ASHRAE Journal - October 2024 - 31

TECHNICAL FEATURE
This analysis indicates that a reduction in the supply
airfl ow rate from 6 ach to 4 ach does not signifi cantly
affect the ventilation performance of the PACU. In
both cases, the high concentration zones are limited
only to the vicinity of the sevofl urane source. Table 2
shows a slight increase in the Spread Index values for
the reduced airfl ow rate (Case 5) for various target
concentrations. This can be attributed more to the
reduced dilution than to the airfl ow patterns.
As demonstrated in the previous studies, the airfl ow
patterns depend only on the space HVAC layout and
not on the supply airfl ow rate.6,10 Therefore, these
analyses show that optimized airfl ow patterns with
proper locations for air supply and return can reduce
the supply airfl ow rate, leading to a reduction in
energy consumption, fi rst costs and operating costs of
HVAC equipment.
Summary and Conclusions
The postoperative patients in the PACU of a hospital
are the sources of WAGs. The health-care workers
there can potentially be exposed to hazardous WAGs.
To protect them, it's important to design a ventilation
system that effectively removes these gases and
reduces exposure. By improving airfl ow patterns,
the concentration of WAGs in the occupant breathing
zone can be reduced. To evaluate the impact of various
HVAC layouts on the ventilation performance of the
PACU, a study was conducted using non-isothermal
CFD simulations. The study used a Spread Index
metric to compare sevofl urane's spread for various
HVAC layouts.
The traditional HVAC layout with four-way supply
diffusers and ceiling returns was found to create
mixing airfl ow patterns. These patterns can potentially
distribute WAGs throughout the entire PACU, increasing
the risk of exposure for health-care workers. Similarly,
the low wall and ceiling returns layouts with ceiling
laminar diffusers also create recirculating airfl ow
patterns, which can bring sevofl urane plumes from the
patient's face into the breathing zone of occupants.
The HVAC layout with laminar diffusers and headwall
returns showed the most promise in reducing the
concentration of WAGs in the breathing zone. This
layout uses horizontal movement of a sevofl urane
plume below the breathing zone of occupants combined
with immediate exit of the contaminated air through
the headwall returns. This signifi cantly reduces the
concentration of sevofl urane in the breathing zone and
limits the spread of WAGs in the PACU.
The study also indicates that the PACU with such an
optimized HVAC layout can be operated at reduced
dilution airfl ow rates without signifi cantly affecting
the ventilation performance. This confi rms that it's not
the air change rates but the airfl ow patterns that play
a crucial role in improving ventilation effectiveness.
By using CFD to analyze and optimize airfl ow patterns
in indoor spaces, it's possible to limit the spread of
contaminants and reduce the exposure of occupants.
Such optimized ventilation designs can further reduce
energy consumption, fi rst costs and the operating costs
of the HVAC system.
References
1. McGlothlin, J., J. Moenning, S. Cole. 2014. " Evaluation and
control of waste anesthetic gases in the postanesthesia care unit. "
Journal of PeriAnesthesia Nursing 29(4)298 - 312.
2. McGlothlin, J., S. Caler, P. Lilley, M. Rosales, et al. 2021.
" Recognition, Evaluation and Control of Waste Anesthetic Gases in
the Post-Anesthesia Care Unit. " White Paper. American Industrial
Hygiene Association.
3. NIOSH. 1977. " Criteria for a Recommended Standard:
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4. EPA. 2016. " Integrated Science Assessment (ISA) for Oxides of
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5. Garcia, A., G. Merk, S. Garner, H. Feng. 2022. " Engineering
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6. Khankari, K. 2016. " Patient room HVAC: airfl ow path matters. "
ASHRAE Journal 58(6).
7. Khankari, K. 2018. " CFD analysis of hospital operating room
ventilation system part 2: analyses of HVAC confi gurations. "
ASHRAE Journal 60(6).
8. Hiller, K., A. Altamirano, C. Cai, S. Tran, G. Williams. 2015.
" Evaluation of waste anesthetic gas in the postanesthesia care
unit within the patient breathing zone. " Anesthesiology Research and
Practice 2015:354184 http://dx.doi.org/10.1155/2015/354184
9. Khankari, K. 2021. " Analysis of spread of airborne contaminants
and risk of infection. " ASHRAE Journal 63(7).
10. Khankari, K. 2018. " CFD analysis of hospital operating room
ventilation system part 1: analysis of air change rates. " ASHRAE
Journal 60(5).
Author's note: The fi ndings and conclusions of this paper are
those of the authors and do not necessarily represent the views
of the NIOSH, CDC. Mention of any product or company name
does not constitute endorsement by the NIOSH, CDC.
O CTO B E R 2 0 2 4 ashrae.org ASHRAE JOURNAL
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