Do I need Primary / secondary piping?

Discussion in 'Boiler Forum' started by Crooz1n, Nov 3, 2013.

  1. Crooz1n

    Crooz1n New Member

    Messages:
    26
    Location:
    Roanoke VA
    I am having a peerless purefire PF-50 put in to replace an old electric boiler. Its a single zone all cast Iron radiator system. I am trying to make sure its installed correctly. I don't think the installer intends to install primary secondary but to just pull out the old system and tie in the new boiler. Is this OK or will it cause problems? The system install instructions all have diagrams of central heat plus DHW or multiple zone piping. boiler piping1.jpg
    Picture is of old system. Return on left.
  2. emd36

    emd36 DIY in AZ

    Messages:
    22
    Location:
    Arizona
    You don't need primary/secondary. It is the way most systems are plumbed in the U.S. Your photo is a bit difficult to interpret. It appears that the pump etc. are out of the photo below the boiler.
    If you have multiple zones, a differential pressure by-pass valve is recommended. I believe that keeps the pump operating at the same pressure no matter what the call for heat. What did your installer do?
  3. Crooz1n

    Crooz1n New Member

    Messages:
    26
    Location:
    Roanoke VA
    Yes its a 2 pipe system with just a single zone. All the radiators get flow all the time. I contacted Peerless and they said that they didn't have to do primary/secondary as long as we had enough flow. They used a B & G NRF-22 which is 22 GPM so I think its OK. (Min flow of 2.2 for heat exchanger) I was just concerned that the Peerless manual did not show a simple direct piping diagram making me think that piping that way may void the warranty.

    The contractor has since come back and changed the pump orientation.

    IMAG1065.jpg
  4. Dana

    Dana In the trades

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    Hopefully you're not pounding 22 gpm through the heat exchanger! Anything more than 5 would be way overkill as far as the boiler is concerned, but you may need higher flow on the radiation to keep the balance dialed in. Did Peerless spec a MAX flow?

    It's worth air-sealing around the old flue where you've run the venting, since it's a large parasitic heat load due to the infiltration it is driving (even if it's sorta-sealed at the top of the flue, it still needs to be sealed at the basement.)
  5. Tom Sawyer

    Tom Sawyer In the Trades

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    3,137
    Location:
    Maine
    I don't see any temperature gauge on the return so I imagine the return temps are coming back pretty darn cold on start up and throughout most of the cycle. At the very least it should have a bypass with a valve running from the feed to the return. There isnt and inspector in the state that would pass the wiring and the gas piping either but maybe VA is less stringent. Also, where does the condensate get pumped too? and is the condensate pump securly fastened to anything or just set on the basement floor.
  6. Dana

    Dana In the trades

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    I was just going to edit-in that he should check the delta-T it's running, to make sure that it stays within spec under all operating conditions as well.

    The gas plumbing really needs to be looked at too- looks like it could be compromized by the house flexing in a high wind, and the teed-off stub should be at the bottom, below the gas input to the boiler to really work as a crud-trap, like on this water-heater hookup, not up at the ceiling well before the stretched out flex:

    [​IMG]
    Last edited: Nov 13, 2013
  7. Crooz1n

    Crooz1n New Member

    Messages:
    26
    Location:
    Roanoke VA
    The chimney has been sealed since I took the picture. The peerless manual says min system pressure of 14.5 and min flow rate of 2.2 but I did not see a max flow. The pump is spec'd from their chart page 20 Table 4.5. I suppose that's where the installer chose the pump from. Condensate pump runs into sewer line you can see just behind top right corner of plywood. And no not secured just sitting there . There is a floor drain 4 feet from the pump as well.I'll ask the inspector about the gas trap. The thermostat wire has a splice in it that I will rectify this weekend. I looked at the return temps earlier in the week and they seemed OK but I forgot to look this morning.

    You have to remember boilers in this area are not to common anymore, everything has gone to forced air. I went thru 6 different contractors before I found one that had at least a little bit of sense when it comes to boilers. Everyone else wanted to put in really large systems and had no idea how to properly size a hot water boiler. I had to insist that we put in the PF-50 instead of the 80. This contractor suggested the Purefire as he was familiar with it. I guess being familiar with it and reading the manual don't need to go together.
  8. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
    3,137
    Location:
    Maine
    Take a picture of where the condensate line enters the sewer pipe. Just curious.
  9. Crooz1n

    Crooz1n New Member

    Messages:
    26
    Location:
    Roanoke VA
    Tom its just the vinyl line inserted into what looks like a cleanout plug and sealed w/ RTV. I'll take a picture tonight when i get home.

    Dana I see no max on flow. Should I throttle back one of the service valves near the pump to reduce flow?
  10. Dana

    Dana In the trades

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    Before making any flow adjustments, what is the delta-T across the boiler looking like? (Hockey tape on the output and return plumbing makes it easy to get consistent readings with an IR thermometer.)
  11. Crooz1n

    Crooz1n New Member

    Messages:
    26
    Location:
    Roanoke VA
    Sorry but whats Hockey tape.:confused: I live too far south to know hockey:) maybe masking tape or duct tape. I could also just see what the controller is reporting as there is a thermistor on supply and return.
  12. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,948
    Location:
    New England
    For a reliable reading with an IR thermometer, you want something that is both non-reflective, and in good contact with the copper pipes - the flat black tape used on hockey sticks or maybe the grip of a baseball bat works pretty well. If you have an IR thermometer that can take a plug-in sensor, you could use that, or if it's has adjustable emissivity, you could dial in that value to get a more accurate reading; otherwise, trying to get an IR reading off of a copper pipe is not that reliable - it is repeatable, but not reliable without help.
  13. Crooz1n

    Crooz1n New Member

    Messages:
    26
    Location:
    Roanoke VA
    just went down (11:54)and boiler is running right now the supply temp is 113 and return 97.
    Its been running for 7 days and has had 22 ignitions 1 failed and run time is 52 hrs.
    When I got home from work it was in standby and supply temp was at 85 I think.

    7 am- Supply is at 120 53%input return @109.
    Last edited: Nov 14, 2013
  14. Crooz1n

    Crooz1n New Member

    Messages:
    26
    Location:
    Roanoke VA
    Here's the picture you wanted Tom.
    IMAG1089.jpg

    Here is supply/return temps from this AM.


    IMAG1093.jpg
  15. Dana

    Dana In the trades

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    A ~10-20F delta at condensing temps is fine- sounds like the guy picked the right pump. The system flow is almost certainly not anything like 22 gpm, but high enough that it probably won't be an issue on a cold-start during colder weather when the reset curve is calling for a higher output temp, and low enough to support an efficient delta-T at the boiler. (Does this boiler have an internal flow meter you can call up on the display?) Without looking it up, the max operating delta on the HX is probably something like 50F. Keep an eye on it- if you see sustained burns with delta-Ts over 40F it's worth looking up the specified max just to make sure, but my best guess is it'll never hit that in normal operation.
  16. Crooz1n

    Crooz1n New Member

    Messages:
    26
    Location:
    Roanoke VA
    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.
  17. Dana

    Dana In the trades

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    Location:
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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.
  18. Crooz1n

    Crooz1n New Member

    Messages:
    26
    Location:
    Roanoke VA
    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/1316205107070/63775_PROD_FILE.pdf
  19. Dana

    Dana In the trades

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    2,812
    Location:
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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.
  20. Crooz1n

    Crooz1n New Member

    Messages:
    26
    Location:
    Roanoke VA
    So do u think I should lower the max boiler temp from 120 to 110?
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