Building Performance

The owner has been very pleased with the performance to date of the home. 

Energy Use

Energy consumption has been recorded for the five years since the house was built and also temperatures have been logged within the house and inside the Trombe walls.

Energy consumption results are provided below

When the house was first occupied an unflued gas heater (rated at 40MJ/hr) was used to provide supplementary heating.  This heater was thought to be causing humidity problems so it was replaced in June 1999 with two 2400W oil column electric heaters.

The quarterly electricity billing data collected to date indicates that the house uses approximately $400 per year on appliances and lighting, and from $100 to $200 per year (3000 - 6000 MJ) on supplementary heating.  There is no supplementary cooling installed in the home.

The gas consumption data has increased slightly each year, even though the gas heater was replaced in June 1999.  The majority of this gas use is likely to be hot water used from taps & showers as well as the washing machine and dishwasher.  The increase is likely due to the birth of a third child in late 1999.

Based on these figures the home is consuming about 15 - 30MJ/m² per year for heating.  This is a very low level of consumption in Canberra where the average consumption has been estimated by Energy Efficient Strategies et al. at 172 MJ/m².  Under the FirstRate home energy rating system which is used in the ACT this level of energy consumption is vastly superior to a 5 star rating (the highest rating recognised at present).

Internal comfort levels

Data logging undertaken over a 24 hour period in June 1997 shows that the house gains significant benefit from its passive solar design strategies.  Over a 24 hour period where the outside temperature ranged from a low of 1 degree C to a high of 12 degrees C, the internal house temperature ranged from a low of about 19 degrees C to a high of 26 degrees C.

Detail of this data logging is provided in the figure below.

As noted previously an unducted gas heater was used in the house when it was first completed.  During this period the occupants noted that they were experiencing very high humidity levels and were noticing substantial condensation on the insides of the double glazed windows.  The gas heater was replaced by electric heaters the following year, but some condensation was still noticed.  The owner monitored humidity levels inside to determine why this was happening.  Measurements were undertaken in the early morning and they found relative humidity levels of 50 to 55% compared to other homes in the area where levels were at about 30% at the same time.

The owner believes that this suggests the need for more ventilation to reduce relative humidity levels, as all doors and windows are fitted with very efficient seals and the design includes an airlock at the front entry.  Use of a heat exchanger ventilation fan is being considered.

No data logging has been undertaken during the warmer summer months yet the owner believes that the house has rarely exceeded 27 degrees C at any stage since it was built.  Achieving this level of summer cooling does require the occupants to ventilate the house overnight by opening the casement windows and encouraging crossflow ventilation.  This ‘night purge’ cycle has worked effectively but does rely on user interaction.

Performance of the trombe walls

Temperature loggers were also installed in a Trombe wall to measure the internal temperature.  Over the same 24 hour period in July 1997 as described above the trombe wall ranged from a low of 18 degrees C to a high of almost 40 degrees C.

This indicates that the trombe walls were capturing and storing a large amount of solar radiation each day.  This heat is released overnight and the walls reach their low of 18 degrees C at about 8am the next morning.  Thus for only about 1-2 hours each morning the temperature of the trombe walls is below that of the rooms, yet it soon increases as it gains further solar radiation that morning.

From this information it would appear that the Trombe walls have a fairly well optimised recharge/discharge cycle that operates over a 24 hour period.