Sterlco 30RA Outdoor Air Cooled Central Chillers 10-60 Tons - Manual (Page 14)

14
SYSTEM PRESSURIZATION — A proper initial cold fill
pressure must be established before the filling of the unit. The
initial cold fill pressure is the pressure applied at the filling
point to fill a system to its highest point, plus a minimum pres-
sure at the top of the system (4 psi minimum) to operate air
vents and positively pressurize the system.
The compression tank (sometimes called expansion tank) is
very important to system pressurization. The compression tank
actually serves several purposes:
1. Provide Net Positive Suction Head Required (NPSHR)
for the pump to operate satisfactorily.
2. Set system pressure.
3. Accommodate expansion/contraction of water due to
temperature changes.
4. Acts as a pressure reference for the pump.
The compression tank pressure must be set BEFORE the
system is filled. The tanks are pre-charged at the factory to
40 psig. If the 30RA unit with expansion tank is the high point
in the system, tank pre-charge pressure of 40 psig will be
adequate. If the 30RA unit with expansion tank is NOT at the
high point in the system, then the minimum pre-charge
pressure for the water system must be determined using Table 3
and the method below:
Tank Pressure = 4 + (height from tank to top of
system in feet/“X”)
For example, assuming a system containing a 20% concen-
tration of ethylene glycol and 50 feet in height from the top of
the system to the expansion tank, the minimum tank pre-
charge pressure would be:
Tank Pressure = 4 + (50
÷ 2.38) = 25.0 psig
Table 3 — “X” Factor for Setting Tank Pressure
NOTE: If expansion tanks are placed elsewhere in the system this
method cannot be used since extra pressure drop between the tank
and the pump must be accounted for.
NOTE: If the system requires a pre-charge greater than
40 psig, increase pressure as described below.
Expansion Tank Pre-Charge — To pre-charge the expansion
tank, do the following steps:
1. Check the tank air pressure at the pre-charge connection
with an accurate pressure gage. Adjust as needed.
2. If additional pressure is required, charge the tank with oil-
free compressed air or nitrogen gas. Occasionally check
the pressure as when filling a tire.
3. Check the air valve for leakage. If it leaks, relieve the
pressure and replace the core with a Schraeder type tire
core. DO NOT depend on the valve cap to seal the leak.
Once the system is pressurized, the pressure at the connec-
tion point of the expansion tank to water piping will not change
unless the water loop volume changes (either due to addition/
subtraction of water or temperature expansion/contraction).
The pressure at this point remains the same regardless of
whether or not the pump is running.
% GLYCOL
ETHYLENE
GLYCOL
PROPYLENE
GLYCOL
0 (pure water) 2.31 2.31
10 2.36 2.33
20 2.38 2.36
30 2.40 2.38
40 2.43 2.38
50 2.47 2.40
Distribution Pump
Expansion
Tank(s)
Air Separator
with Vent
Decoupler
Chiller 1 Chiller 2
Zone 1 Zone 2 Zone 3
x
x
DILUTED
CLEANING
AGENT
SYSTEM
POT FEEDER AND
TRANSFER PUMP
30RA UNIT
TO DRAIN
TEMPORARY
PUMP
TEMPORARY
BYPASS
x
x
DILUTED
CLEANING
AGENT
SYSTEM
SIDE
STREAM
FILTER
POT FEEDER AND
TRANSFER PUMP
30RA UNIT
TO DRAIN
TEMPORARY
PUMP
TEMPORARY
BYPASS
NOTE: Expansion tanks in the 30RA hydronic kits must be disconnected for chillers placed parallel in the primary water loop.
Fig. 12 — Typical Air Separator and Expansion Tank Location on Primary-Secondary Systems
Fig. 13 — Typical Set Up for Cleaning Process Fig. 14 — Cleaning Using a Side Stream Filter