Sanden Compressor Puzzle

[DeniseO30]

Richard would he gain anything by increasing condensing water flow rate? My experience with water cooled equipment has all been on larger systems for AC and heat pump duty, they of course modulate the flow through the condenser.

[dkall]

Ok.... to answer some qsts. The pump that runs the cooling for the condensor and the genset is a Johnson CM90 and pumps 17 gals/min optimum. I don't see any info on head pressures but the exhaust is approx 1' above the waterline. The hose connections are 3/4" and I will check and make sure my strainer is clean.

The system on the DC and Engine driven side are mirror images of each other in plumbing. The refrigeration and the freezer each have their own TX valve. I can also shut off either side with a switch on the control panel.

If Richard has a better graph of the optimum pull down of an engine driven system in the tropics I wouldn't mind having a copy. Maybe he can provide a link to one.

For Denise the compressor is belt driven off the Kubota.

Sorry Richard I don't understand what you mean by this "On this system's design because of its two plates and small reciever do not attempt to fill sight glass with liquid unless all plates are frozen solid. "

All three holding plates frost up and I pull the suface of the plates to below 32 F. The freezer is usually pulled to less the 10 F and the refrigeration is usually pulled to between 18-20 depending on the heat load added.

Is the suggestion to take out another pound or two of pressure. How else to get the 40 minute time closer? I do agree that out here in cruising land I try to do what is needed to maintain where I'm at and am thus not interested in acid treating the condensor unless it is absolutely necessary.

[DeniseO30]

Sounds like a system for a boat 80ft long! How old is it Dave?

[dkall]

It's been running for approximately 4 years while we've been cruising full time. Approx 2-3 month's per year we've been in a marina keeping the boat ship shape and then use the DC-5000.

I've replaced a holding plate once because it was too small and thus recharged both systems approx 18 months ago. I've found approx 3 small leaks over the 18 months and added refrigerant as needed but looks like I've added to much.... actually to both systems as the DC side runs to long too but that is another issue.

In retrospect I almost wish I would have put in three Engles then when one screws up I can throw it away and get another. This is so expensive I can't justify dumping anything and switching over.

[DeniseO30]

Nearly 2 of everything Dave I don't doubt it! I suppose you could sell off the compressors but I don't think the 12 volt condensing units may be large enough to handle the plates. It all kind of makes one wonder if people using small 110 volt boxes on an inverter may know something we don't!

[DeepFrz]

dave, have you checked your engine to see if maybe it is losing power? Maybe you have a fuel flow problem that is limiting your HP output.

[dkall]

That was my initial thought. I've changed the Racor and the filter on the Kubota and changed the fuel pump. When I was 30 minutes or so into the pull down the engine started bogging down and shutting down the refrigeration compressor ended the bogging down. When I'm pulling 150 + amps on the alternator (no compressor) she runs fine at 3 k. So yes; I feel I've eliminated any possible fuel issues.

Thanks

[Richard Kollmann]

Akal, No one can produce a performance chart for your system but you because there are too many variables involved in engine driven holding plate systems. In the section on fine tuning in my do it DIY Boat Refrigeration books I suggest each person run a performance profile and send them to me matching the sample chart. With hundreds of systems built to this design, and over sixty of them in this book none ever operated at your high liquid side pressures, even in tropical water temperatures after fine tuning was completed, mainly because condenser capacity was larger than needed.. A few years ago I was contracted to train personal in maintaining charter boat refrigeration. Part of the two week down island training was to do a punch list of conditions found and correct them on 30 plus boat refrigerators.


As I understand it your Problem began with poor performance do to refrigerant leak.

After adding refrigerant compressor stopped due to tripping 220 psi high pressure switch inside plastic flow control box.

Removed some refrigerant dropping overload pressure from over 220 to 150 psi.

Next you reported small engine lost power do to refrigerator load.

You indicated refrigeration was fine before refrigerant loss even in tropical waters I assume.

