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Products: Desperately Upset at Standby Power Usage of New Water Pump

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    Just installed my incredibly expensive (c 1500 Euro) inverter Grunfoss water pump with pressure sensor - Grunfloss state one of its uses as supporting mains water pressure. It is attached to a 1500 Lt water tank and has an always-on bypass delivering mains pressure after the pump. I should be pleased as punch as I get a bearing life of 45-55 years (on my expected usage), I get 5m3/hr at 20m head (enough for the up to 5 showers I hope to have), I get enough water to carry me over the 4 or 5 water supply outages I get each year and I get guarantied water to cool my 40kW wood burner when/if it overtemps (the std non-UK EU system). I aught to be smiling smugly in the knowledge that my super modern, ultra, quiet hi-tech pump delivers only the water I need maintaining my selected pressure and hence using the absolute minimum in electricity, and even on full power (having an inverter) the thing only draws 150w.

    But I am not happy because my tecnico (who first recommended it - and he is the brightest green man) didn't mention its standby power usage and when I researched the thing I didn't spot it either. It uses 65-70w on standby; that's over 500kW pa or a sixth of my target electricity consumption and I have a PV system sized to give me about what my target consumption is (I get 1 for 1 kW free from the electricity Co for every 1 kW I give them). So, why oh WHY does such a fantastic thing need 70w when doing nothing? I really want the techy answer to this question because I am stuck now. I cannot just turn it off (when the boiler isn't on) because I cannot leave the water in the tank until it is needed; the whole system relies on a continuous usage of the water in the tank - maybe week on week off but also on when the water stops or when I have guests in all my still to be built bedrooms.

    Oh well win some lose some - not that I know what the alternatives were and those systems I have seen locally looked pretty appealing. And if anyone is really interested here it is (CRIE5-4):

    http://kgnpillinger.com/products/view/?cat=4&id=117

    and the relevant tacky manual (3.6MB) is here:

    http://net.grundfos.com/Appl/WebCAPS/streamliterature/Grundfosliterature-1813.pdf

    and if anyone can tell me why the thing is rated at 550w but draws only 150w according to the P2 curve on page 30 that would be nice…


    :cry:
    • CommentAuthormike7
    • CommentTimeJun 4th 2010
     
    It's a multistage pump, and they quote a P2 'Per Stage' (see p23) Your pump has 4 stages, and at 5m3/hr the P2 line on p30 gives a value of about .115kW, so thats .460kW for four stages,which is a good bit closer to .550kW

    (Note that 5m^3 at 20m head would need about .270kW at 100 percent efficiency, so if the pump could really do that on 150W, you'd have a very magical pump!)

    Could you have a pressure switch on the mains water side to switch on your pump system only if the pressure falls below a chosen value?
    • CommentAuthorstephendv
    • CommentTimeJun 4th 2010
     
    Could you install a pressure vessel after the pump and then as Mike suggests, stick a pressure switch on the other side of the pressure vessel? The idea being that the pump shouldn't come on if you just open the taps briefly.

    Water tank -> pump -> pressure vessel -> pressure switch -> taps
    • CommentAuthorbillt
    • CommentTimeJun 4th 2010
     
    I'd guess that it's because you've bought a very fancy pump that is designed to maintain a constant pressure, without using a pressure vessel.

    "Within industrial water supply, E-pumps with integrated pressure sensor are used to ensure a con- stant pressure in the piping network. From the sensor, the E-pump receives inputs about changes of pressure as a result of changes in the consumption. The E-pump responds to the input by adjusting the speed until the pressure is equalized. The constant pressure is stabi- lized once more on the basis of a preset setpoint."

    If you haven't got enough static head to maintain the set pressure, the pump is going to have to operate continuously in order to maintain system pressure, even if no water is being drawn off. Maybe a non-return valve in the supply to the pump could maintain the pressure without the pump operating, but that's guess work.

