1、2010 ASHRAE 189ABSTRACTIt is critical to know or measure the installed insulationprofile in metal building roof and wall systems to determine theeffective thermal resistance with acceptable accuracy.Guarded hot box tests and finite element models can be precise,but are accurate only if the modeled c
2、ross-sections correctlyrepresent the insulation system as practically constructed. Incooperation with others on the Metal Building Task Groupreporting to the ASHRAE SSPC 90.1 Envelope Subcommittee,we developed recommendations for modified thermal trans-mittance values for metal building insulation s
3、ystems to reflectcurrent common construction practices as explained in thispaper. The current version of ASHRAE 90.1 over-estimates thethermal performance of “over-the-purlin” insulation for roofsand walls by approximately 20%INTRODUCTIONThis work was done to support efforts by the AmericanSociety o
4、f Heating Refrigeration and Air-Conditioning Engi-neers (ASHRAE) Standing Standard Project Committee(SSPC 90.1) Envelope Subcommittee Metal Buildings TaskGroup (MBTG) to provide accurate thermal performance datafor insulated metal building enclosure systems. ASHRAEsEnvelope Subcommittee recognized t
5、hat descriptions andcharacterizations of metal building insulation systems inASHRAE Standard 90.1 (Energy Standard for BuildingExcept Low-Rise Residential Buildings) did not reflectcommonly installed assemblies and were based on largelyunavailable or incomplete data. It appeared that most of theinac
6、curacies were from insulation mock-ups and assumptionson insulation cross-sectional profiles in computational model-ing that were not representative of common or practicallyachievable field installations.Traditional construction methods for metal building roofsand walls result in non-uniform insulat
7、ion thicknesses andrequire non-insulating materials in the plane perpendicular tothe dominant heat flow. Because the systems result in non-uniform insulation thicknesses (i.e., insulation thermal resis-tances), and because there are structural members with lowthermal resistance (e.g., purlins and br
8、acing) and differenttypes of insulation (e.g., fiberglass batts plus extruded poly-styrene spacer blocks), it is challenging to determine the over-all insulation effectiveness in typical metal building roofs andwalls.One common insulation system is a layer of fiberglassinsulation laminated to a wate
9、r vapor retarder that is pulledacross the top of the purlins (or outside of the girts)conven-tionally referred to as “over-the-purlin” or “over-the-girt” (OPor OG) systems (also, “single layer” systems) within Standard90.1-2007 (ASHRAE 2007). A variation is “double layer” OPsystems, where a layer of
10、 un-faced batt insulation is placed ontop of the laminated batts and oriented parallel to the purlinsbetween purlin flanges. Both cases result in a parabolic profilewith the minimum insulation thickness where the metal roof orwall exterior fastens to the structural members and the maxi-mum insulatio
11、n thickness at the centerline between the purlins(Figure 1). “Liners systems” are another common assembly refer-enced in Standard 90.1. In this assembly, a liner is attached tothe innermost surface of the steel structural members (purlinsor girts), either with a thermal spacer or directly to the str
12、uc-tural members. Commonly, the liner fabric is a woven poly-ethylene, which results in a double parabolaone betweenASHRAE Standard 90.1 Metal Building U-FactorsPart 4: Development of U-Factors for Walls and Roofs Based on Experimental MeasurementsLes Christianson, PhD, PEMember ASHRAELes Christians
13、on is professor emeritus in the Department of Agricultural and Biological Engineering, University of Illinois, Urbana-Cham-paign, IL. OR-10-020 2010, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions 2010, Vol. 116, Par
14、t 1. For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission. 190 ASHRAE Transactionspurlins and the other between fasteners at the underside of thepurlins (Figure 2).“Filled cavities” are
15、 the third system referenced in Stan-dard 90.1. Here laminated fiberglass is installed with laminatesealed to the top of the purlin flanges. Support is provided tothe underside of the laminate to allow the insulation to beinstalled with less compressionand therefore higher thermalresistancethan typi
16、cally occurs in OP systems. These sys-tems are most commonly installed using proprietary equip-ment that provides the support for the insulation duringconstruction. The resulting insulation profile is not generallyparabolic (Figure 3). Each of the above systems may be installed with standingseam or
17、through-fastened roofs. Only through-fastened wallswere tested and included in Standard 90.1 as they represent themost common insulation installation method for metal build-ing wallsmainly for structural reasons. Thermal spacerblocks of different thicknesses and material properties canalso be used i
