3

3. CLIMATE ANALYSIS3.1 Use of Climatic DataDifferent design situations will require different weather data for the study.

Climate analysis carried out at initial design stage may be used for:

develop design strategies

check condensation problems in some cases

optimisation of insulation

Load and energy calculation carried out at outline and detail design stages will require weather data for:

calculation of cooling and heating requirements

design of heating, ventilating and air-conditioning (HVAC) systems

energy estimation of buildings

3.2 Sunshade Analysis

EXAMPLE OF SUNSHADE ANALYSIS

1. Solar paths requiring shade Studying the sun path diagram for each climatic zone, the shaded areas represent the periods of overheating, related to undesirable solar gain. In the lower latitudes, there is total overheating, whereas in the higher latitudes overheating only occurs during the summer months.3. Insolation The sunpath becomes more southerly as we move north, changing from a 'bow-tie' pattern near the equator to a heart-shape pattern in the temperate zones.

2. Sunshade analysis (vertical and horizontal) The diagrams show the optimum location of vertical sun shading, shielding the building from low sun angles in the morning and evening, and horizontal sun shading blocking the high midday sun. Tropical regions need both vertical and horizontal shading throughout the year. In higher latitudes, horizontal and vertical shading is only needed during the summer on the south-facing sides of buildings.4. Sun requirements during winter There are obviously seasonal variations near the equator. Solar heating becomes more important than in the upper latitutdes. Beginning at the equator and moving north, the need for solar heating increases while the need for solar shading dimishes.

3.3 Wind Analysis

Wind direction Desirable and undesirable winds in each the climatic zones depend largely on local conditions. Any breeze in the lower latitude (tropical and arid climates) is beneficial for most of the year whereas in higher latitudes most wind is detrimental and has to be screened. There is also a small percentage of the time in a year (spring and/or autumn) when comfortable conditions can be achieved naturally, without any need for wind screening or additional breezes.

Cross ventilation Cross ventilation is far more important in the tropics than in temperate zones. The theoretical strategy for blocking or inducing wind flow into a building is based on local prevailing wind conditions. Generally, for the tropical zones as much ventilation as possible is desired. For the arid zone cross ventilation is required, but care has to be taken to filter out high-velocity winds. In the temperate zone, cross ventilation and shielding are both necessary (for summer and winter, respectively). In the cool region, the building should be protected from cold, high-velocity winds, although cross ventilation is still required.

3.4 Humidity, Rainfall and Seasonal Variations

Annual Average Relative Humidity The curve on the left represents the annual average relative humidity in the four climatic zones. In the arid zone, the low level of humidity can be beneficial for evaporative cooling. In the tropical zone, the high level of humidity can be very uncomfortable.

Annual Average Rainfall The middle curve represents the annual average rainfall in the four climatic zones. Rainfall level can be seen to have a direct relationship with humidity levels.

Annual Seasonal Variations The distance of the angled line from the vertical represents the annual seasonal variations in the four climatic zones. Higher latitudes, the cold and temperate zones, have pronounced seasonal variations. The lower latitudes have constant climates throughout the year.

3.5 Influences on Built Form

1. Zoning for transitional spaces The black areas represent the traditional spaces used for lobbies, stairs, utility spaces, circulation, balconies, and any other areas where movement take place. These areas do not require total climatic control and natural ventilation is sufficient. For the tropical and arid zones, the transitional spaces are located on the north and south sides of the building where the sun's penetration is not as great. An atrium can also be used a transitional space. In temperate and cool zones, the transitional spaces should be located on the south side of the building to maximize solar gain. 3. Use of atrium The diagram show the optimum position for atrium spaces in each building form in each of the climatic zones. In the tropical zone, the atrium should be located so as to provide ventilation within the built form. In the arid zone, the atrium should be located at the center of the building for cooling and shading purposes. For the cool and temperate zones, the atrium should be at the center of the building form for heat and light.

2. Zoning for solar gain The black areas are spaces that can be used for solar heat gain. They follow the varying path of the sun in each of the climatic zones: in the tropical and arid zones the east and west sides; in the temperate and cool zones the south side.4. Potential of roof/ground floor as useable exterior space The distance of the angled line from the vertical represents the potential of each zone's roof and ground planes to be used a exterior spaces. In tropical and arid climates, there is a high potential to make use of all external spaces, whereas moving towards the northern latitudes the external spaces have to be covered to be used.

