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How do I relay power to a circulator from two separate 120v inputs?

Jimmie
Jimmie Member Posts: 5
in Thermostats and Controls

I am building a radiant system which will use a heat pump (brand undecided) to heat my home in milder weather and a backup gas boiler (Lochinvar Knight) for the colder days when the heat pump can't operate. I have one Alpha2 26-99 system circulator which will need to be powered when either heat source is operating, and also when both are operating.

What type of relay will power one 120v output to a circulator, from two separate 120v inputs? Any recommendations of a specific brand and model for the relay? Will this kind of relay have the inputs isolated to prevent power from one input being backfed towards the other input?

Or should I use two relays (one for heat pump, one for boiler) to power the system circulator? Would this cause the circulator to see 240 volts when both the heat pump and boiler are operating (both sending 120v)?

relay.png

Comments

  • delcrossv
    delcrossv Member Posts: 1,288
    edited November 21

     "Would this cause the circulator to see 240 volts when both the heat pump and boiler are operating (both sending 120v)?"

    Not if they're on the same phase. That, you'd have to make sure of at the panel. (Wire from a single (single pole) breaker)

    Trying to squeeze the best out of a Weil-McLain JB-5 running a 1912 1 pipe system.
    Jimmie
  • Jamie Hall
    Jamie Hall Member Posts: 24,696

    Two relays, the coil for one from the heat pump and the coil for the other from the boiler.

    Wire the normally open contacts of both in parallel to control the circulator. Very ordinary.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    delcrossvJimmie
  • Kaos
    Kaos Member Posts: 175

    I would figure out which AWHP monoblock you want to use, they all have example diagrams for integrating Aux heat. The units will generally control Aux heat directly so you don't have to do extra controls.

    For example, mine will keep the primary circulator (built into the monoblock) running and enable the aux heat. This way you don't need a 2nd pump.

    About the only issue with most of them is any external drive will be 240V, so you have to use a 240C coil relay to drive any 120v / 24v loads (ie RIB2402B).

    Jimmie
  • Jimmie
    Jimmie Member Posts: 5
    https://forum.heatinghelp.com/discussion/comment/1821550#Comment_1821550

    What exact relay will do this? I am just a homeowner so I don't know exactly what to buy. I was looking at the Taco SR501-4 switching relay but I don't think it will work because the input signal is a 24V thermostat signal, not 120V. My boiler has a 120v output for circulator but the manual says I need the relay because my circulator is larger than 1/8 HP.

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 9,269

    This diagram will not require that you have the same phase on noth source one and source 2. You do not even need to have the output voltage from source 2 ( the heat pump)

    For a 120 VAC circulator output from source 2 to the relay input use this

    https://www.supplyhouse.com/Functional-Devices-RIBU1C-Enclosed-Pilot-Relay-10-Amp-SPDT-w-10-30-Vac-DC-120-Vac-Coil?_br_psugg_q=rib+relay

    For a 220 VAC circulator output from the source to the relay input use this

    https://www.supplyhouse.com/Functional-Devices-RIBH1C-Enclosed-Pilot-Relay-10-Amp-SPDT-1-3-HP-10-30-Vac-DC-208-277-Vac-Coil

    two source to power one pump.jpg

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    delcrossvMikeAmannLarry WeingartenJimmie
  • 109A_5
    109A_5 Member Posts: 1,566
    edited November 23

    Hello Jimmie,

    Two independent 120 VAC control sources, isolated from each other and the load, so no phase issues. Two independent relay coils, and just parallel the Normally Open (NO) contacts of the relays. Makes a 120 VAC 'OR' circuit. Actually any of the control Voltages can be what ever is needed, 24 VAC control = 24 VAC relay coil.

    Or if you are careful and your two independent 120 VAC powered heating units have isolated output contacts to control their own circulator just wire their output contacts in parallel controlling the single circulator from the single circulator's own power source.

    image.png
    image.png

    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
    Jimmie
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 9,269
    edited November 23

    Both @109A_5 top diagram and the diagram I provided with only one relay will work just fine. if your heat pump has a circulator output that is a set of dry contacts then here is an easier way to do it. The boiler circulator output is already 120 VAC from the factory.

    two source to power one pump.jpg

    No relay needed. you just need to use a 120 VAC compatible wire from the HP ciirculator pump relay to the boiler pump control. Can you post what boiler relay you have?

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • hot_rod
    hot_rod Member Posts: 23,222

    the heat pump will have a 120v output for the pump and a dry contact to call the boiler on. Typically when the COP drops to or below 1 you might call on the boiler

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Jimmie
  • HomerJSmith
    HomerJSmith Member Posts: 2,628
    edited November 24

    I might clarify the discussion about this phasing thing. It is all single phase. What is important is that both 120Vac sources is on the same buss in the electrical panel. 120V on one buss and 120V on the other buss = 240V into a device that is only rated for 120V.

    Jimmie

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