A Closer Look at the Prosser familys Healthy HouseAr. Vijaya N. Thakare ,Lecturer , Dept. of ArchitectureKITS,Ramtek

The Challenge

The Healthy House project brought together a multidisciplinary team to produce a prototype low energy, low toxicity house in a suburban environment. The owner occupants worked with designers, contractors, suppliers and building scientists to design a conventional house incorporating readily available products and technology, to set a standard for sustainable design in the area.

The Prosser family's goal To produce a modern pavillion style Queenslander for their growing family. It is located in a high-density residential area, at Mermaid Beach on the Gold Coast. The site was selected to be within easy walking distance of the beach, the local school and the workplace. The key goals for the family were to minimise harmful, toxic elements in their home, and minimise the impact of the house on the environment.

The Prosser family

Design ResponseThe design response was to produce a light timber frame dwelling that makes maximum use of passive environmental control features such as: high levels of daylight, controlled solar gain, cross ventilation and stack ventilation. Where possible, low embodied energy, low toxicity, recycled materials have been specified. The impact of household operations have also been considered; appliances have been selected to conserve energy, and electricity is supplied by photovoltaic panels. Rainwater is stored and treated on site for household use, and greywater is treated for use in the garden.

Location and ClimateThe house is located on the Gold Coast, where the climate is warm and temperate. Humid conditions and heavy rains can occur in the summer. The prevailing winds are easterly onshore breezes in the morning, and westerly offshore breezes in the evening. The site is also subject to cold Westerlies in the winter. Large objects in the vicinity of the house, such as trees and two storeyed houses, redirect the wind, so that the house is predominantly subject to winds from the SE and NE. A lane along the East side of the site facilitates airflow along this side of the house.

Climate information for South East QueenslandAnnual Heating Degree Hours13507Annual Cooling Degree Hours5098Relative Humidity Annual average 9am: 64%Annual average 3pm: 51%Average Annual Rainfall1460mmAverage Daily Solar Radiation4850 Wh/m2

The site is in a relatively high-density beachside suburb, and was clear at purchase (except for two trees, which have been retained). Services available at the site were water, stormwater, sewerage, electricity and telephone connections. Three adjoining sites are occupied by double storeyed, single dwelling buildings, and this is the dominant building form in the neighbourhood.The sandy site was relatively flat at the time of purchase and so few earthworks were required, though excavations were made to accommodate the grey water and rainwater storage tanks.

Site planning OrientationThe building is oriented along a North-South axis, offsetting it from the site.

Building-site interface

The building connection to the ground was designed to be minimal, to reduce the need for earthworks and maintain habitats for local flora and fauna. The house is founded on concrete footings. Excavation was required for the placement of the two large water storage tanks, and slabs were poured for the carport and laundry.

Landscaping

Approximately 1/3 of the 480m2 site has been planted out in locally sourced natives. The garden strongly favours fruiting species to support the bird population in the neighbourhood, which otherwise has only sparse vegetation. Topsoil was imported to establish the garden on the sandy site, and a subsurface irrigation system was installed to reduce evaporation losses.

Building plan

The building plan is based on two double storeyed units, which are connected by a double height breezeway. The breezeway is designed to facilitate cross ventilation through the house, and admit daylight into the centre of the building.Low occupancy wet areas including bathrooms and a laundry are located along the West side of the building. This maximises their exposure to ventilating breezes, and buffers the main body of the house from solar gains from evening sun.

Lower Level Floor Plan

Upper Level Floor Plan

The steps in the building plan also permit access to daylight for all rooms. The density of the development in the neighbourhood limits access to daylight from the West and East, so most rooms are designed to include a north or south facing window.

Response to the climate

The main strategies were:- To maximise airflow through the building- To reduce summer solar gains to a minimum (without compromising daylighting)-To insulate the roof and walls

Airflow

The house was designed to take advantage of the prevailing South-Easterly and North-Easterly winds. Louvres on each facade and concertina doors along the North facade allow the occupants to open the house to cooling breezes. The ground floor is open-planned with a central double height space to facilitate stack and cross ventilation. Louvred ventilation "towers" facing North and South are also used to promote airflow. Wet areas such as bathrooms, the laundry and the kitchen project from the house to capture breezes.

Flume testingAt the design phase flume testing was carried out to evaluate the performance of the building in NE and SE wind conditions.

