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Domestic hot water recirculating loop problems

dfru
dfru Member Posts: 26
I am troubleshooting an existing domestic hot water recirculating loop problem, and have attached a diagram of the system. The system has a series of pressure reducing valves at the lower floors to drop the supply pressure to the floor to 75 psi. The upper floors only have a balancing valve. Water is intended to circulate through the loops at all times.

Pressure reducing valves will open up only when there is a drop in pressure on the downstream side. If there is no demand in the system, the configuration will increase the pressure downstream from the pressure reducing valves, causing them to close, and disrupting flow. Can the recirulating pump be sized to induce enough negative pressure to maintain the downstream side of the prv at below 75 psi at all times, thereby allowing the pressure reducing valve the remain open?

Any suggestions as to how to make this system function properly and circulate through all loops at all times?

Thanks

Comments

  • Mark Eatherton
    Mark Eatherton Member Posts: 5,839
    Interesting concept... As with ALL hydronic related questions, the only correct answer is "It depends"... Probably not what you wanted to hear, but true nonetheless.

    A few observations, if in fact this is a true and detailed drawing, you are missing a check valve between the pump and the vessel to stop short circuiting cold water backwards through the system.

    You are also missing a purge point for the CR pump. Starting on the return at the tank and working backwards to the pump, you'd need an isolation valve, a spring check, a tee with a drain cock, then the pump, and then another service isolation ball valve.

    To completely purge the system, you'd start with all balance valves on the returns closed, then starting from the lowest main, open it's return with the BV next to the tank closed, and the purge drain cock open and a hose going to a floor drain. Run until no bubbles come from return, then open 2nd floor balance valve, and close first floor, running until clear, then move to the third floor, and so on and so forth. It is going to take 2 people with radios to get it done. Once completely purged, you have to go back and balance the returns, trying to achieve the same return temp differentials on all branches.

    Be advised that most PRVs usually have a strainer filter assembly in them that may be in need of service, and may be affecting the pumps ability to move water.

    As for the pumps ability to generate the pressure differential, we need to know who's pump is being used, and if any adjustments were made to the pumps impeller, or if it has been replaced etc.

    What are the symptoms that are causing you to work on the system? What changed? What are the complaints from the end users?

    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • hot_rod
    hot_rod Member Posts: 16,272
    Remember also with manual balance valves, when you change one, you need to go back and re-adjust the others. You might consider a PIV pressure independent valve that self regulates. They can be used in conjunction with one another. Manual to balance an entire floor for example, PIV to adjust branch circuits.

    Low lead valves of course in DHW applications.

    http://www.caleffi.com/sites/default/files/coll_attach_file/idronics_11_1114.pdf

    There is talk about adopting a Euro standard anti-legionella protection method.
    This would require all DHW systems, via recirc to be elevated above 140°F for a 1 hour period, every 24 hours. This will make fixture protection a bit more complicated. EVERY hw connection will need protection when the loop temperature elevates, get ready :)

    I've heard of one resort property in FL that allegdly has 18,000 thermostatic valves on property. Imagine the staff to maintain them, especially in hard water conditions!

    Learning how to properly apply thermostatic valves in recirculation is key, a few components are missing in that drawing as Mark mentioned. See the suggestions in Idronics 11 for DHW record with thermostatic valves.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • SWEI
    SWEI Member Posts: 7,356
    hot rod said:

    There is talk about adopting a Euro standard anti-legionella protection method.
    This would require all DHW systems, via recirc to be elevated above 140°F for a 1 hour period, every 24 hours. This will make fixture protection a bit more complicated. EVERY hw connection will need protection when the loop temperature elevates, get ready :)

    I've heard of one resort property in FL that allegdly has 18,000 thermostatic valves on property. Imagine the staff to maintain them, especially in hard water conditions!

    Who is talking about adopting -- more details? Small UV sterilizers are surprisingly affordable, and could represent a more affordable alternative in many systems.
  • hot_rod
    hot_rod Member Posts: 16,272
    SWEI said:

    hot rod said:

    There is talk about adopting a Euro standard anti-legionella protection method.
    This would require all DHW systems, via recirc to be elevated above 140°F for a 1 hour period, every 24 hours. This will make fixture protection a bit more complicated. EVERY hw connection will need protection when the loop temperature elevates, get ready :)

    I've heard of one resort property in FL that allegdly has 18,000 thermostatic valves on property. Imagine the staff to maintain them, especially in hard water conditions!

    Who is talking about adopting -- more details? Small UV sterilizers are surprisingly affordable, and could represent a more affordable alternative in many systems.
    WHO, CDC, ASHRAE, OSHA, many States have formed committees looking for viable options. Listing agencies are involved as they will write and enforce standards. manufacturers of products also.

    Our Euro based solar controllers all have anti-legionella functions now, not sure if that is mandated in the European Union yet, I heard it is coming if not already required in some countries.

    Committees are established or forming in all sectors. Are you offering to serve on a committee?

    Yes there are a number of methods to control bacteria, and no doubt it will be a multi pronged approach to controlling the potential.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • SWEI
    SWEI Member Posts: 7,356
    hot rod said:

    Committees are established or forming in all sectors. Are you offering to serve on a committee?

    I am interested, and will get in touch with ASSE to see what they are planning. I want to make sure we end up with a standard that leaves room for innovation going forward.
  • hot_rod
    hot_rod Member Posts: 16,272
    SWEI said:

    hot rod said:

    Committees are established or forming in all sectors. Are you offering to serve on a committee?

    I am interested, and will get in touch with ASSE to see what they are planning. I want to make sure we end up with a standard that leaves room for innovation going forward.
    Most times the standards are available for peer review and input. I know ME can get you info on any that IAMPO is involved with.

    I believe the heat metering standard E44.25 is about ready for review, ASTM and IAMPO worked together on that. Rex from our office has been on that TC. It will be another example of a standard largely based on the Euro standard.

    http://www.iapmo.org/Documents/IETS_PowerPoint_Presentations/ETS_2014/Critchfield_Heat_Metering.pdf
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream