Designing safe and comfortable outdoor living spaces

Transcription

1 Designing safe and comfortable outdoor living spaces Christina Mackay School of Design, Faculty of Architecture & Design, Victoria University of Wellington PO Box, Wellington, New Zealand Tel.: -- ABSTRACT: In the warmer climates in northern New Zealand, Maori traditionally lived largely outof-doors retreating to small whares at night during cold weather or to sleep. This concept involves minimum infrastructure and may have lessons for temperate regions of world today where increasing resources are used to build larger and larger houses. This paper investigates strategies for maximising, through design, annual outdoor living time. Design intervention is required in order to make exterior environments both safe and comfortable. Increasing levels of UVR and awareness of skin cancer risk (especially amongst the fair-skinned Pakeha population), mean sun-shading is recommended for up to months of the year. For much of this time people desire warm shade rather than cool shade. Sun and wind control and the use of passive solar design can further extend out-door living time. Using existing climate data in a specific coastal location, the paper identifies the time and duration throughout the year of natural safe and comfortable outdoor living conditions. Secondly, strategies for heating and cooling the space, while providing UVR protection, are investigated. The multipurpose use of sun-shading for wet weather shelter is also considered. The paper concludes that for most of time when UVR protection is needed, occupants of a shaded outdoor space would require additional heating in order to be comfortable. The use of shading materials (i.e. glass and polycarbonate) which shield UVR but transmit heat is an effective design solution. For most of the time, sea breezes are available to cool, if required. Conference Topic: Decision-making and strategies for action Keywords: out-door living, UVR protection, environmental comfort control. INTRODUCTION Outdoor living has been a feature of New Zealand life, since the Maori, the first immigrants, arrived to the new land around A.D. Traditional living centred on an open marae space surrounded by a wharenui (meeting house), small sleeping wharenui ( to. metres long by to. metres wide), cooking shelters and store houses []. th century European settlers sought the shade of the verandahs of Victorian villas in order to preserve their fair complexions. By mid th century, fashions for modernist houses and tanned skin, promoted open patios and terraces for the enjoyment of bathing in the sun. Over the last decade, this sun-loving lifestyle has been challenged. Skin cancer has been recognised as a significant health issue in New Zealand. In the population of million, nearly, new skin cancers (including, new cases of melanoma) are reported annually. Approximately people die of skin cancer each year. [] It is estimated that treatment, of both malignant and nonmalignant cancers, costs more than NZ$M annually. [] Over-exposure to ultraviolet has been established as the leading cause []. The high level of skin cancer in New Zealand has been attributed to relatively high UVR levels and a large proportion of fair skinned population. High UVR levels are due to clear skies and the subsequent effects of ozone depletion over Antarctica []. The public health SunSmart programme recommends people protect themselves from the sun between am to pm (daylight saving time) from October to March []. The programme was set up in and until recently tended to be limited to awareness raising and achieving individual behaviour change. In, a stronger emphasis on environmental change was recommended. [] Shade is now considered as an important skin cancer protection strategy. The New Zealand climate, however, provides challenges for shade design. The islands experience extreme and changeable wind conditions. The majority of the population live near the coast, where temperate air temperatures together with sea breezes encourage people to seek the warmth of the sun even when UV levels are high. This paper aims to determine how often UVR protection is needed when the air temperature alone is too cool for comfort. If it is frequent, then

2 traditional methods of providing solid shade would not be effective. Firstly, the paper establishes a UVR level above which shade would be required over an outdoor living space. Secondly, an acceptable level of comfort for the space is presented and qualified. Thirdly, the methodology in using existing climate data at a specific location is explained. Finally, the results are presented, discussed and conclusions made.. UVR PROTECTION The measurement unit for UVR exposure, a Standard Erythemal Dose (SED) is equivalent to J.m - effective [] when weighted with the erythemal response function of the CIE [] and SEDs is sufficient UVR to cause erythema or sunburn in people with sensitive skin. The World Health Organization (WHO) promotes UV Index as an international measurement of UV levels. [] A risk rating of UVI - is low, UVI - is moderate, UVI - is high, UVI - is very high and UVI > is extreme. WHO recommend people use sun protection when the UVI is over. At UVI, a person would receive J.m - in one hour (almost SEDs). In NZ in midsummer, UVR levels exceed UVI at solar noon and UVI is common for up to hours a day. Sun Smart, the public health programme in New Zealand, in recommending sunprotection between am and pm consider UVI as sufficiently safe for most of the population. This risk level may be appropriate in public parks or urban spaces where people visiting for short periods are likely to be wearing personal protection and intermittently move from the open to the shade. In an outdoor living space, attached or adjacent to indoors, people are unlikely to wear sunscreen, hats and clothing and likely to linger in the space for periods longer than one hour. Therefore, this study adopts the more conservative approach, the WHO recommendation, that shade over living space is required when UVI >.. COMFORT In the absence of outdoor thermal comfort measurement system, an acceptable comfort level was established using the ASHRAE Thermal Comfort Program [] and the following assumptions. In determining the minimum acceptable dry bulb temperature the following estimations were used: the activity level in an outdoor living space would induce a metabolic rate of. met units [], clothing of pants, shirt, T-shirt, sweater, briefs and shoes, air velocity of.m/s, relative humidity of % and that the temperature of surrounding surfaces was linked to the air temperature. (Because the temperature variation at the site was relatively small, with a maximum dry bulb temperature of C, it is assumed the relatively humidity will not significantly affect comfort levels). In the absence of direct solar radiation, it is considered that dry bulb temperature is the prime determinant of comfort. In the above conditions, the ASHRAE Thermal Comfort Program estimates the minimum air temperature of. C would create a cool but comfortable environment where predicted percentage of the dissatisfied people (PPD) would be %. In the following hypothetical case, it is assumed that people (positioned out of the direct sun) will be uncomfortable when dry bulb temperature is less than. C.. METHODOLOGY The site of Paraparaumu Airport was selected for this case study. It is located in central NZ, on the west coast at the south of the North Island (latitude S, longitude E). Hourly recorded meteorological data (dry bulb temperature, solar radiation and wind speed) for for the site was accessed from National Institute of Water and Atmospheric Research (NIWA) Climate Database []. Measurements of UVR levels were provided by NIWA, Lauder. For comparison with other data, the min interval UVR recorded was averaged to give an hourly measure. The UVR levels were unavailable to the following periods: days in March ( - March), day in April, day in May, days in September, days in November and days in December. These omissions affect the accuracy of the analysis but the use the measure of average hours per day per month reduces the effect of the missing data. The analysis assumed that good shelter from the wind is provided (less than.m/s wind speed). In order to determine when UVR protection was required, the hours per day when UVI > were identified. In order to determine when solid shade would provide conditions that would be too cool, hours were identified when UVI> and the dry bulb temperature <. C. In order to gauge if the sun was available for warming the space during these hours, hours where identified when solar radiation was above. J.m - In order to gauge if wind would be available to cooling during these hours, hours were identified when the wind speed was greater than.m/s. In order to gauge if an impermeable shading material would be useful in providing a comfortable outdoor living space in during wet weather, hours were identified when rain fell and the temperature was greater than. C.

3 . FINDINGS. UVR levels The maximum UVR recorded at the site was UVI. The following chart displays the frequency when UVI > and UVR protection is required. average number of hours per day FREQUENCY: UVI> In total, UVI is greater than for the equivalent of % of the time between am and pm throughout the year.. Annual Temperature Range dry bulb temperature (C) jan feb march apr may jun TEMPERATURE VARIATION average daily maximum jul aug sep oct nov dec average daily minimum This graph provides background information on the temperature variation on the site throughout the year.. UVR levels and temperature comparison average nymber of hours per day FREQUENCY: UVI> AND UVI> & air temperature <.C UVI > UV > + temperature <.C This comparison clearly shows that the majority (%) of the time when UVR protection is necessary, air temperature <. C. This is constantly so in spring and early summer. Uneven patterns in March and November may be a result of the missing data available for analysis.. UVI and solar radiation comparison average hours per day FREQUENCY: UVI > and dry bulb temperature <.C compared to UVI > and temperature <.C and solar radiation >.J/m UV > + temperature <.C UVI > + temperature <. + sun radiation >.J/m As might be expected, whenever UVI > heat from the sun is available as well.. UVI and wind speed comparison average hours per day FREQUENCY: UVI > and wind speed >.m/s UV > wind >.m/s At the coastal site, over.m/s wind is available for cooling of the space % of the hours when UVI >. The still hours in summer (December, January

