Apples to apples - Comparing Performance of Design Alternatives
The fixed, unchanging sky conditions within the artificial sky make it ideal for comparative analysis. This involves placing sensors in strategically selected locations or in an established grid pattern within the model interior and comparing these sensor readings with the reading from a sensor placed outside of the building model but within the sky chamber. The ratio of interior illumination to available exterior illumination (daylight factor) can be used as an indicator of performance. Testing one model configuration as described above and then re-testing with an alternate design configuration can reveal the strengths and weakness of various design alternatives. The controlled conditions of the comparative tests and the constant sky conditions give the artificial sky testing method an advantage over even outdoor, real-sky testing due to the high, minute-to-minute variability of real-sky conditions. Design changes that can be compared include comprehensive whole building re-configurations as well as singular and specific aperture, device or component alternatives.
Taste an apple - General Overcast Sky Performance
Although it is best done utilizing outdoor overcast sky testing, it is possible to measure and predict a general level of daylighting performance of a building design under overcast sky conditions via testing in the artificial sky. The ratio of interior illumination to available exterior illumination (daylight factor) as previously described can be used in conjunction with published climatic overcast sky illumination levels for a locale to estimate interior illumination levels in the constructed building under an overcast sky. Care must be taken to adjust for glazing influence if it is not accurately represented in the scale model.
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