Testing Building Envelope Systems Using Infrared Thermography

Transcription

1 John Sne Rob Spring, P.E. Testing Buiding Enveope Systems Using Infrared Thermography Abstract The structures we ive and work in are susceptibe to quaity and performance probems during construction and maintenance that can impact performance and may, in some cases, render them dangerous. Regardess of the buiding type invoved, infrared thermography can provide remarkabe, nondestructive information about construction detais and buiding performance. This paper discusses the numerous appications for the technoogy currenty being used to inspect buiding enveopes. These incude vaidation of structura detais, verification of energy performance (conduction and air eakage), ocation of moisture intrusion, and the identification of structura and system degradation of roofs and facades. Exampes wi be given for each appication and the basic conditions required wi be discussed. Image 1. Excessive heat oss and poor ventiation resuted in costy ice damage to this arge roof. Introduction Buidings of a sorts, from homes to factories to high rises, can be troubed by probems reated to design, construction and maintenance that can be difficut to diagnose and resove. The major probems found in buidings incude: excessive energy use due to missing or damaged insuation, insuation that is performing inadequatey, and excessive air-eakage across the therma perimeter moisture damage due to eaks or condensation, especiay in the was or roofs ice damage to soped roofs poor HVAC distribution or performance inadequate verification of construction detais or structura performance deaminations of façade materias sick buiding syndrome, mod growth and other heath reated issues Often the probems as we as their causes and consequences simpy cannot be seen unti after costy damage has been done. At that point the ony recourse may be extensive, costy reconstruction. The commercia buiding in Image 1, a nursing home, had extensive probems resuting from a poory designed roof/ceiing insuation system; these incuded excessive heat oss during the winter months and, as a resut, extensive ice damage due to snow met. Hundreds of thousand so doars were spend in various, poory panned attempts to correct the underying causes. In the end the owners simpy ived with the continued probem because corrective actions were deemed too expensive. Despite this unfortunate

2 resoution, the thermograms heped the owners negotiate a financia settement with the architects and contractors. A great vaue of infrared thermography is that it provides a means of seeing the invisibe therma signatures reated to many of these probems in buiding. When propery used, thermography enabes buiding owners, architects, contractors and inspectors to ocate probems, verify buiding performance, and vaidate soutions. When peope act on this information, significant savings resut and buidings are more comfortabe! A surfaces radiate invisibe heat energy. You ve fet this energy emitted by the sun or a stove burner. Infrared cameras are speciay-designed eectronic devices that detect therma radiation. They convert this radiation into therma images, or thermograms, which visuay portray temperature differences as sma as 0.05 C. These portabe, battery-operated instruments record the therma data either as sti, digita images or on conventiona videotape or digita video. The image is dispayed ive in a viewfinder or on an LCD view screen. Different radiant temperatures are shown as different coors or shades of gray. Athough it may sometimes be usefu to dispay temperature vaues, this is often not required in buiding work. Rather the differences are what is usuay of interest. Given the right conditions most buidings exhibit characteristic therma patterns that can be interpreted by a quaified person. The infrared systems themseves are quite easy to operate and, thus, a number of thermographers conduct buiding inspections. The tasks of interpreting the imagery, understanding the root cause probems, and finding soutions are a more difficut. Because of this, thermographers often work cosey with a team consisting of buiding speciaists, architects, and contractors. The key to using thermography successfuy is understanding what therma patterns are associated with the probems being studied and knowing when those patterns wi become visibe in the infrared image. Image 2. When conditions are right, it is possibe to ocate missing or damaged insuation, such as this poory instaed injected foam in a residentia buiding. Buiding appications for thermography Thermography has been used since the mid-60s to sove buiding probems. During the ate 70s and eary 80s, a time when fue prices rose dramaticay, thermography was embraced widey as a too to hep determine buiding performance. Since then other appications have been deveoped and refined, especiay reated to verification of structura performance. The major buiding-reated appications for the technoogy are detaied beow. Insuation checks Missing, damaged or non-performing insuation wi stand out ceary in a therma image when there is at east a 10 C (18 F) stabe temperature difference between the conditioned space and the outside air. If is often possibe to do work with ess of a temperature spread due to differences in the therma capacitance of the buiding materias. The inspection is typicay done from both inside and outside. Often the best resuts are gained from inside because of fewer infuences, but a better overa understanding of the buiding can often be gained from arger views of the outside eevations. It is essentia to know the type of insuation in the buiding and construction detais, incuding how the insuation was instaed. Insuation may be in pace but not performing; often a destructive evauation is warranted to estabish baseine conditions or understand the exact construction detai. Each type of insuation has a characteristic therma pattern. Image 2 shows a cassic pattern associated with injected foam insuation in a wood-framed wa. This type of insuation, a soft foam, is susceptibe to shrinkage and cracking when poory instaed.

