2005 piping guide ss-apg002-en

8/6/2019 2005 Piping Guide SS-APG002-En

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Applications

Guide

Tube Size andComponent Selectionfor TTA and TWA Split Systems(7.520 Tons)

May 2005 SS-APG002-EN


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Preface

2005 American Standard All rights reserved Tube Size and Component Selection for TTA and TWA Split Systems (7.520 Tons) SS-APG002-EN

Trane, in proposing these system design and application concepts, assumes no

responsibility for the performance or desirability of any resulting system design. Design of

the HVAC system is the prerogative and responsibility of the engineering professional.

Trane and the Trane logo are registered trademarks of Trane, which is a business of

American Standard Companies.

This application guide provides design engineers and mechanical contractors

with refrigerant piping guidelines for Trane 7.5- through 20-ton split air-

conditioning systems. These guidelines specifically address Model TTA

cooling-only units and Model TWA heat pumps, when used with matching

Model TWE air handlers or matching Trane coils. Use the information

presented here to properly select interconnecting piping and components for

these systems.

This publication also outlines an envelope of component proximity for

standard comfort air-conditioning applications. Applications that exceed this

envelope, as well as non-standard comfort-cooling applications, must be

reviewed by Trane to help assure proper performance.


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SS-APG002-EN Tube Size and Component Selection for TTA and TWA Split Systems (7.520 Tons) 3

Contents

Overview .......................................................................................................... 4Background .................................................................................................. 4

Whats changed ............................................................................................ 5

Smaller liquid lines ................................................................................ 5

Effect on gas-line sizes .......................................................................... 7

Hot gas bypass in comfort-cooling applications ................................. 7

Equipment placement ........................................................................... 8

Liquid-line refrigerant management .................................................. 10

Tube Size and Component Selection ...................................................... 12Liquid lines ................................................................................................. 12

Line sizing ............................................................................................ 12

Routing ................................................................................................. 12Insulation .............................................................................................. 12

Components ......................................................................................... 12

Gas lines ..................................................................................................... 13

Line sizing ............................................................................................ 13

Routing ................................................................................................. 14

Insulation .............................................................................................. 14

Components ......................................................................................... 14

Refrigerant Piping Examples ..................................................................... 15

Illustrations

1 Interconnecting refrigerant lines in a typical split system ................. 5

2 Allowable elevation difference: TTA aboveindoor unit .................... 9

3 Allowable elevation difference: TWA aboveindoor unit ................... 9

4 Allowable elevation difference: TTA or TWA belowindoor unit ...... 9

5 Liquid line elevated above outdoor and/or indoor units .................. 10

6 Liquid-line check-valve placement in heat-pump applications ........ 11

7 Gas-line arrangement at the outlet of a field-supplied indoor coil . 14

8 Typical piping: TTA cooling-only unit and TWE air handler ............ 15

9 Typical piping: TTA cooling-only unit and matched indoor coil ..... 15

10 Typical piping: TWA heat pump and TWE air handler ..................... 16

11 Typical piping: TWA heat pump and matched indoor coil .............. 16

12 Indoor coil with one distributor (single-circuit TTA/TWA units) ...... 17

13 Indoor coil with two distributors (single-circuit TTA/TWA units) .... 18

14 Indoor coil with two distributors (dual-circuit TTA/TWA units) ....... 19

15 Indoor coil with four distributors (dual-circuit TTA/TWA units) ...... 20

Tables

1 Recommendations for refrigerant-piping components ...................... 6

2 Recommendations for expansion valves and indoor check valves ... 6


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4 Tube Size and Component Selection for TTA and TWA Split Systems (7.5 20 Tons) SS-APG002-EN

Overview

Nothing is permanent except change.

Heraclitus of Ephesus, Greek philosopher, 513 B.C.

The refrigerant piping rules for split air-conditioning systems are no

exception to this maxim. Traditional practice was guided by three underlying

objectives:

Make sure that oil returns to the compressor.

Maintain a continuous column of liquid refrigerant at the

expansion valve.

Minimize capacity loss.

Decades of practical experience helped us identify another important goal:

Minimize the refrigerant charge in the system.

