Development of Method and Database of Space Cooling Load Factors of Stratified Air Distribution Systems

Abstract

In this project, one of the key energy saving features of stratified air distribution systems (STRAD) will be investigated. In particular, the project will first demonstrate the benefits of separate location of exhaust air grilles and return/recirculated air inlet, in comparison with the combined exhaust and return grilles in STRAD, and the most common well-mixed air distribution systems (MIX). The objective is to test the validity of using CFD method to generating equivalent space-cooling load factors for the four types of individual heat gains, namely human body, office appliance, lighting, and external heat gain. Then the validated methods will be applied to generate the cooling load factors for 3 different spaces: large spaces of 5 meters or above, high spaces of 3 to 5 meters and office spaces of 2.6 to 3 meters.

The general background is that current air distribution is predominantly well-mixed type, in which the location of exhaust grilles does not affect the space air-conditioning load significantly, while the emerging stratified air distribution systems, including both under-floor air distribution and displacement ventilation, generate a large vertical temperature stratification, and a quasi-upward directional flow in the upper part of a room space, which can be utilized to realize local exhaust of higher temperature air directly to outside, so that the actual coil load of an air-handling unit(AHU) can be much reduced. This can be best realized by a separate location of the exhaust air grilles and return/recirculated air inlets. Consequently, a set of load reduction factors need to be generated, which design engineers can use to downsize the AHU in the design stage. Therefore, the outcome of the project is helpful to reduce both the embodied and operation energy of air-conditioning systems.