1、Manual for Therrnographic Analysis of Building Enclosures 149-GP-2MP February 1986 The CANADIAN GENERAL STANDARDS BOARD (CGSB), under whose auspices this standard has been developed is a government agency within the Federal Department of Supply and Services. The CGSB is engaged in the production of
2、voluntary standards in a wide range of subject areas through the media of standards committees and the consensus process. The standards committees are composed of representatives of relevant interests including producers, consumers and other users, retailers, governments, educational institutions, t
3、ech-nical, professional and trade societies, and research and test- ing organizations. Any given standard is developed on the consensus of views expressed by such representatives. The Ministers Advisory Council on CCSB reviews the results of the consensus process. The CGSB has been accredited by the
4、 Standards Council of Canada as a national standards-writing organization. The standards that it develops and offers as National Standards of C,inada conform to the criteria and procedures established for this purpose by the Standards Council of Canada. In addition to standards it publishes as natio
5、nal standards, the CCSB prodiices standards to meet particular needs, in response to rcquests from a variety of sources in both the public and private sectors. Roth CGSB standards and national standards developed by the CGSB are developed in conformance with the policies described in the Policy Manu
6、al for the Development and Maintenance of Standards by CGSB. CGSR standards are subject to review and revision at any time, so as to ensure that they keep abreast of technological progress. Suggestions for their improvement, which are al-ways welcome, should be brought to the notice of the stand- ar
7、ds committees concerned. Changes to standards are issued either as separate amendment sheets or in new editions of standards. An up-to-date listing of CGSB standards, including details on latest issues and amendments, and ordering instructions, will be found in the Catalogue of Standards and Qualifi
8、ed Products Lists which is published annually and is available without charge upon request. .lthough the intended primary application of this standard is stated in its Scope, it is important to note that it remains the responsibility of the users of the standard to judge its suitabil- ity for their
9、particular purpose. Many tests required by CGSB standards are inherently hazard- ous. The CGSB neither assumes nor accepts any responsibility for any injury or damage that may occur during or as the result of tests, wherever performed. The CGSB takes no position respecting the validity of any patent
10、 rights asserted with any item connected with this standard. Users of this standard are expressIy advised that determination of the validity of any such patent rights are entirely their own responsibility. Further information on the CGSB and its services and stand- ards may be obtained from: The Sec
11、retary Canadian General Standards Board Ottawa, Canada K1A 1G6 La ente norme a t labore sous les auspices de POFFICE DES NORMES GNRALES DU CANADA (ONGC), qui est un organisme fdral relevant du ministre des Appro- visionnements et Services. LONGC participe la production de normes facultatives dans un
12、e gamme tendue de domaines, par lentremise de ses comits des normes qui se prononcent par consensus. Les comits des normes sont composs de reprsentants des groupes intresss aux normes ltude, notamment les fabricants, les consommateurs et autres utili- sateurs, les dtaillants, les gouvernements, les
13、institutions denseignement, les associations techniques, professionnelles et commerciales ainsi que les organismes de recherche et des- sai. Chaque norme est labore avec laccord de tous les reprsentants. Le Conseil consultatif du Ministre pour IONGC passe en revue les dcisions prises par consensus.
