Environmental Controls I/IGEnvironmental Controls I/IG

Lecture 8Microclimate

MicroclimateMicroclimateImmediate local conditions for temperature, humidity, solar radiation, and wind.

MicroclimateMicroclimateAffected by: Earth Wind Fire Water

Earth: TopographyEarth: TopographyThe leeward side of a hill can protect from unwanted winds

ElevationElevationTemperature changes about -3.6 ºF with each +1000 feet change in altitude

ElevationTemperatureSalt Lake City 4200’ 95º FPark City 6800’ ~86º F

Rain & Snow ShadowsRain & Snow ShadowsForm when moisture precipitates out as air moves up slopes

L: p.73 Fig. 5.2d

Ground Cover – Vegetation Ground Cover – Vegetation Trees, shrubbery, and grasses provide shade that prevents moisture from evaporating

Permeable surfaces reduce temperatures through evaporative cooling

Reeves House, Lopez Island, WA

Cutler-Anderson, 2002http://www.greenroofs.com/projects/pview.php?id=562

Ground CoverGround CoverImpermeable surfaces reduce evaporative cooling opportunities

Surface ColorSurface ColorLighter surfaces reflect radiant heat

Darker surfaces absorb radiant heat

Urban heat islandUrban heat islandLarge concentrations of thermal masses with darker and/or impermeable surfaces create urban heat islands

Wind: TopographyWind: TopographyWarm air risesCool air drops

Morning and afternoon “diurnal winds” are intensified in canyons and on sloped surfaces and diverted by hills and ridges

Convective Air FlowConvective Air FlowWarm air risesCool air drops

Recognizing air channels can help reduce discomfort or enhance

comfort

Wind Direction & SpeedWind Direction & Speed Confirm mean (average)

speed direction Consult a wind rose for

prevailing direction

L: p. 89 Region 1

Wind RosesWind RosesJanuary

L: p.81 Fig. 5.6d

Wind RosesWind RosesJuly

L: p.83 Fig. 5.6f

Sea Breeze EffectSea Breeze EffectOnshore winds occur when water temperature is lower than adjoining air temperature over land.Offshore winds are the reverse process.

Bernouli EffectBernouli EffectAir flow closer to the ground is slowed by frictional effects of surfaces

L: p.270 Fig. 10.5j

Venturi EffectVenturi EffectAir follows the path of least resistance

Wind speeds increase as cross sectional area decreases

L: p.318 Fig. 11.8c

Wind Breaks/ChannelingWind Breaks/ChannelingTerrain and vegetation can block or channel wind

Plan Views

Solar (Fire): Mean Daily Solar (Fire): Mean Daily RadiationRadiation

Confirm how much solar radiation is a available

S: p. 1504, T. C.3

Mean Percentage of Possible Mean Percentage of Possible SunshineSunshine

Confirm how frequently the sun shines

L: p. 89 Region 1

Solar OrientationSolar OrientationSouth facing slopes get significantly more solar radiation than north facing slopes

N

Water: Thermal MassWater: Thermal MassLarge bodies of water moderate local temperatures

A thermal mass that can act as at thermal buffer/ heat sink

Lakes & OceansLakes & OceansWarm temperatures are reduced in summer

Cool temperatures are raised in winter

10ºF 10ºF

72ºF 80ºF

35ºF 30ºF

Groundwater Groundwater

Groundwater table affects temperature and humidity

Rivers & StreamsRivers & StreamsMoving water generates air movement

PerspirationPerspirationOccurs as body core temperature rises

In low RH conditions evaporation occurs and cools skin

In high RH conditions evaporation is inhibited

InsolationHumidity and cloud cover affect the amount of solar radiation entering or leaving the local environment

EvapotranspirationTrees and shrubbery give off moisture that increases local humidity