Making a difference at home
The Village guide to sustainability in the home assesses different types of sustainable energy and the government grants available for them, gives guidelines on how to calculate your energy costs and investigates a model for an Irish eco-village.
In Ireland, a horizontal surface of one square meter receives an average of between 1000 and 1100 kWh of solar energy per year, through direct (40 per cent) and indirect (60 per cent) sunlight. There are a number of ways in which this energy can be harnessed for use in the home.
Passive Solar Design involves choosing a sheltered location to build on, constructing a compact building form with high levels of insulation or positioning a house where passive solar heating and daylight can be maximised.
Direct Gain is the simplest passive solar design technique. It necessitates glazing to be concentrated to the south facade and minimised to the north, allowing sunlight to enter the house, where it is absorbed in the walls, to be released slowly at night. It is recommended to use high performance double-glazing, with a low emmisivity coating.
An Active Solar collector can provide up to 50 per cent of the annual hot water demand of a typical home. Commonly used for water heating, four square meters of a solar collector can provide about 80 per cent of hot water needs in summer and 20 per cent in winter for a typical family, reducing demands on conventional heat sources.
Typical design involves a flat-plate collector mounted on the roof which is heated by the sun, thereby heating fluid within pipes in the collector. The fluid is moved to a storage cylinder by use of a pump or by gravity, where it is used for heating of space or water.
Another design involves an evacuated tube collector instead of a flat plate, where the tubes collect energy and transfer it to a heat transfer fluid. The absence of air in the tubes greatly reduces heat loss from the system.
A typical solar water heating system, correctly installed, has a payback period of between 7 and 15 years. Little maintenance is required and systems generally come with a 10 year warranty. Average prices vary greatly, depending on the number of people in the house, roof specifications and installation. One Irish company estimated costs for a house with 2-4 people, a 22 tube panel, a cylinder and installation at €7,500. Another estimated at €5,400, excluding grants.
Photovolatic (PV) solar panels actually generate electricity, unlike the previous methods. The PV cell consists of one or two layers of a semi conducting material, usually silicon. When light shines on the cell it creates an electric field across the layers, causing electricity to flow. PV systems generate no greenhouse gases, saving approximately 325kg of carbon dioxide emissions per year, adding up to about 8 tonnes over a system's lifetime.
The power output of a PV cell depends on its efficiency and surface area, as well as the intensity of sunlight striking its surface. PV panels generate more electricity on bright days, but also work with just normal daylight. PV systems can produce AC current compatible with appliances, and operate as stand-alone systems or interconnected to the electricity grid. The latter system supplies power back onto the grid and electricity is drawn from it at periods when demand in the home exceeds the PV output, removing the need for batteries.
PV panels ideally are orientated facing south, but they still produce around 80 per cent of their optimum output when facing east or west. A number of other components may make up the whole system, including a DC-AC power inverter, a battery bank, a system and battery controller and auxiliary energy sources. An “average” PV system is again difficult to quantify, but one optimistic estimate put it at €4,650 for a regular household, with a grant of €780, leaving the householder with a net cost of €3,850.
Currently in Ireland it is not possible to sell excess power back to the grid.
Ground Source Heat Pumps
Also known as geothermal heat pumps, this method of sustainable energy supply is used for space heating and cooling, as well as water heating. Heat pumps are based on the fact that the earth beneath the surface remains at a constant temperature throughout the year and that the ground acts as a heat source in winter and a heat sink in summer.
In Ireland the ground maintains a constant temperature between 11 degrees Celcius and 13 degrees Celcius. Heat pumps transfer the heat stored in the earth or in ground water to buildings in winter and the opposite in summer for cooling.
An example of a heat pump is a refrigerator; heat is removed from the refrigerator's compartments and transferred outside of the cool refrigerated compartment. Through compression heat pumps can extract heat at low temperatures and release it at a higher temperature so that it may be used again.