    Try asking Grundfos if they have a solution, although I doubt that it's a significant problem in their target market.
    • CommentAuthorevan
    • CommentTimeJun 4th 2010
     
    Yikes, it's a standby pressure setup?

    I think you need an expansion tank, check valve and a pressure switch, i.e the old fashioned way.
    • CommentAuthorCWatters
    • CommentTimeJun 4th 2010
     
    I agree. A check valve, expansion vessel and a pressure switch to switch to pump off.

    By expansion vessel I mean something like an accumulator (not to be confused with thermal stores which are also sometimes called accumulators). ColdStream make some as do others. Not quite sure how big but you probably need to choose one designed to deliver the flow rate you need. Try speaking to a manufacturer direct for advice.
    • CommentAuthorcontadino
    • CommentTimeJun 4th 2010
     
    About 18 months ago, my plumber showed me an electronic pressure controller and suggested that I install it. It operated with the existing pump, but replaced the EV and switch that is currently there. It said on the box that it used a constant 12w, which was too much for me, so I declined. I'm afraid I didn't note down the manufacturer or model number. He said it cost somewhere in the region of EUR60.

    We had one of those conversations that goes along the lines of...So what's better about this one? It's electronic. So does that mean it's better for the pump? No, it's just better because it's electronic. So does the mechanical switch damage white goods in the house? No. So what's better about having an electronic one? It's electronic.

    For EUR1.500, I'd probably have opted for a mains charge controller, batteries, and an inverter for an off-the-shelf sub. pump.
  8.  
    Yes Evan, exactly right, it is a system to maintain pressure when the demand exceeds mains pressure (arriving over a 100m rusty 21mm steel pipe and always significantly less in the summer). It is also there for the future when I hope to run cycling trips and have a double apartment and 3 spare en-suite rooms - one can dream!

    Billt, it is definitely not to do with maintaining static pressure because the graph says that at zero l/s it uses shed loads of power.

    I already have an expansion vessel (25 litres) and a pressure gauge mounted after the pump. I put a NRV (aka check valve?) before the pump as I thought I needed one to prevent the mains by-pass from overfilling the tank through the pump (though perhaps that is impossible) and then through the tank outflow. I didn't fit one between the pump and the pressure vessel because I thought that would interfere somehow with the pump's pressure sensor getting an accurate reading. As is suggested the expansion vessel is there to reduce the number of stop/starts though I also thought to smooth out pressure changes.

    Now then, I hadn't thought about a pressure switch. As I now understand it (post surf), such switches (and I think mechanical is better Contadino, why, well because because mechanical is better than electronic :wink:)have adjustable on and off pressures (literally manually adjustable springs) and so I could set one to turn on when the pressure is below say 1.5 bar and turn off when above say 2.5 bar and here is one I found at under £25:

    http://www.pumpexpress.co.uk/acatalog/pump_controllers_switches_pump_express_19.html

    Is this what you knowledgeable people meant? And do I really need a NRV between the pump and the pressure valve - if not I can simply unscrew my pressure gauge, screw in a double ended Male adaptor with the right sizes for the pressure switch, wire up the power to the pump through the pressure switch and I'm done - ie a jolly simple little fix!

    BTW Mike7 - ref power per stage - of course you're right, how obvious - Ta.

    Indeed thanks all, Duncan
    • CommentAuthorcontadino
    • CommentTimeJun 4th 2010
     
    Yes, that one 2nd from the bottom is pretty similar to the one I have. Mine's set to cut in at 1bar and off at 2.1bar. You can modify the settings by turning the two screws inside it. You should be able to pick one up cheap at your local ferramenta/plumbers yard.

    I think that my pump has a check valve, but putting one in between the switch and the house can't do any harm.

