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Thread: Modulating pumps ...

  1. #1
    Automated Home Legend chris_j_hunter's Avatar
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    Default Modulating pumps ...

    just wondered if there was any experience of doing this - we're about to have them as part of our thermal-store set-up, on the UFH side of things ... idea is to modulate the pumps according to heat requirements, and so avoid the need for throttle & control valves, & the dreaded balancing that's normally required ... ie: with Idratek controlling everything, with all the usual sensors ...
    Last edited by chris_j_hunter; 6th March 2009 at 01:35 PM.

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    Automated Home Jr Member RichardC's Avatar
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    No experience with heat pumps, but to avoid using modulating valves it's pretty standard in my line of work to use an inverter.

    Is your pump 3 phase or single? What kind of power? kw?

    Irdatek does have an output module that does 0-10v analogue. I don't find using analogue voltage in industry a good idea, but if you keep your analog cable runs short and screened then this should work fine at home. (normally use a 4-20ma current loop, fieldbus or other network)

    controlling the flow will need some care, there is a normal minimum and maximum frequency that you can run at, this will depend on a number of things. The cooling needs of the motor, the water head and back pressure.

    As a very rough rule of thumb, I don't normally like to run motors below 40Hz or above 60. You can sometimes get away with a lot more. It also depends on how intelligent the inverter is. Some are very good and will detect if the motor is about to stall and boost the torque. If you run the motor too slow for the cooling fan normally mechanically coupled on the back of the motor, it will overheat. Separate forced cooling and a good inverter to cope with not stalling is then a good idea.

    I haven't been involved with specifying inverters for a good 5 years. I now try to stick to software running plants now!

    Inverters I have had good experience with are Control Techniques or Rockwell. CT tends to be cheaper and IMHO are better at vector control. They do advertise an onboard PLC, but the last time I used this I wasn't impressed, best off using them as a dumb unit!

    Just as a guide, I have not used this company / website before or this particular module of inverter but try this.

    http://www.inverterdrive.com/group/A...P/default.aspx

    I have used alot of control technique inverters in the past. I do have a loose connection with them now, as they are owned by the company that I currently work for. but I have no connection to the division that sells them. I work on the DCS side for a sister company.

    I hope this is of some use!

    Rich

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    Automated Home Legend chris_j_hunter's Avatar
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    interesting, thanks ... in our case it's not a heat pump, just UFH (although, in a way, maybe they are heat-pumps - it's funny how these terms are used) with one pump per each of four zones (200, 350, 350 & 500m of 15mm pipe per zone) - not found or chosen the pumps yet, and I guess we may conceivably subdivide the longer runs & have more pumps (I'm about to ask for quotes for the thermal stores & all the gubbins that'll be on them) ... either way, maybe these are smaller pumps than you normally use ?
    Last edited by chris_j_hunter; 7th March 2009 at 11:12 AM.

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    Automated Home Sr Member mcockerell's Avatar
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    Is there a particular reason that you're going for a number of pumps rather than the tradiitonal approach of actuators and flow regulators attached to a manifold?

    We're currently installing underfloor heating as part of our new build, with a thermal store heated by solar and boiler; we have 14 separate zones (about 19 loops) fed from 2 manifolds with a single pump that runs to meet heating demand.

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    Automated Home Legend chris_j_hunter's Avatar
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    thinking is : E7 & thermal store, no thermostats (pumps modulated on basis of return temperature sensors & demand - ie: presence & anticipated presence & outside temperature & forecast), no manifolds (expensive & high-pressure-drop & turbulence), no long-winded balancing & adjustment, ability to boost or down-play individual zones, minimal ups & downs, more efficient, etc.

    fours major zones with individual pumps, plus sub-zones not individually pumped (balanced by getting the pressure-drops intrinsically about equal) ... house is used in a way that the four are used & not used in various combinations at various times ...

    yet to confirm possible range of modulation, so some details still a work-in-progress - already looking at MoMo valves !
    Last edited by chris_j_hunter; 11th March 2009 at 03:00 PM.

  6. #6
    Automated Home Jr Member RichardC's Avatar
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    Interesting to see that you are looking at using return temperatures. I wrote about considering this on the heating control part of the forum. Since I don't really want to have to bury sensors in all the floors but want to make sure that they don't get too hot.

    Sorry that my post about inverters wasn't so usefull. I guess it helps if I read posts with a bit more care.

    Still wonder, if the water is moving more slowly, will this lead to a noticeable diffrence in temperature across the floor? Thinking that it will give it's heat up in the first part of the floor. Could be talking out of my $%& here.

    I was looking at going down the route of a manifold in my house. But still designing it all and getting quotes in.

    Like the idea of the heat store, but also like the simplicity of just hooking up the boiler directly. If I could get some heat from solar as well, would need to work out the payback.

    Cheers

    Rich

  7. #7
    Automated Home Legend chris_j_hunter's Avatar
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    sensing return temperatures rather than room thermostats = not uncommon way to do it on the Continent, apparently, but just seems to make sense to me !

    your mention of inverters was useful, actually - I've yet to find a suitable pump, so may well end-up having to do something with inverters ... this was one I found :

    http://www.abbeycontrols.co.uk/elect...ducts-c-4.html

    also found this useful :

    http://www.modbs.co.uk/news/fullstor..._parallel.html

    water moving slowly - you may be right, my feeling is we won't be going that slow, though, and anyway slow is only when not much heat is required, so the transfers will be slow, too !

    actually, pump speed is an issue - the workable range will be less than ideal, so some cycling will be unavoidable ...

    also, all the modulating pumps / circulators I've found tend to be self contained auto-adjusting on pressure differential - not what we want ! Best of the bunch I've found so far are Wilo Smart :

    http://www.impeller.net/magazine/news_en/doc2472x.asp
    http://www.wilo.com/cps/rde/xchg/en/layout.xsl/1010.htm
    http://www.wilo.com/cps/p/productsDo...00127379_0.pdf

    but again not really (I think) what we're looking for ... might suit you, though, and I see they suggest no need for manifolds when using it - not altogether sure why / how, though !

    heat stores are not cheap, so pay-back time might be long ... in our case we're going for E7, so don't need a boiler, so can afford the 'store !

    hope I can find a pump - Wilo, for example, do lots of variable speed, even continuously variable speed, pumps, but they all seem to be either manually preset or self-adjusting on pressure differential - wheras we want to control on temperature !
    Last edited by chris_j_hunter; 17th March 2009 at 04:31 PM. Reason: added another point

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