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repiping old radiant boiler

jimmyd
jimmyd Member Posts: 7
I just bought a 2 story 1200 sq ft home with an old boiler. The pipes in the house are bad and I would like to replace them with oxygen free pex. There are 9 radiators ranging from small to one that is about 5610btu/h. I haven't done a heat loss calculation on the house yet. It currently is a 2 pipe system with the circulator on the return. I read Dan's book Classic Hydronics and plan to use one of his models with the circulator on the supply side. I'm not sure what size pipe. Should I pull each radiator to a manifold or use a reverse return design? Any advice would be great.

Comments

  • Zman
    Zman Member Posts: 6,768
    Perfect World

    In perfect world I would like to see 1/2" pex lines from each radiator back to a manifold in the boiler room. I would control the radiators with TRV's or zones valves depending on the house layout and logistics.

    In the boiler room would be a mod/con boiler with outdoor reset control. The heating circulator would be high efficiency ECM like the Grundfos Alpha.

    Hope that helps. If you have more details you can get more specific advice.You are correct that you need to do a heat loss calc. You should also get an idea of how many BTU's of radiator you have. These numbers will play an important role in sizing the system.

    You have come to the right place,

    Carl
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • jimmyd
    jimmyd Member Posts: 7
    heat loss

    Thanks zman. I looked at a heat loss calculator on-line and punched in some rough numbers. I gives me a lot of different measures. UA(btu/hr-f), Design Loss(btu/hr), year loss, fuel costs... What measure am i looking for?
  • Zman
    Zman Member Posts: 6,768
    Design loss

    You are looking for design loss.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • jimmyd
    jimmyd Member Posts: 7
    old boiler

    OK here is some more data. I did a heat loss cal. I got 30246 BTU/hr. Does this sound right for a 2 story 1100 sq ft home? I'm wondering if I can use the old boiler. It was built by dunkirk and sold by sears in 1976 It is a heavy cast iron boiler with input of 112500 BTU/hr and output of 90000 BTU/hr. Can I still use the 1/2" pex? Some radiators are original with the house others came from a salvage yard. There are nine of them 5 on the second floor. I was considering using a menards copper manifold but they don't have a 9 valve. I have questions on the best way to balance the system.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    30246 BTU/hr. Does this sound right for a 2 story 1100 sq ft home?

    It could be right. I have an 1150 square foot Cape Cod home in New Jersey (design temp 14F) and I calculated I needed 29,234 BTU/hour when it is 0F outside and 70F inside.



    Actually, it never goes down that far outside, and I heat to only 69F inside.



    If your heat load calculation is correct, your existing boiler is way too big.



    N.B.: I am a homeowner, not a heating professional.
  • jimmyd
    jimmyd Member Posts: 7
    zone valves or TVR's and outside reset control

    zman talked about using TVR's or zone valves and outside reset controls in an earlier thread. I get what a zone valve is but am unfamilar with the other two devices. Where are they located in the system and what do they do?
  • Zman
    Zman Member Posts: 6,768
    TRV ODR

    A trv   ( thermostatic radiator valve) mounts on your radiator. It will regulate the flow of water to the radiator based on room temperature. Outdoor reset control will vary the temperature of you system water based on outdoor temps. Your system may need  160 degree water on your coldest design day, But only 120 degrees on the average heating day. Outdoor reset makes these adjustments automatically. Making you home more comfortable and efficient.

    I don't think using your old boiler makes much sense. By the time you retrofit it to work with your new system you will have spent a great deal of time and energy on something very inefficient and on it's "last legs". A new mod/con will save at least 30% on fuel and will do ODR with no extra controls.

    Copper manifolds use standard copper pipe sizes. You can cut, combine and cap them as needed. I would use a 1" manifold , and pipe the pex reverse/return.

    How are you heating your domestic water?