Evidence accumulated over years of observation demonstrates that the

lower the refrigerant charge, the more reliably a split air-conditioning system

performs. Anyamount 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.

Reevaluating traditional practice in the context of minimizing the refrigerant

charge led us to refine our recommendations for split-system refrigerant

piping. The current recommendations not only enable reliable operation, butalso simplify the design of the system and lower its initial cost.

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 suction 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 typically located

near the evaporator inlet. Operational problems can occur if these refrigerant

lines are designed or installed improperly.

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 showwater 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 Fittingsby R.J.S. Pigott and Refrigerant Piping Systems

A 2001 Trane Engineers Newsletter

revisits the fundamental rules for

refrigerant piping in light of scrollcompressor technology. You can find this

article, titled As Equipment Evolves, So

Must Piping Practices: Split Systems and

Interconnecting Refrigerant Lines, at

http://www.trane.com/commercial/

library/vol274/en274.pdf.


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Overview


Refrigerants 12, 22, 500by the American Society of Refrigeration Engineers

(ASRE). In his paper, Mr. 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 thesuction gas. In other words, the minimum required velocity for oil

entrainment is not constant.

Whats changed

Smaller liquid lines

Historically, liquid lines were sized to minimize the pressure losses within the

piping circuit. Oil movement through the piping wasnt a concern (nor is it

today) because oil is miscible in liquid refrigerant at normal liquid-line

temperatures. Consequently, designers often attempted to make more liquid

refrigerant available at the thermal expansion valve (TXV) at a wider range of

operating conditions by increasing the size of the liquid line. Ironically, the

condensers response to the oversized liquid lines actually reducedthe

subcooling available at the TXV.

Focusing instead on minimizing the liquid-line charge would prompt

selection of the smallest liquid-line diameter that maintains subcooling at the

TXV throughout the systems operating envelope. This line-sizing strategy

would almost certainly increase the pressure drop; it also would use more

(not all) of the available subcooling.

Figure 1. Interconnecting refrigerant lines in a typical split air-conditioning system


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Overview

Table 1. Recommendations for refrigerant-piping components

TTA090A,

TWA090A

TTA120A,

TWA120A

TTA120Ba

a Be sure to double the component quantities listed above for the following units, which contain two refrigerant circuits: TTA120B, 150B, 180B, and 240B cooling-

only units, and TWA180B and 240B heat pumps.

TTA120C TTA150B a TTA180B,

TWA180B aTTA180C TTA240B,

TWA240B a

Refrigerant circuits 1 1 2 1 2 2 1 2

Minimum unloading 7.5 tons 10 tons 5 tons 5 tons 6.25 tons 7.5 tons 7.5 tons 10 tons

GAS LINE

Tube size (OD)b

b Line sizes shown apply when the total line length and rise complies with the allowable limits for gas lines (Figure 2 or Figure 3, p. 9) and liquid lines (Figure 4, p. 9).

If the piping layout exceeds either of these limits, ask your local Trane office to review the application.

1-3/8 inch 1-3/8 inch 1-1/8 inch 1-3/8 inch 1-3/8 inch 1-3/8 inch 1-5/8 inch 1-3/8 inch

Access port Schraeder

valve w/core

Schraeder

valve w/core

Schraeder

valve w/core

Schraeder

valve w/core

Schraeder

valve w/core

Schraeder

valve w/core

Schraeder

valve w/core

Schraeder

valve w/core

LIQUID LINE

Tube size (OD)b 1/2 inch 1/2 inch 3/8 inch 1/2 inch 1/2 inch 1/2 inch 5/8 inch 1/2 inch

Filter drierc

c A liquid-line filter drier is factory-installed in each refrigerant circuit of a TTA or TWA unit. If a filter drier is installed elsewhere in the liquid line, be sure to remove

the factory-supplied filter from the TTA/TWA. See pp. 1213 for more information.

