Getting the best from solar-thermal energy
Solar-thermal water heating is a virtual must for any project says John Foster of Heatrae Sadia, who provides a lot of tips for specifiers to achieve effective installations.
In this day and age, when a specifier or consultant is tasked with specifying a hot-water system for a commercial or public sector-building, solar-thermal water heating should always be considered. Solar energy — collected via panels or evacuated tubes positioned on the building’s roof — can provide a high proportion of domestic hot water, especially during the summer months.
For a solar-thermal system to work effectively and achieve optimum savings, the roof should ideally be south facing. South east and south west are also options, but it is important to remember that performance will be reduced in accordance with how far the angle varies from the direct south position.
If trees and other buildings are in view care must be taken to ensure they will not shade the collectors, especially in summer when there are obviously more leaves on trees.
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| To maximise the value of solar-thermal energy, the cylinder and its coil should be designed to maximise the use of solar energy and minimise heat loss. This cylinder is part of Heatrae Sadia’s Megaflo solar package. |
At the very least, a site survey should be carried out to establish the best location for the collectors, and which type (flat plate or evacuated tubes) is most appropriate. Some companies, Heatrae Sadia included, offer solar simulation software.
The actual roof type should not make a difference. Evacuated tubes or an A-frame can be installed on a flat roof, and fixing kits are available for both tile and slate.
If a site survey/simulation reveals that a solar-thermal installation is viable, it is important to choose high-quality components (which for simplicity can be provided as one package), or the energy savings might be completely negated.
For example, the hot-water cylinder used within a solar thermal installation makes an important contribution to the system’s overall efficiency, so it is important to choose a high-quality product with an appropriate proportion of its volume dedicated to solar energy as well as having a specific solar coil.
When there is little solar gain, the cylinder should still be capable of meeting the normal hot-water demands through a supplementary fuel source (usually gas or electricity). Therefore the non-dedicated solar volume must be sized accordingly. Further, knowing a cylinder’s dedicated solar volume is crucial for SAP calculations.
We also believe that true solar cylinders should have a dedicated solar-heating coil. With an increased surface area to give better thermal transfer, a dedicated coil will provide maximum efficiency and heat output from the solar energy. Solar-thermal cylinders should also be well insulated to minimise heat loss.
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| Virtually any roof lends itself to some type of solar-thermal collector. |
Meanwhile, to ensure they are choosing the highest quality solar thermal collectors, specifiers can look for the Solar Keymark. A high-performance absorber area will provide the best results.
The issues outlined above are what Heatrae Sadia really thought about when designing the Megaflo solar package, which comprises collectors, the cylinder, the pump station, controls and roof fittings. Unlike most manufacturers, we offer horizontal as well as vertical collectors (whether positioned in-roof, on-roof or on an A-frame) with in-roof sizes going up to 2.5 m — which is ideal for larger commercial buildings. We also offer fittings for slate or tile roofs, ensuring that our collectors can be fitted on every conceivable type of roof. We believe that few manufacturers have a solar package with such wide-ranging capabilities.
It is worth mentioning that even if a commercial or public sector project is not quite ready for a solar-thermal installation, it could still be worth being made ‘solar-ready’ by installing a solar-thermal cylinder with two coils. Then the remaining parts of the system can be added in the future when funds become available.
In today’s energy-conscious world it is essential to think about renewable options when specifying water-heating systems. And, to ensure maximum savings are achieved, it is equally essential to choose systems that are suitable for the application and are high-quality and high-performing.
John Foster is product manager with Heatrae Sadia.
