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Piping distribution to new rads

dave123
dave123 Member Posts: 67
edited November 2020 in THE MAIN WALL


The attached diagram shows the planned location for new hot water rads I’d like to install in my 1900 SF house. Thirteen rads and two low temp baseboard units on the main floor. The boiler would be in the basement directly beneath Rad 7. Each grid block equals two feet.

Most people here seem to favor home runs, but in my case, this seems like an awful lot of tubing. Also, rads 9-13 and both baseboard units are above the unheated garage, which is shown in cross-hatching. Any tubing to these units would need to criss-cross the 750 SF garage ceiling, which is already covered by 10 light fixtures, a bunch of surface conduit, the garage door opener, and a steel I-beam the runs across the garage ceiling and drops down about 12 inches. I was hoping to minimize the tubing here, and much of the heat loss, by going with a two pipe system, at least above the garage.

But the layout of the house also isn’t good for reverse return, unless I skipped the interior rads and upsized the perimeter rads, though this would leave the kitchen and hallway with no rads at all.

That leaves direct return, which had been my plan, using three feeders and TRVs on all rads. But after playing with the head loss and flows, it seems like it’s going to be a challenge to balance. Seems like the more distant rads could still be relatively starved during really cold weather.

Was wondering how people here would approach this issue, given the diagram and the limitations of the house.

Thanks.

Comments

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,600
    edited November 2020
    What are the regular rads?  Cast iron?  European style panels?  Convector?    These should not be on the same loop as the baseboard 

    I can draw something up when I get back to my regular computer 
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • dave123
    dave123 Member Posts: 67
    The rads are euro style panels.

    The low temp baseboard is should be okay with the avg water temp 125 degrees, but it does require a fairly high flow rate, compared to the panels. Around 1 gpm I believe.
  • hot_rod
    hot_rod Member Posts: 21,878
    With bypass style H valves you can get three rads on one loop. I assume you are using TRVs on all?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • dave123
    dave123 Member Posts: 67
    hot_rod said:

    With bypass style H valves you can get three rads on one loop. I assume you are using TRVs on all?

    Yes, TRVs on all rads. Interesting thought to use bypass valves as though it were a one-pipe system. The only downside though is sending a lot of heated water back to the boiler. Lower delta T, higher return temp (?)
  • nosirra1Arrison
    nosirra1Arrison Member Posts: 56
    I’m a little concerned that your low temp plan will need some really big panel radiators to get enough btu’s at 125 degrees. You are probably going to end up running a higher temp which in the end will help the baseboard produce meaningful heat.
  • dave123
    dave123 Member Posts: 67
    I was figuring to upsize the rads to deal with avg water temps in the 125-130 range. During the coldest days, will probably need to be at 140, which, depending on what source I believe, should be a derate of about 48% on the rads compared to 180 degrees. The two rooms with (planned) baseboard already have electric radiant heat, so that could be used to supplement if the baseboard doesn't cut it. But actually the low temp baseboard I've seen runs about 400 BTU/hr/ft @130 degrees, and those two bathrooms have heat loss of 1700 btu/hr on design day, so it should be easy to cover those rooms with hot water alone.

    Running all the pipes is the stumbling block.
  • hot_rod
    hot_rod Member Posts: 21,878
    Often panel rads run a wide 30- 40 delta. If you start with a low SWT, say 125°, you may not be able to run as wide a delta. It really comes down to the load in each room and what the panel can supply at the expected SWT.

    With rads scattered around like that I think grouping them may help.
    Find some useful info here about derating panels.

    https://www.caleffi.com/sites/default/files/file/idronics_25_na.pdf
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • TAG
    TAG Member Posts: 755
    I have done a few projects using the Buderus panels. On my first project over 25 years ago I used two radiators in most of the rooms .... my lower office (walk out basement) needed three to spread out the heat. I zoned each room off a conventional manifold and used the bypass fitting on the bottom of the panel -- thermo head on the included panel valve.

    My memory was the 1/2 pex was good for about 12k BTU per look ... could have linked more together .... but, doing the rooms as a zone made an easier and very clean install. Also insulated all the Pex.

    This was an old brick/ block house with little insulation ... plaster. We took down ceiling and upgraded the ductwork -- but it was never going to be a cozy hot air house. I also oversized the panels a bit -- there are tables available. I tried to keep them all the single size and the doubles are more noticeable. The narrow tall doubles are real problem solvers ... mudrooms and other strange spaces where you don't have wider placement areas.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,600
    here is an idea of your piping plan. You can make changes as needed but I tried to keep the piping in the garage as concise as possible so it works and also can look good. you can use hard copper to keep the pipes strait. O2 barrier PEX for all the other piping. Pipe insulation won't hurt but is not necessary.


    I believe 1" will be good for the main trunk indicated by thicker lines. Depending on the capacity of the panel rads you could use 1/2" or 3/8" PEX for those connections. You can use parallel to each radiator grouping or use series as I have indicated in the drawing, both will work up to 3 rads per group.

    Notice I starter the baseboard with its own circ at the boiler supply. This is to make the flow rate for the baseboard good up to 4 GPM if you decide to use 3/4" PEX or copper to feed them.

    If you are going for a greater ΔT than 20°F you should use parallel piping on the groups

    Finally, the near boiler piping installed as @DanHolohan describes in his books and seminars will allow for purging the baseboard at a common drain valve near the boiler. you just need to be able to isolate the panel rad piping (at the circulator where the valve can also be used to isolate the circ for service) during the purge of the Baseboard.

    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,600
    Here is a slide I created to teach the concept of only one purge location. I have added a second circulator with isolation valves for future service and purging at the central purge valve at the top of the boiler supply indicated by the letter C. where the hose is attached.



    by closing all the isolation valves at the top of the boiler and the discharge side of the circulator for the panel system, the only path for water pressure A to go is to the baseboards pipe B. this pressure will flush and entrain air from the baseboards and move it to the boiler where it will exit the system at valve C.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • dave123
    dave123 Member Posts: 67
    Ed--thanks very much for taking the time to make that drawing. It makes good sense and looks like it solves the problems effectively. I had been imagining something more like three individual branches leaving boiler and fanning out, in a consistent direct return arrangement, running parallel to each rad, but your method saves a lot of piping (and work). Not that pipe/tube is that expensive, but more of it will take up more space and gets in the way more often. Plus, your way solves the problem of the garage ceiling.

    I’d prefer to do all the piping in copper, though the piping exposed on the unheated garage ceiling becomes an issue. Normally the garage never gets below 45 degrees, but could do so in a power failure, etc. Pex might survive better (a little). Any thoughts on that?

    The only reason I have baseboards in the bathrooms is because there is no significant wall space available for rads there, but if it requires another circ just to supply the two baseboards, I could look into other options.

    Hotrod--As for the delta T, I was designing for 20 degrees, but you mentioned rads typically running greater than that. I’m confused by that. Can’t you just change the flow through a rad and make the delta T whatever you want (assuming the btu’s are there)?

    Thanks again for the help.