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On-demand hot water circulators

Post in 'The Green Room' started by cbrodsky, Jul 5, 2007.

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  1. cbrodsky

    cbrodsky Member

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    Last year, I remember a fairly vigorous debate on hot water circulators. I have a big problem with the fact that these are often billed as "green" devices when in fact they spend a lot of time keeping pipes hot when water isn't being used. No doubt they save water, but they also waste heat.

    That being said, with our recently added solar HW system adding about 20 feet to our total hot water supply distance, I am looking to allevaite this delay as I hate to throw the cold water down the drain waiting for the hot water to arrive. I do understand the motivation.

    Having done some more looking around, it looks like there are a couple really nice solutions out there that recirculate on demand, and easily mount undersink. These alleviate my concern of circulating hot water whether you need it or not and seem to be a much "greener" solution to the problem. The main drawback I see is you have to press a button when you go into the bathroom in the morning to trigger it, or while you load up the dishwasher, for example, and it will still bring the water up to temp much faster than a low-flow faucet or showerhead. That's a simple tradeoff I'm happy to make to save oil in the winter when solar isn't doing the job 100%. (and if that's too much work, some even offer motion sensors so by the time you've undressed, the water is hot :)

    My other concern with these was that they are not cheap and I need to be able to trigger it from our master bath, or from our kitchen - the two main places we often need to get hot water. Well that problem is apparently solved - they now offer RF wireless switches for about $20 that let you actuate it from anywhere in the house. Since our kitchen is on the same circuit, this looks like it may do the trick!

    From what I've seen, I'm leaning towards the Metlund systems:

    http://www.hvacquick.com/mtpmconfig.php?fm=S50

    but there is also a similar competing model from a company that also does a thorough job of debunking the problems with systems that run on timers or 24x7:

    http://www.redytemp.com/

    If anyone has experience with either, I'd be interested to hear it. There is a third system called Chilipepper that is cheaper but a couple things I read said it is very noisy. It looks like either of the above two would do what I'm looking for.

    One other interesting point I read on these was that you have to be careful with oversized systems that push too hard to keep hot water ready at all times. In some cases, esp. commercial installations that aim to always keep the lines hot, the flow velocities are far too high and they ultimately degrade copper pipes from excessive turbulence. For that reason, I'm tempted to go a little undersized on the device even if it takes a few seconds longer to exchange with the cold water return to bring up the hot water... the plumbers that did this place weren't exactly top notch and I don't want to stress their handiwork :)

    -Colin

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  2. keyman512us

    keyman512us Member

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    ...NYS, Interesting situation.
    Generally "re-circ" lines are required by code if the most distant fixture is 100 feet away (measured along the piping). Good practice is to consider it after 65 feet. Not much heat is lost (if the pipes are insulated).

    Most HD's and Loews' carry a fairly 'user friendly kit' the 'slightly above average' homeowner can install without too much difficulty. Personally, if I was going to install one, I would start with a TACO 006-BRONZE circulator, fairly pricey (lists for around $145) and then go from there. With a little planning, you could set it up real nice.

    I could offer a few suggestions on how to activate it...but let's see who else in the forum has ideas...lol
  3. cbrodsky

    cbrodsky Member

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    Good point - those pumps can be had for just over $100. Then if you were particularly good with electronics you could make your own differential thermal controller. Commercial ones seem to be $80+ (used in solar applications) - if one could be found cheap, then all you'd need after that is a relay that could be activated from a switch to run the pump until the differential controller reaches the setpoint, along with a mechanism to time out after something like 1-2 minutes and not run again until someone presses the switch. The on-off controls would be a little easier to design cheaply. The wireless automation stuff is getting more and more straightforward these days as well so some people use X10 for a fairly cheap solution. Maybe some electrical engineers on here have some ideas?

    Metlund (ACT) has what look like two fairly strong patents with claims covering any such on-demand system so licensing fees may be part of the reason for the more typical $300-400 cost of these systems as well as the lack of market participation by more companies. I'm not aware of any systems at Lowes or HD that work like this as they would likely infringe if they had all the same features - perhaps they're using simpler manual control pumps?

