LOW ENERGY ?
Energy efficiency is just one aspect of creating a low energy home. We’ve built very large, architect-designed homes which, despite PV panels and appliances with numerous energy stars, have high embodied energy and expensive running costs.
If the layout is well planned with versatile internal spaces and good connection with outdoors, then over-sizing the home can be avoided (a common, inefficient and costly mistake!)
Low energy can be designed in (depending on the clients’ preferences), literally from the ground up: eg. if the brief aspires to a high comfort home we would recommend insulating under the ground slab. Accurately built walls and roof (with high insulation) and careful selection of doors and windows all help to achieve ‘tight construction’, which makes it possible to run an ultra-efficient Heat Recovery Ventilation system.
The following annual chart shows the sum of every hour multiplied by the number of degrees the outside temperature is above or below the comfort temperature. It depicts the amount of heating or cooling required throughout the year to maintain a comfortable internal temperature in Perth
The graph shows 4,000 heating degree hours in the month of July. Each hour the internal temperature needs to be raised by an average of 5 degrees to maintain comfort. For the whole year the total heating degree hours are over 23,000.
Thirty years ago fewer than 25% of Australian homes were air-conditioned. In WA it is now more than 90%. Our energy consumption has sky-rocketed and electricity rates have doubled in the past decade.
Although today’s homes are more insulated than they were, they are still draughty. Every hour the whole interior volume of conditioned air is lost from an average home via leakage to the outside – this is a real waste of energy.
Leakage can be minimised by paying careful attention to construction details, especially around windows and doors, floor, wall & roof junctions and penetrations. Tight construction makes it possible to use a balanced ventilation system in which fresh air is continuously ducted into the living areas of the house at the same rate that stale air is extracted from the kitchen, bathrooms and laundry. The incoming air is heated or cooled by the stale exhaust air in the Heat Recovery Ventilation system, where up to 90% of the energy in the air is transferred, although fresh and used air are never actually mixed. These high quality ventilation systems save much more energy through the prevention of heat losses than they use to run.
Air is exchanged at the rate of one volume of the interior of the house every three hours. Typically the system is driven by nothing more than two 30 Watt fans that together cost about $130 to run non-stop for a whole year. Windows and doors can be open at anytime to make the most of our beautiful weather – and the HRV keeps on going (for less than 40 cents per day) seamlessly taking over when the windows are closed.
Thanks to the high insulation and tight construction, heating and cooling are needed less in a high comfort home. When required, the amount needed can be as little as 10% of the average Australian home! This is because the energy from the lights, appliances and people inside the home is largely captured and reused by the HRV.
The equivalent of one small 3kW reverse-cycle split system is usually enough to maintain internal comfort in a medium to large PassivHaus – operating less often than normal.