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Max flow through 4\" L copper pipe

Weezbo Member Posts: 6,232
i have a few ideas if you have some small time i'd like to roll them by you .


  • Rocky_3
    Rocky_3 Member Posts: 230
    How many gpm can I hustle through 4\" L?

    Bidding job where there will be a remote boiler room (approx 120') away. Need to move approx 3.6 million BTU. Am figuring a 20 degree delta T so 360 gpm flow needed. Will 4" L handle this? If not, what will 4" L handle? I may be able to spread my delta T out a little to handle a reduced flow. thanks in advance,
  • Tony Furst
    Tony Furst Member Posts: 12

    You can move 360 GPM through 4" copper but your velocity is going to be elevated which will create noise and erosion of the pipe walls. I wouldn't push much above 250 GPM through 4". Generally once you go above 2.5" you would be into welded steel and for 360 GPM you should be looking at 5" but in reality 6" is the same or lower in price and will handle a higher flow rate if the system ever needs to be expanded.

  • Rocky_3
    Rocky_3 Member Posts: 230

    Thanks for the info. I have never worked with welded pipe so am a little unsure as to cost comparison to large copper pipe, fittings, etc. I was hoping to use 4" copper due to ease of working on it with my ProPress tools. Sounds like I need to go do a little homework about 6" welded pipe. Have you ever worked with welded pipe? Don't want to use Victaulic or similar as I have heard of them leaking if they go cold. Am replacing 14 HydroTherm boilers with a combined output of 4.5 million BTU with 4 Buderus with an output of 3.6 million. Told the owners it would actually be less expensive to build a separate outbuilding to house the new boilers than to try to shoe-horn them into the space the old boilers are coming out of. This is going to necessitate approximately 120 of piping (one way) from new boiler room to tie into the existing mechanical room. What types of supports have you used for the welded pipe of larger diameter? Should I get an engineer to design the supports for the piping system? Any first hand info you have would be appreciated.

    Warm Regards from chilly Fairbanks,
  • welded pipe

    If you are going to use 6" pipe. and the run is that long for both the supply and return i would use roller hangers, 4 per 20' length. 5/8 threaded rod and check local code for seismic supports. Any large pipe hanging supply company can design a system for you. If you go welded pipe a good fitter and pipe welder can fit and weld 5 to 6 joints a day. Try and prefab as much as possible on the ground the less joints welded in place the faster the work can get done. I would personally go victaulic, there is more play in the fittings and it would be much faster than welding. You can buy 20' sticks already grooved and renting a machine shouldnt cost to much. After you groove the pipe clean the grooves with a wire brush and use plenty of vic lube on the pipe and the gasket. One other thing you may need to consider with the piping is the installation of some expansion joints. Pipe that big and runs that long may require a mechanical expansion joint or just an offset with some 90 degree elbows.
    What type of structure are you hanging from? If it is concrete decking a drop in anchor will do the job. If you are hanging from bar joists side beam hangers will work if you hang from the top of the bar joist. If you are insulating make sure the hangers are over sized to accomodat for insulation some companies off spacers you can put on the pipe to space out for the insulation. If you have any other questions you can email me any time.

  • tim smith
    tim smith Member Posts: 2,360
    Re large pipes etc.

    What about 3 or 4 separate runs of pipe to split up the flow and load. Just a thought. You could then diversify your load, run smaller pumps based on outdoor temps and loads. Could pencil out when you calculate the cost of larger pipe. Also you may even be able to use large dia. preinsulated barrier pex????? just a thought. Tim
  • Tony Conner_2
    Tony Conner_2 Member Posts: 443
    Pipe Supports

    I dunno - the tables I've got for hanger spans on 6" sch 40 steel pipe in water service show a max length between support points of 17 feet. Usually, you won't go that much, because closer spacing - like 2 hangers per length of pipe - will typically make installation easier. Also, if you have something heavy - like a valve, etc. you'll normally have a hanger on each side of it. I haven't got the book in front of me, but I doubt 5/8" hanger rod will be needed. 1/2" will be lots.