TTA:

DHY01123

TTA:

DHY01123

TTA:

DHY01123

TTA:

DHY01123

TTA:

DHY01123

TTA:

DHY01123

TTA:

DHY01123

TTA:

DHY01123

TWA:

DHY01091

TWA:

DHY01091

TWA:

DHY01091

TWA:

DHY01091Access port (1 per ckt) Schraeder

valve w/core

Schraeder

valve w/core

Schraeder

valve w/core

Schraeder

valve w/core

Schraeder

valve w/core

Schraeder

valve w/core

Schraeder

valve w/core

Schraeder

valve w/core

Check valve (TTA

cooling-only units)d

d In an application that pairs a TWA heat pump with an indoor coil (rather than a TWE air handler), provide a check valve (Table 2 below) for each expansion valve

at the indoor coil. See Figure 11 (p. 16) for placement.

VAL08460 VAL08460 VAL08460e

e Reducers are required to install this check valve because it is one size larger than the liquid line.

VAL08460 VAL08460 VAL08460 VAL07030e VAL08460

Moisture-indicating

sight glass (1 per ckt)

GLS00853 GLS00853 GLS00852 GLS00853 GLS00853 GLS00853 GLS00830 GLS00853

Expansion valved See Table 2 (below)

DISCHARGE LINE

Tube size (OD) 7/8 inch 7/8 inch 5/8 inch 7/8 inch 3/4 inch 5/8 inch 7/8 inch 7/8 inch

Table 2. Recommendations for expansion valves and indoor check valves used in

TTA/TWA applications when not paired with a TW E air handlera

a Trane factory-installs the expansion valves for the indoor coil in a TWE air handler.

Indoor coil capacityb

b Choose an expansion valve that matches the tonnage of the coil distributor it serves.

Recommended Trane part

Expansion valvec

c Provide and install one expansion valve per distributor.

Indoor check valved

d For TWA heat pumps, but only when paired with an indoor coil (not a TWE air handler); see Figure 6 (p. 11).

3 tons VAL07364 VAL08459 for

3/8-inch OD liquid line

VAL08460 for

1/2-inch OD liquid line

5 tons VAL07074

7.5 tons VAL07075

10 tons VAL07076

15 tons VAL02824


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Overview


The liquid-line sizes recommended in Table 1 optimize the tradeoff between

pressure loss and refrigerant charge. These recommendations maximize the

system operating envelope and provide a subcooling safety factor of 5F

(2.7C).

Effect on gas-line sizes

Traditionally, gas lines were sized to maintain oil-entrainment velocities

greater than 500 ft/min. (152 m/min.) in horizontal lines and 1000 ft/min.

(305 m/min.) in vertical lines; andto limit pressure drops to not more than

3 psi (20 kPa) in the suction line and 6 psi (40 kPa) in the discharge line.

We now know that oil-entrainment velocity depends on line size and the

saturated suction temperature. Although a maximum suction-line pressure

drop of 3 psi (20 kPa) is a valid goal, the corresponding loss in capacity for

matched Trane split systems is only about 3 percent, for an additional 3 psi(20 kPa).1 Pressure drop in the suction-turned-discharge line of a heat pump

is of no consequence because the line is slightly oversized.

Hot gas bypass in comfort-cooling applications

When diminishing loads force a refrigeration system to operate at unstable

conditions, compressor and evaporator capacities balance at ever lower

suction pressures and temperatures. Unchecked, the eventual result is coil

frosting and compressor flooding.

Hot gas bypass (HGBP) can stabilize the system balance point by diverting

hot, high-pressure refrigerant vapor from the discharge line directly to the

low-pressure side of the system. This tactic keeps the compressor more fullyloaded while the evaporator satisfies the part-load condition. Also, the

diverted vapor raises the suction temperature, which prevents frost from

forming.

For decades HGBP was applied in direct-expansion refrigerating systems to

control capacity at low loads. It was probably conceived to correct a job-

specific problem but was subsequently, and indiscriminately, added to HVAC

systems as a preventive measure. HGBP hasprovided frost control and some

semblance of capacity control in many applications. But in numerous cases,

HGBP failed to safely stabilize the system. Worse still, the increased

refrigerant charge and additional piping often led to insufficient oil return and

refrigerant logging in the HGBP line, undermining reliable operation.

Economically, HGBP increases the cost of the system and its installation.

Hot gas bypass also uses large amounts of energy because it prevents the

compressors from cycling off as the cooling load decreases.

Evaporator defrost control (EDC) provides an effective alternative to HGBP.

