Trane BCHC User guide

Tube Size and Component Selection
for Systems Comprised of BCHC and BCVC Blower Coils, Paired
With R-410A Condensing Units and Heat Pump Units
Application Guide
May 2020 SS-APG010C-EN
SAFETY WARNING
Only qualified personnel should install and service the equipment. The installation, starting up, and servicing of
heating, ventilating, and air-conditioning equipment can be hazardous and requires specific knowledge and training.
Improperly installed, adjusted or altered equipment by an unqualified person could result in death or serious injury.
When working on the equipment, observe all precautions in the literature and on the tags, stickers, and labels that are
attached to the equipment.

SS-APG010C-EN © 2020 Trane. All Rights Reserved.
Warnings, Cautions and Notices
Warnings, Cautions and Notices. Note that warnings, cautions and notices appear at
appropriate intervals throughout this manual. Warnings are provided to alert installing contractors
to potential hazards that could result in personal injury or death. Cautions are designed to alert
personnel to hazardous situations that could result in personal injury, while notices indicate a
situation that could result in equipment or property-damage-only accidents.
Your personal safety and the proper operation of this machine depend upon the strict observance
of these precautions.
Important
Environmental Concerns!
Scientific research has shown that certain man-made chemicals can affect the earth's naturally
occurring stratospheric ozone layer when released to the atmosphere. In particular, several of the
identified chemicals that may affect the ozone layer are refrigerants that contain Chlorine, Fluorine
and Carbon (CFCs) and those containing Hydrogen, Chlorine, Fluorine and Carbon (HCFCs). Not all
refrigerants containing these compounds have the same potential impact to the environment.
Trane advocates the responsible handling of all refrigerants-including industry replacements for
CFCs such as HCFCs and HFCs.
Responsible Refrigerant Practices!
Trane believes that responsible refrigerant practices are important to the environment, our
customers, and the air conditioning industry. All technicians who handle refrigerants must be
certified. The Federal Clean Air Act (Section 608) sets forth the requirements for handling,
reclaiming, recovering and recycling of certain refrigerants and the equipment that is used in these
service procedures. In addition, some states or municipalities may have additional requirements
that must also be adhered to for responsible management of refrigerants. Know the applicable
laws and follow them.
WARNING
Personal Protective Equipment (PPE) Required!
Installing/servicing this unit could result in exposure to electrical, mechanical and chemical
hazards.
• Before installing/servicing this unit, technicians MUST put on all Personal Protective
Equipment (PPE) recommended for the work being undertaken. ALWAYS refer to appropriate
MSDS sheets and OSHA guidelines for proper PPE.
• When working with or around hazardous chemicals, ALWAYS refer to the appropriate MSDS
sheets and OSHA guidelines for information on allowable personal exposure levels, proper
respiratory protection and handling recommendations.
ATTENTION: Warnings, Cautions and Notices appear at appropriate sections throughout
this literature. Read these carefully.
WARNING: Indicates a potentially hazardous situation which, if not avoided, could
result in death or serious injury.
CAUTION: Indicates a potentially hazardous situation which, if not avoided, could
result in minor or moderate injury. It could also be used to alert against unsafe practices.
NOTICE:Indicates a situation that could result in equipment or property-damage-only
accidents.

ii SS-APG010C-EN
Warnings, Cautions and Notices
• If there is a risk of arc or flash, technicians MUST put on all necessary Personal Protective
Equipment (PPE) in accordance with NFPA70E for arc/flash protection PRIOR to servicing the
unit.
Failure to follow recommendations could result in death or serious injury.
WARNING
R-410A Refrigerant under Higher Pressure than R-22!
The unit described in this manual uses R-410A refrigerant which operates at higher pressures
than R-22 refrigerant. Use ONLY R-410A rated service equipment or components with this unit.
For specific handling concerns with R-410A, please contact your local Trane representative.
Failure to use R-410A rated service equipment or components could result in equipment or
components exploding under R-410A high pressures which could result in death, serious injury,
or equipment damage.

