Refrigerator Compressor Running Too Much?

[SVNeko]

How can I tell if my refrigerator compressor is running too much? It seems like it is on all the time. It is a water cooled Isotherm and, granted, we are in a very hot climate with quite warm water. But I think they are drawing too much power by running all the time. Any way I can measure it? And if so, what to do about it?

[SV THIRD DAY]

Hola Neko...
If you have an Amp * hour totalizer aboard and are able to turn off other loads, that's an easy way to get some meaningfull AH data. This is what I think the majority of cruiser do to check on the total daily amp usage of their refrigerator. If you are an anal type of engineer that loves data...it's cool to put a 12v hour meter on your refrigeration unit. This combined with the Amp*Hour meter can really give you some great data, which can be tracked with ambient temp, water temp, etc.

Of course the old fashoned way is to sit there next to the unit while drinking beers and recording the on/off times of the compressor. The problem is the more beers you drink...the less you seem to pay attention and have to start all over the next day with another 12 pack...

You mention a water cooled unit...in Mexico once the water got warm for us...I don't remember our water cooled unit turning off to be honest for the entire summer! Now I can't blame that all on the water cooled unit because our insulation was to put it nicely "crap". Is this your first season down in the hot climate?

[Richard Kollmann]

SV Neko, Troubleshooting is simple if compressor is running too much You can rule out refrigerant loss first. Has anyone tampered with refrigerant recently? Look at evaporator to see what percentage of its surface area is covered with frost. Correct refrigerant charge is when there is frost covering 90% of evaporator and no frost on line returning towards compressor.

Second thing to check is temperature of refrigerant traveling through seawater condenser or if unit has a through hull heat exchanger.
There are two lines connected to compressor pressure and return one is very warm the other 60 to 75 degrees F.
The very warm line from compressor connects to seawater condenser or through hull condenser coil. Refrigerant line coming out of condenser should be no warmer than 100 to 115 degrees F. If temperature of line leaving condenser is too warm it needs to be cleaned.

All seawater condensers must have regular cleaning if your unit has a through hull condenser dive under boat and clean it. If this is a pumped water condenser the complete water piping and condenser must be cleaned. There are reports that through hull condensers and Keel coolers are less efficient in tropical warm waters.

[Terra Nova]

Rich--good post.

The difference between refrigerant and cooling media temperatures (delta T) affects the absolute efficiency and, therefore, run times.

[model 10]

All seawater condensers must have regular cleaning if your unit has a through hull condenser dive under boat and clean it. If this is a pumped water condenser the complete water piping and condenser must be cleaned. There are reports that through hull condensers and Keel coolers are less efficient in tropical warm waters.[/QUOTE]
If I understood the OP, he has a (Iso Therm), self pumping cooling system. The condenser is a small coil in the galley sink drain through hull. Very clever set-up but how can you clean it? Acid down the drain?

[SV THIRD DAY]

Originally Posted by Guy

Very clever set-up but how can you clean it? Acid down the drain?

"Clever" on a critical boat system often leads to questions like "how can you clean it". To me "clever" means not messing around with something as evil as sea water for your refrigeration when a properly designed air cooled unit will work great even down in the tropics.

It's the age old drama I saw in Mexico and experienced myself. The refrigeration unit worked great up North, but then due to the higher heat loads (air and water) the refrigeration power usage shyrocketed. Ours used 45AH in California and then close to 150AH per DAY during our time in the Sea of Cortez for the summers. It damn near killed us from a power usage standpoint, but honestly, it still didn't keep me from making ice...the "show" must go on I would say as I fired up our Honda 2000 to charge the batteries and run our Blender!

[Zanshin]

I am not sure from looking at web pages for Isotherm if they use the ubiquitous Danfoss compressors, but if they do then you should also check to see if they have the smart speed controller plugin or something similar attached. This reduces energy consumption by regulating the compressor speed (and thus the current draw). As the startup cycle is inefficient, these systems tend to maximize the duty cycle while reducing the RPMs; so although you might have 90% duty cycle time your net energy use is minimized. I had such controllers on my last boat and something similar on this one and they do work to reduce energy consumption but result in long duty cycles.
I am in the Caribbean with 28+C in the boat and the water at about the same temperature. One fridge (air cooled, at 5C) and a freezer (keel cooled, at -10C) eat up around 70A (@24V) per day at the moment, but I need to defrost the plates and the insulation on the fridge isn't great so your usage will certainly be less. The duty cycle on the fridge is high, certainly over 75% of the time, but at reduced RPMs while the freezer runs a lot less, perhaps about 20% of the time.

[Richard Kollmann]

Terra Nova, you are correct controlling cooling media temperature is the next step after selecting the correct matching balance of components. On larger water cooled systems application engineers install a means to control water flow this then keeps refrigerant high pressure in an efficient pressure/temperature range. There is no practical way to control this on small Danfoss BD compressor systems today, but maybe in the future.

While waiting for a solution to controlling liquid refrigerant at correct pressure levels I stay away from any type water cooling on compressors 1/6 and smaller. Air cooled condenser’s can easily be made more efficient to compensate for warm or cold ambient climate applications. The simplest method in cold climates is to restrict airflow through condenser. Twenty years ago Adler Barbour recommended using cardboard to block off 50% of condenser air flow. Cold ambient conditions on air cooled units is not as detrimental to refrigeration performance when condensing unit’s cooling medium is cabin or boat interior ambient air.

The real performance problem with keel cooler and through condensers systems is they can not compensate for cooling medium changes as well as fan cooled units. This is because they have too large of an effect on refrigerant volume in a system when capillary tube expansion flow control device is used because there is no room in keel cooler or through hull coil to store excess refrigerant . The warmer ambient seawater conditions there will be more liquid refrigerant and an over charge condition can cause much higher pressure/amperage increasing daily power consumption. On air cooled condenser used on small Danfoss BD compressor systems larger tubing is used in condenser to allow small amounts of condensed liquid to be stored their keeping refrigerant charge less critical in hot conditions.

[senormechanico]

Richard,

Since installing my Vitrifrigo BD35 keel cooled system and the internal box airflow worked out, I've had no problems in water temps from 43 f. to 75 f. Air temps in the area of 75 f. water were up to high 80's. (Desolation Sound in July/August)

Would a small accumulator tank for the refrigerant in a keel or water cooled system be of value ?

[Richard Kollmann]

Originally Posted by senormechanico

Richard,

Since installing my Vitrifrigo BD35 keel cooled system and the internal box airflow worked out, I've had no problems in water temps from 43 f. to 75 f. Air temps in the area of 75 f. water were up to high 80's. (Desolation Sound in July/August)

Would a small accumulator tank for the refrigerant in a keel or water cooled system be of value ?

senormechanico, The only reasons you would have to deviate or change a manufacturer’s or application engineer’s design is poor performance or to correct proven troubles with your type system.. Northern Latitudes do not produce prolonged high compressor temperatures for the BD compressors. Cold temperature may reduce capacity they will not stop compressor above 32 degrees F. From the performance standpoint if your refrigerator maintains your desired box temperature and runs less than 50% of the time do not tamper with it. Refrigerant volume must be precise on that type unit so never let anyone connect gauges to it or tamper with refrigerant.

[senormechanico]

I was just asking a theoretical question.
No problems here.
Summer with big load never exceeds your numbers.
Batteries are always full at the end of the day from solar.