On the various pages of the website, you will hopefully find explanations to your questions about the HoCoSto thermal buffer and the HoCoSto system. Please find some frequently asked questions below. If you want more information, please contact us.

Are there any permit requirements to take into account?
Not all municipalities have immediately figured out how to deal with this innovation in terms of licensing! Our experience is that a report is ultimately sufficient. A HoCoSto buffer is also permitted in groundwater protection areas, provided the PMV notification is properly substantiated. Please contact us for details.
How is the heat stored?
The heat is stored in water. The buffer is filled with ordinary tap water or, if it is of good quality, with the groundwater that is released at source. The water stays in the buffer. Strong industrial protective materials and films retain the water in the buffer. Heat exchangers provide heat transport. The water in the buffer therefore does not come into contact with potable water.
Is there a lower and upper limit to the buffer volume?
The buffer is scalable in length, width and depth. But the lower limit is 85m3. There are two reasons for this. The first is economic: a smaller buffer is technically inefficient in terms of cost (ROI versus reference gas). The second reason is physical: at 85m3 the weight is equal to the buoyancy created by the insulation. A buffer smaller than 85m3 can come up despite the back pressure of the water. The upper limit is determined by the energy requirement and the available surface area. Buffers larger than 1500m3 are preferably placed in cascade.
What is the aluminium space frame for?
This spaceframe is purely constructive: it keeps the slope of the walls intact and provides rigidity. After placement, the buffer is insulated and covered with soil. Afterwards, the upper area can again be used as a lawn, playground, garden or parking space. This way, scarce square metres are used twice!
What is the maximum storage temperature?
The water in the buffer becomes 90-95 degrees Celcius maximum. These high temperatures make seasonal storage possible. When using solar collectors, approximately 50% of the energy generated is transferred to the buffer. The remaining heat can be supplied directly to the building (tap water and space heating).
What temperature can be extracted?
In principle, up to 0 degrees C can be extracted. The way you process this energy is free. With low temperature heating (underfloor heating) you can extract up to 30 degrees without using any aids (heat pump). With radiators, a higher temperature is required. At the end of the winter, a small water-to-water heat pump can help. This then uses the buffer as a source.
When is a heat pump used?
  1. In case of cooling demand: the heat extracted from the building during the summer months is stored in the buffer for use in the winter (in this way the number of heat collectors can be reduced)
  2. At the end of the winter: you then extract residual energy from the buffer at the moment that the buffer temperature has become so low that there is no longer any heat exchange (exergy). It is inefficient to use the buffer when loading it: the heat pump will then run a very low COP.