Building a Green Home

A green house is a building that requires little energy to run; specifically for space heating. This can best be achieved by combining passive design strategies with the most efficient modern materials and technologies.

Passive design strategies involve utilising the free energy provided by our environment without relying on mechanical systems. This strategy alone in our climate is not sufficient to produce a comfortable modern home but when actively assisted by powered machinery can result in a home with only a fraction of the running costs of a traditionally built home.

The first principal to building a green house is to consider the relationship between your home and the environment. To achieve this you must consider the following:

Key Elements of a Green House

Orientation (Passive) - The layout of your site and the position of the house will determine the amount of free solar energy your home receives.

Internal layout and external design (Passive) - The layout of the rooms, the orientation to the sun, position and size of windows should be designed to optimise the use of free solar energy

Building Fabric – A house should be built to be super insulated, airtight yet ventilated and with minimal thermal bridging.

Technology – Use renewable energy sources where possible. Consider innovative & efficient heating / cooling technologies. Use energy efficient house-hold appliances, e.g. low energy light bulbs, Triple A rated electrical appliances etc.

Conserve Energy - The final component of reducing our energy requirements is a life style change. We must learn to use energy wisely and including remembering to turn things off when not needed.

1) Orientation

The orientation of a building is concerned with the gaining and controlling of solar energy that a building receives. Careful consideration must be given to determine at what time of the year solar gain will be beneficial for thermal comfort, and when it should be blocked with shading. By strategic placement of items such as glazing and shading devices, the percent of solar gain entering a building can be controlled throughout the year.

Fig. 1 – Sun Path Analysis to Predict Direct Solar Gain

2) Internal layout and external design

Careful arrangement of rooms completes the passive solar design. A common recommendation for residential dwellings is to place living areas facing solar noon and sleeping quarters on the opposite side.
Fig. 2 – Design Used to Control Direct Solar Gain

3) Building Fabric

Super Insulating - High levels of insulation reduces the heat lost during the winter and the heat gained during the summer to extremely low levels. It then becomes very easy to keep the home at a comfortable temperature with very little energy. Surfaces in the home will also remain at a constant temperature and enable the home to be kept within safe humidity levels for occupants, furnishings and electronics.

Reduce Thermal Bridging - Heat will flow through the path of least resistance such as wood, metal or certain foundation materials. Therefore it is important to not only have high insulation values, but to eliminate thermal bridges from the inside of the home to the exterior that are common in typical construction. Thermal bridging will waste the time and money spent on extra insulation if left unchecked.

Airtight Construction - Building an airtight thermal envelope is important for energy savings, humidity control and ensuring the longevity of the building structure. Gaps in the building envelope will allow moisture to seep in, raising humidity to unsafe levels in the home and damaging the structure of the home over time.

High Efficiency Windows - Windows in a green home must be extremely efficient as well to complement the super insulation. To achieve this they should feature the following:

• Triple glazing with two low-e coatings
• “Warm Edge” spacers between the panes of glass
• Super-insulated frames

Mechanical Ventilation with Heat Recovery - Proper ventilation of a green home is critical especially due to the air tightness in the home that does not exchange the stale air with fresh outdoor air very much at all. Simply opening windows is not an energy efficient method and therefore a mechanical

Fig 3 – Diagram of Passivhaus Building Principals

ventilation system in the form of an HRV or ERV is used to exchange stale air from the most polluted rooms (kitchen, bath, utility) and fresh air is vented into the habitable rooms (living room & bedrooms). A Heat Recovery Ventilator (HRV) or Energy Recover Ventilator (ERV) is used in order to recover 75% to 95% of the heat by passing the warm exhaust air past the incoming cold air in a method that does not mix the two streams in order to make sure only fresh air is being vented into the home and no air is being recirculated.

4) Innovative & Efficient Technology
The key use of energy in a home is for light, power and heat. Low energy lighting and household appliances are already widely available and getting more efficient all the time. The heating requirement for an energy efficient green home should be such that usually the home can be heated by simply heating the fresh air that is being brought into the home via the mechanical ventilation system. Various methods can be used to heat the incoming air inline which eliminates the need for additional ducting in the home. Some of the common methods to heat the air in a Passive House include the following:

• Small condensing oil or gas boiler
• Small biomass fuel boiler.
• Compact unit for all in one heating, ventilation and domestic hot water

5) Conserve Energy
We must learn to use energy efficiently. This will require a conscious change to our behaviour and this may be the most difficult of all the changes to make. Even here we may get a helping hand from technology as low cost energy feedback displays providing real-time information regarding energy consumption is becoming available to homeowners so we can see how much energy we are actually using (costing ourselves). It has been proven that the use of these systems can significantly alter energy using behavior.

Conclusion
It is in our own self interest to build more energy efficient homes as the initial additional capital costs incurred will be rapidly offset by immediate and substantially lower energy bills. In Ireland, it is calculated that a typical house built to the German Passivhaus standard instead of the 2002 Building Regulations would consume 85% less energy for space heating and cut space-heating related carbon emissions by 94%.

Related Links
Sustainable Energy Ireland (SEI)
Commission for Architecture and the Built Environment UK (CABE)
Passivhaus UK