What Size Recirc Pump
I would like some help with a new DHW loop. First, I'll give some experiences I've had and then give you my current situation hoping you can advise me on my next move.
I built a new home in Missouri in 1999 with radiant heat in the floors and a hot water loop for DHW. The DHW system had a propane instant hot water heater by Paloma feeding into a 20 gallon electric heater. The loop encompassed the electric heater (EH) and the recirc pump. Plumbing was copper 3/4" loop and it was insulated. I had a Ranco controller set for 115 degrees high and 105 low controlling the pump. It was nearly a maintenance free system and we always had hot/warm water at all faucets almost instantaneously. The Paloma only kicked on if we used hot water. I didn't have any monitoring equipment hooked up to know what was taking place. Installed it, set it and forgot about it.
I just built a new home. No radiant heat but I do have the DHW loop. I wasn't as involved in the new system in spite of being the GC on the build. I requested a 199,000 btu Navien propane and this time I asked for a 50 gal. electric HWH. The plumbing is Pex-a with copper at the heaters for a few feet until it converts to Pex-a. The 3/4" Pex loop is not insulated yet. The contractor installed a Grundfos bronze pump. Not 100% sure but I think it is a 1/40h.p. cheapie running 24/7.
We went on vacation and I unplugged the recirc. When we returned I plugged it in and held my hand on the return pipe to see how long it took to get hot water through the loop. It was approximately 105 seconds. That got me thinking. It's just my wife and I. We use 3000gal/month or less. Having that tiny pump run 24/7 is certainly a waste, more so for the EH than the pump itself. I could control it like I did at the last house with a Ranco controller. That would cut down on some waste. Now I'm thinking about trying to control it with motion sensors.
We are retired. We might use a faucet at any time of the day or night. We might do laundry at 8:00am or 7:00pm. We might take a shower in the am or pm. No chance a "Smart" pump like Taco offers will be able to "Learn" our routine because we don't have a routine.
Lutron makes a controllable 110v outlet that mates with their motion sensors. I could install a motion sensor near each faucet and have it kick on the pump only when we walk near the faucet. Only pitfall I see of this is if we used the delayed start function on the dishwasher or laundry washing machine going through its cycles while we aren't standing (moving) in front of it. However, those two appliances have self contained means of heating the water.
So, if this tiny, 1/40hp pump takes 105 seconds and probably pushes 12-14 gpm on a good day to complete the loop, what size pump would you recommend if I use motion to control the pump? I see some pricey Taco stainless pumps that can push 44-52gpm with no head. Would that be enough to get hot water through 200' of 3/4" Pex-a in 10 seconds or less?
Comments
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from what I read you have a tankless feeding a tank with a groundfus or the tankless is feeding the tank and the tank has a groundfus with the recirculating coming off the electric tank ? Npump maybe to small you may want a 009 taco S.S. Or a 26/99 groundfus with an aqua stat
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you do not need much flow through a small recirc loop. The gpm required is related to the heatloss of the loop, probably 1 gpm or less is actually needed.
However the circ needs to overcome the pressure drop of the loop, and if a tankless is in the loop you may need a high head version. Got a pic of how it is piped?
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
Yeah, maybe a picture would clear it up a bit. All of my description has obviously caused some confusion.
What I need to know is how many GPM do I need to push hot water through ~180' of 3/4 Pex-a in 10 seconds or less? To be accurate, the bathrooms will get hot water in the first 50'. The kitchen will be farther down the loop at about 130' then another 50 back to the tank HWH.
As I walk into a bathroom and trip the motion sensor, I want the pump to kick on and circulate hot water through the loop in 10 seconds or less. The pump I have takes 1 minute 45 seconds. I'll be done washing my hands and walking out of the bathroom if I have to wait 105 seconds for hot water.
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that circ is just mixing through the loop and storage tank, how does the tank maintain temperature
Looks like the only time hot water enters the tank is when hot water is flowing ? After time the tank will drop in temperature
Many of the tankless manufacturers show proper piping for a tank and recirc
That should be plenty of pump for the loop and tank, but you need some piping changes
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
Tankless is NOT a part of the recirculation. The tankless only comes on when there is hot water demand at the faucet.
The Taco 009 appears to be a high head/low volume pump with a max of 10GPM.
I'm not using an aquastat. I want to use motion sensing to turn the pump on and quickly circulate water through the loop.
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If you look at the picture, you'll see a gray flexible conduit attached to the tank-type water heater along with two access covers where the heating elements are located within the tank. Electricity flows through the wires in the conduit to those heating elements and makes the heating elements hot thereby heating the water inside the tank. That is probably why it is called a hot water heater (HWH) used for domestic hot water (DHW).
It should be and is plenty of pump if I want to run the pump continuously 24/7. If I want to periodically run the pump to circulate hot water through the loop to afford hot water at each faucet within 10 seconds, I'll need a bigger pump. The question is how big?0 -
To give you a direct answer: not less than 6 gpm. However. Keep in mind that it may take at least your 10 second demanded time for the pump to spin up. Maybe longer depending on the pump.
Not that there aren't ways to get this kind of near instantaneous flow response from a system; there are. Basically what you need is an accumulator, pressurised to some convenient pressure greater than the normal system pressure, connected with a fast acting solenoid valve and kept at that higher pressure by a suitable pump — doesn't have to be 6 gpm, but does have to be capable of maintaining the accumulator pressure, and should take suction from the hot water lines to keep the accumulator warm, and needs a check valve.. The accumulator is connected to the hot water storage tank inlet line, which has a suitable check valve before the connection to the tank. The accumulator is connected between the check valve and the hot water tank. The accumulator has a minimum release volume of 6 gallons (that's not the tank volume, that's the working volume between the accumulator pressure and the system pressure).