Like hot gas bypass, EDC protects the coil from freezing, but it does so by

turning off compressors when frost is detected on the coil. The compressors

1 In this case, a matched Trane split system pairs a TTA cooling-only unit or a TWA heat pump with a

TWE air handler or a Trane indoor coil.

For a further discussion of what hot gas

bypass does and the inherent challenges

of implementing it effectively, refer to

the 2003 Engineers Newsletter, Hot GasBypass: Blessing or Curse? You can find

it online at http://www.trane.com/

commercial/library/vol32_2/

adm_apn007_en_0503.pdf.


8/20


Overview

are allowed to resume operation when the coil temperature rises sufficiently.

The EDC strategy reduces the systems overall energy consumption while

preventing the system from operating during coil-icing conditions.

Only use hot gas bypass if all other design options fail to meet the demands

of the application. Do NOT use hot gas bypass in heat pump applications.

Heat pump reliability is particularly susceptible to improper refrigerant

management.

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.

Determine whether the total length of each refrigerant line requires Trane

review. Be sure to account for the difference in elevations of the indoor

and outdoor unitswhen calculating the total line length.

Interconnecting lines of 150 lineal feet (45.7 m) or less do not requireTrane review, but be sure to limit the length in risers.

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

gas must be sufficient to force oil up the suction-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 modemust not cause a pressure drop

sufficient to cause loss of subcooling. Figure 2 and Figure 3 show the

allowable gross rise and run for TTA and TWA units, respectively. Systemdesigns 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 modemust 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.

Heat pump considerations

Heat-pump systems switch from cooling

to heating by reversing the direction of

refrigerant flow. When the cooling

suction line becomes the heating

discharge line, what was a suction-line

drop becomes a discharge-line rise.

During heating, the refrigerant flow rate

through the suction-turned-discharge

line decreases due to reduced heating

capacity and higher pressure in the line.

It is important to account for this fact

when sizing refrigerant piping for split

heat-pump systems. Choose a line size

that entrains oil in the refrigerant during

cooling and heating. The line sizes

specified in Table 1 (p. 6) enable proper

oil entrainment during both modes

within the piping limitations outlined in

Figure 2, Figure 3, and Figure 4 (p. 9).

Under normal circumstances, the liquid-

line rise during cooling will restrict the

discharge-line rise during heating.


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Overview


Figure 2. Allowable elevation difference: Cooling-only TTA above indoor unit

Figure 3. Allowable elevation difference: TWA heat pump above indoor unit

Figure 4. Allowable elevation difference: TTA or TWA be low indoor unit


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Overview

Liquid-line refrigerant management

In applications where any part of the liquid line is above the indoor and/or

outdoor unit (Figure 5), gravity will draw the liquid in that part of the line

down toward the unit(s) below when the system turns off. Do not confuse

this liquid flow with refrigerant migration. Crankcase heaters are installed on

compressors to prevent migration, but these heaters are not sized to prevent

refrigerant flow (due to gravity) from accumulating in the compressors. The

amount of liquid refrigerant that flows into either the indoor or outdoor unit,

while off, will determine the severity of liquid slugs and lubrication issues

faced by the compressor when it starts.

TWA heat pumps and TWE air handlers are equipped with valves that close

to prevent off-cycle flow; these units do not require additional shutoff valves.

However, TTA cooling-only units, when matched with indoor air handlers

other than TWE models, mayrequire shutoff valves to manage liquidrefrigerant when the system is off. Type, use, and placement of these valves

will depend on the gross line length andon the orientation of the liquid line

with respect to the indoor and outdoor units.

Liquid line above indoor unit. When using a non-TWE air handler or coil, use

hard-shutoff thermal expansion valves (TXVs) at the indoor unit for both TTA

and TWA applications; see Table 2 (p. 6) for recommendations. Heat pump

(TWA) applications also will require a check valve at the indoor unit to handle

reverse refrigerant flow during heating (Figure 6). TWE air handlers include

hard-shutoff valves and check valves as standard, factory-provided

components.

Figure 5. Liquid line elevated above outdoor and/ or indoor units


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Overview


Liquid line above outdoor unit: Cooling-only applications. If 50 ft (15 m) or

more of the liquid line is elevated above the cooling-only TTA unit (Figure 5),

install a check valve in the liquid line where the line leaves the TTA (Figure 8

and Figure 9, p. 15).

