Everything above absolute zero radiates infrared energy in proportion to its surface temperature. When the objects are hot enough they radiate visibly and our eyes can see them glow. As they cool their radiation becomes invisible to the eye. We then can use infrared thermal sensors and scanners to measure their self-emitted infrared radiation and relate it to surface temperature. When the inside and outside of a structure are at different temperatures thermal energy flows through the walls and ceilings. The better the insulation, the less energy flow and the more is conserved. Changes in wall and ceiling surface temperatures are an indication of the thermal energy loss. This paper introduces the basic physical laws that make infrared thermal sensing instruments work, and explains how they are used to detect and measure heat loss in structures.

Heat is transferred through a wall structure by the mechanisms of conduction, convection, and radiation. These mechanisms are introduced and developed in terms of their thermal resistances. Temperature difference is identified as the cause of heat flow through the structure which is impeded by the thermal resistances of the structures. Calculations are made of the thermal resistances at several points in a specific test wall section. The performance predicted from these calculations is compared to thermo-graphic measurements made on the wall under laboratory controlled conditions. These comparisons are used to draw conclusions as to the usefulness and limitations of thermographic practices.

Earlier sessions of this review have dealt with infrared physics and with problems of building construction. This session deals with meteorological effects of the real life world as these effects apply to the use of infrared to fine heat loss or heat gain of buildings.

This paper presents a tutorial introduction to the methods used in acquiring and interpreting ground-based thermographic data. It summarizes basic principles used in the anal-ysis of groundbased thermographic data for the detection of building heat losses. The major heat loss mechanisms in buildings which produce the thermal anomalies detectable by infrared scanning systems are described. The paper emphasizes that the analysis of thermographic data is an exercise in pattern recognition and, as such, gives results of a qualitative nature. The thermal patterns of several classes of building defects are presented. Methods for determining from thermographic inspection voids in insulated walls, areas with partial insulation, defective ceiling insulation, fissures and shrinkage in insulation, heat loss around doors and windows, air leakage at wall and floor joints, attic bypasses and thermal bridges, air penetration into interior cavities, and moisture damaged insulation are illustrated by examples of thermograms showing each class of defect. The difficulty of performing thermographic inspection under nonstandard conditions when the building is subjected to a small temperature difference across the building envelope, solar loading on the inspected surface, or transient environmental conditions is discussed. The relative merit of interior and exterior surveys and the effect of environmental conditions, thermal reflections and variation in the surface properties on the interpretation of thermograms are analyzed.

Aerial thermograms of houses, buildings, and steam tunnels are discussed to show typical interpretation.

Basin Electric Power Cooperative, Bismarck, North Dakota, provides wholesale electricity to more than 100 rural electric cooperatives of the Missouri Pasin Region. The Cooperative, in cooperation with Aadland*Hoffmann*Pieri Energy Associates, Inc., Minneapolis, MN has developed a three-fold program which involves the analytical approach, the instructional approach and the motivational approach (A'IsM) to an energy audit. This three-fold program utilizes infrared thermography to pinpoint where heat loss is occurring in the home. The auditor can motivate the homeowner to initiate energy conserving improvements and practices by showing where money can be saved. Infrared thermography is a most valuable tool in helping the rural electrics conserve energy and the nation's natural resources. Over 180 energy auditors have been trained through this program in this area and 5,000 trained in the nation.

Implementing a thermographic inspection service in a residential energy conservation program offers numerous benefits to consumers, the conservation program, and the provider of this service. A description of the need for thermographic inspections, the problems en-countered in setting up this service, the interface of the technical and nontechnical sectors will be discussed in addition to the benefits to be gained through thermographic inspections. The credibility of a residential energy conservation service can be enhanced tremendously through the implementation of a thermographic inspection service. The need for thermography and its resultant benefits can provide a barometer for the future implementation of thermography within residential conservation programs.

