ASHRAE Journal - December 2023 - 36

TECHNICAL FEATURE
FIGURE 2 Area percentage of the 14 projects on
which Method 2 was tested.
FIGURE 3 Comparison of outdoor air, total supply air and exhaust airflow for the 14 projects using Method 2.
Comparison of OA, EA, and SA
(Using New 62.1/170 Calculations Methodology)
calculated based on Standard 170.
That would contradict the feedback
received from SSPC 170. On the
other hand, most spaces in the
scope of Standard 170 require 2
ach of outdoor air, which generally
equates to 0.6 cfm/ft2 (3 L/s·m2) for a typical 9 ft (3 m)
ceiling space. In almost all cases, this is much higher
than what any Standard 62.1 space would require.
Applying ventilation effi ciency (Ev ) to outdoor air
calculated based on Standard 170 would only increase
the total ventilation. Accordingly, the working group
selected Method 2 (code named Individual Additive
Ev-Less for 170) as the method to explore further.
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
2
OA ACH EA ACH SA ACH
31% 29% 29% 31% 30% 28% 32% 34% 46% 28% 35% 36% 38% 39%
OA OA OA OA OA OA OA OA OA OA OA OA OA OA
Project Project Project Project Project Project Project Project Project Project Project Project Project Project
1
3
4
5
6
7
8
9
10 11 12
13 14
Testing the Methods
To test the accuracy of Method 2, the working group
applied it to 14 health-care projects. In addition, to test
the sensitivity of Method 2, the working group made
sure the 14 projects:
* Were mixtures of acute care and outpatient
facilities;
* Represented a large sample (the total area of the 14
projects was 867,000 ft2 [80 547 m2]);
* Were a mixture of small and large projects (smallest
project was 17,000 ft2 [1579 m2], and the largest was
220,000 ft2[20 439 m2]); and
* Had good representation of Standard 62.1/Standard
170 balance in spaces. (See Figure 2 and in particular
projects highlighted in red. Project 5 had a majority of
Standard 170 spaces, while Project 11 had a majority of
Standard 62.1 spaces.)
36
ASHRAE JOURNAL ashrae.org D E C EM B E R 2 0 2 3
The Results
For the 14 projects, Figure 3 shows the resulting
required outdoor airfl ow using Method 2, the total
supply air and the total exhaust air (for reference).
The percentage of outdoor air to total supply air
is indicated in black next to each project's columns.
Except for one outlier project, which had 46% OA,
all the projects had OA between 28% to 38%, with
the majority between 28% and 35%, which is the
typical percentage of OA in health-care facilities
based on engineers' feedback from actual projects
designed. Thus, the working group concluded Method
2 yielded accurate and stable results for different
building sizes, types and mixture of space. The group
recommended this method for adoption in both
Standards 62.1 and 170.
The Addenda
Method 2 was subsequently written in code
language in Addendum f to Standard 170-2021. It
was offi cially published in July 2022. The addendum
changes Standard 170 to allow two pathways for
outdoor air calculations. Figure 4 provides a visual
presentation of Addendum f.
* If a system serves only spaces within the scope of
Standard 170, the total system outdoor air is simply
Air Changes Per Hour

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ASHRAE Journal - December 2023

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