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Adding a Vaughn indirect fired water heater to a combi

Good Afternoon, new guy here. For 10 years now I have a triangle tube prestige excellence 110 combi which performs great. Since I’ve added a third bathroom and also my kids use water a lot longer, the 14 gallon tank cannot keep up. I lucked out at got a 35 gallon Vaughn indirect tank that’s 4 years old from a friend. 

Now question is proper connection to my combi unit? I noticed on top of my combi an aux dhw connection that currently has the t&p valve. 

Am I going to feed indirect with the 14 gallons of heated water ? 

Can seem to find any diagrams on how to plumb it. 

Any opinions would be great thanks 

Comments

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,525
    edited February 11
    Am I going to feed indirect with the 14 gallons of heated water ?
    Is there a priority for the DHW feature for this Triangle Tube Prestige Excellence 110? If there is, then using the built-in indirect to preheat the water before it enters the larger exterior indirect tank may defeat the purpose of the exterior DHW tank.

    When you use the potable hot water, the priority feature will prevent the Central space Heat (CH) circulator from heating the exterior indirect DHW tank. I believe you will need to study the control logic of the Excellence 110 to be able to determine if this is a good idea. If you discover that you can not disable the priority feature of the Excellence 110, then you may want to stop using the internal tank and use a zone controller that has a priority feature for a DHW external tank.

    If you want to be a real creep... you can pipe the internal 14 gallon thak to your bathroom, then the rest of the hot water from the larger tank. That way when you take your shower YOU will get priority over all the DHW. The Larger tank may be enough for one or two shorter showers, but with the recovery from the CH pump off by the Excellence 110 priority for DHW, you will get your shower, then when you are finished, the CH circulator will recharge the larger DHW tank. LOL
    . Not Recommended


    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,525
    After looking at the Excellence 110 I/O manual, there is a way to disable the DHW priority, so it looks line you can pipe the potable cold water to the 14 Gallon internal tank first then from the Hot put of the 14 gallon internal tank to the inlet (cold) of the exterior than.

    For the CH sice of the indirect tank, I would add that as an additional zone.

    How many CH zones do you have now?
    Are they controlled by separate circulator pumps, or by zone valves?
    If by pumps, are they connected to the Pump 3 and Pump 4 terminals inside the Excellence 110?
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • CaptKevin85
    CaptKevin85 Member Posts: 4
    Thank you for the response. I have 5 CH zone valves with 1 circulator. Today the manufacture sent me these two recommended drawings. My question is before the mixing valve there is no longer a cold water feed which I would think the mixing valve is not going to work properly .

  • pedmec
    pedmec Member Posts: 920
    The larger tank temperature will have to be lower than the max inlet on the cold side. Some Watts are 85 degrees cold water inlet. The larger tank is just preheating the cold water inlet. That's the only way i see it on the drawing that can work. Warmer than normal inlet temperature on the cold side to the mixing valve and a less temperature rise needed thru the 14 gallon tank and now you have some capacity. i wonder what the max temperature on the mixing valve there.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,525

    Thank you for the response. I have 5 CH zone valves with 1 circulator. Today the manufacture sent me these two recommended drawings. My question is before the mixing valve there is no longer a cold water feed which I would think the mixing valve is not going to work properly .

    In the drawings sent by the TT it appears that the indirect will be there to preheat the water to the 14 Gal internal tank. SO, that tank must be maintained at a lower temperature. If the 14 Gla internal tank is used as the preheater for the Larger Indirect, that would make more sense because the inlet temperature of the External Indirect does not have a requirement for a lower temperature inlet temperature as mentioned by @pedmec

    If uou wanted to store water in the large tank at the recommended 140° to eliminate bacteria growth in the tank, using the 14 Gallon internal tank as the preheater makes more sense.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • CaptKevin85
    CaptKevin85 Member Posts: 4
    Ok understood now that you guys explained it. Thanks for the help. My current mixing valve has gone up to 140 degrees. I’ll have to test again to see max. I plan on installing a Taco time clock with Auqa stat. 

    The large storage tank has an internal auqa stat. Could I utilize that instead of purchasing this clamp on taco one? 

    Now I think going with drawing label P1A is probably for my application. 

    Would it be beneficial to go with drawing P11? Would the con be that it’s pulling water from CH circuit to heat exchanger?  
  • CaptKevin85
    CaptKevin85 Member Posts: 4
    Last Question drawing p1a has a note when the out going water temp drops below 115 to shut circulator pump off. What’s the reasoning for this? Or am I setting aqua stat to 140-160 degrees?