How to avoid getting caught over a barrel
This article outlines steps that should be followed. These steps are recommendations only and not a substitute for proper training or experience.
1. Inspect the chiller.
Any damage should be reported to the wholesaler or shipping company immediately. This is your responsibility. As with any shipping damage, it is advisable to take a picture of the damage.
2. Use the lifting lug to position the barrel to avoid damaging the insulation.
Additional layers or thicker insulation should be used if the unit will be exposed to temperatures in excess of 95Â°F and 70% relative humidity, or when the leaving water temperature is 32Â° or lower. Units should be painted with a good quality latex paint for outdoor installations.
3. Locate the unit in a way that allows adequate room to remove the heads should service be necessary.
The unit should be within 2 degrees of level and bolted or welded in place.
4. Pipe the waterside.
The entering water should be on the same end as the refrigerant inlet on a multi-pass unit, and on the suction end on a single-pass unit. Remove plastic plugs that are placed in the pipe couplings on the shell and install steel pipe plugs. A high-quality, Teflon®-based pipe dope is recommended for sealing waterside pipe threads.
Note: Use care removing these plastic plugs. There are tubes very close to the outside of the shell. Poking a screwdriver or awl through the plug could damage a tube. The same is true if you need to retap one of the couplings. Threading the tap in too deeply will damage tubes, possibly causing a leak.
5. A filter or strainer with a #20 screen element should be installed on the chiller water inlet if you have silt, particles, or other foreign debris in your water.
The debris can accumulate in or block water flow through the tubes. This will result in excessive pressure drop with localized areas of high water velocity. You also risk freezing the unit, since pockets of stagnant water will accumulate in the unit.
Filters and strainers must be maintained on a regular basis. New piping should be flushed before being connected to the chiller.
6. A flow switch should be installed in the 3/4-in. NPTF coupling on the water outlet flange, or in the outlet pipe immediately after the flange.
Provisions may be made to install wells in the outlet piping for temperature control sensors, if leaving water is being used for compressor control. Always use new gaskets on flanges and clean flange sealing surfaces.
7. Install the expansion valve or a tee connector if you are using a hot gas bypass valve into the liquid line fitting.
Wrap the expansion valve with a wet rag to protect it while soldering. Use a nitrogen flood and wrap a rag around the steel liquid fitting to protect the insulation from scorching and the head gasket from excessive heat.
8. Solder the sight glass into the liquid line, using a nitrogen flood and a wet rag to protect the element.
9. Solder the liquid line solenoid in place, using a nitrogen flood and a wet rag to protect the internal components.
The solenoid should be installed horizontally with the coil in the 12 o’clock position. Verify that the flow is going in the correct direction through the valve.
10. Solder the liquid-line drier in place using a nitrogen flood and wet rags at both ends. Complete high-side piping with a connection to the condenser outlet.
11. Solder the suction line into the suction fitting, using a nitrogen flood and a wet rag to protect the insulation from scorching and the head gasket from excessive heat.
12. Connect the expansion valves equalizer line (if used).
This can be done by brazing the line directly to a hole punched in the suction line, or by using the connection installed on the steel suction fitting. This should only be done after all brazing is done.
If you are going to do this, you will need to thread a 1/4-in. NPT to 1/4-in. SAE adapter into the coupling welded to the steel suction fitting. If the adapter does not thread in easily, the coupling should be cleaned out with a 1/4-in. NPT tap and all shavings should be removed. We recommend using a high-quality sealant on the pipe threads.
13. Attach the expansion valve bulb to the suction line.
It should be clamped to the copper line using the clamps provided with the valve as close as possible to the steel suction fitting in a horizontal orientation in the 4 or 8 o’clock position. The bulb should be completely and thoroughly wrapped with cork tape. The area of contact should be clean, and a thermal transfer gel used between the bulb and the suction line.
14. A suction line drier can be installed at this time and is very helpful after a compressor burnout.
We do recommend that the core be removed after 24 hrs if the sight glass indicates no moisture, and if an acid test shows that the oil condition is satisfactory. Leaving the core in can cause problems later if the pressure drop across the drier gets too high.
15. Once the entire system has been leak checked you can evacuate it, charge it, and adjust all settings and controls.
Water quality and velocityPoor water quality can foul a unit to a point that there is a significant reduction in performance, or a drastic reduction in the service life of a chiller barrel.
Corrosive water can attack and destroy the baffles inside a unit. This can cause an 80% to 90% reduction in performance. Highly corrosive water can also attack the copper tubes, creating leaks.
We recommend that you take a sample of the water to be run through the unit and have a local laboratory run the Langelier and Ryznar indexes, simple tests that will give you an idea of the condition of your water. For further information, we recommend that you contact a local water treatment professional.
Excessive water velocity will reduce the service life of a chiller barrel. This is the result of excessive water volume or pressure put through the barrel. When you have started the unit, verify that the pressure drop does not exceed the values for your particular model.
When the unit is brand new and clean, this is the best time to check water velocity, since pressure drop will rise slightly as the unit accumulates the normal amount of fouling which is acceptable and expected.
Too high of a pressure drop indicates excessive water flow or velocity through the unit. This will cause excessive wear on the tubes and can result in premature tube failure. Too low of a pressure drop indicates too little water flow. This will cause poor and erratic system performance.
Control settingEvery year, many chillers are needlessly frozen. Freeze-ups can be prevented with properly installed and adjusted controls that are protected from tampering.
The two most important controls are the low-pressure cutout and the flow switch, both of which should be set up to shut off the compressor should they be tripped. They can be manually or automatically reset. The low-pressure cutout should be set to trip slightly above the freezing point of the fluid being circulated through the chiller.
Take, for example, a system using R-22 and straight water set at 58 to 59 psi. This is equal to 32Â° to 33Â°. You can go to lower settings to minimize nuisance trips, but this creates a risk of freezing up the unit. The flow switch should be adjusted so that it will trip not only when water flow stops completely, but also when it drops off significantly. In this case, a product like a freezestat can be used. However, with compact, high-performance chillers, there is a much smaller volume of water in the chiller barrel and it must be set at 39Â° for the above example.
The best protection is still the low-pressure and flow switches.
In addition, always verify settings with an accurate set of gauges through several cycles. And remember to account for glide with blends such as R-407C and -409A.
Finally, correct for altitude by lowering settings by 1/2 lb for every 1,000 ft above sea level.
For more information, contact Standard Refrigeration Co., 2050 N. Ruby St., Melrose Park, IL 60160-1133; 708-345-5400; www.stanref.com (e-mail).