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billjduke
22-07-2003, 07:50 PM
I have a model Ransco model 7102-1 thermal shock chamber w/ 1 7.5HP compressor charged w/ 13 lbs of R502 and 1 7.5HP compressor charged w/ 8 lbs of R13.

The unit is 10 yrs old and no technical manuals are available from Ransco. Their technical support
group says that 13 gpm of 85 deg F water is required for compressor cooling (no idea of the discharge temp).

It would be more practical for me to supply 40-50 deg chilled water in a closed loop but they have no idea how much flow or what size cooler would be required.

Does anyone have any thoughts ??????????

Thanks,

Bill

Andy
22-07-2003, 10:06 PM
Hi billjduke:)
what about fitting a thermostaticwater valve on the condenser outlet, controlled on head pressure, which would trottle in the flow automatically to acheive the desired head pressure, or a thermostatic mixing valve returning some of the water from the outlet on the condenser back to the inlet to acheive the desired head pressures.
Andy:)

billjduke
22-07-2003, 11:07 PM
The unit is not in service and was recently purchased from a used equipment dealer who is unable to supply any info.

I am having to purchase and install a chiller and would like to ensure it is adequate but space is critical and I don't want to drastically overkill.

Thanks,
Bill

herefishy
22-07-2003, 11:43 PM
Hi Andy :)


I'm not sure if there is not already a head pressure control/water regulator in the unit.

Nonetheless, billjduke may be primarily concerned in regard to the refrigerating capacity requirement of a chiller employed to cool the first stage of this cascade system.

We had chatted, and were working on the estimated THR of the first stage @7.5hp and using the rule of thirds, estimating approximately 6.5 tons of THR required for condensing capacity, assuming a 45degF SST or so, and a multiplier of 1.3 for heat of compression, motor, etc.

The mfgr recommends city water supply (NOT!) or an evaporative tower for the condenser water supply.

cheers,

herefishy
23-07-2003, 03:01 PM
I guess, more accurately the question would be - If the system requires 13gpm of 85degF water for system cooling, what would the calculated load be?

13gpm * 8# per gallon * 60 minutes = 6,240 pounds of water per hour.

If we assumed a 100degF water temperature leaving the water cooled condenser - 6,240# * 15degDT = 93,600 btu/h

Does 7.8 tons sound like a proper capacity for cooling the first stage 7.5 HP R-502 system?

herefishy
23-07-2003, 03:07 PM
R-13 @ 244.43psig has a saturation temperature of 25degF. Should we assume this our evaporating temperature for the first stage system?

Gary
23-07-2003, 05:56 PM
If they wanted 25F, they would have used R12 in the first stage. The first stage SST is probably more like -25F or even lower. The first stage should have an interlock that prevents the second stage from starting until the first stage evaporator is down to temp. This will be a RA low pressure control or thermostat. We can tell from the cut-in and cut-out settings what the first stage SST runs at.

I suspect we will find that the first stage runs considerably less than 7.5 tons, and the second stage considerably less than the first stage.

herefishy
23-07-2003, 06:46 PM
So perhaps our DT water in and out of the first stage condenser is more like 5degF, and perhaps our required chiller capacity would be more in the line of 2.6 tons?

Gary
23-07-2003, 07:19 PM
I'm thinking more like 10F and 5 ton chiller, but you may be right. Given the control settings and compressor make and model, we may be able to narrow it down using compressor rating @ design SST.

Gary
23-07-2003, 07:33 PM
Something to think about: Once this is all together, in effect we have three stages. First stage is the chiller. Second stage is the R502 system. Third stage is the R13 system. We will need another interlock which does not allow the R502 system to start until the chiller is down to temperature.

We also need to trouble shoot and/or fine tune in that order. Shut off the second and third stages. Get the first stage working perfectly. Then start the second stage, and get it working perfectly (it should be running close to floodback without load). Then start the third stage, and get it running perfectly. In any other order, it will make you crazy, trying to trouble shoot three systems at the same time.

herefishy
24-07-2003, 02:18 AM
No, no, no......

It's not three stages.... the chiller will maintain the circulating water temperature and will cycle as load is applied. These folks do semi-conductor testing that one cycle may run a week at a time.

You were right on the money in your previous post, Gary ;).

Billjduke, you need to provide the model number of the R-502 compressor, and we can determine the required condenser water chiller capacity from that data. Get into the machine and look at the compressor dataplate.

;)

Gary
24-07-2003, 05:01 AM
Yes, I understand it is a two stage machine. But when working on it, it is useful to think of the chiller as another stage. The chiller will have a very strong influence on the operating characteristics of the cascade system.

billjduke
24-07-2003, 02:34 PM
The compressors are Carlyle Compressor CO. models
06DR7240DA3600 and 06DR2280DA3600.I don't know which is which as the lines, accumulators, etc. are identical and there are no refrigerant labels. The type and amount of refrigerant is listed on a nameplate on the cabinet.

They are both water cooled and the final temperature of the chamber being cooled is -70C.

Bill

herefishy
24-07-2003, 04:38 PM
Hi, Billjduke :)

The 06DR724 is a 6.5 horse compressor rated at 24cfm of displacement (@1750 rpm), low temperature.

The 06DR228 is a 7.5 horse compressor rated at 28cfm of displacement (@1750rpm), low temperature.

hmmmm, the nameplate indicates the voltage at 50/60 Hz. The compressor data is listed in the 50Hz. specifications. Is the machine spec'd for 60Hz? The displacement in CMM - 50Hz. is .56CMM for the 6.5 horse, .66CMM for the 7.5 horse. (@1450 rpm)

http://www.carlylecompressor.com/TechnicalInfo/06D06eAG.htm

The compressors are NOT water-cooled. The water is to cool the first stage condenser. It you follow the water connection in the unit to (the) heat exchanger, a pipe from the heat exchanger will connect directly to the discharge of one of the compressors. This would be your first stage R-502 compressor. I think we could assume a -10F evaporating temperature for the first stage, because both compressors are rated for evaporating temperatures of -40C to -7/-1C

So low temp, we could use the rule of thirds, and guess 2.15 tons if the 6-1/2hp is the first stage, or 2.48 tons if the 7-1/2 hp is the first stage.

If we just say 2.5 tons or 30,000btu/h divided by 8# of water per gallon, divided by 60 minutes which equals 62.5 btu/minute (per DT water in and out), right?

If 62.5 btu/m @ the mfgr suggested 13gpm at 85 degree water in, would equate to about a 4.8 DT or about 85F in, 90F out.

:)

Gary
24-07-2003, 06:49 PM
That 2.5 tons is btu entering compressor. We need to add heat of compression, which should bring us up to about 3 tons.

herefishy
24-07-2003, 08:20 PM
yeah.... :)

I talked to my chiller mfgr, and told him 13GPM 85F out and 90F in, and he came up with three tons. ;)


The decision at hand now is - the evaporative tower thingy? Or closed loop chiller? For 3-tons, an evaporative water tower would be about the size of a kiddie pool, wouldn't it?