Development and demonstration of an assembled prototype for decentral ventilation with a spiral shaped heat (Spiralflow 2)

At the end of the project Spiralflow 1 it was recommend that the heat exchanger should be further developed. As the air distribution through the heat exchanger was uneven due to the very lowpressure drops. In Spiralflow 2 the heat exchanger was optimized with strategic placed air resistances which improved the air distribution. As a second benefit the resistances also acts as a spacer material which keeps the distance between the two plastic sheets in the heat exchanger. This was one of the main obstacles in Spiralflow 1.

Tests in Spiralflow 1 had revealed that the optimal heat exchanger length was around 34cm. In Spiralflow 2 a 34 cm long heat exchanger with the resistances has been constructed. From the limitation of the length of the heat exchanger arose a conceptual discussion of how a complete unit should be designed. By market experience from decentral ventilation units from the Breathe55 unit, it is known that especially architects are more concerned by the exterior side than the interior. It was therefore decided to make a unit with an exterior lid that is completely flush with the façade. This separates Spiralflow from other units in the market. The cost of this is that the interior part then is larger than competitors.

Condensation is expected in the unit as it has a counterflow heat exchanger. The project team has from the beginning had the ambition that condensation shouldn’t be allowed to drip freely to the outside. This is known from competitor products and e.g. air conditioners. A solution where the condensation is then drained by a rubber hose to the nearest drainage was therefore developed.

The focus of the Spiralflow unit is bathrooms and kitchens and a drainage near by the unit is therefore expected. Installation in dry rooms would be challenging for this kind of solution. The unit is therefore prepared to allow the rubber hose to the exterior side and let the condensation drip freely. In dry rooms a lot less, condensation is expected and the level of dripping condensation water is therefore believed acceptable.

Besides the overall design of the unit has there have been designed technical solutions for e.g.:

• bypass function with stepper motor
• Condensation drainage
• Filter placement, areas and filter classifications
• How the unit is thought serviced from the inside by taking the unit in and out of the wall
• Extension of the unit for variation in wall thicknesses.

All these details have resulted in a functional prototype used for tests at DTU.

The development of the controls was made in parallel. The controls can control the fans and the bypass valve based on inputs from temperature, humidity and CO2 sensors.

There has been produced one full prototype used for tests in a laboratory and a test house and an acoustic chamber at DTU. An objective in the project was to test the unit in actual buildings including feedback from the occupants. This part has not been successful. The test house at DTU has allowed the unit to be tested in actual weather conditions, but without user feedback.

The prototype has shown superior performance on heat recovery and power consumption, with results greater than the requirements for the 2020 Danish building regulations. This is impressive for a first prototype.

The transmission noise dampening results show superior performance compared to other market available solutions. The results are currently a bit weaker than the market, but this could be made up by a complete installation with sealant. The prototype was just installed in a hole in the acoustic chamber without sealants.

Noise generation was not as positive as the unit currently is a bit too noisy. This is due to the fans. In the current prototype the exterior fan is not yet updated with a software which should increase its noise performance. After the measurements and investigation of the fans revealed that them placement wasn’t optimal regarding performance and thereby noise. An adjustment of this is expected to improve the acoustic results.

On both the interior and exterior lids of the unit was there measured too high short circuiting of air. This is a part which needs to be improved in the future. On the exterior side a greater separation of the two air streams are needed. And on the interior side a downsizing in filter area could increase velocities and thereby ensure separation between the two air streams. This will have a negative effect on the pressure drop and thereby the power consumption.

The technical performance from the first prototype has been good. And with already known improvement possibilities are the potential for the Spiralflow unit great. There are still unknowns regarding production of the heat exchanger which should be investigated further. It will also be a clever idea to perform a user survey in order to reveal if the large interior lid can be accepted.

A market analysis has shown that the current length of the unit is problem for potential sales. If the unit could be made shorter it could adapt to slimmer walls than 390mm which it currently can adapt to. If so, the Danish market would increase.