Energy Concept
Ventilation Concept
The low-tech ventilation system for the renovation part of the coLLab project consists of decentralized trickle vents to ensure a hygienic air change rate year-round. These trickle vents are intelligently combined with a heating element to pre-heat the supply air in winter (“pre-condition through buffer tank” and “pre-condition through solar chimney”). A solar chimney is used to naturally exhaust air out of the building through thermal buoyancy. At the top of the solar chimney an air to water heat exchanger is placed and connected to the supply air heating element via a run-around coil heat recovery system to pre-condition the supply air in selected rooms. In the rest of the rooms, the pre-conditioning element is supplied with warm water from the buffer tank. During shoulder seasons and in summer the heat exchanger in the solar chimney is bypassed and natural ventilation is boosted. The non-load-bearing pillars of the façade of the existing building are replaced by vertical ventilation flaps that allow for nighttime flushing without endangering the safety of the building.
For the ventilation concept, the system with decentralized Supply Air Heating, Solar Chimney as Exhaust Fan and Run Around Coil Heat Recovery System) was chosen for implementation, as it requires the least HVAC equipment and the lowest overall energy demand according to a simulation study.
The residential modules of the extension feature cross-ventilation from the operable windows and are not connected to the solar chimney. In summer the supply air is adiabatically cooled with a water feature in front of the window.
PV System
The GRID is the basic architectural construction and is based on the existing building. It is a constructive skeleton, which is adaptable in size depending on the existing building and its load bearing structure.
The spaces between the wooden structure of the GRID are filled with organic PV modules (OPV), which function as shading elements and generate electricity renewably. They are automatically scaled and distributed based on simulation results in accordance with the greatest benefit for indoor comfort. On the roof of the residential modules, monocrystalline PV collectors are placed.
In addition to the OPVs, the PV system also consists of monocrystalline silicon-based photovoltaic modules placed on the roofs of the extensions. If there is electric yield, the priority is to directly cover the existing building demand. If there is surplus afterwards, it is fed into the battery for later use. When the battery is full, the electricity is fed into the grid. An increased self-consumption rate of solar power reduces the decentralized feed in energy into the grid during peak hours. Hereby, the control complexity to maintain the target frequency in the grid is reduced. If the building demand cannot be met by means of the battery or direct use, electricity is extracted from the grid.
Heating and DHW
The main part of the heating and DHW demand is covered by two 40 kW cascading brine/water heat pumps in bivalent-parallel operation with wastewater as the environmental heat source. Even without the power needed for the heat pump, the electricity demand of the building significantly surpasses the yield generated by the PV-system. Therefore, the heat pumps are operated heating demand driven, eliminating the need for a large puffer tank. The heat pumps operate parallel since the temperature of the wastewater is constant year-round (12°C). A COP of around 7 is maintained, even on cold days with high loads. For smaller loads, only one heat pump, and for higher loads two heat pumps are running. Peak loads are covered by the existing district heat.
If there is solar power excess, and all other building electricity demand has been met, the heat pump is operated, regardless of heating demand. This mainly happens during shoulder seasons and in summer. The generated hot water is stored in the puffer tank and used for domestic hot water production in the residential modules that make up most of the domestic hot water demand. The hot water from the buffer tank is used to supply decentralized fresh water stations in each module. The energy is passed to the incoming fresh water via a heat exchanger. If the desired temperature level is not met, the DHW is further heated electrically. Since the DHW water volume after the fresh water station is less than 3 liters and only heated according to demand, no further legionella protection is required. In the existing building, there are only a few taps (café, tea kitchen) that require domestic hot water. Therefore, electrical decentralized instantaneous water heaters are installed here.
