ASHRAE Journal - January 2021 - 37

TECHNICAL FEATURE

92% of losses could be attributed to
catastrophic leaks, in which systems
lost 50% or more of their initial
charge.
The climate impacts of these losses
are signiﬁcant. Atmospheric concentrations of refrigerants, including both HFCs and older, ozonedepleting compounds phased out
under the 1987 Montreal Protocol, are
continuing to increase. The impacts
are so large that the nonproﬁt Project
Drawdown ranks refrigerant management among the most impactful
solutions for climate change.4
HFCs will eventually be replaced by
compounds with lower GWP; some
promising alternatives, including
CO2, R-32 and R-466a, are currently
in limited use. In addition, air-towater and ground-source systems
may gain market share versus directexchange ASHPs. In these systems,
water or an antifreeze solution is
used to transfer heat in and out of
the building, and the entire refrigerant circuit is contained within a single, factory-made unit. Compared to
a direct-exchange heat pump, these
systems contain less total refrigerant,
and all refrigerant connections are
made under factory conditions.
While new refrigerants and
technologies may reduce future
climate impacts, direct-exchange,
HFC-based heat pumps dominate
the present market, and reducing
losses from these systems is a critical short-term goal. Beyond climate
change, there are other reasons to be
concerned about refrigerant leaks.
Systems that are low on refrigerant
will run less efﬁciently and may be
unable to maintain comfort. Low
charge may lead to premature failure of system components, particularly compressors.

Left unaddressed, these problems
will reduce customer satisfaction and impede adoption of heat
pumps. Anecdotally, we know one
progressive developer who found
that 30% of the heat pumps in his
new multifamily building leaked
refrigerant. The issue was so bad, he
reported, that he was considering
electric baseboard heat instead of
heat pumps for future projects.
Our objectives in this article are to
provide technicians, engineers and
energy-efﬁciency programs with
best practices for reducing refrigerant leaks from ASHPs. We draw on
our experience as an installer and
an HVAC engineer, along with manufacturer's instructions and applicable standards and regulations.
We note areas in which existing
guidelines are vague, inconsistent or
impractical, and recommend standardizing both testing methods and
" pass/fail " criteria.

FIGURE 1 Air-source heat pumps.

FIGURE 2 Tightening a flare nut with a torque

wrench.

Installation
Refrigerant connections for small
inverter-driven ASHPs are typically
made using ﬂare joints. The ﬂaring
process begins with cutting tubing, leaving a few inches of slack in
case a ﬂare is defective and must be
remade. Use a good quality cutter,
work gradually to avoid deforming the tubing and inspect to make
sure that the cut is square. Debur to
remove the thin lip of copper inside
the tubing, but be careful not to
gouge or otherwise damage the tubing wall.
Some line sets come shipped from
the factory pre-ﬂared, but these
ﬂares are often damaged in transport; we recommend making new
ones.
Flaring itself involves site-forging

the end of the copper tubing into a
female cone, which ﬁts over a brass
male cone to form a mechanical
seal. To seal tightly, the ﬂare must be
of the correct dimensions. The ﬂare
angle, speciﬁed in the installation
instructions, is 45°; the size of the
cone varies with tubing diameter.
The ﬂaring tool grips the tubing
and rotates a steel cone around
the inside surface until it is fully
expanded.
Good-quality manual ﬂaring tools
have the following features:
¥ A gauge or stop that ensures
that tubing is positioned at the correct depth;

JAN UARY 2021

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ASHRAE Journal - January 2021

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