Analysis of passive thermal storage opportunities for heating system design

Abstract

Heating and cooling load calculations are critical to size HVAC systems and determine energy use of their operations. The ASHRAE recommended heating load calculation model is most commonly used for heating load calculations. It adopts a simplified approach by considering only steady-state conductive heat transfer. However, due to thermal storage effect, heat generated in daytime may still be stored in buildings and released at a later time. Such assumption leads to significantly over-sized heating systems which are usually accompanied by high initial cost and higher cost of energy use. This study therefore examines the thermal response and passive storage characteristic of heavy construction for typical office building in continental United States. By allowing space air to drift to reasonably lower values, buildings need to be warmed up before being occupied in the morning. The worst case conditions might happen during warm-up or beginning of occupied hours. This article evaluates the optimal size of heating system which satisfies thermal comfort while taking advantage of passive thermal storage. Results show varying downsizing opportunities ranging from 14% to 54% across the United States. These results have the potential of establishing new heating device design standards for certain climate classifications.