Two sources of power to one electrical pump

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Old 10-29-14, 04:40 PM
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Two sources of power to one electrical pump

Man, I loves me this forum.

I have a lot of DIY miles on my odometer, and the following is a new one for me. New (old) house, takes forever to get hot water around. Previous owner used a Grundfos circulating pump. But I don't want to run that sucker all the time, wasting electrical and propane, nor even just on a timer. Here's what I want to do...

Use a Grundfos aquastat that shuts off the pump when returning water is 115F, and turns it back on when below 105F. Plug that into a timer that will allow power to the aqustat (and therefore pump) for the windows of time we typically need hot water. Say 6-8am, noon-1pm, and 6-9pm. Easy.

Then use a flow sensor at the water heater that detects when hot water gets flowing, NOT on a timer. It kicks on the pump for 5 mins whenever someone turns on hot somewhere. I have located the hardware for this, and it, too, needs to switch power to the pump.

So, how do I wire this? I think the aquastat simply plugs into the timer, and the timer goes into the wall receptacle. Then the aquastat splices into the power wires of the pump (thus controlling the pump). The flow sensor plugs into the receptacle, but how do I also wire in the flow sensor to the pump's power, to also control it?

Thanks!

Aztec
 
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Old 10-29-14, 05:54 PM
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Welcome to the forums!

To answer your question, you would just wire the two switches in parallel. So if either condition occurs (temp drops or there is a demand for water) the pump will run. Of course, they should all be on the same circuit.

To throw a wrench in your plan, I do not really see a need for the flow switch unless the pump blocks the flow of water. The open faucet will be the same as the pump running.
 
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Old 10-30-14, 09:09 AM
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The pump doesn't block flow. The flow switch is to kick on circulating hot water when the timer has the pump/aquastat combo off.

I'd run the pump/aquastat during hours I know we usually need hot water. Then rely on the flow switch for the hours in between.
 
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Old 10-30-14, 06:02 PM
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I'd run the pump/aquastat during hours I know we usually need hot water. Then rely on the flow switch for the hours in between.
I really don't think the flow switch is necessary because normal water pressure will probably move hot water through the line quicker than the pump anyway. I also don't think you need an aquastat, just a timer for those periods when you know you usually need hot water.
 
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Old 10-30-14, 07:32 PM
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I wish. Currently, with the pump, it takes about 90 seconds for hot water to reach the master bath. Without it, it takes 20+ minutes, and 13 gallons of cold water.

So we run the pump and timer now. It's about 90 watts and heats the circuit using propane ($$$$). We aren't exactly sure how much water is in that circuit (we think it is the 13 gallons + maybe another 6). I know, that's a crazy amount of supply line for a house of this size, and it's ridiculously inefficient to heat and move all that. So we have to choose between running the pump all the time (waste 90w + propane), or running only when we think we need hot water and then when we need hot water between those pump times, we have to either waste the 13 gallons or dash out to the garage to turn on/off the pump.

Thus the flow switch can detect an open hot fixture (which you then turn back off), and get hot water to the other end of the house in about 90 seconds, wasting very little. The more I think about it, that may be the way to go. Skip the timer and aquastat. Just deal with the 90 seconds all the time. Plan ahead!
 
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Old 10-30-14, 08:15 PM
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it takes 20+ minutes, and 13 gallons of cold water.
You're kidding...... 20 minutes ??
 
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Old 10-30-14, 09:26 PM
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Even with a 1.2 gpm shower head it shouldn't take but ten minutes to flush through 13 gallons of water. But even that wait time is ridiculous to me along with the wasted water.

It takes about two minutes for me to get hot water to my kitchen sink. Assuming I ever regain my health to the point where I can once again work in the crawlspace I am going to install a recirculating line and pump. My plan is to use low-voltage wiring from a push button in the kitchen, laundry room and both bathrooms that would reset a time delay on operate relay and have that control the pump. I won't know until I actually install the system but I suspect the pump will get hot water throughout the house in just a few seconds and I will set the timer accordingly. For the dishwasher I plan on using a current-operated switch in conjunction with the pump timer to maintain the pump operation during the entire time the dishwasher is in operation.
 
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Old 10-30-14, 09:41 PM
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Nope, no kidding. Low-flow. We actually thought we had a crossover because when it goes that long you're thinking it is never going to turn hot. I've had a plumber under the house and I've studied the heck out of it. It's legit. No wonder the former owner ran the pump 6am - 10pm.
 
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Old 10-31-14, 06:41 AM
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Currently, with the pump, it takes about 90 seconds for hot water to reach the master bath. Without it, it takes 20+ minutes, and 13 gallons of cold water.
Does the return line not have a check valve? It sounds as if without the pump you are having to get hot water to flow through both lines to get the hot water to the bathroom. But still.....20 minutes?
 
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Old 10-31-14, 07:43 AM
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It didn't have one when we moved in, and we thought that was the problem. That and the pump was incorrectly plumbed to the top of the water heater (outgoing hot) rather than the return line that goes to the bottom of the heater. Fixed that, installed a check valve... zero change.

It's not really about the time, think about the volume of water. 13 gallons. With a low flow faucet, that is easily 20 mins.
 
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Old 10-31-14, 01:22 PM
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It's not really about the time, think about the volume of water. 13 gallons. With a low flow faucet, that is easily 20 mins.
Something still isn't sounding right. How big is this mansion you live in?
 
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Old 10-31-14, 01:55 PM
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In order for it to take 20 minutes to clear 13 gallons you would have to have a flow rate of 0.65 gallons per minute. That would be an extremely low flow rate as the standard for faucets and low flow shower heads is 1.5 gpm. Most of the very low flow shower heads have a rate between 1 and 1.2 gpm. I think you are wrong about either the amount of water or the time.

If you run water in the washbasin (most likely 1.5 gpm flow rate) how long until the water is hot? If you have a bath tub the flow rate is usually 5 to 7 gallons per minute, how long to get hot water then?

How close is the recirculation piping to the point of use that takes 90 seconds to achieve hot water when the pump is running? What size piping is used in the recirc. line?
 
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Old 10-31-14, 05:25 PM
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I'm being inexact about time with the pump off because it isn't relevant. I am exact about the quantity of water, because we measured it precisely. 13 gallons. It's about 25' out, then 80' down from thew WH. Of course it doesn't take a straight line, so is probably 125'. It's 1" and then returns via a 3/4" pipe. The numbers do not add up to the 13 gallons of water flow you would expect, I know. Been there, done that with plumbers who have given up.

From the tub, which flows really well, it takes maybe 3-4 mins, and is where we measured the 13 gallons. And the water goes from stone cold to hot over just a few seconds, so it isn't a case of the water slowly warming up, from getting cooled by the pipe.

We also tested WITH the pump, first thing in the morning when the system was all cool. It took about 90 seconds to get hot. And about 3 mins for the return pipe at the water heater to start feeling warm. So it's roughly symmetrical.
 
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