I’ve argued with the service company that recently installed a new chiller system on our boat. The job looks nice and neat and no complaints there. My big worry is the materials used for both the sea water and chilled water manifolds. Schedule 40 PVC is what was used. I think it’s too thin of material and will cause problems in the near future. They assure me that the burst pressure exceeds what my operating pressures will be. What is your opinion?
They are correct when telling you the pipe will do the job in regards to burst pressure. A typical chilled water circuit may produce a maximum of 45 psi and the sea water circuit less. The burst pressure of materials they used far exceeds what your system design pressures will operate at. Hard to believe but a 1” Schedule 40 PVC pipe has a burst pressure of 1440, 2” is 1290 and 3” is 1200 at 73◦ F (23◦C). The burst pressure rating decreases with temperature increase but still within tolerable range for your application. Operating pressure is less than burst pressure. Maximum operating pressure for the listed size pipes are between 260 and 450.
The burst pressure is only one part of the equation for selecting the appropriate pipe system. Temperature is the other factor. Expansion and contraction of joint fittings occur when there are fluctuations in the temperature of water being carried within the piping circuit. I’m talking about the heat and cool mode button. If your system has a hot water circulation circuit (most do), your maximum temperature rating is 140◦F for solvent sealed fittings and 110◦F for mechanical thread fittings. The water temperature in heat mode can reach 110◦F. The threaded fitting will most likely start leaking. A leaking closed loop circulation circuit will affect the operation of the chiller / heat system by shutting down on pressure loss or lack of water flow. The big problem is not the lack of cooling or heating but the damage caused by water leaks throughout the vessel. Carpets, headliners and walls are expensive to repair or replace.
I personally wouldn’t install schedule 40 for the chiller water/ heat circuit or the sea water circuit. Drains – ok but nothing carrying pressure, even small amounts of pressure. Schedule 40 PVC is vulnerable to breaks when in a harsh environment. People stand on pipes in engine room as we know and it’s just an accident waiting to happen. If PVC is used a minimum of schedule 80 should be installed. For systems utilizing a heating circuit schedule 80 CPVC should be installed. The CPVC materials have a higher temperature rating and will not expand or contract at mechanical thread joints.
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