(#34) What's the Fun in That? (Part Two)  

Keeping the Water Pipes in the RV Warm  

With Over-complicated Electrical timer in hand, it is time to do some testing!

Our supplies include: a six foot section of 3/4" PEX Pipe from Home Depot, 1" Pipe Wrap from Jax Ranch and Home Store. Two inexpensive temperature sensors from Aliexpress. And water from the tap.

And of, course, the Roof Heat Cable from Lowes.

The heat cable is not wrapped around the PEX pipe, it's simply laid down lengthwise to the pipe and taped (about every 12") to the outside of the PEX.  

One temperature sensors is taped next to the heat cable.

The pipe is filled with water.
 


The PEX is wrapped with pipe insulation and the second temperature sensor placed about halfway down the inside of the pipe.


And the whole assembly placed outside on a winter's day - ambient temperature was mid 20's (°Fahrenheit).



Using the Raspberry Based Pi Electrical Relay system built in Part One, the heat cable is then energized and temperatures measured periodically.


 

Power was applied for 30 minutes and then stopped. It was 30 minutes on, 30 minutes off, then 30 minutes on and 30 off -- for three hours.

Testing shows that the cable starts warming immediately.  And within a minute or two the water is warming up inside the PEX.

Amperage measurements shows that the cable immediately consumed 300 watts and varied very little as long as the power was applied.

I repeated this test 7 times, there was little variation.


I also ran one test with the pipe empty -- no water -- to see just how hot things could possibly get.  Both temperature sensors reached 150°F quickly and stayed there for 90 minutes. Hot but still below the 180-200°F PEX limit.

Conclusion

My conclusions is: the 300 watt Heat Cable could be a solution for keeping the exposed PEX pipes in the motorhome from freezing.

Energizing the heat cable on for 30 minutes then off for 30, keeps the water inside the pipe well above freezing without getting the pipe too hot.

The upward trend of both heating plots show that an optimization would be to lengthen the time the cable is off.

Next up the software that makes this thing work!