Climate Related Building Design

Following climate factors are important for climate-related building: solar radiation (direct and diffuse) temperature and fluctuation in temperature (seasons, day/night) air humidity air movements (main wind direction, storm force) precipitation (quantity and seasonal fluctuation) The basis for climate-related building is the combination of strategies of traditional architecture and modern development. For strategies and concepts of traditional architecture of the different climate zones. Traditional building concepts cannot be completely adopted to the architecture of the metroplitan areas of our complex industrial society. But traditional architecture demonstrates the various possibilities influencing the indoor climate by structural measures without additional appliances and with a mimimum of energy.  The following table provides a reference guides to the main climatic zones as well as the key design responses for each climate: polar/subpolar climate temperate climate dry climate subtropical climate tropical climate thermal mass massive depending on region low * thermal insulation necessary necessary only in case of artificial cooling depending on region only roofs and air-conditioned buildings heat storage heat protection in summer balance of alternation of day and night normally not necessary unwanted heating necessary notwendig regional in winter regional in winter not necessary active cooling not necessary in the majority of cases avoidable often necessary often necessary seasonal necessary ventilation controlled controlled controlled or increased increased ventilation* increased ventilation all the the year* (cross ventilation) air tightness necessary necessary only in case of artificial cooling necessary only in case of artificial cooling shading (without visors) seldom necessary temporary in summer necessary necessary necessary *only in case of no artificial cooling

1.    Polar and Subpolar Climate

 The buildings of this climatic zone serve as protection against cold in the first instance. Effective heating systems are very important. These heating systems require energy, but passive design features given below help to reduce the energy required. Multi-layered wall and roof structures or massive constructions are considered to be climate- related building envelopes. Building elements exposed to weather shall consist of weatherproof materials.

basic constructional requirements:

• protection against cold (heat insulation)
• protection against storms
• protection against humidity, especially around roof areas
• if possible use solar energy in summer

Building Location, Building Surroundings

The temperatures of building's surrounding influence the annual amount of energy necessary to heat the building.

• wind-protected locations reduce heat loss
• usage of vegetation and topography as natural windbreak   

Building Shape

• optimised A/V-ratio for reduction of heat transfer by building envelope
• roof overhangs and steep roof pitches (especially on north facades) shed rain and snow away from the house and prevent premature deterioration of exterior finish materials (northern hemisphere)

 Building Orientation

Depending on the main wind direction, the main facade should be oriented to the south (northern hemisphere) or to south on the southern hemisphere in order to achieve maximum solar gains.

• sun-exposed facades with short roof overhang on the south-facing facade (northern hemisphere)
• south-facing building openings (northern hemisphere) with insulated shutters or roller shutters
• protection against north and north-west

Zoning of Buildings

Zoning implies the location of rooms with higher heating needs such as living areas on the south side, while the north side accommodates function and utility rooms. Garages and secondary rooms oriented to the north act as thermal buffer zones. Attics, basement rooms and entrance porches are thermal buffer zones between inside and outside as well.

• include thermal buffer zones
• porched entrances areas
• living areas are located in the south, whereas function and utility rooms are located in the north

Walls and Roof

• multi-layered wall and roof structures or massive constructions with low U-value
• include snow loads
• vapour barrier should be placed on the inside
• choose jointless and airtight constructions
• protect building elements against humidity, especially in roof areas
• use double or if necessary triple glazing

Windows

• insulated glazing with low proportion of frame and appropriate U-values (quality of glazing, proportion of frame, edge seal)
• glazing with appropriate g-value (SHGC) for solar gains
• appropriate apertures (large south-facing windows, small north-facing windows)
• insulated shutters or roller shutters

2.    Temperate Climate

Moderate climates are determined by distinctive seasonal fluctuations with strong temperature variations between summer and winter. The climatic conditions vary from region to region. Decisive factors are continentality, maritime impacts, latitude and elevation above sea level. The most buildings of this climatic zone have to meet the following basic requirements:

• protection against cold in winter (heat insulation)
• protection against overheating in summer
• protection against precipitation
• if possible use solar energy in summer

Building Location, Building Surroundings

The temperatures of building's surrounding influence the annual amount of energy necessary to heat the building.

