Using Thermal imaging From the Sky to Monitor Nordic District Heating Networks

Dec 14 2012

Introduction
Old Pipes Require a Modern Detection Tool
Thermal Map of the Entire City
Automated Detection and Classification of Leakages
Conclusions
About FLIR

Introduction

District heating is a system that enables distribution of heat generated in a centralized location for commercial and residential heating. Steam or hot water is distributed to companies and households via an underground pipe network. The efficiency of heating systems throughout the city can be increased thus enabling district heating to reduce a city’s carbon footprint. District heating is the most economic method for a city to reduce carbon emissions.

It is difficult to maintain a large district heating network. In order to help large Scandinavian cities to effectively monitor and maintain their district heating networks, the Linköping, Sweden, based company Termisk Systemteknik has developed a district heating scanning system from the sky, based on thermal imaging cameras from FLIR Systems.

Thermography experts at Termisk Systemteknik have mounted a FLIR SC76000 on the bottom of a small plane for district heating inspections. A thermal map is obtained of the entire city by flying over the city and recording the thermal images. Using this it is possible to detect and localize district heating leaks.

An automatic detection system is used on the thermal data for automatic identification of leaks and other issues to the district heat maintenance teams. According to Stefan Sjökvist, director of Termisk Systemteknik, in order to achieve these results, a considerable amount of research had to be done.

The FLIR SC7600 thermal imaging camera that was used for the district heating monitoring system contains a cooled Indium Antimonide (InSb) infrared detector that produces thermal images with a resolution of 640 x 512 pixels at a thermal sensitivity of 20mK (0.02 °C). Stefan added that it is especially useful for this application because of its high frame rate and short integration time. Full resolution at a frame rate of 100 Hz can be captured. While flying over a city at moderate speed and require clear and sharp images such high-speed acquisition and short integration time is indispensable.

The FLIR SC7600 thermal imaging camera is mounted in a plane, looking straight down through an opening in the plane's hull.

A gyro-stabilized platform compensates for the plane’s movements, enabling the FLIR SC7600 thermal imaging camera to record steady thermal images.

Old Pipes Require a Modern Detection Tool

Localizing leaks in district heating is of utmost importance to the companies administering the district heating systems, according to Sjökvist. He added that in Scandinavia, district heating systems have been installed in most of the large cities. However, a significant portion of the district heating infrastructure is quite old.

Installation of certain parts was done in the fifties and sixties. It is possible that old pipes degenerate over time because of corrosion and will start leaking eventually. There may be a difference in the exact numbers but each year, the Swedish companies alone lose several million cubic meters of water. This constitutes not only a large financial loss, but also a loss to the environment as well.

It is however tough to identify these leaks conventionally. The amount of water leaving the centralized heat facility and the amount of water arriving at each building or household is determined by the district heating companies. These measurements are also made by certain substations. With this information it is possible to find out how mmuch water is lost to leaks for small areas. However there is no data on the actual location of these leaks. In order to find the leaks manually, the pavement has to be opened up, which is expensive especially if there is no leak in that location.

This un-analyzed thermal image already clearly shows leaks in a district heating pipe.

Thermal Map of the Entire City

In order to determine this, Termisk Systemteknik developed their district heating service. They fly over the city, mapping the entire area. A Global Positioning System, several gyroscopes, a digital compass and several other pieces of equipment that have been installed on the plane allow us to very precisely geo-reference each captured thermal image. These are then stitched together into one large map of the entire city. To make sure each pixel is accurately linked to the right physical location, the thermal images are compared with official maps and satellite images by specially developed software, where necessary automatically stretching or twisting the thermal image slightly to compensate for tiny differences in the viewing angle due to non-linear motions of the plane.

A thermal map is formed comprising several thousands of single images of the entire city. This map can be accessed in a way that is very similar to Google Maps. The maintenance personnel of the district heating company can easily zoom in and out, ad layers of information, tweaking thermal images to review particular locations.

The thermal images are analyzed and an extra layer of information is added. District pipelines are marked with blue lines. Green outlines mark smaller leaks and red outlines mark serious leaks that require immediate attention.

Automated Detection and Classification of Leakages

In order to help the analysis software to automatically point out leaks to the user, a lot of information needed to be filtered out, according to Sjökvist.

Vehicles, pedestrians, animals, insulation faults in roofs, all of these very common phenomenon cause thermal radiation that can potentially pop up as an unwanted alarm. Hence knowledge about thermal signature detection has been used to identify these parts of a thermal image in order for the automatic leak detection software to ignore those parts of the thermal image. The resulting map comprises an information layer on the location of district heating pipe work and of the location of detected leaks.

Certain locations require immediate attention. Large volume leaks not only lose the company money, but can be dangerous too, with all the boiling hot water spilling out. Other locations indicate leaks that are developing. Old and deteriorating insulation causes warmth to leak out, cooling down the water, effectively losing energy. These may not be urgent, detecting such locations allows the district heating companies to plan maintenance on those pipes before they deteriorate further, which would no doubt cause leaks later on.

After seeing this leak in the report, the district heating company went there to investigate. It turned out to be a very large leak. Needless to say the company was very glad that this major leak was detected.

Conclusions

Sjökvist sees room for improvement in the amount of human involvement required. He states that they want to further automate the map production process. This process is now semi-automatic, which means that human involvement is still necessary, in order to oversee the activities of the computer and to double check for inaccuracies in the stitching for instance. They want to perfect that part of the process in order to limit the amount of man hours needed and speed up the delivery of our reports and of the post analyzing software to the customers.

About FLIR

FLIR was founded in 1978, originally providing infrared imaging systems that were installed on vehicles for use in conducting energy audits. Later, we expanded our focus to other applications and markets for our technology, in particular, designing and selling stabilized thermal imaging systems for aircraft used by law enforcement. We have since grown substantially due to increasing demand for infrared products across a growing number of markets combined with the execution of a series of acquisitions. Today we are one of the world leaders in the design, manufacture and marketing of thermal imaging and stabilized camera systems for a wide variety of applications in the commercial, industrial and government markets, internationally as well as domestically.

Our Thermography business primarily consists of the design and manufacture of hand-held thermal imaging systems that can detect and measure minute temperature differences, which are useful for a wide variety of industrial and commercial applications. Uses for our Thermography products include high-end predictive and preventative maintenance, research and development, test and measurement, leak detection and scientific analysis. A growing distribution network has enabled us to penetrate existing and emerging markets and applications worldwide.