3 Way Hydronic valve Question
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  1. #1
    Join Date
    Mar 2004
    Location
    Columbus Ohio
    Posts
    328
    Im having some trouble with some newly istalled fan coil
    units in cooling mode. With the units Trane provided piping
    package pre assembled for hot h2o coil & chilled h2o coil.
    It included a honeywell 3 way floating control valve &
    actuator. The valve is a VC 6930 (special # for Trane I think) but same as VC6934. I have a low delta T of 7 on air
    side (ra.72 sa 65) and the coil inlet is warmer (45F) than
    coil outlet(39F). After confirming ch. water supply and
    return wasnt backwards I started checking into the valve
    and learned it can be piped 2 ways...diverting or mixing.
    Mine are piped for mixing. My question is What is the
    difference? when might mixing be perfered over diverting?
    I dont recall ever seeing anything but diverting in my
    limited experiance. Im guessing mixing might be better
    if chilled water temp is extremely low

    The heating valves & piping arrangement are exactly the
    same but heat works ok and the inlet & outlet temps are
    ok...the inlet being hotter. I did confirm Hot water not
    flowing in cool mode.
    Thanks for your replies and Ideas

  2. #2
    For simplicity, you can think of a 3 way diverting valve as 1 in and 2 outs, and a mixing valve as 2 in and 1 out.


    Some applications may prefer diverting over mixing because of the pump or piping arrangement.

    Diverting, could be used to change the direction of flow,

    While mixing could change the temperature of flow to the same place, Thats as simple as I can explain say it.

  3. #3
    Join Date
    Mar 2004
    Location
    Columbus Ohio
    Posts
    328
    Thanks Eddie, Any difference in cooling affect that youve
    seen? gpm thru the coil the same for both?

  4. #4
    A lot depends on where the pumps are located, even a three way valve which has the ability to maintain a consistent flow through a coil or a loop, can only do it if the pump is located properly for that type of operation,

    There are a whole host of ways that valves, piping, and pumps can be configured for different apps,

    I would look for a good hydronics book that goes into details about these configs and purposes, I don't know one off hand, perhaps someone will give you a recommendation.

  5. #5
    Join Date
    Mar 2004
    Location
    Columbus Ohio
    Posts
    328
    These are located in plant with several other systems
    on this particular loop. They all work fine so Im told.
    I noticed they were all piped for diverting.
    Dan Holahan has good books on hydronic systems.
    Since you have 1000 posts maybe you can tell me why mine is all broke up like that?

  6. #6
    My guess would be that they wanted to stop flow though the coil and divert it back to the loop so as not to deadhead it but without a diagram I shouldn't even specutlate, like I said there as many ways to pipe it and use it as there is ways you can think of,How are they controlling the valve ? is it two position or modulating ?

    I am familiar with Don Holahan's books I have all of his steam books but have never bought any of his water books, he sure seems to be the guy that would know how to answer these types of questions, and he is a pretty good source for knowledge of those things.

    He always has a real life experience to go with his lessons, that is hard to get out of most other writers that I have read, and his books incorporate some humor, so I would say if he has one and you need one that it will probably be a pretty good investment to buy his.

  7. #7
    Join Date
    Mar 2004
    Location
    Columbus Ohio
    Posts
    328
    Yea Eddiie I agree,Ive got his books on water and steam,
    Dont recall seeing anything on control valves and diverting
    verses mixing. I know Ive got to look at the entire system
    here and intend to next week.
    Let me ask you this..Do you have or see 3 way valves piped
    for mixing (2 in 1 out)? Mine are modulating.
    Ive only seen them piped for diverting and all the other systems here are piped diverting.

  8. #8
    All the time, and I would say at least my experience has been that they are ususally mixing valves, if they modulate,

    I'll give you a typical setup for a mixing valve app. without a pump in the the loop it is controlling and I'll put up one later that shows it with a pump in the loop you will see the obvious difference in control you get with the extra pump.

    Lets say you have a mixing valve, feeding a loop of radiators or some ceiling panels,

    The HWsupply from the primary loop would be connected to the A port of the valve, and the supply line to the radiators.

    The return from the radiators would be connected to the B port of the valve.

    The return line for the primary loop would be connected to the A\B port of the valve,

    This setup would give you control of the radiator loop volume, but not necessarily good control of the temperature of the water, because it can not mix rad loop return with supply to drop the temp of the loop. This config saves a pump though,and uses the primary loop pump for the rad. loop,This is acceptable in some configs, this will maintain a consistent flow back to the primary loop, and will not change the volume of the primary pumps,

    This setup is basically the same as using a two way valve to control the rad loop, because it is just shutting flow down through the rad loop, the only advantage to this over a two way valve is that it will maintain flow back to the pri. loop,

    You could not use a diverting valve in this config.because of the common piping of the return. That doesn't mean that if you pipe a diverting valve in like a mixing valve that it won't work, the flow would just be reversed and the config of the seat wasn't meant to see flow in that direction,and it will not last as long or control as well as a mixing valve.

    Lets say that a simple use for a diverting valve would be an application where you had two seperate appliances, with two seperate returns to the pri. loop, or if they were actually open loop devices, and your control setup said if you don't need water at this appliance then send it to that appliance. Could be a tank versus an appliance,if the appliance is full then send it to a storage tank, something like that,there is no conflict in the piping.

