Zone pump sizing

Discussion in 'Boiler Forum' started by tom3holer, Mar 20, 2013.

  1. tom3holer

    tom3holer New Member

    Messages:
    40
    Location:
    Cape Cod
    I have posted here before on my newly installed system and again thank you all for the help and advice.

    I had a Alpine 150 boiler installed in my home at the recomendation of the plumber. I have done a heat load, as he did not, on the house 2 different ways. Using the "Fuel Used" method over several winter months, thank you again Dana, as well as the SlantFin program. I came out with something between 55-60K BTU.
    So yes the boiler is way oversized. I have breen reading all I can and am trying to tweak the system for best efficiency as best I can given the oversizing.

    As I dig further into my system and try and optimize its operation one thing I am looking at now is the zone pumps.
    I have 4 zones each with its own Taco 007-F5-71FC. From the reading I have been doing It seems that these pumps are way oversized for the needed flow rates. Looking at the chart, if I read it correctly, my kitchen zone which is approx 70' of 3/4 with that pump is flowing at more than 11GPM using 6' head/100'
    Is this correct? All the zone pumps are the same size. Is this really an issue thats worth pursuing?

    Thanks,

    Tom
  2. Dana

    Dana In the trades

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    Over pumping the radiation uses a more pumping power than necessary, but it's usually not a critical flaw on a system that is plumbed primary/secondary. Replacing pumps isn't cheap, and you can buy a lot of electricity for the cost of a new right-sized pump. Getting the boiler-loop rates dialed for a reasonable delta-T across the boiler is of greater importance, but of course the primary & secondary flows do interact. Most systems can run just fine with 1-2gpm flows on the radiation, and it's quite conceivable that your whole house could be served by a single Taco-007 & four zone-valves. (TBD.)

    In your length/head approximations be sure to look up and include the additional head or "equivalent length" of all the ells & tees, etc.

    The Slantfin tools regularly hit 25%+ higher than measured reality, so if it's coming up at 60K, the real heat load is likely to be something in the 45K range.

    Rather than pumping rates on the radiation side, I'd be more concerned about short-cycling a boiler with a min-fire output of ~28-29K in condensing mode on zones with the heat load of most singles zones under 15. Gross mis-matches between zone radiation and min-fire output often prevents systems from being able to run in condensing mode without short-cycling the boiler into an early grave. What's the radiation size/type on that 70' kitchen zone? How about the radiation type/size on each of the other 3 zones, by zone? (I don't recall if you covered this on another thread.)
  3. charlie p

    charlie p New Member

    Messages:
    17
    Location:
    New Jersey
    Hey tom
    Ill be no help to you.But do u no someone that needs a 150? If so,you can take the hit and sell your alpine to them for $5-$600 cheaper then you got it for. Thats what I'm doing right now(but I'm in the position to do it and mine was never installed)
    I just went through the same thing,
    bought a WM ultra 150 (thats what the HVAC guys said to buy)when it turns out I only needed a 60. Luckily I found out about the heatloss before I installed it.
    So after getting schooled from Dana and a couple others I ordered the 80 which should be here by Monday,And the 150 is sitting in the box waiting for a new home.
    I was actually just researching pump sizing and found this thread (which Danas response answered)
  4. tom3holer

    tom3holer New Member

    Messages:
    40
    Location:
    Cape Cod
    Charlie,

    Glad to hear you caught it soon enough.

    I wish I had done my DD before going ahead with the new installation. Actually it was done late last Spring.

    It is very interesting the way most of the people I have dealt with in the heating installation business size boilers.
    Their reasoning I sorta understand but don't agree with. They will always oversize a boiler so as to not get the dreaded call that I can't keep my house warm on a cold day.
    The last contractor, that I actually liked and was quite knowledgeable and long time in the business, had this to say. "You actually have to look at the DHW when sizing a boiler for both heat and DHW and size it accordingly. He said that the SSU 45 that I have requires 140k BTU. I said is that not a max btu input. I thought actually the 80 Alpine boiler with an output of 72K would work fine. He was actually asked to come over to do a Manual J but thought it would not be accurate on an older, 1860, home like I have although it has been updated quite a bit. Instead did a leatloss using a program supplies by Webb, the big supply house. He came in at 91K, he estimated the kitchen with a good deal of glass and 57' feet of exterior wall, 400sq ft at a whopping 17,300 BTU loss alone. Now all the glass in the kitchen is Anderson thermopane type windows. When I asked what he used for windows in the program he said I always err to the safe side. I came in at 52-55K for the entire house using two different methods. The Slant/fin program and Fuel used over a 3 month period.