    -Colin
  4. jjbaer

    jjbaer New Member

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    Only problem I see with these devices is this: generally, hotter water is a breeding ground if there's any bacteria in the water and for that reason they tell you only drink and use cooking water drawn from the cold water tap. These recirc devices take water that's been sitting in the hot water line (and has cooled) and use the cold water line to recirc it back to the hot water tank. This means that without a dedicated hot water return line that your cold water line is filled with what formerly came from the hot water tank so if you turn on the cold water line to get drinking water or water to cook with, that you're essentially using water that sat in the hot water tank and may have higher bacteria levels in it. While only a minor problem, it's there none the less and some people may chose to avoid this device for that reason. So...if this bothers you, this means that now you have to purge your cold water tap until you think you're getting "fresh" water whereas before you purged your hot water until hot water flowed.....so....what's the difference....still wasting money (water) except now it's cold water........but I guess you're saving the cost of energy required to heat it but then you've now got this "parasitic load" sucking power 24/7 under your sink "awaiting your command" to produce hot water..............LOL

    And while use of a dedicated return line obviates this potential bacteria problem, it's also negates the convenience of these devices because their selling point is that you don't have to run a dedicated line to use them........a good example of the theory of unintended consequences......LOL

    Bottom line: between this device sucking power 24/7 and having to purge water anyway, no way this thing is a "net green device".......in fact, my guess is that it adds to the pollution problem........
  5. cbrodsky

    cbrodsky Member

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    Thinking about this some more... this is probably quite feasible for well under $200.

    Rather than using a differential control, a much cheaper solution might be to use a water heater thermostat ($20):

    http://kingsolar.com/catalog/mfg/other/07551.html

    Assuming you can get it to sense the hot water pipe temperature, when powered up it could just turn on a circulating pump that pushes cooled down water from the hot to cold line until the setpoint temperature is reached.

    Then, for $27 more, here is a simple timer with a sharp looking wallplate that you could use to activate the system and then shut down after 5 minutes (or other time intervals):

    http://www.smarthome.com/4254w.html

    Unfortunately, the cheapest cast iron Taco circulator (007) for only ~$60 is probably way too big - it pushes up to 20 GPM in a no-head application like this. (maybe could be used with something to restrict flow rate?) It would let you have a complete solution for about $100. The Taco 003 or 006 both look like good options but run into the low to mid $100 range, so the entire system would push up to $200.

    -Colin
  6. cbrodsky

    cbrodsky Member

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    Why would you have a parasitic load? These have a switch that only powers up when a demand timer is triggered. (may not be true for other systems that constantly monitor and automatically keep the lines hot though...)

    Can't say I worry about drinking what was in the hot water line - I trust that it's all potable water as diffusion will let them all intermix. To my knowledge, most houses don't use a check valve that isolates the hot water branch from backfilling the cold water line, but correct me if I'm wrong in that assumption. Interesting thought though and not one I've run across in all the discussions on these devices.

    Actually, I often fill stove pots with hot water as using the "free" solar means I spend a lot less time and electricity getting it up to a boil on the stovetop :)

    From my perspective, the tradeoff seems to be running a ~50W pump for 1 minute (0.00083 kWH) to conserve roughly 5 gallons of water assuming it previously took you ran your 2.5 GPM faucet for two minutes to bring it up to temp. (these systems typically pump at least twice that rate when exchanging water internally) Scaling this up, for each 1kWh of energy, you save 6000 gallons of water from going down the drain.

    On top of that, you've also avoided the cost of pumping up that water from the well, along with the fact that you send the room temperature water back to your cold lines vs. bringing in even colder groundwater. I think the energy/groundwater net is dramatically positive unless you are holding all your hot water lines hot even when you're not necessarily using hot water.

    -Colin
  7. begreen

    begreen Mooderator Staff Member

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    I was part of the debate. True there is a cost, but if the lines are insulated like we did, then it's really trivial. Actually, we noticed a slight drop in costs once it was installed. I chalked that up to less water being heated. My wife will not tolerate stepping into a cold shower or washing her face with cold water. Unless I keep a bucket in the shower to catch the water that runs until it's warm, it's all wasted.

    FWIW, I love the Grudfos Comfort Series system. Has the electronics and timer built-in with a tiny pump. I set it to it's lowest recirc temp. The system has it's own 1/2" recirc loop on the hot water side of the 3/4" feed to the second floor bath.

    http://www.plumbingworld.com/comfortbygrundfos.html
  8. jjbaer

    jjbaer New Member

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    I'm thinking that since this receiver is plugged in the wall as part of the unit, it sits there monitoring and "listening" for an incoming signal and that takes power.....something like a garage door opener and I'm guessing that's a 24/7 parasitic load........so...if I'm correct, the analogy goes like this.....the trade-off now seems to be running a 50W pump for 1 minute (0.00083 kWH) AND using a parasitic load 750 hours a month to conserve roughly 2 gallons of water and I might do this only once a day when I take a shower........might buy one for convenience but I think the parasitic load will raise your electric bill

