Air Diffusion Performance Index (ADPI) of diffusers for heating mode

• A heating mode ADPI model is proposed.
• We develop an ADPI selection guide for 13 types of diffusers at heating-mode operation.
• The 13 diffuser types can provide ADPI values greater than 80% at various ranges of T0.25/L ratios.

This paper proposes an Air Diffusion Performance Index (ADPI) model for diffuser selection when considering the operation in all-air heating mode. The model uses Fanger's Predicted Mean Vote (PMV) Index adopted by ANSI/ASHRAE Standard-55 to develop the relation between indoor air temperature and velocity. This paper also generates an ADPI selection guide for the application of 13 types of widely used ceiling, high sidewall and linear slot diffusers. The selection guide is developed based on 97 experiments in a full-scale environmental chamber by measuring the ADPI as a function of two factors: (1) the ratio of throw length of jets from diffusers to room characteristic length, and (2) diffuser types. Moreover, the measurements consider different diffuser sizes and manufactures. The selection guide discusses possible thermal stratification occurring at heating mode conditions and incorporates this factor into the proposed ADPI model. Overall, the measurements show that all 13 types of diffusers can generate ADPI greater than 80% when they are properly used. However, some diffusers are less sensitive to the variation of supply airflow rate than others. Linear bar grilles and round ceiling diffusers are the most suitable for application when supply flow varies during HVAC operation.