Does a return pump warm the water?

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From a basic thermodynamics point of view, the more work any pump or motor does (head pressure) the more heat it creates as waste heat.

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I totally agree with that statement Greg. The question is do you really believe that reducing the flow of liquid will require more work? In a pump design there is what we call the Best Efficiency Point. It is true that closing the valve will create the maximum pressure with no flow that can overheat the motor. The same thing will also happen if you let the pump run freely with zero pressure (no water). We avoid and never advice anyone to let the pump run that way. The pump has to run in between for maximum performance.

One time a pump takes too long to fill up the tank so it was decided to replace the discharge pipe to a bigger size diameter to make it easier for the pump. Guess what happened? It burned the motor. It was then replaced with a bigger sized pump. It is true that you are making it easier for the pump but you are also increasing the power demand.
 
Does a return pump warms the water?

That doesn't make sense to me that reducing the demand on a pump increases its energy usage. But in a induction motor, since the coils alternate at the same 60hz speed all the time, it wouldn't react to a load from a pump the same way a direct drive motor would. Maybe that's the difference.


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Does a return pump warms the water?

No, reducing flow is equivalent to head pressure and that places more load on the pump. That's why I never restrict flow but use a Y valve to dump excess water for adjusting flow in things like reactors. Now the difference there is I'm not lifting water very far, I'm just recirculating it.

Good topic. I need to look into it a bit deeper.


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Its true that you increase the pressure by slightly closing the valve but in turn you have reduced the water flowing therefore you are spending less energy.
 
Greg, it is counter intuitive but a throttle valve does reduce flow AND power consumption. But, and this is VERY important in this situation, the reduction is NOT proportional.

If you reduce the flow via a throttle valve buy 50% you will not see a reduction in the consumed power of 50%. It will be closer to a 25% power saving. So if you use 75% of the energy to move 50% of the mass the same distance, what does the extra 25% of the energy do? It creates heat (and a wee bit of extra noise). (And these numbers are in addition to the normal power factor rating of the motors). That is why throttle valves are not used in temperature sensitive situations such as the OP was asking about. They cause temperature increases.

As for my credentials, I am an Electronics Technologist and a practicing Electrician.


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If you reduce the flow via a throttle valve buy 50% you will not see a reduction in the consumed power of 50%. It will be closer to a 25% power saving. So if you use 75% of the energy to move 50% of the mass the same distance, what does the extra 25% of the energy do? It creates heat (and a wee bit of extra noise). (And these numbers are in addition to the normal power factor rating of the motors).

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Assuming those numbers are reliable, you will also have similar effect when the pump is operated more than its manufacturer's suggested specifications. The depth or height of water where your return pump is and the height of your display tank (total head) plus the size of the discharge pipe will have influence on your pump. As Greg has been saying the more work (more flow) the more power you consume and so thus the radiated heat. So it still comes down to the right adjustment to get the Best Efficiency Point.
 
Recently I pulled out my skimmer (SRO 2000 Internal) and reactor. The reactor only had a small pump. I saw a 4C drop in tank temp before I plugged in the heaters again.

[ BTW my ATS feeds directly from my overflow drains so no pump is needed for that; yeah. ]


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Recently I pulled out my skimmer (SRO 2000 Internal) and reactor. The reactor only had a small pump. I saw a 4C drop in tank temp before I plugged in the heaters again.

[ BTW my ATS feeds directly from my overflow drains so no pump is needed for that; yeah. ]


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Did you figured out why it was heating up?
 
How did you find out that its not the other pumps in your tank?

I don't have returns pumps, I have two 240 GPH powerheads, but 3 watts each can't heat the water that much. If I turn the heater off, the water temperature drop at stable 23, 23.5, and when turning off both the skimmer and the heater water will go to room temperature even if powerheads are running.

I don't know the wattage of my PS.
 
From a basic thermodynamics point of view, the more work any pump or motor does (head pressure) the more heat it creates as waste heat. If the motor uses less current under higher head pressures, it doesn't compute to me.

My field is aerodynamics and structural engineering so I am fascinated by the comments.


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Your idea of increasing head pressure that will require more work is when you have a variable speed pump. The increase of speed will increase head pressure that will also allow more flow. Whereas the throttle valve is actually reducing the overall total head pressure.
 
can someone please explain to me how an electro-magnet that is using nominal house current and has no rheostat or other means of adjustment is going to consume more or less energy by virtue of the flow rate???

the current and amperage is the same and constant, the only difference between pumps with more or less flow from these type of pumps/impellers is by increasing or decreasing the impeller size.

I really think some of you are off target because you are extrapolating information from other types of systems and applying it to a completely different type of system.

Again, magnetic drive pumps have a more or less free floating impeller and I fail to see how adjusting the water flow is going to increase or decrease the power consumption when the power is being supplied at a fixed, constant rate.

One of you electricians need to do an actual test to see if there is any increase in the electrical current being drawn/supplied when the flow is restricted or full open.

My gut tells me that in the small pumps we use, there will be no discernible difference in power consumption either way.

We need to see real numbers in action to settle this very crucial, vital and important piece of information once and for all. The future of the free world depends on it!!!
 
