The top six places to look for energy losses in buildings

September 2nd, 2014, Published in Articles: Vector

 

A typical thermal imager’s scan of a building can show energy saving opportunities of up to 15% with varying degrees of repair investments required.

Unlike regular digital cameras, thermal imagers create pictures by detecting infrared energy or heat. The thermal imager then assigns colours based on the temperature differences it detects.

With a small amount of training, most people can readily spot abnormal heat flow patterns and follow the heat trail to energy waste. The technique works best when used by people who already possess a good working knowledge of the structures and systems being scanned and can better interpret the temperature variances they see on camera.

Building envelope

The 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 problem with building envelope inspection is that the degree of temperature variance detected may often be very small. So, the best time to scan is during a heating or cooling season, when there is a large difference in temperature, or ΔT, from the inside to the outside of the structure. In general, the larger the ΔT the better.

Fig. 1: Extend the life of your roof by repairing only damaged areas.

While a ΔT of -8°C is typically recommended for insulations inspections, only a minimum ΔT of -16°C is recommended for air leak inspections. Similarly, beware of solar loading, wind, precipitation and other environmental factors which could mask or distort potential problems.

For instance, be careful to understand the direction and amount of heat flow when scanning an exterior wall if the sun is shining on it. When performing flat or low-slope roof scans, make sure that the roof is dry. Achieve best results by performing inspections on clear, windless evenings after dusk, or before dawn, when thermal differentials in the roofing materials are in a transient state.

Remember, not all roofs can be inspected effectively using thermal imaging. Flat or low-slope, built-up roofs are usually the best candidates. Scan the following:

  • Roofs: Wet roofing insulation loses much of its R rating. This means that heat can escape or enter the building much easier through wet insulating materials. In addition to looking for moisture issues, scan the roof surface and follow temperature differences to possible air leak entry/exit points. Note that 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: Due to the natural flow of air with different temperatures, significant air leaks tend to occur at the top and bottom of conditioned spaces where air either enters or escapes the structure.
  • Construction joints and connections: For example, 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, etc.): Non-insulated or unsealed gaps often exist around roof and wall penetrations.
  • Door and window frames and seals: Locate air leaks around windows and doors caused by worn or missing seals. Window and door casings should be inspected for air leaks as well. Repairs are often as simple as caulking or weather stripping.

Fig. 2: If your facility uses a boiler, scan the steam lines to check for leaks, blockages, and failed traps.

Boilers

Boilers are the heart of steam and hot water heating systems. Scan:

  • Refractory and insulation: Thermal imaging makes possible the in-service monitoring and inspection of the condition of refractory linings for performance issues.
  • Fan motors: As with motors in other applications, check for impeded airflow, electrical unbalance, overheated bearings and failing insulation.
  • Pumps: Look for hot bearings, leaking seals and, as with fans, motor faults.
  • Valves: Thermal imagers can identify blocked valves which are nominally open and leaking valves nominally closed.
  • Electrical connections: As with other kinds of systems, look for loose or corroded connections which increase resistance.

Fig. 3: When inspecting motors, pumps, or other rotating equipment, scan electrical connections, housings, end bearing caps and couplings to obtain the best images from which to determine potential problems. Scan the components of rotating equipment, especially the bearings and shaft. Be aware of shiny metal, or other low-emissivity materials or surfaces, as these can cause confusing results if not accounted for.

Motors and generators

Electric motors are one of the biggest energy users in any facility. Overheating and malfunctioning motors and generators tend to indicate mechanical or electrical inefficiencies that lead to unnecessary energy use and sometimes even failure.

Since generators are, in a sense, reverse motors, diagnostics are similar for both kinds of unit. Scan:

  • Airflow: In fan-cooled motors, restricted airflow can cause general overheating, often manifesting itself on the entire housing.
  • Electrical imbalance: A common cause, a high resistance connection in the switchgear, disconnect or motor junction 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 often called for. Beware that over-lubrication can cause abnormal heating as well.
  • Insulation: Look for higher than normal housing temperatures in areas associated with windings. For each 10°C rise over the maximum rated temperature of a motor, approximately half the life of the motor is lost to insulation failure.
  • Electrical connections: As with electrical connections in HVAC systems, look for loose or corroded connections that increase resistance. Heat losses due to high-resistance connections mean that your energy is being given off as heat instead of being used for work.

Steam heating systems

Today, steam systems are more common in industrial than in commercial settings, but some commercial buildings still use them for central heating. Look for:

  • Steam traps: Check traps using both thermal imaging and ultrasonic testing. Each technology works better than the other for certain traps and trap configurations.
  • Radiator coils: Check for obvious steam leaks in radiators and at all visible pipe and joint connections.
  • Steam lines and valves: Look for telltale signs of leaks and blockages and for blow-by at valves that are supposed to be closed.
  • Condensers: Look for leakage of outside air, which reduces condensers’ vacuum, thereby decreasing their efficiency.
Fig. 4: Correctly operating traps should show a temperature differential from one side to the other. All high or low temperatures on both sides of trap may mean that the trap is stuck open or closed. Be aware that a trap may have just cycled, which can also make it appear to be malfunctioning.

Fig. 4: Correctly operating steam traps should show a temperature differential from one side to the other. All high or low temperatures on both sides of trap may mean that the trap is stuck open or closed. Be aware that a trap may have just cycled, which can also make it appear to be malfunctioning.

HVAC system

The heating, ventilation and air conditioning (HVAC) system is usually one of the biggest energy users within a facility. Scan:

  • Ductwork and registers: Even the highest-rated HVAC system wastes energy without a well-sealed duct system. With thermal imaging one can see the thermal pattern of air loss or gain in ducting and also monitor registers to determine whether heating or cooling output is optimal.
  • Fans and blowers: These mechanical elements are, of course, motor driven. In fans and blowers, 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: Loose or corroded connections increase resistance at the connection point, resulting in increased energy costs.
  • Compressors and coils: Regular inspections of the compressors and coils can also help reduce energy costs. A malfunctioning compressor can have a different thermal signature than a properly-operating one. If coils are blocked, or cooling fins are clogged, improper airflow and heat exchange can take place. This can impact system efficiency greatly and also reduce component lifespan.

Fig. 5: Clogged or malfunctioning cooling fins drastically reduce the efficiency of HVAC units.

Electrical system

Many people don’t realise that electrical systems can actually waste money. Waste occurs as components degrade and resistance increases Scan:

  • Distribution panels: Check for imbalance in circuits and loose and corroded connections at breakers, contacts, fuse clips, buss work, insulation deterioration, etc.
  • Transformers: 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, in panels, and at the fixtures. Be aware that thermal imaging can also be used to monitor low-voltage control circuits.

Fig. 6: Abnormally hot electrical connections are not only a potential early warning of failure and a safety hazard, they’re also using excess energy.

Conclusion

Thermal imagers have come down so far in price that most facilities can recoup the cost of purchase in terms of energy savings within six months. Plus, incorporating infrared inspection into regular maintenance provides significant efficiencies to a maintenance team as well as helping them identify and prevent expensive failures.

Contact Gerrit Barnard, Comtest, Tel 011 608-8520, gbarnard@comtest.co.za

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