Document M4D8ww581OLkJX82L1rY7MwNk

396 CHAPTB? 22 1965 Guide And Data Book insulation having a thermal conductivity of 0.27 at 75 F mean temperature. Vapor barriers are not required on exterior insulation of ducts used for heating alone, but vapor barriers must be pro vided where ducts are used for cooling alone, or cooling and heating alternately. Insulation for Cooling Ducts Ducts for summer air conditioning are insulated with the materials as for heating ducts. Generally ducts in any unconditioned space should be insulated and provided with a vapor barrier for condensation prevention and for economic reasons. In addition to affording significant operating cost re ductions, duct inwilatinn may reduce heat gain enough to reduce cooling equipment size. The insulation must be faced with a vapor barrier, and the surface temperature must be kept above the dew point of the surrounding air. Joints and laps in the vapor barrier must be thoroughly sealed, using vapor barrier compound, impermeable tape or strips of vapor barrier material and vapor barrier adhesive, to prevent entry of water vapor. The approximate U values given for heating ducts may also be for estimating the reduction in heat gain (using the appropriate temperature difference and the thickness of duct insulation to be used). A method with equations for calculat ing surface temperatures and its application in preventing condensation is shown in an earlier section; the Economic Thickness. Summer dew-point temperatures commonly occur ring in the various parts of the United States are: Northern climate zone, high sixties; Central climate zone, mid-seventies; Gulf Coast areas, High seventies. It can be shown that for condensation prevention alone at least one inch of insulation should be used in Gulf Coast areas for duct temperatures of 60 F, and some insulation is advisable in the other zones, de pending on design conditions. Application of Duct Insulation Duct insulation may be used on the exterior or interior of ducts; interior application as a lining is chosen when sound absorption is desired. Attachment to duct surfaces may be made with an adhesive for temporary support and followed by permanent mechanical support, such as pre-attached pins or clips for impaling; encircling bands, wires, strapping, or tapes going around the outer circumference of the insulation. To satisfy some building codes, the materials, particularly fa/iingttj must be noncombustible or have a limited flame spread value. Local authorities having jurisdiction should be consulted. REFR1GERATH) ROOMS OR BUILDINGS Low temperature rooms can be insulated with a variety of insulations and an even greater variety of methods. The engineer, architect, owner, or contractor should select the most suitable method for their specific use. The purpose of this section is to present accepted practice in the field and to describe the insulations in common use together with the generally accepted application methods. It is recommended that the manufacturers' instructions and specifications be followed for specific directions concerning the use of the insulatinnsj adhesives, and finishes. GENERAL PRINCIPLES The following design principles are bade to most low tem perature space installations involving any of the accepted insulations commercially available. A detailed guide to.good practice in design, construction, operation and maintenance of cold-6torage facilities, along with a brief summation of necessary research is given in Reference 23. Envelope Construction It is important that the space to be insulated be surrounded wherever possible by a complete envelope of insulation; that is, the structure of the refrigerated space is completely iso lated from a higher temperature space by layers of insulation. Where the insulation is penetrated by structural supports, hanger rods, electrical oonduits, etc., it is important that these are sufficiently insulated and vapor sealed on the warm side to prevent entry and migration of water. Venting or Heating Floors For storage temperatures of approximately 25 F and higher, the areas beneath the floors present no different problems than in nonrefrigerated buildings. However, if a freezer space b contemplated on or below grade, consideration should be given to the possibility that freezing of the ground may cause heaving of the floor, columns, and wall footings. The risk b considerable with storage temperatures below 15 F. Another limiting factor is the size of the room. Where the distance between two freezer walls adjacent to normal tem perature or heated areas b no more than 15 ft, venting or heating of the floor b not usually necessary if the floor b ade quately insulated.'In all cases positive drainage b essential and must be provided by the use of gravel or cinder fill, and drain tile. In extreme cases when freezer rooms have to be located where the ground water level may approach the subfloor slab, enough heat should be provided beneath the floor insulation to that flowing up into the cold room when the ground temperature is between 25 and 33 F. This can be done by making the subfloor a form of. panel heating. A noncor roding pipe or tubing in the concrete carrying heated oil or water is one way to meet such conditions. Other methods in clude electric strip heaters and air channels beneath the slab carrying heated air."