• wind-protected south slopes reduce heat losses
• fresh air corridors provide ventilation and improve urban thermal environment, broad streets and open building development contribute to better ventilation
• usage of vegetation as natural windbreak or wind-guiding element
• vegetation around the building improves the microclimate (humidity, temperature, dust, air pollutants)

Building Shape

Temperature compensation between building and its surroundings is influenced by building shape and building orientation.

• choose a compact shape

 Building Orientation

• orientation of the building subject to solar access
• south-facing main facade and south-facing apertures for maximum solar gains (northern hemisphere)
• protection against north and north-west (northern hemisphere)
• include the possibility of cross ventilation in summer

 Zoning of Buildings

The rooms are classified according to their function and time of usage. Zoning implies the location of rooms with higher heating needs on the sunny side, while the shady side accommodates function rooms.

• function rooms are located in the north, whereas the living area is located in the south
• rooms of low temperatures act a thermal buffer between inside and outside
• include entrance porches (as thermal buffer zones)

Walls and Roof

• multi-layered wall and roof structures or massive constructions with low U-value
• vapour barrier should be placed on the inside
• choose jointless and airtight constructions
• choose shape of roof, roof overhangs and roof drainage according local conditions (amounts of precipitation and snow loads)
• use insulated glazing

Windows

• insulated glazing with low proportion of frame and appropriate U-values (quality of glazing, proportion of frame, edge seal)
• glazing with appropriate g-value (SHGC) for solar gains
• appropriate apertures (large south-facing windows, small north-facing windows)
• orientation of windows and position of the window in connection with interior spaces for good daylighting: clerestories, skylights and high windows improve the brightness of a room; windows in the centre of the wall distribute the light better in the depth of the room than corner windows
• insulated shutters or roller shutters only if necessary

Shading

During the hot season, shading devices are very important: Shading devices have to be chosen according to window orientation:

• protection against noon sun angle : horizontal shading (for south facades, northern hemisphere)
• protection against low hanging sun : vertical louvers or fins (for east and especially west facades)
• For maximum solar gains, it is a wise idea to choose adjustable shading devices wherever possible

 3.   Subtropical Climate

Subtropical climate zones are determined by distinctive seasonal fluctuations with temperature variations and different amounts of precipitation in summer and winter.

basic constructional requirements:

• protection against overheating in summer
• using of natural air flow for cooling in summer
• protection against precipitations
• shading of exterior spaces (plantings)
• protection against winterly cold (depending on the region)

Building Location, Building Surroundings

The temperatures of building's surrounding influence the annual amount of energy necessary to heat or cool the building.

• wind-exposed locations for effective ventilation in summer
• fresh air corridors provide ventilation and improve urban thermal environment, broad streets and open building development contribute to better ventilation
• usage of vegetation as natural windbreak or wind-guiding element
• vegetation around the building improves the microclimate (humidity, temperature, dust, air pollutants)
• planting provides shade; shade structures to lower ground temperatures
• include evaporative cooling of water bidies and water features
• provide appropriate screened, shaded, rain protected outdoor living spaces

 Building Shape

Temperature compensation between building and its surroundings is influenced by building shape and building orientation.

• choose a compact shape

 Building Orientation

orientation of the building subject to solar access:

• minimise openings in sun-exposed facades (east and west facades)
• maximise convective ventilation with high level windows and cross ventilation (cross ventilation depends on building depth)
• shade sun-exposed facades in summer, but passive solar heating is required during winter months
• orient building openings to the main wind direction in summer
• coastal areas: use cooling breezes from the sea

 Zoning of Buildings

The main element is floor plan zoning to maximise comfort for daytime activities and sleeping comfort:

• function rooms are located in the north, whereas the living area is located in the south
• locate bedrooms for sleeping comfort to the east
• design unobstructed cross ventilation paths
• locate mechanically cooled rooms in thermally protected areas (coolest zone in the house)

 Exterior Building Elements

Similar to the architecture of dry climates, it is good to use multi-layered wall and roof structures. The exterior layer protects against solar radiation, which reduces heat absorption of building elements. The interior layer minimises and retards thermal transfer to the building's interior. This effect is called phase shift (siehe Glossar) and amplitude attenuation (siehe Glossar). The thermal insulation protects against heat in summer and prevents heat loss in winter.

