ASHRAE Journal - January 2020 - 24

TECHNICAL FEATURE

TABLE 3 ADPI selection guide for typical heating loads.

Table 6B Air Diffusion Performance Index (ADPI) Selection Guide for Typical Heating Loads

Adjustable-blade grilles

Fixed-blade grilles
Linear-bar grilles
Nozzles (high sidewall
installation)
Round ceiling diffuser
Square ceiling diffuser
Perforated diffusers, round pattern
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
Linear-slot diffusers
T-bar slot diffusers
Swirl diffusers
N-slot diffusers

T/L Low
T/L High
Limit for
Limit for
ADPI > 80% ADPI > 80%

Installation

Load,
Btu/h·ft2

Max. ADPI
T50/L

Max.
ADPI

45° upward blades, High sidewall
0° horizontal blades, High sidewall
45° downward blades, High sidewall
15° upward blades, High sidewall
15° downward blades, High sidewall
High sidewall
Sill
High sidewall

10 to 12
10 to 12
10 to 12
10 to 12
10 to 12
10 to 12
10 to 12
10 to 12

1.1
1.6
0.7
1.8
1.4
1.2
1.2
1.5

95
94
84
96
88
94
100
92

0.6
1.1
0.6
1.2
0.6
0.6
0.7
1.0

1.9
2.4
0.8
2.8
2.2
1.7
1.8
2.0

Ceiling
Ceiling
Ceiling
Ceiling

10 to 12
10 to 12
10 to 12
10 to 12

1.4
1.7
2.1
2.5

93
91
90
87

1.0
2.5
2.0
2.5

2.3
3.4
2.8
3.4

Ceiling

10 to 12

2.6

88

2.5

4.4

Ceiling

10 to 12

2.1

88

2.1

3.2

Ceiling
Ceiling
Ceiling, periphery of a wall
Ceiling
Ceiling

10 to 12
10 to 12
10 to 12
10 to 12
10 to 12

2.1
1.7
1.6
1.4
1.9

93
90
91
100
100

2.1
1.7
1.3
1.4
1.5

3.0
3.1
2.0
2.1
2.4

Terminal Device in
Heating Mode

Source: Data developed by Liu and Novoselac (2015) 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.

The heating mode ADPI method has been developed in
the format similarly to the cooling ADPI as shown in the
following.6
θ = (ts - t) - 0.08(V - 30) °F
θ = (ts - t)-9.1(V - 0.15) °C
where
θ = effective draft temperature at a test point, °F (°C)
ts = local temperature of the test point, °F (°C)
t = average test zone temperature, °F (°C)
V = time-averaged air speed at the test point, fpm (m/s)
The majority of people would be comfortable at the
heating condition when the effective draft temperature of location is in the range between -4°F (-2.2°F)
and +3.6°F (+2.0°C) with the upper limit of air speed
below 70 fpm (0.35 m/s). In addition, since a warm jet
from a diffuser tends to rise upwards due to buoyancy
rather than dumping into the occupied zone as a cool
jet, an excessive thermal stratification might be caused
between head at 43 in. (1.1 m) and feet at 4 in. (0.1 m)
for sedentary occupants according to current ASHRAE
Standard 55.7 The developed ADPI table for typical heating loads (Table 3) is also included in the 2019 ASHRAE
Handbook-HVAC Applications.
Another adverse consequence of supplying warm air
is reduced air change effectiveness defined by ASHRAE
24

ASHRAE JOURNAL

ashrae.org

JAN UARY 2020

Standard 129.8 Air change effectiveness is the ratio of
room nominal time constant to the average age of air
in the occupied zone. ANSI/ASHRAE Standard 62.19
uses air change effectiveness as an alternative for zone
air-distribution effectiveness. The air change effectiveness reduces for ceiling supply of warm air. Therefore,
the heating ADPI would be inevitably concerned with
air change effectiveness, especially when the supply air
jet not strong or has a high temperature. For instance,
Figure 3 shows that the calculated ADPI values are higher
than 90% for both weak and strong supply air jets generated by a round ceiling diffuser. However, the weak jets
can cause enhanced thermal stratification, air stagnation near the ceiling, and poor air change effectiveness.
Hideyuki Amai, Ph.D., who was also involved in ASHRAE
RP-1546 completed a series of lab tests of measuring
air change effectiveness for five diffuse types following
the decay procedure by ASHRAE Standard 129.10,11 The
results in Figure 2 shows that air change effectiveness is
highly correlated with temperature effectiveness that is
much simpler to calculate using the following equation:

εT =

Ts − TE
[%]
Ts − T o

where
Ts = supply air temperature
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ASHRAE Journal - January 2020

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