    The point to my rant is that I bet over 90%, in older and newer boiler installations, are way oversized for the convenience of the installer because they do not take the time to do a proper heatloss.

    I am going to call plumber back that installed the boiler and see if we can work a deal whereby if he has a Alpine 150 installation coming up he could take mine and I get the proper size installed.

    Tom
  5. Dana

    Dana In the trades

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    "The point to my rant is that I bet over 90%, in older and newer boiler installations, are way oversized for the convenience of the installer because they do not take the time to do a proper heatloss."

    Yer singin' my song! (It may actually be over 99%, but I don't have good data on that.)

    As long as the oversizing factor is 1.7x or less cast iron boilers will usually hit it's AFUE numbers, but small & mid sized houses in MA at IRC2009 code-min will often have heat loads under 25KBTU/hr, at which point just about everything is oversized, even most mod-cons. Mod-cons are a special case- many old schoolers will just shrug and say:

    "It's modulating- it doesn't matter what the oversizing factor is."

    But that belies a profound ignorance of what it takes to unlock the potential efficiency of this technology. A mod con is not a condensing gas furnace (which can run efficiently even at 4-5x oversizing factors, but at lower comfort than a right-sized system.) Oversizing a mod-con to the single-zone loads leads to short-cycling at condensing water temps, and using the same crummy rules of thumb that they got away with for decades for cast iron boilers delivers a MUCH larger hit in as-used AFUE. Yes, it's modulating, and will have long burn cycles with 160F+ output temps even if oversized for the whole house load, but without internal mass in the boiler the zone calls will bring it do it's knees at anything BUT high temps, at which point a 2x oversized 86% AFUE cast iron boiler can do about as well as a 95% mod-con.

    Sizing a boiler to the DHW load is simply brain-dead, 99.9% of the time. At tank sized to the biggest tub you have to fill will work just fine, 99.9% of the time, independent of the size of the burner. A 40-50 gallon standalone HW heater is big enough to serve typical middle-class homes (but not monster showers in McMansions with six 3 gpm sidesprays, or 120 gallon spa-tubs, etc), with 28-30K of burner output. Zoned "priority" an indirect will recover more quickly than the all-American standard type of tank, quickly enough that the hesitation in the space-heating delivery would never be felt.

    A true 91K heat load is all but unheard of, and can/should be brought down to something reasonable before committing to a boiler that big. Very few houses in MA smaller than 5000' would actually need the output of the ALP150, and most NEW 5000-6000' houses would probably be better served with the ALP80. Tight, better-than-code 2000' houses are often better served by mini-split heat pumps, which are modulating and can at least be sized appropriately for the comparatively low whole-house loads, or by heat/HW combi-systems, but you don't see very many old-school heating contractors taking that road.
  6. tom3holer

    tom3holer New Member

    Messages:
    40
    Location:
    Cape Cod
    Once again Dana has profound words for all of us.

    My wife cannot why I am running down to the basement 25 times a day. I tell her its for the exercise but me thinks she knows better.
    My return temps are for the most part only 3-7 degrees below the output temps as read on the LCD on the boiler. I also measure the return temps in each line with an infared handheld on black friction tape rapped around the pipes and I see temps that are within a few degrees of the boiler read temps. I thought this was strange in that with a P/S system my thinking was that the boiler is actually reading zone return mixed with primary zone boiler water giving a false higher temp than actual zone return.
    Something was bothering me and I discovered the zone pumps are located in the retuen line not the supply line as shown in the Apine manual. Is this acceptable or should it be as shown in the manual?

    Another question if I may:

    The required primary loop flow is related to D/T. It goes from 7.9gpm at a D/T of 35deg/F to 19.4 at a D/T of 20deg/f. I assume this is to keep from overheating the HX as the flow requirement goes up as the D/T goes down. The question is where and how do you measure the D/T. I see no where cose to those numbers as mentioned above.

    Oh Dana, I mentioned my use of your very usefull "Fuel Used" method of getting a good handle on the BTU actualy required on another forum. One of the readers asked how I did it. Would you mind if I copied you explanation and posted it over there?

    Again thanks everyone for all the help.

    Tom
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