Environmental Controls I/IGEnvironmental Controls I/IG

Lecture 8Microclimate

MicroclimateMicroclimate

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

MicroclimateMicroclimate

Affected by: Earth Wind Fire Water

Earth: TopographyEarth: Topography

The leeward side of a hill can protect from unwanted winds

ElevationElevation

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

ElevationTemperature

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

Rain & Snow ShadowsRain & Snow Shadows

Form 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, 2002

http://www.greenroofs.com/projects/pview.php?id=562

Ground CoverGround Cover

Impermeable surfaces reduce evaporative cooling opportunities

Surface ColorSurface Color

Lighter surfaces reflect radiant heat

Darker surfaces absorb

radiant heat

Urban heat islandUrban heat island

Large concentrations of thermal masses with darker and/or impermeable surfaces create urban heat islands

Wind: TopographyWind: Topography

Warm air rises

Cool 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 Roses

January

L: p.81 Fig. 5.6d

Wind RosesWind Roses

July

L: p.83 Fig. 5.6f

Sea Breeze EffectSea Breeze Effect

Onshore winds occur when water temperature is lower than adjoining air temperature over land.

Offshore winds are the reverse process.

Bernouli EffectBernouli Effect

Air 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/Channeling

Terrain 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 Orientation

South facing slopes get significantly more solar radiation than north facing slopes

N

Water: Thermal MassWater: Thermal Mass

Large bodies of water moderate local temperatures

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

Lakes & OceansLakes & Oceans

Warm temperatures are reduced in summer

Cool temperatures are raised in winter

10ºF10ºF

72ºF80ºF

35ºF30ºF

Groundwater Groundwater

Groundwater table affects temperature and humidity

Rivers & StreamsRivers & Streams

Moving water generates air movement

PerspirationPerspiration

Occurs as body core temperature rises

In low RH conditions evaporation occurs and cools skin

In high RH conditions evaporation is inhibited

Insolation

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

Evapotranspiration

Trees and shrubbery give off moisture that increases local humidity