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Watt efficiency
Last month’s article stated that there are three fundamental strategies for being sustainable:
1. Use less resources – through reduction and efficient use
2. Use renewable and clean alternative resources
3. Offset (ie. compensate for) any pollutants and waste that are created
In this article we look at the first strategy - using less resources. It has two main areas, which in a sense are the same: reduction and efficiency.
Globally, energy (especially from fossil fuels) and many other resources that we take for granted like water and food, will become scarcer and therefore more expensive. By using less resources we can conserve what we have and be in a better position to live sustainably on renewable resources.
Reduction
Reduction is a matter of choosing to use less. This very simple concept is often very difficult to implement because of habits and ingrained attitudes – both personal and cultural. Nevertheless, we all have to make an effort to reduce consumption.
There are many things that you can do. Altering basic habits may be difficult to begin with but eventually they become second nature. In particular we should make an effort to teach good habits to our children. It is difficult to teach children if you aren’t setting a good example.
Efficiency
Being efficient is a type of reduction. Efficiency can be defined as the ratio of the useful output to the input of any system. Last month’s article highlighted the fact that in New Zealand in 2002, 196.21 petajoules of fossil fuel energy was delivered for transport use. However, only 28.84 petajoules of that energy was useful output. In other words the efficiency, shown as a ratio, was a paltry 14.7%.
Internal combustion engines are very inefficient because most of the energy used is lost as heat and, to a lesser extent, friction. In this case, efficiency is a technological issue. New technologies are continually being developed which are much more efficient. We can make a difference by always choosing the most efficient options whether they are houses, appliances, cars or machines.
An energy efficient house:
With the imminent launch of the Government’s Home Energy Rating Scheme (HERS) the thermal efficiency of houses will become a hot topic, so to speak. Generally, New Zealand homes are notoriously cold and inefficient and require extra energy to keep them comfortable.
House energy efficiency tactics are demonstrated by the Passivhaus Standard in Europe which is a very rigorous system that creates ultra-low energy-use houses which are able to dispense with conventional heating systems – although heat is often distributed through the low-volume heat recovery ventilation system that is required to maintain air quality.
This standard is being used voluntarily in many places in Europe which have colder winter climates than New Zealand. To achieve the Passivhaus standards, a number of techniques and technologies are used in combination:
Passive solar design:
The Standard follows passive solar building design techniques. Where possible buildings are compact in shape to reduce their surface area, with windows oriented towards the north (or south in the northern hemisphere) to maximise passive solar gain. However, the use of solar gain is secondary to minimising the overall energy requirements. Some internal thermal mass is normally incorporated to reduce summer peak temperatures, maintain stable winter temperatures, and prevent possible over-heating in spring or autumn before normal solar shading becomes effective.
Super-insulation:
Passivhaus buildings employ ‘super-insulation’ to significantly reduce the heat transfer through the walls, roof and floor compared to conventional buildings. Special attention is given to eliminating thermal bridges (timber frames for example).
Advanced window technology:
Windows (including the frame) are manufactured with exceptionally high R-values (heat flow resistance). These normally combine triple-pane insulated glazing with air-seals and specially developed thermally-broken window frames.
Airtightness:
Building envelopes under the Passivhaus standard are required to be extremely airtight compared to conventional construction. Air barriers, careful sealing of every construction joint in the building envelope, and sealing of all service penetrations through it are all used to achieve this. Airtightness minimises the amount of warm (or cool) air that can pass through the structure, enabling the mechanical ventilation system to recover the heat before discharging the air externally.
Ventilation:
Mechanical heat recovery ventilation systems, with a heat recovery rate of over 80%, are employed to maintain air quality, and to recover sufficient heat to dispense with a conventional central heating system. All ventilation ducts are insulated and sealed against leakage.
Space heating:
In addition to using passive solar gain, Passivhaus buildings make extensive use of their intrinsic heat from internal sources – such as waste heat from lighting, appliances and other electrical devices (but not dedicated heaters) – as well as body heat from the people and animals inside the building. Together with the comprehensive energy conservation measures taken, this means that a conventional central heating system is not necessary beyond the recovery of heat by the heat recovery ventilation unit if the heating load is kept under 10W/m².
Lighting and electrical appliances:
To minimise the total primary energy consumption, low-energy lighting (such as compact fluorescent lamps), and high-efficiency electrical appliances are normally used.
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