Building performance

Quantitative

The heating and cooling requirements for the building were simulated using the FirstRate energy rating software. This process was originally undertaken using the earlier HERS software by the designers during the design of the building and later verified by Energy Efficiency Victoria (now SEAV) prior to construction of the dwelling. The building achieves 32 points on a scale where -55 points is required for standard 2.2 star performance*, 7 points is required for the highest five star performance and 63.1 is the maximum possible points for this climate zone (see Figure 1).

* A study undertaken by the Australian Greenhouse Office and the Sustainable Energy Authority Victoria entitled, 'Study into the Impact of Victorian Insulation Regulations for Class 1 Buildings' (2000) found that the average energy performance of new dwellings in Victoria was 2.2 stars.

Figure 1: FirstRate energy ratings

The owners were interviewed to determine their actual energy consumption. For approximately 3 months in winter the dwelling is heated with the electric floor coil between 11pm and 6am each night and a further boost between 3-4pm with the thermostat set to 20 degrees Centigrade. The gas heater in the living room is also used during the same three months for an average of one hour each evening. The wood fire is used only a few times a year and has been discounted in the evaluation. No other form of auxiliary heating or cooling is used for the rest of the year.

The metered off-peak electricity consumption for the electric floor coil heating for the winter period is approximately 9110 kwh or 32,796MJ. The gas bill for the same period indicates a usage of 9000MJ. The contribution for water heating and cooking was estimated to be 6390MJ in comparison to summertime gas bills and the remainder of 2610MJ was assumed to be the approximate gas use for heating in winter. Therefore the approximate total metered energy consumption for the dwelling for heating and cooling is 35,406MJ or 110MJ/m2 per annum. This compares with the predicted annual energy consumption of 75MJ/m2 using the FirstRate software.

This difference can be explained for several reasons. Firstly, FirstRate is a rating tool that provides comparative information of one design to another rather than an accurate measurement of the actual energy in use Secondly, the FirstRate software assumes certain user patterns and comfort conditions that may not reflect actual usage patterns. Thirdly, the climate conditions in the FirstRate software use Melbourne data, which is marginally warmer than Clematis. Average climatic data may also not reflect the conditions experienced in the year in which the metered results were taken. The difference of 35MJ/m2, however, is marginal when compared to a standard 2.2 star rated house.

Figure 2: Energy use in MJ/m2 of Clematis compared to standard 2.2 performance

To determine the greenhouse gas emissions associated with the heating and cooling, the metered delivered energy figures were converted to primary energy figures* giving a total of 115GJ per annum, equivalent to 6900kg of CO2 or 21.56kg/m2. The savings in Co2 for Clematis over standard 2.2 star performance for both gas and electric systems are compared in Figure 3. The graph shows small savings over a 2.2 star house with all gas facilities and substantial savings over a 2.2 star-rated house using all electric facilities. In reality the 2.2 star all gas facilities condition is unlikely to exist as the building would use some electricity for cooling.

* Multiplication figures used for the conversion of delivered to primary energy were 1.4 for gas and 3.4 for electricity taken from Treloar, GJ (1997). Extracting embodied energy paths from input-output tables: towards an input-output based hybrid energy analysis method, Economic Systems Research, 9(4), 375-391.

Figure 3: Comparison of CO2 emissions for Clematis and standard 2.2 star house.

The energy use for lighting, appliances, and hot water per annum in Clematis compared to a standard dwelling is illustrated in Table 1*. Despite the installation of an efficient water-heating unit, the dwelling uses comparable energy for water heating to that of a standard dwelling. This may be attributable to the use of the spa. The energy used for appliances and lighting is considerably higher than that of a standard dwelling. Without further investigation it is not possible to determine the reason for this high use of energy, however, it may be due in part to the large size of the dwelling and higher usage demands to that of 'standard' patterns of use.

Table 1: Energy use per annum for hot water, appliances and lighting

Embodied energy and life cycle energy analysis were not undertaken for this dwelling.

*Figures for standard dwelling taken from Perotti (1999) in Fay (2000) 'Comparative Life Cycle Energy Studies of Typical Australian Suburban Dwellings' Ph.D Thesis, University of Melbourne

Qualitative

The owners have found the house to be extremely comfortable in winter and summer. Despite the fact that the shading devices have yet to be installed, the owners did not find the house uncomfortable in summer due to the high ventilation rates. The house is used as the designers intended in summer with the operation of the south casement windows and the high level roof windows to create a thermal stack effect flow through ventilation. The only criticism of the performance of the dwelling by the owners was the lack of cross ventilation to one of the upstairs bedrooms. A roof ventilator is to be installed to alleviate this problem.