Flume testingThis involves placing a model of the building in a liquid and subjecting dyes to currents to assess flow patterns around the house. The results of these tests were used to optimise the size and location of openings. For example the size of the towers was reduced on the basis of the tests.

Solar Gains

The house is laid out to open it up to low incident radiation from the North and East, to allow the house to warm up in the morning and in winter. Service areas (the bathrooms, the laundry and circulation spaces) are used as buffer zones along the West side of the house, to reduce the impact of heat gains from low evening sun on the living spaces. The roof material selected is a light colour to reflect as much sunlight as possible from the roof and reduce solar gains.

Glazing

Glazing has been located to minimise uncontrollable solar gains, with west facing glazing eliminated altogether. The glazing was assessed using the GSL energy modelling programme, developed at the Queensland University of Technology. GSL is used to compare different types of glazing within a given window and building design. The modelling programme Radiance was used to evaluate interior lighting levels. Using these modelling tools, the design team selected a blue tinted glass with a low emittance coating.

Glazing

This reduces the heat gains to the house while maintaining a good level of daylight. The blue tinting is very subtle and does not detract from the outlook. South facing glazing (which is not exposed to direct sunlight) is clear, to reduce the cost of glazing.Shades have been installed over the North facing windows, to reduce solar gains from high summer sun.

Insulation

Foil type insulation was selected for the walls as it is suited to the warm climate. The double layer of foil, which incorporates an air gap, reduces the transfer of heat from the sun through the walls. An R-value of 0.67 is achieved in the walls.

The roof is insulated with a combination of foil insulation and fibreglass insulation. These operate to reduce heat losses through the roof in winter, and solar gains in summer. An R-value of 2.6 is achieved in the roof.

Air quality

The strategies employed to optimise indoor air quality include:- High levels of passive ventilation- Material selection and design- Location of the carport

Passive Ventilation

This house makes use of passive ventilation strategies to maximise airflow through the building. Increasing the rate of air changes ensures that there is no build up of pathogens or toxins from the house or household operations.

Materials

The use of reconstituted wood products, which contain glues (which can emit harmful fumes), has also been kept to minimum. These are used only in structural elements like the portal frames and floor joists. Instead solid timber has been used extensively in the house. The timber was locally sourced, and recycled where possible. Where suitable recycled timber could not be obtained, plantation was specified.

Materials

Materials with low volatile emissions were selected wherever possible. Both interior and exterior timber work in the house are finished with locally sourced organic products, eliminating the need to use varnishes.

The plasterboard walls are finished using a long life organic paint system, as standard paint products are associated with harmful off-gassing.

It was also decided to use HDPE waste water pipes and polypropylene water supply pipes, rather than PVC piping. Greenpeace have shown that the use of PVC involves production and transport of large amounts of toxic material and by-products (). In use, PVC leeches toxins into water systems, and produces toxic fumes in a fire.

Planning

The carport was deliberately separated from the house, and designed to be open to the wind. This prevents harmful fumes from the car being drawn through the house.

Embodied Energy

The design strategies for reducing embodied energy in the building were to:-Minimise site works-Use recycled and local materials where possible-Select low maintenance, long life materials and finishes-Design the building structure for flexible planning and reuse-Select materials and construction methods that facilitate reuse.

Site works

The house was designed with mainly timber foundations to reduce the need for earthworks. Soil removed for construction was also retained on site, for redistribution on the site. This eliminated the transport energy required for disposal, as well as the impact of using the excess soil for offsite landfill.

Materials

Where possible, materials with low embodied energy were selected. For example locally supplied, recycled timber was used for floors, framing and most of the joinery. The timber was tested and certified for soundness by the supplier.( recycled joists). The concrete specified was a special low embodied energy product, which makes use of recycled cementing products, and recycled aggregate. Low maintenance, long life materials were also selected, to reduce the ongoing embodied energy consumption. For example, an interior paint system selected had a guaranteed life of 20 years.

Design for Flexible Planning and Reuse

The building utilises a series of glue laminated portal frames, which minimise the amount of bracing walls required, and thus increase the flexibility of the building.

Internal partitions can be added or removed from any part of the house, without affecting structural integrity. The use of frames also allows the building to be open plan with large areas of windows and doors. This assists with the passive ventilation, heating and lighting strategies.

