Ambient Temp and Compressor Cooling

[comment]

Hey :)

I've been looking around for som specs on the minimum ambient temperature when running a phase change unit.

I couldn't find any general info googleing on the web and the only specific data I could find on Danfoss's site about the FR8.5CL compressor (http://de.refrignet.danfoss.com/TechnicalInfo/Literature/Manuals/06/FR85CL_R404A-R507_220V_50Hz_09-02_Cf53b202.pdf) humming in my Vapo LS states the maximum ambient temp but not the minimum ambient temp :mad:

So as a final resort: All mighty gurus of phase change cooling :worship: do you know of a site where I could find that kind of data or is there a rule of thumb to use?

[Redwolf]

There really is no min. ambient temp. Just min pressure drop across your cap tube. Which is around 100psig for full load capacity. But can be lowered for lower load conditions.
Its very simple to do.. just cycle or variable the condensor fan speed. In order to keep the head pressure up or down.
Dont they alrdy do this.. but use control the fan speed from the evap temp?

[comment]

Originally posted by Redwolf
There really is no min. ambient temp. Just min pressure drop across your cap tube. Which is around 100psig for full load capacity. But can be lowered for lower load conditions.
Its very simple to do.. just cycle or variable the condensor fan speed. In order to keep the head pressure up or down.
Dont they alrdy do this.. but use control the fan speed from the evap temp? If I get you right, it's all a question about regulating the fan speed on the condenser to measure up for the pressure drop due to a cold ambient temperature?

[chilly1]

The lower limit is where the pressure drop due to the cold condenser causes the head pressure to go so low as to slow the flow of refrigerant. If the system is designed for low ambient conditions controls will be in place to keep the head up. If the temperature of the compressor gets too low there will be refrigerant collecting in the oil and a heater should be attached to the compressor to keep it at a higher temperature then the rest of the system to prevent this.

[Redwolf]

Exactly..

Plus what Chilly said. If your going cold, as in cold to a human, then you'll want to install a crankcase heater on the compressor.

Refrigerant loves the oil and the coldest place in system. So it could sit there lying in wait for the next start up to flood the cylinders with liquid refrigerant. If you dont have a crankcase heater.
The heater doesn't need to be on when the compressor is operating. Alot of them now days have a built in or external thermostat set to about 40F or 5C

[comment]

Originally posted by chilly1
The lower limit is where the pressure drop due to the cold condenser causes the head pressure to go so low as to slow the flow of refrigerant. If the system is designed for low ambient conditions controls will be in place to keep the head up. If the temperature of the compressor gets too low there will be refrigerant collecting in the oil and a heater should be attached to the compressor to keep it at a higher temperature then the rest of the system to prevent this. Thanks :)

Just one question: If there is refrigerant collecting in the oil would you expect to hear a seething-like noise coming from the unit?

[chilly1]

That is the refrigerant quickly boiling as it hits the oil. If there is enough refrigerant in teh oil you will know it, the oil/refrigerant mixture will be sucked into the compressor through the suction ports and the pistons will try to compress it and the crank may bend pistons break or the valves will shatter...

[comment]

Originally posted by Redwolf
Exactly..

Plus what Chilly said. If your going cold, as in cold to a human, then you'll want to install a crankcase heater on the compressor.

Refrigerant loves the oil and the coldest place in system. So it could sit there lying in wait for the next start up to flood the cylinders with liquid refrigerant. If you dont have a crankcase heater.
The heater doesn't need to be on when the compressor is operating. Alot of them now days have a built in or external thermostat set to about 40F or 5C When I'm talking cold ambient temp it's about 10°C. From what you are writing that shouldn't be a problem for any well functioning compressor - right?

[comment]

Originally posted by chilly1
That is the refrigerant quickly boiling as it hits the oil. If there is enough refrigerant in teh oil you will know it, the oil/refrigerant mixture will be sucked into the compressor through the suction ports and the pistons will try to compress it and the crank may bend pistons break or the valves will shatter... WOW :explode:

So I guess you wouldn't be supprised to see the evap temp rise under such conditions would you?

Something like this:

[Gary Lloyd]

Those fluctuations could be caused by any number of things, or a combination of things. A lot more information would be needed to figure that one out.

[Gary Lloyd]

BTW, it makes no sense at all to control the condenser fan by evap temp. They would be far better off controlling it by liquid line temp.

If I had to take a wild guess at what is causing this pattern, my guess would be fan control.

[comment]

Originally posted by Gary Lloyd
BTW, it makes no sense at all to control the condenser fan by evap temp. They would be far better off controlling it by liquid line temp.

If I had to take a wild guess at what is causing this pattern, my guess would be fan control. Thanks Gary :)

So you'r implying that it's a pure condenser cooling issue... Well I'll do some testing next week with an extra 120mm fan on the front side of the condenser, and then we'll see what happens.

[Gary Lloyd]

I am implying no such thing. You don't need to guess what the problem is, you need to know what the problem is.

For that, temps and pressures at various points in the system are needed, primarily condenser air in and air out temps, as well as suction line temp a few inches from the compressor and liquid line temp a few inches from the condenser. With these and the display (evap) temp we can guestimate pressures.

[comment]

Originally posted by Gary Lloyd
I am implying no such thing. You don't need to guess what the problem is, you need to know what the problem is.

For that, temps and pressures at various points in the system are needed, primarily condenser air in and air out temps, as well as suction line temp a few inches from the compressor. With these and the display (evap) temp we can guestimate pressures. Well I better get some temp sensors to get on the right track then. Thanks!