    Of course, a pressure switch alone, while providing for the high use, won't keep you supplied with water when ENEL just decide to cut your power off for a morning while the engineers waddle off to the local bar. For that you'll need some sort of UPS arrangement.
  10.  
    Yes, thanks contadino, I'll definitely get the switch locally. I did think about a double failure (water and electricity) remembering that I have a mains always-on bypass for the cisterna and pump - re future possible potential paying guests: well I think they would accept such a long shot and for sure the overlap will not last long; re the caldia: well I judged that a double supply failure coinciding with the caldia being alight and either me not being here or it going super hot so fast I can't control it by changing a few settings was so unlikely that it didn't justify the cost of a UPS or indeed 15m of 28mm pipe and some associated brass to give me some sluggish gravity feed (I have 1m head cisterna to caldia).

    I would still prefer not to put in another NRV - anyone got a definitive opinion........
  11.  
    I use the same pressure switches as you have found. They work well, seem to last about 5 years when the switch contacts give out (my off mains borehole system gives them a continual hard time). By the way the differance between the PM5 and PM12 is the strength of the springs otherwise they are the same. My systems are

    Water tank -> pump ->NRV -> pressure vessel -> pressure switch -> taps.

    The pressure sw can be anywhere convenient between the NRV and the taps, the idea behind the position of the NRV is that the pump seals are not under continual pressure. This is the standard setup here for off mains water supply. Here a 25 ltr pressure vessel would be considered too small (causing short cycling of pump) and 100 ltr is the usual recomended minimum. If the pressure vessel has a diaphram then pre load to about .3 to .5 below pump cut in pressure, if there is no diaphram pre load the PV the same but you will have to check the air quantity (drain and pre load) about once a month (in my experience). BTW my pumps are Pentax, made in Italy and pump up to 6 bar, cost about 100 GBP here and give a very good service life.
    Peter
  12.  
    One point that I forgot to mention is that if the NRV is placed as above then the pump will start with only the load of the head from the water tank rather than the load of the pressure from the PV. this should make for easier start up and less inrush current.
    Peter
  13.  
    OK guys I have a conclusion to this issue after a conversation with the Grunfoss UK CRIE technical expert. Whilst the pump is good for up to 200 activations per hour this means to start/stop pumping water whilst 'on', not electrical isolation. The pump can cope with just 4 full electrical starts per hour and then only "infrequently". The life-cycle costs are still much lower than fixed speed pumping (ie with a large accumulator etc) and in my current application it does not need a NRV after the pump, furthermore, my seals will probably last decades with my set-up. However, what I can do is put it OFF on a timer during the night, most of the time I have mains pressure and my 22 ltr pressure vessel (plus another 22 ltr pressure vessel on the HW loop behind a NRV) will give me a toilet fill or a glass of water. The guest accommodation and associated simultaneous showers, are some way off, even then though I can have it off during the small hours and only on 24/7 when I find I have a mains failure.

    Overall I am happy, if I had replaced an existing fixed speed pump and big accumulator I would have been pleased with my energy saving and reduction in life-cycle costs; my disappointment is more to do with expectation management. The only problem, as with so many of the Green solutions, is the up front capital (1533 Euros for the pump).

    Incidentally, the tecky (a very nice guy) said "yea well of course it will use a tiny amount 24/7" - it shows we have a long way to go when he, and I guess the majority of the populous, think 550 kWh per year is "tiny"!

    But a big thank you to everyone who tried to help me - very much appreciated. Now then back to my 400 euro copper ventilation cowl on another thread...
    • CommentAuthorevan
    • CommentTimeJun 14th 2010
     
    I'm still not convinced this is in any way a "green" solution, sorry, unless it can be demonstrated that it will really use electricity overall than a cycling pump with accumulator, in a domestic application, I just won't believe it.

    Maybe in the context of a hotel or something it does make sense technically and financially and might even come out ahead on energy consumption if there's always water being used somewhere.

    Sorry to be negative!
  15.  
    I do not fear negativity Evan! I don't have the figures so I cannot prove what I am saying (anyway 'lifetime costings' usually allow ample room for debate).

