RP-258 -- Energy Savings Through the Use of Natural Daylighting

The object of this study was the development of a simple method for the calculation of the annual lighting, cooling and heating energy used in a building as affected by daylighting. It is intended for use by engineers and architects in an early building design stage to make preliminary decisions on fenestration, or for evaluation of changes to existing components, such as glazing or daylighting controls.

A need exists for quantitative, rather than qualitative, information on issues such as window size, window transmission and orientation, without resorting to lengthy hand calculations or computer programs. Further, it is believed that savings due to daylighting and thermal effects of windows should be integrated into a single annual energy cost figure.

Several goals helped shape the resulting procedure. The algorithm should be simple, involve a minimum of hand calculation, and be susceptible to nomograph treatment. The approach should be based on calculation techniques, as from ASHRAE and IES, in order to minimize any associated uncertainty. The technique should allow consideration of a wide variety of fenestration options, so as to apply widely and encourage innovation. While the procedure is tailored for use with office buildings, most other types of buildings can be analyzed with only slight modifications, if any.

It is believed that the methodology reported here goes a long way to meet these goals. The algorithm is fully documented and all components are open to inspection. It was thought that this explicitness would enhance the likelihood of acceptance of the algorithm, increase its usefulness as an educational tool, and allow future changes in the procedure.

In this report, the procedure is shown in Fig. 1 (with Table 2 and Figures 2 and 3) and described, first in general terms, then step-by-step. The First Principles approach is discussed. In Related Output a capital cost analysis, computer program written in BASIC, and nomogram treatment are described. Several examples of results obtained by using the procedure are shown in Figures 7, 8 and 9. Directions for using the algorithm, keyed to step and input numbers, are given in Appendix 1. Justification for all algorithm steps and inputs are given in Appendix 2.

In order to simplify the procedure, a number of assumptions and approximations are made. It is believed that these are reasonable, and approximate actual practice. The assumptions are discussed and the methodology is such that most can be modified to suit the needs of any special case.



Product Code(s): D-RP-258