Hot Water recirculation on the cheap

[Dave Turpin]

I have been wanting to install hot water recirculation in my house for some time. The problem is that because of my low-flow fixtures, it takes a long time (like a minute) to get hot water to the shower or the sink, and I am sure that I am wasting just as much water as I would have been using with regular fixtures.

I looked at all the systems that they have on the web, but they all have problems.

1) The Grundfos system is always running, and keeps the water at 85 degrees. They aren't compatible with tankless heaters and it will still take just as long to get HOT water to the fixture.

2) The super expensive units have a lot of bells and whistles but are, well, super expensive, are designed to either be on a timer or a motion sensor, and don't work well with branched plumbing systems (like my PEX system)

So I set out to design a simple system based on a 1/40 HP Taco reciculation pump (the most expensive part) and other easy-sourcable, inexpensive components.

This is the system that I came up with. Feel free to plaigerize for your own personal use, but please don't try to go commercial with my plans.

Parts:
-Taco 1/40 HP 3/4" sweat circulation pump $128 (Got mine from Pexsupply.com)
-DPDT 120VAC 5A relay and socket $8 (Automationdirect.com)
-70 degree open-on-rise thermostat switch $10 (Senasys.com)
(These thermostat switches are just what I was looking for. Super simple, no signal power required. They just open (or shut) when the temp is right, and they mount directly to the outside of the pipe. I am not an official endorser for this product, but here is where I found them: http://www.senasys.com/shop/products-page/375-inch-radius-pipe-mount/)
-2 doorbell transformers $18
-3 doorbell buttons ($7)
-Low voltage wire ($20)
-Shielded 14-2 wire ($15)
-Various wire connectors ($20)
-3 1/2" NPT spring check valves ($22)
-PEX tees and PEX-to-NPT adapters ($50)
(Home Depot, Lowes, etc)

Mechanical:
The pump was installed (pictures to follow) directly into the hot water line leading out of the hot water heater. I also installed a 3/4" swing check valve in parallel so that the pump doesn't affect my hot water flow when not in use. (Optional, and probably unecessary)
In 3 locations (master bath sink, master bath shower, 3/4 bath sink) I installed a spring check valve from the hot side to the cold side. The spring check prevents thermosiphon but is easily opened by the Taco pump.
Now, when the pump is running, hot water flows up the hot lines, through the check valves, and then back through the cold line. Now I just had to design a motor controller to make it turn on when I wanted, and turn off when the hot water had reached all the fixtures.

Motor controller:

Diagram:
http://i207.photobucket.com/albums/bb21/bpestilence/motorcontroller.jpg

The operation of this motor controller is simple. When any of the doorbell buttons are pressed, current flows through the coil of the relay and shuts the DPDT. One side of the DPDT bypasses the doorbell buttons and keeps the low voltage current flowing. (So no short can occur from the pushbuttons, and so that you can release the pushbuttons and wait for hot water) The second side of the DPDT routes line power to the pump. The pump will now continue to run until the thermostat switch breaks the low voltage circuit. The relay opens again, and the pump stops. If you push the button again, nothing happens until the thermostat closes again. The dual transformers simply make it so that the pushbuttons are low voltage. This saves money and effort from having to run 120VAC rated wire and buttons.

Now, there are a few more design things to work out. Since I have a branched system, I have to place the thermostat so that the hot water gets AT LEAST up to each fixture. Going beyond that is not ideal, but much less wasteful than other systems. A non-branched system is easier, and you would only need one spring check valve. I also have a 70 degree and a 100 degree thermostat to play with. I will start with the 70 degree, and if the water doesn't get hot enough I will move up to the 100 degree. There is also the possibility that one of the branches won't get flow at all if it is too restrictive. I may need to install needle valves in series with the spring checks to fine adjust the parallel pathways.

More pictures and testing to come!

[Dave Turpin]

Well, there doesn't seem to be a lot of interest, but I have built it, and so far it works.

Pics:

The motor controller, innards exposed for testing:

http://i207.photobucket.com/albums/bb21/bpestilence/DSCN2022.jpg

The motor controller, closed:

http://i207.photobucket.com/albums/bb21/bpestilence/DSCN2025.jpg

The pump:

http://i207.photobucket.com/albums/bb21/bpestilence/DSCN2023.jpg

Video of the thing (surprisingly) working on the first try:

http://i207.photobucket.com/albums/bb21/bpestilence/th_DSCN2024.jpg

EDIT:

To show changes in the original schematic:

http://i207.photobucket.com/albums/bb21/bpestilence/motorcontroller-1.jpg

I found that the additional indicators were unecessary. As long as you use a lighted bell button, the light is only on when the pipes are cold. I also learned that the 100 degree thermostat was needed (the 70 degree one was affected by ambient temp and would never reclose) and I added a second thermostat between the buttons and the transformer so that the power remains secured to the buttons when the pipes are warm (this prevents buzzing if you decide to push the buttons again after the pump shuts off)

Besides these changes, the controller and pump are working perfectly.

[Stewart Corman]

OK Dave I understand your situation and your solution, which was well executed.

I have a similar effect, perhaps even worse because I have 3/4" copper water feed lines and it takes over a minute to get hot water to the faucets at other end of house.

My idea was to add a recirculation loop out of 1/2" copper w/o any pump or controller.
If proper geometry is used, it will circulate by convection (think Thiele tube from Chem 101)
http://en.wikipedia.org/wiki/Thiele_tube

I gave up on the idea because:
a) cost of copper became prohibitive
b) better things to keep me occupied

The overt conclusion is that you will loose a lot of heat in all these tubes exposed to colder air ie my basement is about 60F all year.

So I choose to waste the extra water flow (well pump not utility $) and heat up the pipes only when hot water is called for.

Stew Corman from sunny Endicott

[Dave Turpin]

Having a continuous loop would waste a lot of heat. This is why my system is on-demand. No more wasted energy than just using the tap, but no wasted water.

[Dave Turpin]

After a few months of operation, it is still working well! I anticipate the DPDT relay will be the first thing to break, which is why I used a replaceable module.

As a secondary benefit of the undersink check valves, I get hot water going to all loops in the house if I use hot water, even without using the pump. I think thermal head is causing this, but it is a welcome effect.