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need somone's 2 cents, or more

Kal Row
Kal Row Member Posts: 1,520
building large spa like system - with copper immersion coils to heat the 9Wx14Lx4H pools, we built the coils with 3/4 copper in a serpentine fashion, 5 rows deep - which is nice for rapid heating - but i need a way to slow down the heating rate for temperature maintenance, could not use ecm pumps cause the commercial boiler room is piped with black and sced10 victaulic with lots of cast iron fitings making the environment unsuitable for ecm pumps, using Wilow 3phase 1.5x50 Top-S pumps, so i have two choices for rate control = put the pump on a Variable Frequency Drive with an associated differential temp control eg a Honeywell T775R control, see this link <a href="http://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=1&ved=0CGkQFjAA&url=http%3A%2F%2Fcustomer.honeywell.com%2Ftechlit%2Fpdf%2F63-0000s%2F63-7147.pdf&ei=cx0HUIOlBsj30gGP05GuCA&usg=AFQjCNGURRK88YdV2oQ3z-DPT1NmDkeIoQ&sig2=niYw-sL3L_KoTa6d1Smdcg ">http://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=1&ved=0CGkQFjAA&url=http%3A%2F%2Fcustomer.honeywell.com%2Ftechlit%2Fpdf%2F63-0000s%2F63-7147.pdf&ei=cx0HUIOlBsj30gGP05GuCA&usg=AFQjCNGURRK88YdV2oQ3z-DPT1NmDkeIoQ&sig2=niYw-sL3L_KoTa6d1Smdcg </a>

 (note:wet rotor cirulators on a vfd even large ones like the wilo top-S or Z or the grundfols versaflow, are limited to 30% control, ie u can drop the frequency from 60hz to 40hz max)



OR



 just use a 3/4 zone valve on a bypass tube between the supply and return in the boiler room driven by a  johnson controls A419, driving the zone valve open when the return water from the coil goes above 150f, with a 10min anticycle delay and a 10f dierential

what would u do? - or has anyone a better idea?

Comments

  • Steve Whitbeck
    Steve Whitbeck Member Posts: 669
    temperature maintenance

    You could use a 4 way mixing valve with a very sensative temp control to control the valve. The boilers and piping stay hot with full flow but the hot tub loop runs only as hot as is needed to raise or maintain temps.

    Are You not worried about chemical erosion of your copper emersion loops?
  • Ironman
    Ironman Member Posts: 6,600
    Or...

    How about using a simple thermostatic mixing valve?
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Kal Row
    Kal Row Member Posts: 1,520
    insuficient flow...

    it would have to be much larger to get same flow, and it would hunt like crazy cause it can only messure on itself , whereas with a controller i can control the differntial, and historeasis - and place the sensor way back on the return line where its not affected by the mix
  • Kal Row
    Kal Row Member Posts: 1,520
    4way with motor and controls...

    way more money than vfd or bypass



    as for erosion  - it's well water  - not to hard and no chemicals
  • Zman
    Zman Member Posts: 7,009
    Sensor

    I would mount the sensor on the hot side of the spa piping. This should give you an accurate reading and reduce the potential for scalding. As for the controls I think it depends. Personally I like VS circulators using tekmar controls. It sounds like you will be doing frequent "cold starts" you may get better range out of a floating mixing valve.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,837
    2 way non electric TRV with remote bulb sensor...

    That way you get PI control.



    Oventrop makes 1



    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.
  • Kal Row
    Kal Row Member Posts: 1,520
    edited July 2012
    need inverse control..

    need to sense the return line and open the bypass as it starts to get close to the supply temp, or come up in temp, did not see an inverse mechanical actuator by anybody, other than a 3way valve

    when the pool is 40-50f the 170-180 supply temp returns at 100-120, when the pool gets to 98f the return line should be in the 140+ range

    we do a lot of these and the avg imparted btus is 11,250btu per sq ft of copper with 4ft per sec internal flow

    i even have a backup pump on the rail with valves to heat at crazy rate, it's a 2.5hp sta-rite pump with 50gpm @ a pipe eroding 120ft head!!!,

    I'm leaning toward the VFD solution, since the pump is 3phase and i would need a motor starter anyway - and the motor starter has to be electronic as we want alarm output - been using the cerus starters http://www.cerusind.com/templates/group.asp?GroupGuid=406

    their ems starters read the motor and will tell u if the motor's speed is out of range eg too slow on bad bearing or too fast on a clogged inlet strainer or air in system - i am using taco's iworx system's alarm modules to see all my temps and alarms on the internet

    what i dont like about vfd's is that the pumps and motors a really in-efficient at the turn down rates its the dirty little secret of the VFD world, the control is there but the electrical saving is not
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,837
    Tell us more about the dirty little secret...

    Kal, The limited information I have about these VFD's is that they shouldn't be used at capacities of less than 30%. I believe that number comes from the motor manufacturer and I think it has to do with cooling the motor. The only "issues" I am aware of is line noise and harmonics, which have allegedly been addressed by the manufacturers.



    Are you talking about the power factor? Or the waste heat associated with their operation?



    Say hey to Moishe.



    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.
  • Kal Row
    Kal Row Member Posts: 1,520
    vfd

    just like they tell u design for the knee of the pump curve, its not just about the impeller, it's everything from the volute shape to the motor's power factor, on an ecm motor where the permanent magnet rotor is essentially free energy, u only have to worry about the stator and that is sensed and switched electronically like a vfd but the but the induced rotor on a regular motor has miserable electrical qualities once u go off design speed. The Wilow top-S/Z or the grundfoss equivalent, have a speed jumper which is only a 10-15% change.

    me and moish wanted this boiler room not to have any steel, only aquatherm pipe and large pex to the loads, but the official Mechanical Eng and the builder were afraid of new pipe technology, so  we are stuck with steel, otherwise the whole show would have been all ecm pumps, at a vast lectrical saving to the client, for now only the space heating loads have a pair of wilo stratos and with a  stainer, and a fernox magnetic filter upstream and tons of conditioner in the system



    ps worldwide has been selling a lot top-s/z pumps for 3yrs now and hasent gotten one back or doa - so this is what the custormer wanted a supper reliable pump - i dont want to be the fist one to kill it with a VFD
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