43
UNLOADING CONSIDERATIONS
Direct expansion coils can have two intertwined refrigerant cir-
cuits. In addition, quarter, half, full and double circuiting configu-
rations are offered to allow optimum system performance and oil
return at full and part-load operation.
Circuiting selection should result in a circuit loading of 0.8 to 2.0
tons per circuit at design load. Circuit loading must be evaluated at
minimum load to ensure that it does not drop below 0.6 tons per
circuit. Solenoid valves may be used, if necessary, to shut off the
refrigerant supply to individual expansion valves to maintain ade-
quate coil circuit loading.
Compressor minimum unloading and TXV quantity is necessary
to determine minimum tonnage per circuit.
Minimum Unloading Equation:
Example:
Condensing Unit:
38ARS012
Minimum Unloading:
33%
Coil:
6 row, 11 FPI, Half Circuit
Coil Tons/Circuit:
1.68
Total TXVs:
2
In the first example we will determine the tons/circuit when both
TXVs are active and the compressor is unloaded to its minimum
of 33%.
= .55 tons/circuit at minimum unloading UNACCEPTABLE
If we install a liquid line solenoid valve before one of the TXVs
and close it so that only one TXV is active when the compressor is
unloaded to its minimum of 33%, we see the following:
= 1.10 tons/circuit at minimum unloading ACCEPTABLE
SPECIAL PIPING WITH 4 SPLITS PER COIL
Manifolding for 2-Face Splits
Refer to Fig. 45 and externally manifold as follows:
1. Connect the 4 expansion valves to the 4 distributors on each
coil and connect the 4 suction lines to the 15-diameter-long
risers as outlined in previous piping instructions.
2. Install common liquid line for upper face split to first
(upper) and second expansion valves. Also, install a common
suction line from suction lines attached to first (upper) and
second suction header connections.
3. Repeat Step 2 for lower face split using third and fourth dis-
tributor and suction connections.
Manifolding for 2-Row Splits
Refer to Fig. 46 and externally manifold as outlined for the 2-face
splits with the following exceptions:
1. Manifold in pairs, the first and third coil connections for one
split.
2. Manifold the second and fourth pairs of coil connections for
the other split.
NOTE: Split section using first and third pairs of coil connections
should be
first on, last off
for coils with right hand (facing direc-
tion of airflow) connections and the reverse for left hand connec-
tions.
Hot Gas Bypass Connection with 4 Splits per Coil
For either face or row splits connect a hot gas bypass auxiliary
side connector to each distributor of coil split that is
first on, last
off.
Refer to installation instructions for Hot Gas Bypass.
(Tons/Circuit) x (Minimum Unloading)
x (Total # of TXVs)
# of TXVs Active
=
(1.68 Tons/Circuit) x (33% Minimum Unloading)
x (2 TXVs)
2 TXVs Active
=
(1.68) x (.33) x (2)
2
=
(1.68 Tons/Circuit) x (33% Minimum Unloading)
x (2 TXVs)
1 TXV Active
=
(1.68) x (.33) x (2)
1