    I do want to caveat my earlier response...depending on your situation, the recirc of hot water into a cold water line only occurs from the location its installed and back to the water heater and I wouldn't normally take cooking water from a cold faucet in the bathroom. Also, the cold water branch to the kitchen (where I would take water) only gets a small fraction of the hot water as the kitchen branch is also close to the water heater. So...I'd be more concerned with the load it uses......maybe someone could plug a kill-a-watt meter into one and report back.....
  9. Eric Johnson

    Eric Johnson Mod Emeritus

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    You can pick up new Taco 006 and 007 circulators, bronze and cast iron, on Ebay for about half what you'd pay retail. Just watch the auctions. There are some nice Grundfos 3-speed circs on Ebay as well.
  10. cbrodsky

    cbrodsky Member

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    Ah - for wireless sensing, yes, I would absolutely agree that there will be some parasitic load if you had such a feature installed. (will have to look at what they really consume - especially if I build my own "hearth.com" edition!) :coolsmile:

    But if you don't need wireless, which you wouldn't need if you are only worried about this for your shower / morning bathroom sink use, then you would just install a hardwired on/off switch that is connected to a timer that breaks the circuit once it's off. You only need wireless if you want to trigger the same device from elsewhere in the house.

    BTW, keep in mind you conserve roughly 2 gallons of water every time you use hot water - not over a month. (in many cases more depending on your layout, if you use hot water in more than one location or more than once a day, etc...) So this adds up to a fairly significant volume over time.

    Overall, I think with the right design, these are great devices. But the ones such as Grundfos and others that run 24x7 or even part of the day on a timer become a trickier tradeoff calculation. Insulation can help, but even there, an insulated hot water pipe doesn't hold heat all that long. For example, assume the case where you lose 20 degrees of heat in the insulated pipes every 30 minutes, causing the system to recharge the loop. And assume the loop is 5 gallons total. Then every hour, you lose:

    1 BTU/(lb*F) * (20 F) * 5 gallons * 8.3 lbs/gallon * (2 cycles per hour) = 1660 BTUs/hour

    unless during the hour you were already planning to use hot water. Assume that you let it run 8 hours per day and you're giving off 13,280 BTUs/day. If you have an oil boiler that heats water at 70% efficiency then you're burning about 4 gallons of oil per month to run this device keeping water lines hot. Of course in the process, you may have saved a few hundred gallons of water, so if that cost is more, or you live out west where water is scarce, you could easily come out ahead financially. And the assumptions may change depending on your situation. Some might argue that you could reduce the amount of time you need it to run automatically on a timer if you can also bring hot water on demand when the timer is off.

    I just don't see the Grundfos system as the greenest option when it's so easy to just push a button and charge it only when you want it on demand, especially with wireless technology to make it so easy to install. Both will save a lot of water, but an on-demand setup will save even more energy.

    -Colin
  11. cbrodsky

    cbrodsky Member

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    Good tip! They are indeed cheap!

    What would be the pros/cons of bronze and cast for this application? There are 007-F5 pumps for $30... if this could be throttled down through a restrictor to 5GPM or so, it would enable a really cheap system - possibly no more than $75 even after finding adapters and such. Coupled with how little time this pump would actually run, it might not really matter if it was stressed by forcing it through something to create and artificial "head" to slow the pump down a bit. (not sure I'd want to let it flow at 20GPM through my 1/2" pipes...)

    Will also look at the Grundfos pumps.

    -Colin
  12. Eric Johnson

    Eric Johnson Mod Emeritus

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    You should really use a bronze circulator for fresh (oxygenated) water applications, although cast iron will work for years without a problem. The only downside is that you might get a little bit of rust in your water, and the pulp will eventually fail. But if a $30 pump lasts you 5 years, why not just replace it?

    Anyway, bronze is recommended for fresh water. Cast iron is generally used in closed loop applications like hydronic heating systems where there's very little oxygen.

    BTW, the 007 is a nice little pump. They run quiet and don't use much electricity. If you need flow control, you can pick up a 007FC, which has a built-in check valve, for about the same price. The Grundfos 3-speed pumps also have a flow control valve built in. Both run direct off regular 120v AC.
  13. jjbaer

    jjbaer New Member

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    Colin,

    Good point! I agree that if it's on an "on demand switch" that there are little to no parasitic losses and this is the way to go.
  14. begreen

    begreen Mooderator Staff Member

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    Agreed. I'm lazy. The grunfoss system takes care of itself and that appeals to me. But there are certainly ways to tweak the system to make it even better.
  15. keyman512us

    keyman512us Member

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    Very spirited debate....I like it. Some things I would like to point out that have been "hinted at":

    Recirc lines, anyway you want to look at them are "energy savers". True they do use some electricity...but look at it this way: You run the water "manually" until you get "hot water"...What are you doing??? For every drop of water (forget 'water conservation' for a minute)...every drop of water is replaced into whatever type of heater you use at 56 degrees farenheit or colder...For those on a well...How cold is your water when it "enters the system"???? Probably a lot colder than 56 degrees I would hazzard to say. By circulating water back into the heater at room temperature vs. ground temperature...is where you save energy.

    Without getting into an algebra equation...I think the economics are fairly easy to contemplate.

    The best way to control the re-circ??? (If I were doing it...) Would be 'idiot proof'...run 'line voltage' off the bathroom light switch to a simple "adjustable time-off after delay industrial 'cube relay'..." (about $20 bucks at the supply house).

    Doesn't get much cheaper, easier or fool proof than that...every time you flip the lights on...the re-circ would do it's job....

    At least you would know how many times a day the re-circ pump would run. ;)
  16. cbrodsky

    cbrodsky Member

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    Yes, I would agree that on-demand recirculation is better than no recirculation; the energy recapture you describe by pumping back the room temperature water is certainly better than throwing it down the drain with its associated energy.

    The main point that is sometimes missed with these systems is that if you don't have a need for hot water, you're better off doing nothing until you do. If these systems run anyway, you now have period of net losses. You are re-heating that water and letting it cool in your pipes whether you need it or not.

    In fact, this is why these systems will often only qualify for utility rebates if they have a timer or demand switch to minimize unnecessary operation. It is always a net loss of energy unless you already had a reason to use the hot water at the moment that the recirculator charged up the line.

    I see that many western states are starting to offer incentives for these systems which is good news - used properly, they look like a great tool. And hopefully prices will decline as they enter the mainstream.

    -Colin
  17. begreen

    begreen Mooderator Staff Member

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    Some technical points. The recirc does not return "room temp" water to the tank. It returns water which is below the set point on the thermostat. In our case this is about 105 degrees. The return and hot water lines are insulated. Our system does have a timer and observation shows that it runs about 2-3 times/hr. when timer is in "on" mode. It runs for about 10-15 seconds each cycle. I've set the timer for 14hrs on and 10 hrs off - or total running time of approx. 10-15 minutes per day. The motor draws 25W for say 15 minutes a day or approx. .006 kw/hrs per day. When the warm water is returned to the tank, it does not directly mean that the hot water heater will come on. The warm water returning is often not enough to trigger the thermostat on the heater to come on.

    I think the savings of not having multiple people run gallons of (expensive) water per day as they wait for hot water offsets the operational costs easily. Could it be made even more efficient? No doubt, but I've put that time and energy elsewhere. Currently I'm directing my efforts towards dollars per day savings.
  18. cbrodsky

    cbrodsky Member

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    Keep in mind - the only reason it runs 2-3 times per hour is because heat is lost through your pipes. If your insulation was perfect or the losses were completely negligible, it would never run. But it sounds like your system is running 30-50 times per day flushing in hotter water and returning cooler water. While it may not be enough to trigger your hot water heater every time, it is indeed steadily extracting heat all day long as this cycle runs. This is a serious parasitic loss IMHO. The electricity to run the pump is nothing to worry about in comparison. Also, the higher your setpoint, the warmer you're keeping your lines all the time, and thus the faster the rate of heat loss to the surroundings, compounding the losses.

    I suspect that Grundfos just can't engineer around the ACT patent for the on-demand switch, but I believe you could easily add a wireless on-off sensor to the Grunfos systems, at which point they would be markedly more energy efficient. In fact, maybe a third party could sell such a device and the end-user could add it on their own.

    No question any of these systems save water, and with pricey water, that may be more important than the wasted heat energy. But with these constantly running systems, they are wasting heat energy - there is simply no getting around that fact if you do the energy balance.

    -Colin
  19. begreen

    begreen Mooderator Staff Member

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    As noted, the temp set point is very low, just above body temperature. The losses are small in this system and we noticed a net drop in the electric bill. I attributed this to decreased hot water consumption. If you run the tap less to get hot water that means less cold water (at 45 deg in the winter) entering the tank to replace the withdrawn hot water. Yes, it can be made more efficient, but I am going after dollars not pennies at this point.

    As to why Grundfos has it's current design vs an on demand system? I suspect simplicity, convenience and the fact that there is no need for user intervention has something to do with it. With the Chili-Pepper type of system one has to remember to hit the button about a minute before they want hot water. Not a big deal at all, but one that guests, etc. might forget, thus defeating the system. FWIW, I would think there are several ways to engineer around it if Grundfos felt there was a strong market demand.
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