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Need Help with Wiring a Flow Sensor and Relay

01/30/2010 6:48 PM

Hello, I am hoping someone can assist me in determine the correct way to wire a project that I am currently working on. I have totally confused myself on how to wire each control.

My Goal: To install a flow switch/sensor into the main hot water line coming from the heater, this will turn on when it senses the draw for hot water. - Then the output from the sensor will activate the 10sec "delay-on" relay. Once the ten seconds has elapsed the relay will turn the pump that circulates the water throughout the system. – Once the draw for the main flow of hot water is stopped, the flow sensor will not recognize this because the pump will generate the flow over the sensor and therefore the pump will continue to run (this is ok). – On the hot water return pipe that the water continues to flow through there is an aquastat which is set to 130 degrees, once the aquastat senses that the water has reached 130 degrees it will break the current to the pump and therefore there will won't be any flow of water over the flow sensor. Then the system will reset itself till the next time there is a demand for hot water. In theory this should work.

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Parts list:

Since I have 110v ac at the location I plan on operating all controls by 110v ac. Due to the large number of wires and connection I have managed to completely confuse myself and would hate to damage any of these devices. Therefore any help would be greatly appreciated.

I should mention that all of the items are installed in the system and that the aquastat has been installed and set to cut out at 130 degrees. The problem I am having is how the flow meter and relay should be energized also where the pump leads and aquastat should be tied into the circuit. I have tried to map the connections out on paper but I get confused with the purpose of each wire on the relay and flow meter.

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#1

Re: Need Help with Wiring a Flow Sensor and Relay

01/30/2010 9:26 PM

Why do you need a flow sensor? If you let the Aqua stat turn on the 10 second timer, and then the water pump. Why does the system need to know when water is flowing?

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#3
In reply to #1

Re: Need Help with Wiring a Flow Sensor and Relay

01/31/2010 2:14 AM

The reason for the flow sensor is to keep the system from turning off and on when there is no call for water.

With out the sensor the system will turn on once the temp falls below 130 degrees then turn off once the temp has been reached this will cause the system to keep recycling.

The sensor will stop that from happening - sensor senses water flow - activates relay - relay waits 10 sec then turns on the pump - call for hot water stops - pump continues to run since water continues to flow over sensor - circulation loop reaches 130 degrees - aqua-stat opens at 130 degrees -power to pump breaks - sensor no longer senses water flow - breaks power to relay - system resets until a call for hot water is made which starts the cycle all over again.

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#2

Re: Need Help with Wiring a Flow Sensor and Relay

01/30/2010 9:31 PM

It seems to me that the overall logic of this defeats the usual purpose of a circulating hot water system. If the system is idle for a while, all the pipes will cool off. Then, next time someone wants hot water, the pipes still have to run for a time. The pump might shorten this time a bit, but the 10-second delay won't help.

However, give this a thought: Put the aquastat just after the circulating hot water line passes the last usage point, at the beginning of the return loop. Set it for about 105°F. Water less than that, pump runs for a short while to recharge the line with hot water; water warms up, pump shuts off. If the line happens to be insulated, better yet; it will hold the heat for a while, and pump run time will be low. This will keep hot water constantly available, but the pump doesn't need to run all the time.

For best operation the deadband (differential) of the aquastat probably should be around 10-15°F. (Rough guess.)

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#4
In reply to #2

Re: Need Help with Wiring a Flow Sensor and Relay

01/31/2010 2:31 AM

Tornado - thanks for the prompt reply.

I failed to mention that the system is a tankless hot water heater. The pipes are insulated and the response time for hot water with the pump running is extremely quick.

The ten second delay can be adjusted to any time frame - Ten seconds is used so that if some one turns the hot water on then off the pump won't turn on. This is to cut down on the cycling of the circulation system - the relay can be set to operate instantly if necessary - also I wasn't sure if the flow sensor could power the pump without a relay.

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#5
In reply to #4

Re: Need Help with Wiring a Flow Sensor and Relay

01/31/2010 3:29 AM

The whole point of a circulating hot water system is that it operates when there is no demand for hot water, so that hot water will be available promptly when there IS demand for it. But it needn't operate all the time to do this.

Combining a circulating pump with an instant tankless water heater is REALLY crazy. No wonder you're trying to shut it off most of the time! (And even then, the time to run the pump would be just BEFORE someone wants hot water, not 10 seconds after).

If anyone can come up with a psychic system to do THAT, more power to them!

You need to rethink all this, and maybe get a partial refund from whoever "designed" it.