- Venting Air Spaces Above Ceilings and in Walls Unventilated air spaces above ceilings or in stud walls generally lead to trouble due to trapped moisture and should be vented whenever possible to the outside. Air spaces, nor mally on the warm ride of the vapor seal, tend to have such high humidity that water may collect on any surface having a lower temperature than that of the dew-point temperature of the air space. This can destroy the necessary strength char acteristics of the structure in the case of wood, or it can cause staining, dripping, or frosting. This may eventually lower the efficiency of the insulation and usually detracts from the appearance of the room. If by venting to the outside, espe cially in railings, drier air is circulated through the air space, the condensation or frosting problem will be minimized. Also, venting with warm dry air tends to warm the surfaces it con tacts and therefore helps keep these surfaces above the dew point temperature of the air. Vapor Barrier Treatments Vapor barriers are necessary to varying degrees with all insulations. In coolers, water vapor migrating through the walls b less critical than in freezers but still can be damaging if the dew-point temperature occurs within the insulation, allowing moisture to collect therein and impair the efficiency of the insulation. In freezers vapor treatment b necessary because conden sation will not only tend to destiny the insulation, but if i* mam Thermal Insulation and Water Vapor Barriers 397 freezes may create forces that will cause the insulation to heave or buckle from its supporting surface. Vapor barriers for the warm side of cold rooms may be sufface costing* applied hot or cold, with or without reinforcing membranes, and sheet materials such as metal foils and lami nates having a maximum permeance of 0.1 perms. Super vision and inspection must be provided during application of vapor barriers to insure that adequate sealing b obtained. Lapping or sealing joints in sheet vapor barriers must be carefully done to maintain the effectiveness of the vapor barrier envelope. AU penetrations through the vapor barrier due to piping, conduits, ducts, and doom must be thoroughly flashed or caulked with a vapor barrier compound to prevent water vapor leakage. The junctures of walls, ceilings, and floors require special . attention to make sure that the vapor barriers are not broken through movement of the structure during expansion or con traction. At such critical locations, vapor barrier ratings should be' reinforced with a strong compatible membrane. Both sheet barriers and membrane-reinforced mating barriers should be provided with a loop at floor and ceiling junctures which will permit structural movement without breaking of barrier. Where adjacent cold rooms operate at different tem peratures, a vapor barrier must be provided on the warmer, side of the common wall, floor, or ceiling. Installations where reversible water vapor flow may be en countered must be specially treated to prevent moisture ac cumulation within insulation. The usual treatment b vapor barriers on both sides of insulation. Interior Finish Treatments It has been shown from test data that, in almost every |i"y where an interior finish acts as a vapor barrier, serious diffi-' culties have occurred. From the standpoint of best results for vapor transmission it would be preferable to have no interior finish. However, where other considerations, such as sanitary regulations, prevention of mechanical damage, and physical appearance are important, an interior finish b required. The interior finish may or may not require mounting inde pendent of the insulation. The interior finish should have a significantly higher permeance than that of the vapor barrier, adhesive, or insulation. The ratio of the interior finish permvalue to the vapor barrier perm-value has not been clearly established. TECHNIQUE Insulation used for low temperature rooms b generally one of the following four types: (1) rigid, (2) loose fill, (3) flexible, or (4) reflective. Rigid Insulation Rigid insulation b widely used for low temperature rooms. Basic installation principles are: larert**8*1 lyP* "sulatioaa generally applied in two or more V AD joints are butted as tightly as possible. In addition, all S^i^f,U?a8sered,.m reltioo to each other in the layer being *PPiMd, between adjacent layers, at the wall to wall juncture juncture, and wall to floor juncture. aJt J5? requires a fairly level surfaoe to start with with If V^por barrier treatment may not be as important as *0tiier types of insulation. For instance, some manurtructicra specificatioQS require no vapor barriers in cooler con-' ^"tniction, the use of a vapor barrier adhesive for 0131 "ye* " specified as sufficient protection. This varies with the various brands; manufacturers' literature should be consulted for exact recommendations. e. In ceiling construction where the insulation is applied from below, the first layer is usually fastened mechanically. /. Any additional layers are usually attached to the preceding' layer with treated wood or plastic skewers driven at an acute angle. This is in addition to the specified adhesive. .. 