Propane as Refrigerant in small Cycles - Institut für Luft- und Kältetechnik gGmbH (EN)

Front and rear views of the evaporator prototype installed in an air duct

Aim of the project

The natural refrigerant propane has a low value of GWP, therefore it is much more environment-friendly than often used synthetic substances. Although propane is an inflammable refrigerant of safety group A3, so that very strict rules for assembly of refrigerating plants or heat pumps with refrigerant propane are defined. However up to a charge of 150 gram inflammable refrigerant no special restrictions for hermetic tightly closed plants are to respect. On that condition a widespread use of propane as refrigerant would be possible, e.g. as refrigerant in heat pump tumble dryers too. Aim of the project was minimisation of propane charge at 150 gram at maximum without any reduction of power.

Results

The major part of refrigerant charge in refrigeration cycle is in heat exchangers (evaporator and condenser). At this point it was useful to examine the possibilities of charge reduction. Therefore as an essential result of project a new evaporator based on mini channel technology was developed. In June 2013 the invention „Mini Channel Evaporator“ was applied for a patent (FILE NUMBER: 10 2013 106484.1). Mini channel heat exchangers in themselves are nothing new. In this manner an industrially made product was used as condenser in the project. But especially by implementation of mini channel heat exchangers as evaporator there were problems with evenly distribution of refrigerant up to now. This problem of refrigerant distribution was solved with the new developed mini channel evaporator. Moreover, the evaporator has a good performance of heat exchange, a small inside volume and thereby only low charge of refrigerant. The construction depth is small and the perfectly circular geometrical form of the evaporator corresponds possibly to a drum of a tumble dryer. In measurement tests the drying performance necessary for tumble dryers was proved. The developed evaporator is also very well suitable for installation in round air ducts or others like them.

Thermal images of the evaporator taken approximately every 2 seconds while refrigerant is being introduced

The sequence of thermographic pictures shows the evenly distribution of refrigerant in the evaporator when the refrigeration cycle was started up. The change of colours reveals the well balanced cooling down of the evaporator from the inside outwardly. This change of colours is corresponding with inflow of refrigerant in the evaporator.

Test bench for testing and measuring the evaporator

In the ILK a test rig for examining and measuring of the evaporator prototype was constructed. It works with refrigerant propane. The test rig is similar in size and composition like the refrigeration cycle of a merchantable heat pump tumble dryer. The refrigerant charge of the test rig is about 140 gram propane. This is less than the maximum value of 150 gram mentioned at the beginning. Therefore the troublefree use of propane for tumble dryers or others like them could be proved. Because of propane charge less then 150 gram no special demands for assembly have to be respected.

Perspectives

In the scope of the project it was proved that propane could used as refrigerant in heat pump tumble dryers easily and troublefreely. For this purpose a new patentable evaporator was developed. This new developed evaporator has a good performance, an evenly distribution of refrigerant and because of the small inside volume a low charge of refrigerant. With manufacturers we have to revive interest in the subject propane as refrigerant in tumble dryers, building dryers, small air-conditionings or similar like them. First conversations already were coducted.