A methodology is presented for the preparation of climatic design criteria independent of hardware configuration which can be incorporated afterwards and tailored to the individual case. In principle, the performance evaluation of a solar space heating system during winter in a cloudy climate is reduced to one parameter So, the level of the incoming global solar radiation.

The method is exemplified for Huntsville, AL. It proves that milder winters may pose more problems than colder winters. It is also illustrated that monthly means of the solar radiation or hourly means (by month) may produce a biased picture of performance of solar space heating systems. Furthermore, the climatic data from the modeling effort permit the engineer to analyze capacity requirement and cost effectiveness of solar space heating systems without the necessity of data from experimental solar space heating systems.