Click here to Find a Contractor in your area.
In fairness to all, we don't discuss pricing on the Wall. Thanks for your cooperation.
Need to contact us? Visit https://heatinghelp.com/contact-us/.

Control Strategy for SHW w/ Tankless Water Heater

matt_sunwaysolarmatt_sunwaysolar Member Posts: 61
Curious what strategies others are using to integrate solar water heating systems with tankless water heaters?

As most tankless manufacturers have set parameters for minimum delta T for incoming/outgoing water temps or maximum incoming water temperature, I'm curious how others have chosen to approach this.

The two options I've considered are:

1) setting the thermostatic mixing valve (from solar to tankless) a bit lower than typical (maybe 110-115F) and the tankless unit to 130-135F to maintain a 20F delta T inlet/outlet.

2) Installing a solenoid valve on the outlet of the solar storage that completely bypasses the tankless when the solar storage is above 120-125F and feeds the fixtures directly.

Again, curious what others have done and/or prefer.

Thanks in advance.

Comments

  • hot rodhot rod Member Posts: 7,059
    Ideally you want to run down the solar tank as low as possible to maximize solar input. I hate to see that tank limited with a mixing valve.

    A 3 way motorized zone valve is one option, be sure it has high shut off pressure. It would need a controller also.

    Or a couple 3 way thermostatic mixers. The mixers do add a yearly maintenance concern in hard water conditions.

    Two mixers gives you the shuttle, a third can be used if the DHW tank is run at elevated temperatures. A final point of distribution mixer.

    Here are some examples we built for a tankless manufacturer that was looking at offering a "solar kit" The cut away view helps you see the operation logic.

    We offer a nice modular valve package in Europe, we felt the Cv was a bit low for the US market.











    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • matt_sunwaysolarmatt_sunwaysolar Member Posts: 61
    Thanks, Bob.

    Any recommendations for a potable three-way valve for the application? 3/4" piping.
  • hot rodhot rod Member Posts: 7,059
    Any mixers with an ASSE 1017 listing should work.

    The ones in the pic are Caleffi 2521 Solar series. There are solar rated with a bit higher max. inlet temperature. They have a wide temperature range 80- 150F.
    Use that for the first in the series maybe. It also includes the check, which need to be in the proper location as show in those cutaway views. The temperature gauge option is handy for adjusting and troubleshooting.


    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • RyanWRyanW Member Posts: 30
    Here is my experience that has worked great for the past 6 years. Our solar tank is about three feet away from our kitchen sink so I opted for a manual three way ball valve coming off the solar tank. Switch it one way and it goes straight to a caleffi 521 mixing valve that does a fabulous job of mixing the solar water down to 120 degrees for our use. When the solar tank is too cold for showers we switch the ball valve which diverts the water through a renni on demand water heater which then comes back to the Caleffi mixing valve. I like that this system bypasses the on demand for the bulk of the year so it does not get the wear and tear of water flow trough it. Plus bypassing the on demand gets the hot water to us much faster. We run 100 percent solar DHW for 9 months a year and about 50 percent solar DUW for 3 months when the bulk of the solar goes to the radiant floor.

    Hot Rod I am curious the difference between the 521 valve and the solar ones you referenced above? Our solar tank gets up to 175 which is within the max 200 degree temp of the 521 which is why I went with it for a much reduced cost over the solar mixing valves.

    I am currently designing a new solar system for a house I am building and I plan on duplicating this system but replacing the manual ball valve with a temperature actuated 3 way motorized zone valve. My brother and Father us a blemo valve for this. Hot Rod can I ask if there is a caleffi that would work with the hot untempered solar water?

    Ryan in virginia
  • hot rodhot rod Member Posts: 7,059
    The 3 way valve is on the domestic water side it sounds like?

    So you need a valve that can shut off against 40- maybe 60 psi. it also should be a low lead valve for domestic, these days.

    The only low lead 3 way valve we have is the Z-one motorized spring return. Is is a 20 psi shut off, I don't think that will be adequate.

    Belimo has a wider selection, not sure how many LF lead free options?

    The solar mixing valve has different seals and o-rings to get that 210° operating temperature. Sounds like you will not be close to that temperature, the 521 is fine for your application.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • RyanWRyanW Member Posts: 30
    Hot Rod, quick thought on shutt off pressure rating. Really all the valve would be doing is diverting the water either through the on demand water heater or bypassing it but not stopping the water flow. The back side of the ball valve would always have the domestic water pressure on both options as they are essentially connected via piping on the backside. So wouldn't the max pressure just be the difference in resistance that the on demand water heater would cause?
    I just checked with my brother and father who are both using belimo ZONE320N-35 120NC for this exact purpose which have a 30psi rating. Theirs have been installed for 6 years with well water 35-65psi. I don't see any info on lead content though.

    Looking at the caleffi listings it looks like the 6443 be the best one for this application? Is it lead free or were you referring to a different valve?

    Thanks
    Ryan
  • hot rodhot rod Member Posts: 7,059
    The 644 series are high pressure ball valve type, but none of those are low lead.

    The Z-one is available in LF lead free, in either a 20 or 30 psi shutoff.

    If the Belimo has worked on the others, then the Caleffi will also.

    Z307433 1/2 sweat 30 psi
    Z307537 3/4 sweat 20 psi

    You are correct, as long as the valve does not have to shut off against a flow over 20- 30 psi.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • RyanWRyanW Member Posts: 30
    Thanks Hot Rod. I really appreciate your willingness to share your vast knowledge. Looks like the Z307537 will be perfect. Looking at the actuators powered by 120 volt the Z116000 looks good to my eyes. Is that appropriate?
  • hot rodhot rod Member Posts: 7,059
    Yep. Pipe the valve so it is NC when in the most frequently used mode. that will eliminating powering the zone valve as often.

    With a 3 way valve, just flop the valve over to determine NO or NC ports
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • jumperjumper Member Posts: 990
    I'm thinking about an instant solar water heater in series with an instant propane powered instant water heater. For an outdoor shower. I presume it will mostly be used during daytime. Upon return from beach.

    Off topic I wonder if it is okay to just drain into ground?
  • hot rodhot rod Member Posts: 7,059
    Best to use biodegradable soaps if you are dumping drain water directly onto the ground.

    But thousands of outdoor showers at beach homes and rentals dump into the yards and driveways :)

    Just came back from the Jersey shore, I'd guess most of the rental homes have outdoor showers in the back yards.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
Sign In or Register to comment.

Welcome

It looks like you're new here. If you want to get involved, click one of these buttons!