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WWWD? What Would Wallies Do? Taco i-Valve/Circ Control Q.

Brad White
Brad White Member Posts: 2,398
Hey everyone,

I have a question and want to get opinions on the details of

controlling my revised HW heating system. I know controls in terms of DDC but

you all do much more hands-on controls work at the level of detail where it

counts.  I was going to post this under “Controls”

and may yet, but thought the wider audience is the best audience.

 In July we moved into our “new” 1913 house with heating

built around the original gravity HW and CI radiator system.  Boiler is a W/M, cast iron with DI fan (1996,

not a Gold Series) and we are keeping that for now to keep costs down. System

will be piped P/S to protect the boiler and allow OD reset out to the spaces.

 All zones now have circulators including separate convector

and fin-tube zones for bedroom and playroom. Each needs different temperatures

so, alas, I cannot use my favored “single ECM circulator with zone valves”


 I am going to use Taco iValves on the master bedroom (fin

tube bbd) zone and the main CI/Gravity Zone.  Circulators will be controlled by a Taco 506-EXP

relay with a Taco 702-1 reset control for the boiler. (I want the option of

generating DHW, so went for the 2-stage control which offers this. The single

stage does not.) The 506-EXP will also control the boiler-loop circulator.

 I am leaving the radiators alone, not installing TRV’s this

season at least.  Not ideal but a

business decision. House does not see a lot of sun.

The other zones (playroom and shop) will be intermittent use

and direct-controlled, no ODR. Keeping those simple.

Space thermostats would be Honeywell types with Smart

Recovery, so the “optimum start” part is taken care of, but will not boost the

HWS temperature above what the iValve gives for ODR at a given time. Working

with that limitation, lack of faster AM recovery from any setback.

 The question I have is how best to control the ODR zones

(MBR and CI/Gravity Main Zone) which will have Taco iValves.  What I am coming up with is a hybrid between

circulator control and zone valve control (ZVC) directed to the iValves and

want to streamline this as best I can.

WWWD? (What would Wallies Do?)

 Here are my basic sequences:

Sequence/Option 1: Intermittent Circulator Operation.

Thermostat calls, Taco EXP relay closes, circulator starts.

The iValves would be separately powered and modulate to ODR sensor and boiler

return sensor whether circulator runs or not.

Plus-Side: Heats the space. Duh. No circulator energy


Minus-Side: Possible expansion noises in BBD and/or delay in

response on any zone. Not as smooth as constant circulation.

Sequence/Option 2: Constant Circulator Operation.

Circulator runs constantly based on ODT,( , circulator is off.)

Thermostat calls,  iValve would be activated by a Taco EXP ZVC

zone valve controller to effect night set-back.

Note: These are the ODR version, not the setpoint version

which allows a 15 degree off-hours parallel shift in setpoint. There is no

setback nor recovery internal to the iValves that I can see.

Plus-Side: An ideal situation. Heats the space, more even

temperature, less likely expansion noises on BBD.

Minus-Side: Another layer of control, perhaps. Not a huge


Sequence/Option 3: Constant Circulator Operation and ODR.

Circulator runs based on ODT,( , circulator is off.)

The iValve will modulate to ODR curve and with WWSD more or

less coincident to circulator.

Heating curve would be adjusted and left at a low level but

constant. (That discussion re: what actual savings does night setback actually

give you vs. what recovery spends, rings in my ears. Another topic to bring


Thermostats would act as a high limit only, otherwise no

interior influence.

How would you go about this, especially to make my ideal,

Sequence/Option 2, work best? This is all a bit outside of the Taco Wiring

Guide, with bits of each in play. I want to keep it as simple as possible, understanding

that the iValves are great devices but limited by not having AM recovery.

 Thanks All, Sorry for the length.

"If you do not know the answer, say, "I do not know the answer", and you will be correct!"

-Ernie White, my Dad


  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    be careful

    the iValve does not take heat demands. It just modulates based on outdoor reset, even if you don't have a heat demand.

    pretty serious ghost flow concern in most cases. It's really intended for use in constant circulation systems. We won't use it in intermittent situations if there is any chance for ghost flow otherwise.

    UP15-10s baby. 25 watts per temp. Not bad.

