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sizing circulator

radmix Member Posts: 194
I have a project that was piped by another contractor and I would like to use a ECM circulator for the project but Im having trouble sizing the pump. The boiler is  399 BTU, The main loop around the house was piped in 2" copper with a distance of 200'. Off of this main there are manifolds feeding radiant zones, The longest loop on there manifolds is 400'. Can any one come up with the flow and head pressure for this scenario


  • Zman
    Zman Member Posts: 7,542

    It looks like you would be in the range of the grundfos magna http://us.grundfos.com/products/find-product/magna-upe/_jcr_content/tabbedpanel/brochures/par2/downloads/download_0/file/file.res/~8189020.pdf

    Those 400' radiant loops are going to be a killer. The near boiler piping are also going to be a factor. Are you piped primary secondary? What type of boiler is it?What are the designed flow of your radiant loops and how many do you have?

    Your supply house likely has software and someone who can run the numbers.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • radmix
    radmix Member Posts: 194

    The Boiler is a Munchkin 399, There's 7 different manifolds in the house with about 35 different loops of radiant. The longest loop is 350', Some of the loops  I cant get the lengths so Aim assuming the worst case scenario. The boiler is piped in a primary/secondary configuration.
  • Gordy
    Gordy Member Posts: 9,546
    Radiant loop pipe size.

    What dia pipe is the radiant loops?
  • radmix
    radmix Member Posts: 194
    Loop size

    The loops are 1/2"
  • CMadatMe
    CMadatMe Member Posts: 3,086
    Heat Loss

    Going to have to calculate the heat losses to get your flow rate for each loop and zone. The head in the radiant loops is going to be dependent on each loops flow rate. Is this 100 percent water or some antifreeze mix? You need to reverse engineer the system.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • sizing circulator

    Agree a "reverse engineer" is required.  My question is are you planning on one circ for the whole job or does the boiler have a dedicated circ?  Reason for the question is if you use a delta P circ you may run into issues with low boiler flows under low load conditions.

    If you are using one circ it is sized to overcome the friction loss of the primary loop (plus boiler and fittings) @ 40 US (assuming a delta T of 20 deg for a 399,000 BTU output boiler) and the highest loop friction loss.  This is where the heat loss of this loop needs to be calculated to determine the flow of the loop.  Once the flow is known then the friction loss can be calculated based on the length of the loop.

    Our Viridian VR20 (2") would deliver almost 40' @ 40 US - enough to cover your butt.  Even better it can be powered from 110/1/60 to 240/1/60.  Plus you can adjust the delta P curve slope from 60% to zero (constant pressure) if there are low load boiler flow issues.  Too bad the Bumble Bee doesn't go larger - would be a perfect fit for this application.

    Information on the Viridian is attached.  If you have any questions feel free to contact me at [email protected] or 401-441-2934.
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,239
    There is a way to do it without

    reverse engineering the whole system. If the boiler is the right size take that btu figure, if it ain't do a heat loss on the building envelope. This will give you your system flow rate. To figure the head loss take a 007 (or whatever you have on the shelf) 2 pressure gauges and an inline flow meter. Put these on with a pressure gauge at the inlet and the outlet of the circ. record the pressure differential at the flow rate produced by whatever circ you choose to use. Take these to figures and the flow rate you determined the building requires. B&G System Syzer will give you the missing number to your equation. If your manifolds are balanced it will get you right on the money.
  • Gordy
    Gordy Member Posts: 9,546
    edited September 2012
    There is a way to do it without

    Harvey that won't get what you need for proper flow rates on the loops.  What the pressure gauge trick will tell you is the head of the whole system if you were using one circ to drive the 2" loop, then you could calculate what the circ is putting out based on its pump curve..  If he has 350' loops its anyones guess if the loops are within 10% of each other to be self balancing. He could have loops from 350' to 200' on the same manifold.

     Further more he needs to know the heat loss of each individual zone. working off the boiler size will not cut it. You still need a zone by zone heat loss to determine flow rates for the zones, and the loops in those zones.

    Building heat loss verses zone heat loss are two different things. Yes you need the heat loss of the whole envelope to determine boiler size, and a zone heat loss for tubing,water temps, and flow rates.

     I would trust nothing if someone ran a 350'x 1/2" loop who knows what the rest of the system is doing let alone the boiler sizing, and installation.

This discussion has been closed.