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cold water recirculation

(47 posts) (31 voices)
  • Started 13 years ago by dykesa
  • Latest reply from Charos

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  1. dmachado

    dmachado
    Member

    Just my experience:I have some 25 meters of plumbing from the hot water tank.

    We used to waste some 50-60 liters just to get hot water to shower and this was making me sick. Anywhere between 2.000 and 3.000 liters of water were being wasted, MONTHLY.

    So, I connected a small fresh water pump from Laing, pumping from hot to cold water pipes under my bathrooms wash basin.

    Before taking a shower, I turn on the pump, it draws the cold water from the hot water pipes and feeds the cold water intake of the hot water heater, creating a recirculating ring. In 5 minutes we have hot water available.

    PLUS: we do not waste energy sending warm water down the drain until it gets hot enough to shower.

    As a result, my bills went from 11-12.000 liter/month to 9-10.000 liter/month, savings of at least EUR 6,00/month. The pump has already paid for itself a long time ago. In 4 years I have saved over 100.000 liters of fresh water and about EUR 300,00.

    Can't get simpler than that.

    Posted Friday 16 Mar 2012 @ 10:54:35 am from IP #
  2. TonyT

    TonyT
    Member

    Clever:
    At the bathroom basin, by pumping from the hot water pipe into the cold water pipe, the cold water that is in the pipe before the hot water arrives automatically refills the Hot Water Tank.

    Simple.

    Brilliant !

    Posted Saturday 17 Mar 2012 @ 8:02:20 am from IP #
  3. TonyT

    TonyT
    Member

    BUT

    (a) If the pump runs for too long, it will fill the cold pipe with hot water.
    - a timer could solve this.

    (b) When the pump is "off" and the cold tap is opened, water from the "hot" pipe will flow through the pump and out of the "cold" tap.
    - a solenoid valve could be added so that water flows through the pump only when it is "on".

    (c) How could the pump control system be designed so that a pumping cycle happens automatically when the hot tap is opened ?

    Posted Saturday 17 Mar 2012 @ 7:03:26 pm from IP #
  4. dmachado

    dmachado
    Member

    Hello, sorry to reply so late...!

    Thanks for the compliments.

    a) this is true, in my case 8-10 min. is the necessary time, a timer and a beeper could improve the use, and eliminate the "I forgot about the pump" problems you get in the beginning;

    b)this is not so true, water always uses the "shorter" path, so if you see the pump in the center of an H setup between the two taps, when we open the cold water we never get warm water except when the pump was just working; even then we get cold water quickly because it comes from the front of the hhouse - shorter path - and not from the remaining cold water pipes into the hot water tank;

    c) the pump I have is a slow speed one, so you although you could do that, I guess you just have to realize that you need to wait a few minutes in order to stop wasting water - just go about your business while you wait for the hot water "to arrive"...

    Regards.

    Posted Monday 9 Jul 2012 @ 11:45:11 am from IP #
  5. johnmath

    johnmath
    Member

    Or buy the right tool for the job...

    http://net.grundfos.com/doc/webnet/homeperformance/apreg/media/5889/comfort.pdf

    This type of pump has been around in other countries for decades

    EDIT: Oops, that sounds a bit blunt. You are to be congratulated dmachado for working it out yourself. I am just frustrated how there are often off the shelf solutions available that we don't see here in OZ because "there is no demand for that type of thing..."

    Posted Monday 9 Jul 2012 @ 12:11:20 pm from IP #
  6. sun2steam

    sun2steam
    Member

    Is it legal (or 'Watermark') to pump water from the hot water circuit back into the mains water?

    Posted Monday 9 Jul 2012 @ 12:56:49 pm from IP #
  7. johnmath

    johnmath
    Member

    sun2steam said:
    Is it legal (or 'Watermark') to pump water from the hot water circuit back into the mains water?

    Don't know, but Grudfos sell the pump I linked to in Australia, $280 at Aqua Pumps:

    http://www.aquapumps.com.au/hot-water-pumps/137-up15-14b-.html

    Plus you can buy a Rinnai preheater that works the same way if you have a spare $2,500 (!!!) What a joke

    http://www.rinnai.com.au/index.php?option=com_products&task=product&Itemid=2&id=287

    EDIT: I stand corrected - it can mow be had for $578

    http://www.scooper.com.au/catalog/item/6653749/6520888.htm

    Posted Monday 9 Jul 2012 @ 1:12:52 pm from IP #
  8. dmachado

    dmachado
    Member

    johnmath said:
    Or buy the right tool for the job...

    http://net.grundfos.com/doc/webnet/homeperformance/apreg/media/5889/comfort.pdf

    This type of pump has been around in other countries for decades

    EDIT: Oops, that sounds a bit blunt. You are to be congratulated dmachado for working it out yourself. I am just frustrated how there are often off the shelf solutions available that we don't see here in OZ because "there is no demand for that type of thing..."

    Hi, no offense taken, I did get the idea from these types of pumps... I just spent 1/3 of the cost of these Grundfos pumps and I got the same results. My house doesn't have a recirculation pipe but it works anyway...!

    Posted Monday 9 Jul 2012 @ 2:28:43 pm from IP #
  9. johnmath

    johnmath
    Member

    dmachado said:
    I did get the idea from these types of pumps... I just spent 1/3 of the cost of these Grundfos pumps and I got the same results. My house doesn't have a recirculation pipe but it works anyway...!

    I plan to do the same - it's on the big long list of worthwhile jobs. Simple manual systems or ones based on a timer or thermostat to finish the cycle and using the cold pipe as the return pipe have been used for decades in North America.

    I inherited a nearly new Rinnai instantaneous gas water heater when I bought my current house. It is clearly a well made, durable unit and highly efficient at moving the heat from combusting gas into water, but...

    I wanted to take advantage of the Preheat button on the Rinnai wall controller, but it does not work with third party pumps like the Grundfos, only with Rinnai's proprietary system, and that requires a return pipe from the far end of the house. My property is a 112 year old villa with four extensions and five different roof spaces, so that just isn't practical. And then there's Rinnai's exorbitant expense for their proprietary system. And it isn't energy efficient in its implementation...

    The heater is designed for Japan with an efficient 100 Vac switch mode power supply. For Australia, the unit is fitted with a roughly 60 VA E-core 240 to 100 volt step-down transformer that sits there burning away about 6 watts day and night like the light bulb in a teenager's bedroom. Calculated from my data logging, 94% of the electricity used by this unit is standby wastage, about $25 per year at my current cost. For a dollar more at the time of manufacture, they could have used a toriodal transformer and cut that wastage by 90%!

    The heater has a cool down cycle when water flow stops. The purpose of this is to "purge the combustion chamber" but it defeats my wisdom and it is not explained why in the owner's, installation or service manuals it needs to run for 65 seconds, a couple of seconds would be enough. The result of the cool down cycle is that you ALWAYs have to draw off cold water even if you have only a minute before been running hot water. With the hand basin in the bathroom just 2.5 meters from the water heater (as the crow flies), this takes 30 seconds! (There is a lot of pipe in the heater exchanger in addition to the pipe between the heater and the basin.)

    Insulated pipes are a waste of time, because drawing off the cold water from the cooled down water heater chills the pipes anyway!

    What kind of moronic thought processes are behind designs like this?

    Posted Tuesday 10 Jul 2012 @ 12:37:17 am from IP #
  10. dmachado

    dmachado
    Member

    I think that what you need to do is to slowly recirculate hot water WHILE having a shower, so the heater won't stop... similar to what I have, just leave it on, turn it off when you finish showering...

    Posted Thursday 12 Jul 2012 @ 1:34:20 pm from IP #
  11. calytrix

    calytrix
    Member

    Check out the Redwater valve http://www.redwater.net.au/index.php/tech-info.html

    Aussie invention - no requirement for electricity, timer or push button, just operates when the tap is turned on (the tap runs at the veriest dribble while diverting the cold water out of the hot water line, and then comes on full when the hot water comes through). There is a couple of video demos at http://www.redwater.net.au/index.php/home.html

    ...I'm guessing it must use a mechanical thermostat?

    The specified use is to divert the run-off cold water back to a tank or similar, but it says that the diverted water is at the same pressure as the supply, so I can't see why it couldn't be connected into the cold water line to feed back into the hot water system, the same way as the pumped systems.

    It wouldn't be as quick as the pumped systems, but it would still save the water (and also wouldn't cost extra $$$ for electricity... or even the wiring for the electricity)... and the valve itself is a lot cheaper than the pump systems (which means that it's affordable to put one in each bathroom, the laundry and the kitchen!($110 each - order from the website.)

    I've sent them a query about running the diverted water into the cold line - will update this when I get a reply.

    ...no, I have no connection with the company except that I've been trying to hunt down a pumped system that will run on 240v (since anything bought from the USA is designed for 110v, and I'd prefer to avoid having to run it from a transformer), and I stumbled on this, which looks better in a lot of ways.

    Cheers,
    Liz

    Posted Saturday 1 Mar 2014 @ 12:48:58 pm from IP #
  12. calytrix

    calytrix
    Member

    Just got a reply back from Redwater Australia - very prompt, I might add!

    Andrew very properly pointed out that with the diverted cold water from the hot water line directed into the cold line, there's no pressure differential to make the water run through the pipes! (...obvious when you think it through, but I clearly didn't!)

    Still looks very cool... just need to send the diverted water somewhere useful. (I think mine will be running into our proposed rainwater tank. Alternatively, you could run it into the garden or something.)

    Cheers,
    Liz

    Posted Saturday 1 Mar 2014 @ 1:06:27 pm from IP #
  13. calytrix

    calytrix
    Member

    PS - the pumped systems I've seen use a temperature sensor to cut the pump off when the hot water starts coming through, so you aren't supposed to get an appreciable amount of hot water in the cold water line.

    Posted Saturday 1 Mar 2014 @ 1:08:29 pm from IP #
  14. johnmath

    johnmath
    Member

    There are pumps for 240 volts, e.g. http://au.grundfos.com/content/gpa/en_AU/products/find-product/comfort.html

    Posted Saturday 1 Mar 2014 @ 1:13:46 pm from IP #
  15. Morbo

    Morbo
    Member

    It takes 8 min for your hot water from the hot water system to the tap? Is your hot water system in another suburb? Mine used to take about 1 min, even though the system was right in front of the tap. Plumbing went into the roof, over the living room, back to the tap. Now thats history. Only takes seconds.
    Pumping 8 mins worth of cold water back into the system, how much energy would that need to heat up?

    Posted Saturday 1 Mar 2014 @ 9:03:50 pm from IP #
  16. Johnnojack

    Johnnojack
    Member

    See "Hot water recirc pump install" thread I have just bumped up.

    Posted Friday 7 Mar 2014 @ 10:39:38 am from IP #
  17. Charos

    Charos
    Member

    What about the Enviro Water Saver? Isn't that the sort of thing the original poster was after?

    http://www.enviro.net.au

    Posted Wednesday 10 Jun 2015 @ 10:10:46 am from IP #

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