June 2009

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Thermal imaging a key to locating HVAC system leakage
a key to locating HVAC system leakage

Colin Plastow

 

Colin Plastow
Industrial Product Manager
Fluke

Just about every property manager today is focused on optimizing the energy efficiency of their building. One of the key areas of focus – and one where the greatest savings opportunities can often be found - is HVAC system efficiency.  

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Leakage issues in particular can be a prime cause of wasted energy. While there are a number of measurement tools that can do a creditable job of identifying leaks, handheld thermal imaging equipment is becoming an increasingly popular device of choice for conducting inspections.  

About air leakage 

Air leakage can work two ways. Cold air from the outside can leak through floors, or warm air leak out of a facility around areas such as the chimney.  Even before turning on a thermal imager, a technician will usually have a general idea of the relative “leakiness” of a dwelling. Generally speaking, the greater the airflow that is required to reach a certain pressure differential, the leakier the occupied space is. 

When conducting an energy audit, bear in mind that locating air leakage the higher temperature difference between inside and outside air the easier it is get good results. Therefore the most effective time to perform a thermal imaging inspection is when a space is being heated or cooled (winter or summer), and not in the spring or fall when there is only a small difference between inside and outside temperatures. 

Many assume that the prime area of concentration for imaging would be windows and doors. However, modern windows and doors often contribute little to total air leakage in most buildings and account for a relatively small percentage of the total heating and cooling losses.  

The most serious leaks occur at the top and bottom of the conditioned building envelope – i.e. under roofs and in basements. Large gaps are often found around plumbing pipes, recessed light fixtures, chimneys, eve soffits, chaseways and basement rim joists.  

Therefore it is important to look carefully at the tops and bottoms of plumbing runs and plumbing vents. Also scan the places where utilities such as telecommunications lines and electrical cables enter the conditioned-air space.  

Convection vs. conduction 

Uncharacteristically cold floors in winter will indicate heat loss by convection. Even if these floors are insulated, there could be air spaces between the insulation and the floor, allowing the floor to cool. 

Using blower doors a technician armed with a thermal imager and a pressure gauge (to verify the pressure differential between the occupied space and the outdoors in various parts of a building) can easily find areas that contribute to the loss of conditioned air by convection, whether that’s heating loss in the winter, or cooling loss in the summer.

 Heating and cooling losses can also occur by conduction. Conduction losses can happen, for example, at floor slabs that extend outdoors and have no thermal barrier between the indoor and outdoor portions. Conduction can also happen in conjunction with convection when insulation is missing from an outdoor wall. 

Technology tools 

When selecting a thermal imager, look for one that offers dual imaging capability. This capability combines visible light capture with infrared images for better identification, analysis and image management. Aligning the two images allows for more detailed analysis, while making it much easier and faster to pinpoint areas where further investigation is needed.  

Control Solutions, Inc A thermal imager detects surface temperature differentials and presents these as thermal patterns on a high resolution screen. However, special care should be taken when interpreting thermal readings, since temperature differences can also indicate something other than a leak, such as underlying moisture damage. 

Follow-up actions 

Fixing energy-wasting leaks is simple for the most part – i.e. to seal the leaks in the problem areas identified by the thermal imager. Sealing can include plumbing runs and plumbing vents at tops and bottoms. Also utility access holes and recessed lighting fixtures should be sealed as required. (Warning: If not done properly, sealing recessed lighting “cans” that are not appropriately rated will create a fire hazard. Seek expert help.) 

Where suspected air gaps between walls and floors and insulation cannot be sealed, seal the ends of the gaps. Also, create thermal barriers where conduction losses have been identified.  

HVAC system leakage is a common problem, but the good news is remediation is relatively simple and cost-effective.  In most cases a leakage inspection will uncover at least a 15% potential savings in energy costs. With the added accuracy and speed of thermal imaging technology, those savings could be even higher.  


About the Author

Colin Plastow has been with Fluke Electronics Canada since 1987 in various support and product management positions. Today, as Industrial Product Manager for Fluke, he brings his expertise in electronic test and measurement to customers in high-tech and industrial markets. Mr. Plastow continues to share his in-depth industry knowledge through various customer seminars, as well as educational articles published in leading industry publications. He may be contacted at colin.plastow@fluke.com

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