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#7
In reply to #5

Re: Need Help with Wiring a Flow Sensor and Relay

01/31/2010 11:22 PM

Now that we know the system is a tank-less, why does he need the stat, and circulator system?

Hi. I'm Joe the plumber. My son needs braces, therefor you need a circulation pump for your tank-less water heater and an Aqua-stat. After I meet with the orthodontist, I'll let you know what else you need.

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#11
In reply to #7

Re: Need Help with Wiring a Flow Sensor and Relay

02/01/2010 10:37 AM

bob c -

Your statment,

"Now that we know the system is a tank-less, why does he need the stat, and circulator system?"

The reason for this should have been covered in one of the other posts.

Sorry I can't help you out with the orthodonist situation, The only advise I can offer is to check with your dental provider to get an understanting of what is covered.

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#10
In reply to #5

Re: Need Help with Wiring a Flow Sensor and Relay

02/01/2010 10:27 AM

Tornado-

Your first point -

"The whole point of a circulating hot water system is that it operates when there is no demand for hot water, so that hot water will be available promptly when there IS demand for it. But it needn't operate all the time to do this."

- With a tankless heater, when the heater senses water flow the heater won't stop until the flow has stopped - that is why we are using an aquastat to break the feed to pump once temp in circ system is at 130 deg. The circ system will only operate when there is a call for hot water at a faucet. This done to cut down on the number of cylces that the circ system needs to run. Once the pump starts, hot water is at the faucet rather quickly. I realize that there may be a short time frame with out hot water but the trade off will be in the savings of electricity used.

Your second point -

"Combining a circulating pump with an instant tankless water heater is REALLY crazy. No wonder you're trying to shut it off most of the time! (And even then, the time to run the pump would be just BEFORE someone wants hot water, not 10 seconds after)."

- Actually, it's not that crazy - Most tankless manufatures, if not all highly recommend having a circulation loop. This is to get the water to the place of use quicker.

The manufactures claims of having hot water instantly is that the water will leave the tank at the temp setting on the heater. - The ten second delay (the relay can be set to what ever time frame you want and can be eliminated) thought process is that the kitchen sink faucet is usually left over on the hot side. So to avoid having someone turn on the water for just cold water the delay will keep the circulation system from engaging.

This project was designed at a gathering of mechanical engineers and plumbers (We use these gatherings to discuss problems experienced in the field and come-up with remedies) This system was tested in a rudimentary way and seems to work quite well) We are now trying to bring it all together with actual components.

Thanks for the concern over the money spent on this project, but we obtained these components at a rather inexpensive costs. We a just looking for guidance on the wiring portion of the project

Don't get me wrong, We do appreciate the constructive criticism.

Thanks for your help and sugestions

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#14
In reply to #10

Re: Need Help with Wiring a Flow Sensor and Relay

02/01/2010 9:51 PM

I stand corrected, at least partly. I was hung up on the individual point-of-use tankless heaters, for which recirculation would be useless expense. However, there might be a way it could work well with a "centralized" tankless heater. I'm not sure how yet, or if the additional expense is too high for whatever may be gained. But I will mull it over some more.

Thanks for explaining further.

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#18
In reply to #5

Re: Need Help with Wiring a Flow Sensor and Relay

02/11/2010 1:56 AM

Most households do not use hot water for 80% or more of the day. The heat dissipated in the pipes with a continuous recirculation system will waste energy. Since most on-demand / tank-less heaters start when water flow begins, running a recirculation system continuously will also keep the heater running continuously, or at least running until the water inlet temperature rises to a limit; however, this is an inefficient way to run a tank-less system.

The recirculation system can be awakened by the consumer when she enters the room and anticipates the need for hot water. The simplest way to request hot water at any/every faucet is a single flow sensor.

Awakening a recirculation system conserves water instead of pouring it down the drain. It may also conserve hot water if the consumer is in the habit of running the tap without hovering to monitor the temperature. It also conserves the recirculation pump and the power to run it. Finally, it conserves better than a timer and is much more flexible, as it responds to demand at odd times.

The simplest way to stop this recirculation system is to install a thermostat on the recirculation line. Of course, it will conserve even more energy if the thermostat is located near the demand point instead of on the recirculation line next to the water heater. Thus, the beginning of the recirculation line is the best position for the thermostat.

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#20
In reply to #18

Re: Need Help with Wiring a Flow Sensor and Relay

02/11/2010 3:25 AM

These additional explanations make sense, and I am liking this idea better now.

