ASHRAE HVAC APPLICATION IP CH 62-2015 MOISTURE MANAGEMENT IN BUILDINGS.pdf

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1、62.1CHAPTER 62MOISTURE MANAGEMENT IN BUILDINGSCAUSES . 62.1MOISTURE TOLERANCE AND LOADS 62.2RISK FACTORS AND MITIGATION . 62.3HVAC Systems 62.3Architectural Factors . 62.4Building Operational Decisions 62.5Occupant Decisions . 62.5SOLUTIONS. 62.6Architecture and Design. 62.6HVAC Systems 62.7MEASURIN

2、G BUILDING DAMPNESS. 62.10Water Activity . 62.10Moisture Content Measurement Variation . 62.11NDOORS, buildings should always be dry. When building inte-Iriors get damp and stay damp, problems often emerge for theiroccupants and for the buildings structure, material, and furnishings.Persistent indoo

3、r dampness has been associated with humanhealth problems, increased risk to buildings structural fasteners andexterior enclosure, shortened useful life of furnishings, and reducedacceptability to occupants because of odors and stains. These andrelated problems can be costly and disruptive, as well a

4、s annoying toall concerned (ASHRAE 2013).Human HealthThe U.S. National Academy of Medicine and the World HealthOrganization determined that there is a clear association betweendamp buildings and negative health effects (NIM 2004). The U.S.Department of Energys Lawrence Berkeley National Laboratoryes

5、timated the cost of documented dampness-specific health effectsto be more than $3.5 billion each year (Mudari and Fisk 2007), andhealth hazard evaluations of buildings around the world haverepeatedly shown that indoor dampness is neither normal nor desir-able from a health perspective e.g., NIOSH (2

6、013). Although notall of the mechanisms are well understood at this time, cognizantpublic health authorities agree that damp buildings can lead tohealth problems.Energy ConservationInsulation can be compromised when rain and snow melt waterleaks into roofs or exterior walls, and when indoor humidity

7、 con-denses inside walls. When insulation gets wet, it allows more heat topass through the building enclosure. The increased heat flow wastesenergy, increases the difficulty of meeting energy reduction goals,and adds needless costs to building operation.SustainabilityDamp buildings generate corrosio

8、n, rot, and mold, which damagestructural fasteners (Zelinka 2013), materials, and finishes. There-fore, a building and its furnishings are not sustainable (because theiruseful lives are shortened) unless they are designed and constructedto prevent moisture accumulation.CostsFixing a moisture problem

9、 after construction is roughly 10 timesas expensive as correcting a drawing at the design stage, and reme-diating a mold problem is roughly 100 times as expensive as cor-recting that drawing.Thus, it is far more cost effective (and moresustainable) to avoid problems at the design stage than to repai

10、rproblems caused by moisture-risky design.Avoiding Litigation RiskHumidity and moisture-related problems in buildings have beenthe single largest category of claims against the errors and omissionsinsurance of architects and engineers (84%).Also, moisture-relateddamage is the single most-litigated c

11、onstruction defect against con-tractors (NAIC 2008).1. CAUSESBased on investigations of problem buildings, dampness suffi-cient to cause problems seldom has a single cause. More often, aseries of events, including decisions in many areas of professionaland personal responsibility, combine in complex

12、 ways to cause aproblem. Therefore, it is not appropriate to assign responsibility forbuilding dryness to any single group, because it is not likely that anyone group can prevent a problematic level of dampness, mold, ormicrobial growth by their actions alone.The interactions that lead to the amount

13、 and duration of moistureaccumulation that creates problems are similarly complex. Figure 1shows an example: the classic and problematic practice of installingvinyl wallpaper on the indoor surfaces of exterior walls in a mechan-ically cooled building in hot, humid climate.High-dew-point outdoor air

14、infiltrates through exterior walls. Itsmoisture is then absorbed into hidden cool surfaces of interior gyp-sum wallboard. Because the vinyl wallpaper is relatively imperviousto water vapor transport, moisture accumulates in the gypsum board,resulting in mold growth and eventually decay, rot, or corr

15、osion ofstructural members or their fasteners.Note that the problems illustrated by Figure 1 required more thanone element: high outdoor dew point for many days or weeks, exten-sive humid air infiltration into the enclosure, chilled indoor surfaces,vinyl wallpaper, and untreated paper-faced gypsum b

