Designing Buildings in Hot & Humid Climates

Raymond E. Patenaude, PE, CIAQP, RPIH

The Holmes Agency, Inc.Consulting and Forensic Engineers

www.TheHolmesAgency.com

Mold Control In BarracksNew and Retrofits

Presented By

Occupant Comfort

Occupant ComfortPrincipal purpose of HVAC is to provide conditions for human thermal comfort and health of building occupantsComfort is a cognitive process in humansBuilding parameters for comfort has been found to be very similar for diverse populationsBody 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 clothingActivity level of occupantsTemperature of ambient environmentMoisture content of ambient environment

Occupant ComfortASHRAE standard 55, “Thermal Environmental Conditions for Human Occupancy”, provides a complete discussion of the parameters influencing occupant comfortBasic variables of human comfort

The surrounding airDry bulb temperatureVapor pressure (Dew point)Relative HumidityVelocity at the skin surface

Occupant ComfortBasic variables of human comfort cont…

The building, its equipment & furnishingsSurface temperature of each object surrounding the occupants

The individualMetabolic rate (activity level in met)Amount, moisture and heat transmission of clothing coverage (clo)

Dew point and vapor pressureThe moisture content of the air within buildings is a strong influence on comfort

Northern climate variablesSouthern climate variables

Occupant ComfortPerceived air quality

Moisture content affects perceptions of air qualityHigh relative humidity reduces perceived air freshness and comfortTypical occupant response is to lower space sensible temperature causing higher relative humidity and increasing possibilities of condensationSurface condensation is water source for molds

Mold GrowthMold Growth

Mold Growth

Enzymes on mold spore combine with surface moisture to dissolve food source… paper, wood, ceiling tileOsmotic pressure causes liquid nutrients to diffuse across spore wall allowing spore to absorb the nutrientsSpore germinates producing filamentous hypheaHyphea grows quickly creating mycelium matMold grows conidia which generates and releases spores into the air

Mold Growth

mVOCs

Product of metabolismSubstrateEnvironmental conditions

Changes with growth cycle OdorousSmall concentration when compared to total building VOC load

Mycotoxins

Secondary metabolitesParticle association

SporesMycelial fragmentsSubstrate

Concurrent production of multiple toxinsCompetition inhibition

Production of Mycotoxins

Fungal SpeciesStrain dependentEnvironmental conditions

SubstrateTemperature

Concurrent production of several toxinsGrowth does not signify presence

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

High Surface Relative Humidity

Water ActivityWater 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% RHWater activity of a material is very different from the relative humidity of the materialMold growth is a risk when surface relative humidity stays above 85% for extended periods

Moisture Content and Surface Relative Humidity

Uncontrolled air flow

Buildings which have never reported relative humidity above 65% still may have mold growth

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.

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 andengineered wood products which have been “chopped up and boiled” are easier for mold to colonize at lower moisture contents.

Mold Risk Increases with Moisture Content

Building EnclosuresBuilding Enclosures

ApplicationApplicationInstall drainage plane so that water is not trappedOverlap building in “ship lap” fashionDrain water to flashing which directs water away from building

ApplicationApplication

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

Application Application –– The Perfect WallThe 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.

Application Application –– Roof Wall ConnectionRoof Wall Connection

Notice the control layer for rain on the roof is connected to the control layer for rain on the walls. And the controllayer for air is connected to the control layer for air on the wall, and so on.

Application Application –– Institutional WallInstitutional Wall

The best wall we build today. It works everywhere, in everyclimate zone. It costs more, but then, it’s sustainable. It will pass from generation to generation.

Application Application –– Commercial WallCommercial Wall

The almost-best wall we construct today. It’s affordable. Actually, it’s thecheapest wall that works, and it works in any climate zone.

ApplicationApplication

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

ApplicationApplicationWater management for exterior windows requires proper placement of window flashing strips and drainage planeNote placement of drainage plane under window

Moisture Control IssuesMoisture Control Issues

THE MOISTURE PROBLEM

Highest enthalpy occurs at peak dew

point.. NOT peak dry bulbASHRAE 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!!

TYPES OF MOISTURE PROBLEMS

Outdoor air82 deg F123 gr/lb74%rh

73 deg F dp Interior Design 72 deg F

Building Envelopewith poor vapor barrier

Dry wall

Vapor transport

Mold growth onbackside of drywall

Ventilation - If it’s not dried… you’re in trouble

Existing Barracks

Barracks Room After 6 Months

Barracks Room After 6 Months

Exterior Envelope

Exterior Envelope

Exterior Envelope

Air, Vapor and Water Barrier

More InformationMore Information

ASHRAE Standards and Publications

Available from ASHRAE in Atlanta, The ASHRAEGuide for Buildingsin Hot & Humid Climates

ASHRAE Standards and Publications

Available from ASHRAE in Atlanta, Humidity Control Design GuideFor Commercial andInstitutional Buildings

Q & AQ & A

Designing Buildings in �Hot & Humid ClimatesOccupant ComfortOccupant ComfortOccupant ComfortOccupant ComfortOccupant ComfortMold GrowthMold GrowthMold GrowthmVOCsMycotoxinsProduction of Mycotoxins Mold - It’s the surface rh that counts.. So keep the dew point down, and things go wellSlide Number 15Water ActivityMoisture Content�and Surface Relative HumidityUncontrolled air flowThe Geography of MoistureMold Risk Increases with�Moisture ContentMold Risk Increases with�Moisture ContentBuilding EnclosuresSlide Number 23ApplicationApplicationApplication – The Perfect WallApplication – Roof Wall ConnectionApplication – Institutional WallApplication – Commercial WallApplicationApplicationMoisture Control Issues THE MOISTURE PROBLEMTYPES OF MOISTURE PROBLEMSVentilation - If it’s not dried… you’re in troubleExisting Barracks Barracks Room After� 6 MonthsBarracks Room After� 6 MonthsExterior EnvelopeExterior EnvelopeExterior EnvelopeAir, Vapor and Water BarrierMore InformationASHRAE Standards and PublicationsASHRAE Standards and PublicationsQ & A