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Solar Hot Water System

Home >> Solar Hot Water System

This is a dhw system which utilises solar energy from the sun. It collects the radiant heat waves in a solar collector usually located on the roof. A simple solar collector consists of a thin vessel painted matt black with piping attached flowing to and from a hot storage vessel. It is covered with double- or triple-glazing and backed by thermal insulation material. The collector is sited at a convenient position to catch the solar heat, usually at an angle of 400 and facing south.

Designs of solar heating can vary, and because of the unreliable weather in Great Britain, it would not be used in any dwelling as the only form of heating for water. Generally, cold water is supplied to a warm store vessel which is heated by solar energy; the water then passes onto the normal conventional hot storage cylinder and is supplied with additional heat (if required) by a boiler or electric immersion heater. Note that in the system shown opposite, the solar collector is fitted above the cold feed cistern. This causes no problems because the primary circuit from the solar collector forms part of a closed system. The water in the primary circuit is made to circulate by means of a pump which is switched on automatically should the temperature in the top of the collector be higher than that in the base of the hot storage vessel. However, it is possible to design a gravity system, providing the collector can be located sufficiently below the warm store vessel to allow circulation to take place.

Thermal performance

Based on a long-term average temperature in London, the system should supply an approximate percentage of that indicated in the following table_ However, the amount of solar energy supplied to the dhw system will vary from area to area, and will depend upon the effectiveness of the solar collector and its location. It should be remembered that trees and buildings causing shade will sig- nificantly reduce system performance.

  %   %
January 2 July 13
February 5 August 13
March 6 September 12
April 10 October 8
May 12 November 4
June 13 December 2

Design considerations

Due to temperature changes the temperature of the heat transfer liquid could vary from about — 15°C to as high as 200°C, when not circu- lating. Where water is used for this medium (see figure for example of this) it will be necessary to prevent the temperature from rising above 100°C by incorporating a pressure relief valve as a minimum requirement, discharging its contents to a safe location. To prevent damage due to excessively cold conditions, an anti-freeze solution may be added; alternatively the system will need to be drained in winter. Usually planning permission will need to given by the local planning authority before a solar heating system can be installed.

Wet Central Heating Systems

Originally, systems were designed to circulate hot water by convection

Radiant Heating

This is a system of heating designed to raise the temperature of a room space

Solar Hot Water System

This is a dhw system which utilises solar energy from the sun.

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