    Regarding expansion of steel pipe, 0.000804 X the temp diff in F will give you inches of expansion per 100 feet. If this line runs at 200*F, and say the installation temp is 50*F, then: 0.000804 X (200-50) = 0.1206" per 100 feet. With 120 feet of pipe, then 0.1206 X 1.2 = 0.14472" total. That's just over 1/8". Note that the pipe diameter isn't a factor in this calculation. For length of expansion for steel pipe at the same temps, it doesn't matter if you're doing 1/2" or 12" pipe. I wouldn't worry about roller hangers or expansion loops for that little bit. 8" clevis hangers will leave enough room for insulation.

    Most of my background is with screwed & welded pipe. I haven't done a whole lot of Vic/Gruvlok, but my recollection is that they have recommended supports span tables in their literature. I doubt that they're much different.
  • Tony Conner_2
    Tony Conner_2 Member Posts: 443
    Checked The Book...

    ... and the table says 3/4" rod for 6" pipe. Disregard the 1/2" rod suggested in my previous response.
  • Brad White_184
    Brad White_184 Member Posts: 135

    Is there any reason you cannot use a 30 or even 40 degree delta-T? That 360 GPM could drop to 240 or 180 GPM.

    Even so, in my book you would still need 4" pipe (even the reduced flow is still way above what a 3-inch pipe should handle) but the pumping costs would go down a good bit.

    If Type L copper, your 360 GPM would induce a pressure drop of almost 7.0 feet of head per 100 feet of pipe and the velocity would be almost 9.5 FPS which is erosive.

    At 240 GPM your head loss per 100 feet would drop to 3.26 feet and your velocity would drop to 6.42 FPS- still a good clip but below the 7 FPS I consider a limit.

    At 180 GPM your head loss per 100 feet would be 1.75 feet and the velocity a more reasonable 4.81- ideal for transporting any bound air.

    I would consider using grooved Sch. 40 steel piping but only if above ground or in a culvert versus direct-buried. My ideal would be welded in a Perma-Pipe or Ric-Wil system though, in that size.

    Going to 4-inch copper takes big brass....
  • bob_46
    bob_46 Member Posts: 813

    With all due respect Tony I think the amount of expansion useing your formula is in feet not inches. Useing ASHRAE,ASME, or the UA factors I come up with about 1.4 inches. bob
  • Tony Conner_2
    Tony Conner_2 Member Posts: 443
    You're Right

    I've got my decimal point shifted. The value SHOULD be 0.00804. My figure should be 1.4", just like yours. I'd still use clevis hangers for this, and depending on the layout, I'd seriously look at cold springing it rather than get into expansion loops or joints.

    Thanks for spotting my math goof.

  • Rocky_3
    Rocky_3 Member Posts: 230
    The specific scenario for this job

    It is a 75,000 sq.ft.athletic club with a 150,000 gallon pool. It is heated 100% by fan coil units inside 5 big air handlers. There is a heat exchanger for the pool, and another heat exchanger for the domestic hot water production. Existing boiler room has 14 HydroTherm boilers that serve the athletic club, and 10 more HydroTherm boilers that serve another part of the building owned by different entitiy. All these boilers are tied into a common venting system and fuel system. Unfortunately, the boilers that are owned by the other entity are closest to the service door to the mechanical room. We would have to carry each individual Buderus 515 section in by hand and assemble it in place. However, the physical space limitations would make the new Buderus install REALLY interesting. Plus, they want their own fuel system now, which means the closest place to install a new 7,500 gallon fuel tank is 100 feet away.
    I told them to build a new outbuilding to house the new boilers and then we can install the new fuel tank inside the same building. Keeps us from having to install submersed tank heaters, day tanks, 200 feet of fuel piping, over-flow piping etc. Only thing we have to do is bring the supply and return heat lines to and from the new location.
    Existing distribution piping is Victaulic. These boilers run at 180 degrees with constant circulation all summer long so Victaulic won't leak. Hope to use outdoor reset to at least drop temp down to 120 degrees or so to get some savings. Dilema I am having is setpoint for DHW and pool heater.

