Preliminary indicators for passive solar greenhouse design

Preliminary passive solar greenhouse design can be supported by design indicators related to solar access, such as the Solar Aperture (SA) and the Solar Fraction (SF), assuming that net solar heat gains are proportional to net incoming solar radiation. However, since net solar heat gains also depend on thermal losses, SA and SF are effective only for comparing greenhouses with similar shapes and, consequently, similar thermal heat loss profiles. Currently, no design indicator exists that combines SA or SF with thermal loss considerations. To address this gap, this study introduces two new design indicators: the Passive Solar Performance Ratio (PSPR) and the Solar Gain-Loss Ratio (SGLR). These indicators integrate solar gains and thermal losses, enabling their application to a broader range of greenhouse shapes and design scenarios. Benchmarking the PSPR and SGLR against transient simulation results revealed their superior effectiveness in ranking design options by expected net solar heat gains compared to SA and SF. Replacing SA and SF with PSPR and SGLR in design explorations led to optimal solutions with reductions in degree days and thermal loads for heating and cooling ranging from 3% to 30%.