Element structured materials cast or mould by pervious concrete or pervious cellular concrete become a new green building material for constructing outdoor underground thermal storage systems, centralised or decentralised, large or small scale, nearby residential, industrial or commercial buildings – conventionally simply to install, strong enough to get be built over, environmentally clean and sustainable, maintenance-free, long lasting and corrosion resistant.
OUTDOOR heat storage block (1) put up by elements made of pervious concrete or pervious cellular concrete filled up with water, and encapsulated by a sealing & geo drainage foil and thermal insulation (2), attached underground and connected to an energy efficient residential house
The heat storage block (1) shown with an sectional view (orange) into its interior
New Building Material
Pervious Concrete Solution
Pervious concrete is available as a ready-mixed solution or a prefabricated-part (-element) solution with coarse and dense aggregates, also called no-fines concrete, or with lightweight aggregates, also called pervious lightweight concrete. At both variants high open porosity is attained by a high interconnected void content. Typically pervious concrete has little to no fine aggregate and has just enough cementitious paste to coat the aggregate particles while preserving the interconnectivity of the voids. And depending on the aggregates and the part of cementitious paste with sand a void volume of up to 25 % can be created, allowing for 3 – 8 gallons of water per minute to pass through each square feed.
And if lightweight concrete is requested the aggregate particles, e.g. like expanded clay pellets - complete or crushed, itself have an additional open-porous network structure with a pore volume of up to 85 %. So the complete lightweight concrete product can reach a final porosity volume of up to 50 %.
The final necessary weight bearing strength of both materials is adjustable by using more or less cementitious paste and sand, what makes the concrete heavier or lighter, and gives him more or less void volume. And the complete pore and void volume defines how much water can be absorbed and to pass through the concrete material structure. And the maximum water volume is the major parameter for maximum thermal storage capacity of the particular heat storage system.
But an important criterion for a successful operation of thermal stores in e.g. a solar assisted heating systems is that the heat generated by solar collectors during the day can be charged into the store in the same time (in combination with an indoor buffer store) during 24 h. Consequently, not only the maximum stored amount of thermal energy has to be taken into account but also the store’s maximum thermal input and output performance. The disadvantage of any kind of dormant heat stores is, that they need to use an indirect charging system designed similar like a floor heating system arranged in several horizontal levels using plastic piping the length, and as a consequence the costs of the plastic piping increases linearly with the size of the store, and is therefore relatively expensive, and complex to design and install. Therefore the thermal power input and output is very slow and its maximum relatively low, because it works only by thermal conductivity.
Prefabricated-Part (-Element) Solution
Beside the ready-mixed solution the prefabricated-part solution seems to have the most technical potential to fulfil the above defined state-of-the-art demand so far, because this new building material opens the great opportunity to install those stores with a direct charging system without separate heat transfer piping by circulating the water directly not only through the void structure of the material, but also through both, the void structure of the material and an additional passageway system. The passageway system is be made possible by prefabricated parts or masonry units with integrated shaped open chambers and/or a hole system. See images above. The shown part (elements) are already used in the conventional building construction market for to put up heavy concrete walls or to reinforce and plant escarpments. And if these parts are used for the new application the complete heat storage block can be solidly piled up by just in time delivered parts like a modular assembly construction kit, and encapsulated by an appropriate sealing & geo-drainage foil and insulation, with all the necessary additional water filling and operating equipment integrated.
The shaped chamber and/or hole system of each prefabricated part can have an average volume of approx. 70 %. And depending on the void structure of the used concrete material (normal concrete or pervious concrete or pervious lightweight concrete) and if a smart pile up system of the elements are created the complete heat storage block can reach an interior hole volume of approx. 80 vol.%, which can be filled up with water very fast and provides a perfect thermal charging property of the whole store during its later operation.
Pervious Cellular Concrete Solution
It is a ready-mixed solution for casting bigger storage blocks by a concrete material with an open-porous cellular element structure, and TEC MANAGEMENT is just checking this material if it is fine for this new application too. A new product from the USA is known, which is an engineered, permeable, open-cell lightweight concrete designed for water drainage, road pavement, backfilling, and ground stabilisation capabilities so far, and might become an alternative option in this concern.
Brief Advantages
All mentioned above concrete solutions can be combined with each other if it makes sense. Prefabricated parts are available in different sizes and configurations on individual request. Completed heat storage blocks can be build over without the need of heavy-duty and expensive basin, tank, and roof constructions before, and can be flexible placed right under the foundation slab if no basement is planned, or attached to the house underground right beneath a patio or winter garden, or garage on individual request and house building design. The material properties are adjustable depending to nearly any individual and static strength purposes.
A brief description of the whole technology, see "Downloads"
Pervious concrete is available as a ready-mixed solution or a prefabricated-part (-element) solution with coarse and dense aggregates, also called no-fines concrete, or with lightweight aggregates, also called pervious lightweight concrete. At both variants high open porosity is attained by a high interconnected void content. Typically pervious concrete has little to no fine aggregate and has just enough cementitious paste to coat the aggregate particles while preserving the interconnectivity of the voids. And depending on the aggregates and the part of cementitious paste with sand a void volume of up to 25 % can be created, allowing for 3 – 8 gallons of water per minute to pass through each square feed.
