ASHRAE Journal - July 2023 - 49

TECHNICAL FEATURE
Guideline 36 controls reference. ASHRAE Guideline
36, High-Performance Sequences of Operation for HVAC
Systems, was created to develop and maintain best-inclass
standardized HVAC control sequences. ASHRAE
Standard 90.1 was updated to make references
to sequences of operation described in ASHRAE
Guideline 36 in appropriate sections of Section 6
where control requirements are stated but lack
specifi city in how the sequences can be implemented.
Energy recovery ventilation (ERV) bypass
requirements. In the prescriptive Section 6.5.6, there
are requirements for the use of exhaust air energy
recovery with ventilation air systems. Standard
90.1-2022 provides revised language to clarify the
requirements for bypass when economizers are being
used for both the outside air and exhaust air. The
pressure drop is limited to 0.4 in water, and there is
an additional requirement to limit energy exchange
to 10% when in bypass mode.
Exhaust air energy recovery. The current enthalpy
recovery ratio (ERR) requirement has caused
confusion when applied to systems that require
only sensible heating energy recovery. For systems
that do not provide humidifi cation, there is no
heating energy benefi t due to latent energy recovery.
Standard 90.1-2022 added language to specify the
sensible energy recovery ratio requirement for these
systems.
DOAS exemption. This change adds an exception
to the DOAS requirements in 6.5.2.6 for units that
use only series energy recovery in climate zones 0A,
1a, 2a, 3a and 4a for reheating dehumidifi ed air. The
rationale for this section is that when the building
needs sensible cooling energy, reheating of the
ventilation airstream causes energy to be wasted,
even with free condenser reheat.
Hospital heat recovery. Section 6.5.6.3, " Heat
Recovery for Space Conditioning, " requires heat
recovery to be used in most acute inpatient hospitals.
The existing language refers to " condenser heat
recovery, " which has led some users to believe that
the heat source can be water leaving the chiller
condenser. While this method does recover heat, it
does not reduce load on the chillers. Users are now
specifi cally directed to use the chilled water return as
the heat source.
Economizer trade-off. Table 6.5.1-2 defi nes the
equipment effi ciency level increase necessary to allow
for the elimination of economizers. In Standard 90.12022,
those requirements were clarifi ed.
Expanded airside economizers. Airside
economizers can provide signifi cant energy savings
during lower temperature cooling, which is common
in commercial buildings. Standard 90.1-2022
extended the threshold for requiring an airside
economizer from 54,000 Btu/h to 33,000 Btu/h (16 kW
to 10 kW) for individual fan-cooling units located
outside of the building envelope.
Small fan effi cacy. This change established
minimum fan effi cacy requirements for low-power
ventilation fans with a minimum cfm/W as listed in
Table 6.5.3.7.
FEI rating clarifi cation. Section 6.5.3.1.3 was
revised to clarify that the Fan Energy Index (FEI) requirement
applies at the highest design airfl ow rate.
Occupied standby. Standard 90.1-2022 requires
a system-level reset of outdoor air levels to ensure
greater energy savings when ventilation air is turned
off to unoccupied zones.
Elevators. Changes were made to Section 10.4.3
to improve elevator fan, lighting, and movement
effi ciency, establishing a minimum energy effi ciency
target of E or better.
Section 7 New Service Water Heating Requirements
Mechanical systems for Service Water Heating
(SWH) are covered in Section 7. There were two major
changes to the SWH requirements for Standard
90.1-2022. First was the introduction of insulation
requirements for SWH piping, which was based on
the structure of current Section 6 requirements for
space heating piping.
The new requirements, presented in Table 7.4-2,
refl ect typical SWH system operation and operating
temperatures. The table reports the required insulation
thickness and thermal conductivity based on
pipe size and temperature range.
Additionally, Section 7.5.3 was modifi ed to require
a thermal effi ciency (Et) of 92% for high-capacity gasfi
red SWH equipment. This applies to single units; the
requirement for multiple units connected to the same
service remains a weighted total of 90% or more; however,
a minimum of 30% of the input in a multi-unit
system must now achieve 92% Et.
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ASHRAE Journal - July 2023

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