    Currently there is no "on-off" demand from pool heat exchanger ( located 120' away in pool mechanical room). The pool heat exchanger pump runs 24/7 with 180 degree water. Pool water pump then kicks on and off as it needs it. I hope to install a setpoint controller to issue a demand to boiler control so the boilers won't have to stay hot all the time. If my boilers are 100 away, and I have 6" steel mains, it seems like an awful lot of mass to heat up when pool or DHW calls in middle of summer and the boilers are running really cool. Thought about maybe just making one boiler dedicated to making DHW and pool heating, and using the others for heating needs. This would neccissitate running two sets of Supply and Returns, but would keep me from having to yo-yo the 6" main up and down temp wise everytime the control goes from outdoor reset temp to setpoint demand temp. On the other hand, it sure would be nice to be tied into the other boilers somehow to utilize their output should I so need. So many things to ponder, so little time.

  • I was thinking the same thing

    How much flow would 2 - 3 inch type L pipes give you ? Or maybe a 3 and 2 inch ? You'd need more supports , but it sure beats hanging and welding 6 inch steel in a 120 foot run .
  • Building Math...

    Here we go again. Ya know, if someone asked me in my senior year of high school, how much math I thought I'd really use on a day to day basis, I'd have told them I only needed it for balancing my check book and making sure I got the right change back. Boy was I wrong... Wish I'd have paid more attention in those math classes...

    Lets disect the swimming pool first. If they drain it for pool wall maintenance, and they need to refill and fire it up over a weekend, then you have three to 4 days to get it back to par. If incoming water is 40 degrees F, and they want to maintain the pool at 75 degrees F (Red Cross recommendation) then, 150,000 X 8.33 X 35 = 43,732,500 BTU's. THose btus divided by 48 hours = 911,093 btuH. Those BTU's divided by a 30 degree delta T and a 500 constant = 60 gallons per minute. So, for the pool, you would need to supply a heat exchanger capable of delivering around 1,000,000 btuH at a 30 degree supply side differential. The overall delta T (system to pool) wil dictate the actual heat exchanger size. If using non condensing heat source, that delta T will be large and the surface area small, if using modcon source, the delta T will be low and the heat exchange surface will be large. Their call...

    Now, for the building, let's assume 50 btu's per square foot per hour. So, 75,000 square feet @ 50 btu/sq ft/hr = 3,750,000 btuH output. That load, divided by the same delta t of 30 and a 500 K value equates to a required flow of around 250 gallons per minute. Only you can fine tune the actual load numbers, but now you have the tools necessary to dictate flow.

    Lastly, the DHW load. Again, you will have to dictate the load in GPM of X degree rise water, but it is obvious that you already have some fairly healthy piping systems in place to handle that minor load, and you have a lot of load diversity between the shower load, and the heating load. Chances of both being maxed out at the same time are slim to none for any long period of time.

    As it pertains to space heating, pool reheating and DHW loading load diversity, you are in the drivers seat. If the pool is empty, there will not be a need for showering, and if you can maintain the air temperature at least a few degrees above the current pool temperature, then you won't have to deal with the water running down the walls of the building due to high humidity syndrome during pool reheat.

    SO, now you know (approximately) what your loads are, you can decide on how large and how many mains you need to run to get the heat from where its made to where it needs to be...

    If it were me, I'd look at the largest flow load only. The others will fall in line. So based on a flow rate maximum of 250 guppies per minute, using Bell And Gossett's Syzer Hydronic Modeling Software, you would need 4" steel pipe. It would give you 3.45 feet of head per 100 foot of pipe, a velocity 6.3 FPS

    Going to 5" would change those numbers to 1.12 feet of head per 100 feet, and 4.01 feet per second. The uptick in pipe size will pay for the incremental increase in energy savings not comsumed in pumping...

    The B&G software is available online for free.

    Don't forget to compensate for fluid viscosities (glycnoids etc) and DO consider the use of a VFD pump for your applications. It will pay for itself in short order, especially at your electric rates.

This discussion has been closed.


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