1. Form The diagrams show the optimum building form for each climatic zone. Research has shown that the preferred length of the sides of the building, where the sides are of length x:y, are:

tropical zone - 1:3

arid zone - 1:2

temperate zone - 1: 1.6

cool zone - 1:1

Analysis of these ratios shows that an elongated form to minimize east and west exposure is needed at the lower latitudes. This form slowly transforms to a ratio of 1:1 (cylindrical) at the higher latitudes. This is a direct response to the varying solar angles in the various latitudes.

2. Orientation Orientation as well as directional emphasis changes with latitude in response to solar angles.

Zone

Building's main orientations

Directional emphasis

Tropical

On an axis 5o north of east

north-south

Arid

On an axis 25o north of east

south-east

Temperate

On an axis 18o north of east

south-south-east

Cool

On an axis facing south

facing south

3. Vertical cores and structure The arrangement of primary mass can be used as a fator in climatic design as its position can help to shade or retain heat within the building form.

For the tropical zone, the cores are located on the east and west sides of the building form, so as to help shade the building from the low angles of the sun during the major part of the day. In arid zone, the cores should also be located on the east and west sides, but with major shading only needed during the summer. Therefore, the cores are located on the east and west sides,but primarily on the south side.

The arrangement of the primary mass in the temperate zone is on the north face, so as to leave the south face available for solar heat gain during the winter. The cool zone requires the maximum perimeter of the building to be open to the sun for heat penetration. Therefore the primary mass is placed in the centre of the building so as not to block out the sun'r rays and to retain heat within the building.

4. HONG KONG WEATHER4.1 Climate CharacteristicsHong Kong is located at latitude 22 18' north and longitude 11410' east (this refers to the weather station at Tsimshatsui, Kowloon). According to a climatological method of classification, the weather of Hong Kong may be classified as "Cwa" (humid subtropical climate). In the winter months between November and February, a winter monsoon coming from the north and northeast directions brings to Hong Kong cold and dry air from the continental anticyclone in Mainland China. The spring season is short and usually characterised by cloudy skies, periods of light rain and sometimes very foggy and humid conditions. In the summer months between May and September, the monsoon blows from the south and southeast directions. The weather is mainly tropical, hot and humid with occasional showers or thunderstorms. The autumn is short as it lasts from mid-September to early November. The winds become more easterly in direction. The amount of cloud in sky and humidity decrease rapidly at this time.

[See also Climate of Hong Kong by HKO]

Figure 4.1 Summary of Hong Kong weather

[Figure 4.2 Annual wind roses for weather stations in Hong Kong]

4.2 Outdoor Design ConditionsRecommended outdoor design conditions for Hong Kong is shown in Table 2. Essential information for the assessment of the climate and determination of design strategies is given. The "design temperatures" are usually the most commonly used and two sets of design temperatures (one for comfort HVAC and one for critical processes) are provided. Other data provided include extreme temperaturs, diurnal ranges of temperatures and wind data.

[Table 4.1 Recommended outdoor design conditions for Hong Kong]As interpreted from the climatic data, major considerations for architectural design in Hong Kong include:

Solar load is important for air-conditioned buildings.

Temperature and humidity is high and will require outdoor air control.

A little bit of winter heating is required for some buildings.

The diurnal range of temperature is about 5 C.

4.3 Graphical AnalysisThe climate of Hong Kong can also be studied using graphical methods. Examples of the graphs and charts are provided here:

[Figure 4.3a - Contour map of dry-bulb temperature (DBT)]

[Figure 4.3b - Contour map of wet-bulb temperature (WBT)]

[Figure 4.3c - Contour map of relative humidity (RH)]

[Figure 4.3d - Contour map of global solar radiation (GSR)]

[Figure 4.4 - Frequency distributions of DBT]

Information relating to sun path and solar design is of much interest to Architects and the following figures show examples of the graphs indicating the sun paths.

