Sunday, March 6, 2016

Automatic RV Hot Water Recirculation System

To minimize waste of water while waiting for the hot water in the sink or shower, I installed an automatic hot water recirculation system in my Agile. I can also use it to prevent the water line from freezing when camping below freezing temperature. I'm already thinking of re-plumbing the hot water line under the RV to provide heat into the fresh and holding tanks via a DIY heat transfer plates which will be installed under each tanks. A manual diverter valve will be used to divert hot water away from the heat transfer plates when it is not needed, that would be my near future project.

The DIY hot water recirculation system is installed into the galley faucet hot and cold water line which is the point farthest from the water heater. It is fully automatic with manual switch override. A digital temperature controller is used to switch the pump on and off to automatically recirculate hot water back into the cold water line. The adjustable fan-control thermostat switch (see below) monitors the water temperature in the water heater tank and the system only becomes active when set temperature is achieved. It will shut the system off when water temperature falls below the set temp, doing this will prevent the recirculation pump to continuously run when water heater is shut-off and hot water falls below a certain temp.

Hot water recirculation system wiring diagram.


Parts used:
  1. PEX tubing and fittings: (2 pcs.) tee fittings, (2 pcs.) PEX to 1/2-inch NPT female elbow adapters
  2. Acrylic plastic for the electronic temperature controller enclosure (optional)
 

The electronic temperature controller with fabricated acrylic enclosure and a manual override push button switch.
 
Tee fittings connected to PEX to 1/2 inch 90 º male thread adapter. Crimping the brass tee fittings into the hot and cold water lines is almost impossible due to very limited space under the sink. It would be easier if I use Sharkbite PEX push-to-connect fittings instead, they are little expensive but it will save you time and sanity.
 
The electronic temperature controller temp probe is epoxied into the brass PEX elbow fitting of the cold water return line (or to the hot water line, if you prefer), and then it's wrapped with an insulation material.
 
An inline brass check valve was installed into the cold water return line. The check valve prevents cold water from flowing back into the hot water line. The check valve cracking pressure also prevents free flow of hot water to cold water line when system is off.
 
A pair of 12-inch flexible stainless steel braided water supply hoses is connected to the recirculating pump inlet and outlet ports and to the hot and cold water lines via the 90º elbow fittings.
 
The electronic temperature controller is mounted under the sink using 3M plastic hoop-n-loop fasteners.
 
 
 
Made an insulation cover for the recirculating pump. I tried to directly mount the recirculating pump into the base of the cabinet but it was running loud. 
 
 The recirculating pump inside the insulated DIY pouch.
 
The recirculating pump is then tucked behind the microwave.
 
Hot water recirculation switch is installed into the factory switch panel above the RT side sliding door. The positive 12-volt line was tapped from the now unused Carbon Monoxide (CO) detector circuit in the AC/DC Distribution/ Fuse panel.
 
I run the ground wire to the adjustable fan-control thermostat switch then wire terminates into the chassis ground. 
 
A close-up view of the adjustable fan-control thermostat switch. The thermostat switch is mounted directly and in contact with the steel water tank, a small piece of  the tank insulation was removed. The thermostat switch is secured in place by a metal strap.

  The adjustable fan-control thermostat switch is adjusted to turn on at about 105ºF and should turn off at around 95ºF ( a  Delta T of 10ºF). I set the electronic temperature controller to 32ºC (89ºF) with Delta T of 2ºC (controller only displays ºC). The recirculating pump runs until the remote temp probe senses water temperature rise to 32ºC and above then it shuts off, pump runs again when temp drops to 30ºC and cycle repeats.
 
Note: Only set the electronic temperature controller activation temp below the fan-control thermostat switch shut-off point.

The controller LED display is visible through a small gap on top of the modified waste bin slider (originally a slide out pantry).
 

Although not necessary, a water leak alarm is installed under the sink.
 
 

8 comments:

  1. Impressive and clever work! I was shopping for the same thermostat controller that you used here, and found your project from your review. I'm also using the thermostat to help with freezing pipes, by controlling an electric heater in an insulated coroplast box around the pipe. I noticed that you seem to favor working with acrylic, which i've never gotten into. Is it pretty easy to work with? Also, what do you use to create your very tidy labels?

    ReplyDelete
    Replies
    1. Thanks for the kind words. I apologize for the late reply; I was out for the memorial weekend with no connection.

      Acrylic is easy to work with; you can cut it with circular saw, router or table saw. I use a water thin Acrylic glue like this: ( http://amzn.to/1P0MROA ) to bond the pieces together. Here is a Youtube link how to glue Acrylic plastics: https://www.youtube.com/watch?v=hT6Ow_cBTps

      Delete
    2. For the label, I use DYMO portable labeler with white/clear label cassette.

      Delete
  2. Thanks for the info, now I'm going to be on the lookout for projects I can try using acrylic for! I'm afraid what will happen if I ever get a label maker, it will be labels everywhere!

    ReplyDelete
  3. Will it work when you are on city water or when the water pump is turned on?

    ReplyDelete
  4. Also will it work with an on demand tankless system

    ReplyDelete
    Replies
    1. It should work...but run time could take a little bit longer as the on-demand tankless water system fires up and heat the water. It could be annoying as every time the recirculation system goes off your on-demand water heater also fires up.

      Greatest benefit of the system is saving water when bondocking and instant warm water at the sink or shower during cold days/nights.

      Delete

Unfortunately due to high levels of spam, all comments are now moderated before they are posted. Thank you.