ASHRAE Journal - January 2023 - 18

COLUMN ENGINEER'S NOTEBOOK
plan and figure out piping routes
that will comply with ASHRAE
Standard 15/California Mechanical
Code Chapter 11 refrigerant concentration
calculations. In multistory
applications, pipe chases are
often used, and those require real
thought. A pipe chase that a building
owner can actually live with almost
always needs to be larger and have
more access provisions than an
architect has planned.
While the pipe mounting and support
method are being determined,
with space allowed for insulation
(insulation can require more space
than you might expect), the first
question in a VRF piping chase layout
ought to be, " Is there physically
room to detect and repair a refrigerant
leak? " The second question
should be, " And how will the shaft
be accessed? " We've had to tear out
many walls over the years; and when
that will permit reasonable access,
the final results are usually okay.
When the piping happens to be
mounted to the wall that is available
to tear out, things don't go so well.
When a bosun's chair must be lowered
down the shaft or other vertical
access measures are needed, the
shaft design can be rather unfriendly
to an owner's long-term needs. If
nothing else, one approach is to
leave adequate space to abandon one
or more leaking vertical pipes and
install others to take their place.
A few piping details. Flare connections
are common-and of critical
importance. The degree of the flare
angle has to match the application
and refrigerant. An installing pipe
fitter either buys the right flare tool
(and learns to use it properly) or
buys the specific flare fitting ends to
braze onto the end of the refrigerant
18
ASHRAE JOURNAL ashrae.o rg
line. Pre-lube (on the nut side of the
piping flare, to permit tightening
without significant flare distortion)
and torque requirements are also
specific.
Some manufacturer's literature
actually recommends periodic
re-torqueing as a maintenance
function. Since the prevailing view
among service contractors is that
this is a " no win " situation (if there
is a leak after a re-torqueing exercise,
the contractor owns it), that is
clearly a pointless recommendation.
It is also important to recognize
that VRF piping wye and other fittings
are not the industry standard
(not on a typical supply house shelf)
and must be installed in a specific
orientation (Photo 1). Another thing
that is frequently missed is expansion
and contraction in long piping
runs. Check with the manufacturer
for how far a straight run can go
before needing an expansion joint
or loop of some sort.
Inverted traps to discourage liquid
(oil or refrigerant) transmission for
VRF system risers are similar to any
good DX piping practice, but condensing
units made up of multiple
smaller modules often have inverted
trap requirements of their own,
such as an inverted trap in any vapor
line between the modules if the line
length exceeds a specific length.
Vertical risers do not use traps.
Distribution Boxes
VRF systems have a device located
in the refrigerant piping between
the condensing units and the fan
coils. Each manufacturer uses a
somewhat different name for this
component, and they are not all
piped the same, but their general
function is to distribute liquid and
J A N U A RY 2023
PHOTO 1 VRF fittings.
vapor refrigerant where it needs to
go, depending upon the individual
fan coil's call for cooling or heating.
For the purposes of this discussion,
I'll refer to the component as a " distribution
box. " The original versions
of this component used solenoid
valves to direct flow. These were " on/
off " in their operation and tended to
make an audible " click " sound.
When open ceiling offices became
all the rage, we ended up having to
take special measures to deaden the
sound emanating from these distribution
boxes because it was quite
audible (not particularly loud, but
distinct) to building occupants. We
often ended up locating the distribution
boxes in less than ideal locations
(from a piping, access and expense
perspective) due to this issue, as well
as sometimes using various sounddeadening
insulation approaches.
I've seen many examples of the
boxes being located in places that
make service work difficult; good
access is needed to these distribution
boxes for diagnosis and repair
purposes. The inside of the box can
be pretty crowded and complex
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ASHRAE Journal - January 2023

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