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Thread: Do I need Primary / secondary piping?

  1. #16
    DIY Junior Member Crooz1n's Avatar
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    Dana Its been running for ~a week and I looked at ignitions 22 and run time 52 hrs. That's giving me burn times of 2 + hrs. too much? I noticed before the call for heat comes on the supply reading will sometimes be ~ 68-69F.
    I have seen no internal flow reading.

  2. #17
    In the trades Dana's Avatar
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    Long burn times at low fire and low temp are what you WANT in a modulating condensing boiler.

    When there is no flow on the system the boiler temperature will fall to about room temp, so 68-69F measured at both the input and output would be normal several hours after the last burn. On a new call for heat after a long stagnation the output temp should rise to whatever the outdoor reset is calling for within a few minutes, but the input temp will remain pretty low until the system water has gone full-circuit.

    On a high water-volume or high thermal-mass system this can go on for quite some time, so if you're starting out with all the radiators at 68F, and the outdoor reset is calling for 150F water it can end up stressing the boiler. This can be avoided by not using deep over night setbacks at the thermostat, or just running the system continuosly, so that the return water is always tracking at a reasonable delta from the output temp.

    Adjusting the outdoor reset curve to where it runs almost continuously but still manages to keep up with the heating load is the way max out the efficiency of these things. A right-sized boiler for the peak load will run VERY long burns, nearly constantly during mid-winter weather once it's dialed-in. Lowering the outdoor reset curve also limits the cold-start delta-T issue. If you tweak the the curves close enough recovery from setback is pretty slow, but running it continously the fuel use is the same or less than when using a deep overnight setback strategy, due to the greater condensing efficiency and near-zero cycling losses.

    The best way to kill efficiency (and the boiler) is to have it doing fifteen 1-minute burns per hour at a high output temp with really big delta-T.

  3. #18
    DIY Junior Member Crooz1n's Avatar
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    I'm not running any setback. Thermostat set @70 BUT... this morning I noticed it overshot 2-3 degrees. I wonder if that's due to the old thermostat and anticipator or that I have the circ pump set to run 20 min after call for heat is met.The default is 10 min but I am trying to make sure to get most of the btu's out of the pipes into the radiators. Top of curve is set to 160 but I have max boiler set at 120 to see if it will heat OK there.

    manual here if interested:
    http://s3.pexsupply.com/manuals/1316..._PROD_FILE.pdf

  4. #19
    In the trades Dana's Avatar
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    Overshooting the setpoint is an indication that the reset curve is calling for a higher temp than needed for meeting the load, or that you had a rapid change on load conditions (the sun came up and started pouring 100,000 BTU/hour through that vast expanse of east-facing window? :-) ) On a high mass radiation system if you dial in the curve really well you can almost dispense with the thermostat entirely.

    Overshoots on high mass systems can be nearly eliminated using PID control algorithm thermostats, but depending on the algorithm that can result in increasing the number of burn cycles. See if you can't dial in the curve closer first.

  5. #20
    DIY Junior Member Crooz1n's Avatar
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    So do u think I should lower the max boiler temp from 120 to 110?

  6. #21
    In the Trades Tom Sawyer's Avatar
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    That condensate line is about as illegal as illegal gets. If its dumping into the sanitary waste system it needs to be indirect wasted into a vented trap
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  7. #22
    DIY Senior Member Reach4's Avatar
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    Quote Originally Posted by Dana View Post

    Nice looking install. What is that gray thing inline with the upper black gas pipe?

  8. #23
    Master Hot Water Mpls,MN BadgerBoilerMN's Avatar
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    Condensing boilers and old cast iron radiators are a perfect match. We have been installing them in Minneapolis/St. Paul since 1990, without the "benefit" of primary/secondary piping. We don't even "pump away" from the boiler since this is missing the point and really less than optimum for any low-mass boiler.

    The installation is amateurish but adequate, but for the illegal condensate hook-up to the sewer system.

    The pump is oriented upright (there is an installation drawing in the box), no drip-leg or union on the gas service (see pages 29 of the installation manual, pictures no reading necessary), Delta T is fine (happy accident), outdoor reset sensor likely still in the box or placed safely inside the cabinet (no wiring needed). I would like to know how the outdoor reset is configured but looking at the pump I think it is safe to assume in would be a waste of time. Old-fashioned air scoop and vent are for hot systems (this never really was) and should have been removed preventing future sources of air and leaks.

    We install Peerless Surefire here in Minneapolis but re-pipe, install outdoor sensors (they come in every boiler box) program and follow the installation check list which includes combustion analysis and tuning as necessary.

    If your condensing boiler installer can produce a heat load and show up with an electronic combustion analyzer he is light-years ahead of his "peers".

    Other than that, it should be A.O.K.

  9. #24
    In the trades Dana's Avatar
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    Quote Originally Posted by Crooz1n View Post
    So do u think I should lower the max boiler temp from 120 to 110?
    No, I think you should set up the outdoor reset curve, and keep tweaking the curve downward until it just barely keeps up.

    Reach4: The "...gray thing..."is a gas pressure regulator. (Not my install- picture clipped from the web as a clear example.)

  10. #25
    DIY Junior Member Crooz1n's Avatar
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    Badger- Thanks for replying. The air scoop is still n place but the relief valve was removed and plugged. new vent valve installed There is a new pressure relief on the boiler.
    Outdoor reset is installed on north wall and hooked up. I have it set to 160 @16 and wwsd at 70. I currently have it limited to 120 boiler max to see how low I could go and still heat the house. Maybe that is a mistake on my part.
    Should I set boiler max back to 160 and reduce the curve top end from 160 down to 120 or lower?
    I am doing the parameter tweaking as the contractor simply turned it on and left everything at default. "Oh we don't mess with the computer!" - I was told.
    The pump orientation has been changed after I bitched about it. RTFI!!
    The drip leg and union are above the unit but I will ask the inspector about the location that it's in.
    Inspector said nothing about pump but I'll ask about that as well.

