Tuesday, June 4, 2013

Cold Plates versus direct expansion evaporator plates

As mentioned in previous posts the days of holding plate refrigeration are numbered and have been for many years.  In certain circumstances they may well be of benefit if they are TRUE EUTECHTIC plates....Most off the shelf self install systems using holding plates are really just "cold storage plates" and occupy precious box space that could be occupied by frozen product that truly benefits in energy terms taking into account LATENT HEAT OF FUSION. The reason for this is that unlike a true hold over plate they are filled with a mixture of propylene glycol and water and this mixture will determine the plate temperature to be a 0 deg F plate or a 20 deg F plate.. There is no physical conversion from liquid to solid, rather liquid to slop or slush at best, it it were a TRUE EUTECHTEC solution then the freeze of the solution and it's expansion would blow the plate. Therefore their advantage is not justified as they do not 100% achieve the thermodynamic heat laws governing  LATENT HEAT OF FUSION. 

Silver Copper Phosphorous Brazed Joints versus "Quick connects" & Mechanical Fittings

As any fridge technician will tell you the biggest problem with a system is a gas leak. Most off the shelf self install systems use quick connects and mechanical fittings. Over time these fittings fail from a combination of vibration and the metal age hardening. 

A typical quick connect actually has 3 possible leak points and there are four of these little beasts in every system = 12 possible leak points. Add to this a thermostatic expansion valve = 3 possible leak points. Now we need a fill valve and an H.P. shut off valve = 4 more possible leak points. Grand total = 17 possible leaks!

The Mexicolder has a fill valve and that's it. It has schrader valve and a cap, just like a car tyre. The valve core is dipped in fridge oil at install and a cap is secured to this with a nitrile "O" ring

Grand total = ZERO leak points.

I rest my case........hard facts and the hard truth!

Latest update: I recently looked at a system for a sailor that had a fridge and freezer with two cold plates in the freezer and one in the fridge. It uses a huge amount of energy he informed me. We run the generator 3 hours a day to keep up with it. Or we can run the main engine to hours a day. On inspection this beast had no less than 60 mechanical joints in the pipe work, four expansion valves, two condensers, two compressors and yards of wires, four solenoid valves and multiple block connections. I explained that with so many mechanical joints even if I added gas and tuned it I WOULD GUARANTEE it would break down in a month, a day or a week or maybe even before I removed my gauges. Mmmm. he said, you are the first person to have been honest with me. Twice a year for the last 5 years I have had a fridge tech charge serious dollars to keep this working ( or not) as was the case. Honesty is the best policy because we ended up gutting the box, re-insulating and installing a new Mexicolder. Now it works silently on solar alone. And get this, we lost 150 lbs of obsolete gear and gained two huge storage lockers.