Failure of Stainless Steel Heat Exchanger

[kiamaian]

I used a stainless steel blazed plate heat exchanger as an evaporator for a heat pump hot water heating system.

Unfortunately the heat exchanger has failed as there is a large leak between the refrigerant side of the heat exchanger and the water side. This has had the effect of filling the refrigeration system with water and I suspect burning out the compressor.

I have not used stainless steel heat brazed plate heat exchangers before and I wondering whether they are generally reliable or whether I have just been unlucky. The system has been operating for about eighteen months and I am concerned because I am also using a similar exchanger for the condenser.

Has anyone any suggestions on how I could dry out the refrigeration system when it has been completely filled with water?

The compressor is a sealed unit of 2hp and the refrigerant is propane.

[gregd1401]

Was the heat exchanger 304 or 316 grade stainless. 304 is very prone to failure if chloride levels increase to >500 ppm. Get your compressor rebuilt by a reputable company and replace the failed HX. The rest of the system can be dried by purging with dry nitrogen and deep evacuation and replacing liquid line driers. Was the propane refrigerant grade and why did you choose to use it in the first place?

[gregd1401]

Just another thought, what water are you using through the evaporator as your heat source?

[kiamaian]

Thanks Greg for your interest,

I used refrigerant grade propane because it suited the the compressor which was designed to use R22 and it didn't require me to change the oil in the compressor.

Another factor was that I was able to buy this gas in Australia without a Refrigerant Handler's Licence.

The water going through the HX is clean rain water which is circulated directly from the rainwater tank.

I am not aware of the grade of stainless steel in the HX and I can't remember it being mentioned on the box that it came in.

I have been thinking of putting some of the components into a drying oven but I don't know whether the diaphragm of the TX valve would withstand the heat.

[AndyHX]

Hi there , there a couple of reasons why a phe fails, pump not working , water flow restricted , no suction pressure control , no water outlet sensing control so basically ice forming inside phe and causing failure. these are the things that have to be thought about when you get this machine running again.

[monkey spanners]

If is metal fatigue rather than corrosion then it can be cause by the plates flexing as the pumps and compressors cycle on and off.
Have you cut open the failed one to see what went wrong?

[NoNickName]

Probably the evaporator iced up because of bad control or missing leaving water temperature sensor.
The system can't be repaired succesfully, especially because the compressor is sealed. Trash it altogether and buy a new one.

[desA]

For future machines, please consider using a vented, brazed PHE for evap & condenser.

[benijoseph]

sir,
Better replace heat ex-er & comp and use more inter locking for fail proof
system.
rgds.

[kiamaian]

Thanks everyone for your responses. I was not aware of the danger to the heat exchanger when the flow of water through it was interrupted. When I get the system working again I will put a flow switch in the water line to the heat exchanger so the compressor stops in the event of pump failure. Before installing the heat exchanger I looked for information to help me but there does not appear to be very much published for using them in refrigeration applications.