Materials and Detailing for Easy Reuse

The house makes extensive use of timber, which can be easily recycled in the event that the house is demolished.

Operational Energy

The design strategies for reducing the operational energy of the house were to:-Plan for passive heating and cooling-Access natural light-Use low energy lights and localised switching-Specify energy efficient appliances-Specify electric boosted solar hot water heating-Install photovoltaic panels

Passive heating and cooling

The house has been planned and detailed to maintain a comfortable temperature, using passive heating and cooling. The main strategies are: planning for stack and cross ventilation, reducing midday and afternoon solar gains, and insulating the roof against heat gains and losses. The success of the natural ventilation strategy has elimnated the need for air conditioning, significantly reducing the total energy requirements of the house.

Natural light

Daylight levels within the house have been maximised, without admitting excessive solar gains. This was achieved by optimising the window size, selecting a glass type which maximises light transmission, and locating windows to control heat gains while maximising light admission.

Lighting

Lighting in the house is predominantly long life, low energy fluorescent bulbs. This not only reduces the energy consumed by lighting, but also reduces the heat load within the house. The lighting design strategy was to localise switching as much as possible. This allows small areas to be lit, at any given time, further reducing the energy consumed by lighting

Appliances

Some energy efficient appliances have been selected for use in the house. Hot water is supplied by an electricity boosted solar hot water system.

Photovoltaic Panels

A 1.44kW array of photovoltaic panels are connected to the local grid, so that surplus supply is exported (there is no need for batteries).

Water and waste water

The water use reduction strategies include:-Treatment and storage of rainwater for household use-Treatment and storage of greywater for future garden use-Selection of plant species suited to the area-Installing an irrigation control system to reduce overwatering

Rainwater

Rainwater is collected from the roof and stored in tanks. The main tank is a 22,000 litre tank buried below the house, this is supplemented by a 1,000L galvanised tank. Water quality is protected by a twenty-micron filter and first flush devices, which divert the first 120 litres (8mm) of each downpour into the local stormwater system. The rainwater supply is supplemented by town supply. The local council required that there should be no connection between the town supply and the rainwater tank, and this was achieved by allowing for an air break between the tap from the town supply, and the maximum water level in the rainwater tank A water level sensor alerts the occupants when town supply is required.

Greywater

Greywater (water from basins, laundry and the showers) is collected and treated on site in a 6000L tank. Settlement and sand filtration are used to treat greywater before releasing it for reuse. The present legislation in Queensland prohibits the use of treatment of waste on site so the house is being used as a test case to assess the viability of this approach. The water would normally be used for the garden, but the local council are waiting for the results of the testing before they will permit the greywater to be reused on site. Because the site is served by the local sewerage system, regulations prohibited the treatment of blackwater on the site.

Plant species

Locally sourced native plants were selected, which would be suited to the local environment, and require minimal watering. The garden was designed according to permaculture principles, in order that it will eventually be self-sustaining. In the short-term, watering requirements were reduced by heavy mulching.

Irrigation monitoring devices

Two devices were installed to help monitor and minimise garden water use. The first is a tensiometer, which measures the dryness of the soil, and indicates when watering is required. The second is a Full Stop Device. This sends a signal to the householder when water has reached the bottom level of the roots of the plants.

Building PerformanceBuilding planOver the first year of occupation both external and internal temperatures have been monitored. Results show that the house warms up quickly in the morning, without meeting the peak midday and evening temperatures. The measured temperatures also show that the insulation works to prevent heat losses at night, allowing the house to maintain a relatively steady temperature throughout the diurnal cycle. The chart below shows temperatures measured at head height on the ground floor.

Summer 1999-2000 Indoor-Outdoor Temperature Differences Average external maximum28.88CAverage internal maximum26.65CAverage difference 2.23CAverage external minimum20.43CAverage internal minimum23.27CAverage difference -2.84C

Average exterior wind speedAverage interior wind speedSouth Easterly2.6m/s0.5m/sNorth easterly2.2m/s0.7m/s

The results show that high levels of airflow are achieved in the house, effectively cooling and adding to the comfort of occupants. The high air change rate was found to continue even when the louvres and windows were closed (a full air change ocurred in under two hours), indicating that the louvres cannot be fully closed off. This has implications for active heating and cooling mechanisms, as heating in particular will be quickly lost through the louvres. Because the house is in a temperate climate, where little heating energy is required, this was felt to be an acceptable compromise, outweighed by the cooling benefits of the high airflow. However, the detail design could be refined by developing a louvre system which could be sealed more effectively. This would allow the occupants to exclude hot air in the summer, and minimise heat loss in the winter.