Note: This check valve is factory-installed in TWA heat pumps to allow proper

reverse flow of refrigerant.

WARNING!Redundant Valves Can Cause Hazardous Pressures!

Liquid refrigerant trapped between two valves can become highlypressurized if the ambient temperature increases. Do not add a liquid-line

solenoid valve in a cooling-only system that is already equipped with a check

valve. Failure to heed this precaution could result in a refrigerant-line rupture

that causes death or serious injury.

Figure 6. Placement of liquid-line check valves in TWA heat-pump applications

when no t paired with a TW E air handler (single circuit shown in heating mode)

Installation notes:

1 Provide one thermal expansion valve

(TXV) and one check valve for each

indoor-coil distributor. See Table 1 (p. 6)

for recommendations.

2 For applications where the length of the

liquid line exceeds 80 ft (24 m) and the

heat pump will start in the cooling

mode, remove the liquid-line filter

driers from the TWA and install a

new bidirectional filter drier at the

indoor unit. See Table 1 (p. 6) for

recommendations.


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Tube Size andComponent Selection

Liquid lines

Line sizing

Proper liquid-line sizing is critical to a successful application. The line

diameter must provide at least 5F (2.7C) of subcooling at the expansion

valve throughout the units operating envelope. Increasing the size of the

liquid line will notincrease the available subcooling.

Table 1 (p. 6) shows the recommended liquid-line sizing for each TTA/TWA

model based on nominal capacity. Using the preselected line diameter will

help to maintain the minimum required subcooling and minimize the system

refrigerant charge.

Note: The preselected line diameters in Table 1 are optimized for any

acceptable length or rise of refrigerant piping.

Routing

Install the liquid line with a slight slope in the direction of flow (during

cooling operation for heat pumps) so that it can be routed with the gas line.

Route the lines as straight, horizontally and vertically, as possible. Avoid

unnecessary changes of direction.

Insulation

To prevent the liquid refrigerant from flashing, insulate the liquid line if it

passes through an area that is warmer than the line.

Components

Several field-supplied components (Table 1, p. 6) may be required in the

liquid line: a filter drier, access port, check valve, moisture-indicating sight

glass, and expansion valve(s). These devices must be arranged in the proper

sequence; refer to the illustrations in Refrigerant Piping Examples (pp. 15

20). Position the components as close to the indoor unit as possible, but with

one notable exception: The liquid-line check valve used with TTA cooling-

only units must be installed at the TTA.

Filter drier. Each TTA or TWA is factory-equipped with liquid-line filter drier(s)

to capture residual contaminants from the installation process. However, the

presence of a filter drier is not a substitute for good brazing practices nor

proper evacuation. Reliable operation demands careful attention to

cleanliness during system installation.

If the TTA/TWA will start in the cooling mode and if the gross line length

exceeds 80 ft (24 m), remove the filter drier(s) from the outdoor unit and

The video, Split System Refrigerant

Piping Design (APP-APV009-EN),

discusses the relationship between

refrigerant-line sizing and subcooling in

greater detail. For ordering information,

visit www.trane.com/bookstore.


13/20

Tube Size and Component Selection


install new filter drier(s) at the indoor unit. Note that heat-pump applications

require a bidirectional filter drier.

Access port. The access port enables refrigerant charging; it also provides a

means for measuring the pressures that are used to calculate subcooling.

Usually this port is a Schraeder valve with a core.

Check valve. A check valve only allows refrigerant flow in one direction and

does not require wiring. In cooling-only applications, if 50 ft (15 m) or more of

the liquid line is elevated above the TTA, provide a check valve in the liquid

line adjacent to the TTA. (This valve is factory-installed in TWA heat pumps.)

For heat pumps paired with non-TWE air-handler coils, provide an individual

check valve for each expansion valve to allow reverse flow around the TXV

during heating. See Figure 6 (p. 11), Figure 10 (p. 16), and Figure 11 (p. 16) for

examples of this valve combination.

Moisture-indicating sight glass. Install one moisture-indicating sight glass in

the main liquid line of each circuit to flag the presence of water.