© 2020 Trane. All Rights Reserved SS-APG010C-EN
Introduction
This application guide provides refrigerant piping guidelines for Trane® split system outdoor unit
models ranging in capacity from 1.5 to 10 tons when matched to Trane® indoor models BCHC and
BCVC 024 through 090. Use the information presented here to properly select interconnecting
piping and refrigerant components for these systems.
These systems are designed and intended for the use of R-410A and POE oil. All components of the
system must also be designed and intended for R-410A and POE oil.
This publication also outlines an “envelope” of application that is based on the proximity of the
refrigerant components. The guidelines presented pertain specifically to the operating envelope
for standard air-conditioning applications that deliver either a constant or variable volume of
airflow and that provide no more than 45 percent ventilation (outdoor) air.
Prospective applications outside this operating envelope—including low-ambient, process, and
100-percent outdoor-air applications—must be reviewed by Trane to help ensure proper
performance.
WARNING
R-410A Refrigerant under Higher Pressure than R-22!
The unit described in this manual uses R-410A refrigerant which operates at higher pressures
than R-22 refrigerant. Use ONLY R-410A rated service equipment or components with this unit.
For specific handling concerns with R-410A, please contact your local Trane representative.
Failure to use R-410A rated service equipment or components could result in equipment or
components exploding under R-410A high pressures which could result in death, serious injury,
or equipment damage.
Trademarks
Trane and the Trane logo are trademarks of Trane in the United States and other countries. All
trademarks referenced in this document are the trademarks of their respective owners.

iv SS-APG010C-EN
Table of Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Updated Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Liquid Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Suction Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Equipment Placement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Line Sizing, Routing, and Component Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Liquid Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Line Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Routing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Insulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Gas Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Line Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Routing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Insulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Access Port . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Expansion Valves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Hot Gas Bypass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Refrigerant Piping Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Heat Pump and Blower Coil Matches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

SS-APG010C-EN 1
Overview
This guide should be used only for new systems design. It is not to aid with the remodel, retrofit,
or partial replacement of older systems. Older blower coils and heat pump systems were not
designed for the higher pressures of R-410A.
Trane’s 4TTA3, 4TWA3, 4TTB3 and 4TWB3 sizes 1-1/2 through 5 ton and TTA073D and TWA120D
sizes 5 through 10 ton cooling only and heat pump products have been matched to Trane® indoor
unit models BCHC and BCVC 024 through 090. Beginning mid-2009, the TTA and TWA 6- through
20-ton product line has been designed for use only with R-410A and POE oil (check unit model
number for specific refrigerant). R-410A is a high-pressure refrigerant that requires the other
components of the system to be rated for R-410A. For compressor lubrication, the refrigerant
requires POE oil.
Trane’s BCHC and BCVC 024-090 blower coil air handler products have also been redesigned for use
with the higher pressures of R-410A.
Traditionally, refrigerant piping practices were guided by four principles:
• Return the oil to the compressor.
• Maintain a column of liquid atthe expansion valve.
• Minimize the loss of capacity.
• Minimize the refrigerant charge in the system.
These piping practices are similar for R-410A and POE oil. However, because of the different mass
flows and pressures, the line diameter required to carry the oil and refrigerant may not be the same
as a similar tonnage R-22 unit. Also, the allowable pressure drop may be greater for R-410A than
R-22.
Evidence accumulated over years of observation demonstrates that the lower the refrigerant
charge, the more reliably a split air-conditioning system performs. Any amount of refrigerant in
excess of the minimum design charge becomes difficult to manage. The excess refrigerant tends
to collect in areas that can interfere with proper operation and eventually shortens the service life
of the system.
To successfully minimize the system refrigerant charge, the correct line size should be used and the
line length must be kept to a minimum.
Resources
This purpose of this Application Guide is to aid the designer in applying the 4TWA, 4TTA, TTA, and
TWA R-410A products with either BCHC or BCVC blower coils. For more information about the
outdoor units, refer to the following application guides:
•Refrigerant Piping Systems [32-3009-03; SS-APG006-EN]
•Tube Size and Component Selection for TTA and TWA Split Systems (6-20 Tons) Using
Refrigerant 410A [SS-APG008-EN]
Background
In a split air-conditioning system, the four major components of the refrigeration system are
connected by field-assembled refrigerant piping (Figure 1). A vapor or gas line connects the
evaporator to the compressor, the discharge line connects the compressor to the condenser, and
the liquid line connects the condenser to the expansion device, which is located near the
evaporator inlet. Operational problems can occur if these refrigerant lines are designed or installed
improperly.

