ASHRAE Journal - May 2023 - 54

TECHNICAL FEATURE
ventilation changes in administration and common
areas. Ventilation delivered to a zone was controlled to
meet the temperature setpoint. Phase 3 minimum ventilation
setpoints were set based on ASHRAE Standard
62.1-2016. (Note to readers outside of California: at the
time of the project, 2 ach was the lowest ach for any
space in a hospital, including administrative spaces.)
The baseline data collection period, Phase 2 data collection
period and Phase 3 data collection period were
60 days of 15-minute interval data for all airborne contaminant
and energy points.
Industrial Hygiene Assessments
In addition to the mounted sensors, an industrial
hygiene team performed two sets of air quality assessments,
one during Phase 1 and the second at the end of
Phase 2. The industrial hygiene assessment included
measurements of carbon dioxide, carbon monoxide,
nitrous oxide, ozone, hydrogen peroxide, peracetic
acid, formaldehyde, acetaldehyde, volatile organic compounds
and bioaerosol fungi and bacteria.
Infection Control Monitoring
During project design, an infection control risk assessment
(ICRA) was performed. The hospital infection
control leads identified which data fluctuations would
be concerning. Project stop criteria were identified. A
regular reporting schedule was established with hospital
leadership.
At no point in the project were the stop criteria
reached. During the project, infection control investigated
several spikes in data. One set of high VOC readings
was investigated and found to be near a hand sanitizer
station. Several sets of unusual particulate readings
were investigated, revealing work practices that contributed
to elevated particulate contamination.
Indoor Air Quality Data
Comparison of the Phase 1 baseline data to the Phase 2
and Phase 3 data yielded the following.
Temperature and RH: The quality of comfort control
was unchanged from the baseline period through
Phase 2 and Phase 3. The overall level of comfort control
was reasonably good: 80% of per-zone and per-ach average
temperatures and RHs fell between 68°F and 72°F
(20°C and 22°C) and between 51% and 62% RH.
CO2 Levels: Contrary to the theoretical relationship,
54
ASHRAE JOURNAL ashrae.o rg M AY 2023
CO2 did not decrease when zone ach increased. This was
particularly surprising, since the system in the hospital
is 100% outdoor air. Rather, the data did not show an
obvious relationship between CO2 and ach in the zones
(Figure 2).
Also contrary to expectations, there was little variance
in levels from space to space or from space type to space
type. All rooms fell into the same range. Patient rooms
and work spaces, for example, which have significantly
different occupant characteristics, did not have notably
different contaminant levels.
Throughout the project, the average CO2 levels across
all zones were in the range of 500 ppm, ±50 ppm, which
suggests over-ventilation. To consistently achieve
500 ppm to 550 ppm of CO2 requires ventilation at or
above 100 cfm/person (47 L/s), which is likely well in
excess of what is necessary to meet the thresholds of
Figure 2. The overall median of all CO2 data points was
477 ppm. (The median CO2 for outdoor air was 460 ppm;
thus, in terms of CO2, indoor air was indistinguishable
from outdoor air.) The per-zone, per-ach averages were
between 460 ppm and 660 ppm. Eighty percent were
between 440 ppm and 530 ppm. In Phase 3, ventilation
in administrative zones was reduced further. As ventilation
levels were reduced, CO2 did not follow any noticeable
correlation to ventilation rates, down to rates as low
as 0.5 ach.
Particulate Levels: Also contrary to the theoretical
relationship, particulate levels did not noticeably
decrease with higher zone ach. Similar to CO2, all spaces
and space types in the hospital had very similar levels
(Figure 3). The median value of outdoor air particles was
2,400 N/L; N is the number of particles in this discussion.
(Please note that the outdoor level is too high to
be displayed on Figure 3; the indoor air had consistently
lower levels than the outdoor air.) The team's established
action level was 846 N/L. The overall median of the particulate
data set is 61 N/L. Eighty percent of the per-zone
and per-ach medians were from 15 N/L to 119 N/L.
Particulate levels stayed well below action levels
throughout the project. Eighty percent of the indoor
particulate data fell between 1% and 8% of the outdoor
levels.
Volatile Organic Compounds: Several spikes occurred
in which VOC was above the action level of 300 ppb.
Based on the team's field investigation, these VOC spikes
were attributed to cleaning products or hand sanitizer.
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