ASHRAE Journal - October 2023 - 35

TECHNICAL FEATURE
reset.1 Through this holistic approach to HVAC system
evaluation, the TSPR metric is able to evaluate HVAC
system performance to identify more effi cient system
confi gurations.
Standard 90.1-2022 Approach
Similar in concept to the Building Envelope TradeOff
Option in Standard 90.1 , the Mechanical System
Performance Rating Method is a discipline-specifi c
performance approach rather than a whole-building
approach.* It has been incorporated into Standard
90.1-2022 as an alternative to prescriptive compliance.
As with prescriptive performance, the mandatory
HVAC requirements in Section 6.4 of the standard
still apply for performance-based compliance under
Section 6.6. Then, mechanical system performance
is evaluated by comparing the proposed HVAC system
design to a reference building system. As shown in
Figure 2, this requires the user to calculate the TSPR of
both systems. This involves a two-step process of fi rst
selecting the system components (Table 1) and second
determining the resulting HVAC load to energy input
*The Building Envelope Trade-Off compliance path in the envelope
discipline of Standard 90.1 that is supported by Appendix C is an
example of a discipline performance rating path.
ratio (i.e., the TSPR). This process is explained in
greater detail throughout Section 6.6 and Appendix L
of Standard 90.1-2022.
Computing the TSPR: Target systems defi ne the
minimum performance level required for compliance
with this approach. Since target systems are changing
with each code cycle, for simulation software stability,
a stable reference system is used as a touchstone, with
MPFs used to defi ne the relationship between reference
and target systems. Reference and target systems are
summarized in Table 1 and further detailed below.
Target systems are defi ned by the Standard 90.1
Standing Standards Project Committee for each climate
zone and building type and represent minimum
prescriptive levels of performance for a " good " HVAC
system installation. The HVAC system selected for the
TABLE 1 Summary of reference and target systems by building type in Standard 90.1-2022.
BUILDING
TYPE
LARGE OFFICE
PARAMETER
VAV/RH
System
Type
(Warm CZ)
System
Type
(Warm CZ)
System
Type
(Cold CZ)
System
Type
(Cold CZ)
Water-Cooled
Chiller
(0.576 kW/ton)/
Elec RH
VAV/RH
Water-Cooled
Chiller
(0.576 kW/ton)/
Elec RH
VAV/RH
Water-Cooled
Chiller
(0.576 kW/ton)/Gas
Boiler (80% AFUE)
VAV/RH
Water-Cooled
Chiller
(0.576 kW/ton)/
Gas Boiler
(90% E t )
Packaged
VAV/RH DX Cool
(COP 3.83)/Gas
Boiler (81% E t )
Packaged
Air-Source AC
(COP 3.82)/
Furnace (81% E t )
Packaged VAV/RH
DX Cool
(COP 3.4)/Elec RH
Packaged
VAV/RH DX Cool
(COP 3.83)/
Elec RH
Packaged
VAV/RH DX
Cool (COP 3.4)/
Gas Boiler
(75% E t )
Packaged
Air-Source
Heat Pump
(Cooling COP 3.0,
Heating COP 3.4)
Packaged
Air-Source Heat
Pump
(Cooling COP 3.82,
Heating COP 3.81)
Packaged
Air-Source AC
(COP 3.0)/Furnace
(80% E t )
VAV/RH
Packaged
Air-Source Heat
Pump (COP 3.4)
Packaged
Air-Source Heat
Pump
(Cooling COP 3.76,
Heating COP 3.54)
Packaged
Air-Source AC
(COP 3.5)/Furnace
(80% E t )
Packaged
Air-Source AC
(Cooling COP
3.76)/Furnace
(81% E t )
Water-Cooled
Chiller
(0.718 kW/ton);
Elec RH
VAV/RH
Water-Cooled
Chiller
(0.68 kW/Ton);
Elec RH
VAV/RH
Water-Cooled
Chiller
(0.718 kW/Ton);
Gas Boiler
(80% AFUE)
VAV/RH
Water-Cooled
Chiller
(0.68 kW/Ton);
Gas Boiler (80% E t )
Packaged Terminal
AC (COP 3.83)/
Furnace (80% E t )
Elec RH - Electric Reheat; VAV - Variable Air Volume; DX - Direct Expansion; AC - Air Conditioner;
COP - Coeffi cient of Performance; E t - Thermal Effi ciency; AFUE - Annual Fuel Utilization Effi ciency
O CTO B E R 2 0 2 3 ashrae.org ASHRAE JOURNAL
35
Packaged Terminal
AC (COP 3.2)/
Furnace (75% E t )
Packaged Terminal
AC (COP 3.2)/
Furnace (75% E t)
Split Air-Source
AC (COP 3.65)
Gas Furnace
(80% AFUE)
Packaged Terminal
Air-Source Heat
Pump (Cooling and
Heating COP 3.1)
Packaged Terminal
Air-Source Heat
Pump (Cooling COP
3.83, Heating COP
3.44)
Packaged Terminal
Air-Source Heat
Pump
(Cooling and
Heating COP 3.1)
Split Air-Source
Heat Pump
(Cooling COP 3.82,
Heating COP 3.86)
MEDIUM OFFICE
SMALL OFFICE
RETAIL
SCHOOL
HOTEL
APARTMENT
FIGURE 2 Using MPF to compare a proposed to a target HVAC system.
TARGET
REFERENCE
TARGET
REFERENCE
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ASHRAE Journal - October 2023

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