Figure 4.5a - Paths of the sun throughout the year [Figure 4.5b - Sun path diagram for Hong Kong]

[Figure 4.5c - Solar geometry and sun angles]

[Figure 4.5d - Sun path diagram at 24 deg. north latitude]

5. PSYCHROMETRIC CHART5.1 PsychrometricsThe atmosphere is a mixture of air (oxygen and nitrogen) and water vapour. Psychrometry is the study of moist air and of the changes in its conditions. The psychrometric chart graphically represents the interrelation of air temperature and moisture content and is a basic design tool for building engineers and designers. Several terms must be explained before the charts can be fully appreciated.

Absolute humidity (AH) is the vapour content of air, given in grammes or kg of water vapour per kg of air, i.e. g/kg or kg/kg. It is also known as moisture content or humidity ratio. Air at a given temperature can support only a certain amount of moisture and no more. This is referred to as the saturation humidity.

Relative humidity (RH) is an expression of the moisture content of a given atmosphere as a percentage of the saturation humidity at the same temperature.

Wet-bulb temperature (WBT) is measured by a hygrometer or a sling psychrometer and is shown as sloping lines on the psychrometric chart. A status point on the psychrometric chart can be indicated by a pair of dry-bulb temperature (DBT) and WBT.

Specific volume (Spv) , in m3/kg, is the reciprocal of density and is indicated by a set of slightly sloping lines on the psychrometric chart.

Enthalpy (H) is the heat content of unit mass of the atmosphere, in kJ/kg, relative to the heat content of 0 deg ?C dry air. It is indicated on the psychrometric chart by a third set of sloping lines, near to, but not quite the same as the web-bulb lines. In order to avoid confusion, there are no lines shown, but external scales are given on two sides.

Sensible heat (Qsen) is the heat content causing an increase in dry-bulb temperature. Latent heat (Qlat) is the heat content due to the presence of water vapour in the atmosphere. It is the heat which was required to evaporate the given amount of moisture.

[Figure 6 Psychrometric chart and climate classification]

Psychrometric processes, i.e. any changes in the condition of the atmosphere, can be represented by the movement of the state point on the psychrometric chart. Common processes include:

Sensible cooling / sensible heating

Cooling and dehumidification / heating and humidification

Humidification / dehumidification

Evaporative cooling / chemical dehydration

Figure 7 Psychrometric processes5.2 Analysis Using PSYCHWINThe program PSYCHWIN (see "Environmental Controls" program in our Computer Laboratory and student LAN) can be used to learn about psychrometric and do some analysis. These are some examples.

[Figure 8a Analysis of cooling strategies using PSYCHWIN]

[Figure 8b Analysis of thermal comfort zones using PSYCHWIN]

5.3 Bioclimatic Analysis for Hong KongBioclimatic approach is used to compare the given climatic conditions with the desirable comfort conditions. Operation strategies can be determined from the psychrometric chart. The following figures shows the charts developed for Hong Kong and the analysis on Hong Kong's climatic conditions.

6. URBAN CLIMATEUrban areas have particular climatic conditions with a higher temperature than exposed countryside, weak winds, and an amount of sunshine that varies according to the degree of pollution, the urban density, the orientation of the streets and the shade provided by other buildings.

6.1 Urban MicroclimatesUrban microclimates are complex because of the number and diversity of factors, which come into play. Solar radiation, temperature and wind conditions can vary significantly according to topography and local surroundings. In addition, layout density can provide further constraints: the precise plot division, the need for access and privacy, and the noise and impact of atmospheric pollution must all be taken into account.

In winter, most urban microclimates are more moderate than those found in suburban or rural areas. They are characterized by slightly higher temperatures and, away from tall buildings, weaker winds. During the day, wide streets, squares and non-planted areas are the warmest parts of a town. At night, the narrow streets have higher temperatures than the rest of the city. In summer, green spaces are particularly useful in modifying the environment during the late afternoon, when the buildings are very hot inside.

Strong local winds can modify the temperature distribution described above. Usually winds in towns are moderate because of the number and range of obstacles they face. However, a few configurations such as long straight avenues or multi-storey buildings can cause significant air circulation. Tall buildings rising above low-rise building can create strong turbulent wind conditions on the ground as the air is brought down from high levels. Strong winds can flow through gaps at the base of tall buildings. To protect pedestrians from this, the turbulent flow has to be prevented from descending to street level, for example by modifying the building form or by using wide protective canopies. In semi-open areas, adjacent buildings can be used as protective screens against some winds.