Walls and Roof

• multi-layered wall and roof structures
• vapour barrier should be placed on the inside or outside (In areas where you heat more than air condition, do place the vapour barrier on the inside whereas in areas where you air condition more than heat place the vapour barrier on the outside)
• bright reflective facades to reduce heat gain
• choose jointless and airtight constructions
• choose shape of roof, roof overhangs and roof drainage according local conditions (amounts of precipitation and solar radiation)
• shade building elements exposed to sun in summer
• thermal insulation to prevent transmission heat loss in winter

Windows

• shade all openings in summer and east and west openings year round
• glazing with appropriate g-value (SHGC)
• glazing with appropriate U-value
• adequate window areas
• orientation of windows and position of the window in connection with interior spaces for good daylighting: clerestories, skylights and high windows improve the brightness of a room; windows in the centre of the wall distribute the light better in the depth of the room than corner windows

Shading

Shading devices are very important all the year round. Include planting design to shade the building. Shading devices have to be chosen according to window orientation:

• protection against noon sun angle : horizontal shading (for south facades, northern hemisphere)
• protection against low hanging sun : vertical louvres or fins (for east and especially west facades)
• there are combinations of vertical and horizontal shading

For maximum solar gains, it is a wise idea to choose adjustable shading devices wherever possible. Shade all windows in summer and east and west windows year round.

Ventilation

Natural breezes are an essential element of passive cooling. For this reason, it is important to include the flow of cooling breezes through a building. Generally, cross ventilation is most effective for air exchange in summer. Cross ventilation depends on the building depth. Hence, design floor plans which do not block cooling breezes.

If possible, use coastal breezes for cooling. Openings oriented to the sea improve the indoor climate.

Include convective air movement. Convective air movement relies on hot air rising at the highest point, drawing in cool air from shaded external areas. Higher room heights increase the effect.

·         cross ventilation

·         include ceiling fans to create air movement during still periods if necessary

 4.   Dry Climates

 Dry climates are determined by high temperatures all the year round. Temperature maximum is in summer, minimum is in winter.

basic constructional requirements:

• protection against heat absorption and overheating
• protection against direct solar radiation (humans and buildings), shades
• usage of solar energy
• heat storage by massive walls in day and night cycle
• optimised A/V-balance small facade areas exposed to sun
• usage of water and vegetation areas in order to improve the microclimate
• shading of exterior spaces (plantings)

 Building Location, Building Surroundings

The temperatures of building's surrounding influence the annual amount of energy necessary to cool the building.

• narrow streets and alleys protect against hot winds
• build the streets narrow so the buildings shade each other during the day
• use vegetation, walls and banks as natural windbreak
• vegetation around the building improves the microclimate (humidity, temperature, dust, air pollutants)
• include water bodies for evaporative cooling

Building Shape

Temperature compensation between building and its surroundings is influenced by building shape and building orientation.

• compact building shape, closed structure with small exterior areas
• include atria and outdoor courtyards for (evaporative) cooling

 Building Orientation

Orient the building with the short wall facing west or southwest for the least solar gain in the summer.

• minimise exterior areas exposed to the sun
• minimise windows on east and west facades
• shade building elements exposed to sun (roof, east and west facades)
• shade building openings

Zoning of Buildings

Floor plan zoning is very important. Locate bedrooms for sleeping comfort on the east side of the building: east-oriented rooms are only exposed to direct sun in the morning, so there is enough time to release the absorbed heat until dusk.

• locate bedrooms for sleeping comfort to the east
• provide multiple flow paths and minimise potential barriers

Exterior Building Elements

Multi-layered wall and roof structures help to reduce the wall thickness of massive traditional architecture of hot climates. The exterior layer protects against solar radiation, which reduces heat absorption of building elements. The interior layer minimises and retards thermal transfer to the building's interior. This effect is called phase shift (siehe Glossar) and amplitude attenuation (siehe Glossar) and it is made possible by thermal inertia of traditional massive wall structures or by insulation materials.

