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The importance of stratification

In order to quickly achieve useful temperatures in a thermal store it is important to add energy to the top of the store first and then continue to progressively raise it's temperature from top to bottom. Stratified charging has a positive effect of the efficiency of the solar collectors as it maintains the collector temperature at the lowest possible level.

There are several ways of achieving stratified charging.

Tank design

A tall, slim thermal store will offer better solar performance than similar shorter, wider store. In most smaller domestic applications simply using a store with this profile will offer good results.

In commercial applications with larger thermal stores or in systems for central heating one of the following solutions should be employed to offer a higher overall system efficiency.

Stratified Charging using a divertor valve

A three way divertor valve may be combined with suitable temperature controls to prioritise the heating of the upper part of the buffer store. This type of arrangement is illustrated below.

Stratified charging of buffer using a three way valve
Stratified charging of buffer using a three way valve

Stratified Charging using the Tisun system

The stratified charging system developed by TiSun is a superior solution as it does not rely on any control or valve components. It has no moving parts whatsoever.

Instead it relies on the natural buoyancy of the hot water to prioritise charging of the tank from the top.

Proclean tank with stratified charging system
Proclean tank with stratified charging system

The principle of operation is simple. A finned heat exchanger coil is contained in the cylindrical heat exchanger which is mounted on the side of the tank. The hot solar fluid circulates through the coil. Colder water from the tank enters the heat exchanger from the bottom of the tank. This water is heated and rises upwards to re-enter the tank through one of the other three tank/heat exchanger connections.

When the top of the tank is cold the warm water enters the tank through the upper heat exchanger connection. As the top of the tank gets warmer, the flow moves to the lower heat exchanger connections.