    Carl
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • jimmyd
    jimmyd Member Posts: 7
    domestic hot water

    The old system was simply a gas hot water tank. I was was rusted out and eleminated so I'm open to suggestions. A new tank is going to cost over 400$.
  • Zman
    Zman Member Posts: 6,768
    Mod/ con Combi

    It sounds like you would be a good candidate for a mod/con combi boiler. Triangle tube challenger is one.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • jimmyd
    jimmyd Member Posts: 7
    balancing valves

    I see some balancing valves manifold conbinations where all you have to do is run each radiator the the manifold and then use the balancing valve to balance. Simple, easy, expensive. What do balancing valves measure? pressure? If it's pressure why not place a cheap pressure guage in each loop and use that to balance the system? Am I showing my ignorance?
  • SWEI
    SWEI Member Posts: 7,356
    balancing valves

    Allow you to adjust the friction (head) in each branch so that each emitter gets the right amount of flow and the space ends up evenly heated.  The pressure drop (differential pressure across the valve) can be read with the little gauges on some models of manifold.  These are usually used to balance loop flows in a radiant floor or ceiling installation (with 100-300 foot loops of tubing as the emitters.)  Assuming the radiator sizing is anywhere near sane and that the branch lines feeding them are not radically different in length (like 20 feet versus 200 feet) TRVs at the radiator should be adequate.  Shut-off valves on the branches will come in handy during fill/purge and for eventual maintenance needs.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Balancing valves.

    My radiant slab has 5 circuits in it. I assume each is a different length, because each of the 5 rooms is a different size and has a different heat loss. Each circuit has a ball valve in it that I use to balance the temperatures in each room. Ball valves in this application are not desirable. They turn 90 degrees, and the first 45 degrees makes little difference. If the loads and resistances were just about equal, they would probably work OK, mostly wide open. But in my application, one valve is almost closed, and that room overheats anyway (big electrical load in that room, and high sun loads in the afternoon. But I do not dare turn it off more than it is already, because I am afraid if I accidentally turned it completely off, I would freeze the copper tubing in the concrete slab. Also, I can hear the ball valve noise as the water rushes through the nearly closed ball. Surely erosion is taking place, so ultimately, that valve will not shut off after a while. It my not matter, but it is not a good thing.



    A balancing valve is designed so that the flow through it is nearly proportional to the amount the control knob is turned. I do not know their price, but I would imagine they cost considerably more than ball valves.



    I am not sure I would want pressure gauges on the circuits. If I did, I would want differential pressure gauges so I could guess the flow rates. But if it is flow I want, and I suppose I do, I would get flow meters instead. That would make it easy to set the same flow in each circuit if I wanted to. As it is, I do not know what flow rate I want in each circuit.



    Instead, what I did was open all the valves full, and then slowly closed off the one to the hottest room until it matched the room that was coldest. I then rinsed and repeated.



    As a practical matter, I did not succeed at that because the hottest room I could not turn down far enough, But it worked fine for the others. Later, I closed down my bedroom down a little because I like that room cooler at night. During the day I just leave the doors open and that equalizes things well enough.
  • SWEI
    SWEI Member Posts: 7,356
    edited July 2012
    balancing valves

    are an application, not a valve type per se.  Gate valves and unmodified ball valves are particularly unsuited to the task, but a number of other configurations can work.



    They are not particularly expensive - in fact, a globe valve usually costs less than a ball valve of equivalent Cv.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Balancing valves.

    I was thinking about a valve something like this one:



    http://www.taco-hvac.com/en/products/Flow%20Measurement/track_file.html?file_to_download_id=8272



    Or like the ones in figures 3-12 and 3-13 of this publication:



    http://www.caleffi.us/en_US/caleffi/Details/Magazines/pdf/idronics_8_us.pdf



    This publication has many different kinds of balancing valves in it.
  • Zman
    Zman Member Posts: 6,768
    I don't see a need

    I don't think I would be to concerned about balancing. A pressure gauge on the supply and return would do the trick.This approach would get the job done, but would not be very practical. There are many manifolds with flow gauges available that will show GPM. They are not very expensive and are fun to look at. As SWEI said, the trvs will keep the system in check. Unless your loops are drastically different in length and load,, you should be fine with a simple manifold.Isolation valves are always a good idea.

    Carl
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • jimmyd
    jimmyd Member Posts: 7
    Globe valve

    What is a globe valve and how does it perfom different from a ball valve aor gate valve?
  • SWEI
    SWEI Member Posts: 7,356
    balancing valves

    The Taco valve is a modified ball design - note the venturi.  Belimo does this with a special characterizing disc with geometry that varies depending on the Cv rating of the valve (see PDF below.)



    The Caleffit valve uses a globe design.
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