Solar Energy: Your Questions and Answers


SolarUK: Glossary

Pre-feed cylinder

A cylinder placed between the cold water feed and the existing hot water cylinder.

Assuming the existing hot water cylinder is being retained, a separate pre-heat cylinder is placed between the cold water feed and the existing hot water cylinder. This new pre-heat cylinder raises the temperature of the water which enters the existing cylinder, thus reducing the load on the conventional heat source. The existing heat source would then only increase the water temperature further to the desired set point if and when required. In some cases there will be no need for further heating if the desired water temperature has been achieved by the pre-heating alone. Pre-feed/pre-heating is an efficient use of low temperature heat inputs and also a convenient arrangement in many circumstances. As the size constraints of many buildings do not allow for an increased volume (larger vessel) of stored hot water in the desired location, a pre-feed/pre-heat system is often favoured in these situations. Many large buildings will duplicate plant as protection against service/maintenance downtime, which can sometimes be used in a manner that increases the performance of renewable energy sources and lowers the energy consumption of the building.

A solar pre-heat cylinder will normally perform better (that is, be more efficient) than a combined heat source cylinder as the solar pre-heat cylinder will often be at lower temperatures and so heat/energy transfer can occur in less favorable climatic conditions.

Going a step further, sequential heating of different coils/ different volumes of water provides the best service provision as recovery rates through solar heating alone are reduced while efficient use of the energy available is maintained. By sequential switching of solar heat destinations, the concept of pre-heating can still be achieved, as whenever the water surrounding a solar coil becomes saturated with heat (lowering the efficiency), solar heat can be redirected to a coil which is surrounded by pre-feeding water. (I.e. solar energy heats the water surrounding the bottom coil of a primary cylinder first, the top being heated by just a gas-fired heating coil. Next solar energy is directed to heat the water surrounding the top coil of a pre-feeding cylinder, and then redirected to heat the bottom coil of the pre-feeding cylinder).

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Other Associated glossary terms : Commercial

Solar Thermal
The collection of the sun's energy as heat rather than converting it to electricity.

Vacuum Tube Solar Collector
This is a technology that uses a glass tube, think of a long thermos flask to insulate the solar collector and ensure that effectively all solar energy is retained.

Feed in Tariff
A method to reward the producer of renewable energy (electricity) by paying a fixed amount of money for each unit of electricity generated.

Recirculation - pumped secondary
Pipework carrying secondary hot water.

Sequential heating arrangement
The heating that occurs as the solar thermal system heats the water before the conventional heat source provides any necessary additional heating.

Heat store
Stores the suns energy as heat captured by the collector.

Refers to any period when the heat transfer fluid is not circulating, even though the solar panel is receiving the suns energy.

Primary and secondary systems
This refers to the water travelling round the boiler and the water in the cylinder which is heated by it.

Stratification / de-stratification
The layering of hot water on colder water.

Expansion vessel
A trapped volume of pressurised air or gas inside a steel vessel to allow for the expansion that accompanies temperature increases.

Buffer vessel
A tank storing heated water in anticipation of variable demand requirements.

Pre-feed cylinder
A cylinder placed between the cold water feed and the existing hot water cylinder.

Any pipe with several outlets to or from other pipes, or a junction of pipes.

A water storage vessel, which has the capability to increase the temperature of the water contained within it.

The controller compares the different temperatures at specific locations in the solar systems circuit.

Circulation module / Pump module
Operates the heat transfer system.

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