In the past a couple of years after I completed an ASHRAE sponsored project on ADPI (RP-1546), I have heard the following feedback the most:
The ADPI concept does not apply for heating mode because ADPI is used to assess the uniformity of air in the occupied zone but thermal stratification mostly always exists to some extent in the heating condition.
Below is my answer:
First, the thresholds/boundaries of the ADPI equation for cooling were determined based on thermal comfort studies. That being said, ADPI is implicitly linked to thermal comfort. This sounds like a myth until you dig out the paper published by Houghten et al. in 1938. I would be happy to share a copy if you are interested.
Second, ADPI calculates the percentage of space meeting the equation boundaries. If 100% ADPI is achieved and since the boundaries are so narrow, we could safely claim that ADPI is a metric to calculate uniformity of space air. I agree on that, totally.
Third, ADPI was developed mainly for mixing ventilation/air distribution that aims to achieve a uniform air condition. A perfect mixing condition will result in 100% ADPI, while 80% means that 20% of the entire occupied space does not fall into the equation boundaries as the majority does. As such, a higher ADPI value corresponds to a higher mixing level in the space. However, it is inappropriate or somehow counter-intuitive to use ADPI to assess other types of ventilation/air distribution systems, such as displacement ventilation, because their goal is not to achieve better mixing. In other words, we probably want to have a lower “ADPI” for displacement ventilation.
Then we inch towards the answer. Since mixing ventilation at both heating and cooling modes aims to maximize uniformity, why cannot we use the ADPI concept for heating? For further info, please read the enclosed paper.
Liu, Shichao, and Atila Novoselac. “Air Diffusion Performance Index (ADPI) of diffusers for heating mode.” Building and Environment 87 (2015): 215-223. (here)
