feet of head loss tables

Discussion in 'Vertical and Horizontal Loops' started by milkweed, Mar 16, 2016.

  1. milkweed

    milkweed Member

    The manufacturer of the heat pump that we have provides a table in their loop design guide
    for feet of head loss per 100 feet of various pipe and diameter sizes.
    Below the table it says:
    * These head losses are for water at 40 degrees F temperature.

    After picking out a circulator pump for the current loop design, I considered whether
    the same pump could be used to flush the loop portion at 2 feet/second.
    The gallons per minute is just out of range for ft.hd loss table provided,
    so I searched online and found other tables... which have different (smaller)
    values (less loss) than the table provided in the design guide for the same pipe to GPM rate.
    All of the tables I found online were values for 70 degrees F water temperature.
    This makes sense to me at the moment that when I would be flushing the loop,
    it would be during the summer months and I could use these online values,
    as the loop piping should be expanded due to warmer temperatures and have less
    head loss.

    None of the tables mention the equation used to compute the values.
    At https://plasticpipe.org/pdf/chapter06.pdf it mentions the Hazen-Williams method,
    but there doesn't appear to be a variable for the temperature.
    I found a remark, elsewhere, that the Hazen-Williams method was good for
    the water temperature range of 40 to 70 degrees F.

    What other method is used to figure feet of head loss values in these tables?
    Should I just use the tables I found online to figure whether the same circulator
    pump will be able to used during flushing?
  2. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    heatoldhome likes this.
  3. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    You can bring in the circuits in the house separately, otherwise it makes no sense. Otherwise you would install a pumping power you only need once. You seem to be falling also for the illusion of precision. Why don't you tell us what you are trying to achieve, and we will be happy to help.
  4. milkweed

    milkweed Member

    urthbuoy wrote:
    Back when I was thinking about a series horizontal with 2" diameter pipe, by isolating the loop from the heat pump, it seemed like it would be possible to use the same pump... at least on paper. I haven't done any calculations yet for a parallel horizontal configuration, but I would assume that largest diameter pipe would govern the minimum flow rate that is needed to achieve 2 feet/second.

    urthbuoy wrote:
    No :), but I was thinking that maybe if I knew some key words I could find a table that would give me confidence in the head loss values at a 70 degree temperature.
    In the mention I found that says that the "Hazen-Williams method was good for the water temperature range of 40 to 70 degrees F", why then are there two sets of values: (1) supplied in the design guide for 40 F and (2) online tables that say for 70 F ??? There must be an equation that factors in temperature that they are using. I'll take a look at that PDF hyperlink when I get time. Thank you.

    docjenser wrote:
    Agreed, I think heatoldhome did that, with header for 3 ton inside his basement, so six perforations through his basement wall. I think he said he isolated each of the three loops when flushing.

    docjenser wrote:
    Thank you. Over arching, I want to convert our heat pump open loop to a closed loop configuration. I had originally thought using propylene glycol in a series horizontal, but now I have a better understanding of the cons of using that as an antifreeze. Now I'm on to methanol, and looking into a parallel horizontal design. We use the heat pump now only in the summer, but if I bury the pipe and leave the heat pump in the open loop configuration, I would not be in a hurry to get it all flushed and connected, and flush the new loop during the summer months. Looking into the idea that I would not need separate pump(s) for flushing.
  5. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    What size is your heat pump and what flow does it need?
  6. milkweed

    milkweed Member

    3 ton with 3/4" piping, 7 GPM for antifreeze, though I suspect with methanol 6 GPM it would still operate effectively
  7. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    Using 2" SDR11 HDPE;
    - the heat pump required 7gpm = 0.78 ft/s
    - the 2 ft/s to purge the 2" SDR11 HDPE = 18 gpm

    If you had a 1" header (not looking at head loss for now), you could get >2ft/s flows with 7gpm.

    But really, that is just accidental. You want to optimize the loopfield layout to a number of parameters that include minimizing headloss. And then size circulators for the flows required for heat exchange. The purging part just comes after the fact with a purge cart or the ability to isolate circuits.

    P.S. The Darcy-Weisebach equation is more what you're looking for, though the above calcs are just volume/area stuff.
  8. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    What kind of ground do you have? Where are you located?

    You could bring in 3 lines, 600ft each of 3/4" pipe in 300ft trenches (800ft for slinkies), 6 ft deep, return and supply 2 - 3 ft apart in the trench, bring them in the house separately, fuse a header inside and fuse in 3/4" shut off valves. Put a 26-99 non pressurized flow center with a single pump on it and call it a day. Will get you in the range of 7-9 gpm.

    Shut off the other 2 circuits when purging the each individual circuit. If you are not sure about this, hire someone who is.
  9. milkweed

    milkweed Member

    urthbuoy wrote:
    Thank you for that. After a cursory look at it, maybe the variable that is changing is the diameter of the same pipe based on temperature, which is what I was first thinking, but I thought maybe an equation had a direct substitution with temperature included. Alternatively, the one table in the design guide may be using a low value for the C variable, but I doubt that. I think this gives me the confidence to calculate with the lower head loss values at higher temperatures.

    docjenser wrote:
    All clay down to about 18 feet. Dayton, OH

    docjenser wrote:
    Sorry, I don't follow this part. If the header is inside, and the trenches 2 pipe stacked (one out, other return), wouldn't each loop supply and return be very close the entire run? Or do you mean that the header connections to each loop be spaced 2 or 3 feet apart?

    So with the shut off valves at each loop there would be four purge cycles for the three parallel loop configuration, one for each loop, then a faster flow with the loops shutoff to flush the header? MMM that wouldn't be right unless both headers are connected with shutoff valves to be able to bypass the loops.
  10. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    Geo-flow has a nifty calculator up and running on their web page if you register. It will give you hours of enjoyment, or torture entering the variables to satisfy your want of information. Enjoy.
  11. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    You should have a few feet (2-3 ft) of separation between supply and return for each circuit, so they do not steal too much heat from each other.

    You usually don't have to worry about the header purging, since the interior header sees all the flow all the time which you purge one circuit and have the other circuits shut off. The issue is if you have multiple circuits running in parallel, so the flow gets divided up by the circuits, thus you don't have enough flow anymore through each circuit. One shut off valve per circuit blocks the flow, you don't need two.
  12. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    One for flow.

    Two for servicing.

    None, because valves cost money. Some time to somebody.

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