Selecting Chilled Water Pumps for Efficiency

First and foremost, properly sizing and selecting pumps is crucial to sustained energy savings. Pumps should be selected to meet the requirements of a system as a whole. Why? The energy consumption required for any system depends on the flow rate of the entire system. By reviewing the entire system, the right pump for the application can be selected and the proper control methodologies can be implemented that best match pump performance to the needs of the system.

Chilled Water Pump Optimization

Chilled water pumps consume significant amounts of electricity when operating. Monitoring pump efficiency therefore requires an accurate assessment of actual consumption including such parameters as system flow, head, pump, motor and/or drive efficiency, and run time. In existing systems, the energy requirements can be measured over time as a benchmark to aid in identifying where energy consumption can be optimized.

Because system pressure varies with flow rate, it is important to understand the control sequence that is maintaining the flow and pressure in a system. Why does this matter? The way the pumps are controlled is a key component of HVAC optimization. Many facilities utilize pumping power that is not needed via inefficient control strategies, such as running chilled water pumps at constant speed. Optimization solutions like tekWorx Xpress® will determine the number of chilled water pumps and condenser water pumps necessary to deliver the required volume of water at the lowest total power per unit of cooling production (kW/ton).  With Xpress®, this algorithm will often operate more pumps at lower speed rather than less pumps at higher speed to minimize pumping energy, per pump affinity laws. 

Chilled Water Pump Optimization and Maintenance

Routine checkups and maintenance are necessary to ensure chilled water pumps are in good working order and functioning efficiently. Best practices include:

• Monitoring pump vibration
• Checking mechanical seals for leaks.
• Monitoring bearing lubrication and temperature
• Checking water pH and clarity
• Monitoring pump and motor shaft alignment to prevent uneven wear of couplings

Proper maintenance of chilled water pumps helps to build immunity against unnecessary wear and tear on a system while routine checkups help to ensure pumps will operate as designed for many years.

The most common chiller failures are caused by compressor, electrical, or motor problems.

Compressor Maintenance to Optimize Chiller Performance

Compressor failure can be the result of any number of factors and is often attributable to problems elsewhere in the system. One simple routine task to prevent compressor failure is checking strainers and filters for dirt and debris and ensuring the compressor and pumps are appropriately sized for the load.

Eddy current testing, at a suggested interval of every three years, reduces the risk of chiller failure caused by condenser evaporator tube leaks or failures. Chiller tubes undergo daily stress as part of their normal operation which can allow rust and corrosion to take hold. Additionally, these rust particles can trickle into the evaporator tubes of the chillers, leading to corrosion that damages the compressor itself.  An eddy test determines the wall thickness of the chiller tubes and can detect possible pitting, cracks and bulges that can precipitate tube leaks. Identifying issues before a major problem occurs prevents downtime and expensive replacement costs.

Chiller Electrical Maintenance to Optimize Chiller Performance

Electrical issues in the chiller plant can be caused by a host of issues including wires rubbing equipment frames or condenser fans not working appropriately.  Electrical overload conditions will cause motors to draw in more current to maintain torque and can lead to overheating and damage to winding insulation.  Regular attention to amperage draw, voltage, and contactors can avoid such issues.

Chiller Motor Maintenance to Optimize Chiller Performance

Chillers, pumps and tower fans use motors to move water and air or compress refrigerant. The failure of any of these motors threatens the operation of the entire chiller system. There are many reasons why motors fail, but three fairly simple, non-damaging tests can avoid a world of headaches when performed consistently.

• Oil Analysis: Regularly scheduled analysis of your chiller’s oil is a valuable aid in assessing internal mechanical condition. Oil comes in contact with many important internal components and can therefore hold valuable information about chiller health. An oil analysis will indicate whether there is moisture, acid, corrosion, bearing wear, impeller rubbing, or other equipment problems present. When an oil analysis reveals the presence of wear, a possible bearing or motor failure can be imminent, and a vibration analysis is recommended. The combination of these assessments will typically identify the failing component.
• Vibration Analysis: Every piece of HVAC equipment with rotating components has its own vibration signature. Any change in this signature can be used as an accurate means of identifying developing problems with chiller bearings, impeller imbalance, or open rotor bars in the motor. Vibration analysis should be performed on a regular basis to build a baseline and trend which can significantly aid in avoiding unplanned downtime and replacement costs
• Motor Insulation Resistance: Insulation problems on motors and drives are typically caused by improper installation, environmental contamination, mechanical stress, or age. Insulation tests should be performed on all chilled water system motors to monitor motor health. These assessments measuring the winding resistance. A low resistance indicates that the winding is deteriorating and indicates potential failure. Insulation-resistance trending can ensure that any changes are readily addressed.

Monitoring Chiller Performance

Selecting quality equipment and performing regular maintenance specific to the needs of each unit ensure a long and efficient life cycle. To protect such investments, the remote monitoring of chillers and cooling system can significantly aid maintenance and service efforts.

Chilled water system monitoring, like that of the Xpress® Energy Optimization Dashboard, provides facilities teams with real-time energy data for all chilled water equipment. Understanding how energy is used can help quickly identify energy waste and equipment problems, as well as overcharges and errors on energy bills. Xpress® also acts as an early warning system, sending emails or texts to staff when equipment such as a fan, pump or chiller is operating outside expected parameters.