16、oard. If any oneof those elements were absent, little or no mold growth might haveoccurred (Zelinka 2013). In this example,The owner or interior designer decided to install vinyl wall cover-ing rather than a more permeable wall covering.The architectural designer designed and/or the contractor built

17、 abuilding that allows extensive humid air infiltration, and alsoselected untreated gypsum wall board for a location likely to expe-rience high humidity in a climate where high humidity continuesfor many months.The HVAC system was apparently designed and/or installed suchthat it overcools wall surfa

18、ces. The toilet exhaust duct system wasalso either designed, installed, or operated such that it extracts airfrom building cavities as well as from the bathroom, therebyincreasing humid air infiltration and leading to high relativehumidity inside the cavities. High relative humidity inside cooledwal

19、ls leads to moisture absorption and high water activity in vul-nerable paper-based backing of the wall board.The preparation of this chapter is assigned to TC 1.12, Moisture Manage-ment in Buildings.62.2 2015 ASHRAE HandbookHVAC ApplicationsAll of these factors combine to support mold growth, givene

20、nough time.This example illustrates that risks from multiple decisions madeby many different professionals usually act in combination to pro-duce enough moisture accumulation in the wall cavities, for a long-enough period, to create a microbial growth problem.Further, the risk of excess moisture acc

21、umulation can be eitherincreased or reduced by occupants as they use the building. Forexample, if the occupants of an apartment generate a significantamount of moisture from cooking and cleaning activities withoutopening windows or using exhaust fans, excess moisture accumula-tion and mold growth ma

22、y occur, most commonly on the inside sur-faces of exterior walls during cold weather. A building is a complexand dynamic system, and the actions of its occupants are an integraland constantly changing component of that system.Finally, with respect to health issues, people in the same buildingare oft

23、en quite different in their individual sensitivities to airbornemicrobial contaminants. A low level of contamination that causesadverse health effects for one sensitive individual often causes nohealth effects for others.Consequently, the prudent course of action is to keep all of thematerials that

24、make up a building and its HVAC systems as dry aspossible, consistent with their normal functions. Building profes-sionals and building occupants can reduce risks byRemembering that the risk factors for microbial contaminationand corrosion are excessive long-term moisture accumulation inmaterials, r

25、epeated wetting, or catastrophic water damage.Making decisions and take actions to keep the building and itssystems, furnishings, and finishes as dry as possible, given thefunction of the component in question and the available re-sources. To help establish threshold levels of concern for materialda

26、mpness, microbiologists and building investigators observethat mold growth is rarely a problem when the water activity of in-terior building materials and furnishings is held consistently be-low 0.8 (below an equilibrium relative humidity of 80% rh in thesurface layers of a material) (ASHRAE Standar

27、d 160).Being aware that, if adequate resources are not made available tokeep the building, systems, and contents dry, then the risk ofmicrobial growth including mold will increase.Addressing persistent dampness inside a building; constant, stag-nant water in condensate drain pans; or constantly damp

28、 insula-tion, filters, or sound lining of HVAC systems.2. MOISTURE TOLERANCE AND LOADSConcrete, masonry, stone, and heavy wood timbers are muchless moisture sensitive than untreated paper-faced gypsum board,light-gage steel studs, and carpet adhesives. That is why the tradi-tional heavy construction

29、 assemblies typical of buildings builtbefore the twentieth century sometimes tolerated rainwater loadsand moisture accumulation in exterior walls with fewer problemsthan the lighter construction of most modern buildings.Consequently, it is useful to recognize that not all buildings havethe same risk

30、s, and each type responds differently to equal amountsof humidity and moisture accumulation. When building materialsand finishes tolerate moisture exposure, as in the case of a ceramictile-lined shower room, there is less risk of mold and microbialgrowth than if that same shower room were lined with

31、 painted gyp-sum wall board.Similarly, not all exterior surfaces of the same building are sub-ject to the same level of environmental moisture stress. Risks fromrain exposure and moisture accumulation are quite different on eachface of the building. Beginning with the matter of moisture loading,Figu

32、re 2 shows an example of the fact that the volume of rain oftendepends on the predominant direction of wind-driven rain. InToronto, Canada, the majority of the rain comes from the east(Straube 2010). In other locations, most of the wind-driven rain cancome from quite different directions, varying by

