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Highest output heat exchanger

I have an outdoor wood boiler running at 180 degrees F, what heat exchanger would i use to run this to a closed loop system at 15 psi to get as close to 180 degrees F out?

Comments

  • hot_rod
    hot_rod Member Posts: 21,898
    That is what is know as close approach sizing, where the output is within a few degrees of the inlet temperature. So it generally takes more surface area to get those close temperatures, larger dimension HX or more plates.

    The best way to size is using one of the free online calculator programs. You need a few pieces of data, temperature and flow rates. You know two temperatures, you need to know or guesstimate the flow rates.

    The programs usually give you a few option for sizing. Manufacturers will also help you with sizing if you contact them at their websites, or if you have a local rep.

    This example is for domestic water incoming at 50 f
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • GroundUp
    GroundUp Member Posts: 1,868
    That is entirely dependent on the BTU load and piping. Your wood boiler may be set to 180, but it has a differential (typically 10+ degrees) as well as some line loss underground, plus the probability that the water leaving the jacket is not actually what the sensor is reading. Many OWB (Central seems to be the worst) will show 180 on the display but are actually only sending 165-170 out of the supply port due to poor internal mixing and sensor probe location. Simply put, if you always need 180 degree water supplied to your emitters, you will never achieve that with a wood boiler set to 180 on the high side.

    What is the connected load on the indoor side?
  • hot_rod
    hot_rod Member Posts: 21,898
    Does the building heat adequately now, with whatever temperature that actually enters the building?

    Often times on a single pump system with undersized runs, you may not be getting adequate flow.

    If the furnace comes up to temperature and shuts down, but the building is not heating adequately, that is often an indication of undersized lines from the furnace.

    plan on loosing a few degrees if you install the HX inside.

    IF the building struggles or falls behind on cold days, you have two means to increase heat output. Increase supply, or increase flow rate.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • BeardedWoodsman
    BeardedWoodsman Member Posts: 2

    Thank you for the information and info to look into.

  • Mad Dog_2
    Mad Dog_2 Member Posts: 6,768
    I love Flat Plate HX....MD 
  • leonz
    leonz Member Posts: 1,055

    I have an outdoor wood boiler running at 180 degrees F, what heat exchanger would I use to run this to a closed loop system at 15 psi to get as close to 180 degrees F out?

    =================================================================

    A large storage tank in the basement with multiple copper coils piped in series is about the only way to make enough hot water to heat your home as you need more thermal mass i.e., water.

    Pumping the boilers water through the multiple coils piped in series will heat the water in the tank
    and the tank with a small circulator can be used to circulate the hot water through the heating loops.

    By doing this you will have created a heat source that will give smooth even heat over time as long as you keep the forest eater from going hungry.

    I tell a lot of folks to fill their forest eaters half full of standard firebrick all the way to the flue breech which creates a heat sink to store heat from the wood fire and shed it back into boiler walls and water over time.

    I filled my hand fed boiler half full of standard firebrick all the way to the flue breech and I had a much hotter wood fire that burned cleaner and very coal fire and a huge heat sink holding lots of heat that did not go up the chimney.

    In addition to the above I burned much less wood and coal.
  • hot_rod
    hot_rod Member Posts: 21,898
    From a heat exchange perspective a HX of any design will exchange much better with flow on both sides. Counterflow picks up even more performance.

    I have done a number of open tanks with copper coils, one with pex coils. They work okay, but...

    One challenge is the tank stratifies, so you need to load with flow in one direction, pull heat from opposite flow to leverage that hottest top layer. The taller the tank, the wider that temperature layer difference.

    A reverser can be built from a 4 way valve with movement from one position to the opposite. Load by pulling cool water from bottom to boiler. Pull the load from the top layer.

    Almost impossible to beat a plate HX performance, especially considering the size. At the cost of a second circulator.

    A tank could still be used as the "thermal battery" Using plate HX for the transfer, instead of $$ copper coils.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream