# Is there a flow rate so high that it will not heat up a swimming pool?

My friend and I had a disagreement about heating up a pool. We both agree that a a pump with a heating element with faster flow rate will heat it faster than a slower one. However, I argued (maybe wrongfully) that there has to be a flow rate so infinitely high that you actually won't be able to heat up the pool because the heat transfer is so small that it will get overwhelm by the pool water. That is given that the speed increases but the heating element has a fix output. Is there anything to back this up or is faster better regardless of speed not taking into consideration electricity cost?

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• 3 months ago

NO

Simple thermodynamics. You apply x joules of heat to the heating element, and almost all of that is transferred to the pool. Some is lost to the material surrounding the pump and pipes, but higher flow rate actually minimizes that.

That applies no matter how high the flow rate is

So higher flow rate actually increases the heat transfer, for several reasons:

1. less heat loss to the material surrounding the pump and pipes.

2. more heat generated due to the increased friction and turbulence.

And there is no upper limit, before other factors come into play, such as flow rate in the pipes hitting the speed of sound, or cavitation in the pump, both of which limit the flow rate, but also generate heat.

edit, and of course you cannot increase the speed without limit. Speed of sound comes into play, as does pump problems. What does cost of electricity have to do with this, since you are assuming a fixed heater capacity?

• billrussell42
Lv 7
3 months agoReport

But this is not a real life application. The question was about pushing the pump speed to extermes.

quote: there has to be a flow rate so infinitely high that you actually won't be able to heat up the pool

• Who
Lv 7
3 months ago

" We both agree that a a pump with a heating element with faster flow rate will heat it faster than a slower one"

you are both wrong

Ignoring the heat loss if you pump real slow then the rate of heating depends on the amount of heat you put into the water - not how fast you pump the water

(If you could pump REALLY fast then the pumping itself woudl make a contribution comparable to the amount from the heater - but with normal pumping it would be negligible

• 3 months ago

I assume a closed system (a loop) in which case the heat will be added at a rate depending on the heater output without regard to flow rate. there will be an optimum flow rate where heat transfer is maximized per unit volume, but even instantaneous contact (exposure) of the passing water to the heat source will allow transfer of some heat.

Having a an open system where water can leave and take heat with it would change everything. In that case, it appears that the maximum temperature which would be attained in the pool would be the temperature of the water as it left the heater. Slower input (up to the point where the water in the heater achieves thermal equilibrium with the heat source but does not remain afterward) would be better than faster input in such a situation.

• 3 months ago

The heat transferred to the pool id the same for all flow rates but at high flow rates the pump cost is higher, the pump uses more current.

There is a limit to how slow. You don't want the water coming into the pool to be higher than 105 degrees or it will burn people. Set the flow rate high enough that the temp is below ~ 95 degrees F.

• Bill
Lv 6
3 months ago

both are right

it is physics and heat transference rules

it will take longer to hreat up with a fast flow rate up to a point where th intake water starts to get warm

after that it will be in the same ratio to a slow flow rate

you have to consider the lossof heat to the atmosphere and the surrounding ground

• Joe
Lv 7
3 months ago

At normal swimming pool temperatures, faster or slower makes no difference.

Yes, a faster flow rate reduces the amount of heat energy transferred to each gallon. But you're adding heat to more gallons per minute. The total energy transferred from the heater to the pool water does not change.

• Anonymous
3 months ago

Wouldn't water with a higher flow rate across a heating element have less contact time with the heating element, therefore less heat transfer to the water passing it compared to less water / slower moving water?