2SS-APG010C-EN
Overview
Figure 1. Interconnecting refrigerant lines in a typical split air-conditioning system
The origin of the requirements for equivalent line lengths of components, line pressure drop, and
minimum and maximum refrigerant velocities is uncertain. It appears likely that at least some of
the supporting data was derived from measurements and/or equations involving water. Some
resource materials even show water components when illustrating refrigerant piping
requirements.
Subsequent reviews of analytical and empirical data for refrigerant piping resulted in the
publication of two research papers: Pressure Losses in Tubing, Pipe, and Fittings by R.J.S. Pigott
and Refrigerant Piping Systems—Refrigerants 12, 22, 500 by the American Society of
Refrigeration Engineers (ASRE). In his paper, Pigott described his use of refrigerant as the fluid
and his direct measurement of pressure drops. His findings indicated that the pressure drop of
many line components is small and difficult to measure. For these components, he used
experimental data to derive a formula relating the geometry of the component to its pressure
drop. Overall, his calculated pressure loss of the components was less than originally
determined.
The conclusion of the ASRE research paper stated that the minimum required velocity to
maintain oil entrainment in vertical risers and horizontal lines will vary with the diameter of the
tube and with the saturation temperature of the suction gas. In other words, the minimum
required velocity for oil entrainment is not constant.
Updated Guidelines
Liquid Lines
Historically, liquid lines were sized to minimize the pressure losses within the piping circuit. Oil
movement through the piping wasn’t a concern (nor is it today) because oil is miscible in liquid
refrigerant at normal liquid-line temperatures. The historic and traditional 6 psid liquid line
pressure drop had the unintended consequence of requiring line sizes with large internal
refrigerant volumes. Since our objective is also to minimize the refrigerant charge to make the
most reliable systems, we increased the allowable liquid pressure drop to 35 psid (R-22), which
allows for the selection of a smaller liquid line while still maintaining refrigeration operation.
vapor or gas
line

SS-APG010C-EN 3
Overview
With R-410A refrigerant and POE oil, this pressure drop can be as high as 50 psid. Within these
guidelines, refrigeration operation is maintained while minimizing the refrigerant charge. It is
still required to limit the liquid line velocity to 600 ft/min to help avoid issues with water hammer.
The liquid line sizes in the component section of this guide reflect these rules.
Suction Lines
R-410A is a high-pressure refrigerant and allows higher-pressure drops in the suction lines. With
R-22, a 2°F loss in the suction line means a pressure drop of 3 psi. With R-410A refrigerant, that
same 2°F loss is a 5 psi drop. Additional pressure drop may be tolerated in certain applications.
R-410A refrigerant suction lines must be sized to maintain oil-entrainment velocities in both the
horizontal and vertical risers. Oil entrainment for R-410A is based on suction temperature as well
as tube diameter. At the time of this writing, no known direct oil-entrainment tests have been
conducted. Trane has used ASHRAE data to create equation-based formulas to predict the
entrainment velocities of R-410A refrigerant and POE oil. These minimum velocities are reflected
in the line sizes listed in the component selection summary (Table 3, p. 16).
Equipment Placement
Minimize Distance Between Components
For a split air conditioning system to perform as reliably and inexpensively as possible, the
refrigerant charge must be kept to a minimum. To help accomplish this design goal:
• Site the outdoor unit (cooling-only condensing unit or heat pump) as close to the indoor unit
as possible.
• Route each interconnecting refrigerant line by the shortest and most direct path so that line
lengths and riser heights are no longer than absolutely necessary.
• Use only horizontal and vertical piping configurations.
Interconnecting lines of 150 lineal feet (45.7m) or less do not require Trane review, but be sure to
limit the length in risers.
Be sure to review the required accessories for long lengths.
Allowable Elevation Difference
An acceptable riser height represents the summation of all individual risers and is a function of the
total line length.
Outdoor unit above indoor unit. In this case, the velocity of the refrigerant must be sufficient
to force oil up the gas riser in order to maintain proper oil movement during cooling operation. The
gross height and line length for a heat pump in the heating mode must not cause a pressure drop
sufficient to cause excess loss of subcooling. Figure 2 and Figure 3 show the allowable gross rise
and run for TTA and TWA units, respectively. System designs outside the application envelopes
defined in the charts require Trane review.
Outdoor unit below indoor unit. In this case, the pressure drop and accompanying loss of
subcooling due to the total liquid-line length and lift limits the allowable gross lift. The velocity of
the refrigerant gas for a heat pump in the heating mode must be sufficient to force oil up the hot
gas riser in order to maintain proper oil movement. Figure 4 shows the allowable gross “rise and
run” for TTA and TWA units. System designs outside the application envelope defined in the chart
require Trane review.