6.2 Urban Heat IslandVisit any city on a hot summer day, and you will feel waves of blistering heat emanating from roads and dark buildings. Stay in the city past nightfall, and you will notice that the streets are still radiating heat, while surrounding rural areas are rapidly cooling.

Figure 10 - Urban heat islandAlmost every city in the world today is hotter - usually between 1 to 4 deg C hotter - than its surrounding area. This difference between urban and rural temperatures is called the "urban-heat-island" effect", and it has been intensifying throughout this century. During hot months a heat island creates considerable discomfort and stress and also increases air-conditioning loads and the incidence of urban smog (do you notice this in Hong Kong!). Research shows that for every degree of increased heat, electricity generation rises by 2% to 4 %, and smog production increases by 4% to 10%. People also believe there is a direct link between global warming and urban heat islands. First, the greenhouse effect could aggravate rising urban temperature significantly. Second, heat islands may contribute to the greenhouse effect.

In general, there are three main factors causing the urban heat islands:

Surface - The characteristics of the surfaces in urban and rural areas are different and their thermal properties also differ a lot. As compared with rural areas, urban districts have high absorption (of the heat of the sun and atmosphere), low reflection, low evaporative heat loss and fast transmission of heat.

Heat emission - "Artificial heat" emitted in urban districts is much higher than that in rural areas.

Air quality - Air pollution in urban areas is high and the particulates will form a shield for trapping heat.

7. PASSIVE DESIGN IN HOT CLIMATESOne should attempt to perform the control task by passive controls (i.e. by the building itself), and resort to active controls (i.e. by energy-based heating or cooling systems) only when the passive controls cannot ensure comfort. This approach is suggested for three main reasons:

Economic - the installation of mechanical equipment means a capital cost and also the recurrent cost of energy consumed and system maintenance.

Ecological/environmental - passive buildings impose the least load on the ecosystem, consume less energy, and produce less amount of waste.

Aesthetic - passive buildings are more likely to be in sympathy with their environment, and more likely to increase diversity and interest.

7.1 General Climate Control StrategiesPassive control of heat flows:

When cold discomfort (underheated) conditions prevail:

minimise heat loss

utilise heat gain from the sun and internal sources

When hot discomfort (overheated) conditions prevail:

prevent heat gain

maximuse heat dissipation

Figure 3 General climate control strategies7.2 Passive vs. Active ControlsIn most climates, any attempt to ensure thermal comfort by passive means would reduce the active control requirements. In a cold climate or in the winter of temperate climate, passive solar heating, good insulation, and careful control of air infiltration would reduce the heating requirements. In a hot-dry climate the massive building, evaporative cooling and good shading may succeed in ensuring comfort.

The only exception is the warm-humid climate. Here, a building designed for passive cooling would be as open as possible, to ensure the maximum possible cross-ventilation, consequently it would be totally unsuitable for air-conditioning. If the building is to be air-conditioned, a completely different design approach must be adopted. The result would be that the building would be closed, sealed and well insulated. In such a climate therefore an early decision must be made whether passive or active controls would be used, whether cross-ventilation would be relied on, or air-conditioning.

The recommended procedure for warm humid climates is to compare the psychrometric chart climate plot with the air movement control potential zone. If the climate lines are fully (or nearly fully) covered by this zone, we can confidently proceed with the passive system design. If this is not the case, the client should be advised of the two alternatives: either air-conditioning will be required, with a closed building, or the upper comfort limit would be exceeded at some of the time.

The length of climate lines beyond the control potential zone should give an indication of what proportion of time such overheated conditions could be expected. The decision will have to involve a value judgement and can only be reached in consultation with the client or the future users.

7.3 Design Strategy in Warm-humid ClimatesIn warm-humid climates, the nights are usually warm and there is very little diurnal variation (often less than 5 deg C). As the humidity is high, evaporation from the skin is restricted. Evaporative cooling will be neither effective nor desirable as it would increase the humidity.