It is a proven fact that SeaFrost plastic tank type condensers lack equal max capacity of Sanden compressors in tropical waters especially if overcharged with refrigerant. It does not appear you can do anything with condenser cooling if there is good flow, so remove some refrigerant a little at a time until high pressure drops to125 psi is the only solution. Before reducing pressure run system till plates have frost on them then reset generator to its normal operating speed before reducing refrigerant volume. Refrigerant must be removed through suction port while watching suction pressure gauge to insure gauge pressure always remains positive pressure; this prevents air from interring system. If suction pressure is below 10 psi stop compressor and then let out some refrigerant. After restarting compressor wait several minutes before taking reading of sight glass bubbles and high pressure readings. What you are looking for with both refrigerator and freezer valves open is just a very few bubbles.

When a system is overcharged your liquid receiver will not be able to handle all the excess liquid causing high pressure liquid to back up into condenser increasing high pressure gas vapor even higher. When this type system has a large enough capacity condenser, compressor’s 1200 rpm increased to max rpm will have little to no effect on high pressure as long as it has the correct amount of refrigerant.

[dkall]

Thanks R, I believe I'll take a little more out and then plot the results. However I have your book and can not find the suggestions about a performance test and anything about sending it to you!

I've been reading and re-reading what you say in your book and on line here and what I'm hearing is that basically it is NOT the head pressure to really be concerned with, but the LP side as the box cools down.

As you said in your book that after the condenser the temp should be below 100 mine look pretty good even though you say the Seafrost units are not the best!

Thanks for eveyone's time in reading and replying to my post. I'll report back the results after I make those changes.

[Richard Kollmann]

Akal, Fine tuning chart is on page 157.

High head pressure makes a difference when receiver is too small to hold extra refrigerant and condenser can not provide adequate sub-cooling.

[DeniseO30]

I wonder if the seafrost's designs were not changed for 134A refrigerant. I know in my trade (mostly AC) 410A coils were just re-tagged from R-22 use.

[dkall]

Ok, here are my results using one of Richards charts. I screwed up and instead of 5 min, 10 min, 20 etc I went 5, 15, 25 etc. Doubt that that makes any difference. Notes are provided as I observed the situation:

Engine RPMS 3 k
Water Temp 81
Engine Pulley 4.5"
Plate Temp is on upper outboard corner of first plate in series on the Freezer side
Plate Temp is on upper outboard corner of plate in Refer.

Notes: Removed approx 2 psi of refrigerant as suggested on this forum.

Start
LP 20 psi
HP 20 psi
Ref Plate Temp 35.3

5 min
HP 124 psi
LP 6 psi
Freezer Suction Temp 42
Refrigeration Plate Tem
Suction Frost Line Approx 6" on the compressor side of the Epoxy Sealed SPU
Notes Freezer suctions temp was measured as close to the epoxy Control valve as possible. Changed for next reading

15 min
HP 120 psi
LP 5 psi
Freezer Suction Temp 22.8 F
Refrigeration Plate Tem 31.7
Suction Frost Line None
Notes Took the freezer temp as close to the tubing exit as possible.

25 min
HP118 psi
LP 6 psi
Freezer Suction Temp 22 F
Refrigeration Plate Tem 29 F
Suction Frost Line Frost forming 6" from SPU unit towards the compressor
Notes RPM's began to bog down at approx 22 min and I reduced the generator speed to approx 2550 rmps.

35 min
HP 118 psi
LP 6 psi
Freezer Suction Temp 19.8
Refrigeration Plate Tem 25.3
Suction Frost Line Frost at the SPU fitting on compressor side
Notes


45 min
HP 120 psi
LP 0 psi
Freezer Suction Temp 22.1
Refrigeration Plate Temp Refrigeration has reahed the temp of 22 F so I shut off that side of the unit.
Suction Frost Line Frost tom Low side compressor hose back to SPU. No frost visible on hose or on compressor
Notes


55 min
HP 115 psi
LP -1 psi
Freezer Suction Temp 15.2
Refrigeration Plate Tem
Suction Frost Line Same
Notes

65 min
HP 115 psi
LP -1
Freezer Suction Temp 8.3
Refrigeration Plate Tem
Suction Frost Line Same
Notes Usually the plates in the Freezer are at temp of less then 10 degrees by now. Currently the plate is recorded at approx 15 degrees in the Freezer


75 min
HP 115 psi
LP -1 psi
Freezer Suction Temp 6.8
Refrigeration Plate Tem
Suction Frost Line Same frost on Tubing to the hose from the SPU to the compressor hose.
Notes: No frost on line to the SPU. Frost on on fitting going out.