    Here are the parameters as set
    Boiler settings
    1 Pump mode -19 (CH)
    2 Location -USA
    3 Vent material PVC
    4 Freeze protection 40
    5 Blower Post purge-30 sec.
    6 additional Safety - LWCO not installed

    CH settings
    1 CH mode 1 thermostat and ODR
    2 CH pump purge- 20 Min
    3 Gen circ purge-0
    4 Pump delay step modulation-OFF
    5 system Type- User Defined
    6 wwsd-70
    7 reset curve design- Boiler 160, outdoor 16 Changed to140@16
    8 Reste curve mild weather- 120,70 Changed to 80 @65
    9 Reset curve boiler min-80 max 150
    10 Boost function-Temp 18,Time 20
    11 Anti cycling-10
    12 CH response time was 60 now 40
    13 CH rate100%

    FYI-- 580 Sq ft of cast Iron radiators in the house.
    Last edited by Crooz1n; 11-15-2013 at 02:54 PM. Reason: Made changes to settings

  11. #26
    In the trades Dana's Avatar
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    Carefully read the section titled " 3. Outdoor Reset Operation:" on p42 (p45 in PDF pagination), and how to set up the curve in figure 8.6, using a user-defined reset curve. (preset 7 in table 8.7)

    It looks like you set up the curve to deliver 160F water at an outdoor temp of +16F (which is about your 99% design temp), and deliver 120F water when it's 70F out (which is a bit much!) I suspect you'll never need more than 140F water @ +16F, and may not even need 130F water. With the curve as-is it'll be delivering ~140F output when it's 43F outside, a temp that would probably have you covered even at +16F.

    Start by dropping the mild-weather output to 80F @ 65F outdoors and see if it short-cycles (probably won't, in a high mass system), and set the design temp output to 140F @ 16F outdoor. Hopefully it'll still keep up, but without overshooting on the warmer days.

    If it turns out that it won't keep the house up to temp during cooler weather, raise the design temp up by 10F to 150F @ 16F and see how it makes out. If it fails to keep up, bump it another 10F on the design end. When you find the point were it keeps up, back off 5F, see if it continues to keep up, then ride it out for awhile. If it always keeps up, never overshoots or short-cycles during milder weather, you're golden.

  12. #27
    DIY Junior Member Crooz1n's Avatar
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    Tom the inspector agreed about the condensate drain once I pointed it out (Thank You!) and the contractor has been told he has to install it into a trap. he said sort of like one you'd dump a washing machine in. Both will be back tomorrow to hopefully get the final inspection done.

  13. #28
    Master Hot Water Mpls,MN BadgerBoilerMN's Avatar
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    With all due respect. There are currently no residential ModCon boilers in the US with built-in flow meters, mechanical or electronic. As you suggest, Delta 'T' is the benchmark. Most manufacturers of ModCon boilers prefer a 20F Delta 'T' but many will suffer 45 depending on the orientation of the pump.

    It is interesting that the some European manufacturers mention "over" pumping in contrast to the manic preoccupation we have with P/S and minimum flows to the point that many manufacturers including our own Weil McLain and the German built Buderus void warranties if P/S pumping is not employed regardless of system engineering. The fact is the more you pump, the more you spend. KISS.

  14. #29
    In the trades Dana's Avatar
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    I've never seen a mod-con with an internal flow meter either, but since several tankless water heaters out have some sort of kludgey flow metering I couldn't rule it out completely. Without intimate knowledge of this particular boiler, it didn't seem completely outside of the realm of possibility since the technology exists.

    Dumping the condensate into it's own trap isn't really the right solution, since that trap is all but guaranteed to run dry when the heating season ends. It really needs to be a shared trap with something that gets more regular use, and higher volumes.

    Having tweaked the curve how is it behaving? Any hint of short-cycling? Is it keeping the place up to temp overnight? Time the burns if the burns per day start climbing. If it's not quite keeping up, bump the output temp at +16F up by 10F- if it always keeps up there, back off by +5F. You'll eventually zero in on the number that works. On the +65F outdoor temp end of the curve there's no point in changing it unless it's short cycling or too unresponsive. Bumping it up would make it more responsive during mild weather, but you'd run into the room-temp overshoot issue again if you go too far.

  15. #30
    DIY Junior Member Crooz1n's Avatar
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    The burn times have averaged around 2.5 hrs. The total run time has been 97 hrs and 4500 Cubic feet in the last two weeks. I forget exactly how many ignition cycles there have been ( 57 maybe with 5 fails ) as I am not at home with my data but I have started writing this info down each Wednesday morning before I leave for work so I can obsess over it.
    This past week has not been too cool. Several days have been in the 50-60 range but its supposed to cool down over the weekend and next week. I'm still getting 2-4 degrees overshoot but it also seems to wait until the temp dips below the setpoint by nearly as much before calling for heat as well. I have adjusted the anticipator on the thermostat in the hopes that it will further bring the temp swings closer to 70. I haven't been able to catch it exactly when the boiler starts but I know the supply temp was 64 the other day and still not calling for heat. And the supply temp is measured at the boiler in the cold basement as well so that may not have much bearing on when the call for heat actually starts.

    But overall the house is keeping warm although the wife is cold in the morning (Not unusual though as she has several circulatory issues where she gets cold easily)

    As to the condensate pump there is a check valve in the pump to prevent backflow.

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