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International Journal of Lighting Research and Technology, 34, 1, pp. 79-81, 2002-01-01
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Comment on 'Simulation of annual daylighting profiles for internal
illuminance' by John Mardaljevic
Reinhart, C. F.
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Comment on 'Simulation of annual daylighting
profiles for internal illuminance' by John Mardaljevic
Reinhart, C.F.
A version of this paper is published in / Une version de ce document se trouve dans: International Journal of Lighting Research and Technology, v. 34, no. 1, 2002, pp. 79-81
www.nrc.ca/irc/ircpubs
1 2 3 4 5 6 7 8 9 10 11 12 13 19 20
21 Lighting Res. Technol. 34,1 (2002) pp. 79–81 22
26 27
28
Discussion of a previously published paper
29 30 31 32 33 34
35 Comment on ‘Simulation of annual 36 daylighting profiles for internal 37 illuminance’ by John Mardaljevic* 38 CF Reinhart (National Research Council 39 Canada)
40 Dr Mardaljevic’s recent paper on his implemen-41 tation of the concept of daylight coefficients into 42 the RADIANCE simulation environment is a 43 well-written and a logical extension of his pre-44 vious work on the validation of RADIANCE 45 daylight simulations under real sky conditions. 46 The interested reader might further want to learn, 47 that the computational efficiency of Tregenza’s 48 concept of daylight coefficients has been recog-49 nized by a number of researchers, and the calcu-50 lation approach has been implemented into 51 RADIANCE by at least two other groups: one 52 version has been implemented into the building 53 simulation program ESP-R by Janak and Mac-54 donald at the University of Strathclyde in Glas-55 gow, Scotland1 and another version has been 56 developed by Reinhart and Herkel at the Fraun-57 hofer Institute for Solar Energy Systems in Frei-58 burg, Germany.2 Both approaches also dis-59 tinguish between direct and diffuse daylight 60 coefficients although some differences exist in 61 how direct sunlight is treated.
62 Reinhart and Herkel carried out a performance 63 evaluation concerning accuracy and required 64 simulation times for six RADIANCE-based 65 simulation algorithms which calculate annual 66 daylighting profiles: ADELINE; ESP-R; the day-67 light factor approach; a brute force approach; 68 classified weather data; DAYSIM. Dr Mardal-69 jevic’s algorithm was not considered in that 70 work as it had not been published at the time. 71 Reinhart and Herkel concluded that daylight 72 coefficients outperform all other dynamic day-1
17 *Published in International Journal of Lighting Research and 18 Technology, 2000; 32: 111–18.
1
2 The Chartered Institution of Building Services Engineers 2002
3 10.1191/1365782802li032xx
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73 light simulation methods and discussed
differ-74 ences between the two investigated daylight
75 coefficient methods. An advantage of DAYSIM
76 compared to ESP-R and Dr Mardaljevic’s
77 method is that the original RADIANCE code has
78 been adapted to allow for a calculation of a
com-79 plete set of daylight coefficients in only two
ray-80 tracing runs. This results in calculation times
81 which are around 6–8 times longer than for a
82 standard static daylight simulation (Dr
Mardal-83 jevic mentioned a factor of 145 for his method).
84 A validation and description of the approach has
85 been published in Energy and Buildings.3
86 Dr Mardaljevic also rightly mentioned that
87 there is a need for short-time-step irradiance data
88 series to model the intrahour dynamics of natural
89 daylight. To address this issue, Walkenhorst,
90 Luther, Reinhart and Timmer have adapted and
91 validated an existing model of Skartveit and
92 Olseth4 which generates 1-minute data series of
93 external direct and irradiances from hourly
94 means.5The resulting data series can be further
95 processed by any dynamic daylight simulation
96 method to simulate 1-min indoor illuminance
97 data series.
98 Summing up, the work presented in Dr
Mard-99 aljevic’s paper is an important contribution to an
100 active field of research which aims to develop
101 reliable and easy-to-use dynamic daylight
simul-102 ation tools. As Dr Mardaljevic concludes, future
103 research should concentrate on ‘interpreting and
104 applying the annual daylighting profiles
effec-105 tively’.
106
References
107
1 Janak M, Macdonald IA. Current
state-of-the-108 art of integrated thermal and lighting simulation
109 and future issues, Conference Proceedings
110 International Building Performance Simulation
111 Assciation (IBPSA) ’99. Kyoto, Japan, 1999:
112
1173–180.
113
1 80 Discussion 2
114 annual daylight illuminance distributions – a 115 state of the art comparison of six RADIANCE 116 based methods. Energy & Buildings 2000; 32:
117 167–87.
118 3 Reinhart CF, Walkenhorst O. Dynamic 119 RADIANCE-based daylight simulations for a 120 full-scale test office with outer venetian blinds. 121 Energy & Buildings2001; 33: 683–97.
122 4 Skartveit A, Olseth JA. The probability density 123 and autocorrelation of short-term global and 124 beam irradiance. Solar Energy 1992; 49: 477–
125 87.