The designer should ensure that the indoor temperature does not become higher than the outdoor. Adequate ventilation may ensure this by removing any excess heat input, but this is not enough. Undue increase of ceiling temperature may be prevented by:

using a reflective roof surface

having a separate ceiling

ensuring adequate ventilation of the attic space

using reflective surfaces both for the underside of the roof and for the top of the ceiling

using some resistive insulation for or on the ceiling

The whole building should be lightweight to allow rapid cooling down at night. East and west walls should have minimum or no windows in order to exclude the low angle east and west sun. They should be reflective and/or well insulated. North and south walls should be as open as possible, to allow for cross ventilation. This requires that the plan arrangement should avoid double-banked rooms. The spacing of buildings should be carefully considered to avoid obstruction of the wind. The openings require protection from the sun and driving rain but also from mosquitoes and other insects which abound in these climates.

At times orientation for wind and for sun give conflicting requirements, solar orientation should take precedence, as there are ways of deflecting wind, but no ways of altering the suns movement. With oblique wind incidence a projecting wing wall at the downwind end of the building would create a positive pressure zone. On the leeward side a similar wing wall at the upwind end would help to create a negative pressure zone. The combined effect of these may ensure a better cross ventilation than that given by wind with normal incidence.

Web Links

Passive Cooling in Tropical Climate

8. CONCLUSIONA building may be considered as a 'climate modifier' which shields the indoor environment from the external climate. Before designing a building in once place, the changes of weather from season to season (i.e. the climate) must be well understood so that the building can be built to shelter people all the year round.

To assess the climate in a certain location, one must study the climatic data and, sometimes, make use of them for evaluating design options and determining design strategies. Knowledge about climatology and engineering design is required to achieve better understanding of the information and climatic properties. Architects and building designers are, perhaps, also "part-time" climatologists.

FURTHER READING

Aronin, J. E., Climate and Architecture, Reinhold Publishing Corporation, New York, 1953.

Givoni, B., Man, Climate and Architecture, Second Edition, Applied Science Publishers, London, 1976.

Goulding, J. R., Lewis, J. O. and Steemers, T. C. (Edited by), Energy Conscious Design: A Primer for Architects, B. T. Batsford, London, 1992.

Gut, P., Climate Responsive Building: Appropriate Building Construction in Tropical and Subtropical Region, First Edition, Swiss Centre for Development Cooperation in Technology and Management, St Gallen, Switzerland, 1993.

Koenigsberger, O. H., et al., 1973. Manual of Tropical Housing and Building, Longman, London.

Lam, J. C. and Hui, S. C. M., Outdoor design conditions for HVAC system design and energy estimation for buildings in Hong Kong, Energy and Buildings, 22 (1995): 25-43.

Loftness, V., Climate/Energy Graphics, World Climate Applications Programme, WCP-30, World Meteorological Organization, September 1982.

Olgyay, V., Design with Climate, Van Nostrand Reinhold, New York, 1992.

Szokolay, S. V., Thermal Design of Buildings, RAIA Education Division, Canberra, Australia, 1987.

Watson, D. (Ed.), The Energy Design Handbook, Chapter 1, The American Institute of Architects Press, Washington, DC.

Watson, D. and Lab, K., Climatic Design: Energy-efficient Building Principles and Practices, McGraw-Hill, New York, 1983.

Yeang, K., 1994. Bioclimatic Skyscrapers, Artemis, London.

EXAMPLES

1. Harmony Resort, St. JohnU.S. Virgin IslandsContact:

Stanley Selengut, President

Maho Bay Camps

PO Box 310

Cruz Bay, St. John

U.S. Virgin Islands 00831

tel: (800) 392-9004; (612) 348-4400

fax: (612) 348-9335

email: mahobay@maho.orghttp://www.maho.org/index.htmlDescription

Harmony Resort, located adjacent to the U.S. Virgin Islands National Park on St. John, is a luxury resort employing the latest in energy- and resource-efficient technologies in both its construction and operation. Built using recycled materials and low-impact construction technology, the resort uses only renewable energy generated by the wind and sun, maximizes efficient use of water and minimizes waste production. Harmony serves as the prototype for environmentally sustainable resorts in sensitive ecosystems and landscapes.

The genesis for Harmony can be traced back nearly 20 years when owner Stanley Selengut decided to build an environmentally-responsible campsite on 14 acres at Maho Bay on St. John. "My original intent was simply to offer an inexpensive vacation that was close to nature but provided a degree of comfort and convenience not found in a traditional campground," says Selengut. Inspired by his success in developing a community of three-room "tent cottages" using environmentally-sound technologies, Selengut recently set out to develop a full-scale resort dedicated to the principles of sustainable development. The result is Harmony Resort.

