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Heat Transfer Issue

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by Mass Heat, Oct 7, 2012.

  1. Mass Heat

    Mass Heat New Member

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    Hello, I'm having an issue transferring heat from my outdoor boiler thru a 50 plate heat exchanger to my indoor Burnham oil boiler. I have 175 degrees on the feed line to the heat exchanger. The return line is 165 to 170 degrees. I turned the Honeywell controller on the Burnham down to 140 and can't get the temp in the Burnham to rise using the exchanger. I bled the lines, several 5 gallon buckets but could never get the water crystal clear. It always had some color to it. Should I have clear water after the flush? Should I shut down the boiler while doing so? I'm concerned that I still have air in the line or that the exchanger is dirty from the brown water. I'm also concerned about the 007 pump being too small between the Burnham and the exchanger. Please advise, looking for help.

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  2. Mass Heat

    Mass Heat New Member

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    Heat exchanger photo

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  3. Mass Heat

    Mass Heat New Member

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    Tied in on top for the loop.

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  4. Mass Heat

    Mass Heat New Member

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    Black Taco 007 is returning water from the heat exchanger loop in line with the other pumps.

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  5. Eric Johnson

    Eric Johnson Mod Emeritus

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    Looks and sounds like you know what you're doing, so I'll probably insult you by asking a few simple questions that pop into my head, but you gotta start somewhere.

    1.) What temp is the water entering the exchanger on the Burnham side? If you're putting hot water from the oil boiler in, you won't get much, if any, heat exchange.

    2.) Are you drawing the Burnham water from the supply or the return? Obviously, the greatest differential is going to be from the return water.

    3.) Is the flat plate hx piped to counterflow? It's a relatively minor point for the purposes of this discussion, but one to consider.

    4.) Are you sure you've got it piped correctly, i.e., correct inlets and outlets used on the flat plate?

    5.) Is the flat plate new or used?

    6.) It sounds like you're getting flow through the flat plate, but who knows? Do you have a way of venting the loop at the hx or nearby?

    It would probably take more than a little discolored water to jam up the plates, but that's something you need to be aware of in an open system like your typical OWB. I assume the OWB is new and it's been flushed. One typical flat plate installation has hose bibs on the OWB supply and return lines so that you can periodically flush it.

    For troubleshooting purposes, I think I'd shut off the oil burner and let the Burnham cool way down, and then fire up the OWB and see what happens. I'm pretty sure it would overheat pretty quick without any heat transfer, assuming it's not serving any other zone. Has it overheated? If not, then the heat must be going somewhere. And IMO, a 007 is plenty of circulator for the loop between the Burnham and the flat plate.

    Just as a side note, I've never been very impressed with flat plate hx performance. In a situation where you're not getting much heat transfer, the water just keeps cycling in a big loop, and any inefficiencies in your system are going to be magnified dramatically over time as a result. So, heat that is lost on one pass with a direct piping configuration is going to be lost again and again as the heat that wasn't transferred through the hx gets sent back to the OWB. That's just been my limited experience.
  6. Mass Heat

    Mass Heat New Member

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    Eric, thanks for the response.
    Q1.) Not sure on the exact temp. Boiler temp was set at roughly 140, so the temp entering the exchanger should be close to that.
    Q2.) Water is drawn from the supply side and forced to the return side.
    Q3.) Not setup for counter flow. I like the logic and can't see it hurting. I need to bring the Burnham temp up from 140 to at least 170. Can't see this making that much of a difference. Something to consider.
    Q4.) Yep, pretty sure on the piping. Unit is rectangular and runs length wise. Poured water in during the install to verify. Plumber had it backwards and I made him switch it.
    Q5.) Brand new 50 plate heat exchanger from Outdoor Furnace Supply.
    Q6.) Checked the flow by opening the y-strainer and it flowed. I'm hearing flowing water when I turn on the pumps, so I'm thinking its air. Just doesn't sound right. OWB is new and isn't the issue. Dealer isn't giving me much help because the issue is on the Burnham side and he didn't do the install. It hasnt over heated by much. Set at 180 and I saw it go 185. The blower shut off and killed the fire.
  7. Eric Johnson