All such systems have an external (ground) loop and an internal (building) loop, each containing refrigerant. Secondary loops that contain water are popular for ground loops because they are not pressurised, so cheap plastic tubing can be used and because they reduce the amount of expensive refrigerant required.
Depending on the amount of space available and the type of ground around the house, different types of heat pumps can be installed.
In an Open Loop system the thermal transfer fluid (water) does not return and is a ‘once through' type system. This system draws water from a well or lake, passes it through a heat exchanger in the building, and then discharges it. The water can be discharged to a stream or lake, or injected into a second well.
A Closed Vertical Loop system uses a single well (or borehole) with the fluid in the pipe constantly recirculated to and from the well. If a borehole is used, it can go as deep as 100m and is commonly filled with a bentonite grout surrounding the pipe to provide a good thermal connection to the surrounding soil or rock. It is typically used when there is limited square footage available.
The Closed Horizontal Loop is placed below the frostline (1 to 2m underground). In this system the pipe is often laid out flat or as a helix to increase the contact area per length. The horizontal loop requires a large area of flat space or a body of water.
Initial costs of heat pump systems are generally higher than conventional central heating, due to the high cost of installation of the ground collector (one estimate given was €27,000). That said, it is among the most energy efficient and cost efficient heating and cooling systems available. For every unit of electricity used to operate the heat pump, up to four units of heat are generated, and payback is typically 8 to 10 years, with a life expectancy of over 20 years.
Also known as bioenergy, this sustainable resource is derived from organic matter, such as residues from forestry, agriculture and industry, or from purpose grown crops.
Wood is a carbon neutral fuel as it absorbs as much CO2 when it grows as is released when it burns. Wood fuel takes 5-20 years to grow, whereas fossil fuels such as peat and coal were formed over thousands of years.
Wood fuel comes mainly in chips and pellets. Chips are cheaper than pellets but bulky, meaning they are largely unsuitable for domestic use. Pellets have the advantage of being small, of uniform size and composition, are easy to ignite, dry and create little ash. They flow freely through feeding mechanisms such as hoppers, making them ideal for automatic appliances.
Once manually filled, the hopper supplies fuel to the stove, allowing it to operate independently for 20-40 hours. For larger systems it is possible to install a completely automatic system, with the storage facility adjacent to the boiler. The pellets are bulky and require about 3 times the storage space of oil. Prices vary between suppliers, depending on whether pellets are bagged or loose, and are often sold in quantities from 10kg up to 3 tonnes.
Pellets are burned in a boiler or stove, providing full central heating and hot water. These appliances use thermostatic controls and fans to distribute warm air around the room so they are safer than traditional stoves, which rely on radiated heat to warm the room, making the rooms temperature uneven and the body of the stove hot.
The Greener Homes Scheme provides assistance in the form of grants to homeowners who intend to purchase a new renewable energy heating system for either new or existing homes, with the aim of increasing the use of renewable energy and sustainable energy technologies in Irish homes.
Eligible products include a new wood pellet, solar or heat pump based heating system, installed by professionals registered with Sustainable Energy Ireland (SEI), who are administering the project. For solar heating, a hot water system and / or a solar space heating system are eligible.
In terms of heat pumps, a horizontal ground collector, vertical ground collector, a water to water or an air source qualify. Wood chip or pellet stoves and boilers also meet the criteria. Only products on the list of SEI approved products are allowed.
If a combination of technologies makes sense in terms of reduced overall CO2 intensity, capital costs, value for money and operating service it is possible to apply for a second grant. An example of this would be a Wood Chip or Pellet Stove for room heating combined with a Solar Hot Water Heater (to a maximum collector area of 6m2), or a Heat Pump and Solar Hot Water combination.
