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Green Building Bible, Fourth Edition
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    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.
    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).
    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?
    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.
    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
    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

    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.
    • CommentTimeJul 1st 2015
    Hello, everybody,
    Our home was originally plumbed with an indoor Firebird Oil Fired Boiler, situated in a cupboard under our kitchen counter-top. This supplied the heat for our central heating, which is split up into 4 zones, with TRVs on all of our 31 radiators. It also heated our Domestic Hot Water via a Heat Exchanger and an 80 gallon Storage Tank (Insulated Copper Cylinder).
    Now, we have installed a new Multi-Fuel Boiler in our shed along with a 2000 litre Buffer Tank, which is tee-d into the old system. (Please see the attached drawing). This new system is wonderful, we have heat all over the house with loads and loads of hot water. Our home is a Bed and Breakfast and needs a constant supply of hot water and heat most of the time.
    Our old oil fired system would cost a bomb to come near the comfort the new system offers. It’s amazing! It is set up in a way that allows for the oil boiler to come on should the temperature at the top of the Buffer Tank fall below 45 degrees C. (this can be adjusted to suit our needs, but we have it set to 45 degrees C.)
    Should the temperature at the top of the Buffer Tank fall below 45 degrees C. Thermostat T4, at the top of the Buffer Tank (on the drawing), opens MV1, closes MV2 and switches on the Oil Boiler (OB), thus isolating the Multi-Fuel Boiler (MFB) and Buffer Tank (BT).
    The cartridge in the Laddomat (L) is 63 degrees C. and the Multi-Fuel Boiler is set at 65 degrees. With these settings the Temperature Gauge (TG1) at the top of the Buffer Tank normally reads around 70 degrees C., with the bottom Temperature Gauge (TG2) normally reading around 60 degrees C.
    We have one problem, though, when we have no heating on (during warm weather) the heat in the Buffer Tank can go up to 80 degrees C. at the top and up to 70 degrees C. at the bottom. This can cause the Domestic Hot Water to become very hot and, at times, cause the water in the Storage Tank (ST) to over-heat and push hot water up the Expansion Pipe (DHW/EP). At this stage the water in the taps becomes dangerously hot and is a worry. We certainly don’t want anyone getting scalded.
    Thermostat T1 for the Heat Exchanger is set to 60 degrees C. and Thermostat T2 is set at 55 degrees. Thermostat T1 switches on the Heat Exchanger Circulating Pump (P1) when the temperature reaches 60 degrees in the flow pipe from the boiler. Thermostat T2 switches off P1 when the temperature at the bottom of the Storage Tank (ST) reaches 55 degrees C.
    We are also afraid of children touching the radiators when they come on with 80 degree water in them. There’s something telling me that we need to fit a mixing (blending) valve between the flow and return at the house side of the Buffer Tank. Would I be correct in saying this?
    I would really appreciate any help or advice on this.
      Plumbing Diagram.jpg
    As mike (up north) said you will need to slow the speed and use a blender valve between the CH flow and return. Actually I think a blender valve may have more impact that the speed. My system has a mixer (blender) valves on each of the 2 CH circuits (system serves 2 houses) between the CH flow and return to reduce the return temperature to the TS and to minimise the hot water taken out of the TS. Set the flow temperature to the lowest that will work for your system, possible adjusting between autumn and winter. This should help maintain stratification. I also run DHW from my TS into a separate DHW tank and adopted a different approach to maintain stratification from the DHW tank flow,see

    As I said in the thread I am pleased with the result and now in the summer using DHW only I am lighting the boiler every 4-5 days with a 3/4 load to supply 2 families with DHW and stratification in the TS is maintained wonderfully.
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