Two different ways to cool a building

Passive cooling

This is where the brine medium or the groundwater absorbs the energy from the heating circuit via a heat exchanger and transfers it outside. This function is also called natural cooling, as it transfers the excess heat to the natural ambiance. Apart from the control unit and circulation pump, the heat pump remains switched off.

Active cooling

For this, the function of the heat pump is simply reversed. This method of cooling can be achieved with reverse operation. This means that the refrigerant circuit is reversed internally or reversal is achieved by an external changeover of the primary and secondary circuits. As with a refrigerator, the heat pump then actively generates a cooling capacity. This is called active cooling.

Viessmann Vitodens, Gas Boiler range

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Natural and active cooling product line-up

Active cooling boc


Active and passive cooling with a heat pump

The AC-Box, when combined with a heat pump, is able to deliver both natural and active cooling for effective and efficient cooling on warm days.

  • Active / passive
  • Designed for
    Heat pumps
  • Ideal for
    New builds
  • Keeps interiors
Discover the AC-Box
Natural Cooling box


So your heat pump can cool the building in summer

Affordable and energy efficient cooling for your building in warmer weather using a heat pump.

  • Natural / active
  • Designed for
    Heat pumps
  • Ideal for
    New builds
  • Affordable &
Discover the NC-Box

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Design & Technology

Besides generating high levels of heating comfort and reliable DHW heating, our innovative natural and active cooling systems use heat pumps to create a pleasant interior in hot weather. 

Our AC-Box has a cooling capacity of up to 13 kW and is made for use with the Vitocal 300-G/350-G, whilst the NC-Box has a cooling capacity of up to 5 kW.

"active cooling" Box

The AC-Box - Effective cooling on hot days

The AC-Box, when combined with a heat pump, is able to deliver both natural and active cooling.

In the case of natural cooling, excess heat is removed via the heating circuit into the relatively cool ground or groundwater. Electricity is required only for the circulation pumps.

For  active cooling, the heat pump works like a refrigerator. With the aid of the AC-Box, it reverses the inputs and outputs and channels chilled water via the compressor circuit into the interior, thereby cooling it.

Utilising extracted energy

The heat extracted from the building's interior can in turn be utilised, for example for DHW heating or to heat a swimming pool.

This means cooling and heating functions can be combined extremely effectively.

The NC-Box - Energy-efficient and affordable cooling

On hot summer days, the heat pump control unit switches to natural cooling via the NC-Box and removes excess heat from the interior via the heating circuit into the cooler ground or groundwater.

This requires only a small amount of electricity for the circulation pumps. All other functions of the heat pump remains switched off, making natural cooling an energy efficient and affordable way to cool interiors.

All in one box

The compact NC-Box is fitted at the factory with all necessary components and can be rapidly installed by your heating contractor.

Natural Cooling box
A jar of money with a plant growing out of it

Operating a heat pump saves valuable resources

Unlike traditional heating appliances, heat pumps utilise renewable energy from the ground, sun, groundwater or air. They lower consumption of fossil fuels, conserve valuable resources and reduce CO2 emissions that damage the environment.

Benefits of natural and active cooling:

  • Affordable and energy efficient
  • Compact and thermally insulated
  • Pre-assembled at the factory
  • Quick and easy to install
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