SWH Collector Diagnosis with Thermal Imaging

Intermediate

Inside this Article

A thermal imaging camera
A thermal imaging camera
Thermal imaging camera screen display
Thermal imaging camera screen display
The shiny barium in the tube on the left indicates that the vacuum is still intact.
A barium getter coating is used to sustain the vacuum in an evacuated tube and can identify tubes that have lost their vacuum. The shiny barium in the tube on the left indicates that the vacuum is still intact. The getter in the tube on the right has turned white, indicating that it has been fully exhausted and that the vacuum has failed.
A neoprene boot is typically placed over this end of the tube to help protect it
A neoprene boot or other style of end cap is typically placed over this end of the tube to help protect it where it is secured to the mounting rack. The boot also can conceal the getter.
An infrared image of a collector
An infrared image of a collector (taken from the ground) shows problem tubes, which appear as a lighter pinkish-purple color. After adjusting the camera’s span and range, an image taken at closer range (from the rooftop) reveals more details.
The evacuated tubes that show up on the IR image
The evacuated tubes that show up on the IR image as dark blue or purple have a lower surface temperature, which indicates the integrity of the vacuum and heat pipe. The dark-red tubes indicate a failed vacuum, heat-pipe issue, or both.
Visual inspection revealed small cracks in some of the heat pipes
Visual inspection revealed small cracks in some of the heat pipes, likely due to freezing of the fluid inside. Other failures occurred at the seam between the heat pipe and the condenser bulb; these failures were revealed by the IR camera.
Two different types of condenser bulbs
Two different types of condenser bulbs. The heat pipe on the left uses a snap switch that isolates the condenser bulb from the heat pipe if overheating occurs. The condenser bulb on the right does not have this feature and transfers heat to the manifold continuously.
The temperature of the condenser bulb exceeded the temperatures of those in the failed heat pipes
The temperature of the condenser bulb in the functional heat pipe (far right) exceeded the temperatures of those in the failed heat pipes. The IR camera is reading the temperatures of the silicone wrap; the dark areas shown on the heat pipes in the IR photo are where the copper is reflecting the cold sky.
Using an IR camera to check water temperature
Using an IR camera to check water temperature at a hot water fixture. The water temperature was well below the temperature expected from the mixing valve.
The mixing valve was set to its highest setting
The mixing valve was set to its highest setting, yet it was only delivering 105°F water. Replacing the valve resolved the issue.
A thermal imaging camera
Thermal imaging camera screen display
The shiny barium in the tube on the left indicates that the vacuum is still intact.
A neoprene boot is typically placed over this end of the tube to help protect it
An infrared image of a collector
The evacuated tubes that show up on the IR image
Visual inspection revealed small cracks in some of the heat pipes
Two different types of condenser bulbs
The temperature of the condenser bulb exceeded the temperatures of those in the failed heat pipes
Using an IR camera to check water temperature
The mixing valve was set to its highest setting

Having issues with solar water heating (SWH) collector performance? A thermal imaging camera can simplify the diagnosis.

Last year, a homeowner with a five-year-old SWH system contacted me for a second opinion. She told me that the designer claimed she was expecting too much, but she was sure that the system had produced more hot water when it was first installed.

Upon arrival, I performed an initial system inspection. The fluid pressure was within the normal operating range for an antifreeze-based, closed-loop system. The differential controller settings were reasonable, and the flow meter indicated that the pump was circulating the heat-transfer fluid (glycol) at an appropriate flow rate. After verifying that the temperature sensor in the storage tank was properly installed and operating, I headed outside to inspect the collectors on the roof.

Collector Maintenance Issues

Diminished collector performance can result from a variety of factors. In systems in which potable water is heated directly by the collectors, calcification in the collector or pipes may occur due to high-mineral-content water. Deterioration of the absorber surface may occur depending upon the quality of the absorber coating and the age of the collector.

Most flat-plate collectors tend to be quite durable but will show deterioration toward the end of their service life. These issues may include leaks where the riser tubes are joined to the headers or failure of the bond between the riser tubing and the absorber plate. There may also be issues related to failure of the glazing seal.

Evacuated-tube collectors are inherently less durable. This is primarily due to the type of glass used (nontempered borosilicate or soda-lime glass) and the need for the collectors to maintain a vacuum to ensure proper performance. A crack or leak around the seal of an evacuated tube will lead to the loss of vacuum, rendering the tube ineffective. When evacuated tubes are manufactured, a barium getter is fired inside the vacuum. If there is oxygen remaining in the tube after the vacuum has been created or there is a small leak, the getter will serve to maintain the vacuum by consuming this oxygen. The getter is typically made of barium, which is silver. As the getter absorbs oxygen, it becomes barium oxide and turns white. The silvery surface is an indicator of the integrity of the vacuum.

While the barium getter can provide visual confirmation of whether or not the vacuum is intact, it is not always simple to observe whether the getter is still present. For instance, some tube manufacturers apply the barium on the tubing behind the absorber. With collectors mounted on tilted racks, the getter can be observed from behind. But the getter on parallel-mounted collectors, which lie close to the roof, may be difficult to observe. Other manufacturers apply the barium getter to the lower end of the tube.

Troubleshooting with the IR Camera

Infrared cameras are particularly effective at diagnosing issues with evacuated-tube collectors without needing to go on a roof. Where standard cameras capture visible light, IR cameras capture infrared radiation and indicate the heat with color or shades of gray. A properly configured IR camera can indicate the surface temperatures of various objects, including solar collectors.

Although not as prevalent, issues with flat-plate collectors can be diagnosed with IR camera technology. If there is a significant variation in flow between two banks of collectors, the bank with the higher flow will have a cooler surface since the heat is being removed faster compared to the bank with the slower flow rate. In large banks of flat-plate collectors, the flow through the collectors may be uneven. An IR camera can diagnose whether the center of the bank is hotter than the outer edges as a result of uneven flow rates. In older flat-plate collectors, an IR camera may be able to assist with diagnosing the detachment of the absorber from the riser tubing or failure of the glazing seal by illustrating temperature variations on the collector glazing or indicating higher temperatures around the seals.

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