NOTE: Do not use automobile anti-freeze, or any other fluid that is not approved for heat exchanger duty. Only use appro- priately inhibited glycols, concentrated to provide adequate protection for the temperature considered.
SYSTEM PRESSURIZATION — A proper initial cold fill pressure must be established before 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 pressure at the top of the system (4 psig minimum [27.6 kPa]) to operate air vents and positively pressurize the system. The expansion tank is very important to system pressurization. The expansion tank serves several purposes:
1.Provide NPSHR (Net Positive Suction Head Required) 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 expansion tank pressure must be set BEFORE the system is filled. Follow the manufacturer’s recommendation for instructions on setting the pressure in the expansion tank. NPSHR information is provided on the Pump Curves in Fig. 33-36 for units with factory-installed hydronic kits. See Table 4 for pump impeller sizes.
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.
Since the expansion tank acts as a reference point for the pump, there cannot be two reference points (two expansion tanks) in a system, unless manifolded together. Where two or more 30XA chillers with the hydronic option are installed in parallel, there should not be more than one expansion tank in the system, unless manifolded together as seen in Fig. 27. It is permissible to install the expansion tank(s) in a portion of the return water line that is common to all pumps, providing that the tank is properly sized for combined system volume.
If the application involves two or more chillers in a primary secondary system, a common place for mounting the expan- sion tank is in the chilled water return line, just before the decoupler. See Fig. 27 for placement of expansion tank in primary-secondary systems.
If a diaphragm expansion tank is utilized (a flexible diaphragm physically separates the water/air interface) it is not recommended to have any air in the water loop. See the section on air separation on page 51 for instructions on providing air separation equipment.
FILLING THE SYSTEM — The initial fill of the chilled water system must accomplish three goals:
1.The entire piping system must be filled with water.
2.The pressure at the top of the system must be high enough to vent air from the system (usually 4 psig [27.6 kPa] is adequate for most vents).
3.The pressure at all points in the system must be high enough to prevent flashing in the piping or cavitation in the pump.
The pressure created by an operating pump affects system pressure at all points except one — the connection of the expansion tank to the system. This is the only location in the system where pump operation will not give erroneous pressure indications during the fill. Therefore, the best location to install the fill connection is close to the expansion tank. An air vent should be installed close by to help eliminate air that enters during the fill procedure.
When filling the system, ensure the following:
1.Remove temporary bypass piping and cleaning/flushing equipment.
2.Check to make sure all drain plugs are installed.
Normally, a closed system needs to be filled only once. The actual filling process is a fairly simple procedure. All air should be purged or vented from the system. Thorough venting at high points and circulation at room temperature for several hours is highly recommended.
NOTE: Local codes concerning backflow devices and other protection of the city water system should be consulted and followed to prevent contamination of the public water supply. This is critical when antifreeze is used in the system.
SET WATER FLOW RATE — Once the system is cleaned, pressurized, and filled, the flow rate through the chiller needs to be established. On units with the hydronic package, this can be accomplished by using the balancing valve. Follow the manufacturer’s recommendations for setting the balancing valve. Local codes may prohibit restricting the amount of water using the balancing valve for a given motor horsepower. In this case, use the method listed in the Pump Modification/ Trimming section. See below for the type of combination valve in 30XA units with the optional hydronic package.
30XA UNIT SIZE | SINGLE/DUAL PUMP |
090-160 | FTV-5 in. |
NOTE: Carrier recommends a differential pressure gage when measuring pressures across the pumps or balancing valves. This provides for greater accuracy and reduces error build-up that often occurs when subtracting pressures made by different gages.
A rough estimate of water flow can also be obtained from the pressure gages across the 30XA heat exchanger.
Figure 33 and 34 shows the relationship between gpm and heat exchanger pressure drop. It should be noted that these curves are for fresh water and “clean” heat exchangers; they do not apply to heat exchangers with fouling. To read the chart, subtract the readings of the two pressure gages on the hydronic kit. This number is the pressure drop across the heat exchanger. Adjust the factory-installed balancing valve or external balanc- ing valve (in units without hydronic package) until the correct pressure drop is obtained for the required flow.
