ASHRAE Journal - May 2020 - 13

TECHNICAL FEATURE

for minimum ventilaFIGURE 1 Surgery center: a) basic layout, b) multizone software model; O.R.1 to O.R.4: operation rooms 1 to 4; 1: access corridor; 2: locker rooms; 3: staff access corridor; 4: stretcher access; 5: staff room; 6: bathrooms; 7: decontamination room;
tion rates are based on
8: sterilization room; 9: sterile storage; 10: mechanical room; 11: emergency exit.
ASHRAE standards.2,3 An
11
N
air-handling unit (AHU) is
3
dedicated to each OR. Part
6
O.R.1
O.R.2
10
O.R.3
of the air is returned to
5
2
2
the AHU, and, after mixing with outdoor air, it is
6
1
4
ﬁltered, cooled, reheated
and supplied to the related
8
7
10
OR. All AHUs are located
O.R.4
9
in a mechanical room, and
no equipment is located
inside the ORs. These sysA.
tems shall maintain the
3
rooms in positive pressur6
6
10
ization and are equipped
O.R.1
O.R.2
O.R.3
2
2
5
with HEPA ﬁlters, given
that specialized surgeries
4
1
are expected. HVAC for the
sterilizer equipment room
10
O.R.4
is sized to provide a mini8
9
7
mum of 10 ach of outdoor
air. The decontamination
B.
rooms are served by a
dedicated HVAC system,
and envelope cracks. The former represents the gaps
sized to provide a minimum of 6 ach of outdoor air, and
between the doors and its frame. The latter represents
negative pressurization. Bathroom exhaust makeup
the unintentional construction cracks related to sealing
air is from the locker rooms. All air supplied to the
decontamination and sterilization rooms are exhausted and ﬁnishing inefﬁciencies. There are no windows in
the modeled OR.
directly to outdoors.
Envelope leakage depends on construction practices
Room Pressurization Analysis
and techniques, which change from one country to
A key element in room pressurization is the relationanother. Therefore, envelope cracks were modeled
4
ship between room airtightness and offset airﬂow.
to represent a high-performance building. An ELA of
Due to a lack of engineering-based criteria on sizing the
242 mm2/m2 (0.035 in.2/ft2) was adopted for the enveoffset airﬂow, many controlled spaces fail to perform as
lope cracks, based on sealing performance of ASHRAE
intended.4 Manual calculations for room pressurization Standard 189.1-2014.5 In many cases, especially with a
tend to be cumbersome or even impractical for a large
ceiling plenum, the tiles are a major source of leakage.
building with several interconnected rooms. Therefore,
This study adopted the basic premise that a monolithic
the multizone software may be a relevant tool for that
ceiling was considered, along with walls that connect
task.
to the slabs above the suspended ceiling. Therefore,
A parametric test relating the effective leakage area
all the related cracks were modeled by the envelope
(ELA) and the necessary outdoor airﬂow rate to meet the cracks.
relative pressurization criteria was conducted for the
Three types of door gaps were tested, representing difsurgery center, using the multizone software. Two basic
ferent door airtightnesses. The associated ELA for each
types of construction cracks were considered: door gaps
case is presented in Table 1.
M AY 2020

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