4 and February) could coincide with times of high solar radiation. At these times, other means of cooling i.e. solid shade would be necessary to achieve a comfortable environment.. UVI and rainfall comparison Analysis revealed UV levels were always under UVI when rain fell. At no time was shading material necessary for UV protection when rain protection was required (or vice versa). average number of hours per day FREQUENCY: hours with rain compared to hours with rain when temperature>.c shading of solar radiation could be used to create a comfortable environment. This study confirms wind is available % of the time sun protection is required. Because of the relatively low air temperatures, it has the potential to cool the occupants effectively. However, further analysis is required to determine if wind can provide sufficient cooling in high summer. Should additional cooling be required, strategies could include introducing shielding of direct sun to the space by adjustable louvres, shade cloth or planting. Horticultural glass houses typically do this by temporarily coating the glass with white paint. As an example, the award-winning house in Freeman s Bay, Auckland, by architects Julie Stout and David Mitchell, uses translucent material combined with planting in the design of the outdoor living area. average hours with rain per day average hours with rain when temperature>.c per day Rain frequency was constant throughout the year, with the most rain falling in winter (June and July). Very rarely was the temperature higher than C when it was raining (around the equivalent of one hour a day, January to March).. DISCUSSION For % of the time when UVR protection is required, an outdoor space would also require to be heated to create acceptable comfort conditions. As the heat of the sun is available at these times it makes sense to use direct solar radiation to warm the space. This could be achieved by either, or both, of two strategies: the use of a shade material that transmits heat but is a barrier to UVR and/or designing the shade to allow surrounding materials to be heated by the sun (when UV levels are low) and, in turn, radiate heat to the occupants later in the day. Selected glass and polycarbonates are excellent barriers to UVR but allow the penetration of solar radiation. Technical product information states mm clear float glass provides only % UVR elimination, but in the UVB range (which is most dangerous to health) this glass filters out over % UVR []. This glass has a shading co-efficient [] of. []. A clear polycarbonate roofing material prevents transmission of more than.% UVR, but has a shading co-efficient of. []. This strategy, while being optimum in spring, early summer and autumn, is likely to cause the space to over-heat for some of the day in mid-summer. Ventilation and/or solid Figure : Outdoor living space using a combination of translucent roofing and vines []. An easterly orientation of the space could allow surfaces to be warmed by the low morning direct sun while UVR levels are still low. Traditionally, the mahau (verandah) of Maori whare were built eastfacing, towards the rising sun. [] Although this orientation has symbolic meaning, it may have had a practical purpose also. Further analysis is required to determine to best orientation to create a comfortable verandah space throughout the year and the degree of UVR protection that could be achieved. An impermeable shading material has the additional benefit of providing a dry outdoor living space during rainy weather. However, this research confirms that the temperature would be comfortable (over C) for outdoor living only % of the hours with rain. Less solar energy is available during rain, so it is not possible to provide heat to the space naturally. However, the dry outdoors space could be used for more energetic activity which raise the bodies metabolic rate e.g. children s play.

5 . CONCLUSION At the selected coastal site at Paraparaumu in central New Zealand, for most of the time when UVR protection is required, the air temperature is too cool for comfort. If people are going to choose to occupy shade structures, then methods for warming these spaces need to be used. As heat from the sun is available most of the time when UVR protection is needed, the most direct strategy is the use of a shading material that transmits heat but is a barrier to UVR. Glass and polycarbonates do this well. Climate data confirms that sea breezes are usually available for cooling, if required. Without artificial heating, a covered outdoor living space would be too cool to use during rain. ACKNOWLEDGEMENTS Christina Mackay, Faculty of Architecture & Design, Victoria University of Wellington would like to acknowledge Richard McKenzie, NIWA Lauder New Zealand for his advice and the supply of UVR measurements for the site, colleague Mike Donn, Faculty of Architecture & Design, Victoria University for advising on comfort criteria and graduate Quentin Jackson for assistance in down-loading and formatting data. REFERENCES [] J. Salmond, Old New Zealand Houses, p, Reed Publishing (NZ) [] D. O Dea, The Costs of skin cancer to New Zealand. Wellington: Wellington School of Medicine, University of Otago,. [] R. McKenzie, B. Connor and G.Bodeker (), Increased summertime UV radiation ion New Zealand in response to ozone loss. Science : - [] Cancer Society of NZ (Inc) and Health Sponsorship Council, Sunsmart in New Zealand, accessed June [] A.I. Reeder, Skin cancer prevention in New Zealand: A discussion document to help guide future SunSmart programme directions. Dunedin: Social & Behavioural Research in Cancer Group, Department of Preventive and Social Medicine, Dunedin School of Medicine, August, August. [] CIE, (), Standard erythemal dose, a review. [] CIE Research Note ().A reference action spectrum for ultrvoilet induced erythema in human skin. CIE J,, pp- [] World Health Organization,, Global Solar UV Index A Practical Guide, World Health Organization [] M. Fountain, C, Huizenga, ASHRAE Thermal Comfort Program, Version, UC Berkeley, - [] One met is defined as. watts per square metre which is equal to the energy produced per unit surface area of a seated person at rest. The surface area of an average person is. square metres. [] National Institute of Water and Atmospheric Research (NIWA), Climate database (CLIDB), accessed June [] The Cancer Council Australia, Consensus statement on tinting of car glass and window glass for protection against solar ultraviolet radiation, Draft # The Cancer Council Australia, June [] Shading co-efficient: A ratio of the warming effect of the sun s rays through a sheet divided by the sun s warming effect through mm float glass. [] Metropolitan Glass, Catalogue and Reference Guide -, accessed June [] Alsynite, Laserlite Polycarbonate Roofing Technical Data, accessed June [] J. Stout, D. Mitchell, House -Freeman s Bay, Auckland, Architecture NZ, pp-, Nov/Dec [] Barlow, C., Tikanga Whakaaro Key concepts in Maori culture, p, Oxford University Press, New Zealand