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Solar Prism - Renovated townhouse

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Before renovation

Before renovation

A zero-carbon renovated townhouse with a solution combining technologies in order to meet the demands of sustainable housing with comfort requirements of the future. The combined energy technologies include solar thermal collectors, photovoltaic collectors, a ground source heat pump, a 160 l solar hot water tank, mechanical ventilation with heat recovery, use of daylight through roof windows, passive solar energy, natural ventilation and renovation with highly insulated facade elements, a grass roof and new windows.


Solar thermal collectors use the sun’s energy to heat water for consumption and space heating. In average 2 m² of solar thermal panels supply sufficient hot water for 2 person’s daily use. Integrated in the prism corresponding to the family size, the solar thermal collectors can be configured to meet the housing needs. Solar photovoltaic collectors convert the sun’s energy into electricity, substituting main grids supply for regular electricity consumption. Estimated 10.5 m² of solar cell surface supplies 1.67 kW of electrical energy, sufficient for 2 person’s regular consumption. The solar photovoltaic panel is made providing highly efficient solar cells, and good ventilation of the rear side.

A heat pump by Danfoss COMBI-305 3,5 kW is installed for the supply of space heating. The ground source heat pump draws the natural ground heat in the winter for heating the living space, supplementing the hot water system, and supporting the solar collector system. The passive solar energy, the solar collectors together with the heat pump fully replace the central heating system, this way reducing the dependency of fossil energy consumption in the housing. Solar hot water tank stores the hot water heated by the solar thermal collectors. The water tank is a custom made storing 160 litres and has very limited heat loss. Heat Recovery Ventilation by EcoVent, dedicated system S450 for ventilating the housing and hot air based heating. The ventilation system permits a continuous air exchange, while recycling the heating via an inbuilt heat exchanger. This way, around 90% of the space heating is recycled while ventilating. The unit has low operating energy consumption SEL value 0,9kj/m³. The capacity of the ventilation system is 150 m³/h.

Indoor climate:

Solar Prism provides sunlight source by replacing part of the flat roof with roof windows that are utilised to provide daylight, passive solar energy, natural ventilation, and thereby savings for heat, cooling and electric lighting while ensuring a healthy indoor climate.

The prism shape is chosen to optimise the interior space for hosting the technologies, and enabling access to servicing. As well as for optimal surfaces for effective solar energy sourcing, and insulating qualities of the construction. The interface of the Solar Prism makes the intelligently reinvented roof function possible for simplified energy renovation of the existing housing stock.

Further description
  • Simplified house upgrade to Active House principles.
  • One installation for renewable energy sourcing for individual housing.
  • One installation for improved indoor climate with natural ventilation, daylight, and heat recycling background ventilation.
  • Saved energy with daylight and passive solar energy.
  • Configurable functions in modules to meet the needs of individual families and multi family housing.
  • Upgradable technologies and surfaces to meet additional family needs.

The renovation is part of the Energy Demonstration Project (EUDP). The project consists of renovation proposals and the energy charge and total economic calculation of 350 concrete element townhouses from 1975 to CO2 neutral construction, based on Solar Prism concept.

The renovation consists of exterior installation of new prefabricated, highly insulated facade elements, inserted new window elements. Roofs with insulation and the roof mounted "solar prism" with solar panels, solar cells and roof windows. The roof is covered with grass to relieve the sewerage system. A newly developed heat pump combined with a high efficiency heat recovery plant and a solar collector, provide heating instead of the current site, which is based solely on the district. The project includes the possibility of covered terraces, bay windows and canopied entrances and staircases.

Lessons learnt

The finished renovation fits well into the existing design of the other houses, providing a subtle renewal of the building design. The Solar Prism combines all technologies 'in a box' and offers an aesthetically pleasing addition to the roof of the building, reducing complexity and resulting in no visible pipes or leads.

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Operational date

Venerdì, 1 Gennaio, 2010