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Old 04-03-2015, 21:22   #1
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Size of condenser for engine driven refrigeration system...

I am thinking about replacing my DIY condenser with a factory version but can't get my head around the sizing

3GM30f
Sanden 508
About 4-5cu ft box with holding plate.

Would a 0.5HP rated condenser be ok?

As in something like this:
SCH 06 Standard Refrigeration Company Condenser New | eBay
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Old 04-03-2015, 22:15   #2
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Re: Size of condenser for engine driven refrigeration system...

The ebay condenser is a water cooled condenser. A 1/2 hp condenser is about 1200 btu's. That looks pretty close to the sanden 508. Though a bit overkill for a 4cf box. I assume you have a holding plate. Should be good. The water cooled unit is also 1/2 hp 1200 btu., though you'll need a pump for the water side
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Old 04-03-2015, 23:13   #3
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Re: Size of condenser for engine driven refrigeration system...

Darn! lost my post so will have to do over.

Ta for the help.
Box is 4.81Cuft.
Current condenser water feed is part of the suction line before going to heat exchanger on Yanmar. Holding plate(?) is about 50mm thick and 55cmx55cmx40cm.
Dunno whats inside it, but it appears to be filled with something

A pic of the current condenser below.

Drier & sight glass are rusty & need replacing as well. The accumulator Has R12, R22 R500, R502 on it. Can it be used with R134A?
Appreciate the help as refrigeration is something I have no experience with.
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Old 05-03-2015, 14:30   #4
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Re: Size of condenser for engine driven refrigeration system...

Latest development is the discovery of a small amount of greasey goo emanating from where the copper evaporator tube enters the holding plate in the bottom of the fridge. The consistency of grease.
Holding plate repair requires complete demo of the ice box as the SS box must have been TIG'd up with HP insitu.

I guess a pressure test of everything is in order.
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Old 06-03-2015, 05:30   #5
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Re: Size of condenser for engine driven refrigeration system...

For the 3GM 30 my designs have always used a 4 inch pulley bolted to crankshaft pulley. This works well up to holding plate solution size of ten gallons. If you want the compressor to outlast the boat its speed must be limited to less than 1600 rpm at max engine cruise rpm.

Counter flow tube in tube copper nickel water tube and copper refrigerant outside jacket. Condenser water cooling is to be provided by engine water pump. Condenser recommended for warm climates 1 ton. For boats that remain in seawater temperatures 75 degrees F and below a one ton condenser is adequate. You must always consider volume of heat transfer in condenser based on variations in water temp and flow. Most of the compressors work freezing plates is when motoring at low rpm out of an anchorage.

For boats operating in seawater below 60 degrees my designs call for a seawater bypass around condenser to allow for adjusting refrigerant liquid pressure.
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Old 08-03-2015, 12:13   #6
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Re: Size of condenser for engine driven refrigeration system...

Thanks Richard for your reply and PM.
On pressure test the holding plate held 104psi for 24 hrs so the origin of the goo at the point
the low pressure leaves the tank (bottom) to the accumulator is a mystery.

My boat is a complete rebuild from keelson up, but all the hardware is as removed from the old and has been sitting for ten years with orifices taped up.
https://boatfolly.shutterfly.com/pictures/8

So, I will replace the hoses & copper lines, flush the expansion valve and holding plate & accumulator refrigerant lines, and perhaps do the seals in the compressor.
The condenser is questionable it worked before but at very least complete de-scale & pressure test. New dryer & sight glass.

I would like to set myself up to be able to re-gas if necessary so will purchase a manifold & gauge set up. My sanden sd 508 has the flares so will need those connections.
Does this sound like a reasonable approach?
I have do have welding and bending gear.
Thanks again Richard; your dedication to the science/art of refrigeration is epic & appreciated worldwide.
Roly
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Old 08-03-2015, 15:14   #7
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Re: Size of condenser for engine driven refrigeration system...

