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To 3 way valve or Diverter valve?!?

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bobby32x
bobby32x Member Posts: 34
edited January 2022 in Radiant Heating
Hello all. I have a Navien condensing boiler (110,000BTU). It is turned down because my system didn"t need to be that big, but I had considered the possibility of needing more over time. Well, that time has come. I currently feed an old farm house with drafty areas. As I remodel rooms, I replace windows with higher efficiency windows and insulation wherever possible. My kitchen is roughly 12'x20'. My intention is to remodel the kitchen. that will include all new cabinets, countertops and hardwood flooring. I am looking to add radiant heat under the subfloor with 1/2" pex, long with radiant transfer plates 8" on center spacing and finally insulating with something after all of this. I don't really need anyone to get hung up on my selections or any of that nonsense. I am actually here to understand a little about mixing valves. According to what I have read, you should use a 3 way mixing valve (not a 4 way). In the documentation that I viewed, it showed the 3 way valve on the supply side of the radiant loop prior the CH pump a check valve on the line leading to the 3 way valve. I just read an article saying that this was improper and that by doing this type of install (which was noted a a typical install for this setup), you would not have the pressure tank feeding the radiant loop, while the 3 way valve was in bypass mode (circulating the radiant loop) and this would cause the CH to cavitate. This makes sense to me, but the article says to use a diverter valve instead and to place the check valve down stream of the radiant loop so heat doesn't back-feed into the radiant loop. This also makes sense to me, but why a diverter valve and not a 3 way valve? isn't it essentially the same thing in this case? I mean a 3 way valve diverts flow based on a setting.
I have a Navien smart zone controller, which basically controls the CH pumps based on demand. I am considering running a separate thermostat for the kitchen to help control the radiant loop as needed for the kitchen. The kitchen is always a little colder and the wife would like the radiant on the floor because we are used to cold tiles at the moment.
Any insight on these 2 types of valves would be greatly appreciated.

ps: again, not looking for remodel material debates, just wondering about the valves.

Thanks

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  • bobby32x
    bobby32x Member Posts: 34
    edited January 2022
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    This is the picture of the 2nd discussed loop where the diverter valve is used in place of a 3 way valve on the loop
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,840
    edited January 2022
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    A mixing valve and a diverter valve are both "3 way valves" A mixing valve has 2 inlets and 1 outlet. A diverting valve a has 1 inlet and 2 outlets

    In your drawin the diverter valve "common port" is the port on the right connected to the secondary return line.

    The diverter valve will devert return water into the boiler loop when you need more heat. When it does that the secondary circulator pulls water from the primary loop through the check valve heating the secondary loop. "Heat on"

    When the secondary loop is hot enough the diverter will send water to the secondary pump and just recirculate water round and round the secondary loop "heat off"

    Of course the valve can also modulate in an inbetween position
    Daveinscranton
  • hot_rod
    hot_rod Member Posts: 22,479
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    Here is a graphic showing how 2, 3 and diverting vs mixing valves look inside.
    A 3 way mix valve has A to AB or B to AB flow path.
    Diverting either straight thru, or to 1 port.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • bobby32x
    bobby32x Member Posts: 34
    edited January 2022
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    ok thanks all. I will study this a little better. I assumed that with a 3 way valve, you essentially adjust the flow from the recirc loop (radiant loop) so that it bled hot water into an almost always recircing loop when calling for heat. Sounds like a diverter valve is more proper for my needs after viewing the info you guys shared.

    Here is another question. If typical radiant runs somewhere between 125F to 135F, how does this valve decide when to stop pulling hot water in and start recirc? I mean, if I set my thermostat to 70, kitchen is 65, and now the water starts to circulate 165-180 degree water into the loop, how does it know when to stop diverting the cold water away during the 5 degree difference? To me, it would seem that the thermostat would turn the CH pump on and pump hot water until a temp is reached. Do these diverter valves come preset to a temperature setting or something? This system is already connected to a hydronic fin tube baseboard hot water system, so I am confused.
  • hot_rod
    hot_rod Member Posts: 22,479
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    Valves can be manually operated, a simple lever handle, this is called a “dumb” valve, it has no intelligence to make adjustments. You do the thinking🤪

    3 way valves for mixing commonly have a wax, thermostatic cartridge. You set the desired temperature and it opens hot and cold ports to blend the temperature. You never shut off either port completely with a thermostatic valve. As one port is opening, it is closing  the opposite the same amount. TMV for thermostatic mixing valve.