    What I can say is that Grunfoss sell literally thousands of these pumps in the UK alone (usually the 5-8 whereas mine is the smaller 5-4), given the huge initial capital investment one has to wonder why. Meanwhile my good friend here, a truly tight Scot, can't wait to install his 5-8 and get rid of his 5 year old but now noisy 1.2kW pump and big accumulator as it absolutely eats power (his words not mine - btw I haven't seen mine above 200w yet). Besides being 'tight' he was a mechanical engineer who ended up in vibration and to say he is anal about researching stuff would put most people on here to shame. Then there is my technico, the man with the greenest blood I know, who also researches things to the nth degree and runs the only Green Energy Centre in Umbria (a bit like setting up a vegan food shop in Texas!). It was his recommendation that I buy the 5-8. Finally the teck guy at grundfoss talked me through 'qualitatively' the improved efficiency over constant speed options - he isn't the sales type (definitely back office) and I had already bought one and was happy.

    There's a type of Maths that doesn't prove things but shows them to be true by implication - so, until demonstrated otherwise, I too will hold to my view.

    Sorry to be long winded!
  16.  
    Conversely, there is something called cognitive dissonance where by our self protective minds create a scenario where a potentially lesser situation appears to be the better in some way. So, anyone with an energy monitor and an 'old fashioned' constant power pump, pressure switch and large accumulator want to compare energy usage and water usage for a week or 2. It won't approach the whole life cycle cost issue but I for one would be very interested to see how much more power (if at all :wink:) my pump uses.

    Do you have such a beast Evan?
    • CommentAuthorevan
    • CommentTimeJun 14th 2010
     
    No, never needed a water pump of any sort (living in Scotland probably helps) - my experience is with oil hydraulics.
    But I'd love to hear some comparative results too, and will be happy to concede if the Grundfoss looks better!
  18.  
    C'mon then Peter in Hungary, you sound like the type of man to have an energy monitor....
    • CommentAuthorcontadino
    • CommentTimeJun 15th 2010
     
    I know that the submersible pump/mechanical pressure switch system I have in place consumed just over 31kwh last year, out of a total consumption of 286kwh for the whole household. At €0.11/kwh that equates to a cost of €3.41/year for a completely off-grid water system. The switch/pump/EV/etc are all at least 10 years old. What I can't tell you (because I don't know) is the volume of water consumed over the course of the year.

    A replacement pump setup would cost me about €350, and the payback period against your pump would be 450 years.

    However, any system you pick will be different from yours, as you have a massively high specced system, a completely different set of requirements, and a huge implementation budget. So as far as I can see, comparisons are pretty pointless.
  20.  
    Hi,
    I (as most do where i am) have a pressure set - Dab Aqua series being most common. It dosnt seem to have used a great deal of electricity although with a relatively small cold water accumulator if the pressure set point is not adjusted it will kick in every time the taps are even slightly opened. The electric consumption is meaningless with out the volume. I cant see why a decent sized cold water accumulator or a headter tank would not have achieved the same. Some folk i know who's wells are a much greater distance away use an extra (and larger) accumulator. In terms of cost: the pump/motor/vessel/pressure switch on a small skid is £300ish all in.

    Cheers
    Mike up North
  21.  
    Hi,
    We are off of mains water, so if we as a 2 adult 2 kids house use 150lit/day each (that’s 50 hot and 50 cold??) to include all bathing, toilet, cooking , drinking etc etc then in 1 year we shift 219k litres of water per annum. If the pump runs at 20 lit/min (it can of course do more dependant on lift vs delivery pressure), then the pump is running for 657k seconds per annum (30 minutes per day). If the pump is rated at 1kW, then we use 657,000 kW per annum (i.e. 657,000,000 J/second) so divide 657,000 by 3600 to get kWh = 183. This is units so at say 11 pence per unit gives £20 per annum.
    So about £1.50 - £2 of electric per month should cover pumping in all water needs.
    It’s based on a bit of a guestimate of water usage, but if it’s out by 100% it would only double a relatively small number, it doesn’t feel to be a whole order or worse out.
    Can some one reality check that??