The system operation is as follows; the motion sensor trips. This opens the fast acting solenoid valve, which discharges accumulator water into the hot water tank which, in turn, discharges hot water from the tank into the water lines to the various demands (the cool water in the piping is discharged back to the house plumbing, which — because of the check valve on the inlet to the hot water tank — remains at house pressure). A pressure sensor on the accumulator activates a pump (from the house lines) which restores accumulator pressure once the fast acting solenoid valve closes after the motion sensor demand stops.
You will probably, but not certainly, need a water hammer arrestor on the hot water lines, possibly at each fixture, as the pressure spike from the accumulator and solenoid valve may otherwise create a considerable water hammer.
Slightly complex — but you are making a system demand which cannot be met in any simpler or conventional way.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England1 -
so basically you have an electric water heater doing most of the work
What exactly are you hoping to accomplish with that size electric hw tank?
If you look at the commercial units that Rinnai builds a tankless hanging on a 50 gallon tank, a pump keeps the tank heated from the tankless for large batch draws, commercial kitchens for example
A circulator creates pressure difference as soon as it is powered, some of the ECM take 5 or do seconds to boot up. A pressure gauge on the outlet will indicate when flow starts moving
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream1 -
the formulas for sizing a recirculation pump here
https://idronics.caleffi.com/sites/default/files/magazine/file/idronics_21_na.pdf
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
Hi, I'd look into demand controls instead of (or maybe in addition to) motion sensors. You very likely know thirty seconds before you plan on using hot water. If you had wireless remote buttons around the house, you could simply push one and have hot water waiting for you. The most common place to put one is on the nightstand. This way, you won't need a huge pump, or try to push the limits of what can flow through the plumbing.
Yours, Larry
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Jamie and Hot Rod, thank you so much!! We are getting to the meat and potatoes now. I never even considered the fact that it might take a few seconds for the pump to rev up. I have been looking at ECM driven pumps but didn't consider their soft start feature.
Now you guys have me thinking about a different method than using motion sensors. Jamie's idea is more complex than I want to tackle but it sounds like a trick system. Hot Rod, thanks for the link to the PDF. Larry, If I was the only person living here, your option would be great! I'm pretty sure I'd get stink eye from my wife from that option.
So now I would like to know if anyone is aware of a controller that employs both, a programmable timer as well as Hi/Low thermostat? The Ranco Hi/Low controller (ability to set the delta between on and off) worked very well on my old house but now I want to also be able to shut the pump off with a timer from midnight to 6:00am while we sleep. Sitting idle for 6 hours every day should save a little bit in energy and wear and tear.
I've searched Google for hours looking for just such an item but haven't found one. Amazon has something called "Inkbird" which also featured Wi-Fi controllability but it was a POS so I returned it.0 -
Take a look at the Grundfos Alpha recirc pumps, I think all that is built in. I run mine from the GO app.
https://product-selection.grundfos.com/us/applications/domestic-buildings/domestic-hot-water-recirculation?tab=products
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
An example of the calculation. This is with 100' of 1" copper out, 100' of 1/2 copper back from the end. Pex would have a lower heat loss number, so lower gpm probably.
In this example the circ pump needs to be .96 gpm at 2.4' head, a tiny circ pump. I suspect your number would be close to this.
Are you sure your pump is actually moving water? that big screw slot in the rear end can be removed to see if the pump is spinning. Next the loop needs to be purged.
That pump should take seconds to make the loop circulate.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream1 -
May want to consider this. It will turn the circ on and off based on your usage.
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Oh Yeah! That looks like exactly what I am looking for!! This only works via a Bluetooth app, not over the internet from a remote location, right? Does your Bluetooth work from a distance say from main floor to basement or do you need to be closer to the pump to change the settings?
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I did some similar calculations for my situation. I found that 3/4" pex holds .0189 gallons per foot. If I have 180' of that I still only have 3.4 gallons being held in the loop. That should clear out in less than 1 minute once pumps starts. My pump is approximately at my head height (6') with 9' pour so I'm guessing my head pressure is in the 3-4' range. The plumber also installed a spring loaded check valve. I used a swing valve on my old house because I thought these tiny pumps woouldn't produce enough pressure to overcome the spring pressure of the check valve but it appears to be able to. I'm certain the pump is moving water. I have hot water at all my faucets instantly and as I said in my first thread, the return pipe gets hot after 105 seconds of me plugging in the pump.
Keep in mind that I'm not having any problems with my current system. My original question was to implement a different system to prevent a 24/7 ON situation. The smart pump you referenced sounds like it will accomplish my goals. That pump looks like it's around $600 and I still need to buy some pipe insulation for the loop. Those two upgrades should save me a few pennies a month on my electric bill. 😂
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I saw that unit and read some reviews. Seems to get mixed reviews. If I can accomplish the same thing with the smart controls being built-in to the pump I will probably elect to go that route. Thank you!
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Head in a close loop piping circuit refers to the resistance of the piping valves and fittings in the loop. Nothing to do with the elevation of the piping.
Use the free calculator at PPI.
https://plasticpipecalculator.com/PressureDropHeadLoss.aspx
I used 120' of 3/4 pex with a 1 gpm flow rate. Head would be less than 1 foot.
Most spring checks have a 1/2 psi "pop" pressure, so no problem.
The issue with a swing check at low flow the gate inside may not be opening fully. Sometimes they will rattle if that is the case. A low lead spring check would be ideal. Some recirc pumps have checks inside them.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream1
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