Harmony Resort features 12 two-story housing units constructed with the green philosophy pioneered by Selengut nearly two decades ago. Construction was designed to minimize site disturbance to ensure the preservation of natural beauty and habitat, while the installation of environmentally sound technologies ensures low-impact operation. Electricity at Harmony is generated by the sun and wind, with timers and sensors to maximize efficiency. The architecture employs passive solar design and water and light fixtures minimize resource use.

The Research and Education Center (REC) at Harmony is helping researchers learn more about efficient resource use, and their findings will be made available to other builders. Local school children visit Harmony's REC to learn about sustainable development, renewable energy resources, and recycling. Finally, in-room computer systems, another project of the REC, allow guests to receive information about the numerous technologies and products they encounter at the resort.

Program Highlights

Environmental and Efficiency Features

Energy for each house is provided by a photovoltaic array, while passive cooling is achieved through the use of wind scoops, cross-ventilation, generous overhangs to provide shade, the preservation of trees and other vegetation and the use of heat-rejecting glazings.

Water for each unit is heated through solar power and each unit has a solar oven on the deck.

Electrical appliances are kept to a minimum.

Lighting fixtures employ the latest energy-efficient designs and technologies.

Cisterns in each basement collect rainwater, which is filtered before use. Harmony uses no groundwater.

Gray water is captured and used to flush toilets and water plants.

Whenever possible, waste is composted and returned to the soil.

Recycled materials have been put to maximum use in the construction of the Resort:

The floor decking is made from 100-percent recycled newspaper.

The siding and roof shingles are made from a composite of cement and recycled cardboard that comes with a 50-year guarantee.

Bathroom tiles and furniture tops are made from recycled glass bottles.

Other materials used in construction include recycled plastic for lumber, recycled steel nails, and salvaged wood scraps and rubber tires for the rugs.

The Resort features a solar-powered ice machine.

Construction

Regenerative landscaping practices were used during construction to help reduce the size of the Resort's environmental "footprint."

During construction, solar photovoltaic energy was used to power all electric construction tools.

Each house was designed and built so that no trees needed to be cut during construction. Elevated wooden walkways connect the beaches and buildings, leaving the soil and vegetation undisturbed.

Pipes and cables are hidden under the walkways instead of being buried to minimize disturbance to the environment.

Future

Currently, all water consumed at Harmony -- beyond what is captured as rainwater runoff -- is brought in by truck. In the future, a solar-powered desalinization plant will be constructed to meet the Resort's water needs.

Research and Education Center

The Research and Education Center, a facility being constructed adjacent to the Harmony Resort, will enable researchers to perform engineering and system performance analysis regarding resource use at Harmony. The objectives of the research center are to evaluate the adaptation of humans to sustainable living, to evaluate the performance of the recycled materials used in the construction of Harmony and to evaluate the performance of the Resort's "off-the-grid" energy system.

Each unit contains a computer so guests can monitor and adjust their energy use depending upon prevailing conditions.

Information collected from each dwelling unit at the Resort will be collected to develop a comprehensive database regarding resource use patterns of Resort guests.

Researchers will evaluate all solar and wind resource data in a variety of weather conditions to determine the best way to achieve optimum performance from available resources. To provide a basis for this analysis, instruments collect energy and weather data every minute on a 24-hour basis.

Vital Statistics

Program Management/Partnerships: The Harmony Resort is a project of Maho Bay Camps, Inc. in partnership with the U.S. National Park Service, the U.S. Virgin Islands Energy Office and Sandia National Laboratories (Albuquerque, NM). Substantial materials were supplied by Real Goods Trading Corporation.

Budget: Please contact the program directly for the latest budget information.

Community Served: Visitors to the U.S. Virgin Islands who seek to enjoy nature's beauty while exerting the lowest environmental impact possible.

Measures of Success:

Harmony Resort is the the world's first luxury resort to operate exclusively on sun and wind power.

The facility was the 1994 winner of the Grand Award for Environmental Technology by Popular Science magazine.

The Resort is the 1997 winner of the American Society of Travel Agents (ASTA)/Smithsonian Magazine Environmental Award

Published: February 1998Success stories designed by Mark W. Nowak