J&E Hall JEHR-0050-B1-M-1, Руководство по установке

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Issue: 01.05.2019 Page 5
Installation
Field 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.
•
Where the condensing unit is situated below the indoor unit
(coldroom evaporator / display case), the height difference
between the two units should be no more than 6 metres.
•
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.
•
Additional oil may be required if piping length exceeds 20m or
multiple oil traps are fitted. Check the oil level closely during
commissioning and add oil as necessary. Add oil in small
amounts. Do not overfill the compressor!
•
When installing a single compressor condensing unit with
multiple evaporators connected which operate independently,
care should be taken to ensure that the evaporating
pressure/temperature does not fall outside the compressor
operating limit at minimum load. If there is a potential for this
scenario, consider multiple evaporators fed by a single
solenoid valve or separate condensing units.
•
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 (maximum 6m).
•
In some circumstances, a suction accumulator (not supplied)
may be required. It offers protection against refrigerant flood
back during operation and also against off-cycle migration by
adding internal free volume to the low side of the system.
•
Tests must be conducted to ensure the amount of off-cycle
migration to the compressor does not exceed the compressor’s
charge limit.
•
Wherever possible the system should be installed to utilize a
pump down configuration.
•
An MOP expansion valve is recommended for all Low
Temperature installations.
•
Maximum recommended pipe length is 25m for Reciprocating
units and 50m for Scroll units.
Correct line sizing will minimize the pressure drop and
maintain sufficient gas velocity for proper oil return.
Pipe size selection (For EVI units only)
Sizing of liquid and suction lines for EVI model will be different
from standard scroll models. Piping sizes of this model need to
follow the recommended correction coefficient of cooling capacity.
This is vital as if the pipework selected is oversized, especially for
the suction pipe, the gas velocity will be decreased at low mass
flow rate / low evaporating temperature, causing oil return
problems. Undersized suction lines will also cause decreased
capacity due to increased pressure drop.
The correction factor of refrigerant R404A is shown as below table:
For instance,
At condition of Te -35°C, Ta +32°C
Refrigerant R404A
Published cooling capacity = 5.9kW.
Cooling capacity = Correction factor x Published cooling capacity
= 0.63 x 5.9 kW
=
3.707kW
Therefore, the pipe sizes should be selected against the
corrected
capacity of 3.71kW.
Ta Te (Watts) -40 -35 -30 -25 -20
27 CF 0.64 0.66 0.68 0.70 0.72
32 CF 0.61 0.63 0.65 0.67 0.69
35 CF 0.59 0.61 0.63 0.65 0.67
38 CF 0.57 0.59 0.61 0.63 0.65
43 CF 0.54 0.55 0.57 0.58 0.60
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.
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