18、n these systems. Continuous (e.g., uninterruptedconstant thickness insulation systems) can be installed inseries with the metal building systems described in this paper,and the effective thermal resistance can be determined byadding the thermal resistance values of the two systems.The MBTGs charge f
19、rom the Envelope Subcommitteewas to review and, if necessary, modify the thermal resistancevalues in Standard 90.1 for insulated metal building assem-blies. We did not attempt to characterize proprietary systemsor any other systems not currently included in the Standard.The objectives addressed with
20、in this paper are:1. Define the insulation profiles for commonly installedmetal building insulation systems.2. Verify laboratory data with field measurements andobservations.3. Determine the effective thermal resistance for the metalbuilding systems currently included in Standard 90.1 bycalculation
21、methods for single layer (Choudhary andKasprzak 2010b) and double layer (Gavin and McBride2010) systems.The data, analyses and discussions in the remainder of thispaper are for metal frame buildings and for the non-continuousinsulation systems commonly installed in these buildings.PRACTICAL ASPECTS
22、OF INSULATION INSTALLATIONMetal buildings are installed year-round and often inwindy, wet and similarly hostile weather conditions. Gener-ally the roof is a gable roof with 50 ft (15 m) or longer roofsections and 14 ft (4.1 m) or taller side walls. For laminated OPand OG insulation systems, the insu
23、lation with vapor retarderFigure 1 Schematic of typical over-the-purlin (OP) insula-tion systemend purlin and next purlin only, notto scale.Figure 3 Schematic of typical filled cavity insulationsystemend purlin and next purlin only, not toscale.Figure 2 Schematic of typical liner insulation systemen
24、dpurlin and next purlin only, not to scale. 2010, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions 2010, Vol. 116, Part 1. For personal use only. Additional reproduction, distribution, or transmission in either print o
25、r digital form is not permitted without ASHRAEs prior written permission. ASHRAE Transactions 191is typically a minimum of 3 ft (0.9 m) wide with a lengthslightly exceeding that of the roof or wall section. To install OP systems, the laminated fiberglass insulationis rolled out on the roof edge, fas
26、tened at one end of a roofsection, and a tension in the range of 50 lb (23 kg) is appliedto the other end while shaking the insulation to get a relativelyuniform profile between purlins along the roof line (NAIMA,2006). Once the insulation is relatively uniform, installersrelease as much tension as
27、possible (i.e., without causing non-uniform sagging of insulation and difficulty in fastening adja-cent rolls of the insulation) before fastening the other end.When tension is released in minimal wind conditions, theinsulation tends to slide back for the first two purlin spacingsafter releasing the
28、initial tension used to get the insulationprofile relatively uniform. This is 10 ft (3 m) for the widestcommon purlin spacing (5 ft, 1.5 m). Friction of the laminateover the tops of the purlin prevents “fluffing out” for the restof the between-purlins sections even when the tension neededto pull the
29、 unfastened end in place is released.This prevents the insulation thickness from increasing atthe mid-points between purlins without someone manuallypulling the insulation down between purlins.With even modest wind, a tension of 50 lb (23 kg) orsometimes greater must be applied continuously until bo
30、thends are fastened to keep the insulation and vapor retarderfrom blow-off.Even in minimal wind conditions, tension must be appliedto the insulation and vapor retarder systems while pullingthem in place to get the uniformity needed for aesthetics andfor seams to match up and be sealed. Generally a d
31、ouble-layersystem will have a maximum center-line depth of 3 in. (7.5cm) below the top of the purlin flange; single layer systems amaximum of 2.5 in. (6.2 cm).While it may be technically possible for installers to havepersonnel lean over the roof edge between each set of purlinsto pull the insulatio
32、n down to achieve greater center-linedepths, it is not done for safety and cost reasons.For liner systems, wind, safety and labor costs are also ofconcern. One of the important differences, from a thermalperformance perspective, is that the liner is attached to thebottom of the inside purlin flanges
33、. Once the liner is attached,unfaced fiberglass batts are laid between the purlins over theliner and in some cases with the top layer perpendicular to andcrossing over each purlin. The installer has the purlin cavity(typically 8 in.; 20 cm), the space above the purlins if a stand-ing seam roof is us