33、 season of the year.Also, the drying potential of the building varies according tobuilding orientation. For example, in the northern hemisphere, thenorthern side of a building is shaded from direct solar radiation,Fig. 1 Mold Caused by Complex Combination of FactorsMoisture Management in Buildings 6

34、2.3reducing the annual drying potential on the north wall to far lessthan on the south and west sides of the same building. In the north-ern hemisphere, the risks of equal amounts of rain are much higheron the north side than on the southern and western elevations.Therefore, when designing any build

35、ing enclosure, it is useful torecognize differences in moisture tolerance of materials and toremain aware of differences in moisture loading and drying poten-tial both outside and inside the building. Chapter 44 outlines usefulsuggestions for architectural designers to limit the potential forproblem

36、s in building enclosures.The concern continues after construction is complete. An ownerof an existing building should recognize that some types of con-struction and some systems and assemblies in a building are moresubject to problems from moisture accumulation than others. Build-ing operations beco

37、me more economical and the building itselfbecomes more sustainable when designers avoid moisture-sensitivematerials and assemblies in parts of the building where annual waterexposure is high and drying potential low, rather than treating allparts of all buildings equally. In both design and operatio

38、n, anappropriate hierarchy of concern will be based on how much watera given problem can potentially add to moisture-sensitive indoormaterials and furnishings.Architects should keep in mind that the side of the building thathas the greatest annual wind and rain exposure needs the mostwater-resistant

39、 materials and the most effective building enclosuredesign details.Engineers should remember that buildings in hot and humid cli-mates experience thousands of hours at high outdoor dew points, sothe ventilation and makeup air systems must be sure to dry incomingair with more certainty than buildings

40、 in dry climates.Building owners and operators should remember that, no mat-ter what the construction age or type, rainwater leaks are a biggerconcern than high humidity, and plumbing leaks are a bigger con-cern than air leakage from ducts.All of these problems can cause mold growth, but a simple ru

41、leapplies to all circumstances: more moisture exposure means ahigher potential for problems in a shorter amount of time. There-fore, designers and owners benefit from understanding some of thespecific factors that have historically been most influential in damp-ness problems.3. RISK FACTORS AND MITI

42、GATIONEach area of professional and occupant activity involves deci-sions and actions that can either increase or reduce the risk of prob-lems related to moisture, mold, and other microbial growth. In mostcases, the individuals involved are not aware they are making fatefuldecisions. When reviewing

43、these factors, it is important to remem-ber that moisture and mold problems can develop for different rea-sons in cold and hot climates, and can also occur throughmechanisms caused by regionally specific building designs, mate-rial selections, and construction practices in different parts of theworl

44、d. Therefore, recommendations based on local conditions areoften needed to avoid dampness-related problems.Note also that these factors have seldom been responsible in iso-lation for moisture and microbial growth problems. More com-monly, the risks have increased when more than one of these factorsa

45、re present, or when an architectural risk factor is combined withrisk factors associated with either HVAC systems or occupant activ-ities.3.1 HVAC SYSTEMSRisk FactorsRedistributing microbial air contaminants, including mold, froma contaminated space into occupied areas. Examples of contami-nated spa

46、ces can include parts of the building under constructionor renovation, hidden building assemblies (e.g., damp crawl-spaces or attics), or spaces above dropped ceilings or below raisedfloors (Harriman and Lstiburek 2009).Failing to make air distribution components and joints in returnplenums and supp

47、ly and exhaust ducts sufficiently airtight. Jointsand connections must be tight enough to prevent suction that oth-erwise pulls humid outdoor air into the building, and/or leakagethat allows cold supply air to chill surfaces inside humid buildingcavities (Harriman and Lstiburek 2009; Harriman et al.

48、 2001).Failing to keep the long-term average indoor air pressure positivewith respect to the outdoors when the outdoor dew point is higherthan indoor surface temperatures (Harriman et al. 2001).Failing to prevent dirt and dust accumulation on cooling coils andon duct surfaces and sound lining downst

49、ream of cooling coils.Accumulating a damp layer of dust can lead to microbial growth.Install access panels that allow inspection and cleaning of thecondensate pans and areas upstream and downstream of coolingcoils to ensure the condensate pan is not accumulating water, thatcoils are clean, and that upstream and downstream surfaces areclean and dry. Regular cleaning and ultraviolet lamps can reducethe impact of occasional lapses in filtration, but over time, effec-tive filtration is the most important factor in preventing microbialgrowth in parts of the system likely to accumulate moist