4SS-APG010C-EN
Overview
Figure 2. Allowable elevation difference: R-410A cooling-only unit above indoor unit.
Figure 3. Allowable elevation difference: R-410A heat pump unit above indoor unit
Figure 4. Allowable elevation difference: R-410A cooling only or heat pump unit below indoor
unit
blower
coil
(4) TT
blower
coil
(4) TW
blower
coil
(4) TT or
(4) TW

SS-APG010C-EN 5
Line Sizing, Routing, and Component Selection
Figure 5 illustrates an example of a (4) TTA/TWA blower coil split system component arrangement.
Use it to determine the proper, relative sequence of the components in the refrigerant lines that
connect the (4) TTA/TWA outdoor unit to the blower coil. Refer to “Refrigerant Piping Examples,”
p. 12, for more detailed schematics of evaporator piping when a single-circuited blower coil is
piped to a single-circuited outdoor unit; when a dual-circuited blower coil is piped to two outdoor
units; or when a dual-circuited blower coil is piped to a single-circuited outdoor unit. All new (4)
TTA/TWA units and BCHC/BCVC units are R-410A products, and all the selected components
installed in the field must also be rated for use with R-410A.
Figure 5. Placement of liquid-line check valves in TWA heat-pump applications when paired
with a BCHC/BCVC blower coil (single circuit shown in heating mode)
Liquid Lines
Line Sizing
Properly sizing the liquid line is critical to a reliable split system application. Table 3, p. 16, shows
the recommended liquid-line sizing for each (4) TTA/TWA model based on its nominal capacity.
Using the preselected tube diameter will maximize the operating envelope and is the line size
around which the installation literature charging charts were generated. Increasing the line size will
not increase the allowable line length.
BCHC/BCVS unit
see INSET
INSET
Heat pump liquid line filters
check valve
check valve