14、Le Conseil canadien des normes a confr IONCC le titre dorganisme rdacteur de normes nationales. En consquence, les normes que lOffice labore et soumet titre de Normes nationales du Canada se conforment aux critres et procdures tablis cette fin par le Conseil canadien des normes. Outre la publication
15、 de normes nationales, IONGC rdige galement des normes visant des besoins particuliers, la demande de plusieurs organismes tant du secteur priv que du secteur public. Les normes de IONGC et les normes nationales tablies par cet organisme sont conformes aux politiques nonces dans le Manuel des politi
16、ques dlaboration et de mise jour des normes de IONGC. tant donn lvolution technique, les normes de IONGC font lobjet de rvisions priodiques. Toutes les suggestions suscep tibles den amliorer la teneur sont accueillies avec grand in, ail, except radiant temperature, can be controlled by the heating,
17、cooling, and ventilating system. Since radiant temperature is much more difficult to control, com fort cannot al ways be assured. Temperature. Effective temperature, (as defined in the ASHRAE Handbook of Fundamentals, 1977) is the combined effect of wet-bulb temperature, dry-bulb temperature (see se
18、ction 2.2.6, psychrometry) and air movement, which create a sensation of warmth or cold and therefore have the greatest influence on phy- sical comf ort . To achieve human comf ort ,it is recommended that al1 the components of the environment be considered holistically, rather than following a rigid
19、 standard for certain dry-bulb air temperature, relative humidity and air changes per hour. People tend to be comfortable when the heat generated by their bodies equals the heat lost from their bodies by convection, radiation, perspiration, and respiration. If there is an imbalance, however, skin te
20、mperatures change, affecting internai body temperature and making the person uncomfortable. When the dry-bulb temperature is below the normal body temperature of approximately 37“C, the body loses heat by convection at a rate proportional to the difference between body and air temperatures. Similarl
21、y, as the temperature of air increases relative to that of the body, the amount of body heat lost by convection and radiation decreases. The temperature of the skin and body rises, causing more heat to be lost by respiration (through increased breathing rate) and by evaporation of perspiration. If t
22、he air tempe- rature rises above body temperature, the person becomes extremely uncomfortable because his body is unable to lose heat by convection or radiation. In addition, although perspiration continues to evaprate, the energy that causes evaporation to occur is supplied by the environment rathe
23、r that by the body, so that minimal body cooling is effected. The radiant temperature of an interior area refers to heat which is emitted as electromagnetic uaves through the atmosphere and is determined by the temperatures of surrounding surfaces. These surfaces are referred to as the “radiant fiel
24、d“ and include ceilings, floors, interior walls, partitions, windows, heat- ing and cooling units, and lights. Ceilings, floors, and partitions vary in temperature according to the temperature of the inside air. However, other surfaces, such as exterior walls and windows, are affected by outside air
25、 temperature, solar radiation, level of illumination, and design of the HVAC (heating, venti- lating and air-conditioning) system. The radiant field as a whole exposes a person to many different surface temperatures at one time, and adjustments made by the body to balance its heat level are complex.
26、 Parts of the body are losing heat by radiation while other parts are gaining heat in the same manner, and the entire body may be losing heat by convection at the same time. A person becomes uncomfortable when one part of the body loses or gains an excessive amount of heat relative to the general he
27、at balance of the rest of the body. If you stand by a warm heater under a cold window then you will experience this discomfort. Relative Humidity. Respiration and perspiration allow the evaporation of moisture frorn the human body and therefore a lowering of body temperature. Since relative humidity
28、 affects the amount of rnoisture the body is able to lose, the cooling rate of the body through evaporation decreases as the ambient rela- tive humidity increases. This can cause discomfort, especially in summer; the body is unable to cool itself through the evaporation of moisture when the air temp
29、erature is the same as the body temperature or when the air contains aimost as much rnoisture as it can hold.2 Normally, humidity levels Vary between 20% and 70% at less than 25OC, and people at rest or doing light work will not be uncomfortable. Human beings are adaptable enough, however, to work i
30、n more extreme, speciaiized conditions. Textile mills for example, operate at humidity levels as high as 80% or 90% to prevent the fabric that is produced on high-speed machines from becoming charged and dinging together. Air Movement. Air movement increases the quantity of heat lost from the body t
31、hrough increased con- vection and evaporation of perspiration. If both the air temperature and relative humidity of a room are high, the human body can be comfortable at relatively high air speeds, whereas the body may be uncom-fortable in air of even very low speed if the air temperature is less th
