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Panel Radiators Low GPM Requirements

ced48ced48 Posts: 453Member
Any one know why panel radiators are limited to a flow of 1 1/2 GPM?

Comments

  • hot_rodhot_rod Posts: 11,753Member
    small connection size, and they generally run a wide 30- 40 delta T
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • IronmanIronman Posts: 5,144Member
    Why would you want any more gpm?

    A 24" X 72" panel rad is the largest standard size available. It has an output of slightly more than 10k btus at 176* AWT. That translates to 1 gpm at a 20* delta T. With 1/2 pex supplying it, you'll do well to get .7gpm.

    As Hot Rod said, they generally are designed with a 30 - 40* delta T.
    Bob Boan


    You can choose to do what you want, but you cannot choose the consequences.
  • ced48ced48 Posts: 453Member
    Just trying to understand things a little better- so if water enters one of these units at 120 degrees, it is going to exit at 90 degrees of less?
  • IronmanIronman Posts: 5,144Member
    edited September 17
    Like any hydronic system, that depends on what it's designed to do. I'm simply saying that with 1/2" pex, that's the gpm you're gonna see.

    You can design for whatever delta T you want. 20* is the norm in American hydronics because it's easy to figure: for every 1 gpm, you get 10k btus with a 20* delta T. Europeans design for higher delta Tees because they wanna save on energy consumption with lower flow rates and lower return temps.
    Bob Boan


    You can choose to do what you want, but you cannot choose the consequences.
  • ced48ced48 Posts: 453Member
    All I want to do is swap out 17 feet of baseboard and piping and substitute the same amount of panel radiator, in btu output, no h- valve, and have it work.
  • IronmanIronman Posts: 5,144Member
    What's an "h" valve?
    Bob Boan


    You can choose to do what you want, but you cannot choose the consequences.
  • hot_rodhot_rod Posts: 11,753Member
    Are there more baseboards in that loop with the 17 footer? How many feet total? 3/4 fin tube?

    Once you know the gpm requirement of the entire zone or loop you could determine if the panel could swap in and assure the rest of the loop gets adequate flow.


    17' X 500 btu/ft for example would be 500 btu/ hr.

    H valves and adjustable bypass H valves
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • clammyclammy Posts: 2,261Member
    I believe if the flow is over 1.5 gpm there are velocity noises at the built in trv ,hence the by pass valve .plus the internal supply is a little over 3/8 and as iron man stated higher delta across the panel but in my own system I see only about a 10 degree td but my highest water temp is about 140 at 10 oat and the smaller td is when all is running and boiler Is at design temp .peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
  • IronmanIronman Posts: 5,144Member
    edited September 17
    hot_rod said:


    H valves and adjustable bypass H valves

    That's what I thought he might be referring to.

    He's been posting about this for a while and I think that I suggested panel rad's with a bypass sometime back.

    @ced48
    Why don't you wanna use the bypass valves?

    Given the situation that you have, I don't see any other way of reasonably making it work. You're proposing to replace 17' of BB with panel rad(s). The BB loop cannot be forced through the rad's: it has to maintain a higher flow rate. The bypass valve is specifically designed to accommodate your scenario.

    Here's a piping diagram out of Buderus' design manual for panel rad's.



    Bob Boan


    You can choose to do what you want, but you cannot choose the consequences.
  • JohnNYJohnNY Posts: 2,318Member
    edited September 17
    Replacing 17 feet of finned tube means you're looking for about 9,800 BTUs, doesn't it? That's about one 10' section of Runtal UF-4.
    I would split that into two 5' sections piped in 2-pipe parallel.
    1.5 gpm supports that heating load just fine.
    For installations, troubleshooting, and private consulting services, find John "JohnNY" Cataneo here at :
    "72°F Mechanical, LLC"
    Or email John at [email protected]
    John is a professional Master Plumber, licensed by The Department of Buildings of The City of New York, and works extensively in NYC while consulting for clients in and out of state.
  • ced48ced48 Posts: 453Member
    edited September 17
    I have 12 feet of additional baseboard that would be downstream from the panel radiator. I am asking if I could put the panel radiator first, and supply the 12 feet of baseboard last, direct piped series. I have flow of about 1.5 GPM calculated using the universal hydronics formula. I do not want to create more head pressure than needed, thus wanting not to use any diverter valve, because I have another loop about the same size , a simple split loop system. I think it would be fine, but would like some assurance that I'm not missing something.

    I think I am overthinking the thing, and keep coming back to simple direct piping. I am replacing the baseboard, 3/4", with a panel radiator producing the same BTU's. I know it will heat the room, my only concern is added head pressure, that will disturb the balance of the two loops. I know the radiator has only .25 of head, and getting in to the unit should be like adding 7 feet of 3/4" pipe, 3/4" to 1/2", right? If so, the pressure drop would be less than .5, no big deal.
  • mattmia2mattmia2 Posts: 106Member
    The panel rad will deal with lower water temps a lot better than the fin tube, right? Probably better to put the fin tube first then then panel rad, but you really need to calculate your water temps and outputs per section.
  • ced48ced48 Posts: 453Member
    The water leaving the radiator or fin tube should be at the temperature, same btu's delivered, right?
  • mattmia2mattmia2 Posts: 106Member
    The heat delivered is dependent on the entering water temp, entering air temp, and flow rate of the water. If you have radiation in series the entering water temp will be the exiting water temp of the previous radiation and the output of that second piece radiation will be dependent on the exiting water temp of the first.

    If you want to be technical about it is a calculus problem where each infinitely small section is its own radiator with its own infinitely small change in entering and exiting water temp with the overall effect that the heat output at the inlet is significantly more than the heat output at the outlet.
  • bob eckbob eck Posts: 878Member



    Check out these Ecostyle steel wall radiator panels.
    Great unit and competitively priced.
    Email me for pricing.
    [email protected]
  • IronmanIronman Posts: 5,144Member
    What you're missing is you can't push 1.5 gpm through a panel rad. The bypass valve is designed to compensate for that. Your reasoning is in reverse.
    Bob Boan


    You can choose to do what you want, but you cannot choose the consequences.
  • mattmia2mattmia2 Posts: 106Member
    You have a multi faceted problem that you need to do the circuit analysis to solve.

    You need to find the hydraulic resistance of the whole circuit including the fin tube and the panel rad with the bypass(and the analysis will tell you how much should go through the bypass vs the rad and what you need to do to get the required output) and you need to find the water temps at the various points from the flow through the radiator and the bypass which will be the same as the flow through the baseboard. It is a simple problem but isn't something you can solve with conjecture.
  • ced48ced48 Posts: 453Member
    I'm becoming to think this banquette is more trouble than it's worth. Maybe a table and chairs will work.
  • ced48ced48 Posts: 453Member
    bob eck said:




    Check out these Ecostyle steel wall radiator panels.
    Great unit and competitively priced.
    Email me for pricing.
    [email protected]

    Tell me how to do this and I'll by the radiator from you-
  • hot_rodhot_rod Posts: 11,753Member
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • ced48ced48 Posts: 453Member
    Thanks Bob, I will study this tonight. I watched a video on panel radiators and I now see the issue with trying to pump directly thru one of them. The tubing is just too small. So the only option is to move just a small amount of water at a time into the radiator, more like filling it slowly, rather than passing water thru it, thus heating by radiation and convection. Now I see what others were saying about some type of diverter valve being a must.
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