ASHRAE Journal - October 2023 - 40

TECHNICAL FEATURE
6. WLHP + Higher Eff + DOAS-ERV + DCV: Water
loop heat pumps with higher efficiency (than code
minimum), with DOAS, ERV and DCV control.
7. VRF + Higher Eff + DOAS-ERV + DCV: Variable
refrigerant flow (VRF) systems with higher efficiency
(than code minimum) with DOAS, ERV and DCV control.
8. GSHP + Higher Eff + DOAS-ERV + DCV: Groundsource
heat pumps (GSHP) with higher efficiency (than
code minimum) with DOAS, ERV and DCV control.
The following HVAC systems were analyzed for
Climate Zone 5A:
1. Reference System: PVAV with hot water (HW)
reheat, based on the requirements defined in Standard
90.1-2022 for the specific use type and climate zone.
2. Target System: PVAV with hot water (HW) reheat,
based on the requirements defined in Standard
90.1-2022 for the specific use type and climate zone.
3. PSZ Gas Furnace + CAV Fan + Higher Pan Power:
PSZ gas furnace with minimum prescriptive efficiency
with a CAV fan with fan power higher than the target
system.
4. PSZ HP + Higher Eff + DOAS-ERV + DCV: Packaged
single zone heat pump (PSZ HP) with higher efficiency
(than code minimum) with DOAS, ERV and DCV.
5. GSHP + Higher Eff + DOAS-ERV + DCV: Groundsource
heat pumps (GSHP) with higher efficiency (than
code minimum) with DOAS, ERV and DCV control.
Conclusion
Until recently, energy codes relied on either the
prescriptive compliance approach or the wholebuilding
performance compliance approach to
determine code compliance.
For the first time, the new Mechanical System
Performance Rating Method gives the energy code a
metric and a minimum standard for evaluating the
overall efficiency of a building's HVAC system, without
prescribing the technical means of achieving that level
of efficiency. This approach can be tailored to meet
goals and objectives of the adopting jurisdiction.
The stringency of TSPR metric thresholds can be set
initially to eliminate only the least efficient systems
from consideration and can then be strengthened over
future code cycles to require progressively higherperforming
systems.
This encourages an integrated design approach for
the selection and analysis of HVAC systems and can
40
ASHRAE JOURNAL ashrae.org O CTO B ER 2023
potentially shift the focus of code compliance from that
of simply complying with the prescriptive provisions
to that of designing complete integrated systems that
interact in a manner that provides the highest levels
of efficiency.
The Mechanical System Performance Rating Method
can be applied to any model energy code or beyondcode
program.
Standard 90.1 is using energy cost as the TSPR
evaluation metric, but this could just as well be carbon
emissions, site energy use or source energy use based
on the policy goals of the city, state or jurisdiction
applying the Mechanical System Performance Rating
Method. Informative material supporting the use of
these alternative metrics is included in Standard 90.12022
Appendix L.
Aspects of a high-performance system design which,
through the prescriptive approach to compliance, were
not credited or recognized are now a critical aspect for
system evaluation.
The simplified implementation of the Mechanical
System Performance Rating Method through the MSP
tool provides a mechanism for designers to perform
quick analysis to identify how different system design
strategies impact the overall performance of the
HVAC system.
This approach is a critical step toward a systems-based
approach for building design and evaluation.
The Mechanical System Performance Rating Method
is a bridge between the prescriptive compliance path
and the whole-building performance compliance
path making it a highly viable option to facilitate the
transition to performance-based codes and to meet
aggressive energy efficiency goals.
References
1. Goel, S., R. Hart, J. Gonzalez, J. Lerond, et al. 2021. " Mechanical
Performance Factor Development for HVAC System Performance. "
PNNL-32140. Technical Documentation. Pacific Northwest National
Laboratory for U.S. Department of Energy, Office of Energy
Efficiency and Renewable Energy. https://tinyurl.com/yc54mf8m
2. WSEC. 2018. Washington State Energy Code. Washington State
Building Code Council.
3. ANSIASHRAE/IES Standard 90.1-2022, Energy Standard for Sites
and Buildings Except Low-Rise Residential Buildings.
4. Goel, S., R. Hart, Tillou, M., M. Rosenberg, et al. 2021. " HVAC
System Performance for Energy Codes. " PNNL-31571. Technical
Brief. Pacific Northwest National Laboratory for U.S. Department
of Energy, Office of Energy Efficiency and Renewable Energy.
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ASHRAE Journal - October 2023

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