ASHRAE Journal - August 2014 - 59

Technical FeaTure
Fea

basis of design. That way, the engineer could accept New
York's chiller and make the contractor responsible to adjust
the pump selection, probably with a minor impeller size
change, to accommodate the contractor's preferred vendor.
§ Minnesota's chiller has a painted steel cabinet. The
others have painted or powder coated galvanized steel
cabinets. Is a galvanized steel substrate key to the success
of the job? It might be, if the chiller will be in a corrosive
environment like near water or in an industrial area. If
so, Minnesota is not equal, but the requirement for galvanized steel should be specified up front, not used as a
secret weapon to exclude Minnesota.
§ New York's condenser is aluminum tube with aluminum fins. Pennsylvania says its condenser tubes and
fins are of the same material to avoid galvanic corrosion but does not identify the material. Most likely it is
aluminum, but Pennsylvania would have to identify the
tube and fin material if submitted as an equal to New
York. What about Minnesota and Wisconsin with their
copper tube/aluminum fin condensers? Most engineers
would say copper tubes are better
than aluminum based on thermal
conductivity and ease of repair.
The long, successful history of copper tube/aluminum fin coils, both
evaporator and condenser, says that
the potential for galvanic corrosion
between those materials in air coil
applications should not disqualify
Minnesota and Wisconsin as equals.
§ New York's chiller requires a
minimum circuit ampacity (MCA)
of 155.7 amps and maximum
overcurrent protection (MOCP) of
175 amps. Pennsylvania's chiller
requires the next larger size circuit
(MCA of 179 amps/MOCP of 200
amps). If Pennsylvania is accepted
as equal, who pays for the increase
in electric circuit size, and who
pays for the additional design services to coordinate that circuit size
increase with the rest of the electrical system? To avoid a fight, the
specifications should say who bears
that responsibility. There is nothing wrong with assigning it to the

contractor or vendor who wants to use a product different from the basis of design. Of course, the engineer
might also decide that the complications of the electrical
change and required electrical design analysis mean
Pennsylvania is not equal in this case.

General Suggestions
The end suction pump and the air cooled chiller are
two examples of the situations engineers encounter
every day when they evaluate proposed equals. The
analysis presented in this article illustrates a thought
process engineers can use to help define what is "equal"
and determine whether a proposed product is "equal."
While engineers generally have broad discretion when
determining whether a submitted product is "equal," it
is important to exercise that discretion fairly and objectively. Here are some suggestions that apply to almost all
equipment:
§ Be sure the specifications match the basis of design,
and enforce the specs fairly and uniformly. Be clear,

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