    Hope the maths is right.

    Cheers

    Mike up North
    •  
      CommentAuthorted
    • CommentTimeJun 16th 2010
     
    "then we use 657,000 kW per annum "

    Well, the notional units there would actually be 'kiloWatt seconds' rather than kW, but otherwise the figures look OK.
  23.  
    Golly, I have inadvertently opened a can of worms here. Of course it is right that the spec is high: over 80 lt/min up a 20m head, I just hope I do eventually get the house set up and then the business in to need that! So, actually comparing dis-similar specs is a little pointless even if the same volume of water is moved. Still it is intriguing. I shouldn't bother with the costings because not only is electricity very expensive over here but mine is wrapped up in a PV scheme as well so it is Kil Ar Wot ours that is relevant.

    We use a lot of water each year (treble yours Mike(U-N), not only do we have 23m3 pool (full water change this year - but every year requires topping up), we also irrigate many pots and one small lawn, for which is too difficult right now to get a pipe too from our rain water system that does all the other stuff.

    Crikey Contadino 286 kWh pa total house usage - talk about setting targets high (low), I think I need to carefully reconsider which planet I am on!
    • CommentAuthorevan
    • CommentTimeJun 16th 2010
     
    Re-reading the thread properly (the bits about the swimming pool and the 5 showers!) I now think I could see this sort of pump fitting the bill.

    Horses for courses and all that.

    Do switch it off at night though!
    • CommentAuthorcontadino
    • CommentTimeJun 16th 2010
     
    Well, we're currently on target to scrape in at under 250kwh for the year. Although sometimes it seems pointless worrying about it when the government seems intent on building nuclear power stations in UNESCO world heritage sites down here, just to keep you power-hungry northerners happy.

    Here's some interesting figures for you on average annual country home electricity consumption by region (kwh):

    Sicilia: 476
    Calabria: 514
    Puglia: 523
    Lazio: 831
    Le Marche: 760
    Piemonte: 978
    Toscana: 1.129
    Umbria: 1.158
    Veneto: 1.350

    These are from a supplement from Il Quotidiano from maybe 3 months ago and are figures from 2008.

    So if 500kwh (if I understand correctly) is a sixth of your anticipated electrical consumption, then yes, maybe you do need to have a bit of a re-think.
    • CommentAuthorGotanewlife
    • CommentTimeJun 16th 2010 edited
     
    The average usage in the UK is around 5000 kWh and I expect to use 6800 but we have a pool pump, an irrigation pump and an unexpectedly powerful wood burner fan. Plenty of opportunity for some reductions that I have not yet explored though. I wonder what the avg US house uses...
    • CommentAuthorcontadino
    • CommentTimeJun 16th 2010
     
    Yes, I've seen figures of between 3.000 and 7.000 kwh as the UK average, but it often includes heating.

    Besides, you're not in the UK.
  28.  
    The figures are not in my defence but a sanity check - no need to slit my wrists in abject failure yet....and for sure when I set to it I can reduce this figure. We have only today had our elecky bill and we are making 96% of what we use but now we have the pump on top. I am sure we can reduce this figure but not on this thread.
  29.  
    gotanewlife
    Yes I have got an energy monitor, its the water meter that is the problem, I am hoping to get that sorted next week and I will post the results

    Mike (up north)
    When we came to Hungary we were in a flat for 8 months, 3 adults and 2 children. our water usage was 11cu M per month which is about 366 per day and as it was a flat this was domestic only, so your estimate of 150 lt / day might be a bit off

    Peter
  30.  
    Those figures have just got to be wrong - not 500 - 1000kWh per year. Thats only 1.5 - 3kWh per day, average. A fridge uses 1kWh/day alone. Lighting another 1kWh easy, Tellys, Washing Machines, Heating, computers, kettles, coffee makers, etc. etc.
    Maybe they are per quarter. I just don't beleive them!##

    Tim

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