Operation and Maintenance

Absorption chillers are characterized by their simple design with few moving parts and relatively low operating temperatures and pressures. Following is a description of some of the basic recommended O&M practices.

Regular O&M of the purge unit at manufacturer recommended intervals is required to maintain design pressure within the system. The purge pump oil level must be checked and changed as necessary, the pump motor bearings must be oiled, and the belt tension must be adjusted as needed. A monthly inspection of the non-condensable accumulation rate should also be performed.

Manufacturer's specifications should be followed for inspection of refrigerant and solution pump-motor assemblies. Typically, bearings and shaft seals should be inspected every three years and hermetic pumps every five years.

Absorption machines use corrosion inhibitors to protect internal components from corrosion and to limit the formation of non-condensable gas. They also use a heat-transfer additive to improve refrigeration capacity, particularly during initial start-up. The solution must be analyzed each cooling season, and more frequently when chillers operate year-round, to ensure that both inhibitor and additive levels are within acceptable limits and to determine when replenishment is required. Periodic analysis of refrigerant water is also recommended and manufacturer's procedures should be followed for treatment of evaporator and condenser water to ensure coverage by equipment warrantees.

Evaporator, condenser, and absorber tube surfaces require ongoing maintenance. The primary fouling deposits are scaling and sedimentation (or sludge). Scale deposits can be removed by chemical cleaning. Sludge deposits must be removed mechanically by removing the headers, loosening the deposits with a brush, and flushing the loosened materials from the tubes with water.

In order to minimize long-term maintenance costs, ready access should be provided to the tubes for cleaning and inspection. Marine water boxes are useful in this regard. Whereas standard water boxes require disassembly of the water piping and removal of the water box for tube access, marine boxes provide side connections for water piping and a removable cover on the end of the box for full access to the tubes.

For direct-fired units, the combustion air fan and motor must be inspected at least semiannually and lubricated annually. Exhaust flue, flue damper, and exhaust devices should be inspected semiannually or in accordance with the manufacturer's specifications. Exhaust flue gases should be analyzed for emissions and for combustion performance evaluation.

Combustion controls (i.e., gas/oil pressure and

Fig. 38-25 Basic GAX-Cycle Schematic Diagram. Source: Energy Concepts Co.
Fig. 38-26 VX GAX-Cycle Schematic Diagram. Source: Energy Concepts Co.

airflow switches, solenoid valves and proof-of-flame controls) should be checked regularly, typically every one to three months. The gas train valves and switches and, where applicable, oil pump and oil supply system should be inspected and tested regularly for leaks. If the equipment area is subject to adverse conditions, more frequent inspections are recommended.

Crystallization

Crystallization, or solidification, of the LiBr solution has been an important historical operating concern of absorption chiller operators. As the temperature of the solution decreases, the maximum possible concentration also decreases and it can begin to solidify and block piping in the machine. It is then necessary to heat the piping where the blockage has occurred in order to melt the crystals. Crystallization can result from condensing water temperatures becoming too low, from operation under very low load, or as a result of other occurrences, such as power failure or air leakage into the system.

Typically, condenser water is limited to a minimum temperature of about 55 to 60°F (13 to 16°C), with a bypass valve used to maintain this temperature limit. Most designs also include an overflow pipe, which allows heated solution to pass from the generator to the absorber section and raises the temperature via a heat exchanger to liquefy any crystallization. This configuration allows for automatic decrystallization whenever necessary.

An important improvement in absorption equipment is the development of various flow schemes that allow the equipment to operate at lower solution concentrations and temperatures, reducing the potential for crystallization. Modern microprocessor based controls have virtually eliminated crystallization nuisances, in part through the development of internal responses to rapidly changing external conditions.

Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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