5 Steps to Improve Chiller Efficiency

Step 1: Maintain a daily operation log

Chiller operators should log chiller performance with accurate and detailed logs on a daily basis, comparing this performance to design and start-up data to detect problems or inefficient control set points. The process allows operators to collect a history of operating conditions, which can be reviewed and analyzed to identify trends and provide advance warning of potential problems.

For example, if a machine operator notices a gradual increase in condensation pressure over the course of a month, they can consult the daily operating log and systematically check and correct possible causes of this situation, such as condenser tube fouling or non-condensables.

Chiller manufacturers can provide a list of recommended data points specific to the equipment upon request. Operators can read data every day, approximately once at the same time per shift. Today's chillers are microprocessor-controlled, so managers can automate this process using microprocessor-controlled building automation systems.

Step 2: Keep the pipes clean

One of the potential barriers to the required performance of a cooler is heat transfer efficiency. The performance and efficiency of a cooler is directly related to its heat transfer capacity, starting with clean evaporator and condenser tubes. Large coolers contain miles of piping in their heat exchangers, so keeping these large surfaces clean is critical to maintaining efficient performance.

When mud, algae, sludge, scale, or contaminants accumulate on the water side of the heat transfer surface, the efficiency of the cooler decreases as the pipes become dirty. The contamination rate depends on the type of system – open or closed – as well as water quality, cleanliness and temperature.

Most chiller manufacturers recommend cleaning condenser tubes once a year because they are usually part of an open system, and they recommend cleaning evaporator tubes in a closed system every three years. But if the evaporator is part of an open system, they recommend regular inspection and cleaning.

There are two main methods of pipe cleaning that managers can consider:

· Mechanical cleaning removes slurry, algae, sludge and loose material from smooth pipes, including removing tank caps, brushing tubing and rinsing with clean water. For internal reinforcement tubes, managers should consult the cooler manufacturer for mechanical cleaning recommendations.

· Chemical cleaning removes scale. Most chiller manufacturers recommend consulting your local water treatment supplier to determine the appropriate chemical solution required. Thorough mechanical cleaning should always be followed by chemical cleaning.

The new chiller is equipped with an automatic tube brush system that can be retrofitted to an existing chiller. These systems use a small nylon bristle brush through the tube for cleaning. A custom 4-way directional valve is installed in the condenser water pipe system, and every 6 hours, the system automatically reverses the water flow through the condenser tube for approximately 30 seconds.

Coupled with proper water treatment, these systems virtually eliminate dirt inside the cooler and keep the design close to temperature. These systems typically show payback periods of less than two years.

Step 3: Make sure there is no leakage device

The manufacturer recommends that the compressor be leak tested on a quarterly basis. The refrigeration system section using the low-pressure coolers of the obsolete CFC-11 or HCFC-123 operates at sub-atmospheric pressure. While these coolers are common in today's facilities, it is difficult to build a fully sealed machine, and leaks can cause air and moisture (often referred to as non-condensables) to enter the equipment.

Once inside the cooler, non-condensable material is trapped in the condenser, increasing condensing pressure and compressor power requirements, and reducing efficiency and overall cooling capacity. The low-pressure chillers have a high-efficiency purification unit that removes non-condensable material to maintain the designed condensation pressure and promote efficient operation. One cooler manufacturer estimated that 1 psi of air in the condenser equates to a 3% loss of cooler efficiency.

The moisture in the chiller can also produce acid, corrode the motor windings and bearings and rust inside the housing. Small rust particles called fine powders float in the vessel and are trapped inside the heat exchanger tube. The fine powder on the tube can reduce the heat transfer efficiency and overall efficiency of the unit. If left unchecked, they can lead to costly plumbing repairs.

A good way to monitor low-pressure cooler leaks is to track the operating time of the purge unit and the amount of moisture build-up at the purge unit. If any of these numbers are too high, there is a leak in the device. Other signs of the presence of air in the system include increased head pressure and condensation temperature.

High-pressure coolers using CFC-12, HFC-134a, or HCFC-22 operate at pressures well above atmospheric pressure, and leaks in these types of coolers can release potentially hazardous refrigerants into the environment. Environmental regulations limit the amount of refrigerant leakage that can occur each year.

Leaks can also lead to reduced refrigerant charge and other operational issues such as reduced evaporator pressure, which causes compressors to work harder to produce lower cooling capacity. For positive pressure chillers, technicians should monitor refrigerant charge and evaporator pressure to detect leaks.

Step 4: Maintain proper water treatment

Most chillers use water for heat transfer, so water must be properly treated to prevent scaling, corrosion, and biological growth. Closed water systems require a one-time chemical treatment, which is typical of chilled water systems connected to chiller evaporators.

Open systems are typically used for condenser-chiller systems connected to chiller condensers. Condenser systems that use water sources such as cooling towers require continuous chemical water treatment. Managers should work with chemical treatment suppliers familiar with local water supplies and can provide full-service maintenance of all facility water systems.

If the supplier maintains proper chemical treatment of the evaporator and condenser water systems, fouling should not be a problem. The presence of scale in the condenser or evaporator tube indicates improper water treatment. Suppliers are required to test water quality and correct water treatment procedures every three months, which helps clean chiller piping.

In addition, all system filters should be cleaned every three months. Sand filters and side stream filters for condensate systems are very effective in keeping clean water if properly maintained. To determine when cleaning is required, the technician should monitor the pressure drop of the filter and refer to the manufacturer's cleaning recommendations. The filter should be cleaned quarterly, regardless of the pressure drop.

Maintenance of filters and filters limits cooler tube erosion caused by sand or other small particles moving at high speeds. Erosion and pipe pitting can reduce overall heat transfer efficiency and reduce efficiency. If left uncorrected, these conditions can lead to clogged pipes or catastrophic pipe failures.

Technicians should annually inspect chilled water and condenser water piping systems for signs of corrosion and erosion. Most manufacturers recommend eddy current inspections of heat exchanger tubes every three to five years, including electromagnetic procedures to assess tube wall thickness.

Step 5: Analyze oils and refrigerants

Annual chemical analysis of oils and refrigerants helps detect cooler contamination problems before they become serious. Testing includes spectrochemical analysis to identify contaminants that affect performance and efficiency, including moisture, acids, and metals. Analysis must be carried out by a qualified chemical laboratory specializing in HVAC equipment. Most manufacturers offer annual oil and refrigerant analysis services.