Oil management

WITT oil management returns refrigerant oil where it belongs

Compressors in refrigeration systems need sufficient lubrication with appropriate refrigerant oil. Some oil is always carried over with the refrigerant into the refrigeration system - even the latest compressors cannot avoid this.

To prevent the oil is not causing capacity losses, i.e. blocking heat exchanger surfaces, it needs to be removed from the refrigeration cycle. By occupying the evaporator surfaces with refrigerant oil, the COP of the system drops by approx. 3% per Kelvin.

With the automatic WITT oil management, valuable refrigerant oil is returned from the collection point back to the compressors in a controlled manner.

That way it does not need to be manually drained, which is not only time saving, but also prevents accidents related to this kind of maintenance.

In addition returning and re-using the oil saves operating costs (maintenance, disposal, refill of oil) and protects the environment.

A comparison

Efficiency with automatic oil recovery

refrigerant ammonia
performance [Qo] 500 kW
refrigeration system floated evaporator
inlet temperature of glycol [T ein] -3°C
outlet temperature of glycol [T aus] -6°C
operating hours 6.000 h per year
electricity 6 € provision per month | 0,12 € per kWh


clean evaporator oily evaporator
evaporation temperature [To] -10°C -12°C
compressor power consumption 156 kW 166 kW
COP 3,20 3,01
operating costs per year 112.392 € 119.592 €
savings 7.200 €

An oil management saves based on that example 7.200 € per year just for electricity. Thus it makes sense to install an oil circle to your system.

With an automatic oil management from WITT you will have further benefits: Also the regular costs for maintenance and material will decrease.


refrigerant ammonia
performance [Qo] 500 kW
mass flow of compresser [kg/h] 2.809,45
oil discharge to system 0,1 ppm of volume flow
oil volume flow [l/h] 0,038
evaporation temperature [To] -10°C
condensing temperature [Tc] +35°C
operating hours 6.000 h per year
disposal costs for used oil 0,60 € per liter
new refrigeration oil 6,50 € per liter
monthly maintenance costs 120,00 €

manual oil drain WITT oil management
oil discharge per year 228 liter
disposal costs 137 € ---
new oil 1.482 € ---
maintenance costs per year 1.440 € 240 € (2x per year)
installation (incl. material) --- approx. 4.500 €
amortization within 1,5 years (4.500 / 3.059)

Already after approx. 18 month you will save in this example another 2.800 € per year.

That is a representive example using a WITT BDP incl. piping to one compressor. The exact savings could vary at your refrigeration system.

How the WITT oil management works

The WITT oil management is initiated right where the majority of refrigerant oil is collected in the refrigeration system. For ammonia system this is the lowest spot in the surge drum. Since refrigerant oil is insoluble in common ammonia systems and the densities differ (oil is heavier than ammonia) it settles at the bottom of the surge drum. The WITT oil management is also possible with soluble oils, i.e. in CO2 systems.

The WITT BDP oil recovery unit is installed at the lowest point of the ammonia surge drum and collects that way the refrigerant-oil-mixture entering the BDP vessel. With hot gas that is either time-controlled or demand controlled with the optional oil sensor the refrigerant-oil-mixture is pushed to a heat exchanger (WITT DWR). Inside the WITT DWR remaining liquid refrigerant is evaporated. An optional oil filter (WITT OF) at the outlet is making sure only clean oil is returned to the compressor.

In refrigeration systems with multiple compressors it is recommended to use a HDB3 stainless steel oil receiver to collect and distribute the oil to the compressors.

You can find above mentioned optional equipment such as sight glasses, oil filters or oil sensors under Accessories.

WITT oil management diagram
WITT oil management diagram
BDP2 Barrel dosing pump
BDP2 Barrel dosing pump

BDP oil  recovery unit

HDB3 stainless steel oil collector
HDB3 stainless steel oil collector

HDB3 stainless steel oil receiver

DWR heat exchanger
DWR heat exchanger

DWR heat exchanger