126 5 Walkenhorst O, Luther J, Reinhart CF, Timmer 127 J. Dynamic annual daylight simulations based 128 on one-hour and one-minute means of irradiance 129 data. Solar Energy (submitted for publication). 130
131
4 Author’s response to CF Reinhart 5 J Mardaljevic
6 Mr Reinhart is indeed right to note that more 7 than one RADIANCE daylight coefficient (DC) 8 implementation exists, and that these have been 9 described in various papers. Furthermore, those 10 papers mentioned were published more or less 11 contemporaneously. However, Mr Reinhart is 12 incorrect in his remark that published work did 13 not predate the papers noted in his comments. 14 In fact, the first description of a RADIANCE DC 15 system, including preliminary validation results, 16 was presented in 1997 at the Lux Europa confer-17 ence.1A second mention, including screen-grabs 18 of the end-user software, was presented in 1998 19 at the SIGGRAPH conference in Orlando, 20 USA.2 That paper has been available for down-21 load from the RADIANCE website since that 22 time. Although neither are journal publications, 23 Lux Europa is a major lighting event and the 24 SIGGRAPH conferences were a showcase for 25 RADIANCE several times. It is unfortunate that 26 both of these publications were overlooked. 27 Nevertheless, it was remiss on my part to not 28 have made a journal publication of the, at the 29 time quite novel, work on daylight modelling 30 until the Lighting Research & Technology paper 31 in 2000 (32,2).
32 The DC approach described in my paper is
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33 implemented in software as an expert-user
sys-34 tem for research and demonstration of
proof-of-35 principle. The suite of programs are referred to
36 in-house as XDAPS (for eXtensible DAylight
37 Prediction System). A end-user version called
38 the Dynamic Lighting System (DLS) has been
39 made available.3As the name suggests, XDAPS
40 was designed to be highly adaptive and scalable.
41 Regarding accuracy of DC derived illuminances,
42 XDAPS has been validated using the
BRE-43 IDMP dataset.4 This dataset consists of
simul-44 taneous measurements of the sky luminance
dis-45 tribution, the direct normal illuminance and the
46 internal illuminance in a full-size mock office
47 (together with other measurements). With this
48 dataset it is possible to specify to an
unpre-49 cedented degree of precision the conditions at
50 the time of measurement e.g., the sky luminance
51 distribution, the direct normal illuminance, the
52 office dimensions, the photo-cell locations, etc.
53 The BRE-IDMP dataset provides the most
rigor-54 ous test of daylight illuminance predictions
cur-55 rently available. The XDAPS DC formulation
56 was proven to be exceptionally accurate, and, at
57 present, it is the only DC system to have been
58 tested using this unique validation dataset. In
59 contrast, the evaluation of six
RADIANCE-60 based algorithms carried out by Reinhart and
61 Herkel is an inter-model comparison test and not
62 a validation. The more recent Energy and
Build-63 ings paper (Reinhart, Walkenhorst, 2000) is a
64 genuine validation, but less rigorous than that
65 possible with the BRE-IDMP dataset because the
66 true sky luminance distribution is an unknown
67 quantity.
68 Overall, the simulation time required to
com-69 pute the DCs is noted by Reinhart to be longer
70 for XDAPS than DAYSIM. However, it is
71 notoriously difficult to compare like-with-like in
72 RADIANCE simulations when calculation
para-73 meters and luminous conditions are very
differ-74 ent. Suffice to say that, the DC matrices for the
75 BRE office used for the validation take only an
76 hour or two to compute on a reasonably fast
77 workstation. It is worth noting that DAYSIM
78 uses a modified version of a key RADIANCE
79 program (rtrace) whilst the XDAPS DC
formu-1 Discussion 81 2
80 lation was designed to work with the standard
81 (UNIX) release of RADIANCE. Although
82 XDAPS is for in-house use only, the algorithms 83 could be implemented by anyone with modest 84 programming experience in the language of their 85 choice e.g., FORTRAN, C, C++ or even Java 86 (as with the DLS). Modifying the code of key 87 RADIANCE programs however raises a number 88 of issues. For example, will the modified code 89 be compatible with any future releases of RADI-90 ANCE? Will it become freely available, say as 91 part of an end-user system? If so, then the com-92 patibility issue becomes even more important. 93 To conclude, I am grateful to Mr Reinhart for 94 his comments and for providing an opportunity 95 to clarify the history of daylight coefficient 96 research at the IESD. The traditional modes of 97 daylighting analysis have changed little over that 98 past 30 or so years. The venerable daylight factor 99 approach – either by scale model or computer 100 simulation – is still the most commonly used 101 daylighting assessment technique, and there is 102 much work to be done to demonstrate the advan-128
129
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103 tages that dynamic lighting simulation can offer.
104 Vigorous research to this end, carried out by a
105 number of investigators employing contrasting
106 or complimentary techniques, is to be welcomed.
107
References
108
1 Cropper P, Lomas KJ, Lyons A, Mardaljevic J.
109 A dynamic lighting system: background and
110 prototype. Proceedings of Lux Europa 97
111 Conference, Amsterdam, 1997: 480–92.
112
2 Mardaljevic J. Sections on (a) Daylighting
113
applications (18 pp); (b) Advanced daylighting
114
calculation (14 pp); and (c) Validation (16 pp),
115
in Rendering with RADIANCE: A Practical
116
Tool for Global Illumination. ACM
117
SIGGRAPH’98, Course Notes CDROM,
118
Orlando, USA. Available for download from:
119
http://radsite.lbl.gov/radiance/refer/s98c33.pdf
120
3 The Dynamic Lighting System (beta version)
121
for Linux/Unix is available for download from
122
http://www.iesd.dmu.ac.uk/dls
123
4 Mardaljevic J. The BRE-IDMP dataset: a new
124
benchmark for the validation of illuminance
125
prediction techniques. Lighting Res. Technol.
126