Walls and Roof

• multi-layered wall and roof structures or massive structures of high thermal mass
• double skin roof with a light outer layer with reflective surface
• vapour barrier should be placed on the outside in case of mechanical cooling
• bright reflective facades to reduce heat gain
• choose jointless and airtight constructions in case of mechanical cooling
• shade building elements exposed to sun (planting, roof overhang...)

 Windows

• shade all building openings
• appropriate window areas (only small or no windows on east and west facades)

 Shading

In hot and dry climates shading devices are of special importance.

Shading devices have to be chosen according to window orientation:

• protection against noon sun angle : horizontal shading (for south facades, northern hemisphere)
• protection against low hanging sun : vertical louvres or fins (for east and especially west facades)
• there are combinations of vertical and horizontal shading

Building elements and openings exposed directly to the sun should be shaded.

Ventilation

Due to high temperatures, natural breezes often cannot be used for cooling the building. Using breezes for cooling requires outdoor temperatures below 35°C. But it is possible to include convective air movements (stack effect) for cooling. Traditional devices using this effect are so called "wind catchers" (Persian: Badgir). Badgirs can be found in Persia and Egypt.

5.   Tropic Climate  basic constructional requirements: protection against heat absorption and overheating protection against direct solar radiation (humans and buildings), shades protection against mugginess (humidity) protection against humidity penetration and driving rain usage of solar energy

Building Location, Building Surroundings The temperatures of building's surrounding influence the annual amount of energy necessary to cool the building. wind-exposed locations wind-guiding elements (walls, hedges, trees) shading of the building shading of exterior spaces (plantings) vegetation around the building improves the microclimate (humidity, temperature, dust, air pollutants)  Building Shape Temperature compensation between building and its surroundings is influenced by building shape and building orientation. stilt houses elevated above the ground allow ventilation beneath the floor use single room depths where possible to enhance cross ventilation and heat removal pitched roofs protect agains heavy downpours roof overhangs shade the facade and protect against intense rain design properly ventilated roofs add open-sided storeys or stilt floors in multi-storey buildings to allow better ventilation  Building Orientation orient the building to the main wind direction, exposure to cooling breezes should be maximised minimise sun-exposed facades (east and west facades) shade outdoor areas such as courtyards, balconies and verandas orient building openings to the main wind direction openings on the opposite side of the house draw the breeze through and out (cross        ventilation) shade all building openings  Zoning of Buildings The main element is floor plan zoning to maximise comfort for daytime activities and sleeping comfort: locate bedrooms in cool areas of the building design a layout that allows cool breezes to pass right through the house

Exterior Building Elements The use of high mass construction is generally not recommended in hot humid climates due to their limited diurnal range. Passive cooling is generally more effective in low mass buildings, because lightweight construction responds more quickly to cooling breezes. Insulated roofs might be advantageous. Insulated walls are only necessary in case of artificial cooling. Otherwise, heat accumulation might be the result. Walls and Roof use low thermal mass constructions multi-layered, well ventilated roof structures for quick heat removal ventilated wall structures enhanced ventilation of roof space insulate roof structures in case of mechanical cooling or in case of sun-exposed roofs avoid fixed glazing design light coloured external surfaces controlled rain water run-off protect the structure against humidity penetration include appropriate shading devices Tropical cyclones are an accepted part of life in some tropical areas. These thunderstorms or cyclones cause pressure on surfaces of buildings, which leads to loads on the structure. Hence, there are structural materials standards to select elements that can resist the required wind actions. A large number of structural elements must be functioning correctly to avoid wind damage caused by pressure and suction. Tropical thunderstorms often come along with heavy downpours. So there might be a need for circumferential drainage in order to protect the building against undercutting.  Windows shade all building openings appropriate window openings (according to orientation: small apertures in east and        west facades) no fixed glazing, use windows equipped with flexible louvres  ShadingIn tropic climates shading devices are of special importance. Shading devices have to be chosen according to window orientation:: protection against noon sun angle : horizontal shading (for south facades, northern hemisphere) protection against low hanging sun : vertical louvres or fins (for east and especially west facades) there are combinations of vertical and horizontal shading sun shade devices must not reduce the air flow considerably include natural vegetation for shading (plants contribute to cooling by evaporation) Shade sun-exposed external surfaces and all building openings. Choose endemic plants for shading. Plants create pleasant filtered light and assist cooling by evaporation.

