Infrared to detect energy wastage
December 2011, Analytical Instrumentation & Environmental Monitoring
Hot or cold air leaks from buildings, systems and equipment result in energy wastage. However with a small amount of training it is possible to use a thermal imager to spot the abnormal temperatures which lead to energy waste. Unlike regular digital cameras that capture images of the visible light reflected by objects, thermal imagers create pictures by measuring infrared energy or heat. The thermal imager then assigns colours based on the temperature differences it measures. This works best when the imager is in the hands of someone with a good working knowledge of the structures and systems being scanned, who can then interpret the temperature variances seen on the camera.
A typical scan can show energy saving opportunities of up to 15%, with varying degrees of repair investments. Thermal imaging experts suggest that building owners, building managers and facilities engineers inspect the following systems to identify energy losses.
Building envelope refers to the building structure as well as the climate controls within it. The envelope is what separates the outside environment from the inside, and it is frequently imperfect. The degree of temperature variance may be very small – one or two degrees. The best time to scan is when the outside temperature is at least 10°C higher or lower than the inside temperature. Thermal loading or other environmental factors could also mask or distort potential problems. Exterior walls should not be scanned when the sun is shining on them and roofs should be dry and free of water or ice. Inspections should be performed on clear, windless evenings after dusk or before dawn, when thermal differentials in the roofing materials are in a transient state. Not all roofs can be effectively inspected using infrared thermography.
What to scan
Roofs: Wet roofing insulation loses its R-rating. Scan the roof surface and follow temperature differences to possible entry and exit areas for conditioned air. Spot repairs are less expensive than replacement and old roofs are often a challenge to dispose of because of their contents.
Walls between conditioned and unconditioned spaces, including outside walls: Concentrate on the top and bottom of conditioned spaces and also look for indications of missing or wet insulation.
Construction joints and connections: At floor slabs that extend outdoors, there are often heating or cooling losses by conduction through the slab.
Penetrations of the building envelope (pipes, conduits, chimneys): Uninsulated gaps often exist around roof and wall penetrations.
Door and window frames and seals: Look for leaks due to poorly fitting doors and windows but bear in mind that spot repairs to major losses such as roof leaks usually offers faster payback than fixing door and window seals.
The Department of Energy estimates that following up on the findings of an energy audit of a building’s envelope saves most facilities at least 15%.
The heating, ventilation and air conditioning (HVAC) system is usually one of the biggest energy consumers within a facility.
What to scan
Ductwork and registers: Even the highest rated HVAC system wastes energy without a well sealed duct system. With infrared technology the thermal pattern of air loss or gain in ducting can be seen and registers can be monitored to determine whether heating or cooling output is optimal.
Fans and blowers: These mechanical elements are motor driven. Mechanical imbalance will manifest itself in overheated bearings and other components. Thermal images of these systems can also identify shaft misalignment in couplings between the motor and fan.
Electrical connections: A loose or corroded connection increases resistance at the connection, resulting in overheating.
Studies indicate that commercial buildings with constant air volume systems often experience energy losses from air leakage of as much as 33%. Also, studies indicate that air supply temperature differentials due to conduction losses can be as great as 6°C. Considerable savings can be achieved with duct sealing and insulation remedies.
Motors and generators
Electrical motors are one of the biggest energy consumers in any facility. Overheating and malfunctioning motors and generators result in mechanical or electrical inefficiencies that lead to more energy use and ultimate failure. Since generators are actually ‘reverse motors’, diagnostics are similar for both kinds of units.
What to scan
Airflow: In fan cooled motors, a restricted airflow will cause general overheating on the entire housing.
Electrical unbalance: A high resistance connection in the switchgear, disconnect or motor connection box, can usually be pinpointed by an infrared inspection and confirmed using a multimeter, clamp meter or a power quality analyser.
Bearings: When thermal images reveal bearing housings with abnormally high temperatures, either lubrication of the bearing or its replacement is called for.
Insulation: Look for higher than normal housing temperatures in areas associated with windings.
Electrical connections: As with electrical connections in HVAC systems, look for loose or corroded connections that increase resistance.
With motors and generators, specific energy losses are usually of less consequence than failure of the unit. The impact of a motor or generator failure will be contingent upon the nature of the enterprise and the systems affected. The best ways to reduce motor energy expenditures are to keep motors well maintained and operating at maximum efficiency and to size them appropriately and operate at constant speeds.
Boilers are the heart of steam and hot water heating systems.
What to scan
Refractories: Thermography makes possible in-service monitoring of the condition of refractory linings.
Leakage of outside air: This condition is difficult to pinpoint with diagnostic technologies other than thermal imagers and it can lead to substantial inefficiencies.
Boiler casing insulation: Look for heat loss from damaged insulation.
Fan motors: Check for impeded airflow, electrical unbalance, overheated bearings and failing insulation.
Pumps: Look for hot bearings, leaking seals and motor faults.
Valves: Thermography can identify blocked valves that are nominally open and leaking valves that are nominally closed.
Electrical connections: Look for loose or corroded connections that increase resistance.
In boilers, major energy losses associated with stack losses as well as radiation and convention losses typically represent 10 to 20% of fuel input, depending upon fuel type. Insulation and boiler economisers can reduce these losses.
Electrical systems can waste money as components degrade and resistance increases.
What to scan
Distribution panels: Check for unbalance in circuits and loose and corroded connections at breakers, contacts, fuse clips and busses.
Transformers: Monitor high and low voltage bushing connections, cooling tubes and cooling fans and pumps. Look for overheated connections, comparatively cool cooling tubes and hot or cool pumps. Be aware that if the temperature of one electrical leg on a transformer is significantly hotter than the others that leg may be failing.
Lighting control circuits: Check all wiring splices and connections at fuses, switches, and fixtures. Be aware that thermography can also be used to monitor low voltage control circuits.
According to some estimates, lighting accounts for about 20% of all electricity use in the USA and more than 40% of electricity use in offices, stores, and other commercial buildings. While complete retrofits of lighting systems are producing phenomenal returns on investment, keeping lighting controls such as time clocks, photo sensors and occupancy detectors operating properly will help save energy.
Thermal imagers have come down so far in price that most facilities can recoup the cost in terms of energy savings within six months. Incorporating thermal imaging into a regular maintenance programme contributes to efficiency as well as helping a maintenance team to identify and prevent expensive electromechanical failures.
For more information contact Val Verwer, Comtest, +27 (0)11 608 8520, firstname.lastname@example.org, www.comtest.co.za