32、an 21C. Since air infiltration and convection drafts are largely responsible for this discomfort, airtightness is a prime requisite of any buil- ding enclosure. Conclusion. Designing a building to provide maximum com fort for the occupants is com plex, considering al1 the factors which affect comfor
33、t. For example, providing natural ventilation through the use of win- dows may interfere with the airtightness of a structure and defeat the purpose of its mechanicai systems. In the end, the design is likely to be a compromise, providing as much physical comfort as possible, given the functional re
34、quirements of the occupants and the building. BUiLMNC ENCLOSURE SCIENCE Principles of Building Enclosures To understand the fundamental principles and concepts of a building endosure, it is necessary to question why people construct buildings. One simple and satisfactory explanation is that building
35、s provide space so that the endosed environment can be different from the uncontrolled natural environment as required by the season. In order to achieve a controlled interior environment, it is necessary to have a building enclosure equipped with efficient and economical mechanical systems. Because
36、 of the differences between the interior and the exterior, the building endosure must act as a separator of different environments, by preventing, limiting or allowing flows of mas and energy through it. The primary function of the building envelope is to control these flows in ways determined by th
37、e differences between these environments. However, an endosure can be designed to respond dynamically to the exterior environment for the benefit of its occu- pants. The diagnosis of building enclosure performance requires an understanding of the interior environment: what is required, desired or wi
38、ll be ultimately provided to suit the occupants needs; the range of condi- tions of the natural environment; and how to control the mechanisms which promote the flow or transfer of mas and energy. The aim, therefore, in diagnosing and retrofitting a building endosure is to choose materials that will
39、 perform the intended function over a maximum period of time, and at the same time meet certain aesthetic and economic criteria. In the natwal environment, there are many mechanisms which cause the decomposition of materials. Fungi and bacteria decompose organic matter, and various elements in combi
40、nation can break down stone. These and other factors contribute to the global ecosystem and are essential to life on earth. The effects of such mechanisms on building materials, however, need to be controlled or at least retarded if buildings are to perform satisfactorily over time. A thorough under
41、standing of these mechanisms is a pre-requisite for the sucessful performance of building enclosures. These mechanisms will be discussed in detail in Chapter 2. An Integrated Approach Building science entails the application of the fundamental laws of physics and chemistry to the design, constructio
42、n, and renovation of buildings. This requires an understanding of the functions of each element of an enclosure in response to thermal differences, moisture migration, air flow, structural movement, and standards of building safety. Proper application of the principles of building science permits th
43、e opti- mai selection of building materiais and the creation of an environment that minimizes the deterioration of those materials, as will be discussed more fully in Chapter 3. 1.3 Ideally, an architect designs a building according to the occupants needs as well as a knowledge of its intended funct
44、ion, the physical properties of materials, the performance of the materials in combination, and the interaction of materials and environment (see Figure 1- 1). One should be aware, for example, that durability is not an inherent property of a building material, but is determined by the interaction o
45、f that material with a given environment. Interaction between materials is also involved in the process of deterioration. The combination of two building components can cause one, both, or even a third compo- nent to deteriorate. For example, the calcium chloride added to concrete to promote quick s
46、etting can cause corrosion of reinforcing steel. Optimum building performance is seldom achieved, however, because materials are neither matched to the environrnent nor to one another, nor are they matched to the func- tion they are expected to perform. FIGURE 1-1 This diagram depicts the interre1at
47、ionship.of function, material and environment in achieving the optimum performance of a building enclosure. This design helps to remind us, for example, that the durability of a material or assembly is determined by the interaction of the elements of the environment with the mate- rial. Building det
48、erioration and high energy consumption can often be prevented by appropriately rnatching materials to the environment, or modifying the environrnent to suit the materials, thus permitting the material to successfully achieve its function. The poor performance of many existing buildings can be direct
49、ly related to errors in matching materials to their function and their environment. Many of the resulting inadequacies have a thermal expression which can be interpreted using thermography. BUiLDING ENCLOSURE DIAGNOSIS A building is a space enclosure which separates the outside from the inside through either dynarnic or resistive responses to factors such as precipitation, wind, Sun or other sources of radiation, heat, water vapour and noise. In some cases, the space enclosure acts as a barrier to forces which mo
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