Hot water tank - condenser rupture - what will happen?

[desA]

We have a hot-water tank (called a geyser in SA), which has a safety relief valve set to 6 barg. Water inlet feed is at 4 barg.

A pipe-coil condenser is placed inside the geyser. When the hot water is at 60'C, the condenser ruptures *suddenly* inside the geyser at 27 bar (alternatively at 42.6 bar).

What will happen?

[monkey spanners]

It go BANG!

http://www.youtube.com/watch?v=Cv178...eature=related

Jon

[desA]

LOL... it sure does.

http://www.youtube.com/watch?v=0rXwcDkobUY&NR=1

That is what I have been telling people. I've had responses that the gas will 'fizz' into the water and be absorbed. Not sure that nature will agree with that argument, though.

[Gary]

Well... I'm not so sure. The refrigerant pressure would drop very quickly and the relief would pop.

[Brian_UK]

The geyser safety valve should lift to release the pressure however it should, perhaps, be sized to accommodate the large increase in pressure over the steady increase expected.

[Bigfreeze]

I've seen an installation where a plate exchanger burst and vented into the ufh system and tank. No damage bar water in the refrigeration circuit. All displaced water vented through the relief valve. It really is no biggie

[MikeHolm]

Des, standard water heaters here are designed to double the rated pressure. This is the standard fudge factor. A 300l tank rated for 125 or 150 psi, as standard tanks here are, will need a much larger volume than the 20-30L of a refrig system hooked up to the coil in the tank to take 60psi to the burst pressure. The standard PRVs used on the tanks will let out 50kw instantly (well... after it drips for a while.

I have had a solar system with 100L in volume and internal pressures of 25+ bar and temps of 200C (due to pump control failure) burst a flat plate HX and the 1500L tank PRV just started to drip (exp tank was toast though).

[lencerpetro]

It is the fact that the coolant pressure would drop very fast and the relief would pop. And it is also true the geyser safety valve must lift to relieve pressure, however, should perhaps be sized to accommodate the large increase in pressure at the steady increase expected.

[lencerpetro]

It is the fact that the coolant pressure would drop very fast and the relief would pop. And it is also true the geyser safety valve must lift to relieve pressure, however, should perhaps be sized to accommodate the large increase in pressure at the steady increase expected.


Rainwater tanks

[desA]

Thanks everyone for your comments. An interesting scenario that probably plays out different ways, depending on the RV sizing & selection.

[MikeHolm]

RV sizes are based on the maximum possible increase in energy (temp and/or pressure) expected with a failure of the heat source to limit itself. In Canada a standard 250L natural gas powered tank with a 10kw input (at 55% eff by the way) will have a relief valve setting of approx 75kw at 9 bar (approx) and ours have a temp failure at 95C usually.

I know your tanks run at lower max pressure standards than ours do but given the energy available in the coil volume, can that safely be absorbed by the tank volume? Is there an expansion tank on the DHW system as we have to do more and more?

Nice video on youtube but there is no PRV so it is irrevellant.

[arne22]

I guess that how fast the pressure will drop or build up, will depend of how much volum the tank and the tubes can expand. If there is some vapor, gas or air, some plase in the system, this will "take the first shock". If there is nothing that can take the first load by expanding, the one way or the other, it will be a question if the safety valve will be fast enough. I thinkt that there is only one way to know for sure, and that is to try it out. I guess that if the system were buildt with some a some kind of gass or air chamber that can be copressed, the system would be safer. (Because thsi would take the first shock out of it, if something should happen.)