ASHRAE Journal - June 2019 - 36
TECHNICAL FEATURE
FIGURE 9 Contours of temperature at the central plane for non-isothermal conditions with heat source near the ceiling show uniform temperature distribution at very low sup-
ply airflow rate and decreasing thermal gradient between the cold air jet and the surrounding air with increasing supply airflow rate.
b) 400 cfm (188.8 L/s)
a) 200 cfm (94.4 L/s)
c) 600 cfm (283.2 L/s)
d) 800 cfm (377.6 L/s)
parameter (n) and the computed value is presented
below.
A Arr = n
Q
V Ts (l ++ w ) (1)
3
2g
n=
ρcp
where
Q
V
(1a)
= sensible cooling load in the space, Btu/h (W)
= discharge velocity of the supply air from a
laminar diffuser, ft/min (m/s)
Ts
= supply air temperature, R (K),
l and w = length and width of a laminar diffuser array,
respectively, ft (m)
g
= gravitational acceleration 32.17 ft/s2 (9.81 m/s2)
ρcp
= heat capacity of the air, 0.018 Btu/ft3·R
(1206 W/m3·K)
The calculated value of n from the parameters listed
above using the Equation 1a is as follows:
36
A S H R A E J O U R N A L a s h r a e . o r g J U N E 2 0 19
Example:
Consider a hospital operating room (OR) with a 3 ×
3 array of 2 × 4 ft (0.6 × 1.2 m) laminar diffusers with
a sensible cooling load of 7541 Btu/h (2210 W) and the
supply air temperature of 67°F (19.4°C). Compare the
Archimedes number for 15 and 30 fpm (0.1 and 0.2 m/s)
discharge velocities.
For 15 fpm (0.1 m/s)
A Arr =
214, 467 × 7, 541
(15) × (67 + 459.7) × 3( 2 + 4)
3
= 50.5
For 30 fpm (0.2 m/s)
A Arr =
214, 467 × 7, 541
(30) × (67 + 459.7) × 3( 2 + 4)
3
= 6.3
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ASHRAE Journal - June 2019
Table of Contents for the Digital Edition of ASHRAE Journal - June 2019
Contents
ASHRAE Journal - June 2019 - Intro
ASHRAE Journal - June 2019 - Cover1
ASHRAE Journal - June 2019 - Cover2
ASHRAE Journal - June 2019 - 1
ASHRAE Journal - June 2019 - Contents
ASHRAE Journal - June 2019 - 3
ASHRAE Journal - June 2019 - 4
ASHRAE Journal - June 2019 - 5
ASHRAE Journal - June 2019 - 6
ASHRAE Journal - June 2019 - 7
ASHRAE Journal - June 2019 - 8
ASHRAE Journal - June 2019 - 9
ASHRAE Journal - June 2019 - 10
ASHRAE Journal - June 2019 - 11
ASHRAE Journal - June 2019 - 12
ASHRAE Journal - June 2019 - 13
ASHRAE Journal - June 2019 - 14
ASHRAE Journal - June 2019 - 15
ASHRAE Journal - June 2019 - 16
ASHRAE Journal - June 2019 - 17
ASHRAE Journal - June 2019 - 18
ASHRAE Journal - June 2019 - 19
ASHRAE Journal - June 2019 - 20
ASHRAE Journal - June 2019 - 21
ASHRAE Journal - June 2019 - 22
ASHRAE Journal - June 2019 - 23
ASHRAE Journal - June 2019 - 24
ASHRAE Journal - June 2019 - 25
ASHRAE Journal - June 2019 - 26
ASHRAE Journal - June 2019 - 27
ASHRAE Journal - June 2019 - 28
ASHRAE Journal - June 2019 - 29
ASHRAE Journal - June 2019 - 30
ASHRAE Journal - June 2019 - 31
ASHRAE Journal - June 2019 - 32
ASHRAE Journal - June 2019 - 33
ASHRAE Journal - June 2019 - 34
ASHRAE Journal - June 2019 - 35
ASHRAE Journal - June 2019 - 36
ASHRAE Journal - June 2019 - 37
ASHRAE Journal - June 2019 - 38
ASHRAE Journal - June 2019 - 39
ASHRAE Journal - June 2019 - 40
ASHRAE Journal - June 2019 - 41
ASHRAE Journal - June 2019 - 42
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ASHRAE Journal - June 2019 - 49
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ASHRAE Journal - June 2019 - 80
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ASHRAE Journal - June 2019 - Cover4
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