United Trades Exclusive
maximizing chiller efficiency
By Dale Yelnich
The best way to understand a chiller is to think of it as a giant sized refrigerator for commercial machinery operations. They are most commonly employed for plastic blow molding operations, metal working and machine tooling, power generation plants and they are even used in the semi-conductor industry, just to name a few. The need to cool these specialty machines comes at a hefty energy use price tag, since chillers are some of the most expensive units to run. But they are absolutely needed and necessary for many commercial tasks.
Modern high efficiency chillers can be up to 50% more efficient than older centrifugal chillers of just 10 to 15 years ago, through the use of better cooling transfer rate technology and software based computer controls. But although both of these advancements are important, there are other design functions that also contribute. Things like direct drive adaptations that eliminate power loss through gearing, which boosts efficiency two ways. By eliminating gears, it automatically makes the unit more efficient, which is the first way. The second way is that it also eliminates the need to lubricate the gearing, and that keeps oil contamination out of the cooling system to boost cooling effectiveness.
Newer purge systems allow the user to purge the system of containments without losing any refrigerant. This advance is built-in to new chillers, but in most cases, they can be retrofitted to older models to augment their efficiency. Of course, even the highest efficiency chillers are most efficient when they are not running. To that end, industries are beginning to adapt their cooling needs by installing two (or more) chillers. Instead of having one large chiller running at all times, in many cases during off-peak manufacturing hours, one smaller chiller can adequately get the job done. In this scenario, they can both be used during peak hours for maximum cooling, and if one breaks down, the other can always serve as a back up.
But design alone does not an efficient chiller make. No matter how efficiently a chiller is designed to run, routine maintenance will keep it at its most efficient chilling apex.
Keeping a log of chiller performance, although it may seem old school, is the best way to keep track of efficient performance. Logging in temperature, pressure, flow rate and fluid level is the best hands-on method to detail findings on a day to day basis. This written history is indispensable to the overall efficiency of any chillers operation.
One of the most overlooked aspects of chiller efficiency is to reduce the water temperature before it enters the condenser. By doing this, the condenser doesn’t have to work as hard to cool the incoming liquid, and by not working as hard, it naturally becomes more efficient.
When using open water sources, the condenser water should always be treated to reduce fouling in the condenser tubes. Always check sensors that may alert you to containments in the cooling system. Things like sand, dirt and corrosion will pit or damage pipes or valves, and this will make any chiller less efficient and potentially cause other problems. The best cure for this situation is a cooling tower blow down, or bleed, that drains and removes contaminants before they can damage the cooling system.
Always purge non-condensables that have entered the cooling lines. Both air and moisture can leak into low pressure chiller lines, and once inside, they can reduce chiller effectiveness by up to 7% at high loads. The most modern chiller units are essentially hermetically sealed and reduce or eliminate non-condensable contaminants from entering. That is one of the biggest advances in modern designs.
Keep them clean. Chiller systems lose efficiency as their tubes become gunked up with such things as algae, rust, scale and mud, among others. All of these impurities within the system, will compromise a chillers efficiency, and the tubes need to be cleaned out on a regular basis. Although there are chemical washes that will do the job, the best way to clean the tubing is by annual mechanical brushing using a rotary cleaning machine. Keeping them clean will always keep heat transfer efficiency at its highest.
Other things to consider are regulating flow rate. A lower flow rate uses less energy and reduces the wear and tear on the internals. Have the compressor oil analyzed, in a lab, for contaminants. Moisture in compressor oil may mean there is a purge unit problem. Check wiring and switches for hot spots, worn contacts and general degradation. Run diagnostics on sensor calibrations and diagnostic controls. Calibrations that are even slightly off lead to increased inefficiency.
Although high efficiency chillers begin with design and function, keeping them efficient is the key to lowered energy costs and greater effectiveness. Regular maintenance counts for just as much as design and implementation, and that’s the best way to make sure that your high efficiency chiller stays efficient.