3 Air eakage ocation Excessive air eakage can account for up to haf of the energy consumed to condition buidings. Of course adequate air exchange is essentia for the occupants heath and safety, but most buidings have a far higher rate of air exchange than is necessary. The root cause is often poor design and/or construction which aows air to move across the therma perimeter. The probems can be as straightforward as a faied door weather sea or as compex as an air pathway through a pumbing chase in an interior wa or ceiing penum. The eakage pathway is often compex and, without infrared, extremey difficut to visuaize. Image 3: The impropery instaed fibergass yieds an irreguar therma pattern. The resuting cod spots commony host wa stains or mod growth. Many factors impact the image you wi see. When work is done in the daytime or eary evening, the impact of soar oading must be considered. The affects of the sun can easiy ast 6-8 hours on both the inside and outside after a wa has been exposed. This often resuts in the direction of heat fow being reversed, making for confusing images and misdiagnosis. Wind must aso be reckoned with, as it can both quicky eiminate the therma difference on a surface as we as enhance others. If buiding probems are wind-reated, i.e. we are cod on windy days, then it is wise to conduct the inspection with a wind oad. The costs of poor performance of insuation are huge. In addition to excessive energy consumption, there may be costy freeze-ups of water pipes or fire sprinker systems; heath issues associated with mod growth in cod spots, damage to roofs and interiors caused by ice dams, condensation, and water intrusion. Image 4: Propery instaed ceuose is an exceent insuation. Unfortunatey, it is often poory instaed with missed areas and setting the most common quaity probems. Image 5: Many types of insuation are susceptibe to air infitration. The fibergass shown here does not stop air fow through the wa section. Air eakage inspections are best conducted when air fow is directed and controed. This can be accompished with exhaust fans, speciaized bower fan door, or, in arger buidings, by temporariy atering the HVAC system, to create a negative pressure inside. During the heating season the resuting sites of air infitration appear cooer. The work can be done any time of year the indoor/ outdoor temperature difference is greater than a few degrees. Bower door fans can aso be used to quantify air eakage rates. This technique is invauabe in predicting buiding performance and monitoring air seaing work. Most types of insuation are not effective at reducing air movement through the therma perimeter. Good construction practice incudes interior air seaing; if this is not in pace effectivey, air can move through the interior and exterior surfaces and through the insuation. Unfortunatey, fibergass is particuary susceptibe to the this probem. Thus, whie the insuation may be present, it does not perform as expected when the buiding is

