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An RVR solar water heating systems may be designed for a new home or as a retrofit installation for an existing home.

Design

New Houses

Compliance with the building regulations is a key requirement for new houses. Part L of the current Irish building regulations require that there is a reasonable minimum level of energy provision from renewable energy technologies. For thermal energy, this is defined as 10 kWh/m2/annum contributing to energy use for domestic hot water heating, space heating or cooling.

A solar water heating system may be used to partially or completely meet this requirement. Compliance with the building regulations is checked using the DEAP (Dwelling Energy Assessment Procedure) software. The aperture area and efficiency values of the collector will be required for the DEAP calculation.

A solar water heating system will easily allow full part L compliance to be achieved for houses with a floor area of up to about 250 m2. For larger houses, it may be necessary to consider a second renewable energy technology such as a biomass boiler or heat pump.

Retrofit Installations

Compliance with part L of the building regulations will not usually be an issue for retrofit installations. However, the purchaser of the system may wish to claim a grant such as the Greener Homes scheme.

The output of the solar water heating system may be calculated using a software-based design tool. However this approach may be over elaborate for small domestic systems. Application of simple rules of thumb will normally suffice.

Rules of thumb

Solar water heating Systems sized based on the number of people living in the house.

Collector sizing per person

For vacuum collectors - allow 0.8m2 - 1.0m2 of aperture area. (do not size systems exist on the number of tubes or any measure of capacity, other than the aperture area!)

For flat panel collectors - allow 1.02 to 1.2 mm2 of aperture area.

Water heater sizing

If using a twin coil tank, allow 50-70 litres per person.

Example
  • For a house with 5 occupants;allow 42 - 5m2 of vacuum collector aperture area.
  • Select a twin coil water heater with a capacity of between 250 and 350 litres.

Typical Solar Water Heating Systems for Houses

Twin coil tank based system

Image:Dual coil tank.jpg

This is the most common system design. Solar energy is transferred to the water through the lower coil of the tank and the back up boiler energy is put into the upper coil of the tank. It is simple, compact and inexpensive. In a retrofit installation, it will normally be necessary to change the existing water heating tank for a twin coil model.

Click here for more information on the range of solar water heating kits available from RVR.

Solar Pre-heat tank

This is an option in applications where one does not want to change the existing water heater. A single coil, solar pre-heater may be installed upstream of the existing water heater as shown in the diagram. The preheater tank should be sized at about 50 L per occupant.

Heat exchanger

Image:Heat exchanger.jpg

Fitting a heat exchanger onto an existing cylinder may be a good option where the existing water heater is of an adequate size to store the solar energy and in good condition. RVR Energy Technology supplies a range of heat exchanger kits, which may easily be fitted to existing water heaters. Click here for details