1
5 4 0 0 9 3 2 3 9
1 9 0 3 2 1 0 3 9
2 5 1 2 2 0 4 4 9
0 1 5 2 3 3 6 9 9
1 4 5 6 5 4 9 9 9
3 3 4 4 3 1 0 9 9
0 9 9 9 9 9 9 9 9
2[0[ Using the CIE daylight model The results in Table 2 show that the ratios of daylight illuminances at the workplane point to the photosensor signals "ED:SD# from open!loop proportional control vary monthly by small amounts for clear and partly cloudy skies[ Because an overcast sky distribution changes only in magnitude across di}erent solar positions\ this ratio is a constant for this model sky[ December has the highest ratio for a clear sky and a partly cloudy sky\ whereas
Table 2 Correlation between ED and SD Sky type "CIE#
Month
Open!loop
Closed!loop
ED:SD ratio
R1
ED:SD ratio
R1
Clear "9899Ð0299#
0 1 2 3 4 5 6 7 8 09 00 01
9[5481 9[4758 9[4072 9[3617 9[3381 9[3303 9[3319 9[3404 9[3669 9[4295 9[4888 9[5550
9[5851 9[5671 9[6429 9[7186 9[7627 9[7706 9[7552 9[7386 9[7270 9[7435 9[7183 9[6587
0[7416 0[6093 0[4545 0[3594 0[3949 0[2760 0[2802 0[3030 0[3577 0[4576 0[6949 0[7303
9[7314 9[7075 9[7354 9[7832 9[8189 9[8208 9[8000 9[8910 9[8947 9[8114 9[8019 9[7673
P!cloudy "9899Ð0399#
0 1 2 3 4 5 6 7 8 09 00 01
0[9336 9[8287 9[7239 9[6531 9[6151 9[6984 9[6953 9[6112 9[6610 9[7696 9[8702 0[9560
9[8394 9[8221 9[8021 9[7080 9[7425 9[7447 9[7463 9[7688 9[7601 9[7570 9[7795 9[8013
1[2167 1[1990 1[9277 0[8164 0[7543 0[7283 0[7370 0[7502 0[8235 1[9690 1[1076 1[2257
9[8826 9[8809 9[8786 9[8756 9[8726 9[8730 9[8656 9[8761 9[8754 9[8785 9[8803 9[8825
Overcast "9899Ð0699#
0 1 2 3 4 5 6 7 8 09 00 01
9[7750 9[7741 9[7748 9[7744 9[7755 9[7750 9[7745 9[7752 9[7759 9[7756 9[7741 9[7756
9[8888 0[9999 9[8888 0[9999 0[9999 9[8888 9[8888 0[9999 9[8888 0[9999 9[8888 9[8888
0[8855 0[8820 0[8803 0[8890 0[8843 0[8828 0[8806 0[8815 0[8839 0[8850 0[8801 0[8880
9[8887 9[8888 9[8887 9[8888 9[8887 9[8886 9[8887 9[8888 9[8888 9[8888 9[8888 9[8887
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A[!S[ Choi\ R[G[ Mistrick:Buildin` and Environment 23 "0888# 120Ð132
June has the lowest values of ED:SD for a clear sky and July has the lowest ratio for a partly cloudy sky[ Considering di}erences between sky types\ a clear sky has the lowest values of ED:SD throughout the year\ while a partly cloudy sky and overcast sky have relatively simi! lar values[ Through March to October\ an overcast sky has higher ratios\ whereas a partly cloudy sky has higher ratios from November to February[ Figure 1 shows that each sky type across the year has di}erent ED:SD ratios for open!loop proportional control[ Closed!loop proportional control also provides di}er! ent ratios of ED:SD for each sky type across the year[ The ratios of ED:SD increase for a clear sky and for a partly cloudy sky from June to January\ while an overcast sky provides a constant ratio as in open!loop control "Table 2#[ Closed!loop control has slightly higher R1 values and smaller seasonal changes compared to the open!loop con! trol case[ Across di}erent sky types\ the results are similar to those for open!loop control[ A clear sky has the lowest values of ED:SD through the entire year\ while a partly cloudy sky and overcast sky have similar values[ The ratios are more similar in the closed!loop case[ Figure 2 shows that closed!loop control has di}erent ratios of ED:SD for each sky type across the year[ The calibration procedure which initially determines the relationship between daylight illuminance at the workplane and the photosensor signal would likely be accomplished in the morning on a clear day[ It is assumed that this relationship for a clear sky represents all other
sky conditions[ The lower ratio of ED:SD in open!loop control for a clear sky would result in higher resulting illuminance than the target level during overcast or partly cloudy days[ This is because daylight illuminances at the workplane for overcast or partly cloudy skies are higher than those for a clear sky with the same photosensor signal[ The seasonal changes in the ratio of ED:SD also cause the resulting illuminance to vary from the target level[ For resulting workplane illuminance and dimming level\ the January results are shown as examples[ The illuminance ranges from the target level are −8[6Ð7[9) "clear#\ 9[0Ð02[2) "partly