A 32 kilobyte microcomputer is used for merging radiant (IR) temperatures of roof sections and building enclosures with meteorological data to produce per unit Energy Intensity Factors (EIFs) that are required for Comprehensive Energy planning. The EIFs can also be used as building blocks for a low cost RCS-type energy audit that has been shown to approximate the DOE model audit in terms of accuracy and completeness. The Type I or "Interactive Energy Audit" utilizes EIFs that are calculated from diffuse density levels of aerial IR recordings, supplemented by resident-supplied information concerning structural charac-teristics of a house and energy life-style of its occupants. Results of a statistical comparison between ASHRAE-based and IR audits of 175 single family homes in Garland, Texas show that, on the average, the aerial based heat loss estimates fall within a 10 percent error envelope around the true BTUH losses 90 percent of the time. The combination of an aerial infrared picture and an Interactive Energy Audit print-out have proven effective in (a) providing homeowners with the information they want from an energy audit; (b) persuading them to take appropriate remedial weatherization actions, and (c) screening out the homes that do not need a Class A audit, thereby eliminating the cost and bother of an on-site inspection.

The evaluation of the thermal integrity of building envelopes by infrared scanning tech-niques is often hampered in mild weather because temperature differentials across the envelope are small. Combining the infrared scanning with positive or negative building pressures, induced by a "blower door" or the building ventilation system, considerably extends the periods during which meaningful diagnostics can be conducted. Although missing or poorly installed insulation may lead to a substantial energy penalty, it is the search for air leakage sites that often has the largest potential for energy savings. Infrared inspection of the attic floor with air forced from the occupied space through ceiling by-passes, and inspecting the interior of the building when outside air is being sucked through the envelope reveals unexpected leakage sites. Portability of the diagnostic equipment is essential in these surveys which may include access into some tight spaces. A catalog of bypass heat losses that have been detected in residential housing using the combined infrared pressure differential technique is included to point out the wide variety of leakage sites which may compromise the benefits of thermal insulation and allow excessive air infiltration. Detection and suppression of such leaks should be key items in any building energy audit program. Where a calibrated blower door is used to pressurize or evacuate the house, the leakage rate can be quantified and an excessively tight house recognized. Houses that are too tight may be improved with a minimal energy penalty by forced ventilation,preferably with a heat recuperator and/or by providing combustion air directly to the furnace.

Infrared imaging systems can be classified into three general categories, low resolution, medium resolution and high resolution. It is the purpose of this paper to highlight specific applications best suited to high resolution, television capatable, infrared data acquisition techniques. The data was collected from both ground loped andoaerial based mobile positions where the temperature differentials varied from 15 C to 25 C. Specific applications include scanning building complexes from the exterior using a ground based moving vehicle, scanning buildings, concrete bridge decks and terrain from the air using a helicopter and scanning building interiors using a mobile hand truck.

Much is unknown about the in-situ thermal behavior of buildings under transient conditions. Heat-flow meters and infrared scanners both have many uses in the area of qualitative and quantitative analysis of thermal performance of buildings when steady-state thermal conditions can be assumed. As will be shown in this paper, however, much is still unknown about them to correctly predict when reliable data can be col-lected to make a valid quantitative analysis that can be used, e. g. for accurate in-situ 11-value calculations. Combining heat-flow meters and infrared scanners may avoid some of the complexities of a quantitative analysis. However, further studies are needed to improve the accuracy of such measurements. A continuous 24-hour infrared scan of a residential dwelling showed, however, that a qualitative analysis may be possible to a certain extent, even during expressively transient conditions. It is recouliended that further in-situ studies be made in various constructions during extended periods to gain more knouledge in this very exciting subject. Responsible for the actual field test were R. H. Alnis, J. Casey, S. Marshall and J. Wood. The data-reduction and interpretation has been provided by Dag Holmsten, who is solely responsible for opinions expressed in the paper.

