Daikin JEHBSCU0200M1 Technical Manual page 23

9.4 Field piping
Important Note:
Pipe sizing should only be determined by qualified personnel. All local codes of practice must
be observed in the installation of refrigerant piping.
To ensure satisfactory operation and performance, the following points should be noted for field
piping arrangements:
•
Pipework routes must be as simple and as short as possible.
•
Avoid low points on pipework where oil can accumulate.
•
Suction gas velocity must be sufficient to ensure good oil return.
•
Use only clean, dehydrated refrigeration grade copper tube with long radius bends.
•
Avoid flare type connections and take great care when brazing. Use only silver alloy rods.
•
Run braze without over filling to ensure there is no leakage into the tube.
•
To prevent oxidation, blow oxygen free nitrogen through pipework when brazing.
•
Install insulation on all suction lines and on all pipes penetrating walls or passing through hot areas.
•
Adequately support all pipe work at a maximum of 2 metre intervals.
•
In vertical pipework, the use of U-trap and double suction risers is often required. These suction
risers must always be fitted with a U-trap at the bottom and a P-trap at the top and never be higher
than 4m unless a second U-trap system is fitted.
•
When installing a single compressor unit with multiple evaporators connected, care should be taken
to ensure that the evaporating pressure/temperature does not fall outside the compressor operating
limit. Ideally, multiple evaporators when operated in pump-down mode should be fed by a single
solenoid valve.
•
Suction pipework should slope gently back towards the unit to assist oil return to the compressor. A
fall of approximately 2cm per metre of pipework is acceptable.
•
Liquid lines should be sized to ensure a full supply of liquid refrigerant to the expansion device.
Careful attention should be paid to sizing of liquid lines on large risers (above 6m).
•
Piping length less than 25m is highly recommended. An additional oil might be required if piping length
exceeds 20m or with many oil traps. Normally quantity of top up oil required should not exceed 2% of the
total refrigerant charge.
Correct line sizing will minimize the pressure drop and maintain sufficient gas velocity for proper oil
return.
Important Note:
One of the main factors affecting equipment reliability and compressor service life is
refrigeration circuit contamination. During installation, circuit contamination can be
caused by:
• Brazing & Welding Oxides
• Filings & Particles from de-burring pipework
• Brazing Flux
• Moisture & Air
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