Note: The sole purpose of this sight glass is its moisture-indicating ability.

Always use actual measurements of temperature and pressurenot the

sight glassto determine subcooling and whether the system is properly

charged.

Expansion valve. The expansion valve is the throttling device that meters the

refrigerant into the evaporator coil. Metering too much refrigerant floods the

compressor too little elevates the compressor temperature.

Each TWE air handler is factory-equipped with a correctly sized expansion

valve. For TTA/TWA units paired with other indoor coils, provide an

expansion valve for each coil distributor. Size the TXV to match the capacity

of the distributor; see Table 2 (p. 6) for recommendations. Make sure that the

expansion valve is externally equalized and balance-ported.

Gas lines

Line sizing

Proper gas-line sizing is required to guarantee that the oil returns to the

compressor throughout the systems operating envelope. At the same time,

the line must be sized so that the pressure drop does not excessively affect

capacity or efficiency.

Table 1 (p. 6) lists preselected pipe diameters for TTA cooling-only units and

TWA heat pumps in normal air-conditioning applications. Use the preselected

pipe sizes for both horizontal andvertical runs.


14/20


Tube Size and Component Selection

Routing

Route the line as straight (horizontally and vertically) as possible. Avoid

unnecessary changes of direction. To prevent any residual or condensed

refrigerant from flowing freely toward the compressor, install the gas line so

that it slopes by inch to 1 inch per 10 feet (1 cm per 3 m) toward the

indoor coil.

Do not install riser traps. With field-supplied air-handler coils, what appears

to be a riser trap is located at the coil outlet; see Figure 7 for an example. This

piping arrangement, which isnt a riser trap at all, results from two

requirements:

Drain the coil to a common low point

Rise at least 1 ft (30 cm) from the common low point to prevent any

off-cycle condensed refrigerant in the coil from attempting to flow tothe compressor.

Note: Do not install double risers. All 7.5- through 20-ton TTA and TWA units

unload such that a single gas line size, preselected in Table 1 (p. 6), provides

sufficient velocity to push entrained oil up the permissible riser height.

Avoid underground refrigerant lines, which make it virtually impossible to

maintain proper cleanliness during installation. Refrigerant condensation,

poor service access, and abrasion/corrosion can quickly impair the systems

reliability.

Insulation

Always insulate the gas line to prevent the refrigerant vapor from cooling

enough to condense during the heating mode (TWA heat pumps) and to

prevent the line from sweating during the cooling mode (TTA andTWA

applications).

Components

Adding a suction-line filter drier is unnecessaryprovided 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 tocheck refrigerant pressure and determine superheat at the evaporator/indoor

coil. Usually this port is a Schraeder valve with a core.

Figure 7. Gas- ine arrangement at t e

outlet of a field-supplied indoor coil


15/20


Refrigerant Piping Examples

Figure 8.

TTA cooling-only unit and

TWE air handler (typical arrangement)

Installation notes:

1 Do not install this check valve unless

50 ft (15 m) or more of the liquid line is

elevated above the TTA.

2 Never add a check valve and a solenoid

valve to the same liquid line. (Increased

temperature will cause any liquid

refrigerant caught between these valves

to become highly pressurized.)

WARNING!

Redundant Valves Can Cause

Hazardous Pressures!

Liquid refrigerant trapped betweentwo valves can become highlypressurized if the ambienttemperature increases. Do not add aliquid-line solenoid valve in a cooling-only system that is already equipped

with a check valve. Failure to heed thisprecaution could result in arefrigerant-line rupture that causesdeath or serious injury.

3 If the total length of the liquid line

exceeds 80 ft (24 m), remove the liquid-

line filter drier from the TTA and install a

new one (Table 1, p. 6) at the TWE air

handler.

Figure 9.

TTA cooling-only unit and matchedindoor coil (typical arrangement)

Installation notes:

1 Do not install this check valve unless

50 ft (15 m) or more of the liquid line iselevated above the TTA.

2 Never add a check valve and a solenoid

valve to the same liquid line. Increased

temperature will highly pressurize any

liquid refrigerant caught between these

valves.

WARNING!

Redundant Valves Can CauseHazardous Pressures!