0- AH wood used in the refrigerated area, including skewers, bucks, sheathing, furring, etc., shmild be of pressure treated wood that will resist the rotting action of the moist conditions. The following procedures normally apply to the application of rigid insulation to various building components. a. Wall*. The first layer can be applied to masonry walls with adhesive alone and any succeeding layer with adhesive and skew ers. Horizontal wood supports are necessary in the first layer when using certain insulations or adhcaigM or on excessively high walla. Walls made entirety of insulation can be erected with rigid insulation. Although one layer can be used, usually the waUia made up of two or more layers. The wall can either be built up against a temporary framework which is later removed or the wall can be erected block by block as in laying brick. b. Ceilings. Ceilings can be classified into three general types: overdeck, underdeck, and suspended, Overdeck ceilings are those for which insulation is applied from above, directly to the top surface of what normally is the roof deck. The first layer is applied with adhesive, or mechanical fastening, or both. Additional layers are applied with adhesive' and, generally, treated wood skewers. The built-up roof system is then applied directly over the insulation. Underdeck ceilings are similar to the overdeck except that insulation is applied from beneath directly to the underside of the roof dock. In this case the first layer of insulation must be fastened mechanically in addition to being held by an adhesive. Additional layers are applied from beneath with adhesive and treated wood skewers. Suspended ceilings have many variations but all basically are suspended from a higher ceiling with wires or rods. The initiation, is applied from above quite similarly to that described for over deck ceiling. The hanging rods or wires must be intnl^tM suffi ciently to prevent condensation on the rods or wires, and be vapor sealed to prevent entry of water into the insulation. One type of suspended ceiling is the T-iron ceiling. In this con struction the T-irons with the web on top are suspended from the ceiling or span the room. The first layer is generaUy routed out to fit snugly around the T-irons between which the insulation is placed. The second and any succeeding layera are applied from above or below with adhesive and skewers. Finally, the top sur face is covered with hot asphalt or a Portland cement grout and vapor sealed. c. Floors. Because of the moist conditions that generally exist below floors of refrigerated rooms, it has become a general rule to apply a vapor seal of some kind over the subslab before applica tion of the insulation. With concrete floors, the first layer is applied in hot asphalt mopped onto the subslab. Additional layers are bonded with ad hesive and may be held with skewers until the wearing floor is poured. In some cases, the second layer may be put in dry. _ Most insulations also require a water seal between the insula tion and.the top slab. This is used generally to prevent water from seeping into the insulation, either from cracks that are always present in a floor of any rise or from the wet concrete during the pour of the wearing slab. A coating material is also needed over some insulations to prevent a bond between the slab and the insulation. In coolers the floor insulation can sometimes be omitted altogether or at the most, consists of a ribbon of insulation around the perimeter of the room extending under the 1ab or down the foundation as best suited to the plant or area conditions. d. Miscellaneous. Columns or beams penetrating the insulation are insulated with pieces of rigid insulation, fabricated so as to completely fill any voids. Round columns can be insulated with lagging bonded in place. Rectangular shapes of insulation are. usually held by skewers and adhesive. One rule of thumb is to insulate all projections with a minimum of one-half this insulation thickness specified for the walls and to insulate along the enhimn or beam a distance equal to four timw the specified wall thick- Curba and bumper rails ore generally provided and are located around the perimeter of the refrigerated room. Bumper rails can be anywhere from a few feet high to the full height of floor to' ceiling. They not only provide the wall protection bum meehani-