6SS-APG010C-EN
Line Sizing, Routing, and Component Selection
Routing
Install the liquid line with a slight slope in the direction of flow so that it can be routed with the
suction line.
A height limitation exists for liquid lines that include a liquid riser because of the loss of subcooling
that accompanies the pressure loss in the height of the liquid column. Figure 2, Figure 3, and
Figure 4, p. 4, depict the permissible rise in the liquid line (without excessive loss of subcooling).
Again, system designs outside the application envelope of the TTA/TWA unit require Trane review.
Insulation
The liquid line is generally warmer than the surrounding air, so it does not require insulation. In
fact, heat loss from the liquid line improves system capacity because it provides additional
subcooling. If the liquid line is routed through a high temperature area, such as an attic or
mechanical room, insulation would be required.
Components
Liquid-line refrigerant components necessary for a successful job may include a filter drier, access
port, solenoid valve, moisture-indicating sight glass, expansion valve(s), and ball shutoff valves.
Figure 5, p. 5, illustrates how to sequence the components properly in the liquid line. Position the
components as close to the indoor unit as possible. Table 3, p. 16, identifies suitable components,
by part number, for each outdoor unit.
Liquid Filter Drier
There is no substitute for cleanliness during system installation. The liquid filter drier prevents
residual contaminants, introduced during installation, from entering the expansion valve and
solenoid valve. All outdoor units have a filter drier pre-installed. However, on the
6-, 7-1/2-, and 10-ton TTA/TWA units, if the refrigerant line length exceeds 80 ft, this filter should be
removed and a new one selected from Table 3, p. 16, and installed close to the indoor unit. Only
units this size require the filter to be moved because of their larger line sizes and greater amount
of introduced contaminants. If choosing a filter other than the one listed in Table 3, p. 16, make sure
its volume, filtering, and moisture-absorbing characteristics are equivalent.
Note that TWA units will require two filters and two check valves due to the reverse flow nature of
a heat pump.
Access Port
The access port located at the (4) TTA/TWA allows the unit to be charged with liquid refrigerant and
is used to determine charge level. This port is usually a Schraeder valve with a core.
Solenoid Valve
In (4) TTA cooling-only split systems, solenoid valves may be used to isolate the refrigerant from
the evaporator during the off cycles. This is only done when the indoor unit is well below the
outdoor unit. The solenoid valve on the TTA unit is a drop solenoid—open when the compressor
is on, and closed when the compressor is off. If used, the solenoid requires code compliant wiring
to the (4) TTA condensing unit. (The solenoid is not shown on the unit wiring diagram.)
Note: Solenoids should not be used on heat pumps due to the reverse flow of the liquid.
Moisture-Indicating Sightglass
A moisture-indicating sightglass should be installed in the main liquid line at the blower coil.
Note: The sole value of the glass is its moisture-indicating ability. Use the Installation manual
charging curves—not the sightglass—to determine proper charge levels.

SS-APG010C-EN 7
Line Sizing, Routing, and Component Selection
Expansion Valve
The expansion valve is the throttling device that meters the refrigerant into the evaporator coil.
Metering too much refrigerant floods the compressor; metering too little elevates the compressor
temperature. Choosing the correct size and type of expansion valve is critical to ensure that it will
correctly meter refrigerant into the evaporator coil throughout the entire operating envelope of the
system. Correct refrigerant distribution into the coil requires an expansion valve for each
distributor.
For improved modulation, choose expansion valves with balanced port construction and external
equalization. Table 4, p. 17, identifies the part number of the valve recommended for (4) TTA/TWA
systems.
The tonnage of the valve should represent the tonnage of the portion of coil that the TXV/distributor
will feed.
The expansion valve is inclusive on the outdoor (4) TWA units for reverse flow heat pump
operation.
Compressor Crankcase Heater
Smaller split systems may not ship with a compressor crankcase heater. For line lengths over 60
feet, compressor crankcase heaters are a requirement. Be sure to consult the product data
catalogue to determine if the crankcase heater ships with the unit. If it does not, a Trane field-
installed crankcase heater may be obtained from your local sales office.
Gas Line
Line Sizing
Proper line sizing is required to guarantee that the oil returns to the compressor throughout the
system’s operating envelope. At the same time, the line must be sized so that the pressure drop
does not excessively affect capacity or efficiency.
Note: Preselected suction-line diameters shown in Ta b l e 3, p. 16,are independent of total line
length for properly charged (4) TTA/TWA units in normal air-conditioning applications.
Routing
Route the line as straight (horizontally and vertically) as possible. Avoid unnecessary changes of
direction. To prevent residual or condensed refrigerant from “free-flowing” toward the
compressor, install the suction line so that it slopes by ¼ to 1 inch per 10 feet of run (1 cm per
3 m) toward the indoor coil.
Do not install riser traps. With two circuit blower coils and one circuit outdoor units, what appears
to be a riser trap is located at the coil outlet; see Figure 8, p. 14 for an example. This piping
arrangement, which isn’t a riser trap, is the result of two requirements:
• Drain the coil to the low point
• Rise at least 1 ft (30 cm) from the common low point to prevent anyoff-cycle condensed
refrigerant in the coil from attempting to flow to the compressor.
Double risers must not be installed. All (4) TTA and TWA units gas line size, preselected in Ta b l e 3 ,
p. 16, provides sufficient velocity to push entrained oil up the permissible riser height.
Note: If a gas riser is properly sized, oil will return to the compressor regardless of whether a trap
is present. If a gas riser is oversized, adding a trap will not restore proper oil entrainment.
Avoid Underground Refrigerant Lines
Refrigerant condensation during the off cycle, installation debris inside the line (including
condensed ambient moisture), service access, and abrasion/corrosion can quickly impair