The oldest and largest building thermography consultant in Sweden, Riksbyggen, is also an innovative building developer and contractor. By using thermography not only on their own projects, but also offering a wide variety of thermographic services, Riksbyggen has probably acquired more experiences than any other single inspection unit in the world. As a response to the increasing need for a cost-efficient technique to make energy audits on existing buildings as well as to control the workmanship in retrofits made, Bengt Axen at Riksbyggen has developed a unique building inspection program that efficiently utilizes thermography without compromising the benefits of the technique. As an observer from the outside, the co-author, Dag Holmsten of AGA Corporation, has discussed improving inspection efficiency with Bengt Axen on several occasions and has met with the people invloved in the first test of the "Sundsvall model" in northern Sweden. He gives the institutional background to this new and very practical approach to energy auditing and shows the urgent need for such a technique with global applicability in order to avoid expensive misinvestments of energy conservation funds.

A theoretical model is described for calculating flat roof total heat losses and thermal conductances from aerial infra-red data. Three empirical methods for estimating convective losses are described. The disagreement between the methods show that they are prone to large (20%) errors, and that the survey should be carried out in low wind speeds, in order to minimise the effect of these errors on the calculation of total heat loss. The errors associated with knowledge of ground truth data are discussed for a high emissivity roof and three sets of environmental conditions. It is shown that the error in the net radiative loss is strongly dependent on the error in measuring the broad-band radiation incident on the roof. This is minimised for clear skies, but should be measured. Accurate knowledge of roof emissivity and the radiation reflected from the roof is shown to be less important. Simple techniques are described for measuring all three factors. Using these techniques in good conditions it should be possible to measure total heat losses to within 15%.

Infrared thermography has advanced to the stage where it is feasible for the owners of commercial and industrial buildings to secure an infrared survey to detect and priortize definitive areas of heat loss. The nature of the information required determines the type of infrared equipment to be used. The information obtained from the survey can be recorded on video tape with an audio overlay which is quite definitive and permits easy review by the client. Another area of heat loss is moisture laden roof insulation. An infrared survey can detect with startling accuracy areas of wet insulation. Both of these types of surveys are very compatible with either the mini or maxi audits and are conspicuously useful at the retrofit stages.

Infrared technology played an important part in dealing with school energy problems in Berlin, New Hampshire. It provided the school board and administration with information and data which proved useful in prioritizing the expenditure of limited capital improvement funds. It enabled the board and administration to diagnose the extent of building heat loss problems and compare the heating oil component of our energy problems with independently diagnosed electricity and gasoline components. Since seventy (70) percent of school energy expenditures are on heating oil, infrared assumed the role of a very important diagnostic tool. The Berlin (NH) Public Schools manifest problems faced by public schools in many areas of the country; declining enrollments, inflation, and taxpayer resistance to increasing public expenditures. With eight buildings to heat and light (six schools, a bus garage, and a vocational forestry building), rapidly escalating energy prices threatened to raise total school energy costs as a percentage of total budget from less than seven (7) percent to almost twenty (20) percent, unless consumption reductions were effected. There were minimal obstacles to infrared implementation in Berlin, for a number of reasons. First, the cost was not prohibitive. Second, there was little community understanding of the technology along with an historic separation of specific, relatively low cost school expenditures from close public scrutiny. Finally, the school board and administration realized that, if the energy problem was to be adequately dealt with, a clear understanding of the problem was necessary. The best way for that understanding to be developed was through professional examination of our buildings using the most modern techniques. At this juncture, after only one winter, it is clear that the payback period for Berlin's investment in infrared technology has been surpassed.

Visual examination is a reliable means of moisture detection in building walls after serious damaR'e has been done. Traditional spot measurement instruments are inexpedient devices for elusive moisture detection in heterogeneous materials. The infrared thermal imaging system was found t be a more versatile tool for in-situ moisture detection because of its unique characteristics. Several thermographic examples of moisture detection in. building walls are presented, which will aid the reader in the qualitative interpretation o1 therm.ograms 1or moisture problem.s.

Infrared Thermography is a quick, positive and economical method of identifying infiltration and exfiltration of air around. windows, construction joints and foundations of school buildings. The method can be successfully utilized to detect problems with the heating and ventilating systems and to detect moisture beneath the roofing membranes which lowers the R factor of the insulation. The cost to complete and document an Infrared Thermographic survey of an elementary school building varies between. 2.c. and 5,1. per square foot. Infrared Thermography also has the capability t detect heat losses in many areas which normally appear to be efficient in retaining heat within the building.

