USE OM - JANUARY 2017
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6.2
Temperature Measurement Requirements:
6.2.1
Temperature measurements shall be taken per the latest edition of ASHRAE Standard 41.1.
6.2.2
Temperature measurements shall be taken using the preferred method of refrigerant temperature
measurement (resistance temperature devices (RTDs) per ASHRAE Standard 41.1 Section 8.1). If used, RTDs
shall be installed with tubing arrangement such that pressure drops due to application do not exceed 0.5 psig.
6.2.3
When thermocouples (TC) are used for measurement of refrigerant temperature by application to the
outside of tubing, the following requirements shall be met:
6.2.3.1
TC material used shall have special limits of error of 0.75°F or less.
6.2.3.2
Two (2) TCs (for each liquid and vapor, total of four) shall be applied within 3 inches
of each other, with one TC at the
10 o’clock position and one TC at the 2 o’clock position, as there may
be oil in the lower half. Each TC shall be measured individually. Average of the two temperatures on
each liquid and vapor line shall be used for calculations.
6.2.3.3
Each and every TC shall be applied to the tubes per ASHRAE Standard 41.1 Section
10. This entails ensuring that:
There are no more than three (3) turns of wires contacting each other;
T
he wires are ‘tinned’ or soldered together before application to the tube;
The wires are secured to the tube via soldering or welding (without burning
insulation or melting wire); and
The wires outside of the joint described in Section 6.2.3.3.3
are prevented from
touching each other or other metallic surfaces, preferably by applying electrical
tape between the wire and the tube outside of the solder bed.
6.2.3.4
Each and every TC shall be applied per ASHRAE Standard 41.1 Section 8.2, having
insulation with R-value of at least 3.1, extending along the tube for at least six (6) inches on either side
of the TC.
6.2.4
TCs shall be applied at the exiting side of the refrigerant mass flow meter assembly. For heat pumps,
this means both sides of the refrigerant mass flow meter assembly shall have TCs applied.
6.2.5
It is preferred, but not required, that TCs are individually calibrated per ASHRAE Standard 41.1 Section
10.
6.3
Refrigerant Mass Flow/Refrigerant Properties
6.3.1
Use NIST REF PROP 7.0 or higher for reference to refrigerant properties (saturated and enthalpies)
6.3.2
Refrigerant mass flow rate calculation must account for the mass flow rate of oil in the refrigerant line,
as oil contributes to the mass flow rate but not productive heat transfer.
6.3.2.1
If the quantity of oil circulating is not measured, a 1.0% oil circulation rate shall be
assumed (
x
= 0.99)
6.3.2.2
If the quantity of oil circulation is measured, the calculation shall follow ASHRAE
Standard 37, Section 7.5.2.3.
6.3.3
Mass flow rates must be measured by equipment meeting ASHRAE Standard 41.10 requirements.
