ASHRAE Journal - September 2024 - 40

TECHNICAL FEATURE
FIGURE 5 Temperature contours at chairs.
Temperature (°F)
86
84
82
80
79
77
75
73
72
70
68
supplied by displacement ventilation create an
acoustical environment with contributions from air
handlers, terminal units, diffusers and structure-borne
sound. In the case of the Riad Salameh Auditorium,
the main differences between a more typical supplyexhaust
system and a displacement ventilation system
are the type of diffusers and the duct network system,
which is laid in a technical fl oor under the auditorium
and that is sized at the minimum required air velocity.
Supply air fl ows to a large concrete chamber (concrete
plenum) under the seats, and air terminal devices are
connected to this chamber.
A very important part of a displacement ventilation
system is the supply diffusers. Diffusers are used for
uniform distribution of airfl ows in the space. The
catalog sound performance rating of a displacement
diffuser is usually expressed in terms of a noise criteria
(NC) level based upon a typical space with room
absorption of 10 dB in each octave band per ASHRAE
Standard 70-2006 (Appendix D). Properly sized and
selected displacement ventilation diffusers are rarely
the cause of noise complaints because they operate
at low pressure and low velocity and therefore do not
generate audible noise.
CFD Analysis
To determine the actual heat loads (external and
internal) affecting the auditorium space throughout the
year, a thermal cooling load simulation was carried out.
Moreover, a CFD model was simulated at steady state
and for peak load conditions considering the presence of
nearly 300 occupants as listed below for reference:
* The sensible and latent loads released by 300
persons seated at rest were 78,000 Btu/h (23 000 W)
and 41,000 Btu/h (12 000 W), respectively. No additional
40
ASHRAE JOURNAL ashrae.org S E PTEM B E R 2 0 2 4
latent load other than the one released by the occupants
was included.
* An additional sensible load of 41,000 Btu/h
(12 000 W) of heat load was added to the occupied
space as a result of overhead and task lighting as well as
electric equipment.
From inspecting the simulation results, especially
Figure 5, it can be deduced that a uniform thermal
fi eld is established at occupant level with no drafts.
Indeed, temperatures at the stair level are observed
to range between 70°F - 72°F (21°C - 22°C), while air
speeds remain below 40 fpm (0.2 m/s), except near the
auditorium's entrance where temperatures reach 75°F
to 77°F (24°C to 25°C) as a result of the positioning of
the return outlet. In fact, the vertical throw air velocity
from the fl oor supply of cool air and ceiling return is less
than or equal to 50 fpm (0.25 m/s) at a height of 4.5 ft
(1.4 m) above the fl oor. As the area near the entrance is
only a transitory space before the occupants reach their
seats, the higher temperatures reported there are not
detrimental to the performance of the system. In fact,
the higher temperatures could be preferable as they
correspond to a reduction in cooling capacity since no
cooling is actually required at this area.
Of special note is the fact that there is no loss of
cooling capacity in the volume of air above the occupant
zone as a result of the optimized supply and return
confi guration, which promoted the establishment of a
clearly visible stratifi cation (Figure 6).
The above observations for the thermal distribution
are further substantiated by inspecting Figure 7a and
Figure 7b depicting contours of PMV and PPD at 4 ft
(1.2 m) above the fi nished fl oor level, respectively.
Indeed, both PPD and PMV fall in the comfort range
(PMV range between 0.1 and 0.4 while PPD is below
10) as a result of the laminar rise of the supply airfl ow,
which helped minimize any detrimental mixing.
Conclusion
The system and method that were fulfi lled in
the Riad Salameh Auditorium were a successful
implementation of displacement ventilation.
Construction and commissioning of the auditorium
were completed on schedule, and the auditorium was
opened in November 2017. Based on the study fi ndings,
it can be concluded that the displacement ventilation
system is well suited for an auditorium with a high
http://www.ashrae.org
ASHRAE Journal - September 2024

Table of Contents for the Digital Edition of ASHRAE Journal - September 2024
