Solar water heating for the commercial market

Published:  19 September, 2006

Yan Evans
Responding to pressure from consultants — Yan Evans

Andrews Water Heating has developed a packaged approach to applying solar energy to the commercial water-heating market.

While renewable energy such as solar and wind is in plentiful supply it cannot be relied on to deliver power on instantaneous demand. The application of solar and wind energy thus requires instantaneous backup or energy to be stored.

However, as Yan Evans, business-development director with Andrews Water Heaters, points out, one application that lends itself to effectively storing energy is domestic hot water.

While it is increasingly common practice to generate domestic hot water on demand using high-power direct-fired water heaters with just a small amount of storage, the provision of DHW is traditionally based on storage to meet sudden demand — with longer-term recovery of that stored water.

Packaged solution

It is just that principle that Andrews Water Heaters has re-embraced in developing a packaged solution for DHW using solar thermal panels.

Yan Evans explains that this is not a solution for individual houses but for larger-scale projects such as hotels and residential accommodation served by central plant. ‘There is an increasing trend in blocks of flats,’ he says, ‘for flats to have heating and hot water provided via an hydraulic interface served by centralised heating plant. This approach makes possible individual heat metering, the technology of which is becoming cost effective. The trend is away from flats having individual boilers to centralised heating systems — as it used to be, but now with individual metering.

The Andrews approach is to design engineered solar solutions to work alongside direct-fired water heaters in, for example, hotels, student accommodation, care homes and other properties served by central plant.

’Our target is for 60% of the DHW requirement over a year to be provided using solar energy. In summer, this fraction could rise to 95 or, even, 100%. It is important, however, that the primary heating appliance can meet the total demand,’ he explains.

Those figures are chosen on the basis of what can be achieved with a reasonable size of plant and storage.

Response

The concept has been given the name SOLARflo, reflecting existing brand names such as Supa-Flo (gas-fired condensing water heaters for instantaneous operation or with a buffer store), FASTflo (continuous-flow wall-hung balanced-flue water heaters) and MAXXflo (condensing storage water heater).

It is being launched at the M&E Show at Olympia in London on 10 and 11 October.

Yan Evans tells us that SOLARflo has been developed in response to pressure from consultants over the last year for a DHW package with integrated renewable energy. The package includes plate solar collectors, a variety of roof mountings, solar-side pump station, controls and solar hot-water cylinder. To complete the package, Andrews will also commission the system. The plate solar collector has been chosen for its lower cost compared with evacuated tubes and its ability to integrate with roof constructions. An evacuated-tube option will follow.

The demand is based on a general move towards using renewable energy and not on economic criteria. ‘We would not offer this concept on the basis of payback,’ says Yan Evans. Its attraction is due to the environmental benefits. With gas costing 2.5 to 3.5 p/kWh, the payback of a solar system is 20 to 30 years.’

The economics can be improved by funding available for DTI low-carbon building programmes. 50% of the total installed cost, including commissioning, is available — with a cap of £50 000.

Control interface

The successful application of solar water heating depends heavily on the control interface between solar and primary water heating. The storage cylinder has to be larger than if it were just served by a boiler and has two coils — one for the solar loop and one for the boiler loop. In the case of direct-fired water heaters, a single solar coil inside the cylinder would be used to pre-heat the cold water inlet. Because solar heat is low grade, ideally the solar coil needs to be larger in size than the boiler coil.

A demonstration rig for solar water heating is to be set up outside the company’s premises in Wednesbury. It will enable the effectiveness of solar water to be evaluated against data from a weather station also to be installed on the site. Clients, installers and specifiers will be able to use this facility, and training can also be provided.



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