ASHRAE Journal - January 2020 - 22

TECHNICAL FEATURE

TABLE 2 ADPI selection guide for typical cooling loads.

Table 6A Air Diffusion Performance Index (ADPI) Selection Guide for Typical Cooling Loads
Terminal Device in Cooling
Mode

Installation

Adjustable-blade grilles

45° upward blades, High sidewall
0° horizontal blades, High sidewall
45° downward blades, High sidewall

Fixed-blade grilles (high sidewall
installation)

15° upward blades, High sidewall
15° downward blades, High sidewall

Linear-bar grilles (high sidewall
installation)

High sidewall
Sill

Nozzles (high sidewall
installation)
Round ceiling diffuser

High sidewall

Square ceiling diffuser

Ceiling

Perforated diffusers, round pattern

Ceiling

Perforated diffusers, directional
pattern (4-way)
Louvered face diffusers, with lip
on deflector blade
Louvered face diffusers, without
lip on deflector blade
Plaque face diffusers

Ceiling

Ceiling

Linear-slot diffusers

Ceiling

T-bar slot diffusers

Ceiling, periphery of a wall

Ceiling

Ceiling
Ceiling

Swirl diffusers

Ceiling

N-slot diffusers

Ceiling

Load,
Btu/h·ft2

Max. ADPI
T50/L

Max.
ADPI

8
16
8
16
8
16
8
16
8
16
8
16
8
16
8
16
8
16
8
16
8
16
8
16
8
16
8
16
8
16
8
16
8
16
8
16
8
16

0.8
0.9
1.7
1.8
0.9
1
1.4
2.1
1.9
2
1.3
1.3
1.3
1.3
0.7
1
1.6
1.9
1.8
1.8
1.9
2.1
2.1
2
2.5
2.6
2
1.8
1.6
1.6
1.8
1.8
1.3
1.5
1.3
1.3
1.8
1.8

98
96
94
88
76
70
96
94
85
82
92
88
94
90
96
89
99
98
100
100
95
95
100
95
100
100
100
100
100
100
100
100
96
90
100
98
100
95

T/L Low
T/L High
Limit for
Limit for
ADPI > 80% ADPI > 80%
0.4
0.5
1.2
1.4
NA
NA
0.5
1.2
1.5
1.8
0.7
1.0
0.9
1.0
0.4
0.4
0.4
0.5
0.8
0.6
0.5
0.9
1.2
1.0
0.5
0.6
0.5
0.4
0.3
0.4
0.5
0.5
0.7
1.1
0.4
0.4
1.3
1.3

1.3
1.2
2.2
2.2
NA
NA
2.4
2.9
2.2
2.2
1.8
1.6
1.7
1.6
2.0
1.9
3.2
3.2
2.8
3.1
3.3
3.4
3.1
2.9
4.4
4.5
3.6
3.4
3.0
3.2
3.0
3.1
1.9
1.9
2.4
2.4
2.4
2.3

Source: Data developed by Liu et al. (2016) for this chapter from ASHRAE research project RP-1546 (Liu 2016), and air speed limit (70 fpm) extrapolated from data. Additional
data point used to create new regressions for ADPI curves to better represent current diffusers/grilles. Table applies to spaces with maximum 12 ft ceiling.

1. Develop Tv /L and obtainable ADPI values for products not included in the current literature but currently
available in the commercial market.
2. Evaluate the ADPI calculation methodology to
recommend an ADPI calculation for spaces in heating
mode, and spaces at low loads, to better correlate with
the ASHRAE comfort standard.
3. Create an updated database of ADPI values, with the
revised ADPI calculation, for overhead mixing heating and
cooling systems for a selected range of typical spaces (classrooms, office spaces, restaurants, supermarket, retail
spaces) and air outlet types that will be used by mechanical engineers to determine the optimum diffuser selection and spacing for these spaces at today's lower loads.
4. Determine the values of ADPI that prove compliance
22

ASHRAE JOURNAL

ashrae.org

JAN UARY 2020

to ASHRAE Standard 55's vertical temperature stratification limits, and update the ASHRAE table.
The results of RP-1546 are presented in the revised
ADPI table included in the 2019 ASHRAE Handbook-HVAC
Applications. Table 2 shows the results for cooling and
Table 3 shows the results for heating. The Handbook
includes a detailed description on how a designer can
use ADPI to optimize outlet placement to maximize thermal mixing.
The University of Texas at Austin, led by Liu, conducted
further tests on outlets used in overhead heating applications. Although not included in the work statement for
RP-1546, the results are significant. The research determined how critical it is for designers to set minimum velocities when designing an overhead mixed heating system.
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