Ventilation High temperatures and high humidity require maximum ventilation to reduce heat and humidity loads. Natural air flow may contribute to cooling: openings on the opposite side of the house allow cross ventilation ventilated roof spaces for heat removal stilt structures and open-sided storeys allow better ventilation use convective air movements (stack effect) include ceiling fans to create air movement during still periods if necessary (e.g. at night)

Almost Zero Energy – Michigan LEED Home give 2011 Energy Report (Owners Report)

As of October 2010 the Jay & Liz McClellan home officially earned a LEED Platinum rating, which is the highest of 4 levels of certification offered by the USGBC. They achieved a HERS index of 20, which one of the best in the state of Michigan.

This summarizes the building's energy production and consumption for calendar year 2011.

Statistics

Solar electricity produced: 6033 kW h (16.5 kW h per day)
Electricity consumed: 6150 kW h (16.8 kW h per day)
Non-heating: 5350 kW h, heating: 800 kW h
Net electricity deficit: 117 kW h (-2%)

Owners Report: Our first 12-month report started April 1 2010 when we first activated the PV system and went through April 1 2011, but this report covers calendar year 2011 so there are a few months of overlap. For calendar year 2011 we fell just short of our goal to produce more electricity than we consumed, with a net deficit of 117 kW h for the year. Compared to our first 12 months of operation, average daily production dropped by 0.3 kW h but consumption increased 1.8 kW h. Some of that is due to having an additional family member living here since mid-year, and some is due to adding an upright freezer that uses about 1 kW / day.

Below is a graph showing the inside (red) and outside (blue) temperatures that we recorded throughout the year. Overall the house was very comfortable, with just a few days in the upper 70s during some hot summer weather when allergies made us reluctant to open up the house at night since our ventilation system filters out pollen from the incoming air.

The graph below shows the heat storage tank temperatures over the year. The big gap is when we drained the tank due to a leak, and we were able to get the tank warmed up again in the fall but not to the degree we would have liked.

Here is a list of some of the features of our home that qualify for LEED credits. This is not an exhaustive list, just some of the more interesting features:

• Universal Design - every room in the home is usable by persons with limited mobility
• Limit conventional turf - we will have no conventional turf at all, just gardens surrounding the house
• Reduce irrigation demand - all our permanent plantings will have far less water demand than typical landscaping in this region
• Water reuse - our rainwater harvesting system collects water from more than 50% of our roof, to be used for watering the gardens and flushing toilets
• Indoor water use - all our toilets, lavatories and showers have very high efficiency fixtures that use much less water than conventional fixtures
• Optimize energy performance - our home is designed to generate more energy than it consumes, using a combination of superinsulation, energy efficient appliances, active and passive solar heat collection, and solar electric generation
• Construction waste reduction - our construction will generate about 1/10th as much waste per square foot as a typical home construction
• Combustion venting - our wood stoves are EPA certified for low emissions, and have an outside combustion air supply to avoid drawing warm air from the house
• Outdoor air ventilation - we use a heat recovery ventilator (HRV) to provide continuous ventilation, and to recover about 70% of the heat from the outgoing stale air
• Local exhaust - our bathrooms are equipped with humidity sensors, which will increase the airflow through the HRV whenever excess humidity is present
• Air filtering - the ventilation air intake is equipped with a high efficiency air filter (rated MERV 13) to reduce particulates in the incoming fresh air
• Indoor contaminant control - we have a shoe removal and storage space near the front door, and a central vacuum system that exhausts to the outside

In addition, here are some of the environmentally preferable products in our home that earn LEED credits:

• Floor - polished concrete generates far less emissions and traps far less dirt than carpet
• Walls & ceilings - our drywall was made less than 200 miles away from 96% recycled material
• Paints - All walls and ceilings use zero-VOC paint
• Countertops - we're making our own countertops using recycled glass
• Insulation - our cellulose wall insulation is about 85% recycled paper

Source: Alliance for Environmental Sustainability & Jay & Liz McClellan Homepage

Illinois Net-Zero-Energy masterpiece producing 40 percent more energy than it consumes

Starting with an eco-conscious dream for a truly green home transformed owner Michael Yannell’s Chicago residence into a $1.6 million, two-story 2,675-square-foot, four-bedroom and two-bath Net-Zero-Energy masterpiece, producing 40 percent more energy than it consumes.

