Modeling energy savings of glazed and unglazed collectors used for space heating, water heating, and space cooling

Glazed and unglazed solar thermal collectors were compared in TRNSYS simulations for a multi-use application of water heating, space heating, and space cooling. The collectors provided space cooling by radiating heat to the night sky. The overall solar fraction achieved by two (7.6 m2) of the glazed collectors was similar to the solar fraction achieved by six (22.8 m2) of the unglazed collectors in the climates of Raleigh, NC, Jacksonville, FL, and Albuquerque, NM. However, the unglazed collectors produced less energy cost savings at these sizes because a greater proportion of their energy was provided as cooling, which was supplied more efficiently by auxiliary equipment. For each type of collector, the greatest solar fraction of space heating and water heating were achieved in Jacksonville, and the greatest solar fraction of space cooling was achieved in Albuquerque. The climate of Raleigh generally produced heating and cooling performances that were in the middle of the range produced by collectors in the three geographic regions. For glazed and unglazed arrays of equal size in Raleigh (15.2 m2), the ratio of the unglazed solar fraction to the glazed solar fraction was 0.26 for space heating, 0.73 for water heating, and 2.71 for space cooling.