Chillers suffer from reduced efficiency caused by refrigerant contaminated with air, oil, moisture, or acid. Unaddressed, many are in danger of catastrophic failure.
Oil: The Most Common ContaminantA recent ASHRAE research project (601-TRP) sampled refrigerant from 10 randomly selected chillers. All contained excess oil even though three of them had recently had their refrigerant recycled. The oil content in the refrigerant of those three was 3 to 7 percent. The others had oil contamination ranging from 9 percent to more than 20 percent. Table 1 shows approximately how energy efficiency declines as excess oil builds.
Until recently, however, little has been done to identify and remove excess oil from chillers until it becomes a major problem. The reasons? First, aside from decreasing efficiency, oil on the refrigerant side does no damage to the system and gives little indication of its presence. Compared to moisture, which creates acids and leads to machine wear and catastrophic shutdowns, oil is a benevolent contaminant. Second, it costs more to learn of its presence. Most mechanical contractors routinely perform oil analysis to detect moisture, acids and metal fragments. But refrigerant analysis, which reveals the presence of oil, costs as much as five times more, so it usually is not performed. And, because oil usually accumulates gradually in refrigerant through migration, the attendant loss in efficiency usually is diagnosed to be some other cause. It isn’t until performance has significantly degraded that oil is suspected.
So, the typical way of dealing with oil has been to wait until it becomes a serious performance problem, belatedly identify oil as the cause, and then decontaminate the refrigerant charge or install a fresh one. Unfortunately, this is an expensive solution both in the ramped up power demands for the chiller, and the cost of decontaminating or replacing the entire refrigerant charge.
Water and Acid: The Most Dangerous ContaminantsMoisture in the refrigerant side presents one of the most common and costly problems to a chiller. Moisture in refrigerant not only reduces chiller efficiency, it also creates serious damage in several different ways. Undetected, moisture can lead to significant downtime and repair expense. When moisture gets into the refrigerant side of a chiller or refrigeration system it can do more damage than any other contaminant. Moisture can:
- Form as ice in expansion valves, capillary tubes and
- Combine with lubricating oil in the compressor to form acids that
attack the motor windings, leading to burnout.
- Remove copper ions from tubing and deposit them on hot surfaces,
causing bearings to seize.
- Join with oil to form a sludge that blocks oil flow passages, pits
polished surfaces, and restricts metering devices.
Significantly reduce chiller efficiency.
Air: The Non-Condensable ContaminantAir is one of the most difficult contaminants to remove from a chiller or refrigeration system. If left in the refrigerant side, this non-condensable can cause excessive head pressure and higher operating temperatures. The result is higher utility costs, degradation of lubricant effectiveness, and premature compressor problems.
Fortunately there are many solutions for these kinds of contaminants such as purge units that retrofit to chillers. Some units decontaminate chillers for air, others remove oil, moisture and acids. In process heating applications where cooling is required and where lost production can cost a fortune, these purge units make solid sense.