    Setbacks are the achille's heel of TRVs though IMHO. I haven't seen any solution for that, which isn't kludgy, other than water temp based solutions like the built in option on veissmann boilers.

    I would run constant circulation circuits in most cases, with a master season-on, season-off switch, if I were "keeping it cheap".

    Otherwise, you might consider something like a teknet 4 master temperature which can response to setbacks, and attempt proportional mixing for the lower temps you need. then you could very the temp based on indoor feedback and it would "cascade" through the system. more of a "tweaker" kind of a system, but Brad, I have to imagine you'd be the ultimate tweaker kind of guy with your own system ;)

    If the house is still leaky and such, setbacks are a bigger deal than if you've done your highly recommended envelope upgrades first.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • Brad White
    Brad White Member Posts: 2,398
    Thanks, Rob

    for slogging through my novel, too. I am with you on the heat demand. My use of the ZVC would be in the power train as I see it, not a direct action as a valve input if I gather correctly what you are saying.

    We agree on constant circulation too. Me a tweaker? Yup. :)

    So, Rob, you recommend the master switch approach with no role for an indoor thermostat and I tweak it down as low as my dear wife will allow? You sir are a pioneer after my own heart. Leaning that way too myself.

    Re: the Teknet approach: I already have the Taco controls and my intent is to make the house as "Taco" as I could with no regrets, down to the pall ring air separator.

    I already own two Wilo Stratos Ecos and the Bumblebee is not to market yet, although I have heard that some have escaped the laboratory in Beta testing. That full Taco profile would be an ideal and working of delta-T too. Pressure drop? I HAVE no pressure drop.

    Re: ghost flows. The MBR zone is all 3/4" copper with an circulator (Taco 003, I own already) and with a soft check in the discharge, plus a u-trap incident to how I have to pipe it, so OK there.

    But, interestingly, on the CI/Gravity zone I am using a Wilo Stratos Eco. The low flow rate (3.5 to 4.0 gpm) at less than 4 feet of head (nothing in the old piping, this is all valves and the i-Valve itself), ought to be enough to start the "Gravity Engine" working again.

    Just a little push is all it should take and the Wilo ought to settle on the very low right side of the operating range and low system curve. "Too much pump" you may say, but this should settle on about 8-10 Watts. If ever I install TRV's, the VS feature will have something to respond to. Likewise, I am using an Eco for the boiler circulator, 8.0 gpm at 4 feet of head, again, very low Watt draw, lower than any fixed speed circulator even if it does not turn down. They both will still drop to minimum at night, too. Thanks, Rob.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    well, tough question

    First, I'm presuming the house is leaky. I'd fix that first if I could.

    If you can't fix it up and it is a leaky house, setbacks are attractive and hard to get with TRVs alone. I have no idea what taco has that can do this, but I'd tend toward a more complete control solution that can reset the water temp while taking setback into account... I know it's achievable with Tekmar, but I'd have to poke through taco and honeywell catalogs to see if they have anything that can do it....

    But it would be very expensive to do this for all water temps, so I would consider just doing it for the highest water temp, and proportionally mixing the lower temps off of that one. With TRVs still for "normal" operation levels, though in setback they'd probably go to full open and you'd want a balancing manifold for that situation for any multiple loop situations. You *could* do it without TRVs, but honestly... i wouldn't recommend it. Though I'd probably try it first, just for fun ;)

    IF the house is tight, so we don't care about setbacks, constant circ in all zones with the smallest pumps I can finagle, and the iValves, is good. No need for heat demands. Maintain a header, insulate it, keep the electrical draw down, rock and roll. could add a thermostatic leg for radiant if you want to, but be sure of your ability to stop flow if the thermostat stops calling.

    I'm a little surprised you need multiple temps though. I mean, come on Brad, can't you get it down to one or two temps???
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • CMadatMe
    CMadatMe Member Posts: 3,086

    Brad see if any of these will help. You can also make a zone control a slave to a master cric relay.


    There was an error rendering this rich post.

  • hot_rod
    hot_rod Member Posts: 22,271
    have you seen the Heimeier

    setback TRV. I believe they have a rep/importer for this brand in the US now, Heatlink maybe, formerly the Oventrop rep :) Heimeier is one of the largest TRV manufacturers in Germany

    Try this link

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
This discussion has been closed.