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Panel radiators with TRV's and a t-stat???

skyguyMT Member Posts: 1
edited March 2021 in Radiant Heating
I'm looking for some advice from one of the trusted professionals here. I'm a GC in Montana (finally building my own house for a change!) I decided on a homerun panel radiator with TRV setup. I've done the heatloss calcs and picked out slightly oversized myson panels to try and reduce the water temps to under 140deg at design load so a mod/con boiler would stay in condensing mode. I have a total of 15 panels of various sizes.

My issue is I (and my heating sub) have done all in floor or staple up zoned systems and have little experience with this setup. I contact Blue Ridge Company out of Washington to purchase the radiators/boiler/parts. They are suggesting I use 2 zone manifolds (8 for upper/3 loop for lower) and have a tstat to control an alpha pump on each manifold. This doesn't make sense to me as to why you use a tstat to control a CP pump that is supposed to by controlled by the TRV's? I can see 2 pumps would be more efficient than one large pump given the number of panels but why control the pump with a tstat at all? They said the Laars Mascot FT needs to have a trigger to fire it and the primary loop.

I thought about using a takagi TH3 with a solar electric heated buffer tank instead as it has an internal flow switch has good reviews and given the buffer tank offset the issues with a tankless for radiant. My DHW will be a separate system and use the Takagi/solar elec buffer tank between the well pressure tank to reduce the deltaT from the 40+deg well water.

I can see putting 2 large ones in the living room in series on one TRV but what they are telling me doesn't make sense to me. I've read John Seigenthaler's homerun system design


but I'm in over my head on the specifics of my system. The only engineer I found locally is non responsive after several phone calls and emails.

Happy to pay for professional design services, but now I am running out of time before rough in. Any suggestions if Blue Ridge Co. is giving good advice and/or finding a good radiant engineer/designer? Any feedback on the Laars Mascot FT (non combi)?

Thanks to all for any input you can provide!


  • hot_rod
    hot_rod Member Posts: 21,855
    Correct that you need something to detect flow and trigger the boiler.
    Phenix makes and adjustable induction relay that you wire to the Alphas. It is adjustable to very low flow (current draw) They are a bit finicky to dial in. I bought one to play around with on a test bench.

    Sika flow switches work well also, they have versions that trip at or below 1/2 gpm. Same switch found in combi and tankless water heaters to trigger on the burner with a low flow faucet draw. Put one just downstream from the Alphas. Sika has a branch in the US now, near Madison, WI, so they are easy to source without going to an OEM.
    Harwil is another nice low flow switch, uses a reed switch, very rugged. Not sure if they are temperature rated, mostly used for spa control.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Turbo Dave
  • TAG
    TAG Member Posts: 754
    My first project was a radiant/ panel retrofit of an old masonry house. Used the Buderus panels and the Danfoss head. In my case I split the rooms on a manifold loop. Think each 1/2 pex run could take something like 12 or 15k BTU. Since most rooms had two radiators (oversized as well) and under the limit BTU max .... I used the bypass fittings on the panels and looped the Pex. On the bathrooms -- I did three together. The bypass on the bottom of each panel allowed all the panels to see the same water temp. You are doing the same just a different way. I still have the property ... works great almost 30 years later. All the radiators (more than you have) run off one small Grundfos pump .... controlled by the outdoor reset on the boiler. When the temp drops low enough the system starts.

    I'm building a new house -- used the Alpha 2 on that one. Bought one for this place ... I'm going to switch it out once no more heat needed. The alpha is a nice upgrade. slick little pump
  • Paul Pollets
    Paul Pollets Member Posts: 3,656
    edited March 2021
    I'd be installing the panel rads for home runs using 2 manifolds and one Alpha pump. I'd be using a mod-con propane boiler if nat. gas was not available. Preferably a Viessmann Vitodens 200, which will modulate and provide continuous circulation. I'd be very careful about Blue Ridge Supply, they are not considered the real experts among radiant specialists in the NW, and I have personal experience fixing their projects. You may want to try Thermal Products in Seattle...they sell both wall panel rads and are a distributor for Viessmann and sell wall panel rads, as well as design assistance. Ask for Jay.
  • skyguyMT
    skyguyMT Member Posts: 1
    Thanks for the feedback guys, this is very appreciated. Tying the boiler/pump(s) to the outdoor reset to start the system makes sense. The Sika flow switch downstream of the alpha to trigger the boiler should be straightforward. The adjustable bypass valves were included in my quote so I should have some flexibility in running my tubing from the manifolds if I need to loop a couple of the smaller panels.

    I'll look at the manuals and see what the flow rates are for all the panel rads and see if I can use just the one alpha. I'd rather buy 2 and have one stored for emergency backup.

    Thanks Paul for the feedback on BR Supply, that is the feeling I was getting based on my conversations. I'm going to chat with my heating sub and get in touch with Thermal Products. The Vitodens 200 seem like a high quality product (and price to go with it). I'm willing to pay for reliability as long as parts are available because everything breaks eventually. I've received the "Help I have no heat" call at 9am christmas morning and that makes you think about more than just the pricetag!
  • ewang
    ewang Member Posts: 77
    @skyguyMT Do you have a heat-loss estimate per each space?

    I started with Slant-fin's App to get a rough idea on heat-loss, then built a spreadsheet to marry up panel radiator outputs with varying width/heights and supply water temps to try to match the ratio of Heating Capacity versus Heat Loss. If you keep the ratio of each room's ratio of Capacity/Loss similar to one another, the magic of TRV's and ODR make running it all together something magical.

    Feel free to reach out via message if you want to discuss.
  • SuperJ
    SuperJ Member Posts: 609
    edited April 2021
    This is a good article about constant circulation approach written by a fellow Wall member Harvey.

    I would run your system in constant circulation.

    Panel rads + TRV + AutoAdapt + ODR = equals a system that can load match pretty well. (it's what I use). I don't have any room thermostat, I just put the Alpha in summer mode (exercises occasionally), and shutoff the boiler from May to September.
    If you have one, the thermostat can just function as a high limit to shut off the heat when the house gets too warm, but wouldn't be the primary control. You can have warm weather shutdown enabled too to shutoff the boiler when it's warm out.
    As long as your boiler has a safe min flow, and enough thermal mass in the system it should be good to cycle without a thermostat. You can just put a jumper in the call for heat and forget the thermostat.

    IMHO with your setup you can just hardwire the pumps to a disconnect, and let them run constantly for the entire heating season.

    I don't have a thermostat, but I do run a aggressive outdoor reset, and have carefully balanced panel rads, so that the ODR and TRV does the heavy lifting for control and keeps things comfortable. The Grundfos autoadapt reduces differential pressure as the flow goes down, giving another layer of response. I find my rooms stay very comfortable and always get just the right amount of heat with having any thermostat.

    Better to go to big than too little with rads. As long as they have the balancing adjustment, you can turn down the Cv if you find you are getting overshooting. If you go too small somewhere, it means you have to raise the system temp. Having a uniform water temp requirement is key for comfort with constant circulation, so balancing is important and the TRVs make up for the differences throughout the day with solar gain etc.

    With a properly set ODR, I try and set the TRVs so they hardly ever actually close off completely. They throttle the flow so the top of the rad is hot but the bottom 80% is cool to the touch. If most of your TRVs need to fully close simultaneously then your water is too hot IMHO.

    This is a very elegant setup that avoids any electrical controls in the building and performs well.
    Note you can get TRV's with remote sensing, or adjustment if the rad isn't' placed in an ideal position for sensing. But I find the standard under the window rad position makes the TRV work even better since it's the first place to get cold. With constant circ and TRVs the rad always has just enough heat coming off to get rid of any sense of cold draft from the window without ever overheating the space.

    Also it amazing how little power it takes to run the pumps when things are dialed in. My pump rarely indicates more than 11watts.
  • SuperJ
    SuperJ Member Posts: 609
    edited April 2021
    Some more thoughts:
    I don't think you'll need two alpha's.
    Since the manifold's won't be the point of control, you don't need to go overkill here.
    A simple copper manifold with ball valves would be sufficient.

