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baseboard heat pipe question

bthomasb1 Member Posts: 2
edited November 2021 in Solar
Hello everyone I'm new here.Im a contractor but I don't work with heating systems.I am building myself a small offgrid house to retire to,it is 16 x 40 1 floor 8 ft walls 2 bedrooms,1 bath and a 21 x 15 living /kitchen area.
 I am planning on using evacuated tube solar collectors for my baseboard radiant heat and my domestic hot water,3 zones was what I was thinking,but I am here to ask for some help/ recommendations from people with more knowledge than I have on the subject, it will be well insulated I was planning on 3  8-foot heaters and one small 30in in the bathroom everything will be on one level solar collectors in the heat should be pretty much all on the same plane.
So can I use 1/2 PEX to run from my heat exchanger to my heaters or should I stick with 3/4 ,with that small of a building should I run on 1 zone?I will be running 12 volt circulators and what would be my best choice of thermostats to use ,any other information you have would be greatly appreciated I live in Pennsylvania where it gets to negative degrees sometimes but mostly twenties to thirties during the winter, thank you


    EBEBRATT-Ed Member Posts: 14,483
    First thing you need is an accurate heat loss of the building. You can't design anything until that is done. Slant Fin has an app you can download and then there is the manual J calculation
  • How did you come up with that amount of baseboard? Was it a guess or did someone tell you or maybe you did the calculations. If the latter, you're on the right track. If not, start here and do it right.

    If that were my retirement nest, I would install a manifold with separate loops to each radiator or each zone.

    Solar collectors are great, but what do you do when there isn't enough sun to heat the water?
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • eclecticmn
    eclecticmn Member Posts: 120
    I would be surprised if solar worked in PA but I do not know the local conditions. I once worked in Buffalo NY and did not see the sun for 4 weeks once. It was gray haze. Maybe in Feb. I would seek out some site planning software for solar to get some idea. They have histories of past solar going back decades, day by day and month by month. I would look into outside boiler using wood or coal or inside backup stove. Coal requires cast iron and a stove designed for it.

    I have recently learned some about cast iron baseboard heat. Burnham Baseray and Weil McLain are some brand names.

    Cloud cover is very important.

    Here is one insolation data source, from searching. Most are for solar electric it seems.

    Here is a link to a program that does a calc for room BTU requirements.
    Home owner near Minneapolis with cast iron radiators, one non working slant fin now ripped out, and hot water heat.
  • eclecticmn
    eclecticmn Member Posts: 120
    I came across this guy and posted on some solar thermal collectors in Ukraine.
    Home owner near Minneapolis with cast iron radiators, one non working slant fin now ripped out, and hot water heat.
  • mattmia2
    mattmia2 Member Posts: 8,826
    Normally t-stats are 24vac if they are electronic. Circulators are normally switch be 24vac relays. Could use mechanical t-stat and 12vdc relays. Might make sense to use ss relays or other solid state switching to avoid the loss in energizing the relays in this situation.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 6,688
    edited November 2021
    You need to consider several things. What is the water temperature in the baseboards going to be when you need the heat the most? Baseboard heaters give off less heat as the water temperature in the pipe drops. How hot will your storage tank of water be? How large will your water storage tank be? Will you be using some type of antifreeze in the solar collector? The specific gravity of the antifreeze solution will transfer less heat than strait water. Will your entire system be antifreeze or will you use a heat exchanger to keep the amount of antifreeze to a minimum? After you figure out your basic design, then it is all in the mathematics. 1 BTU equals the amount of energy it takes to raise the temperature of one pound of water one degree Fahrenheit.

    After all your calculations, Heat Loss of the structure, solar gain into the collectors, heated water (or whatever medium you decide) storage capacity, among other things, you will have everything designed just perfect. Then you get to a unusually cold and cloudy 3 weeks in January. You should plan on a back up oil fired boiler with a back up generator to power it.

    Once you have that all done, you may never need the oil boiler, but if you don't have it, guaranteed you will have a freeze up the year after you install it. Check with a local plumber on getting a used oil boiler form someone who is converting to gas. I bet you will find something in pretty good shape that is less than 10 or 15-years old you can get for free, or maybe even a 5 year old one for a few hundred dollars.

    These are just the rambling thoughts of an old man in a wheelchair

    Good luck with your project.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • bthomasb1
    bthomasb1 Member Posts: 2
    Thanks everyone for the comments, I plan on running a 150 gal collector with antifreeze to a heat exchanger in a 1500 gal tank and a propane hot water heater as a backup all the heaters will be thier own zone ,I still have lots of time so I just keep researching,and the building should have very little heat loss through holes as I'm building it new calling studs to sheating sealing can lights and all protrusions  through ceilings studs plates,r 19 walls and r 50 ceilings
  • Zman
    Zman Member Posts: 7,493
    edited December 2021
    You will want to carefully design this to move the water with as little energy as possible. Oversized tubing and generously sized heat exchangers will help with this.
    You should also consider emitters that are sized to work with very low water temps. I would suggest 120 degrees or lower. This will allow your collectors to work more effectively on less sunny days and will increase your "effective storage". If you go with standard baseboards, they may start underperforming when your storage water drops to 150 degrees. With low temp emitters, you could double the usable energy. Runtal makes some nice low temp emitters. https://runtalnorthamerica.com/residential-radiators/
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • eclecticmn
    eclecticmn Member Posts: 120
    I was looking into some phase change materials for use with thermal solar and found some links and posted under a different topic. Here is a source.
    From India, shipped to Chicago distributors and elsewhere.
    Home owner near Minneapolis with cast iron radiators, one non working slant fin now ripped out, and hot water heat.