8SS-APG010C-EN
Line Sizing, Routing, and Component Selection
reliability. R-410A is hygroscopic. Even small amounts of moisture in the system introduced during
installation can harm the compressor.
If refrigeration lines must be installed below grade, consult your local sales engineer, territory
manager, or field service representative.
Insulation
Any heat that transfers from the surrounding air to the cooler gas lines increases the load on the
condenser (reducing the system’s air-conditioning capacity) and promotes condensate formation.
After operating the system and testing all fittings and joints to verify that the system is leak-free,
insulate the gas lines to prevent heat gain and unwanted condensation.
Components
Adding a gas line filter is unnecessary—provided that good refrigeration practices (including
nitrogen sweeping during brazing and proper system evacuation) are followed.
Access Port
Providing an access port in the gas line permits the servicer to check refrigerant pressure and
determine superheat at the evaporator/indoor coil. Usually this port is a Schraeder valve with a
core.

SS-APG010C-EN 9
Expansion Valves
Expansion valves meter refrigerant into the evaporator under controlled conditions. If there is too
much refrigerant, the refrigerant will not completely vaporize and the remaining liquid will slug the
compressor. If there is too little refrigerant, there may not be enough cooling for the compressor.
Table 4, p. 17, lists expansion valves. Each evaporator distributor requires a dedicated expansion
valve in order to maintain proper coil distribution. The expansion valve should be selected to match
the capacity of the coil that the distributor feeds.
Example: 10-ton coil with two equal distributors
10 / 2 = 5
Each TXV should be selected for 5 tons.
The proper balance for feeding refrigerant for a (4) TTA/TWA system is to provide 18°F of
superheat—the difference between the saturated and actual refrigerant temperature leaving the
evaporator. Expansion valve superheat is preset from the factory, but it isn’t set to 18°F. Use the
turns listed in Tabl e 1 to adjust them to the correct 18°F superheat.
Table 1. Expansion valves
Sporlan
Standard off-the-shelf nominal valve settings (90 PSIG air test setting) Field adjust for 18°F
Valve Superheat, °F CW turns available CCW turns available Superheat change
per turn
ERZE 12 4.5 4.5 2.4°F 2 1/2 CW

10 SS-APG010C-EN
Controls
ReliaTel™ or thermostat control may be available on some model (4) TTA/TWA units. It is important
to understand that if the staging of compressors is turned over to a third party, the compressor
protection, provided through system stability, is also turned over to the third party. Simply stated,
this means that when a compressor turns on, it shouldn’t turn off until the expansion valve comes
under control. And, once the compressor turns off, it should be allowed to stay off until the
crankcase heater has warmed up, or if the system doesn’t have a crankcase heater, until the
compressor sump stabilizes.
System stability must be programmed in the third-party system control. To accomplish this, the
system controls must incorporate a 5-minute-on, a 5-minute-off, and a 5-minute-interstage
differential on each compressor stage.