Can you describe a bit more about the implementation? I'm used to flow switches that are rather spendy, though aquastats are economical. What are you using to sense flow?

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#6
In reply to #4

Re: Need Help with Wiring a Flow Sensor and Relay

01/31/2010 11:09 PM

Ha

your tankless boiler will not allow water to circulate through it when the there is no pressure difference between the cold water point at the boiler and the taps (faucet) this pressure difference happens when you open a tap (faucet)

tap water pressure 50 psi

Boiler water pressure 55

boiler then open solenoid valve and the flow triggers the gas valve so the solenoid will not open when there is equal pressure at the taps and the boiler

I hope this helps

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#12
In reply to #6

Re: Need Help with Wiring a Flow Sensor and Relay

02/01/2010 10:50 AM

Pace,

You may be mixing up systems, this is not a boiler unit used to provide hot water, this is a tankless water heater (a seperate unit that mounts on the wall) which operate very differently than your typical boiler systems.

The rec system I am talking about is highly recomended by the tankless manufactures. We are just trying to improve the system to cut down on the constant cycling as they (manufactures) describe as normall.

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#19
In reply to #6

Re: Need Help with Wiring a Flow Sensor and Relay

02/11/2010 2:07 AM

If the recirculation pump provides 5psi (beyond losses in the pipes) such a boiler will work.

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#8

Re: Need Help with Wiring a Flow Sensor and Relay

01/31/2010 11:58 PM

Use a ladder diagram to simplify the wiring.

I drew it out in auto cad but CR4 didn't like it.

Its pretty simple: Normally open flow contact sensor to relay coil (timer)

normaly open relay contact in series with normal closed temp stat: this circuit is then parrelled around the normally open flow contact. (this holds the timer "on" after it times out until the the stat opens the circuit)

last normally open contact (timer) to power the motor pump

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#9
In reply to #8

Re: Need Help with Wiring a Flow Sensor and Relay

02/01/2010 12:06 AM

my bad:the temp stat normally closed contact should be in series with the timer intiation circuit (coil or contact depending on the timer) rather than around the flow sensor.

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#13
In reply to #9

Re: Need Help with Wiring a Flow Sensor and Relay

02/01/2010 10:59 AM

MIKE L,

I will work on designing a ladder system drawing and will post it for review. Please bear in mind that this is alll new to me and will be my first attempt at drawing a ladder diagram.

Thanks for the suggestion.

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#15
In reply to #13

Re: Need Help with Wiring a Flow Sensor and Relay

02/01/2010 11:05 PM

As you are new to ladder some basic stuff. Usually the left ladder leg is the power or controlled power (ie master contact), the right leg is usually the return-neutral (if 110v neutral is not normally disconnected so this leg is continuous) ground leg is understood can be shown at each component or as third leg to neutral again (usually not disconnected so continuous)

All series contact are drawn "in line" power to end coil/motor etc. as a "rung"

parallel circuits are a little more complicated as the parallel may be only "around" one contact or switch or "around" multiple contacts and then can include an arrangement of series and parrell circuits.

"Rung" is usually all contacts series and parallel to complete a circuit (ie end device relay, timer, coil, motor etc)

Your circuit is quite simple, so good luck. Any ideas on getting drawings into CR4?

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#16
In reply to #13

Re: Need Help with Wiring a Flow Sensor and Relay

02/01/2010 11:15 PM

Tmasco

In the UK there are two types ''Heating boilers'' and instantaneous hotwater boiler (Tankless) and after 22yrs working with these I am quite sure that even if he gets the the wiring right unless he can find a way round the circulation through the hotwater boiler

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#17

Re: Need Help with Wiring a Flow Sensor and Relay

02/09/2010 3:27 PM

Hi tamasco,
I think I know exactly what you want. Lets see:

1.0) A consumer draws water from a hot water faucet - just for a moment.
1.1) The flow sensor at the water heater activates.
1.2) The flow sensor sends power to the timer. After this occurs, the hot water faucet may be turned off.
2.0) The timer sends power through the thermostat contacts. The thermostat is located in the recirculation line, preferably at the far end of the plumbing.
2.1) If the water is not hot enough, the thermostat sends power to the pump and the water heater starts.
3.0) After some time, the hot water reaches the temperature sensor. The hot water line is charged to the far end of the plumbing, and part way back to the water heater.
3.1) The temperature sensor removes power from the recirculation pump.
3.2) The timer sequence eventually ends.
4.0) The consumer begins drawing hot water at the intuitive moment.

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