ASHRAE Journal - April 2013 - 58

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dramatic. If for instance, large air-side
and (as applicable) water-side DTs can be
obtained, much more cooling can be done
with the same size of CRAH unit, and
less fan and pump power will be needed.
The number of hours of economizer
operation will also increase dramatically,
and in some climates, vapor-compression
cycles can be eliminated. The combination of high DT and compressor-less
heat rejection technologies could have a
dramatic impact on capital costs, in addition to the energy cost impact.
On the downside, there is an increased
risk of IT equipment failure with higher
inlet temperatures, but this risk can now
be quantified. In many climates, the elevated temperatures only occur for a few
hours per year, and the increased risk of
these short-term thermal excursions can
be offset by providing lower temperatures
at other times of the year.2

Chilled Water Supply Temperature

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58

ASHRAE Journal

Chilled water conditions were adjusted
in Standard 127-2012 to emphasize the
higher system efficiency that typically occurs when higher temperatures are used.
The 2007 standard used a temperature
of 45°F (7.2°C) as the basis for rating,
and 50°F (10°C) as the basis for energy
calculations at part-load conditions. The
2012 standard assumes that the 50°F
(10°C) entering chilled water is used for
the design rating, as well as the energy
ratings.
When referencing only the Class 1
return air condition, a given CRAH unit
will have a reduced capacity when rated
per Standard 127-2012 than when rated
per Standard 127-2007. However, when
referencing the same unit’s capacity at
Classes 2, 3, and 4 (assuming that the
same model can operate at these higher
return air temperatures), the unit’s rated
capacity will be greater than the Standard
127-2007 rating.
This increase in capacity occurs
because the differential temperature
between the supply water temperature
and the return air temperature will be significantly greater, allowing for increased
air-side DT. For both the 2007 and the
2012 standards, the chilled water DT for
rating purposes is set at 12°F (6.7°C), but

most manufacturers can provide ratings at
higher water-side DT if desired.

iNSenCOP, Weighted Metric
A new “normalized” or “weighted”
efficiency rating was created to provide
a single efficiency number, thus simplifying the comparison of similar units. The
raw numbers were retained, however, so
engineers could continue to calculate
the unit’s efficiency at any geographic
location.
The new rating is called the Integrated
Net Sensible Rating (iNSenCOP). The
calculation of the iNSenCOP for each
type of equipment is, in turn, a function
of the efficiency of the unit (NSenCOP)
at specific ambient conditions.
The general form of the equation for
the calculation of the iNSenCOP is:
iNSenCOP = (0.134 × Test A NSenCOP)
+ (0.271 × Test B NSenCOP) + (0.381
× Test C NSenCOP) + (0.215 × Test D
NSenCOP)
For instance, per Table 1 of the 2012
standard, for equipment with a remote aircooled condenser, the iNSenCOP would
take the following form:
iNSenCOP = (0.134 × NSenCOP at
95°F) + (0.271 × NSenCOP at 80°F) +
(0.381 × NSenCOP at 65°F) + (0.215
× NSenCOP at 40°F)

Normalization of Ancillary Equipment
Normalized values were provided for
fluid coolers, fluid cooler pumps, and
chilled-water-loop pumps, so all technologies could be more easily compared.
For instance, pump power is now added to
unit total consumption for chilled water
air-handling units.

Future Work for Standard 127
The changes incorporated in the 2012
revision to Standard 127 are reflective of
return air conditions corresponding to the
recommended and allowable ranges of
the 2009 edition of Thermal Guidelines
for Data Processing Environments for
ITE Classes 1 and 2. Since that time,
changes have continued to occur:
• As indicated previously, new A3
and A4 ITE Equipment Classes have
allowable inlet conditions as high as
April 2013
ASHRAE Journal - April 2013

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