Coal, Nuclear

External temperature monitoring for power plants

By John Lenkey III
Aquatemp Global Inc.

During summer break in the mid-1980s two college professors decided to canoe out onto the Delaware River to investigate a theory. They suspected a nearby power plant was exceeding limits set by the Environmental Protection Agency (EPA) and U.S. Army Corps of Engineers for water discharge temperatures. If they were right, the power plant would be fined and the professors entitled to a cash reward. The plant would also be ordered to build a cooling tower to mitigate the thermal pollution problem.

The professors set out on the freshwater river that was influenced by ocean tides and waited for the current to calm at high tide when it was easier to paddle. They took measurements only during that time and recorded some incriminating data against the plant. However, a 15-point monitoring system was ordered from Aquatemp Global and was quickly installed that showed that the violation duty cycle was so short when the river was moving that the agencies’ claims for fines — and for constructing a cooling tower — were found to be unreasonable.

This balanced data saved the utility not only the cost of fines, but also the millions of dollars it would have cost to construct what turned out to be an unnecessary cooling tower.

Decades and many EPA regulations later, utilities are still finding new ways to use monitoring to stay in compliance, increase efficiency and avoid unnecessary spending. Managers of steam turbine power plants that use water to cool condensers can look to three main reasons to monitor discharge and intake water temperature.


  1. Federal, state and, in some cases, municipal laws regulate the temperature of water that can be returned to the public sources such as rivers, lakes and bays.
  2. Plant efficiency can be confirmed by a healthy ΔT (differential in intake from discharge temperature).
  3. Proper discharge temperature must be maintained to avoid shocking and killing water life by a maintenance plant shutdown when the ΔT between the plant discharge canal and the public waters is high. Monitoring a plant’s water systems can lead to more cost-effective anticipatory solutions and avoid government fines.

Long Distance Sensors
Most electric power stations that have water temperature monitors use long distance assemblies to track the mixing of hot water right out of the condensers and to watch its decline in temperature as it mixes with ambient river and lake water.

One tool utilities use to monitor water temperatures is multi-conductor cables with sensors imbedded inside the cables themselves. These cables can be installed by the manufacturer or the utility. The cables are often laid on the bottom, if the discharge canal is shallow, starting at the public domain (the river). Conduit runs all the way to the control room where recorders or computers monitor and sound alarms if limits are being approached.

The longest such sensor cable used to date is three miles. It monitors cooling in a river along a power station’s rapids before the water enters another state. The rapids’ turbulence proved to be quite efficient in lowering temperature. Through monitoring, the final, most-distant sensor confirmed that the temperature was within legal limits and assured that the plant manager could run generate heat output higher than was previously thought.

Applications for Various Installations
Some users install sensors on pilings driven in the center of the discharge canal. One power station on Tampa Bay spaces the pilings at near, middle and at far distances from the condenser and at spacings five, 10 and 15 feet from the surface, which is tidal. In other cases, cable sensors have been suspended from surface floats to maintain a desired distance from the surface during tidal action, including dammed lakes where water levels can vary greatly. Each assembly on the pilings contains three spaced sensors. The cable runs 25 feet to the shoreline, then is spliced into a multi-conductor cable at three spaced locations to run to the control room.

A Long Island utility needed to instrument its weir, built to tumble-cool water before returning it to Long Island Sound. The sensors, which bridge the weir, confirmed that the tumbling process was working. An electric producer in North Carolina uses a lake which varies 12 feet and was provided a sensor assembly on a lengthy gimballed arm and float which swung up and down on a bushing to maintain near-surface monitoring.

Where icing is a problem, steel wires have been used to protect the sensor-installed cables. In an installation on the eastern shore of Lake Michigan, four layers of steel wires were laid over the multi-conductor sensor cables because alternative east-west winds create mini-icebergs that were blown out from the shore. When the wind shifted they floated back and butted into the shoreline like a bulldozer. Lighter weight steel applications are used for middle New York State and Midwest installations.

Creative Uses
Most companies that have used these long-distance monitors maintain them for at least 20 years, during which operators record water performance against ambient air temperatures and weather conditions. Eventually, they build a profile of operations that can enable managers to run a plant with higher output and efficiencies.

Another use of the systems is to profile the public waters before the power station goes online and then compare it to what temperature changes, if any, have occurred once operations are underway.
An extreme example that Aquatemp Global fulfilled is the nuclear generating station at Hancock’s Bridge, New Jersey. The facility is jointly owned by three companies and uses Delaware Bay water for cooling. The engineers installed the system to monitor conditions before operations commenced. This station was located in a soggy, swampy venue although the station itself was on firm ground. The area needed for monitoring, however, posed some major obstacles. Aquatemp eventually succeeded in running cables down a buoy-to-anchor supporting aircraft steel strength member, underwater to shoreline and then to a pump house where the recordings were made. Later, when the station began operations, data showed the impact of heat output from the plant in the large body of Delaware Bay reported by the Aquatemp sensored cables proved to be negligible.

Another northern nuclear utility installed Aquatemp monitors in a river that led to salt water. A maintenance shutdown in winter shocked and killed some 600,000 fish due to the sudden drop in temperature around the formerly warm discharge canal; the utility was fined per fish. Upon installing discharge canal sensors and ambient water sensors in the public domain for comparison, the problem was solved. The sensors now help managers better plan for maintenance shutdowns and predict the effect changes at the plant may have on surrounding marine life.

About Aquatemp
Aquatemp was formed in 1971 when “thermal pollution” became a buzzword in the industry and has instrumented utilities up and down the East coast. Originally located in New Jersey, the engineering design center is now in Littleton, N.C., and production of shorter units is in LaVale Maryland, where chief technician Paul J. Dudeck molds polyethylene seals and splices into polyethylene cables. The choice of polyethylene was based on trans-Atlantic cables, which were found to last seemingly forever.
Aquatemp offers long distance underwater sensor cables that monitor temperature, parts per million, chlorine, pressure, and much more. For more information, contact the author at [email protected].