Designing Buildings in Hot & Humid Climates

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Catherine Harper
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1 Designing Buildings in Hot & Humid Climates Mold Control In Barracks New and Retrofits Presented By Raymond E. Patenaude, PE, CIAQP, RPIH The Holmes Agency, Inc. Consulting and Forensic Engineers

2 Occupant Comfort

3 Occupant Comfort Principal purpose of HVAC is to provide conditions for human thermal comfort and health of building occupants Comfort is a cognitive process in humans Building parameters for comfort has been found to be very similar for diverse populations Body temperature and therefore comfort is an energy balance of sensible and latent heat loss from the skin. Thermal exchanges with the environment are influenced by: Type and amount of clothing Activity level of occupants Temperature of ambient environment Moisture content of ambient environment

4 Occupant Comfort ASHRAE standard 55, Thermal Environmental Conditions for Human Occupancy, provides a complete discussion of the parameters influencing occupant comfort Basic variables of human comfort The surrounding air Dry bulb temperature Vapor pressure (Dew point) Relative Humidity Velocity at the skin surface

5 Occupant Comfort Basic variables of human comfort cont The building, its equipment & furnishings Surface temperature of each object surrounding the occupants The individual Metabolic rate (activity level in met) Amount, moisture and heat transmission of clothing coverage (clo) Dew point and vapor pressure The moisture content of the air within buildings is a strong influence on comfort Northern climate variables Southern climate variables

6 Occupant Comfort Perceived air quality Moisture content affects perceptions of air quality High relative humidity reduces perceived air freshness and comfort Typical occupant response is to lower space sensible temperature causing higher relative humidity and increasing possibilities of condensation Surface condensation is water source for molds

7 Mold Growth

8 Mold Growth Enzymes on mold spore combine with surface moisture to dissolve food source paper, wood, ceiling tile Osmotic pressure causes liquid nutrients to diffuse across spore wall allowing spore to absorb the nutrients Spore germinates producing filamentous hyphea Hyphea grows quickly creating mycelium mat Mold grows conidia which generates and releases spores into the air

9 Mold Growth

10 mvocs Product of metabolism Substrate Environmental conditions Changes with growth cycle Odorous Small concentration when compared to total building VOC load

11 Mycotoxins Secondary metabolites Particle association Spores Mycelial fragments Substrate Concurrent production of multiple toxins Competition inhibition

12 Production of Mycotoxins Fungal Species Strain dependent Environmental conditions Substrate Temperature Concurrent production of several toxins Growth does not signify presence

14 Mold - It s the surface rh that counts.. So keep the dew point down, and things go well

15 High Surface Relative Humidity

16 Water Activity Water activity indicates how much water is biologically available to fungus in its food source. Water activity of 0.8 refers to the amount of water absorbed into a material when the surrounding air is at 80% RH Water activity of a material is very different from the relative humidity of the material Mold growth is a risk when surface relative humidity stays above 85% for extended periods

17 Moisture Content and Surface Relative Humidity

18 Uncontrolled air flow Buildings which have never reported relative humidity above 65% still may have mold growth

19 The Geography of Moisture Moisture content can vary widely over a distance of just a few millimeters. So it s important to take many readings to be sure the construction is dry all over, before attaching finish materials.

20 Mold Risk Increases with Moisture Content The real world of construction and buildings is complex. Assemblies get wet, and then they dry out. Also, antimicrobial treatments can delay the onset of mold growth at a given moisture content. So there are no firmly established threshold limits on mold growth versus moisture content. But in general, the probability of mold growth increases with increasing moisture content, and with more time at warm temperatures, and with the presence of organic nutrients on surfaces. Also, in the absence of antimicrobial treatments, paper and engineered wood products which have been chopped up and boiled are easier for mold to colonize at lower moisture contents.

21 Mold Risk Increases with Moisture Content

22 Building Enclosures

24 Application Install drainage plane so that water is not trapped Overlap building in ship lap fashion Drain water to flashing which directs water away from building

25 Application Provide air space between finish (cladding, stucco, etc) and drainage to drain water

Application The Perfect Wall In concept, the perfect wall has the rainwater control layer, the air control layer and the vapor control layer all under the cladding, but all

26 Application The Perfect Wall In concept, the perfect wall has the rainwater control layer, the air control layer and the vapor control layer all under the cladding, but all directly on the exterior of the structure. The cladding s functions include shedding rain, but it s principal purpose is to protect the control layers from ultraviolet radiation.

27 Application Roof Wall Connection Notice the control layer for rain on the roof is connected to the control layer for rain on the walls. And the control layer for air is connected to the control layer for air on the wall, and so on.

28 Application Institutional Wall The best wall we build today. It works everywhere, in every climate zone. It costs more, but then, it s sustainable. It will pass from generation to generation.

29 Application Commercial Wall The almost-best wall we construct today. It s affordable. Actually, it s the cheapest wall that works, and it works in any climate zone.

30 Application Water management for exterior windows requires proper placement of window flashing strips and drainage plane

31 Application Water management for exterior windows requires proper placement of window flashing strips and drainage plane Note placement of drainage plane under window

32 Moisture Control Issues

33 THE MOISTURE PROBLEM Highest enthalpy occurs at peak dew point.. NOT peak dry bulb ASHRAE 2009 Fundamentals lists Extreme DB with MCWB.example Richmond, VA (1%) 94db/76wb (108 gr/lb) 44% RH Extreme DP with MCDB (.4%) 84dp/76db (137 gr/lb) 77% RH.. poor performance at part load!!

34 TYPES OF MOISTURE PROBLEMS Dry wall Outdoor air 82 deg F 123 gr/lb 74%rh Vapor transport Mold growth on backside of drywall 73 deg F dp Interior Design 72 deg F Building Envelope with poor vapor barrier

35 Ventilation - If it s not dried you re in trouble