34、ed, and the option to offset the liner belowthe bottom purlin flange as much as needed to achieve thedesired insulation depth and effective thermal resistance with-out compressing the insulation.Liner systems used with walls are similar, but there is theneed for “hook-like” supports to hold the fibe
35、rglass insulationin place during installation and to minimize sag over time.Filled cavity systems are generally supported during andafter the installation to allow for greater installed thicknesses.Fiberglass batts laminated to a vapor retarder are attached tothe top side of the purlin flanges. The
36、insulation thickness isgenerally limited to the purlin depth or height of cross-brac-ingwhichever is more limiting.DEVELOPMENT OF LABORATORY METHODS FOR DETERMINING INSULATION SYSTEM GEOMETRIESRoof OP SystemsThe OP roof insulation systems were tested using a 7 ftwide 25 ft long (2.1 m 7.5 m) frame t
37、hat allowed for simpleadjustment of purlin spacings. In earlier work, purlin spacingsof 20, 30, and 60 in. (50, 75, and 150 cm) were tested andanalyzed (Christianson 2007).“C” channel purlins were used on the ends and “Z” chan-nel purlins in the middle. Purlin depths were 8 in. (20 cm), andthe flang
38、e widths were 3 in. (7.5 cm). Purlin depth and wallthickness do not affect the insulation thickness geometries;purlin flange widths do affect insulation profiles slightly.To decide on the minimum size needed to replicate fieldinstallations, a series of tests were conducted with 5, 15, and45 lb (2.3,
39、 6.8, and 20.4 kg) tension on 3 ft (0.9 m) laminatedfiberglass insulation. To install insulation a minimum tensionand “shaking” of the insulation of approximately 50 lb (23 kg)was needed to get the insulation relatively uniform to adjacentinsulation (important for both aesthetics and for the uniform
40、ityneeded to attach laminate). Once the insulation was uniform,we released the tension back to the 5, 15, and 45 lb (2.3, 6.8,and 20.4 kg) tension for comparisons.When tension was released to no tension, the insulationend pulled off the end purlin and fell between it and the 2ndtoend purlin, and sag
41、ged noticeably in the adjacent section, butwas virtually unmoved for the earlier sections. Five pounds(2.3 kg) was sufficient to prevent the insulation from slidingoff the end purlin. This suggests friction and weight of thelaminated insulation are such that a test system length in the 25ft (7.5 m)
42、range with a minimum tension of 5 lb (2.3 kg) isadequate to replicate the best field installation conditions; alength of 10 ft (3 m) with no tension is inadequate.Five replications at three different tension rates for everysystem were tested during development of the test methodol-ogy (Christianson
43、2007). These replications showed an aver-age standard deviation of less than 0.2 in. (0.5 cm) forinsulation profiles at the center-line, quarter-points and 1/8-points between purlins. This equates to a variation of approx-imately 5% among effective R values for any given insulationsystem as practica
44、lly installed.All data reported in this paper and used by SSPC 90.1pertain to 60 in. (150 cm) purlin spacings. However, the datareported by Christianson (2007) for different purlin spacingswere useful in development and proof of key assumptions forthe integrated models developed by Choudhary (2010b)
45、 andGavin (2010) for single layer and double layer systems,respectively. Their models allow a designer or installer todetermine the effective thermal resistance for any purlin spac- 2010, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Published in A
46、SHRAE Transactions 2010, Vol. 116, Part 1. For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission. 192 ASHRAE Transactionsing. They are incorporated in the proposed modifications toStanda
47、rd 90.1.Generally, 48 in. (120 cm) purlin spacings and 30 in.purlin spacings reduce the effective thermal resistance byapproximately 10% and 25%, respectively, compared to 60 in.(150 cm) spacings (Christianson, 2007).Roof Liner SystemsThe liner systems were tested using a 25 ft 25 ft (7.5 m 7.5 m) p
48、urlin grid, because these result in a “double parab-ola” system. That is, the insulation exhibits parabolic profilesperpendicular to the purlins and parallel to the purlins. Thelatter condition is caused by the frequency of liner fastening tothe purlins, which is generally 5 ft (1.5 m) on center.Roo
49、f Filled Cavity Systems and Other SystemsDetermining insulation profiles for filled cavity systemswas not included in this study. Similarly, there was no attemptto model proprietary and emerging insulation systems thatmay produce different profiles.Wall OG SystemsA 14 ft (4.2 m) high wall was used for laboratory mock-ups. A “C” girt was used at the base. A 7 ft (2.1 m) girt heightwas used for the first “Z” girt height, which allows for conven-tional side door heights. The next “Z” girt spacing was 5 ft(1.5 m), which is typical girt spacings up to the top girt spac-ing
