CPVC-Aluminum Collector

This page looks at using CPVC instead of PEX-AL-PEX for the plastic pipe version of the collector.  The PEX-Al-PEX version is described here...

 

The potential advantages of using CPVC/aluminum collector  instead of PEX-AL-PEX/aluminum are that the CPVC/aluminum collector could use a riser and manifold type design (like the copper/aluminum collector) for bombproof drain back.  And that it could be very fast and easy to build.  If you have not worked with CPVC plumbing, its hard to appreciate how easily this stuff goes together -- it cuts with a pair of special shears they sell for this, and the joints just need to be primed and glued and pushed together -- very very quick and simple.  CPVC pipe and fittings are also very cheap.

 

I did a little testing to see how well the CPVC might perform in a collector compared to PEX-AL-PEX.  The bottom line is that the thermal performance of the CPVC/aluminum collector  is about 4% worse than the PEX-AL-PEX/aluminum collector  -- this is a pretty small difference, and could probably be ignored.  But, the Oven Test that looks very roughly for an upper limit to service temperature indicates (to me) that the CPVC is pretty marginal even at 200F.  It would be very hard to keep a glazed collector from going over 200F on occasion.   Even with steep or vertical tilt and single glazing, the stagnation (no flow) temperature is likely to go above 200F, and it is nearly impossible to avoid stagnation over the full life of the collector.

So, for the reasons listed above, I think its best to avoid using CPVC for this collector design.  The only exception might be if you can assure yourself that the collector temperature will not get up to 200F.

I also feel that for most situations, the copper tube/aluminum fin version will be better than either the PEX-AL-PEX or CPVC  with aluminum fins.  While the copper version costs a bit more, and is a bit more work to put together, it will have better performance, and has a higher collector stagnation temperature capability.  Copper prices have dropped enough to reduce the cost difference significantly.

Small Panel Thermal Performance Test -- CPVC Collector

This is a small panel test of a collector made using CPVC pipes with aluminum fins, compared to an identical size and construction collector made from PEX-AL-PEX and aluminum fins. 

The test is done using the same procedure as was used to compare the PEX tube - aluminum fin collector to the copper tube - aluminum fin collector as shown here... The idea is have a way to compare the thermal performance of two collectors under exactly the same conditions in a simple and accurate way.  The collector that heats up the water in its reservoir more has better thermal performance.

Click on pictures for full size.


Small panel test setup.


CPVC/aluminum on left and
PEX-AL-PEX on right.


Making the CPVC small collector
test panel.

 

The collector using PEX-AL-PEX tubes and aluminum fins outperformed the collector using CPVC tubs and aluminum fins by about 6%. 

Collector Construction Start Temp End Temp Temp Rise % of Base
  PEX-AL-PEX tube - alum fins 52.86 90.06 37.2 base
  CPVC tubes - alum fins 52.38 87.26 34.9 94%
           

The performance of the CPVC collector is about 6% down from the PEX-AL-PEX collector.  Based on earlier tests, this would make it about 79% of the performance of the copper tube - copper fin soldered collector.

The CPVC collector was made in the same way that the PEX collector was made.  The CPVC is standard hardware store type tubing for house plumbing.  The aluminum is the same 0.018 aluminum soffit material that was used for the PEX collector. 

A 2nd test test was done the following day starting with pre-warmed water, and using a smaller water charge (29 lbs) in order to develop higher temperatures.  The idea was to get a bit closer to actual service conditions for water heating.  The clouds were in and out for this test with the first couple hours being mostly sunny.  After about 3pm, solid clouds rolled in, and I ended the test.

Just to make sure there was not something different in the two setups, I switched the container and pumps from the day before test. 

The result of this test was that the PEX-AL-PEX collector did about 3% better than the CPVC collector.  When you look at the graph, it looks at first glance that the CPVC does better -- this is just because the initial water charge was about 1.5 degrees hotter in the CPVC tank.  The PEX collector is able to close this gap between the two by a little bit over the course of the test, and ended with only about a 1 F difference -- so the PEX collector collected just a bit more heat during the test.

 

2nd Test Results:

Collector Construction Start Temp End Temp Temp Rise % of Base
  PEX-AL-PEX tube - alum fins 84.86 101.46 16.6 base
  CPVC tubes - alum fins 86.21 102.37 16.2 97%
           

Oven Test

A quick test exposing CPVC, PEX and Pex-Al-Pex tubes to high temperatures in an oven...

Gary March 21, 2009