Air QualityIndoor air quality testing was carried out by Envirotest and the University of Queensland, immediately prior to occupation and after a full year of occupation. The table below summarises the findings of the tests after a full year of occupation, and compares them with standard acceptable levels. The tests have demonstrated the Healthy House has levels of volatile organic compounds, polar compounds and formaldehyde below detectable limits, and that carbon dioxide and respirable particles are well within acceptable guidelines in the entire house. The only contaminant to exceed acceptable levels is the level of airborne micro-organisms, which reach a high level in the master bedroom and children's bedrooms. This could be due to the half height walls which separate the bathrooms from the other upstairs rooms. These permit damp air to circulate in the upstairs rooms, and possibly facilitate the growth of airborne micro-organisms. With respect to all other contaminants the house has performed well within acceptable limits.

Contaminant measured AreaLevelAcceptable standard CO2Whole house

Embodied energyWhile the house makes use of low embodied energy materials and construction strategies, it is still a relatively large house, with a large surface to volume ratio. While the house may achieve a low level of embodied energy per metre squared, the large amoount of materials required to construct this house may lead to a relatively high level of embodied energy per occupant.

Operational energyElectrical systems have been metred over the first year of occupation, to breakdown the proportions of energy used in each area of the house and evaluate the solar hot water and electrical systems. The following pie chart summarises energy end use characteristics of the house.

The household uses an average of 15kWh/day, and this compares with a Queensland average of 19kWh/day.* Given the high level of occupancy in the house (five people, compared with a Queensland average of 2.7 people per household), this represents an impressive reduction in energy consumption. The savings can mainly be attributed to the passive cooling strategy, but also to the solar-electric hot water system. The solar-electric hot water system typically uses 2.5kWh/day, compared to (approximately) 10 kWh/day for an all electric system.

The pumps which pressurise the household water supply and recirculate the greywater through the sand filtration system consume 2.2kWh/day, on average. The research team suggest that the municipal system would use approximately 0.6kWh/day to perform the equivalent functions. Thus there is a potential energy penalty of 1.6kWh/day for the decentralised water services used in the house.

The monthly end use breakdown for household electricity shows that there is a seasonal trend, peaking in winter. The increase can be attributed to cooler temperatures and reduced sunshine hours, as the rise is mainly due to increases in hot water energy and electricity use in bedrooms. Winter energy use could be decreased by sealing the house more effectively, reducing heat loss through the louvres, for example. Increasing the level of insulation in the house would also reduce heat losses. The energy consumed by the solar-electric hot water system could also be reduced, by installing low-flow devices at showers and hot water taps in the house (this would have the added benefit of reducing water use).

When supply from the photovoltaic system is taken into account, the amount of energy imported from the grid will be further reduced. As the system was commissioned in September 2000, supply information is not yet available, but it is anticipated that the PV array will supply approximately 10kWh/day, more than half of the household requirements.

Water and waste waterBoth rainwater and grey water were monitored for quality and quantity used over the test year, and the systems have been refined in response to the testing.Rainwater testing established that levels of nitrogen, phosphorus and heavy metals were well within the levels specified by the National Health and Medical Research Council Australian Drinking Water Standards. However, drinking water often didn't pass tests for faecal and total coliform counts. As the acceptable level for these contaminants is zero, the design team consider the standards to be very strict. After heavy rainfall (ie more than 50mm), the faecal and total coliform levels have exceeded 300cfu/100ml, and it is suggested that the main source of contamination is bird and possum faeces. Because the source is non-human, it is not considered likely that the water contains pathogenic organisms. However, a domestic UV disinfection unit is to be installed.

Over the test year it was found that the greywater could not meet the guidelines set by the Department for Natural Resources for reuse on site. As a result, an additional UV disinfection unit was installed in the system. After UV treatment, the greywater has a measured total coliform count of less than 10, which is well within guidelines for use in above ground irrigation and for toilet flushing. However, current regulations prohibit the use of greywater by individual households. The Healthy House research team hope that by proving that onsite greywater treatment can meet health standards, they will help to pave the way to modification of the statewide guidelines.