Common Piping Problems with Split Ducted Systems

The current Temperzone range of residential and commercial one to one split ducted machines offers a wide capacity range for 8 to 95KW and custom engineered to 160 KW. Temperzone’s split ducted range includes integrated technologies, such as variable capacity compressors (both Digital Scroll and Inverter), electronic expansion valves, EC motor fans, intuitive controls and the introduction of the UC8 (Temperzone unit controller ensuring refrigeration system control, balance and adaptively).

With the release of this range of split ducted product, Temperzone have focused on making it easy to select the correct refrigeration pipe size and determining the correct refrigerant charge ensuring an efficient and reliable installation.

The refrigeration system pipe design and refrigerant charge, if not sized and selected correctly, can lead to erratic operation and nuisance trips, added expense of refrigerant that was not needed and sadly costly failures.

Here are some of the most common problems and how to overcome them.

1. Over sized liquid line, system over charged and then compressor failure.

2. Oil trap not fitted, lack of lubrication and compressor failure

3. Re using old refrigeration pipe can lead to oil contamination, breakdown and eventually compressor failure.

4. Incorrect refrigerant charge leading to nuisance trips and erratic operation and possibly compressor failure.

Split Ducted Pipe Length and Refrigerant Charge Calculation:

What is the right Pipe Size:

The design of refrigeration piping is, nearly always, made up of compromises. We all want the maximum capacity, minimum cost, proper oil return, minimum power consumption, minimum refrigerant charge, low noise level, proper liquid refrigerant control, and stable system operation from 0 to 100% of system capacity without lubrication problems.

In general, pressure drop in refrigerant lines tends to decrease capacity and increase power requirements, and excessive pressure drops should be avoided.

Don’t get caught in the old trap of presuming that diameter of service valves or other fittings on a condenser, evaporator or accumulator determine the refrigerant line sizes. They almost certainly don’t!

Equivalent Length:

The equivalent length of a refrigeration pipe is usually about 1.2 to 5 times longer than its real length, depending on the number of elbows. Each valve, fitting, and bend in a refrigerant line contributes to the friction pressure drop because of its interruption or restriction of smooth flow. This allows the consideration of the entire length of line, including fittings, as an equivalent length of straight pipe.

Rule of thumb to determine equivalent length value for bends and elbows.
When calculating performance losses for long line lengths allowances must be made for bends in the pipework.
Add this allowance for every bend to the total line length to calculate an 'effective' line length for performance loss.
No allowance has been included for any effect from vertical lift.
Typically 0.5M is the rule of thumb used (based on 22mm Suction Line Size)

Pressure Drop:

As refrigerant flows through pipes the pressure drops and changes the refrigerant saturation temperature. Decreases in both pressure and saturation temperature adversely affect the compressor performance. Proper refrigeration system design attempts to minimize this change to less than 1.1°C.

Liquid Lines:

Liquid lines connect the condenser to the evaporator and carry liquid refrigerant to the expansion device. If the refrigerant in the liquid line flashes to a gas because the pressure drops too low or because of an increase in elevation, then the refrigeration system will operate poorly. Liquid sub-cooling is the only method that prevents refrigerant flashing to gas due to pressure drops in the line. The actual line size should provide no more than a 1.1 to 1.7°C pressure drop.

Oversizing liquid lines is discouraged because it will significantly increase the system refrigerant charge affecting the oil charge.

Suction Lines:

Suction lines allow refrigerant gas from the evaporator to travel into the inlet of the compressor.

Under sizing of the suction line reduces the compressor’s capacity by forcing it to operate at a lower suction pressure to maintain the desired evaporator temperature.

Oversizing the suction line increases the piping costs and can result in insufficient refrigerant gas velocity to move oil from the evaporator to the compressor. This is particularly important when vertical suction risers are used. Suction lines should be sized for a maximum of 1.1 to 1.7°C pressure loss. The actual pressure drop in kPa will depend on the refrigerant. The suction line is filled with superheated refrigerant vapor and oil. The oil flows on the bottom of the pipe and is moved along by the refrigerant gas flowing above it. When the system stops, the refrigerant may condense in the pipe depending on the ambient conditions. This may result in slugging if the liquid refrigerant is drawn into the compressor when the system restarts.

While it is important to understand the basic design principles behind good refrigeration piping design and correct refrigerant charge calculation Temperzone makes this easy with our comprehensive split system installation. This easy to use guide will ensure that the pipe design and the refrigerant charge of your new Temperzone split system is accurate every time saving you time and money.


It is as easy as finding the outdoor unit model number and reading the table.

Download the complete Guide Here
The guide also covers, pipe insulation, oil traps, refrigerant charging and much more.