    All of these setups require balancing piping and need to have there balance set by the balancer, I have omitted those pipes in this explanation,

  9. #9
    Join Date
    Apr 2002
    Posts
    11,808
    Originally posted by ac/dc
    Im having some trouble with some newly istalled fan coil
    units in cooling mode. With the units Trane provided piping
    package pre assembled for hot h2o coil & chilled h2o coil.
    It included a honeywell 3 way floating control valve &
    actuator. The valve is a VC 6930 (special # for Trane I think) but same as VC6934. I have a low delta T of 7 on air
    side (ra.72 sa 65) and the coil inlet is warmer (45F) than
    coil outlet(39F). After confirming ch. water supply and
    return wasnt backwards I started checking into the valve
    and learned it can be piped 2 ways...diverting or mixing.
    Mine are piped for mixing. My question is What is the
    difference? when might mixing be perfered over diverting?
    I dont recall ever seeing anything but diverting in my
    limited experiance. Im guessing mixing might be better
    if chilled water temp is extremely low

    The heating valves & piping arrangement are exactly the
    same but heat works ok and the inlet & outlet temps are
    ok...the inlet being hotter. I did confirm Hot water not
    flowing in cool mode.
    Thanks for your replies and Ideas
    From what I have seen, in cooling they tend to divert flow. You alter the gallons per minute through the coil. The water can still be fairly cold and will dehumidify a bit even at lower flow rates. This type of job must have circuit setters or some pressure gauages so you can figure out what is flowing through the coil.

    You say it is piped correctly yet the cooling sounds backwards. You want the leaving water (warmer water) upstream with respect to the airflow through the coil.

    In heating it is common to mix.





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  10. #10
    Carn, I was trying to answer his question of what is the difference between the mix and the divert,

    His chilled water coil is obviously either not piped right or he has his measurements recorded incorrectly,

    Either way, mixing valves are more common than diverting valves , it is very unusual for us to use or even see a diverting valve specified by an engineer in this type of app.

    The mixing valve on small appliances without a dedicated pump will as you say, decrease flow to the coil, The heat in the same config will do the same, it doesn't really mix and maintain a volume with out a pump dedicated to it. You can not pull off of a primary loop, chilled or hot and get mixed water at the same volume through the coil and still control the temp of that water , without a pump for that appliance.

    If you know of a config that can do this, please let me know I have never seen it, and could never figure one out, without using a series of valves which inevitably end up costing more than the pump would.

    I would not know how to pipe a diverting valve to do the same thing as the mixing valve does in that example , without reversing the flow through the valve,

    The type of valve he has, is probably a small valve on a small appliance, I have seen valves that claim to be both diverting and mixing, in small sizes. I think he is looking at a mixing application.

    Ac, can you post the piping config, just tell us what is piped where on the valve.and on the coil ?

    [Edited by fat eddy on 03-26-2005 at 10:23 AM]

  11. #11
    Join Date
    Apr 2002
    Posts
    11,808
    Originally posted by fat eddy
    Carn, I was trying to answer his question of what is the difference between the mix and the divert,

    His chilled water coil is obviously either not piped right or he has his measurements recorded incorrectly,

    Either way, mixing valves are more common than diverting valves , it is very unusual for us to use or even see a diverting valve specified by an engineer in this type of app.

    The mixing valve on small appliances without a dedicated pump will as you say, decrease flow to the coil, The heat in the same config will do the same, it doesn't really mix and maintain a volume with out a pump dedicated to it. You can not pull off of a primary loop, chilled or hot and get mixed water at the same volume through the coil and still control the temp of that water , without a pump for that appliance.

    If you know of a config that can do this, please let me know I have never seen it, and could never figure one out, without using a series of valves which inevitably end up costing more than the pump would.

    [Edited by fat eddy on 03-26-2005 at 10:05 AM]
    Eddy

    If you were a native American I think your name would be 'Pisses in the Wind'.

    Prior to your edit, I was going to ask you for some examples.

    However, to elaborate what I said, from my experience with chilled water and we are not talking about on/off control, is you divert flow. The way of modulating is to alter the water flow through the coil. You do this by diverting, not mixing.

    Mixing valves can modulate the supply temperature to a coil or they can be used to try and keep a constant supply temperature to a coil. However the only way I have seen the supply temperature to a cooling coil being altered is by resetting the chilled water supply temperature at the chiller(s).

    Diverting valves can also be used in on off applications, however the OP mentioned 'floating' and said the were capable of mixing so I assumed modulating. With on/off the flow either goes through the coil or bypassed around the coil.

    I am not arguing the cost of a modulating valve vs a pump on something with 3/4 inch connections here.

    I would be greatly interested in hearing of some projects of yours where they mixed the water supply to cooling coils though. This is not a sarcastic barb, its just that I have only seen them use diversion.



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  12. #12
    I wasn't taking it as a barb,and I try no to piss into the wind, but sometimes I can't move the tree just cause the winds blowin.

    I am just trying to get an idea as to what you typically see, we always see mixing valves specified even if the piping config doesn't allow it to mix anyway, I agree that cooling is done more often than not by diverting flow, but it is rare that it is done with a diverting valve.On larger coils, in air handlers we always control water temp to the coil and maintain the same volume, because they will spec a run around pump for that coil.I don't know how else you would stop the water from leaving the unit at a possible high temp, that the chiller is not going to want to see,and if the temp of that water is able to some dehum, why wouldn't you want to do it across the whole coil ? My experience has been that diverting chilled away from the coil leads to hum problems in buildings that have a lot of small fan coils.

  13. #13
    Carn,

    How would you control a fan coil that wants to see 45 degree water, with a chiller that is making 40 degree water, for some other process ?

    It is much the same as seeing a HW pri loop with a 140 minimum but you want a loop to be at 120, without lowereing the volume.

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