SS-APG010C-EN 11
Hot Gas Bypass
Many years ago, hot gas bypass (HGBP) was successfully added to HVAC systems to correct a
number of operational problems. Hoping to avoid such problems altogether, it eventually became
common practice for designers to specify hot gas bypass in systems. Unfortunately, the practice
often degraded rather than improved reliability.
Hot gas bypass increases the minimum refrigerant charge; it also inflates the first cost of the
system. Besides adding more paths for potential refrigerant leaks, hot gas bypass increases the
likelihood of refrigerant distribution problems. Finally, hot gas bypass uses excessive amounts of
energy by preventing the compressors from cycling with fluctuating loads.
Trane now has several years of successful experience with Evaporator Defrost Control (EDC). Like
hot gas bypass, the EDC system protects the coil from freezing, but it does so by turning off
compressors when a sensor detects the formation of frost on the evaporator coil. The compressor
is released to operate when the coil temperature rises a few degrees above the frost threshold. The
EDC control strategy may reduce the overall energy consumption of the system while maintaining
system control.
Systems should be designed to avoid HGBP whenever possible.
For more information, refer to the Engineers Newsletter, “Hot Gas Bypass – Blessing or a Curse?”
(ADM-APM007-EN).

12 SS-APG010C-EN
Refrigerant Piping Examples
Figure 6. Indoor coil (non-TWE) with one distributor (single-circuit TTA/TWA units)
1Pitch the liquid line 1 inch per 10 feet (1 cm per
3 m) so that the liquid refrigerant drains toward
the indoor coil. Use the liquid-line size
recommended in Table 3, p. 16.
2Provide one expansion valve (TXV)
per distributor.
TWA heat pumps only: Provide one check
valve for each expansion valve.
3Pitch the gas line leaving the coil so that it
slopes away from the coil by 1 inch per 10 feet
(1 cm per 3 m).
4For vertical risers, use the tube diameter
recommended in Table 3, p. 16. Ensure that the
top of the riser is at least 1 foot (30 cm) above
the lowest point.
5Pitch the gas line 1 inch per 10 feet (1 cm per
3 m) toward the indoor coil.
6Insulate the gas line.

SS-APG010C-EN 13
Refrigerant Piping Examples
Figure 7. Indoor coil with two distributors (dual TTA/TWA units)
1Pitch the liquid line 1 inch per 10 feet (1 cm per
3 m) so that the liquid refrigerant drains
toward the indoor coil. Use the liquid-line size
recommended in Table 3, p. 16.
2Provide one expansion valve (TXV)
per distributor.
TWA heat pumps only: Provide one check
valve for each expansion valve.
3Pitch the gas line leaving the coil so that it
slopes away from the coil by 1 inch per 10 feet
(1 cm per 3 m).
4For vertical risers, use the tube diameter
recommended in Table 3, p. 16. Ensure that the
top of the riser is at least 1 foot (30 cm) above
the lowest point.
5Pitch the gas line 1 inch per 10 feet (1 cm per
3 m) toward the indoor coil.
6Insulate the gas line.
unit 2
unit 1

14 SS-APG010C-EN
Refrigerant Piping Examples
Figure 8. Indoor coil with two distributors (single-circuit TTA/TWA units)
1Pitch the liquid line 1 inch per 10 feet (1 cm per
3 m) so that the liquid refrigerant drains toward
the indoor coil. Use the liquid-line size
recommended in Table 3, p. 16.
2Provide one expansion valve (TXV)
per distributor.
TWA heat pumps only: Provide one check
valve for each expansion valve.
3Pitch the gas line leaving the coil so that it
slopes away from the coil by 1 inch per 10 feet
(1 cm per 3 m).
4Arrange the gas line so that suction gas leaving
the coil flows downward, past the lowest gas-
header outlet, before turning upward. Use a
double-elbow configuration on all lower branch
circuits to isolate the TXV bulb from suction-
header conditions. See “Gas Line: Routing,” p. 7.
5For all coil branch circuits in the gas line, use a
tube diameter that is one size smaller than the
gas-line size recommended in Table 3, p. 16.
6For vertical risers, use the tube diameter
recommended in Table 3, p. 16. Ensure that the
top of the riser is at least 1 foot (30 cm) above
the lowest point.
7Pitch the gas line by 1 inch per 10 feet (1 cm per
3 m) toward the indoor coil.
8Insulate the gas line.