Alpine 150 not meeting setpoint.

Discussion in 'Boiler Forum' started by chobs, Jan 29, 2014.

  1. chobs

    chobs New Member

    Messages:
    2
    Location:
    Pennsylvania
    Hi, I just had a Burnham Alpine 150 mod/con boiler installed last Oct. Everything works well, except when we got really cold conditions. When it was below 5 degrees, the house didnt seem to warm up. Had thermostats set at constant 68 degrees, but it seemed furnace had trouble keeping that temp. I checked boiler and noticed that outdoor reset had the setpoint for 175 degrees. But furnace only ever reached 147 supply degrees, and 122 return degrees.Never comes close to setpoint. Our house temperature on thermostats dropped 4-5 degrees from setting of 68 degrees. Seemed to take an awfully long time to get back up to 68. We have big radiators in our house and I would say the house is a little drafty. Do you think the outdoor reset should be shut off when it is bitter cold? Thanks for any help.

    chobs
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,013
    Location:
    New England
    The curve may not be set properly. AT that return temp, it should have been condensing, which is good, but not if it cannot maintain your desired setting. It sounds more like programming rather than the actual reset device.
  3. mage182

    mage182 Member

    Messages:
    64
    Location:
    NY
    I concur. I have the same model so unless your house is enormous then it's most likely the programming. If you have large radiators (cast iron I assume) then heating mass shouldn't be a problem. Maybe the installer dialed back the max fan speed on a heating call like I had to do because my unit is oversized. Even though the curve is set to 175 which sounds a little high (I run mine at 165 at a design day temp of 15 on Long Island), if the max fan speed is set to something less than required then the water won't be heated fast enough to keep up with the demand especially when you have calls on more than one zone at a time. If the unit is oversized which it probably is, you should do some calculations based on what your total heating capacity needed is and then set your max fan speed based on that.

    The manual does a decent job of explaining the programming of the unit. An important point to take away is setting the curve based on max and min temps vs you design day temp as well as fan speed (modulation) which can be controlled. It's a multi variable equation that can take some time to get right based on your comfort.
  4. Dana

    Dana In the trades

    Messages:
    2,841
    Location:
    01609
    It's at least remotely conceivable that 147F output is the balance point of the full-output of the ALP-150 with the size of the radiation, and that +5F outdoor temps could be bigger than the output of the unit. At 150K input, assuming ~90% efficiency @122F return water temps you're looking at 135,000 BTU/hr.

    That would be a HUGE heat load for a tight 2500' house with at least some insulation, and at least storm windows over single panes. But for a 2-3 story barely insulated air-leaky 4000' Victorian with single pane double hungs it wouldn't be unthinkable.

    A two story or taller house with a lot of air leaks ends up with a VERY significant stack-effect air infiltration heat load. A house with a lot of single-pane windows can also have an inordinate heat load. Can you described the house (size/age/windows/R-values/basement)?

    Test the ALP-150 against your radiation sizing: Set it up to run 175F fixed-temp output (taking it off ODR control), bump the T-stat up another 5F and see if it EVER hits 175F. If it can get there, the ODR probably needs tweaking. If it can't, and peaks out at 145-150F output, the radiation is delivering as much heat as the ALP-150 can deliver at whatever temp it stabilizes, which means you probably really DO have a heat load in excess of 135K @ +5F outdoor temps.

    In a house that's "a little drafty" it's likely you can bring the heat load down significantly and cost-effectively with blower-door & infra-red imaging directed air sealing, and some spot insulation. If you have a lot of single-pane glass, tight low-E storm windows can improve window performance to that of a code-min replacement window at about 1/2-2/3 the installed cost. (It's a pretty straightforward DIY for the handy.) Even though low-E storms cost more than clear-glass, the improved performance makes it a quicker payback. (IIRC in PA there is even subsidy money available for low-E storm windows.)

    BTW: Try to refer to a boiler a "boiler", and not "furnace"- a term that explicitly refers to ducted/forced hot air heating (to distinguish it from other heating system types.) It may be regional dialect conflates the two- I've met several people from central PA who always seem to refer to their boiler as "the furnace", but it's sometimes a point of confusion to others.
  5. chobs

    chobs New Member

    Messages:
    2
    Location:
    Pennsylvania
    Wow!, you guys are awesome. I thought I knew a little bit about alot of stuff, but you fellas take it to the next level. I will certainly try your solutions and let you know how it goes, but you seem to have helped me tremendously with your knowledge. Thanks to your help, I am pretty confident that I will get boiler running just right. Thank you so much, again to all of you. And I will also try to use 'boiler' instead of 'furnace' . I think it is a central PA thing. Ha ha.
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