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Renewable Energy: Grunflos "alpha" or other self? modulating circulating pumps, how do they work?

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  1.  
    As in I, from perusing the Grunflos webpage, figger that these pumps are controlled by pressure rather than temperature.Yes?
    Reason I am asking is that we have a 40kw wood burner linked through a Laddomat to a 2200 litre buffer tank.
    I can get the tank up to say 90 deg at the top & 80 at the bottom.
    BUT when I start drawing off heat during the spring or autumn when my heat demands are marginal, I lose stratification,............ in the dead of winter no problems since I am lighting every day anyway.
    So I reckon that I need a TEMPERATURE controlled circulating pump.
    btw I pump straight out at max temp to hot cyl (in the house,) rads and also underfloor with its own self contained blending setup.
    So I may need fit a blending valve as well? yes
    though I am pleased with the higher temps at the rads,and indeed for domestic hot water, I simply run the pump for a shorter time.
    cheers
    M
  2.  
    Hi,
    basically you need to slow down the turn over if you can. If you blend the store output down to say 70 you wiull reduce the flow out proportionally.
    Also the returning water is not that cool, probably at best 10-12 deg lower than the outlet, thus you are pumping hot (ish) water in at the bottom.
    As you say not such an issue when you are running at max during the coldest times, but ideally you want to take as little as possible and return it as cool as possible.
    But if its returned too cool there is too much work to do in order to raise it back up to 80 odd degrees - your boiler can only raise the temp by about 20deg in one pass.
    I would look into keeping the radiator water in the radiator cicruit for a bit longer with a temp controlled divertor to basically lock into the circuit till itsd cool enough be returned to the store.
    Have a search on the many many buffer / wood threads here.
    The grudfoss alpha plus will indeed slow down as pressure rises (if set to do so) and will come down to a near dead head as demand falls ie TRVs close in. Thus the flow will reduce. If not then again you are returning hot water to the bottom of the store (not good).
    Cheers
    Mike up North
    • CommentAuthorjezza22
    • CommentTimeFeb 9th 2010
     
    I'm using a Wilo-Smart self modulating pump on my rad flow circuit set to the lowest setting and all rads have TRVs except one. I left one rad without so the circuit would not 'close' and damage the smart pump.

    I'm now wondering if the smart pump would stop pumping completely if all TRVs closed down and I shut off the LSVs on both sides of the other rad?

    All rads get nice and hot with the LSVs turned right down to balance the temp accross them. The downside to this is you can hear the water flowing through under pressure.

    Is there anything you can do to eliminate this noise other than open up the LSVs?
  4.  
    I had not considered that option Mike.
    So basically TWO 3 ports, one on the outlet from the buffer tank, to blend down if needed & tother on the return pipe to recirculate if still above a preset limit.That should work.
    Hmmmmmm
    Part of my problem is when I plumbed the house( myself) I used the one set of 28mm pipes to feed both the rads & the hot cyl ) & for that matter the underfloor)
    So if I want skelping hot water I need to keep my flow temps as high as poss.
    Though I have electric two ports so that I can isolate all sep sections ie downstairs rads only, ditto for upstairs rads, ditto for underfloor OR for the hot cyl alone.
    Anyway thanks Mike
    Cheers
    M
  5.  
    Erm?
    I bin pondering that Mike.
    I only need one thermostatically controlled three port on the ret pipe, between the buffer tank & the circulating pump, with the thermostat att to the ret pipe & set at say 40/45 deg, if the return flow is hotter than the limit, it diverts the hot water back into the "flow" pipe via a plain "T" .ie. rather than into the buffer tank.
    If the ret water is cooler than the preset limit of 40/45 if dumps it straight back into the buffer tank, drawing the hotter water off the top of the buffer tank.
    I figgered this because no matter if I fit a blending valve on the hot output from the buffer tank, it will still dump a %age of warmer water into the bottom of the tank
    I can ( and do already ) run the underfloor to dump the low grade /temp heat, I can pull the entire buffer tank down to 25/30 deg this way, whilst usefully heating the house.
    NOW HOW this will interface with the workings of the laddomat?
    cos at present when my buffer tank is cold, and I light the boiler, the tank STAYS cold, bottom to top whilst the hot water is sent straight to the radiators, but through the buffer tank? Cos that is how it is plumbed.
    Quibber & titch & numble
    • CommentAuthorMiked2714
    • CommentTimeFeb 12th 2010
     
    Jezza

    Are you sure you're not negating the benefits of a smart pump by having a radiator without a TRV? Do the Wilo instructions require this? I don't know about Wilo pumps, but certainly the Grundfos smart pumps have no need for a bypass, if all rads are off the pump is automatically off, it's part of the pressure sensing.

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