    Lastly you can add a actuator to a manual type valve. Usually they are electric, pneumatic actuators are also available

    If you add an electronic actuator you need a “box”
    A control to tell the actuator what to do.

    It could be a control that powers it to one extreme or the other, a 3 way zone or diverting valve. Or a floating type control that can stop at any point to maintain a set temperature, a floating 24 volt signal is common. 0-10vdc is another, PWM also.






    difference with a 3 way zone valve is either A or B is open to AB

    with a diverting valve flow is straight across, or to one of the branches

    Air handlers in a commercial building will use diverting, so when no heat or cooling is calling, full flow returns. This keeps large circulators happy so they can never dead head
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Zman
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,840
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    @bobby32x

    The best way in my opinion is an electric valve with a control and a sensor mounted in the radiant loop to control the valve
    Rich_49
  • Zman
    Zman Member Posts: 7,607
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    @bobby32x

    The best way in my opinion is an electric valve with a control and a sensor mounted in the radiant loop to control the valve

    And Outdoor Reset...
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    Rich_49bobby32x
  • bobby32x
    bobby32x Member Posts: 34
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    hello all. I live in an old farm house (pretty sure all old houses are farm houses...). That said, I have several subfloors in place where they have built up the floor in the kitchen several times. This floor is actually about an inch higher than all the rooms that adjoin this room. Same area as the above mention radiant area in question. So... my thoughts here are; I wont be able to rip all these subfloors up. Im not afraid of doing extra work, but would it be worth my while to rip up enough of these subfloors and get the floor within the sub floor level below what will be my new hardwood floor. We are thinking of going with engineered bamboo (not 100% sold on that yet, but kicking the idea around. So, anyway, I am willing to cut plywood and lay it down to sink the pex in between the plywood orientation. What are your guys thoughts? I have a woodshop, so this all doesn't seem like a lot of difficult work to me, plus I am pretty handy in that I never get any contractors, no matter the task, be it electrical, plumbing, construction, destruction, you name it.

    My fear is that I won't get enough heat transfer going through several subfloors.
  • bobby32x
    bobby32x Member Posts: 34
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    Zman said:

    @bobby32x

    The best way in my opinion is an electric valve with a control and a sensor mounted in the radiant loop to control the valve

    And Outdoor Reset...
    My main hydronic system is using the outdoor reset. I think the fact that the radiant only needing 125F to 135F and the main system being well above that, the mixing valve should suffice the water temp based on however hot the hydronic system is, not necessarily the radiant loop.
  • hot_rod
    hot_rod Member Posts: 22,479
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    No doubt that the closer to the final flooring the tube is the better the output, and the lower the water temperature to operate it. There are tables showing the R-value of various woods and their thickness.

    Ideally a room by room heat load calculation would show you what output you need to get from a square foot of floor.

    in some cases the floor alone will not cover the load and supplemental heat would be needed. Radiant walls and ceilings are sometimes a better option.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • bobby32x
    bobby32x Member Posts: 34
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    hot_rod said:



    Ideally a room by room heat load calculation would show you what output you need to get from a square foot of floor.

    I looked up a calculator and it says to do squarefoot X ceiling height X temperature difference from outside to what you want for comfort X .135 I picked 50 for temp difference because during winter it is typically around 20 or better, with occasional dips into the single digits and even in the negatives. so my calculation looked like this
    Keep in mind this is a 12X20 room. I rounded up from 240 SQFT to 300 to err on the side of needing a little more
    300SQFT X 7.9H X 50DIF X.135= 15,997.5 round up to 16,000 BTUs?
    Now i want to mention again that this room has a small hydronic baseboard of roughly 3ft and possibly another 8 feet guessing. for a total of 11feet in one corner of the kitchen. So, along with the radiant being on its own loop (possibly with a thermostat), I was thinking that the radiant would take on most of the heating needs of the kitchen and if the radiant isnt keeping up, chances are that the thermostat in the living room will be calling for heat as well, which would feed the hydronic baseboard loop. I would imagine that the radiant will not be enough to keep the living room happy, even with the rooms adjoining, since the kitchen is always like 2-3 degrees less than the living room and sometimes more depending on how cold it is outside. I intend to insulate the floor even if I do the above mentioned subfloor channels.
    Also, I might have mentioned it above. I have the condensing boilers ratio turned down, based on my BTU needs prior to the added radiant addition I am proposing. I am hoping that this load will still be under my total usable BTU's. I can recalculate before attempting anything.