Incremental energy costs for solar pool heating

[russ]

Yes ocdave, it is true that incremental energy cost is zero since you would have to run pool pump anyway but i know that if you dumping water directly back into water then you get some solar benefits definitely because solar collectors are using there and this is good thing. Do not worry about incremental energy cost while using solar collectors.

Welcome to Solar Panel Talk but be aware that you just posted one meaningless statement.

[Ezrio315]

Solar Pool Heating

I have talked to a few vendors about installing a solar pool heating system and when I ask about the incremental energy cost of running the system, the answer I get is that it is basically zero since I would have to run my pool pump anyway. Rather than dumping water directly back into the pool, they are running it through the solar collectors before dumping it back into the pool so I get the solar benefit without any incremental energy cost. Sounds a bit too good to be true. Surely, this is going to cost me more to run since my variable speed pump would have to be run at a higher RPM? Any real world experience out there to help me get a non-sales answer?

Thanks!

Yes ocdave, it is true that incremental energy cost is zero since you would have to run pool pump anyway but i know that if you dumping water directly back into water then you get some solar benefits definitely because solar collectors are using there and this is good thing. Do not worry about incremental energy cost while using solar collectors.

[inetdog]

After we have all beat our gums, fingers and each other to a pulp, I'd submit that a short reply to your comments/questions might be it will cost a bit more to pump the water a bit further through the extra equipment, but probably not much, provided the system is well designed and laid out. The well designed part includes, among other things, checks to ensure the pump is still adequate, the flow rate is acceptable, the piping is well designed for fluidmechanical, service and appearance considerations. As with any solar job, I'd get several quotes from reputable vendors and ask a lot of questions. Bottom line : pool heaters do work and can be cost effective, pool covers work and cost less but don't look as sexy and require more involvement.

One thing that I cannot tell without actual controller design, pump curves and plumbing diagram is whether the variable speed pump will in fact be forced to run at a higher speed to deliver the required gravity head, or whether it will just be running faster to drive the required flow thorough the flow resistance of the original piping.
Either way it will not be free.

The power used by a centrifugal type pump depends more on the flow rate than the speed of the motor. Closing a valve or otherwise restricting the flow will cause the pump motor to draw a lot less current. This is backwards from most people's first impression.
The maximum head for a centrifugal type pump depends strongly on the rotor speed.

[J.P.M.]

I have talked to a few vendors about installing a solar pool heating system and when I ask about the incremental energy cost of running the system, the answer I get is that it is basically zero since I would have to run my pool pump anyway. Rather than dumping water directly back into the pool, they are running it through the solar collectors before dumping it back into the pool so I get the solar benefit without any incremental energy cost. Sounds a bit too good to be true. Surely, this is going to cost me more to run since my variable speed pump would have to be run at a higher RPM? Any real world experience out there to help me get a non-sales answer?

Thanks!

After we have all beat our gums, fingers and each other to a pulp, I'd submit that a short reply to your comments/questions might be it will cost a bit more to pump the water a bit further through the extra equipment, but probably not much, provided the system is well designed and laid out. The well designed part includes, among other things, checks to ensure the pump is still adequate, the flow rate is acceptable, the piping is well designed for fluidmechanical, service and appearance considerations. As with any solar job, I'd get several quotes from reputable vendors and ask a lot of questions. Bottom line : pool heaters do work and can be cost effective, pool covers work and cost less but don't look as sexy and require more involvement.

[Naptown]

I'd suggest it's only meaningless if air can get into the system by virtue of the location of the termination(s) - a spigot outlet for example without a u bend, that sort of thing. The way I learned it, if air cannot enter the system once full, designed to stay that way and operating normally, the pumping losses will be only those losses normally associated with any system pumping fluids around, viscosity, pipe friction, velocity head changes, valves or other restrictions, etc. Attempting to fill a system with a large elevation change with a low head pump might be fun however.