Solar Thermal Space and/or 2300 per m2 (max12m2)
Hot water heating
Heat Pump Horizontal ground collector 24,300
Heat Pump Verticalgrouncollector 26,500
Heat Pump Water (well) to water 24,300
Heat Pump - Airsource 24,000
Wood Chip/ PelletStove 21,100
Biomass / Wood pellet Stove 21,800
with integral boiler
Wood Chip/Pellet Boiler 24,200
Application forms are available from www.sei.ie, as well as product overviews, product buyers advice, registered product and installer lists and model contracts to use as a basis for agreeing a contract with your chosen installer/supplier.
Deciding which energy source to use for the practice of sustainability in the home requires knowledge of what system is right for your energy needs, based on your energy use patterns.
Your electrical consumption and costs
Collect your last six two-monthly ESB bills, covering a one-year period. Calculate your electrical energy use by subtracting the “Previous” reading on the first bill from the “Present” reading on the sixth bill. This gives you the total number of “units” of electricity used in the year. These units stand for kilowatt-hours (kWh), which are used for measuring energy use. To calculate your electrical energy costs multiply cost per kWh, or “unit”, i.e. the tariff you pay, by the number of kWh used. This is the cost of your electricity. Add the two monthly standing charges x 6 and then the VAT to get the total cost of electricity.
Heating Consumption and Costs
Calculating the amount of energy used for heating will vary depending on the type of fuel you use to heat your home. If you use natural gas or electricity the procedure is very similar to the one shown for electricity. The number of kWh, or “units”, and costs are simply totaled for a one-year period and added to the standing charges and VAT.
The procedure for other fuels is also simple. List all the fuels that you use for heating - perhaps these include coal or oil - and estimate how much you use in a year. Now use the Energy Content of Fuels table below to covert the fuel amount purchased into energy consumed in kWh.
kWh = Kilowatt Hour. One Kilowatt Hour is equal to 1000 watt hours. One watt-hour is the amount of energy expended by a one-watt load (eg, light bulb) drawing power for one hour.
Your House's Energy Rating
Your house's “energy rating” is a figure that compares your annual energy usage to the internal floor area of your home. In other words, it measures your annual energy consumption per square metre of floor area in a particular year. It is quoted as kWh per m2 per year. To calculate your “energy rating”, first estimate the approximate floor area of all the rooms in the house which are heated. Do not include garages or outhouses unless they are heated or have high electrical loads - perhaps a tumble dryer or washing machine.
The annual total number of kWh (or units) used for electricity and heating, calculated previously, are added together. This figure is then divided by the floor area. This will give you the energy rating for your home, for a particular year.
For example, a house of 120m2 area, which uses 7,002 kWh of electricity and 27,456 kWh of heating energy in a year, has an energy rating of 287 kWh / m2 per year.Similarly, having spent €890 on electricity and €985 on heating oil this home will have a cost rating of m15.61/ m2. If gas is the source of home heating an expenditure of €686 will result in a lower cost rating of m13.45/m2.
The values you arrive at will depend on how many people occupy your home and your specific heating patterns. The same is true for the savings you will be able to make. For example, poorly insulated older houses will benefit substantially more from additional insulation than newer highly insulated ones.
For more information see www.sei.ie
Sustainable CommunityThe Village
One of the main organisers of The Village in Cloughjordan, Co Tipperary, said that they were “not trying to build a green housing estate. If we wanted to do that we could have done it a long time ago. We are building a community”.
The project is Ireland's first eco-village, an experiment in environmentally sustainable living inspired by other similar communities around the world. Davie Phillips explained that he and others in Sustainable Projects Ireland (SPI) had been working since 1999 to create the basis for the eventual construction of a community consisting of residencies, community buildings, and educational and cultural centres.
Currently there is planning permission for 132 houses and 4 community buildings. SPI are not actually selling houses in The Village. They sell fully serviced sites, ranging from €40,000 to €140,000, on which buyers will then construct their own buildings. Some will self-build, others will join together to build clusters of houses and apartments with communal gardens. A notably sustainable feature of the project is the District Heating plan, whereby all buildings will be provided with hot water from a central pellet and coppiced wood-burner.
Sites are still available. See www.thevillage.ie for more information.