cloudy# and −02[7Ð−7[7) "overcast# for the open!loop control case[ In the cases of partly cloudy and clear sky conditions\ the dimming levels are not at minimum "9[09# around sunset when daylight illuminances are higher than the target level[ This is because the direct sun component from lower solar alti! tude angle reaches the back wall which results in higher point illuminance\ but does not have a corresponding e}ect on the photosensor[ The results of closed!loop control across the year show similar trends to the open!loop control case\ but overall\ the closed!loop control tracks the daylight levels slightly better than does open!loop control[ 2[1[ Using the Perez daylight model with weather data For seasonal changes of the ED:SD ratio\ an overcast sky condition was investigated[ Table 3 shows variations
Fig[ 1[ Correlation between daylight point illuminance at the workplane and photosensor signal for open!loop[
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Fig[ 2[ Correlation between daylight point illuminance at the workplane and photosensor signal for closed!loop[
Table 3 Correlations between EDand SDfrom the Perez daylight model "seasons# Sky type 0 "overcast# Month
2 5 8
Open!Loop
Closed!Loop
ED:SD ratio
R1
ED:SD ratio
R1
0[0039 0[9401 0[9750
9[8896 9[8625 9[8815
1[2327 1[1570 1[2433
9[8878 9[8818 9[8874
Note] 9899Ð0399 for sky type 1Ð6 and 9899Ð0699 for sky type 0[
in the ED:SD ratios from a bin method for sky clearness type 0 "overcast#[ Under an overcast sky condition\ the ED:SD ratio increases by 5[9) from June to March[ This is most likely due to the fact that an overcast sky varies azimuthally and provides di}erent relative luminance gradations at di}erent solar altitude positions in this day! light model[ To further examine correlations of ED:SD for di}erent sky types\ the entire year was simulated with a bin method[ Figure 3 and Table 4 shows that each sky type across the year has di}erent ED:SD ratios for open!loop proportional control[ As the sky condition changes from a dense partly cloudy sky "sky clearness type 1# to a totally clear sky "sky clearness type 6#\ the ratios of ED:SD decrease continuously[ The ratio for an overcast sky "sky clearness type 0# is higher than for type 1[ Under a partly cloudy sky condition\ the di}erence in ED:SD between the
lowest value "sky clearness type 4# and the highest value "sky clearness type 1# is a 08[4) increase[ In comparing all sky clearness types\ the di}erence in ED:SD between the lowest one "sky clearness type 6# and the highest one "sky clearness type 0# is a 71[0) increase[ Closed!loop proportional control also provides di}er! ent ratios of daylight illuminance at the workplane point to the photosensor signals "ED:SD# for sky clearness type 0 "Fig[ 4 and Table 4#[ The trends in correlations of ED:SD for closed!loop proportional control are relatively similar to those of an open!loop proportional control system[ Seasonal changes are reduced compared to the open!loop control case and across all sky clearness types\ the ratios are more similar in the closed!loop case[ For resulting workplane illuminance and dimming level\ the larger di}erences in partly cloudy and clear sky conditions occur around sunset due to rear wall re~ection as in the CIE daylight model case[ The largest di}erence in those conditions are 21[9) "clear\ open!loop# and 30[1) "partly cloudy\ open!loop#\ and 12[6) "clear\ closed!loop# and 18[9) "partly cloudy\ closed!loop# in January[ 2[2[ Field measurements The results of the dimming level from _eld measure! ments on each day during September 0884 to January 0885 are shown in Table 5[ In Table 5\ the dimming level for the open!loop proportional control indicates lighting input power\ not lighting levels[ Since _eld measurement
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Fig[ 3[ Correlation between daylight point illuminance at the workplane and photosensor signal for open!loop[
Table 4 Correlations between ED and SD from the Perez daylight model "sky types# Sky type
0 1 2 3 4 5 6
Open!Loop
Closed!Loop
Relative ED:SD ratio
R1
Relative ED:SD ratio
R1
0[9582 9[8851 9[7805 9[7950 9[7224 9[5422 9[4762
9[8683 9[3319 9[6013 9[6991 9[6142 9[7307 9[7534
