Novel spiralshaped counterflow heat-exchanger for decentral ventilation (Spiralflow 1)

The product

The heat exchanger we have developed consists of two 9m long plastic foils, which is rolled together with a 2mm gap in between. The short distance between the foils makes it possible to retrieve a high heat exchanging efficiency. A variety of solutions for the heat exchanger has been tested. The latest development is a solution using only one air intake and one exhaust. 

A plastic foil heat exchanger

The choice of material is highly important. Both regarding cost but also functionality. From the beginning of the project, a plastic foil has been chosen due to its low costs, flexibility and functionality. It is important that the material have good stabile thermal capabilities, so it does not deform when subjected to different temperatures. At the same time the material has to be rel-atively strong so that it does not bend when over- or under pressure is present in the air channels. In order to air tighten the heat exchanger it is also important for the plastic foil to have a surface with a good adhesiveness. Many types of plastics are inert and can therefore not be welted together nor glued.  

A high rate of heat recovery and a low electrical consumption

Several prototypes have been tested in the project. As a proof-of-concept, a 1.22m long heat exchanger was constructed and followed by shorter heat exchangers of 28 and 34cm, fitted to be installed within a wall. The results of the proof-of-concept unit are highly promising. A heat exchanging efficiency between 75% og and 85% for air flows 4.5-13.5 l/s, with an extremely low pressure drop. Which, if installed in a ventilation unit would result in a SFP of less than 400 J/m3. Current Danish requirements for SFP is that it has to be less than 1000 J/m3, this is expected tightened to 800 J/m3 by 2020. The test of the 1.22m long unit has shown that the results are in line with the theoretical simulated and calculated results. The extremely low pressure drop has challenged the air distribution and heat recovery. For further development, it is suggested to work with strategic placed resistances, such as baffles or similar. The resistances will ensure a better air distribution and then an improved heat exchanging efficiency. It will however increase the pressure drop. The placement of these resistances are therefore important and shall be designed with care.

A good transmission noise sound dampening
There have been performed transmission noise measurements. The results shows that the installation of the heat exchanger itself reduces outdoor noise roughly as much as a stand-ard window. When a final version of the ventilation unit is ready, the transmission noise sound dampening will be improved, since several components will shield the outdoor noise. There is therefore no increased noise disturbance from the outside, e.g. traffic noise, street noise etc., when installing a decentral ventilation unit with the new type of heat exchanger. This is an important result as the noise reduction potentially could put an end to the use of the heat exchanger.