Liquid refrigerant trapped betweentwo valves can become highlypressurized with increased ambienttemperature. Do not add a liquid-linesolenoid valve in a cooling-onlysystem that is already equipped with acheck valve. Failure to heed thisprecaution could result in a

refrigerant-line rupture that causes

death or serious injury.

3 If the total length of the liquid line

exceeds 80 ft (24 m), remove the liquid-

line filter drier from the TTA and install a

new one (Table 1, p. 6) near the indoor

coil.

4 Provide one expansion valve (TXV) per

distributor; see Table 2 (p. 6) for

recommendations.


16/20



Figure 10.

TWA heat pump and TWE air handler

(typical arrangement show n in cooling

mode)

Installation note: For applications where

the length of the liquid line exceeds 80 ft

(24 m) and the heat pump will start in the

cooling mode, remove the liquid-line filter

driers from the TWA heat pump and install

a new bidirectional filter drier (Table 1,

p. 6) at the TWE air handler.

Figure 11.

TWA heat pump and matched indoor

coil (typical arrangement shown in

cooling mode)

Installation notes:

1 Each coil distributor requires one

thermal expansion valve (TXV) and one

check valve. See Table 2 (p. 6) for

recommendations.

2 For applications where the length of the

liquid line exceeds 80 ft (24 m) and the

heat pump will start in the cooling

mode, remove the liquid-line filter driers

from the TWA heat pump and install a

new bidirectional filter drier (Table 1,

p. 6) at the indoor unit.


17/20



Figure 12.

Indoor coil w ith one distributor

(single-circuit TTA/ TWA units)

Installation notes:

1 Pitch 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 1 (p. 6).

2 Provide one expansion valve (TXV)

per distributor.

TWA heat pumps only: Provide one

check valve for each expansion valve.

3 Pitch 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).

4 Use the tube diameter recommended in

Table 1 (p. 6). Assure that the top of the

riser is at least 1 foot (30 cm) above the

lowest point.

5 Arrange the gas line so that suction gas

leaving the coil flows downward, past

the lowest gas-header outlet, before

turning upward.

6 Pitch the gas line 1 inch per 10 feet

(1 cm per 3 m) toward the indoor coil.

7 Insulate the gas line.


18/20



Figure 13.

Indoor coil with tw o distributors

(single-circuit TTA/ TWA units)

Installation notes:





Table 1 (p. 6).


per distributor.









turning upward. Use a double-elbow

configuration on all lower branch circuits

to isolate the TXV bulb from suction-

header conditions.

5 For 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 1, p. 6.

6 For vertical risers, use the tube

diameter recommended in Table 1

(p. 6). Assure that the top of the riser is

at least 1 foot (30 cm) above the lowest

point.

7 Pitch the gas line by 1 inch per 10 feet(1 cm per 3 m) toward the indoor coil.


19/20


Figure 14.

Indoor coil with tw o distributors

(dual-circuit TTA/ TWA units)

Installation notes:





Table 1 (p. 6).


per distributor.






4 Use the tube diameter recommended in

Table 1 (p. 6). Assure that the top of the

riser is at least 1 foot (30 cm) above the

lowest point.




turning upward.

6 Pitch the gas line 1 inch per 10 feet




20/20

TraneA business of American Standard Companieswww.trane.com

For more information, contact your local Traneoffice or e-mail us at [email protected]

Literature Order Number SS-APG002-EN

Date May 2005

Supersedes (New)

Stocking Location e-Library

Trane has a policy of continuous product and product data improvement and reserves the right tochange design and specifications without notice.


Figure 15.

Indoor coil w ith four distributors

(dual-circuit TTA/ TWA units)

Installation notes:





Table 1 (p. 6).


per distributor.


check valve for each expansion valve

(see inset).


it slopes away from the coil by 1 inch per

10 feet (1 cm per 3 m).




turning upward. Use a double-elbow

configuration on all lower branch circuits

to isolate the TXV bulb from suction-

header conditions.

5 For 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 1 (p. 6).

6 For vertical risers, use the tube diameter

recommended in Table 1 (p. 6). Assure

that the top of the riser is at least 1 foot

(30 cm) above the lowest point.

7 Pitch the gas line by 1 inch per 10 feet



2005 piping guide ss-apg002-en

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