Uses Of Educators

It’s been reported several times that on the screw chillers that use Eductors for the oil return, while operating at a low load condition it looks like the educator doesn’t efficiently operate enough for returning the oil to oil separator or the sump for maintaining the level of oil. It then causes the chillers to completely shut down on the low oil, a result of retained oil in refrigerant charge in evaporator.

For this type of chillar that employs educator for returning oil, the main cause of failure might not be the low load but a low lift. In a comfortable and cool environment, the chiller load could be responsive to the temperature outdoor. This is when it’s very hot outside but the heat flows into building rapidly and the chiller load becomes high.

Cool temperature

When the temperature outside is cool, little heat is required to be removed from conditioned space and thus the load of the chillar is also low. This low load of chillar is accompanied by low lift conditions as ambient temperature comes down from the high value. This low lift is considered to be the main cause of a loss in the effectiveness of educator. The educator gets driven by a difference in pressure between the evaporator and the condenser. When the difference in pressure falls, the capacity of inducing flow is also reduced. The capacity of inducing flow of educator is proportional to square of difference in pressure. Thus the difference reduction in pressure leads to induced reduction in flow to approximately 25% of the design.