Sportsmobile Service Bulletins - Flat Plate heat exchanger

[kzemach]

Originally Posted by bryanlaws

I guess the key phrase here is "if you don't drain it prior to freezing"? Did yours crack like after having drained it in freezing temps or is that while "full"?

You are absolutely correct. I did not drain prior to freezing; it was full. This is the single wall unit before SMB realized they had a problem and before there was a way to drain it (without disabling your entire water system).

So, you know the drill- freeze/thaw = expansion and contraction and eventually you'll break it.

When I talked to the people at Flatplate when this whole fiasco started, they told me that I should absolutely not let water freeze inside it or it will break (like it did). They recommended that I replace it with a double wall "for more buffer" but they also said that a double wall will _also_ eventually break if you let water freeze in it, it'll just take longer.

So those of you with double wall units: You still gotta drain it and not let it freeze!

[daveb]

OK, I let my flatplate stay full when I'm in the low to mid 30s and have yet to have a problem. When I am camping in cold weather I have the Hydronic run before bed time and then have it crankup about 3AM and run for 2 hours. Also yet to have a problem (that I know of) so far. I figure that the lines will freeze before the flat plate and that has yet to happen. Anybody know what will happen if you fire up the Hydronic with 1/2 the water (the fresh water side) drained out of the flat plate? What kind of damage would that do? Seems like that would be just as bad but I don't know what it can take. My luck is I would zone out one day and fire it up W/O fresh H2O in it.
Dave Boyer

[kzemach]

Dave,

I can't imagine it would be a problem to have hot coolant going through with no water. Coolant, whether hot or cold, won't crack anything as other than expansion/contraction of the metal itself (which it's designed to take allegedly), you're not putting excessive stresses on the unit. The coolant pressure in the coolant portion of the flatplate won't change, which is distinctly different from the pressure on the water side if water is allowed to freeze in there.

If I were in low to mid 30s I wouldn't bother draining it; especially if you're running the hydronic. I also agree with your lines vs flatplate freezing analysis. It's if you're not keeping the unit warm and temps are below 30.... that might be another story.

Ken

[DUKCSUN]

I had the opportunity to be in sub-zero temps in the Owens Valley with the first single-walled exchanger where the plastic feed-line promptly froze leading into the heat exchanger and popped. I was scheduled that next week to have the double-walled unit installed (pure lucky timing) and then went back to the sub-zero temps the next weekend armed with the double wall unit and the ability to drain it.

I drained it and while the lines outside the van didn't freeze (nor did the heat exchanger to my knowledge) but the lines INSIDE the van froze. I had a skim of ice on the top of the water in the under-goucho water tank which will tell you how cold it got inside the van that night. A water bottle I had on the floor froze also.

So, that was a lesson learned. I'm a mountaineer so I was as cozy as could be sleeping but I vowed to use the timer-defeat switch on the furnace if for no other reason than to keep the insides above freezing or just below.

Once I turned the furance on in the morning and the inside warmed up everything was fine.

Additionally, once the water started flowing (I waited to turn on the hydronic) which is how I knew it was the inside that froze.

Another note regarding low temps. The first weekend I also had diesel freeze in the fuel line leading to the hydronic. I hadn't used any fuel modifier (I use standyne sp?) and it froze up such that the "low fuel" error came on the display.

The following weekend I used the fuel treatment and nothing froze at all. So, I do recommend using some fuel treatment if you're going to go super-cold.