This project was funded under Energy Commission's PIER Energy Innovations Small Grant Program (EISG), which supports the development of
new technologies that are in the proof-of-concept stage.
EISG Grant Number: 00-23
Organization: J&D Thermo-Fluid Technology, Inc.
Status: Completed 2004
Contact: David Michel III, Energy Systems Research Office, Energy Innovations Small Grant Program (916) 651-9381
Chillers are major energy-consuming devices in large commercial and institutional buildings. They provide chilled water in central-air-conditioning
systems in schools, hospitals, public and commercial buildings, and in industrial process equipment. The electricity consumed by medium-to-large
chillers (200–2,000 tons) ranges from 0.25 kilowatt (kW)/ton to 0.57 kW/ton, at 40% and full load respectively. A 2,000-ton system, operating at full
load on a hot afternoon, will consume over one megawatt-hour per hour. Fouling of condenser tubes decreases chiller efficiency dramatically. To
limit fouling, water in the cooling tower is drained to carry away the concentrated mineral salts, and fresh water is introduced. Fouling still occurs and
results in increased electricity consumption. This is particularly serious on hot afternoons, when air conditioning consumes 30% of all electricity.
If the method studied in this project can alleviate the problem of fouling of the condenser tubes, chillers will run more efficiently during the entire
cooling season, resulting in substantial and continuous savings in electricity. Increasing the efficiency of cooling systems will reduce the peak
demand for electricity during the hottest days of the year and save a substantial volume of water.
This project studied a unique, electromagnetic precipitation and filtration method to prevent or mitigate fouling in chiller condenser tubes. It is based
on two technologies: solenoid-induced precipitation and side-stream filtration. Solenoid-induced precipitation utilizes a square-wave pulsating
current to create time-varying magnetic fields. The magnetic fields then produce an induced, pulsating electric field in the circulating water. The
electric field causes excess mineral ions such as calcium and magnesium in cooling-tower water to precipitate as mineral salts. These salts
provide nucleation sites for other dissolved mineral ions. As the cooling-tower water continuously circulates, the precipitated seed crystals grow into
larger particles that are removed by side-stream filtration. Removal of scale-causing mineral ions from cooling-tower water prevents or significantly
mitigates fouling at the condenser tubes, resulting in direct electricity savings. The removal of mineral ions by the side-stream filtration system also
permits an increase in the concentration cycle of the cooling water (the time period between replacements of the cooling water) resulting in
substantial water savings.
The goal of this project was to determine the feasibility of using solenoid-induced precipitation and side-stream filtration to maintain 90% heat-
transfer efficiency of chiller condensers by limiting scale deposits on the condensers. The researchers established the following project objectives:
1. Fabricate a prototype system using both solenoid-induced precipitation and side-stream filtration for medium-to-large chiller applications,
(greater than 200 tons).
2. Demonstrate that this technology can limit scale deposits to maintain 90% heat-transfer efficiency using a concentration cycle of five.
3. Demonstrate that this technology can limit scale deposits to maintain 90% heat-transfer efficiency using a concentration cycle of eight.
1. The researcher constructed a test-flow loop that consisted of a laboratory cooling tower, heat-transfer test section, an automatic blow-down
system, a flow meter, solenoid-induced precipitation, and side-stream filtration.
2. The researcher conducted fouling tests using a high heat flux of 90-100 kilowatt/square meters (m2) in order to accelerate the fouling process,
a practice common among fouling researchers. Controls limited variation of the electric conductivity of circulating water in the simulated cooling
tower to within 5% of the set conductivity value. A solenoid valve controlled the blow-down using input from the electric conductivity meter. This test
ran for five cycles of concentration. The heat transfer coefficient remained above 90% for 150 hours with no detectable trend to lower values.
3. The test procedure used for eight cycles of concentration was similar to the above. In this test the heat-transfer coefficient remained above
90% for 150 hours, with no detectable trend to lower values. In a control test, the heat-transfer coefficient dropped below 90% after about 50 hours
and displayed a marked downward linear trend thereafter.
• This project successfully constructed an experimental apparatus to test the feasibility of the method.
• The heat-transfer coefficient remained above 90% for 150 hours and five cycles of concentration.
• The heat-transfer coefficient remained above 90% for 150 hours and eight cycles of concentration.
• Particulate matter captured in the side-stream filter caked into a hard substance during the test. Continued operation would result in an
inoperable filter. Some back-washable filters are designed specifically to reduce the accumulation of calcium carbonate scale crystals so that the
scaling is minimized and does not become a problem. It is recommended that tests be done to verify the benefit of these filters when operating
specifically in the conditions created by the use of this method.
Based on findings in this project, chiller condensers equipped with a device incorporating this method could be operated within 10% of maximum
peak performance. This could result in significant energy savings for operators of medium-to-large chillers. The present project demonstrated the
feasibility of integrated anti-fouling technology.
The heat-transfer performance of a water-cooled chiller degrades as the condenser tubes become fouled. As the fouling decreases the efficiency of
the chiller, energy consumption increases. Typically, a large chiller consumes 0.6 kW/ton when its condenser tubes are clean free of and scale.
When the condenser tubes become fouled, the chiller runs at a level substantially greater than 0.8 kW/ton. The cost of correcting this problem is
relatively small compared to increased energy costs due to fouling in the condenser tubes. If the results from the project are widely used in
California, water-cooled chillers can be operated near initial peak efficiency. Ratepayers who operate large chillers will be the primary beneficiaries.
Other ratepayers will benefit from the decreased load on the grid during peak summer hours, when air conditioners are widely used.
The manner in which particulates are filtered from water remains a technical challenge for this project that must be solved prior to
commercialization. Calcium carbonate and other crystals accumulated at the top of the filter medium, caking into a hard substance over time. The
researcher must redesign the filter to avoid caking of calcium carbonate scale crystals. Some filters are designed to be back-washed to reduce the
accumulation of materials. Other solutions should also be investigated. Once that problem has been overcome, the researcher should work directly
with a commercial chiller manufacturer. That work should entail integration into standard commercial products and a field test of prototype units.
This project is part of the research portfolio of the California Energy Commission. The Energy Commission supports energy research and
development that improves the quality of life in California by bringing environmentally sound, safe, reliable, and affordable energy services and
products to the marketplace.