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pump selection with Caleffi isolar controller

EternalNoob Member Posts: 34
Starting with the simple question i need answered, what kind of pump do i need to mesh with the variable speed control feature of the caleffi isolar type controllers? Will the standard Taco 009 work?

I see there is the variable speed version: the 009 - VTSF5, but appears to have it's own self-contained controller so that would be redundent with the isolar controller.

More details...: I am helping update a 15-year-old drain-back solar thermal system that has been out of commission for some time. They have a total of 3 pumps and 3 panel arrays, operated by 3 separate steca (on/off) controllers. One of the pumps is broken, melted impeller, and due to the fact that it was also full of rust, would like to replace it with the stainless 009 rather than cast iron this time. There are some issues with all three controllers (perhaps the thermistors are broken, or the connection is faulty, or perhaps because the wrong type of thermistor was installed by someone trying to fix the system...). In any case, before going into trouble-shooting the controllers and thermisotors, i'm thinking maybe it's time to update the whole dealio to the isolar type controller(s). However i'm not sure if it's worth the investment if the two functional pumps (both taco 009's, an 009 BF5 and an 009 F5) will need to be replaced, in addition to the broken one.


  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 3,198
    Best source on this forum is @hot_rod
    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org
  • hot_rod
    hot_rod Member Posts: 16,307
    If you use the variable speed function, it needs to be a standard PSC motor, not an ECM.
    You can lock the relay at 100% and use any pump.
    I'd run the pump directly from the I-solar control to use all the functions. It has some unique drainback functions built in to prevent short cycling, assure the siphon is established, etc.

    Another option if you want more motor efficiency is run two pumps in series, a standard, and an ECM. Once the siphon establishes drop off the standard and flow the array with an ECM at 10- 40W! The control has a two pump option, it will use both of the relays to do that.

    I-Solars have 1 amp relay rating, but I have run 15-100 Grundfos for drainbacks without a problem, 1.1 or so Amp draw.

    The larger high head circs would need an isolation relay to run in VS mode. I ran a 5 hp shop vac off a I-solar with a $20 triac from Graingers. You'll need a heat sink behind the triac if you load them up with current draw, they get very hot.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • EternalNoob
    EternalNoob Member Posts: 34
    Thanks Hotrod, you're such a wealth of information. I'm still confused by some of your points though.

    I have pontificated about the two-pumps in series scenario, but always thought it sounded like a hypothetically possible but maybe too complex in reality idea? It sounds like you're saying the i-solar has the built in capability of doing this?

    Generally, pump efficiency is a concern to me of course, but I think limiting short-cycling seems more important, both in terms of excessive pump wear, and also the energy lost every time it has to work like a dog to push all that water through an empty pipe to the second story rooftop. The pathway for the pipes is loooong on this system and goes over a 25' roof peak. Also, for other reasons I would like the system to achieve higher temperatures, so it seems like a pump that modulates down in flow rate for those sunny but not too sunny days would be ideal (?).

    In any case, yeah, the 009 says it draws 1.4 amps, so I guess i would need an additional relay, and that doesn't seem too complicated or expensive, though it seems a little funny design-wise that the i-solar controller is not built for higher amperage pumps considering drain-back solar thermal systems typically need higher head pumps. Isn't the taco 009 specifically designed for solar thermal?

    Also, can you expand on what you meant by "You can lock the relay at 100% and use any pump. "?
  • hot_rod
    hot_rod Member Posts: 16,307
    edited March 26
    Actually the relay is a 2 amp, but the traces on the printed circuit boards were listed as 1A, that would be the weak link.

    There were a few versions of the I-solar control. Not all had DB function. The I-solar Plus which is a Resol DeltaSol 4 has it.

    Attached is the set up sheet showing how drainback works, if you enable that option.

    Once the collector heats up, the control watches the temperature for a few seconds, called tDTO (temperature delta T on) this prevents short cycling on cloudy days. factory default 60 seconds

    Then fill tFIL, tell the control how long the pump or pumps need to run to fill and establish the siphon, typically 3 - 5 minutes.

    Next is tSTB this will prevent the pump from shutting boff right away if a cloud comes over for example. again to prevent on/ off cycling 5 minutes of default.

    now the system is ready to run.

    OBST is option boost. this is for two pumps. Wire the second pump to relay 2. It will run for the time period you select, typically 3-5 minutes to fill. then the pump on relay 1 takes over. That is where I put an ECM. On mine I had a 15-58, connected to an Alpha 15-55 on relay 1.

    OR, use two 15- 58 or whatever brand you prefer. When the second pump shuts off, the first will run on variable speed. there is a function called DTS delta T step. set at 20° So if the collector gets 20° degrees hotter then the tank temperature the pump increases 10% in speed. If it gets another 20° hotter, the pump will go up another 10%, all the way to 100%. So this is how the pump speed is controlled as the collector gets hotter. or as it cools the pump slows.

    In drainback function the pump will only reduce to 50% speed.

    If you have a pump that can take a PWM signal, there is an HE setting, you need to use an interface reay however.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream