ASHRAE Journal - February 2014 - 69

COLUMN ENERGY MODELING

Baseline Service Hot Water Systems are now defined
in a table. Based on the building type, a type of water
heating system, gas or electric resistance, is assigned for
the baseline building. The minimum efficiencies of the
type specified are to be modeled for the service hot water
system.
The number of Baseline HVAC Systems has increased
from 10 to 13. The three new systems are single zone VAV,
single zone constant volume using chilled water and
heating water, and single zone constant volume using
chilled water and electric resistance heat. Furthermore,
the method of selecting the baseline HVAC system has
been redefined to be more specific to building types.
Additional requirements have been added for public
assembly facilities and retail spaces.
An additional section has been added for Modeling
Building Envelope Infiltration. Depending on the
method used to determine infiltration (i.e., function
of the floor area, exterior wall area, or when using the
measured air leakage rate of the building envelope at a
pressure differential of 0.3 in. w.c. (74 Pa), a formula has
been provided to calculate a more definite value.

Baseline HVAC Efficiencies are now required to be
modeled in both full load and part load. For Systems 1
through 6, additional formulas have been provided for
calculating the COP of cooling and heating.
Economizers for computer rooms are now required for
select systems. Furthermore, if planning to increase the
system efficiency to exempt the economizer requirement
for the proposed building, be sure to look at the new
increased requirements for this system. Several of the
climate zones received a substantial increase to the efficiency to successfully comply with this exemption.
Requirements for Dehumidification in the baseline
HVAC system are included for when used in the proposed building. This only applies to Systems 3 through 8.
Although this does not contain all of the changes
reflected in the newest version of the performance rating
method, it certainly gives the impression to determine
the new requirements before starting a new model. In
addition to all of the changes listed in Appendix G, be
sure to go through all of the technical sections to determine what has been modified in both the mandatory
requirements as well as the prescriptive sections.

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FEBRUARY 2014

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ASHRAE Journal - February 2014

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