ASHRAE FUNDAMENTALS SI CH 36-2017 MOISTURE MANAGEMENT IN BUILDINGS.pdf
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1、36.1CHAPTER 36MOISTURE MANAGEMENT IN BUILDINGSEffects of Humidity and Dampness 36.1Elements of Moisture Management . 36.1Envelope and HVAC Interactions 36.2Indoor Wetting and Drying 36.2Vapor Release Related to Building Use. 36.4Indoor/Outdoor Vapor Pressure Difference Analysis 36.6Avoiding Moisture
2、 Problems 36.10Climate-Specific Moisture Management 36.11Moisture Management in Other Handbook Chapters . 36.12HE TERM moisture encompasses the gaseous, liquid, andTsolid states of water and any dissolved contaminants. Examplesof liquid moisture include precipitation, wind-driven rain, construc-tion
3、 moisture, rising damp, and water from incidental pipe drip-pings. Precipitation wets pitched roofs, low-slope roofs, and inclinedfacades, whereas wind-driven rain wets the enclosure as a whole.Buildings, including the envelope, start their service life containingsignificant quantities of constructi
4、on moisture. This is particularlytrue for concrete, aerated concrete, mortar, and plaster. Groundwaterand rain sinks may lead to rising damp, and pipe leakage reflects badworkmanship, lack of maintenance, failing fixtures, or pipe corro-sion (Hens 2016; Mumovic and Santamouris 2009; Trechsel 1994).T
5、his chapter presents data on indoor vapor release and measuredindoor/outdoor vapor pressure or vapor concentration differencesnot included elsewhere in the ASHRAE Handbook, and discussesmoisture sources and sinks that can reduce materials durability, aswell as the negative effects of insufficient or
6、 excessive indoor rela-tive humidity.Gaseous water (vapor) comes from outdoor humidity and frominterior vapor releases. Water vapor in the air, expressed as relativehumidity, governs hygroscopic loading of materials. High relativehumidity values at surfaces favor mold growth and, if reaching100%, ca
7、n lead to surface condensation. When vapor pressure andtemperature gradients in and across assemblies point in the samedirection, interstitial condensation is possible.Chapter 25 contains an in-depth analysis of heat, air, and moistureloads; Chapter 15 discusses surface condensation on windows; andC
8、hapter 16 covers interstitial condensation caused by air leakage.Excessive indoor moisture and humidity interferes with the useand enjoyment of buildings and may shorten their useful life over thelong term. Problems affecting owners and occupants include reducedcomfort, poor indoor air quality, nega
9、tive health effects, damage tothe buildings materials and structural fasteners and wasted energy inHVAC operation. Consequently, moisture management demandsattention from the architect, the builder, the mechanical systemdesigner, and those charged with budgeting, management and main-tenance of the b
10、uilding and its mechanical systems.All buildings experience occasional extremes in relative humidityand moisture. Short-term occurrences of these extremes can gener-ally be accommodated by storage in the building materials, but whenmoisture and humidity accumulate for extended periods in vulnerablem
11、aterials, major problems can and often do occur. Moisture problemsare unfortunately quite common in buildings. It is the responsibilityof those in a position of authority to reasonably reduce the risks asso-ciated with excessive moisture accumulation. Successful manage-ment of moisture and humidity
12、requires understanding the complexand dynamic relationship between the buildings enclosure, its fabric,and the mechanical systems over the entire life of that building. Thisdynamic interaction holds the potential for either an excellent resultover decades, or for frequent, disruptive, and expensive
13、problems.Experience suggests that human behavior can overcome virtually anybuilding technology, so owner and occupant education are importantelements in the successful design and usage of a building.1. EFFECTS OF HUMIDITY AND DAMPNESSMoisture tolerance and appropriate indoor relative humidity levels
14、must be considered requirements for a sustainable built environment:relative humidity affects comfort, indoor air quality, and health, andexcessive wetness can shorten the service life of materials and assem-blies. The preferred relative humidity range for human health andcomfort is between 40 and 6
15、0%, although that interval is often broad-ened from 30 to 70%. High relative humidity degrades thermal com-fort once the operative temperature passes 25 to 27C, making theenvironment feel oppressive. It also facilitates release of volatileorganic compounds (VOCs), especially of formaldehyde, thusdeg
16、rading indoor air quality and triggering olfactory dissatisfaction.Finally, high relative humidity in specific environments (e.g., beds,on surfaces) activates dust mite reproduction and related allergy risks,and can activate mold germination and growth (ASHRAE 2012; IEA-EBC 1990a, 1990b).Very low re
17、lative humidity activates electrostatic discharge andleads to complaints of dry mucous membranes (e.g., nose, lips,throat) and eyes, especially by people wearing contact lenses. On theother hand, some respiratory ailments can be relieved by dry envi-ronments.Excessively low or high relative humidity
18、 creates conditionsfavorable to bacterial and viral infections, allergic rhinitis, andasthma. Chapter 9 gives a more in-depth analysis of the impact ofhumidity on thermal comfort. Chapter 10 discusses the effects of rel-ative humidity on indoor environmental quality, Chapter 11 coversmold, and Chapt
19、er 12 discusses the relationship between relativehumidity and olfactory perception. Additional information is avail-able in Holm (2008).Prolonged and excessive relative humidity and wetness candegrade materials physically, chemically, and biologically. Examplesof physical degradation are frost damag
20、e and salt attack. Chemicaldegradation includes lime/gypsum reaction, carbonization of con-crete, alkali/granulates reaction in concrete, and corrosion of ferrousand nonferrous metals, where moisture determines whether damagewill occur in the presence of corrosive agents (e.g., sulfide, aceticacid).
21、 Wood rot by fungi and bacteria is an example of biological deg-radation. Very dry conditions also can damage wood, causing crack-ing and warping. Fluctuations between extremes of high and lowrelative humidity can induce cracking in hygroscopic materials.2. ELEMENTS OF MOISTURE MANAGEMENTDesigning f
22、or moisture and humidity management includes thechoice of building materials and the layering of the envelope as wellas the design and component selection of the HVAC system. Forinformation on the building envelope, refer to Chapter 15; for detailson building assemblies, see Chapters 25, 26, and 27.
23、The preparation of this chapter is assigned to TC 1.12, Moisture Manage-ment in Buildings.36.2 2017 ASHRAE HandbookFundamentals (SI)The largest contributors of liquid moisture are water from wind-driven rain in building envelopes with insufficient drainage, leaksfrom roof or gutters, and leaks from
24、internal plumbing. Thesesources must be addressed and resolved for the building envelope tosucceed.Once liquid water is addressed, the next factors to consider arevapor pressure and relative humidity. The driving forces responsiblefor water vapor movement within buildings and across the envelopeare
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