Chiller compressor rest period

[einsteins]

I read that it is not good for a chillers compressor to be cycled on and off in short periods of time.

Do any of you know what would be considered a safe time for the compressor to be off before restarting it?

I want to put my chiller on my AC3 but I dont want to ruin the compressor by cycling it to often. If I can find out a safe down time I can program a delay in the AC3 to help protect it from damage from over cycling...

Thanks
eins

[geno7]

3 minutes. The compressor should have an overload to protect for this very reason.

Mfg. usually suggest 3 minutes for the refrigerant high and low side to balance in pressure depending on what type system it is. I would assume that these being simple systems would have a capillary tube for the expansion devise. So 3 minutes would be ok.

The system could as well have a timer to not allow an early restart. The most stressfull time for any refrigerant based system is when the compressor starts. The amp draw is the highest. Once it gets going the amps drop.

Good luck

[DarG]

3 minutes may allow the system pressures to stabilize but on and off every 3 minutes is going to still reap havoc on the compressor. If you have a chiller that drops the tank temp in 3 minutes then it must be massively oversized. Many chiller manufacturers actually recommend sizing for about a 45 minute run time. The off time will usually be longer than that unless there is a very high heat load. This probably has something to do with placing an average/reasonable load on the compressor over time as far as how often it cycles on and off etc.

One more consideration. You dont want to drop the tank temp in a matter of only a few minutes ... not very stable for the inhabitants. Larger fluctuations over longer periods are different and ok.

[einsteins]

I put a 20 minute delay in to start...

Think that will be OK? I dont see the tank shifting to much in that time frame.

Thanks eins

[DarG]

Im not sure what you are wanting to do. What is the run time of the chiller to chill the tank and then what is the off time until it switches off again? Im talking with the chiller controller. If the unit is cycling on and off that quickly, you have a high heat load and yoi either have a oversized chiller or you are set for a 1 degree temp drop. Try setting for 2 degree drop.

[einsteins]

If I let the chiller control the temp it has 2 degree temp swings and I would like to keep that inside of 1 degree.

So I am trying to have the AC3 control the chiller. I just want to make sure I am giving the compressor enough down time so that I dont damage it. So far with the AC3 controlling the temp I am able to keep fluctuations inside of 1 degree.

eins

[DarG]

There should be no issues with 2 degree pull down per cycle if it is occuring over a little time ... 30 or 40 minutes or more.
The problem with a 1 degree cycle can be efficiency as well as wear and tear. If I pull down 1 degree the chiller may run for 15 - 20 minutes depending on time of day (lights on or not) but then the off time is also only 20 minutes or so because of heat load when lights are on and maybe and hour in the middle of the night.
If I set for a 2 degree pull down, the chiller may run for 40 minutes give or take a few (depending on lights on/off, ambient temp in fish room etc) but the off time is over 1 hour no matter what and approaching 2 hours when it is cool in the house and fish room later at night and early morning and lights are off etc. Keeping track of things, overall the chiller runs less with a 2 degree pull down. Less frequent cycle and less run time overall.
In other words, it takes over twice as long for the tank to rise 2 degrees in temp. than it rises 1 degree in temp. overall. Its a signifigant difference when looked at over a 24 hour period and beyond. Obviously it translates to less chiller run time by using a 2 degree differential which is the bottom line when it comes to energy usage. But it also means less on cycles for the compressor which is a positive for longevity over time as well.

I do use fans to help cool the lighting and tank to limit the chiller use as much as possible. The heat load is high as the fish room is a heat trap so I fan cool as much as is feasible. Also, choosing a set point can make a big difference in how much the chiller runs and how often is cycles. I keep the tank under 80 degrees and the chiller actually does not run that much considering that the tank wants to be in the mid 80's when the lights are on and over 80 when they are off. Chiller is set for 78 and it would run signifigantly more set at 77 ... which is where I always ran it before doing some real watching of how much the chiller ran at different temp settings. Obviously I could set it in the low 80's and it would run less, much less. But I am set in my ways and even moving to 78 bothered me (stubborn and maybe even stupid, I know). So, it comes on at 79 and off at 77 on the Ranco controller.

You should do some of your own research with your system with temp set point and differential as well. It will really help you optimize the chiller run time within what temp. range you are willing to keep your tank at. I have run chillers for a long time. I have used both 1 and 2 degree differentials and never had a single issue with 2 degrees with pull down occuring over 30 minutes or longer.

BTW ... what type controller came with your chiller. You should be able to set differential. If you have a Ranco you can.

Just my 2 cents.

[sivert55]

can you tell us what language you put in the AC3 to make it wait 20 minutes before turning back on?