Some tips you should think about before going any further:
  • Your SD 508 compressor was serviced with Freon 12 and most likely Wax free Mineral refrigerant oil. This mineral oil now is spread out a little in each component. I understand NZ was one of the first countries to convert automobiles to refrigerant 134a refrigerant and Castrol ISO 100 Ester oil. Mineral oil is not considered mixable with 134a where Ester oil is and insures positive oil return to compressor. Each component in system, compressor, suction line accumulator, condenser, holding plate and receiver will contain oil so try to determine total volume of oil trapped throughout system as each component is drained. If you can obtain refrigerant flush solution flush each component and seal openings until system is again assembled but do not add new oil. If you come up with little or more than 8 ounces of oil let me know of the dimensions of accumulator and receiver and I will give you the total quantity of oil to add after Vacuum dehydration is completed.
  • Refrigerant is a great cleaning agent so you can expect material to be washed from line and components so I recommend a larger than normal new filter/dryer be installed with Packless hand valves on each side so filter can easily be replaced. It is also important to clean or replace expansion inlet fine screen.
  • Your engine drive system should be protected with both a high and low pressure switch.
  • Do not mess with seals in compressor if they are wet with mineral oil they are preserved and protected to handle Ester Iso100 conversion oil.
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Old 18-05-2015, 15:24   #8
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Re: Size of condenser for engine driven refrigeration system...

Hi Richard,
Thanks for the tips. I am back on the refrigeration project after being side-tracked.
I need to source the high/low pressure switches and methodology to set.
Does your DIY book cover this? I applied for a login & pw to your forum but got no response.
Obviously the high will be open high covering the 95-135psi range and I guess manual reset (high)?
The low is a mystery open high or low or both? manual or auto or a combination?
Are johnson -Penn suitable or can you use fixed automobile auto reset AC units for protection?
The old system had no protection devices. Relied on manually turning the clutch off.
Thanks again,
Roly
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Old 19-05-2015, 07:53   #9
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Re: Size of condenser for engine driven refrigeration system...

First I recommend Your systems design may be different than the designs in my DIY boat refrigeration book, so automatic reset for low pressure switch adjusted to stop compressor when pressure drops to 2 psi. and resets on differential set at 15 psi for restarting compressor. If this pressure switch is used as a substitute for a timer or thermostat and items are freezing in refrigerator section increase low pressure cutoff from 2 psi to 4 psi.

If seawater condenser cooling is supplied by engine cooling water pump automatic reset high pressure switch I would recommend to be set at 175 psi maximum and later adjusted down to 25 psi above maximum operating pressure. High pressure switch differential setting 40 psi if it is an automatic switch.
If water cooling is supplied by an electric pump a manual reset switch is advisable do to reliability of electrical pumps.
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Old 08-06-2015, 16:07   #10
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Re: Size of condenser for engine driven refrigeration system...

G'day Richard,
I emailed you direct but no response as yet.
Your DIY book arrived (thanks) and what an amazing reference it is too!

As I stated my system is a little different in as much as it has 1/4" pipe on the High side an 3/8 on low side. Also no receiver but an accumulator on low side, with a expansion valve (not fixed orifice) odd.
Will the 1/4" vs 3/8" cut efficiency significantly?
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Old 09-06-2015, 14:34   #11
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Re: Size of condenser for engine driven refrigeration system...

Refrigerant tubing size is important to keep high and low pressure in a range where refrigerant changes from liquid to vapor inside evaporator. The SD508 engine driven compressor was designed for High Back Pressure air conditioning applications so line connections at compressor are in pressure side and 5/8 in suction side. I think you can get buy with in high pressure side all the way to expansion valve but 3/8 after that through evaporator and accumulator to compressor could be a problem. This 3/8 tubing may cause low suction pressure to operate in a vacuum shorting life of compressor. One solution is to reduce capacity of compressor by lowering its speed to less than 1200 rpm. If you can keep suction pressure above 2 psi at all times and frost away from compressor it should be OK.
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