1[2152 1[1814 1[0920 0[8641 0[7450 0[6317 0[5134
9[8265 9[7547 9[8179 9[8971 9[8522 9[8534 9[8219
the minimum level during a portion of any partly cloudy sky and clear sky day[ 3[ Discussion
Note] 9899Ð0399 for sky type 1Ð6 and 9899Ð0699 for sky type 0[
was sometimes interrupted in the analysis space being used\ the results are shown on a daily basis rather than monthly[ The dimming level "lighting power# was averaged hourly and then daily from 4 min interval data[ These dimming levels result from a measured low end light output of 03)\ which was the limit of the electronic ballasts and lighting controller[ Due to the large window on the west side\ daylight illuminance alone exceeded the target illuminance level and dimming was maintained at
In this section\ the following are compared] "0# ED:SD ratios of the CIE daylight model and the Perez daylight model^ "1# Dimming levels of the CIE daylight model and the Perez daylight model^ "2# Dimming levels of DayDim and _eld measurements^ and "3# Open!loop and closed! loop proportional systems[ The ED:SD ratios from the CIE daylight model and Perez daylight model show similar trends across di}erent sky types and seasons[ A partly cloudy sky has higher ratios than a clear sky and the ratios during winter are higher than during summer for the same sky conditions[ Since an overcast sky has an almost constant ratio throughout the year "the Perez model showed little vari! ations#\ the ratios are the highest among di}erent sky types during summer[ For partly cloudy sky conditions\ the average ED:SD ratios from the Perez model are similar to the ED:SD ratios from the CIE model[ However\ the ED:SD ratios for overcast sky conditions are di}erent between the two daylight models[ The monthly average dimming levels for the CIE day! light model and Perez daylight model are shown in Table 6[ The di}erences are caused by two factors[ The _rst
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Fig[ 4[ Correlation between daylight point illuminance at the workplane and photosensor signal for closed!loop[
Fig[ 5[ Comparison of measured dimming levels with hour!by!hour simulation using the Perez sky models in a large o.ce space[
factor results from the di}erent assumptions used for calculating the average dimming levels[ The same sky type was assumed throughout one day in application of the CIE model\ while each hour had di}erent sky types for the analysis with the Perez model[ The second factor is due to the di}erent daylight illuminances calculated
from both sky models[ The CIE model represents the annual average\ but the Perez model utilizes a particular year of actual measured weather data[ The actual performance of a daylight responsive dim! ming system employing open!loop proportional control was compared to the computer simulation results[ The
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Table 5 The dimming levels "lighting power# from _eld measurements
Table 5 The dimming levels "lighting power# from _eld measurements
Month
Day
Watt
Avg dim
Month
8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8
0 1 2 3 4 5 6 7 8 09 00 01 02 03 04 05 06 07 08 19 10 11 12 13 14 15 16 17 18 29
9[264 9[285 9[273 9[273 9[274 9[272 9[285 9[310 9[443 9[257 9[263 9[258 9[370 9[392 9[263 9[359 9[256 9[264 9[399 9[340 9[567 9[275 9[257 9[604 9[276 9[256 9[261
9[257 9[277 9[265 9[265 9[266 9[264 9[277 9[302 9[432 9[250 9[256 9[251 9[361 9[284 9[256 9[340 9[259 9[257 9[281 9[331 9[554 9[267 9[250 9[690 9[268 9[259 9[254
Month average
9[310
9[302
9[263 9[270 9[273 9[472 0[905 0[998 0[900 0[997 0[997 0[904 9[614 9[855 9[267 9[305 9[267 9[261 9[268 9[279 9[400 9[256 9[265 9[325 9[390 9[317 9[381 9[484 9[347 9[320 9[522
9[256 9[263 9[265 9[461 9[885 9[878 9[880 9[877 9[877 9[884 9[600 9[836 9[260 9[397 9[260 9[254 9[261 9[262 9[490 9[259 9[258 9[316 9[282 9[319 9[371 9[472 9[338 9[312 9[510
Month average 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09 09
0 1 2 3 4 5 6 7 8 09 00 01 02 03 04 05 06 07 08 19 10 11 12 13 14 15 16 17 18 29 20
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
Day
0 1 2 3 4 5 6 7 8 09 00 01 02 03 04 05 06 07 08 19 10 11 12 13 14 15 16 17 18 29
Month average 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01
