Small hermetic compressor run-times

[en9ech]

In order to reduce the temperature fluctuations in a refrigerator, I would like to reduce the hysteresis set in the controller. However, this results in short run times ...(1 minute 20 seconds on and 5 minutes off). For a small hermetic system of about 200W -is this likely to be an issue?

I know the compressor life may be reduced by the increased number of compressor starts, but are there any other issues to consider such as oil return.

Ed

[taz24]

is this likely to be an issue?

I know the compressor life may be reduced by the increased number of compressor starts, but are there any other issues to consider such as oil return.

Ed

Yes.

The comp will only be designed to start so many times an hour.
Rule of thumb about 6 times an hour.
Thats every 10 mins.

Cheers taz.

[en9ech]

:) great, thank you.

I'll work with that and see where I end up.

Ed

[Gary]

Assuming this is electric defrost, you might try running a very small current through the defrost heaters during the run cycle to lengthen the run time.

Possibly the heat could be made proportional to the setpoint?

[bill1983]

can you give us more details about the problem eg cabinet type, temp range req, controller type and probe position. defrost type,probe position and heater wattage would also help us to understand your problem so that we can offer better advice. also any details like case make model and any previous repairs made would also be worth throwing into the mix.

[NoNickName]

1'20" on and 5' off definitely assesses the chiller to be huuuuugely oversized, at any hysteresis. Try excluding one or more compressors from the system (if it's a multiple compressor unit....EDIT oops 200W, not 200kW).
So, is the actual heat load 50W? Less than a light bulb?

[en9ech]

The unit is primarily used as a rapid chill unit, hence being hugely oversized, but once the load is chilled the cycling gets rather short if left running. It works fine with a 3'C hys, I was just trying to improve the control without changing the refrigeration system. The controller is a Dixell XB570L.

[NoNickName]

Well, why don't you make use of one of the digital outputs (AUX or defrost) of the controller and install a small 20 or 30W resistor in the chilled space to increase the heat load in specific situations, like e.g. if setpoint = -20°C, heater on at -18°C

[en9ech]

Great! You have given me an idea! The output is currently used to drive a set of additional fans to boost cooling rates in rapid chill mode on this beast so I can't use it at the moment. But, these fans pull about 40W so they would be an ideal heat load, just let them run with the other fans, all of the time.

:)

Ed

[Gary]

Great! You have given me an idea! The output is currently used to drive a set of additional fans to boost cooling rates in rapid chill mode on this beast so I can't use it at the moment. But, these fans pull about 40W so they would be an ideal heat load, just let them run with the other fans, all of the time.

:)

Ed

You might want to shut the booster fans off during the off cycle, when additional heat load is not needed nor wanted. This way you will lengthen the on cycle without shortening the off cycle.

Let us know how it works out.