It’s time to consider solar thermal

When it comes to installing hot water systems, it’s important to consider solar thermal water heating says John Foster, Product Manager at Heatrae Sadia.

Today, if a commercial or public sector building is in need of a new water heating system and has a high demand for hot water, perhaps having a large number of sinks and basins, catering facilities or showering facilities on site, it’s always worth considering the installation of a solar thermal system. 

Taking this approach can save energy thereby reducing fuel costs and carbon emissions and also helping to ease the burden of the CRC Energy Efficiency Scheme.  So, when it comes to installing new heating systems, it is important for building services managers to consider renewable technologies, such as solar thermal water heating, to lower energy consumption and fuel bills. 

Renewable technology

Solar thermal systems collect free solar radiation, which is available throughout the year – even on cloudy days.  More solar radiation can however be collected in spring, summer and autumn, as the sun is higher in the sky than it is in winter. 

The solar energy is collected via flat plate panels or evacuated tubes positioned on the  roof of a building, which is then used to heat water stored within a specially designed cylinder.  The cylinder then serves taps, showers and any appliances with a hot water feed.  Where necessary, a supplementary boiler or immersion heater will bring the water up to temperature (at least 60°C to kill legionella bacteria). 

Even though this type of water heating system still relies on fossil fuels to a certain degree, the solar radiation nonetheless provides a high proportion of hot water, especially during sunny summer months.  Systems are capable of providing all of a building’s hot water during the summer and up to 60% year round.  And even on cold, cloudy days the solar radiation will still be pre-heating the water in the cylinder, saving gas or electricity.

However, we believe that optimum energy savings and performance can only be achieved with a high quality, correctly sized solar thermal cylinder, with an appropriate proportion of its volume dedicated to solar energy and the inclusion of a dedicated solar coil.   

Importantly, cylinder sizing needs to allow for the fact that in the UK solar gain differs throughout the year.  As we have said, during the summer months solar energy can provide as much as 100% of a building’s hot water requirements, but during the winter months this will be significantly reduced because there is less sunlight and fewer daylight hours. 

As the usable hot water derived from solar energy will vary, it’s likely that the facilities will sometimes be almost totally dependent on the supplementary fuel source (usually gas or electricity) for water heating.  So, when there is little solar gain, the cylinder should still be capable of meeting normal hot water demands – so the non-dedicated solar volume must be sized accordingly.

Look at the options

Another appropriate option for large buildings that have the potential to collect significant amounts of solar energy is to install a solar thermal preheat cylinder.  Being totally dedicated to solar energy, this ensures a building receives the greatest benefit from its solar collectors.  The preheat cylinder stores the solar energy and passes it on to the main cylinder as water is drawn off.  In this case the main cylinder should again be sized to meet normal hot water demands. 

We also believe that a true solar cylinder should have a dedicated solar heating coil.  This is something that some cylinders lack, simply using heating coils designed for traditional boiler systems.  With an increased surface area to give better thermal transfer, a dedicated coil will provide maximum efficiency and heat output from the solar energy. 

Furthermore, solar thermal cylinders should also be well-insulated.  After all, once the sun’s energy has essentially heated up the water for free it’s crucial for heat loss to be minimised. 

It’s worth mentioning that even if a business or public sector organisation isn’t quite ready for a solar thermal installation, when a new hot water system is required it could still be worth becoming ‘solar ready’ by installing a solar thermal cylinder with two coils.  Then the remaining parts of the system, such as the collectors and pump station, can be added in the future when the necessary funds become available.

Flexible solution

Megaflo Commercial, Heatrae Sadia’s new range of unvented cylinders designed for commercial and industrial applications, includes eight cylinders suitable for use with solar thermal technology, in capacities of 400 to 2,500 litres.  To increase the storage capacity, any of the cylinders can be installed in parallel, in any combination.   

An unvented system will provide powerful, mains pressure hot water for the whole building, without a significant loss of performance if taps and showers are used simultaneously.  This type of water heating system is also very flexible, as the cylinders can be sited almost anywhere. 

Megaflo Commercial boasts high flow rates, fast recovery, the option of a unique 10 bar operating pressure and highly effective insulation to minimise heat loss.  The range also includes extra protection against the risk of legionella; not only do we offer an optional de-stratification loop to thoroughly circulate hot water, but we have also designed the product with the requirements of HSE document L8 in mind. 

This strongly recommends that cylinders should be serviced and cleaned periodically – and Megaflo Commercial allows for this via 125mm inspection hatches.  We have also ensured there are no dead legs; even though these are a potential breeding ground for legionella, not all manufacturers address this in the design of their cylinders.

Solar thermal water heating can help to save energy and fuel costs, so it’s always worth considering this technology when a new water heating system is required, especially if the building’s occupants use a large amount of hot water.  However, to ensure maximum savings are achieved, it is essential to select a high quality and high performing solar thermal hot water cylinder, and to ensure that it is correctly sized for the application.

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