    Eric Johnson Mod Emeritus

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    I'll be curious what other, much more experienced (than me) members have to say. When solid fuel boilers don't have any heat transfer, they overheat rather dramatically, simply because a bed of coals can't be shut off by killing the blower. They just keep glowing and putting out the btus. Steam and water tend to shoot out the top. So I'm guessing you're getting a fair amount of heat dissipated somehow. And if you're getting 175 degrees at the hx from the OWB, then you're not losing it in the piping or anywhere else. My guess is that it is transferring heat into the Burnham, just in a way that you fail to appreciate, if that makes any sense at all.

    Again, I'd let the Burnham cool off overnight, then fire the OWB up tomorrow and see what works and what doesn't. Always good to isolate things and cut the number of variables when troubleshooting.

    My mom has a Heatmor OWB connected to a pressurized propane boiler in the basement of her farmhouse. My late dad set it up. Somehow, she gets plenty of pressure at the gas boiler and in the system as a whole, even though it's a direct connection--no heat exchangers--and the OWB is "unpressurized." The system is full of antifreeze. Works like a dream. So, that may be an option for you if the flat plate can't get the job done. Just something to consider. I went from a flat plate to a direct connect on my EKO/Weil McLain gas boiler (both pressurized), and remain very impressed with the quick response. When on vacation or otherwise unable to keep the wood side going, I simply crack the valves enough to let hot water flow (through convection) from the gas side out to the EKO in the barn, some 100 feet of 1" pex away.
  8. jebatty

    jebatty Minister of Fire

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    Kind of like saying, "red is not my favorite color." In my experience flat plate problems result from: 1) failing to size the flat plate correctly; 2) incorrectly determining or ignoring pump head on either or both Sides A and B; 3) failing to match circulators on Sides A and B with pump head at required flow rates to provide needed btuh transfer at the desired approach temperature.

    I've had experience with flat plates (about $200) with flows at 3 gpm (40,000 btuh transfer rate) for in-floor radiant all the way up to 75 gpm and a 5F approach temp (about $5,000) for a Garn WHS3200 (500,000+ btuh transfer rate). Properly sized for the application, flat plates can be stellar performers, and in many pressurized/non-pressurized applications they are probably essential.
  9. Eric Johnson

    Eric Johnson Mod Emeritus

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    So, what do you think about his installation, Jim?
  10. Mass Heat

    Mass Heat New Member

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    I'm concerned with the pumps as well. I have 2 Taco 007s running thru the heat exchanger. I have a 2600 sq ft house and 5 zones plus domestic hot water. I have a 40 ft run down to the basement from the OWB. Should I switch the pumps. I was thinking Grundfos 1558, 3 speed but the gains per spec are minimal. Do I need to step up to a Taco 009? I shut the Burnham down and bled the entire system. I'm gonna fire up the OWB, turn on the pumps and see if I can get some transfer without a load. The Burnham is cold, so I should get some transfer, right?
  11. Eric Johnson

    Eric Johnson Mod Emeritus

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    Either that or your OWB is going to overheat. I'd start with a small fire and see what happens.

    Good luck. I'm sure you'll get some clarity.
  12. Mass Heat

    Mass Heat New Member

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    Ok, the Burnham is off and I have successfully brought the temp up from 60 to 130. Hopefully it keeps on rising. Still sounds like the line has some air pockets. The heat exchanger is 170 on the feed and 160 on the return. Keeping my fingers crossed.
  13. Eric Johnson

    Eric Johnson Mod Emeritus

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    I have a similar setup with a remote wood-fired gasifier pumping hot water into a gas boiler. I just shut the gas off during the heating season. Everything is so much simpler that way.
  14. Mass Heat

    Mass Heat New Member

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    Stuck on 135 for a while. Got 175 and 165 at the exchanger. Doesn't seem to be exchanging heat at this point. Not sure what's going on?
  15. Armaton

