Improve Chiller Efficiency via Automatic Tube Cleaning Systems
You may not be aware, however, that there is another method to further increase the chiller efficiency at your chilled-water plant, a type of continuous chiller tube cleaning system included in a family of technology dubbed Automatic Tube Cleaning Systems.
Fouled condenser tubes are a primary culprit of chiller efficiency losses, and are common even in chillers receiving good water treatment. In fact, it’s not uncommon to find chillers that appear to be in good working order operating at elevated fouling factors — causing compressor power consumption to increase by 15% or more. Chiller manufacturers also recognize the impacts condenser tube fouling has on chiller efficiency, and a quick review the Carrier Handbook indicates that a layer of buildup as thin as 0.3mm can reduce condenser efficiency by 25%.
A 900-ton chiller can draw 0.547 kW/ton, which, at a rate of $0.09 per kWh, adds up to more than $150,000 per year in electricity costs. Factor in fouled tubes and operating costs can easily escalate 10 to 15 percent, costing you an additional $15,000 to $30,000 per year.
Curious to know how tube fouling might be affecting your bottom line? This free calculator can help you estimate how much the fouling in the condenser tubes at your chiller plant is costing you.
HOW CONTINUOUS TUBE CLEANING TECHNOLOGY IMPROVES CHILLER EFFICIENCY
According to Carrier, “fouling of tubes occurs as soon as a heat exchanger is placed into operation.” Typically, a facility will clean the condenser tubes in the off-season and place a chiller into service in spring. Immediately, the tubes begin to foul and over the course of several weeks the chiller efficiency degrades—which means your chiller efficiency is lowest during the hottest months of July, August, or September, right when you need it the most!
Automatic Tube Cleaning Systems are installed at clean-tube conditions (prior to chiller commissioning for new equipment or right after tube cleaning for existing chillers) and work by periodically passing nerf-like sponge balls through the condenser tubes. Typically, injection cycles occur every 20 minutes but the schedule is tailored to meet site-specific needs. The balls are slightly larger than the tube diameter, and as they move through the tubes, they prevent the build-up of scale, biofilm, silt, or other foulants. The entire injection and collection process is fully automated and controlled by means of a single programmable logic controller. The controller also provides monitoring and alarm functions to ensure the system is continuously operating optimally. You can learn more details on continuous tube cleaning technology by checking out this info on how an automatic tube cleaning system works.
As shown in the figure above, the tube cleaning system is actually a continuous cleaning system and preventative measure the keeps the condenser operating at peak efficiency throughout the operating season. Optimum chiller efficiency is obtained by never allowing fouling to get started.
In August of 2012, a sponge-ball type tube cleaning system was installed in one of two identical 300-ton chillers at The Plaza Hotel and Casino in Las Vegas, Nevada. The tube cleaning equipment was installed on Chiller 1 while Chiller 2 served as the control. The two chillers shared a common cooling tower, eliminating potential differences of environmental variation on the chillers.
The UNLV Center for Energy Research conducted a 3-month study on the impact of the tube cleaning system on chiller energy efficiency, overseeing monitoring equipment installation and operation as well as data analysis, and Figure 3 below demonstrates the tube cleaning system yielded energy efficiency gains of approximately 12%.
Chiller Energy Efficiency Improved 12% by Tube Cleaning System Implementation
Sponge-ball type continuous tube cleaning technology is another tool for facility managers to use in optimizing chiller efficiency in their chilled water plants, and can offer substantial energy savings over the “status quo” of annual condenser tube cleaning. Actual savings opportunities depend on the size of the chilled water plant and local water quality, but can range from $10,000 per year to more than $100,000 in annual savings.