The potential for building thermography within Public Works Canada has been established. Thermography is a building science tool that identifies problems at the design or construction stage before the structure deteriorates and maintenance costs escalate. In addition, this technology is a valuable tool for teaching quality assurance of construction and preventive maintenance. Thermography can be used to teach thermal principles of building and enclosure performance which previously required advanced knowledge of physics and chemistry. Thermography can help provide insight into problems involving building science expertise as required by the building industries, building design and maintenance operations.

We are developing a method for measuring the R-values of large area of building envelopas. This is a summary of progress to date. We locate temperature extremes on the building surface with an infrared videocamera, determine the R-values at those locations with contact thermal sensors, and interpolate R-values for all other locations from the thermograms.

A hand held, low resolution, infrared imaging system was used to evaluate the effects of solar gain on a typical, air conditioned, office building. Areas that were addressed focused on the impact of the sun and the early morning temperature changes in the eastern section of a building. Isolating pockets of moisture in a concrete block wall and the probable cause were determined during this survey. Evaluating wet insulation in a built-up roof are described. The implementation of this technology with respect to roof maintenance is discussed.

High energy usage in the "North Country". How it came to be and what concerns we had in relation to this energy problem. The plans and procedures that were set in motion to cope with the situation. How did infrared techniques come to be used. What problems did infrared bring and what Problems did it solve.

In the summer of 1977 ASHRAE Standard Committee 101P was authorized to prepare standards and requirements to assist industry and the general public in the applied use of Infrared Radiation Sensing Divices for assessment of building heat loss characteristics.* In the spring of 1980 the draft of the proposed Standard was opened for public review. The public review period closed June 30, 1980 and the Project Committee is now attempting to reach consensus with the commentors. If consensus is reached in the fall of 1980 the Standard is expected to be approved for publication as an ASHRAE Standard in early 1981. Recognizing that official responses to the formal comments are still in preparation this paper, as an interim step, broadly catagorizes the comments received into four areas: 1) Editorial, 2) Technical Content, 3) Procedural Requirements, and 4) Methods for Usage of the Standard. Some generalized unofficial remarks are outlined as a preliminary response to the comments.

In the summer of 1979 a task group was formed under ASTM Subcommittee C16.30 Section 7. The task group was asked to develop standard practices for the utilization of infrared (IR) imaging devices for the in-situ evaluation of building insulation systems. The group's work to date has concentrated on bounding the problem and prioritizing the needs for standard procedures. Most recently, the group has concentrated on a very specific utilization of infrared (IR) imaging as a qualitative instrument for building retrofit insulation inspections. White papers on equipment specifications and interpretation of imagery were generated as guides to writing the first draft of a standard practice document on this insulation retrofit inspection problem. The first draft describes the knowledge level of the inspector, the procedures for the inspection and the instrumentation required for various levels of diagnostics. Care has been taken to insure compatibility with ASHRAE Draft Standard 101P and to insure that the document will serve the user community as a guide to proper application of infrared in this infrared (IR) applications area.

The man/machine system - the two basic elements required for the conduct of an infrared survey are the infrared instrument and the operator or technician. The quality of performance can be limited by either one. Generally speaking, the performance of the instrument is predictable as it has predetermined parameters of operation. Given the same ambient conditions, nature of subject, and system calibration, the instrument will perform consistently. The greatest variable occurs when the operator is considered. The background, training, experience and attitude of the individual can influence what is seen and how it is interpreted. Accordingly, it seems appropriate to emphasize the role of the infrared system operator and the need for formal training according to established standards.

