Two-zone principle

Advantages at a glance

Up to 100% more yield with solar systems

Up to 200% more capacity in the buffer tank

More energy through heat pumps or CHP systems

Reduction of the amortization period

Save fuel - every year

Hot water faster and for longer

How much heat fits into your buffer cylinder depends on how well the system stores, or rather stratifies, the heat in the buffer. Most systems work like a spoon in a latte macchiato and inevitably destroy the layering. Generated heat is fed into the upper buffer zone and removed from it for heating. Return water from consumers (radiators, underfloor heating, etc.), regardless of temperature, is fed back into the lower zone in an uncontrolled manner. This often leads to mixing of the desired temperature layers, so that only an average temperature is achieved. Sooner or later, it will not be possible to prevent destruction of the stratification due to downtimes.

How does the two-zone principle work?

The loading assembly ensures that the upper zone of the buffer becomes hot as quickly as possible and the lower zone remains cold for as long as possible by first removing the water from the middle. The discharge assembly only draws the heat from the buffer that is required for the respective consumer, thus making the buffer in the lower zone cold more quickly and keeping the upper zone hot for longer. The two-zone principle is the more efficient way to charge or discharge a buffer cylinder with heat. This is because only the most well-layered cylinder can still absorb heat when it is already relatively full and release heat when it is already relatively empty. The secret of this benefit lies in the fact that with good stratification, the cylinder is always hot at the top and always cold at the bottom (image, buffer 2-4), while the mixed cylinder is warm from top to bottom (image, buffer 1). The boundary between hot and cold should be as abrupt as possible. The fuller the cylinder is, the lower (image, buffer 3), the emptier it is, the higher (image, buffer 4) this limit is. In any case, a well stratified cylinder should contain as little hot water as possible. Our rendeMix multi-port mixing manifolds use a central third connection on the cylinder to ensure that the hot water is used first in order to create optimum stratification according to temperature level. In theory, this creates a clear separation between hot and cold because, as can be seen in the illustration, the hot water is drawn off first, reducing it to a small separating layer. This ensures that the buffer cylinder can be charged through to the bottom at the highest possible temperature if the consumption by the consumers is lower than what the boiler feeds in.

Loading

The loading module (rMix 2×3 or rMix 3×3) for connecting heat generators to buffer cylinders ensures that the upper zone of the cylinder heats up as quickly as possible, as it uses the warmer water from the middle of the cylinder first. This means that the cold water in the bottom of the cylinder remains untouched for longer, making the use of renewable energies and flue gas heat exchangers more efficient. In the video you can see our rMix 2×3 which is used as a return flow booster. The mixer is set to take water from the middle of the cylinder after the boiler circuit has heated up. If the temperature is too low, a certain amount of boiler water is added from the flow. If the boiler has heated the cylinder sufficiently up to the middle connection, cold water from the lower zone is only then added.

Discharge

The discharge module (rMix 3×2 or rMix 3×4) for connecting heat consumers ensures that the upper zone of the cylinder remains hot for as long as possible, as it first removes the water from the middle of the cylinder that is still sufficiently warm. This means that the hot water in the top of the cylinder remains untouched for longer and the bottom of the cylinder becomes cold much faster, which makes the use of renewable energies and flue gas heat exchangers more efficient.

Solution for 1 heating circuit

In the video you can see our rMix 3×2, which is used as a mixer for a mixed heating circuit. The mixer is set to take water from the middle of the cylinder first. If the temperature is too low, a certain amount of hot water from the upper zone is added. If it is too high, cold water from the lower zone is added. In the best case, the temperature in the middle of the cylinder is sufficient to feed the circuit without adding hot water from the upper zone. The smaller the temperature spread between the cylinder flow and the heating circuit return, the less the flow needs to be cooled with return water and the more return water enters the cylinder, so that it becomes cold more quickly in the lower zone.

Solution for 2 heating circuits

The video shows our rMix 3×4, which is used as a mixing manifold (with integrated return utilization) to combine an unmixed heating circuit (H) with a mixed heating circuit (M) (also available as rMix 3×4+ for two mixed heating circuits). The mixer is only set to take water from the middle of the cylinder. As the return flow of the first heating circuit (H) is connected to the middle connection (7), this can still be used as a flow for the second mixed heating circuit (M) if required before it is fed to the cylinder (return flow utilization). If the temperature is too low, a certain amount of hot water from the upper zone is added. If it is too high, cold water from the lower zone is added. In the best case, the temperature in the middle of the cylinder is sufficient to feed the circuit without adding hot water from the upper zone. The smaller the temperature spread between the cylinder flow and the heating circuit return, the less the flow has to be cooled with return water and the more return water enters the cylinder, so that it becomes cold more quickly in the lower zone. In this way, the entire amount of heat in circulation is utilized before further heat is taken from the cylinder.

Are there any other advantages?

Tripled storage capacity

CHP systems (CHP, fuel cell...) and solar systems can run for longer and pay for themselves more quickly!

Up to 100% more solar yield!

"If it stays cold in the floor area of the buffer, the solar system can store more energy, up to double the previous amount of heat over the year. This halves the amortization time." (Dipl.-Ing. Fritz-Jürgen Hertweck, Friedrich Hertweck GmbH) "We've never had temperatures of around 20°C down there in the buffer before." (Josef Bock, SHK Guild Schweinfurt)

Longer service life and fewer boiler starts

As with a car engine, frequent starts in a short space of time are the cause of high wear and tear and therefore frequent repairs. Two-zone operation with rendeMIX reduces this to a minimum.

Gain in comfort

"We promise the log boiler operator a considerable gain in convenience. The reloading interval is doubled. What used to be two days becomes four days." (Dipl.-Ing. Fritz-Jürgen Hertweck, Friedrich Hertweck GmbH) "The hot water is there after just 20 minutes!" (S. Ohnmacht, Haslenhof in Dauchingen)

Brochure

For more information, you can download our brochure Buffer storage tank - The two-zone principle free of charge.

Buffer storage tank brochure - The two-zone principle

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