Thermal Stratification

The density of water is a function of its temperature – see figure 1. When water is warmer than 4°C it gets less dense for each increment in degree Celsius. This allows for thermal layering; where warmer water is stored on top of colder water – defined as “thermal stratification”.

Figure 1 – Density of water as a function of temperature

Thermal stratification is possible as water becomes less dense when heated, meaning water weighs less per unit volume. Therefore, warmer water will be lighter and colder water will be heavier. Due to this, there will always be a level of “self-induced” thermal stratification in a water storage. However, this can be greatly disturbed by undesirable and uncontrolled water flows, which stirs the otherwise thermally separated layers together and mixes them into a uniform temperature.

When referred to a stratified storage tank, it is meant that thermal stratification is actively maintained – thereby no mixing of the thermal layers occurs. It requires a stratification device to achieve this, and EyeCular Technologies has developed a relatively cheap and very effective stratification device – StratiFlexTM.

Figure 2 shows an equal amount of energy stored inside two different tanks. The first tank is thermally stratified, and the other is fully mixed. These two temperature profiles are an example of how a stratification device will affect the energy distribution inside a storage. The first temperature profile depicted in figure 2 will yield better working conditions for a heating systems, even though both tanks have an equal amount of energy.

Stratification vs. Fully mixed

Figure 2 – Stratification vs. Fully mixed