4 under a pressure gradient. Image 6 shows the impact of warm air eaking out of this commercia buiding. This wi typicay go unnoticed unti the fue bi is paid. Image 6: A the framing and insuation is ceary visibe in this commercia buiding. Norma pressure differences on the top foor resut in air eaking past the enveope through various pathways. EIFS construction The growing popuarity of buidings using Exterior Insuation and Finish Systems (EIFS) has been accompanied by numerous cases of moisture-reated structura damage. Athough often attributed to eaking windows, water typicay intrudes where seaing or fashing systems were inadequate or have begun to fai. Moisture is then trapped under the reativey impervious foam. In warm cimates the decay of structura wooden eements, which can occur very rapidy, is a major probem. Mod growth aso often accompanies the moisture resuting in heath concerns. Thermography is an invauabe too to ocate moisture in EIFS systems. Inspections are best conducted in the eary evening from the outside after a sunny day with itte or no wind. It may aso be possibe to ocate moisture from inside during cooing or heating conditions. The expanded foam insuation boards tend to become more absorbent to water over time. Moisture intrusion or condensation As buiding designs and techniques produce tighter therma enveopes, moisture (from eaks or condensation) has created more and more probems. The water can intrude through a sma crack but it is then trapped between the reativey impermeabe buiding materias. Good buiding techniques typicay must dea with both air seaing and moisture retarders to keep moisture from accumuating inside the wa sections. Locating moisture with thermography is often simpe because water has both a high therma conductivity and a high heat capacitance. Determining the source of the moisture, however, can be difficut. Condensation, rather than eakage, is often the cuprit so it is important to identify sources of air eakage that can transport moist air into the wa sections and the cod spots that can resut in it condensing. The cassic case is that of warm moist air eaking past the insuation in a meta buiding or mobie home; as it contacts the cod underside of the meta roof it condenses, and often freezes, causing the occupants the think, mistakeny, that the roof is eaking. Damage in buiding from condensation incudes mod growth, brick spawing, roof membrane fastener corrosion and reduced insuation vaues. Image 7: EIFS construction is particuary susceptibe to water intrusion resuting in both mod growth and wood rot probems. HVAC performance HVAC systems can be pagued by design and instaation probems resuting in excessive energy use and/or uncomfortabe buidings. Thermography heps buiding speciaists visuaize the otherwise invisibe impact of this poor performance as indicated by excessivey hot or cod areas. Once these have been ocated, the root causes can be determined; these may incude reversed or misdirected airfow or poory paced suppy ducts, eading to shortcircuiting of air directy to the return ducts.

5 Unfortunatey many of these probems resut from poor design; by the time the thermographers spots them, it may be too ate to correct some of them. One the other hand, some, such as reversed diffusers, are very easy to correct. It is aso possibe to visuaize air fow itsef! Severa thermography studies have been conducted by hanging ayers of pastic netting in a room. As the air fows through it, the temperature of the netting can be imaged. In most comfort-reated cases it is probaby as usefu to simpy image the was and objects in the room a technique that is much easier. Image 8: Hydronic heating cois embedded in a concrete foor show up in this therma image. As a side note, thermographers are often asked to ocate reinforcing stee in buidings. This is much more difficut. Heating the stee is not a simpe task, usuay accompished with an inductive coi or direct DC-powered heating. Secondy, the heat is often insufficient to express itsef on the surface. Other methods, based on sending and receiving radio signas, are probaby more usefu. Verification of construction detai No area of appication is more important these days, particuary in commercia buidings, than the verification of construction detais and performance. Thermography is being used with great success to verify bond beams and pacement of reinforcing in concrete masonry unit (CMU) was as we as structura eements of pre-cast, tip-up was. How? The soid portions of the wa change temperature more sowy than the rest. The inspection can be conducted anytime the wa is in a thermay transient condition typicay in the eary evening as it coos down. Because the inspection is conducted during construction, deficiencies can be corrected prior to occupation with reativey minor inconvenience. Verification of pacement of insuation in masonry unit was is aso more important than in the past due to high energy costs and heath concern regarding mod growth in cod wa cavities. Subsurface heat sources Heating cois are being used more and more either to keep outside wakways or entrance ramps snow free or to provide heat to areas and rooms via hot water or eectric cabes. Thermography provides a quick way to verify ocation and performance of these subsurface devices. Typicay the therma pattern shows up very ceary even when the heat source is embedded in severa inches of concrete. Simiary, water pipes in wa sections can usuay be ocated quite readiy. Water eaks from pipes, whether in a wa section or under a sab, may aso be ocated using IR, athough airborne utrasonics may be a simper method. To use IR a temperature difference must be induced generay by simpy running hot water through the pipe. Leaks under concrete sabs may not express themseves because the water if the water is drained away in the sand/grave base ayer. Image 9: This bock wa is not uniformy grouted as was specified, eading to severe structura probems. Image courtesy Phi McMuen.

