Maneurop MTZ 100 internal relief problem on heat reclaim

[brassmonkey]

Hi All,
Been a member of this forum for a long time now, enjoying everyone sharing their knowledge, this is my first post and would appreciate some feedback from around the globe.

I've been working on a milk vat run by 2 maneurop mtz100's that has recently had a heat reclaim hot water system added into it. We were called out due to a slow pull down time and found the compressor to be venting on the internal relief valve. (Set at 30bar) R438a which equates to approx 70c) the hot water system is supposed to be set for 85c with electric booster elements of course)

I guess my questions are

Should there be a check valve installed in the discharge line to prevent higher pressures coming back to the compressor when the electric booster elements kick in?

Could this high pressure coming back onto the head of the compressor caused the failure of the relief valve?

Thanks for your time, hopefully you guys can give me some good feedback.

Cheers

[chemi-cool]

I guess something went wrong when the heat reclaim was installed.

You should not heat the same water to 85C. It is much too high for the discharge temp.

[joe-ice]

Is the discharge just piped through the heat exchanger with no valves or are there valves bypasses etc. A lot of these systems use a pressure regulator to keep the pressure high in the exchanger ,this is often to the detriment of the overall system . You really need a pressure reading before and after the exchanger before you go any farther

[brassmonkey]

Thanks joe-ice,
The discharge is piped directly to the exchanger, no valves or bypasses. The only extra bit of gear on the discharge side is an oil seperator.
I didn't design or install either the heat reclaim or any of the system, just one of the lucky ones that gets to fix it I guess.
Have changed out the compressor but would like try and work out why it failed.

[Len Fiddler]

The internal relief valve opens at 30 bar above crankcase pressure and will fully re-seat below 8 bar diff
Should the valve open the gas will hit the internal Klixon and cause it to trip and under these circumstances could take about 2 hours to reset.

[Glenn Moore]

Hi brassmonkey
Can you make a sketch of the components in the discharge line with the heat recovery unit. The HR once up to temperature should bypass the gas to the normal ambient condenser. The condenser and HR can be piped in series or parallel but needs proper discharge temperature control to prevent cooking the compressor. Show us whats on the system and we can try to advise