14
6.1 - Refrigerant line connections (30SZV)
6.1.1 - Recommendations for the installation of liquid
chillers with remote condensers
To guarantee optimum and reliable performance of the 30SZV
units (split units for connection to condensers) it is necessary to
comply with the regulations described below, when these units
are connected to remote condensers.
1.
Install a valve in the discharge piping.
2.
Size the discharge and liquid line piping according to the
recommendations in the following paragraphs (if neces-
sary, install a double riser to ensure correct oil circulation
in the refrigerant circuit).
3.
Depending on the layout and the routing of the discharge
piping it may be necessary to install additional silencers
(to reduce pulsations and noise emission) between the
liquid chiller and the condenser.
4.
Select a condenser with an integrated subcooler to obtain a
minimum of 3 K subcooling at the inlet to the expansion
device.
5.
Keep the condensing pressure as stable as possible
(pressostat staging or fan control via Pro-Dialog Plus). A
speed controller may be required for the first fan stage for
operation at low ambient temperature and partial load.
6.
If the system can have several operating modes (summer/
winter, dual set point etc.), it is necessary to install a tank
(or receiver) to absorb the variations in charge.
6.1.2 - General
Refrigerant pipe sizing must be carried out, taking account of
the following constraints:
Oil return to the compressor must be ensured for the majority
of applications. Oil return is ensured by entrainment. A
minimum refrigerant velocity is required to ensure entrainment.
This velocity depends on the pipe diameter, the refrigerant and
oil temperature (these are treated as being the same in most
cases). A reduction of the pipe diameter permits an increase of
the refrigerant velocity. The problem of a minimum entrain-
ment velocity does not exist for the pipes that carry liquid
refrigerant as the oil is fully miscible here.
The pressure drop at the compressor discharge (pipes linking
the compressor outlet with the condenser inlet) must be limited
to avoid system performance losses (the compressor power
input inceases, and the cooling capacity decreases).
As a first estimate and for standard air conditioning applica-
tions, a one degree Celsius pressure drop on the discharge side
decreases the cooling capacity 2% and increases the compres-
sor power input by 3%. Increasing the pipe diameter permits
limiting the pressure drops.
The pressure drop in the liquid line (linking the condenser
outlet to the expansion device) must not result in a change in
phase. The estimate of these pressure drops must include those
for the possible accessories, such as solenoid valves, filters,
dehumidifier etc.
6.1.3 - Use of pipe sizing diagrams
On page 16 of this document two pipe sizing diagrams are
shown. They allow an estimate of the cooling capacity,
corresponding to 1.5 K pressure drop for different pipe
diameters, based on the pipe length.
The following procedure can be used for pipe sizing:
1.
Measure the length (in metres) of the piping under
consideration.
2.
Add 40 to 50% to take account of special characteristics.
3.
Multiply this length by the appropriate correction factor
from Table 1 (this correction factor depends on the
saturated suction and discharge temperatures).
4.
Read the pipe size from diagrams “Discharge piping” and
“Liquid line piping”.
5.
Calculate the equivalent lengths for parts included in the
piping under consideration (such as valves, filters,
connections).
The equivalent lengths are normally available from the
component supplier. Add these lengths to the length
caculated in step 3.
6.
Repeat steps 4 and 5 is necessary.
The diagrams in the appendix can obviously be used to calculate
the actual pressure drops for the piping under consideration:
7.
Based on the pipe diameter and the cooling capacity find
the equivalent length, producing 1.5 K pressure drop in
Figs. “Discharge piping” and “Liquid line piping”.
8.
Calculate the equivalent pipe length as described in steps
1, 2, 3 and 5.
9.
Calculate the length ratio from steps 8 and 7 (equivalent
length from step 8 DIVIDED by the equivalent length
from step 7).
10. Multiply this ratio by 1.5 to find the equivalent pressure
drops in °C.