    In your living room, don't put them in series or you'll be giving up a lot of output on the second radiator. Series make sense when you're trying to bring down the RWT from a high temp emitter before it hits a condensing boiler.
    You can use a TRV controlled valve on a common line that feeds both rads in parallel, or put a separate TRV on each rad. Most good panel rads come with the built valve that accepts a TRV, so that is how I would do it.
    You don't necessarily need to home run both living room rads to the manifold, run a single line to the room and parallel to the two rads (reverse return). You can likely do this with 1/2" pex.
  • Paul Pollets
    Paul Pollets Member Posts: 3,656
    edited April 2021
    You'd only need 1 Alpha. It can pump 15gpm at max, which would handle way more than 15 radiators. One of the keys to sizing the panel rads for mod-con design, is to increase the size of the radiators to work at a system water temp of 140. Then the boiler will be in condensing mode most of the time. The correction factor is 35% (larger) which increases the size and output and slightly ups the cost.
  • TAG
    TAG Member Posts: 754
    I oversized all of my panels to lower the water temp .... did need a couple of the double thick units .... used the tall narrow and you don't notice them. Also used one Runtal -- tall and thin in a corner room to give some help to the radiant.

    The nice thing about the TRV on all or most of the panels -- each room can be set differently w/o changing anything. I have a panel in one area near my desk and I just turn it up when I'm there .... they heat so fast.

    Oversizing keeps the temps lower and you quickly can figure out the ODR slope .... This house has a walk out basement and I sized for that ... most of the panels don't need the heads.
  • skyguyMT
    skyguyMT Member Posts: 1
    I contacted Jay who sent me a quote on the panel radiators. He suggested a Viessman or a NTI. I have not heard of the NTI but the specs look nice and he says he sells quite a few of these.

    Happy to hear how quickly the panels heat up. I only adjust the tstat on my current in slab system 2x a year, once in the fall and once in late spring. Never had any issues with it (grundfos 3 speed pumps/slant fin elec boiler as house is all electric).

    Jay hasn't been able to provide more than the rads info right now (I told him my schedule so we just need the rough in parts right now). It's amazing how busy all of my subs (heck everyone in the construction industry) are right now! You'd think the price of lumber would have scared more people off!
    TAG said:

    The nice thing about the TRV on all or most of the panels -- each room can be set differently w/o changing anything. I have a panel in one area near my desk and I just turn it up when I'm there .... they heat so fast.

    Oversizing keeps the temps lower and you quickly can figure out the ODR slope .... This house has a walk out basement and I sized for that ... most of the panels don't need the heads.

    I have a daylight basement also, how did you adjust the panel sizing? would you go less than the 35% oversize correction factor Paul has recommended? I am guessing that you have an open plan if most of the rads don't have TRV's?

    Thanks for all of the info. Lots to learn which keeps me engaged even if I'm a little over my head on the tech side of this system. I would have gone staple up but I don't like the inefficiency or having to install in i joists (open web trusses are much easier)

  • TAG
    TAG Member Posts: 754
    I used the tables for the radiators -- they give the output of the panels at different water temps. With the walk out basement needing lower per SF BTU's --- it was easy to get them to work at lower temps. The upper rooms (above ground) being exposed required me to basically size the panels for looks and see where they fell on the tables. I started out not wanting to use the double panels under any windows -- too noticeable. With two in most rooms this was no problem. As I said ... I did have a couple odd situations where I used the taller doubles.

    So -- it was really a question of sizing the uppers for looks and seeing what temp they were going to need .. using that temp to size the lower panels. I was in the 145 range if my memory was correct. I did not size for the really odd cold snaps that happen every four or five years. Figuring -- I could always adjust the curve on the boiler to use hotter water for those few times.

    It just worked out that the lower level is basically perfect on ODR ... I did put one head on a panel down there. In a little used area of a bar area that we don's use very often. Why keep it 71 when it fine a bit colder ..

    The nice thing about the panels -- you can set it all up (all of them full open) and see how it works. For those spaces getting a bit hot on ODR ... you can just close the manual flow on the panel if you want it to stay with the curve on the rest of the house. In my case -- I just bought some of the heads. Put them on the ones needing adjusting -- or rooms you want cooler. We have two bedroom/ bathrooms in that house that are not used very often. The heads make it really easy ..