| An Evaluation of the Greenhouse Solar Hot Water System. |
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| An Evaluation of the Greenhouse Solar Hot Water System. |
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When assessing the environmentally beneficial changes that could be made to the Greenhouse we examined issues such as energy usage, insulation and building materials. It was important to address our energy efficiency before we installed renewable energy sources. The building now incorporates triple and quadruple glazing, recycled paper, cork and wool wall and roof insulation and energy efficient light bulbs. Once we had reduced our energy requirements we then examined the potential for solar energy, for both electricity generation and water heating. Mindful use of energy is a key consideration in all activities within the Greenhouse. One of the first steps in working out whether you can benefit from a solar water system is to examine the resource available to you. Refer to the map in section 2 to compare the solar resource at your location with that at Norwich. The Greenhouse has an almost south-facing roof at an angle of 45°, a different orientation and location will alter the efficiency of your system. The best yield is obtained from a collector situated on a surface or roof at 20°-50° to the horizontal (pitch), facing roughly to the south (between south-west and south-east). Figure 13 shows how the pitch and the direction affect the potential resource available13.
Be aware that shadows cast by objects such as chimneys, dormer windows and trees will reduce the performance of solar collectors. Calculating Your Hot Water Usage The next step is to work out your hot water usage. A rule of thumb is to allow 40 litres of hot water per person per day so a family of four would use about 160 litres per day. An area of 1 square metre of collectors should provide 45 litres of hot water per day, so around 3½ m2 would be typical for a family house. One Thermomax 30-tube system covers 3.9 m2. A standard domestic water cylinder holds 200 litres (45 gallons). This will provide enough hot water for 1 deep bath (60 litres), 3 showers (45 litres), a washing machine load (55 litres) and water for washing-up. Think about your water usage in relation to the solar resource. The water is hottest in mid to late afternoon but with a well insulated tank you can store it for the following evening/morning. However, if you use half the tank, cold water will fill up the space so it is wise to make efficient use of the hot water. The cost of installing a solar water system varies greatly, ranging from £1500 to £4500, with a lifetime of 20-25 years and annual output of between 1000 and 1500 kWh per square metre8. The running costs are about £6 per year. At the current operating rate the Greenhouse system will pay back the outlay costs in 10½ years. This is twice the size of a standard domestic system but the payback time is likely to be similar. You may be able to obtain financial assistance from your local authority to install solar water heating. Contact the local officer in your area who will be able to advise on whether grants are available. The Greenhouse has shown that installing solar water heating can have impressive environmental and economic benefits. If you are considering installing solar water heating and would like to know more about the Greenhouse system, please get in contact. See the bottom of this page for our contact details.
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| An Evaluation of the Greenhouse Solar Hot Water System. |
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