85 min
HP 115 psi
LP -1 psi
Freezer Suction Temp 8.3
Refrigeration Plate Tem
Suction Frost Line
Notes


95 min
HP 115 psi
LP -1 psi
Freezer Suction Temp 8.5
Refrigeration Plate Tem
Suction Frost Line


Over all notes. Cleave at Seafrost tells me that the SPU is designed to let refrigerant through to aid in keeping the compressor cooler. There was from what I saw no frost line anywhere near the SPU at any times. Actually the frost line in the freezer didn't occur after the second plate till the refrigeration was shut down. This indicates to me that there was not enough refrigerant in the system. Further after pulling out 2 psi it appears to require a longer run time. I did ensure that the raw water strainer was entirely clean for this run.

[sfnz]

no puzzle at all really
1/ compressor too fast, 800>1000RPM ( or as close as you can get it) max in freezer duty, air is inducted via the shaft seal due to compressor running in a vacuum which as previously mentioned here takes up condensor space and can induce moisture to the system
2/ add oil/ lubricant, for the SD 508 regardless of mineral or polyolester oil the oil charge as per manufacturers specs, approx 175ml, is for auto A/C duty not refrigeration and certainly not for a freezer application approx 150ml max
3/ saltwater pump should be 1/2" jabsco impellor,, variable engine speed. variable compressor speed + fixed water flow is asking for it, particularly from a DC voltage pump
4/ refrigerant flow through evaporator with a TX valve is controlled by valve superheat not amount of refrigerant in system (unless it is low) open superheat to allow more flow (and oil return)

[sfnz]

Originally Posted by sfnz

no puzzle at all really
1/ compressor too fast, 800>1000RPM ( or as close as you can get it) max in freezer duty, air is inducted via the shaft seal due to compressor running in a vacuum which as previously mentioned here takes up condensor space and can induce moisture to the system, also allows condensor to remove more refrigerant heat as opposed to generated mechanical heat
2/ add oil/ lubricant, for the SD 508 regardless of mineral or polyolester oil the oil charge as per manufacturers specs, approx 175ml, is for auto A/C duty not refrigeration and certainly not for a freezer application, add approx 150ml max
3/ saltwater pump should be 1/2" jabsco impellor,, variable engine speed. variable compressor speed + fixed water flow is asking for it, particularly from a DC voltage pump
4/ refrigerant flow through evaporator with a TX valve is controlled by valve superheat not amount of refrigerant in system (unless it is low) open superheat to allow more flow (and oil return)

corrections

[dkall]

With the Seafrost setup the TVX is epoxy sealed and not possible to adjust the valve.

As for the variable engine speed for 4 years I ran at a fixed speed and for almost two years the DC raw water pump ran at it's constant velocity. As I'm trying my best to understand the system please forgive me if I sound obtuse. I'm not looking for a simple formula else I'll never be able to understand and maintain it. In Sanden's literature for the compressor they say that the working speeds are max RPM of 6k and I was running at 1/2 that.

Until this last change my min pressure was approx 3 psi but now personally I believe I'm a little low on refrigerant because the pull down took approx 20% longer!

Curious, if I have more then adequate cooling of the condenser then how is the fixed water speed an issue? Richard suggested that there isn't quite optimum cooling with the Seafrost system but most of what I've read suggests that if the exit temp of the refrigerant in the condenser is under 100 degrees then the system is fine and mine cooled the refrigerant 20 degrees to approx only 10 degrees above the water temp and 8-10 degrees F under 100!

Are you suggesting I should add 150 max ml of oil? And I've not seen where there should be a different amt of oil in the compressor for the different system except that I understand there should be more oil for each holding plate which would be similar to what your suggesting but not as per function.

Back to the valve; with both systems on (refrigeration and freezer) I get the bogging down after approx 20 minutes. That's when the valves ought to be open more and letting everything through including the oil.

Are you suggesting I would get better performance running at 1,000 rpms? It is hard to run the single cylinder diesel that low and would require some new pulleys - which are not possible yet where I'm at but could maybe be in a couple of months.

As for the suggestion of air getting into the system and thus mosture wouldn't I be getting a freeze up of the TVX's and then the HP rising, the safety valve shutting it down and restarting. I don't have that condition at all and I've watched for it!

Thanks for your response.