The introduction of standards on acceptable procedures for assessing building heat loss has created a dilemma for the contractor performing airborne thermographic surveys. These standards impose specifications on instrumentation, data acquisition, recording, interpre-tation, and presentation. Under the standard, the contractor has both the obligation of compliance and the requliement of offering his services at a reasonable price. This paper will discuss the various aspects of data acquisition for airborne thermographic surveys and various techniques to reduce the costs of this operation. These techniques include the calculation of flight parameters for economical data acquisition, the selection and use of maps for mission planning, and the use of meteorological forecasts for flight scheduling and the actual execution of the mission. The proper consideration of these factors will result in a cost effective data acquisition and will place the contractor in a very competitive position in offering airborne thermographic survey services.

The application of the proposed ASHRAE Standard "Application of Infrared Sensing Devices to the Assessment of Building Heat Loss Characteristics" afford the design professional and the construction industry with a standard of performance and a test of the quality of the Building Envelope. An established standard is required to communicate a uniform performance test that can be included in Section 00200 supplementary conditions of a new project specifications or contracted for as a special test before commencing a remodeling -retrofit project. Thermograms provided to the design professionals will assist in more thermally effective future designs.

Owing to the relative newness of building thermography, Public Works Canada (PWC) developed a generic methodology for infrared diagnosis of building construction. To date, PWC has offered two thermographic training courses and a third course open to international applicants is tentatively scheduled for February/81. The recently established Canadian Infrared Thermographic Association (CIRTA) will soon be offering thermographic training until universities and technical colleges have adequate courses. CIRTA will use the PWC training program which assists in guaranteeing the quality of national thermographic practices and ensures that the technology of thermography is transferred to the private sector at an acceptable level of competence.

The cost of thermographic information obtained by contracting for a service is compared to that of buying equipment and doing the work in-house. A breakeven analysis method is used to find the number of days per year an instrument must be used to justify buying it. Life-cycle costing techniques are used to find the equivalent annual cost of various classes of thermographic instruments. Results indicate that a full-time person earning $20,000 annually must use a $30,000 instrument at least 73 days per year if thermography can otherwise be contracted for $675 per day. By devoting a person to thermography part-time, the number of inspection days for this case can be reduced to about 28. Further in-house advantage can be gained by considering investment tax credits, salvage value and, to some extent, accelerated depreciation. Techniques for finding the breakeven number of inspection days for other costs are developed. A nomogram is included for rapid comparisons.

I have come here today to describe as best I can, the emergence of consumer-oriented IR imaging devices. The infrared instrumentation base of today's industry is rapidly dwindling because it does not fulfill expanding consumer needs. This new growth area is largely com-posed of non-technical people (not research scientists and engineers). They are looking for simpler, easier-to-use consumer devices that will fulfill specific applications and will not require more complex measurement techniques, more infrared educational training, and of course, not more expensive equipment and accessories.

Energy audits are a major component of a number of Federal and State energy conservation programs. To various degrees, these programs provide an opportunity for the application of infrared remote sensing (thermography) to the conduct of these audits. The following programs are reviewed and an indication given of how each might make use of infrared as an audit tool: o Residential Conservation Service Program o Schools and Hospitals Program o Federal Energy Management Program o State Energy Grants Program o Weatherization Assistance Program o Energy Extension Service Program o Industrial Energy Conservation Program

This paper discusses solar energy collector systems analysis using thermography. The research at the Solar Energy Research Institute (SERI) in this area has focused on infrared (IR) scanning techniques and equipment to determine temperature distributions, flow patterns, and air blockages in solar collectors. The results of this extensive study, covering many sites and types of collectors, illustrate the capabilities of IR analysis as an analysis tool and operation and maintenance procedure when applied to large arrays. Infrared analysis of most collector system showed temperature distributions that indicated balanced flow patterns with both the thermographs and the handheld unit. In three significant cases, blocked or broken collector arrays, which previously had gone undetected, were discovered. Using this analysis, validation studies of large computer codes could examine collector arrays for flow patterns or blockages that could cause disagreement between actual and predicted performance. Initial operation and balancing of large systems could be accomplished without complicated sensor systems not needed for normal operations. Maintenance personnel could quickly check their systems without climbing onto the roof and without complicated sensor systems.