February - March 2008
ensure chiller
By Rory S. Reiley HBEC, MBA
Chiller plants represent up to 53% of the total energy used in a building and consume large amounts of electricity. Chillers represent a substantial capital investment for our building and are a major contributor to operating costs in commercial buildings. For many buildings, chillers are the largest single energy users, and comprehensive maintenance is critical to ensure their reliability and efficient operation.
Here
are five simple things you can do to ensure a sustainable chiller plant.
Daily logs — keeping a daily log lets you trend data to see when things are going bad. What is the correct lube oil temperature for your chiller when it is not running? A typical Trane centrifugal chiller would have an oil temperature of 120 -140 degrees when it was idle to keep refrigerant from migrating to the coldest area of the oil sump. When it is running, oil temperature would be from 90 to 100 degrees.
Others readings of importance would be the approach temperature to determine when to clean the tubes of your chiller. Lastly the high and low parameters should be shown on the logs. This will help the operator’s to identify problems with the chillers.
Condenser tube cleaning — is the biggest factor in energy savings. Dirty condenser tubes in a chiller impede heat transfer and as a result, decrease efficiency and consume large amounts of electricity. Centrifugal chillers operate with a large amount of tubes that carry water through them. When they get dirty, the heat transfer becomes less and the machines experience high head pressures in their condensers and it is detrimental to the compressors and lessens their life cycle. It is essential that they be cleaned at least annually,
Leak free Chillers — Low pressure chillers operate below atmospheric pressure and can suck air into their condensers causing high operating conditions. We log our purge units daily and can see when a machine is starting to leak. This is accomplished by the purge counts that are counted on our purge equipment. Air trapped in a condenser will become trapped otherwise and cause high pressures in our machines, increasing compressor power requirements and reducing overall efficiency and cooling. Low pressure chillers operate below atmospheric conditions and have dedicated purge units installed on them to maintain designed condenser pressure limits. It is estimated that a one pound increase in pounds per square inch (PSI) equated to a three percent loss in chiller efficiency.
Stop Scale and dirty tubes — hire a water treatment company to help you with your plant. Some systems require more frequent treatment and monitoring of the chemical injection system. Over treatment and under treatment can cause severe problems for you.
Oil and refrigerant analysis — should be conducted annually when you do the annuals on your condenser for cleaning. Oil and refrigerant analysis can help you to detect problems with your chiller. Testing is done by spectrometric chemical analysis to determine contaminants, moisture, acids, and metals in your systems.
To read the full version of this article, go to the Hawaii building engineer’s association site @ http://www.hawaiibea.com
Rory S. Reiley, engineer, educator, contractor, has worked in all phases of new construction, facility management and design-build project over the last 10 years. He is head of maintenance at TOPA Financial Center, the president of the Hawaii Building engineers Association and holds a master’s degree in business.