Completed in 2009, it is not only Chicago’s first LEED Platinum-certified home, but it has scored higher than any other LEED-certified project in history. Architect Farr Associates, builder Goldberg General Contracting Inc. and engineering MEP firm dbHMS created this urban infill project to utilize aspects of alternative energies through passive solar, solar grid technology, a greywater system and closed looped geothermal heating and cooling components. According to owner Michael Yannell, the main goal of this project was to create a more energy- and water-efficient, environmentally conscious place to live and to set an example by building a home as sustainable as possible. Incidentally, the green materials generally were no more expensive than conventional alternatives.

This Net-Zero-Energy residence was built using the U.S. Green Building Council’s (USGBC) LEED for Homes Pilot Program regulations. In order to earn the coveted LEED Platinum-certification, a project must meet the 100-point requirement, in which the Yannell residence scored 115.5. According to Net-Zero statistics, the Yannell residence generates 18,000 kWh/yr and uses only 12, 689 kWh/yr, earning the Yannell property an approximate $52,000 in tax credits in 2008-2009.

According to Jonathon Boyer, principal and director of architecture for Farr Associates, the permit and design processes were a challenge from the beginning, but thanks to help from a hand-picked team, deadlines were met and the project was a success.

“We put together a team of engineers, contractors and a landscape architect, and the entire project was a team effort,” Boyer said. “Building Net-Zero-Energy is very difficult, and it requires cooperation between all components and consultants. We believe we’ve broken the sound barrier with this house, especially in the Chicago area.”

This being the first LEED-certified home came with obstacles along the way. According to Boyer, by creating new systems such as the greywater system, which recycles water used from the toilets for the washing machine, it was tricky trying to solidify the permit process. It has opened up new options for Chicago to consider when building more sustainable homes.

“It was a learning process, the city of Chicago was open to it. We didn’t have any hard and clear standards in the city for permitting this kind of system,” Boyer explained. “As a result of this house, the city of Chicago Committee of Standards and Tests is adopting a new state / city code for rainwater / greywater reuse. “We were pioneers and induced the city to think about changing permits to use more sustainable elements into the residential market,” Boyer said.

Other than utilizing alternative energies, the Yannell residence’s modern design integrated into the traditional neighborhood fuses form with function in a dense infill space. The home was built on a recycled lot where the previous building could not be salvaged. Boyer explained that typically energy-efficient homes are bland and lack style, but in this case, the owner and the building team wanted something well-designed and unique.”He [owner, Michael Yannell] wanted something aesthetically compelling and functional,” Boyer said.

The floor plan is designed as a dual-wing connected by a foyer, which acts as an entry and passageway, both equipped with south-facing windows to utilize natural light and garden views. The positioning of the wings help compete with the Midwestern climate year-round. With temperatures ranging from the high 90s in the summer to blistering zero-below winters, it was crucial to find the most sustainable design possible. Each wing has a uniquely shaped multi-functional V-shaped green-roof designed for stormwater management and for concealing the 48 photovoltaic grids on the home. “The

butterfly pattern roofs are designed to screen the solar panels from view, while providing an ideal angle for the panels to harness the sun’s energy,” Boyer said. Although the Yannell residence has received the highest LEED score, the materials it took to achieve the title are not unattainable for other eco-conscience projects. According to Boyer, “LEED for Homes is less than $3,000 for certification.” In this case, it assisted in the construction process by acting as a detailed guide when installing aspects such as air quality, water systems and when planning the positioning.

Although there is no set specific standard definition for a Net-Zero- Energy home, Boyer said that there are other homes out there that claims to be Net-Zer-Energy, but many have only lowered their energy consumption. Only the Yannell property has the data to back it up. According to Principal of MEP firm dbHMS, Sachin Anand, “It’s [the Yannell residence] the future of housing and power generation where each home is a greenhouse emission-free power plant.”

Source: Alliance for Environmental Sustainability

Carbon Footprint Calculator

Heat Island

What Is a Heat Island?