6 Sick-buiding syndrome When buidings are too tight or too moist, heath-reated probems quicky come to the forefront. Grouped together as sick buiding syndrome, these can stem from inadequate HVAC performance, moisture trapped in was, mod growth on cod, damp surfaces and inadequate air change rates. Many of these can be visuaized and diagnosed, at east in part, with thermography to hep sove these very serious and common probems. Diagnosing these probems is often a very compex process and, given the fact that itigation may be invoved, it is not something to be entered into ighty. Facade deaminations A great dea of work has been done in SE Asia inspection the facades of arge buidings for deaminations. Faiures of these materias can resut in serious personne injury. The masonry ties used to face the buidings tend to change temperature rather quicky when they begin to deaminate compared to the underying structure to which they were affixed. The diurna cyce is typicay the driving heat source and inspections are best done in the eary evening hours after a warm sunny day. Roof moisture inspections The inspection of fat roofs, especiay buit-up roofs (BUR) has been proven for a number of years. The technique aows for the detection of moisture trapped in a roof system; over time this moisture eads to the pre-mature degradation of the roof. The moisture appears warmer at night after a sunny day due to its greater therma capacitance. The roof surface must be dry and the technique works best on roofs with absorbent insuation. Inspection work can be accompished either in a roof-top survey or an aeria survey conducted from a heicopter or fixed-wing craft. Standards and references Severa important standards exist to support the work of thermographers conducting buiding inspections. These incude, among others, the foowing: ASTM C Practice for Thermographic Inspection of Insuation Instaations in Enveope Cavities of Frame Buidings ASTM C Practice for the Location of Wet Insuation in Roofing Systems Using Infrared Imaging ISO 6781 Therma insuation, quaitative detection of therma irreguarities in buiding enveopes, Infrared Method American Concrete Institute Design Standard 530 / American Society of Civi Engineers Standard 5, Masonry Buiding Code and Specification Another exceent reference, athough not a standard, is the Canadian Genera Standards Board Manua for thermographic anaysis of buiding encosures (149- GP-2MP). Numerous buiding reated papers have been pubished over the years; many are coected on a CD-ROM from SPIE, entited Seected Papers from the Proceedings of Thermosense, edited by John Sne and Doug Bureigh, avaiabe from Quaifications of the thermographer Athough buiding appications may appear simpe, successfu use requires quaified personne with reated experience. Both training and experience are essentia. An intimate knowedge of construction techniques, practices, materias, and faiures is aso important. It is aso not unusua for the thermographer to work with other buiding scientists who have expertise in other areas. Faiure to conduct an inspection in a professiona manner can resut in serious damage to the buiding and/ or harm to the occupants. Image 10: The wet insuation in the roof system shows up ceary due to its greater therma capacitance. Image 11: During the commissioning of this buiding thermography reveaed an extreme probem invoving exfitration through the soffit. Courtesy Phi McMuen.

7 Concusion When propery used by quaified individuas, this remarkabe technoogy can pay a powerfu roe in visuaizing otherwise invisibe buiding probems and conditions. Contractors and architects aike are both using thermography to assure the performance of their buidings. Buiding speciaists count on thermography to hep them diagnose tough probems that, eft unsoved, are costy or dangerous. Owners rey on thermography as a too for commissioning a new buiding. Whie a foundation of expertise must underie the successfu use of thermography for buiding diagnostics, getting started with most of the appications is often not difficut. An appropriate infrared system is required, with proper training and experience for the operator as we. Having suppementary knowedge of buiding sciences or access to that information is aso vita. The primary return on an investment in buiding thermography is gaining a higher eve of assurance buidings wi perform as intended and occupants wi be more comfortabe, often at a ower cost. For additiona information about thermography, buiding inspections, and infrared training, visit com or contact The Sne Group at