ACRD502 compressor drive speed spikes every hour

Anonymous user · ‎2021-07-09

We have a cooling group consists of two ACRD502.

Configuration type: HACS; Max Fan Speed: 65%; Supply Air Setpoint: 18.0 C; Fan Speed Preference: Medium. There are no warnings or critical alarms, and heat load is constant.

Every 60 minutes or so each of cooling units suddenly bumps its compressor drive speed up to 75..80 Hz, and then drops down to normal speed (about 40 Hz). Why does it happen?

Can we do something against dropping supply air temperature down every hour?

Anonymous user · ‎2021-07-09

From "InRow RD Technical Data Manual (JBOR-7B6KGE_R5_EN)":

VFD firmware is written to include oil return protection in cases where pipe velocities may drop to low speeds during low loading periods.

I believe compressor drive bumps its speed up every hour exactly to return oil from pipes.

See Answer In Context

Anonymous user · ‎2021-07-09

From "InRow RD Technical Data Manual (JBOR-7B6KGE_R5_EN)":

VFD firmware is written to include oil return protection in cases where pipe velocities may drop to low speeds during low loading periods.

I believe compressor drive bumps its speed up every hour exactly to return oil from pipes.

BillP · ‎2021-07-09

Andrej,
I just wanted to give you a quick confirmation that this is by design to ensure the oil gets back to the compressor.

The unit monitors the time the compressor speed is below 50 Hz. After 30 minutes, the compressor is forced to run 50 Hz or higher for a set amount of time.

This is all written into the unit firmware.