Can’t get a brine chiller down to temperature.

[dkemper]

All,

I’ve a Carlyle 5H80 compressor using R404a on a brine chiller and I cannot get temperatures, and pressures right. Being quite new to refrigeration (6 months), I’m running out of ideas.
A bit of history, the brine chiller is an Italian design, originally running a Frascold TSL1-70-2404 screw compressor. My company has seen a limited life of only about 2 years continuous use on the compressors and made the decision to replace the compressor with a less expensive, easier to source and repair (here in the US) reciprocating compressor.

A Carlyle 5H80 was chosen as the replacement, driven by a 50 HP (37Kw), 1770 RPM motor.

Expansion valve is an ALCO TER using an X9117-B8B cage assembly. Power head assembly is correct for R404a/low temp.

Load on the system is from 32 oz (900g) of sugar water at 30F (-1c) dropping into forms 22 times a minute and being drawn down to -15F (-26c) in 3 minutes in the brine bath.

The initial install was very poorly done. My predecessor had Carlyle engineer the solution, then attempted to build and commission himself.

To date, I’ve added head pressure controls on the condenser to get head pressures up, built and installed a bypass for the unloader system on the 5H80 to keep capacity up on the compressor and corrected a major flaw/shortcoming in the oil separator/return system.

I’ve made huge progress. Initially, temps were 10F/18c warmer than they are now head pressure 60% of current and suction about double, brine was barely at -15F(-26c)



But I’ve still got a ways to go. My target is to maintain -30F (-35c) brine with an increase on load of about 10% (25 drops per minute)


At this point:

Compressor discharge is 225 psi (15.5bar) / 117F (47c)
Condenser discharge is at 86.5F (30c)
Precooler discharge is at 64F (18c) – Total of about 30F subcooling.
Evaporator discharge is at 10 psi (.7 bar) / -11F (-24c) Makes it about 19F of superheat!

Only frost back on the compressor is at the service valve so I don't think I'm flooding the evaporator.



Clearly, superheat on the system is WAY off. But, before I jump in and make further alterations, am looking for advice. Am I down to the expansion valve, or are there pieces I’ve missed elsewhere?

Many thanks in advance!

Win

[Gary]

Try holding the TEV sensing bulb in your hand. This should cause the evaporator to flood. If it does, then adjusting the superheat on the TEV is the answer. If it does not, then there is not enough liquid at the TEV inlet or the inlet screen is restricted or the orifice is too small.

[lana]

Try holding the TEV sensing bulb in your hand. This should cause the evaporator to flood. If it does, then adjusting the superheat on the TEV is the answer. If it does not, then there is not enough liquid at the TEV inlet or the inlet screen is restricted or the orifice is too small.

DO what Gary says.
Also check the compressor capacity.
Cheers:)

[dkemper]

Gary, lana

Thanks for the input folks, next time the unit is down and I can run some tests, I'll pull the foam from around the bulb and try Gary's test.

Gary, To watch for compressor flooding, would I be expecting the suction pressures to change, or simply for frost to start building past the inlet valve on the compressor or will my evaporator outlet temperature drop? Is there a "best" way to monitor for that condition?

Lana, at least on paper (Carlyle's docs), the compressor is rated at 10 tons at -40 using R404a. Likewise, Alco/Emmerson lists the valve combination at 10 tons at -40 and R404a so the basic match up should be workable. With the original Frascold screw compressor, those temps & pressures were achieved at one point so again, I'm thinking the basic evaporator setup should be up to the job as well.

Again, Many thanks!

[US Iceman]

I have a question...



...built and installed a bypass for the unloader system on the 5H80 to keep capacity up on the Compressor (http://www.refrigeration-engineer.com/forums/glossary.php?do=viewglossary&term=60)...


What type of bypass did you install? And why would a bypass for the capacity control keep the capacity up?

Those compressors have internal unloading. Does the compressor have the correct unloader spring in it for the refrigerant? Carlyle used to ship different springs for R-12, R-22, and R-502 so I'm assuming they do the same thing for the current refrigerants.

Have you checked the motor amps to make sure it is loaded up according to the required power input?

[Gary]

If I am reading your measurements correctly, your condenser outlet subcooling is about 10F (5.5K). Before doing anything else, I would add refrigerant until the condenser outlet subcooling is about 15F (8.5K), then measure the superheat at the evaporator outlet.


Gary, To watch for compressor flooding, would I be expecting the suction pressures to change, or simply for frost to start building past the inlet valve on the compressor or will my evaporator outlet temperature drop? Is there a "best" way to monitor for that condition?

Your evaporator outlet superheat should drop.

[dkemper]

Gary, thank you for the suggestion, I'll target for your 15F/8.5k subcooling out of the condensor. The condensor has plenty of capacity left, I should have no troubles getting there.


US Iceman. My current solution is not really elegant, but by forcing all 4 unloaders to maintain a loaded condition, I've pulled temps and pressures down to a usable level to manufacture a product. (makes the boss happy)

Carlyle has two different spings for the internal unloader. One with 7lbs of force, the other with 11. With the low pressure (R134/R500) spring in the internal unloader, and set to it's minumum loading pressures, the system was hovering at an incipant unloading at the 18 to 20 psig range and could not go lower.

I was able to find a Carlyle doc that stated that with a low temp R404a unit, the internal unloader was not an appropriate control system. At $4000 US, and 30-45 days out, I was not able to persue Carlyle's external unloader system. (as had been spec'd out in the original Carlyle design for this implementation).

To save money, my predicessor sourced the compressor from a rebuilder (and omitted the external unloader) so it is possible the internal unloader does have a mechanical fault. Unfortunately, that also costs me access to Carlyle's support staff. Even if there is a mechanical problem with the internal unloader, did not see the point in chasing that down with Carlyle stating to use an external unloader in my situation.

So, I blanked off the oil passage ways between the endbell and bearing housing, tapped into the oil supply from the oil cooler and currently meter the oil to the unloaders via a distribution manifold and valves. Metering is set to allow the unloaders to load in sequence on startup and then maintain a loaded condition. (hey, for a hundred dollars in valves, copper and brass, was an quick and inexpensive test)

Once I can start reaching target temps in the brine, I'll update the distribution mainifold with some solenoid valves and pressure controls.

Again, many thanks,

Win

[DeB]

Lana has given good advice.If you take -40C sst,40C condensing -20C rst and 3C nominal subcooling.The evaporator capacities are according to their respective computer programs:5H80 16.4 k/watts. RTSL1-70-240Y 29.6k/watts, and 45 k/watts with an economiser.Dont Think I'd waste time looking elsewhere

[setrad7791]

Well for some one new to refrigeration (6 months) you sure seem to have it down packed! Why did i bother with a 4 year apprenticeship?