    Armaton Member

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    The GEA flatplate select program says that a 5x12, 50 plate, 117kbtu flat plate with 175 degree water input at 14gpm should raise 140 degree water to 170 degrees at 7-8 gpm thruput, and the side A return temp is from 155-160. of course these are for their plates, but gives you an idea. Also if the Burnham side pump is pumping 9gpm or higher, the program says you would need a bigger flatplate. SO if you're using a 007 on the burnham side it might be going through to fast.
  16. jebatty

    jebatty Minister of Fire

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    The GEA info provides some clues to help out. For some reason GEA is not letting me into their selection software, so I can only generalize at this point. If required Side A flow to get needed btu's is 14 gpm, and if you are using a 007, then pump head for the 007 to move this amount of water is about 5.75 feet. What is the pressure drop on Side A at 14 gpm? Then pressure drop x 2.3 is about feet of pump head for Side A of the hx. What is the pump head in the plumbing between Side A and your boiler at 14gpm? Add this to the Side A pump head. How close is this to 5.75 feet? If more, then the 007 is moving less water which = less btu's. If less, then the 007 is moving more water which = more btu's. But watch out, because pump head increases by a power of 1.75 as flow increases, and vice versa, so a change in pump head will impact flow rate +/- greatly. And a change in flow rate will impact pump head +/- greatly. And each also will impact btu transfer (delta-T x 500 x gpm = btuh).

    Do the same thing on Side B.

    You will note that everything is a moving target in this determination. Change one parameter and all parameters change.

    If I am able to get back into GEA selection software, I may be able to help out more.
  17. Mass Heat

    Mass Heat New Member

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    Jebatty, not sure exactly how to measure the pump head and pressure drop. The entire loop is 18ft. The system has a 32 in vertical drop, as the pump pulls and a 48 inch vertical incline from the pump up to the exchanger. The rest of he system is horizontal. Here's a photo of the drop returning to the Burnham.

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  18. RobC

    RobC Minister of Fire

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    Does it make any difference where the circulator is located ? Should it be pushing the water into the exchanger ?
  19. jebatty

    jebatty Minister of Fire

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    This is the info needed to get close on determining the sizing of a circulator and/or hx to meet your needs.

    For Side A: round trip for all info (outdoor boiler/hx/outdoor boiler)
    diameter of pipe (1", 1.25", etc.)
    type of pipe (copper, pex, steel, etc.)
    length of pipe
    # of L's
    # of ball valves
    # of check valves
    # and description of other fittings

    For Side B:
    same thing

    Based on your prior info, you are seeking 175/155 at 14 gpm on Side A and 140/170 at 8 gpm on Side B. With these temperatures, 14 gpm on Side A will deliver to the hx 140,000 btuh, and 8 gpm on Side B will deliver 120,000 btuh from the hx. If these are not your operating parameters, then provide new info.
  20. Armaton

    Armaton Member

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    The numbers were mine, Just showing what the GEA site showed for a similar plate. Not knowing his system setup I plugged in numbers till they worked for his size plate. However with the info he provided I was pretty close. I would approximate his side A flow at about the 14 gallons I used, (depending on the length of run of course). His side b with 18' run and 4' of head shows about 18 gpm for a 007, so my guess would be side b is over pumped for the plate. What do you think, Jim?
  21. jebatty

    jebatty Minister of Fire

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    My mistake, I thought your numbers were those of Mass Heat. So, Mass Heat, what performance are you looking for? what is the btu output from your OWB? what btu input do you need into your system?
  22. Mass Heat

    Mass Heat New Member

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    The OWB is an Empyre Elite 200 and I need roughly 100,000 BTU +\- 10,000.
  23. Mass Heat

    Mass Heat New Member

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    My side A run is about 85 feet. 40 outdoors and the rest indoors.
  24. heaterman

    heaterman Minister of Fire

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    Not enough flow. Not large enough tube to allow enough flow.
  25. Mass Heat

    Mass Heat New Member

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    I bled all my zones last night and removed air from the lines. Last night a zone called for heat and I heard air in the lines. I think the I have an issue with air in my circulating loop within the exchanger and pump? I'm hearing rushing water and it doesnt sound right. I pretty much drained the entire system. Can the side B pump be to big? I would think that the return line would be colder if it was.

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