0 1 2 3 4 5 6 7 8 09 00 01 02 03 04 05 06 07 08 19 10 11 12 13 14 15 16 17
Watt
Avg dim
9[472
9[461
9[796 9[517 9[332 9[333 9[343 9[597 9[362 9[348 9[604 9[422 9[631 9[778 9[695 9[446 9[364 9[377 9[388 9[411 9[659 9[408 9[371 9[431 9[679 9[414
9[680 9[505 9[323 9[324 9[334 9[485 9[353 9[349 9[690 9[412 9[616 9[761 9[581 9[435 9[355 9[367 9[378 9[401 9[634 9[498 9[362 9[420 9[654 9[404
9[474
9[463
9[577 9[593 9[331 9[359 9[457 9[368 9[319 9[396 9[394 9[270 9[390 9[416 9[332 9[513 9[337 9[272 9[274 9[306 9[268 9[306 9[304
9[564 9[481 9[322 9[340 9[446 9[369 9[301 9[288 9[286 9[263 9[282 9[406 9[323 9[501 9[328 9[264 9[266 9[398 9[261 9[398 9[396 continued
A[!S[ Choi\ R[G[ Mistrick:Buildin` and Environment 23 "0888# 120Ð132 Table 5*continued The dimming levels "lighting power# from _eld measurements Month
Day
Watt
Avg dim
01 18 01 29 01 20 Month average
9[329 9[361 9[350
9[311 9[352 9[341
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Month average
9[429 9[467 9[380 9[300 9[359 9[441 9[396 9[347 9[423 9[356 9[335 9[354 9[790 9[459 9[529 9[682 9[339 9[331 9[519 9[493 9[418
9[419 9[456 9[370 9[392 9[340 9[430 9[288 9[338 9[413 9[347 9[326 9[345 9[674 9[438 9[507 9[666 9[320 9[322 9[597 9[383 9[408
0 1 2 3 4 5 6 7 8 09 00 01 02 03 04 05 06 07 08 19 10 11 12 13 14 15 16 17 18 29 20
Note] The numbers in bold type indicate days when measurement was interrupted during some hours[
results of the dimming level and resulting illuminance from _eld measurements for March 0885 are compared to values from computer simulations using the Perez day! light model[ The results of the dimming levels from the computer simulation of the Perez daylight model and _eld measurements show a similar trend\ but not identical dimming levels or illuminances "Fig[ 5#[ The results from _eld measurements show that the minimum dimming level is sometimes not achieved when the resulting illu! minance is much higher than the target level[ Variations of the maximum and minimum wattages in lighting power and a selected control algorithm slope MOP "open!loop slope\ ð4Ł# from pre!determined slopes of the lighting con! troller at the calibration time a}ect the dimming levels in _eld measurements[ In addition\ the dimming levels in computer simulations are a}ected by the system cali! bration[ If the information input at the time of system
130
calibration is di}erent\ di}erent dimming levels will result[ Under open!loop proportional control\ the results show that the magnitudes of ED and SD as well as the varying ratio of ED:SD a}ect system performance[ Target illuminance was not achieved with the same ED:SD ratio as at the calibration time "Table 7#[ This is caused by a non!zero value of SEM "signal produced for d "dimming level# 0 without daylight\ ð4Ł# in the open!loop pro! portional control governing equations[ The results from the simulations of the CIE daylight model showed that the di}erences were reduced as daylight illuminance increased\ with the same ED:SD ratio[ The results from the simulations of the Perez daylight model showed that low daylight illuminances in early morning or late after! noon resulted in lower illuminances than the target level\ whereas high daylight illuminances around noon resulted in higher illuminances than the target level[ If SEM is zero\ the target illuminance is achieved with di}erent magnitudes of ED and SD\ which is an inherent objective of open!loop control[ In the results of this research\ full electric light "0[99!computer simulation dimming level\ 0[91 kW!_eld measurement full load# does not happen at night because the photosensor still detects some ~ux from the electric light\ which causes the controller to dim the electric light[ In this research\ the night time dimming level was 9[80 in the computer simulation "CIE model# and therefore full load power rarely occurred at night in the _eld measurements[ In closed!loop proportional control\ however\ only the ratio of ED:SD a}ects system performance[ The target illuminance was achieved with di}erent magnitudes of ED and SD\ but with the same ED:SD ratio as at the calibration time "Table 7#[ 4[ Conclusions The following are the major _ndings from the appli! cation of DayDim and _eld measurements of a space employing a daylight responsive dimming system[ "0# The correlation between daylight illuminance at a critical workplane point "ED# and the photosensor signal "SD# is an important factor a}ecting the per! formance of daylight responsive dimming systems[ Choosing an appropriate calibration time and a pro! per location and con_guration of the photosensor are critical in order to reduce the di}erences among di}erent sky types and seasons[ "1# The ratio of ED:SD across the year depends on sky conditions\ season and photosensor orientation[ Di}erent ratios of ED:SD produce variations from the target lighting level for di}erent sky types through the seasons of the year[ "2# Closed!loop proportional control shows slightly bet! ter system performance than open!loop proportional control in this particular study[ The non!zero value of
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A[!S[ Choi\ R[G[ Mistrick:Buildin` and Environment 23 "0888# 120Ð132 Table 6 Comparison of the average dimming levels from di}erent computer simulations Month
Min[ dim 9[0 Open
Min[ dim 9[90 Closed
Open
Closed
CIE
Perez
CIE
Perez
CIE
Perez
CIE
Perez
0 1 2 3 4 5 6 7 8 09 00 01
9[382 9[138 9[130 9[054 9[054 9[024 9[043 9[096 9[017 9[116 9[286 9[252
9[322 9[114 9[114 9[069 9[059 9[028 9[015 9[098 9[031 9[114 9[251 9[230
9[377 9[126 9[114 9[037 9[028 9[008 9[018 9[093 9[010 9[198 9[273 9[249
9[271 9[074 9[081 9[030 9[030 9[013 9[008 9[092 9[021 9[085 9[201 9[188
9[363 9[082 9[075 9[984 9[091 9[952 9[980 9[919 9[936 9[057 9[254 9[214
9[397 9[051 9[056 9[090 9[977 9[952 9[936 9[913 9[950 9[055 9[218 9[293
9[350 9[079 9[069 9[968 9[962 9[931 9[948 9[906 9[939 9[035 9[236 9[185
9[249 9[007 9[017 9[955 9[952 9[930 9[921 9[905 9[940 9[017 9[162 9[142
Annual
9[124
9[110
9[110
9[083
9[032
9[059
9[048
9[016
Table 7 The percentage di}erence of resulting illuminances from the target level with the same ED:SD ratio Open!loop Point E
Senser "O#
ED:SD "O#
)Dim "O#
Ele[ E "O#
Total E "O#
)Di}[ "O#
207[4 230[2 258[6 287[0 315[5 344[9
22[5 25[9 28[9 31[9 34[9 37[9
8[37 8[37 8[37 8[37 8[37 8[37
9[17 9[12 9[07 9[01 9[95 9[90
011[6 091[8 67[0 42[3 17[5 2[7
330[1 333[0 336[7 340[4 344[1 347[7
9[9 9[6 0[4 1[2 2[1 3[9
Point E
Senser "C#
ED:SD "C#
)Dim "C#
Ele[ E "C#
Total E "C#
)Di}[ "C#
207[4 232[9 256[4 281[9 305[4 330[9
02[9 03[9 04[9 05[9 06[9 07[9
13[49 13[49 13[49 13[49 13[49 13[49
9[17 9[11 9[06 9[00 9[95 9[99
011[6 87[1 62[6 38[1 13[6 9[1
330[1 330[1 330[1 330[1 330[1 330[1
9[9 9[9 9[9 9[9 9[9 9[9
Closed!loop
SEM in the open!loop proportional control governing equations causes a problem in achieving the target illuminance level on the workplane[ The magnitude of ED\ as well as the ratio of ED:SD\ a}ects the resulting workplane illuminances in open!loop proportional control[ "3# The lighting controller should be improved to account for the dynamic nature of the sky[ MOP and
MCL "closed!loop slope\ ð4Ł# should be computed at a calibration condition instead of pre!determined[
Acknowledgments This work was generously supported by Lutron Elec! tronics Co[\ Inc[ The authors would like to thank Dr
A[!S[ Choi\ R[G[ Mistrick:Buildin` and Environment 23 "0888# 120Ð132
Richard Perez "SUNY# for advice in applying his daylight model[
References ð0Ł Choi A\ Mistrick RG[ On the prediction of energy savings for a daylight dimming system[ Journal of the Illuminating Engineering Society 0886^15"1#]66Ð89[ ð1Ł IESNA\ IES lighting handbook\ 0883[
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ð2Ł Perez R\ Ineichen P\ Reals R\ Michalsky J\ Stewart R[ Modeling daylight availability and irradiance component from direct and global irradiance[ Solar Energy 0889^33"4#]160Ð78[ ð3Ł Choi A\ Mistrick RG[ Application of the Perez model in daylight dimming system analysis[ IESNA Annual Conference Proceedings 0886^634Ð56[ ð4Ł Rubinstein F\ Ward G\ Verderber R[ Improving the performance of photo!electrically controlled lighting system[ Journal of the Illuminating Engineering Society 0875^04"0#]69Ð83[ ð5Ł Perez R\ Reals R\ Michalsky J[ Modeling sky angular luminance distribution from routine irradiance measurements[ Journal of the Illuminating Engineering Society\ 0882^12"0#]09Ð06[