Heat islands are characterized by urban air and surface temperatures that are higher than nearby rural areas. Many U.S. cities and suburbs have air temperatures up to 10˚ F (5.6˚ C) warmer than surrounding natural land cover. The heat island sketch below shows a city's heat island profile. It demonstrates how temperatures typically rise from the urban-rural border, and that the warmest temperatures are in dense downtown areas. On the other words heat island is the presence of any area warmer than its surrounding landscape. They can be developed on urban or rural areas. As it would be expected, there is a relatively minor knowledge about non urban heat islands, since they usually do not represent a risk for the human being or the environment. Meanwhile, urban heat islands have been profusely addressed during decades in urban areas with a wide range of climates and landscapes.

Heat islands are often largest over dense development but may be brokenup by vegetated sections within an urban area.

What Causes Heat Islands?

Heat islands form as cities replace natural land cover with pavement, buildings, and other infrastructure. These changes contribute to higher urban temperatures in the following ways:

•Displacing trees and vegetation minimizes the natural cooling effects of shading and evaporation of water from soil and leaves (evapotranspiration).

•Tall buildings and narrow streets can heat air that is trapped between them and reduce wind flow.

•Waste heat from vehicles, factories, and air conditioners may add warmth to the air, further increasing temperatures.

Heat islands are also influenced by a city’s geography and prevailing weather conditions. For example, strong winds and rain can flush out hot, stagnant air from city centers, while sunny, windless conditions can exacerbate heat islands.

When Do Heat Islands Form?

Heat islands can occur year-round during the day or night. Urban-rural temperature differences are often largest during calm, clear evenings. This is because rural areas cool off faster at night than cities, which retain much of the heat stored in roads, buildings, and other structures.

Effects of Heat Island

The well-known phenomenon allusive to the atmospheric temperature rise experienced by any urbanized area. The heat island phenomenon has been commonly associated to cities, because their surfaces are characterized by low albedo, high impermeability and favorable thermal properties for the energy storage and heat release. Besides, many cities present narrow urban canyons with reduced sky view factors that tend to absorb and reemit the radiated energy from their surfaces. These factors contribute to urbanized areas increasing their temperatures in relation to their rural peripheries that are usually more vegetated, and therefore moderate the temperatures mainly through the evapotranspiration process, shades production and solar radiation interception.

How Do Heat Islands Affect Us?

Increased urban temperatures can affect public health, the environment, and the amount of energy that consumers use for summertime cooling.

Public Health: Heat islands can amplify extreme hot weather events, which can cause heat stroke and may lead to physiological disruption, organ damage, and even death – especially in vulnerable populations such as the elderly.

The Environment: Summertime heat islands increase energy demand for air conditioning, raising power plant emissions of harmful pollutants. Higher temperatures also accelerate the chemical reaction that produces ground-level ozone, or smog. This threatens public health, the environment, and, for some communities, may have implications for federal air quality goals.

Energy Use: Because homes and buildings absorb the sun’s energy, heat islands can increase the demand for summertime cooling, raising energy expenditures. For every 1°F (0.6°C) increase in summertime temperature, peak utility loads in medium and large cities increase by an estimated 1.5 – 2.0 percent. Cities in cold climates may actually benefit from the wintertime warming effect of heat islands. Warmer temperatures can reduce heating energy needs and may help melt ice and snow on roads. In the summertime, however, the same city may experience the negative effects of heat islands.

A brief definition of the main Heat Island types

Surface urban heat island: The remotely sensed urban heat island. It is observed by using thermal infrared data that allow to retrieve land surface temperatures. Usually, close relationships between the near surface air temperatures and land surface temperatures have been found. Therefore, the surface urban heat island is a reliable indicator of the atmospheric urban heat island.

Micro urban heat islands: They refer to urban hot spots as poorly vegetated parking lots, non-reflective roofs and asphalt roads. Micro urban heat islands are strongly affected by micro climate factors, therefore remotely sensed data are more suitable than atmospheric data for identifying heat spots.

Urban heat sink: Also called negative heat island. It is the expression of a city colder than their countrysides. There are few references about this phenomenon. Heat sinks have been observed in cities with temperate, tropical, semi-arid and arid climates, and mainly during the mornings.

Source:

United State Environmental Protection Agency

Urban Heat Islands.