Energy Supply & Efficiency
Energy supply and efficiency are strongly related. At times when energy seems to be endless, the efficiency tends to be low. At times when the energy supply is becoming short, energy efficiency improves and new energy efficiency innovations start to be developed. As the human population has expanded, demand for energy has increased. The 1973 oil crisis highlighted our dependency on oil and nuclear energy was sought as an alternative, but the Chernobyl disaster of 1986 put an end to this movement. A green movement for renewable energy began after this, and people began to thermally insulate their homes. This caused issues with thermal bridging, air tightness and condensation leading to health hazards like mould, fungi and sick building syndrome. Demand for comfort in Australia in recent years has caused the price of electricity to increase around 50% in the past five years. As a solution to this problem, the Passive House seems the most economical, globally well-established and, therefore, viable means of energy efficient housing.
The Passive House
The Passive House concept was developed in Germany in the early 1990s and has since spread across Europe and the world. The concept has a dual aim of low energy consumption and affordability (a 0% to 15% investment cost).
The concept revolves around five different components:
- Thermal insulation, which reduces heat transport between the outside and inside of the building.
- Windows, which allow short-wave radiation (sunlight) through, but absorbs long-wave radiation (heat).
- Airtightness, which protects the thermal insulation from air movements to assure its optimal performance.
- Thermal bridging, which is a spot on a building where heat can pass through easily (such as a building corner or a material change like a metal fixing). This can lead to heat loss in the winter and heat gains in the summer, and so must be minimised in the case of the Passive House.
- Ventilation, which moves air in and out of a space. This acts as a means to both keep air fresh (to reduce the carbon dioxide levels) and, in the case of the Passive House, act as a heating and cooling system.
A building must be in line with a strict performance criteria in order to be considered a Passive House by the Passive House Institute.
Energy Recovery Ventilation
The Energy Recovery Ventilation (ERV) is a ventilation unit that can recover both sensible and latent heat in an air exchange between outside and inside air. ‘Energy recovery’ refers to an air-to-air heat recovery system, which can recover energy (heat/mass) from an air flow at a higher energy level by exchanging this energy to another air flow at a lower energy level. The energy recovery process can maintain a comfortable temperature level of between.
The concept is based on thermodynamic equilibrium. For example, if ten litres of water at a temperature of and ten litres of water a temperature of are mixed, the twenty litres of water reach a temperature of , which is an equilibrium. If the ten litre buckets were refilled, the temperature in both buckets will be , a 50% energy recovery. In an ERV, the two fluids are the air leaving the building and the air entering the buildings. Due to the smart design of the ERV, up to 95% of energy recovery can occur. There are many different designs of ERV available.
The New Passive House Standard
A new criteria, called the ‘Primary Energy Renewable (PER) sustainability assessment’ has been added to the ‘Passive House Planning Tool’ (PHPP – the tool used to determine if a building is of Passive House standard) to integrate a distinction between electricity generated by renewables and fossil fuels, which was lacking in the previous version of the PHPP. This new criteria establishes three ‘classes’ of the Passive House: Classic, Plus and Premium.
These classes are based on the potential for the building to produce a certain level of energy through renewable means and the demand the building would have for the same produced renewable energy. The new PHPP then includes not only the new PER criteria, but also includes the maximum percentage of hours per year that the indoor area is allowed to overheat, have excessively high humidity, what level of minimal thermal protection and occupant satisfaction is needed.
A study in 2011 called ‘Passive House in Different Climate Zones’ chose five different climate locations with huge variations in climates, population concentrations and industrial development and applied detail examinations on the same model in each location. The result showed what Passive House components in each zone was required and that Passive House was indeed applicable worldwide.
The Passive House in relation to the Perth climate:
The excessive (high) temperature allowance for the Passive House, according to the Passive House standard, is fulfilled in the Perth climate, meaning that a Passive House is able to operate in the Perth temperature. Due to the fact that outside temperatures have a high influence on indoor temperatures, a combination of ERV and different cooling means (such as a ground-heat exchanger) is required to maintain the optimum indoor comfort range of 20°C – 27°C. At low-temperature months, only an ERV is needed to keep indoor temperatures in this range as the Passive House was designed in colder climates and, therefore, does not allow indoor temperatures to dip below 20°C (only 10W per m2 is needed to heat a Passive House. Humidity is another factor that influences indoor comfort and is maintained at an optimum level of 30%-70% indoors due to the design of the Passive House.