Long Lineset Instructions

ManualsBrandsBlueridge Manualsair conditioning cooling14.3 SEER 70,000 BTU System Bundle Horizontal Air Conditioner Gas Furnace and Coil

Page 9

Table 10. Refrigerant Charge (Pounds) in 100 feet of Type L Copper Tubing

Line

Size

3/8” 1/2” 5/8” 5/8” 3/4” 3/4” 7/8” 7/8” 1-1/8” 1-3/8” 1-5/8” 2-1/8

Liquid Liquid Liquid Suction Liquid Suction Liquid Suction Suction Suction Suction Suction

HCFC−22 3.8 7.0 11.3 0.3 16.8 0.4 23.4 0.6 1.0 1.6 2.2 3.9

HFC−410A 3.1 5.8 9.2 0.4 13.8 0.6 19.2 0.8 1.3 2.0 2.9 5.0

2. Pressure drop in the liquid line produces no significant

capacity loss as long as 100% liquid is delivered to the

expansion valve and the pressure available is

adequate to produce the required flow. Pressure drop

due to lift must be added to the friction losses to

determine total pressure drop. At normal liquid

temperatures, HCFC-22 pressure drops 0.5 psi per

foot of vertical liquid lift. HFC-410A pressure drops 0.43

psi per foot of vertical liquid lift.

One contributor to pressure loss in refrigerant lines is

elbows and fittings. Figure 3 illustrates how lines can be run

to avoid pressure losses.

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ELBOWS AND FITTINGS PRODUCE PRESSURE DROP.

CAREFULLY ROUTE LINES TO AVOID OBSTACLES IN PATH OF

LINES.

ACCEPTABLE HIGHER PRESSURE DROPS.

RECOMMENDED LOWER PRESSURE DROPS.

Figure 3. Pressure Drops

Line Sizing in Detail

The first step in the design of a piping system is to layout the

entire system (i.e. relative location of the condensing unit

and the evaporator, length of each segment of the piping

system, length of suction risers and liquid risers etc). Start

by making a sketch of the system including lengths of pipe,

number of elbows, tees, valves, and any other irregular

piping and fittings needed. This information will be used to

determine total equivalent length for calculating pressure

drop due to friction.

The same methods apply to both A/C and heat pump

systems. A suction line sized to produce adequate velocity

for oil entrainment and pressure drop with minimum

capacity reduction will function properly as a hot gas

discharge line during a heating cycle. Also, if there is a

vertical difference in height between the outdoor and indoor

units, there is always a vapor and liquid lift to consider in

sizing due to the reversal of refrigerant flow.

OEM split system condensing units and heat pumps (four

tons and under) match with line sets of varying lengths of up

to 50 feet (linear). These applications offer quick and simple

installations that are trouble free if the line sets are properly

installed. On split commercial applications and residential

installations beyond 50 feet, special design considerations

must be followed to assure satisfactory system

performance. An improperly designed system could result

in a serious loss of capacity or even compressor failure.

The purpose of the liquid line is to convey a full column of

100% liquid from the condenser to the metering device at

the evaporator without flashing. The amount of liquid line

pressure drop which can be tolerated is dependent on the

number of degrees of liquid subcooling leaving the

condenser and the saturated condensing temperature. If

the condensing temperature and subcooling are known,

the maximum allowable pressure drop can be calculated.

All OEM equipment is designed so that the charge may be

adjusted to provide adequate subcooling leaving the

outdoor unit. This will allow a 30 pound drop in the

HCFC-22 liquid line (including pressure drop due to friction

loss and vertical lift) and 35 psi in the HFC-410A liquid line.

Refrigerant charge may be added to increase subcooling to

overcome pressure drop due to liquid lift. Heat pumps

require special consideration when adding charge because

both cooling and heating modes must be considered.

Consult the installation guide for the specific unit you are

working with.

A major cause of compressor failure is liquid slugging. Due

to the additional refrigerant required to fill the lines, the

likelihood of slugging is greatly increased with lines over 50

feet in length. It is desirable to use the smallest liquid line

that will not result in refrigerant flashing due to pressure

drop. Table 10 shows that each incremental increase in

liquid line size results in a 40 to 50 percent increase in liquid

to fill the line.

The liquid line must not directly contact the vapor line. If the

refrigerant line plan results in a pressure drop of 20 psi or

more, the liquid line should be insulated in all places where

it passes through an environment (such as an attic) which

experiences temperatures higher than the subcooled

refrigerant (approximately 105F to 115F liquid at 95F

ambient).

Refrigeration lines must not be buried in the ground unless

they are insulated and waterproofed. Un-insulated copper

lines buried in wet soil or under concrete can cause serious

capacity loss and erratic operation as well as early failure

due to corrosion. See Appendix for more information.