You are correct.
Pool systems however are designed to drain back to the pool when either the pump shuts down of for winterizing.
The vacuum breaker in the system is spring loaded and under normal conditions should not open up when the pump is on. It takes a good bit of vacuum to open them which should not be present while operating. So there will be the additional head on the pump when initially filling the system. They do however empty on a daily basis when the pumps shut down.

[LFM]

Surely, this is going to cost me more to run since my variable speed pump would have to be run at a higher RPM?

Thanks!

No, your flow rate/RPM's should not change (the why is in my other post, but don't look at it if your just looking for an answer to your question). You will have an increase in power consumption from the solar controller/solenoid valve and/or motorized valve. I use a single speed pump I have not seen any difference in power consumption and the flow rate stays the same heating cycle or not.

[Naptown]

I have talked to a few vendors about installing a solar pool heating system and when I ask about the incremental energy cost of running the system, the answer I get is that it is basically zero since I would have to run my pool pump anyway. Rather than dumping water directly back into the pool, they are running it through the solar collectors before dumping it back into the pool so I get the solar benefit without any incremental energy cost. Sounds a bit too good to be true. Surely, this is going to cost me more to run since my variable speed pump would have to be run at a higher RPM? Any real world experience out there to help me get a non-sales answer?

Thanks!

Since all piping originates and terminates under the surface of the water it is essentially a closed loop. Yes some additional power is needed to initially pump the water up to the roof but once filled it should balance out and only have the additional static head.
The only way to be sure is to plug the pump into a kill a watt meter or use an amp meter to see what if any difference there is in consumption during non heating mode, pump up to collectors and filled collectors circulating.

We are talking about generic pumping systems - you are talking about a specific small sector under special conditions - how many of those you have installed is of no consequence.

Read the original post

I did and this is specifically about a pool solar system read the first post and the selected ones above.

[russ]

What I am talking about is the specific system question the OP asked not a generic system that may or may not apply to his situation.
Why are we talking about things that do not apply to the original question.

Read the original post

[LFM]

The flow rate of water returning to the pool after the solar panel cancels the energy needed to lift the water to the panel. The flow rate of the water exiting the solar panel/panels in most cases exceeds the lift flow rate. So a throttling valve needs to be installed in the effluent line of the solar panel, to insure the panels and return line stay full of water during the heating cycle. If the effluent line of the panel is not throttled the bleeder valve at the top of the system will not be under a positive pressure and will pull in air. This is true in a closed loop where the influent and effluent lines run to and from the pool return or open loop the water returns from the panel direct back into the pool with a air gap. If your using a variable speed pump (your already saving 60 to 70% on energy cost) it should not be necessary to make any chances to flow rate.

[Naptown]

We are talking about generic pumping systems - you are talking about a specific small sector under special conditions - how many of those you have installed is of no consequence.

What I am talking about is the specific system question the OP asked not a generic system that may or may not apply to his situation.
Why are we talking about things that do not apply to the original question.

[russ]

I have installed hundred of these. There is a vacuum breaker at the top of the system. as long as the pressure remains only marginally higher than a vacuum no air enters system. If you have bubbles in the poo after the initial purge you have trouble.

We are talking about generic pumping systems - you are talking about a specific small sector under special conditions - how many of those you have installed is of no consequence.

[Naptown]

I have installed hundred of these. There is a vacuum breaker at the top of the system. as long as the pressure remains only marginally higher than a vacuum no air enters system. If you have bubbles in the poo after the initial purge you have trouble.

[russ]

Depends on pipe diameter and layout.

[J.P.M.]

Is the pipe constantly 100% full or not - where it terminates is meaningless

I'd suggest it's only meaningless if air can get into the system by virtue of the location of the termination(s) - a spigot outlet for example without a u bend, that sort of thing. The way I learned it, if air cannot enter the system once full, designed to stay that way and operating normally, the pumping losses will be only those losses normally associated with any system pumping fluids around, viscosity, pipe friction, velocity head changes, valves or other restrictions, etc. Attempting to fill a system with a large elevation change with a low head pump might be fun however.

[russ]

Is the pipe constantly 100% full or not - where it terminates is meaningless