It is a very simple physics. Moving an object requires work. The heavier and/or farther/higher distance the more work is required. More work requires more power.
 
It is a very simple physics. Moving an object requires work. The heavier and/or farther/higher distance the more work is required. More work requires more power.

the current and amperage is the same and constant, the only difference between pumps with more or less flow from these type of pumps/impellers is by increasing or decreasing the impeller size.

Again, magnetic drive pumps have a more or less free floating impeller and I fail to see how adjusting the water flow is going to increase or decrease the power consumption when the power is being supplied at a fixed, constant rate.!


Yes sir, and not all electromagnet pumps require the same amperage.
Also I don't think by restricting the flow it will increase the consumption... You can test it with an ampere meter.

I don't think my protein skimmer is working with a free magnet impeller... The protein skimmer makes my floor vibrating, so I guess the engine is strong. I don't know the wattage. Also the water flow of my PS is very low (even if I block the air intake)
 
It is a very simple physics. Moving an object requires work. The heavier and/or farther/higher distance the more work is required. More work requires more power.

yes it is very simple, and why all these type of pumps have a max head height, because that is the limit that they can produce at the rated power and impeller size/design.

Sorry, but I think absent a rheostat or any means of adjusting the power being delivered to the pump, I think that it is pretty simple that it is not going to draw more power from a fixed source........ how can it unless you rewire your house for 220 instead of 110.

I think it is pretty straightforward, there is NO direct link between the factors of the valves/hoses/whatever controlling the flow rate and electrical power consumption considering that any and all electricity powering it is simply flowing through the coils of the electro-magnetic completely irrespective of what is going on with the impeller/flow rate.

really, think about it, there is no direct connection between the two and therefore no way the flow rate would influence the current draw.
if you pull the impeller out I'm gonna guess the coils are still drawing the same current.
That in itself accounts for the heat.
any adjustments to flow rate that impact temps are going to be related to what I previously mentioned, contact time.

maybe I'm missing something, it would be nice to see actual testing of this.....like I say the future of all fishkind depends on it!
 
really, think about it, there is no direct connection between the two and therefore no way the flow rate would influence the current draw.
if you pull the impeller out I'm gonna guess the coils are still drawing the same current.
I guess same heat, same amps too.
 
can someone please explain to me how an electro-magnet that is using nominal house current and has no rheostat or other means of adjustment is going to consume more or less energy by virtue of the flow rate???

the current and amperage is the same and constant, the only difference between pumps with more or less flow from these type of pumps/impellers is by increasing or decreasing the impeller size.

I really think some of you are off target because you are extrapolating information from other types of systems and applying it to a completely different type of system.

Again, magnetic drive pumps have a more or less free floating impeller and I fail to see how adjusting the water flow is going to increase or decrease the power consumption when the power is being supplied at a fixed, constant rate.

One of you electricians need to do an actual test to see if there is any increase in the electrical current being drawn/supplied when the flow is restricted or full open.

My gut tells me that in the small pumps we use, there will be no discernible difference in power consumption either way.

We need to see real numbers in action to settle this very crucial, vital and important piece of information once and for all. The future of the free world depends on it!!!

Well, here goes. [flash back to 2nd year electrical apprenticeship - 10 week course all compressed into a couple paras] :popcorn:

First off, your obviously not well informed about electrical. Not a jab, but you will have to accept the fact that much may be over your head. there is NO such thing as nominal electrical current. Electrical current varies greatly depending on the load applied. nominal electrical voltage is 120v (for arguments sake). the current will vary depending on the impedance. Impedance, what the heck is that???:( Its a combination of resistance caused by wires and other physical devices [Resistance is constant for a motor] and inductive reactance. Reactance can change greatly in a motor under changing loading. Reactance has a much greater effect on impedance than resistance. In fact, resistance has a negligible effect on the motors load characteristics.

When a motor is under greater loads, the phase angle between the voltage and the current increases greatly due to the electro magnetic force applied. This increased phase difference is responsible for the increased impedance
(by cos[theta]). Because the impedance increased, the current also increases proportional to impedance, drawing MORE power (I=V/Z). BTW, current and amperage IS the same (second para), because they mean the same thing. Current is measured in amperes. But it is NOT constant.

Now, as for the pumps, FORGET about pressure. Pressure is constant in a throttle valve situation. What :eek:. Look, water is not compressible. Pressure is proportional to the pipe diameter and flow rate squared. If the pipe diameter before and after the throttle valve is the same, and, because the throttle valve cannot add or remove water, then the flow rate before and after the throttle valve is the same. Therefore, if both factors are the same on both sides of the throttle valve then the pressure is the SAME. Now, I think everybody can appreciate that shutting a throttle valve some DECREASES the flow, then it also DECREASES the pressure. I know it sucks, but there it is.

If you have decreased the flow, you have also decreased the work required because, as Jeff has pointed out, moving less water the same distance requires less work.

BUT, and this one is for Jeff, by throttling back the pump/motor you have rendered it less efficient, and they will heat up somewhat. They will draw less power, but they will convert a greater percentage of the drawn power into heat, which is why throttle valves are not used temperature situations
 
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