A potential D.I.Y. system for solar heating and filtering . . . .

[Vince-1961]

My two month old above ground pool is already getting cold and it's still August, so I am thinking about heating the water. The roof of my house faces south and would be ideal for solar heating as it gets very little shade, whereas the pool gets tons of shade. The biggest problem is that the roof is three stories up, some 60-80 feet by sight guessing w/o actually measuring, so obviously the biggest hurdle is how to get water from the pool up to the roof. I thought of the following:

View attachment pool diagram.pdf

The idea is to add an in-wall skimmer with valve that flows to a trash can which is elevated to the height of the pool so that gravity can not make it overflow. The trash can gets filled with sand and clean water collected at bottom where there's a valved outlet allowing gravity to take water over to the pump and provide some positive pressure at the pump's intake. The pump will be located some 35-45 feet away at ground level. The pump then sends the cold water straight up to the roof. (Will need to purchase an appropriate pump....any suggestions?) On the roof will be solar heating devices. (No, I haven't made any decisions as yet in this regard.) Then, gravity can bring the hot water back down to the pool.

In order to backwash the unpressurized sand filter, I attach a garden hose from a faucet to an inlet valve on the bottom of the trash can, turn on the faucet, and let the dirty water (and hopefully not much sand) overflow to the ground.

Anyone see any problems, flaws, defects, just plain stupidity here or otherwise have any comments?

 

[JohnT]

I don't see any benefit to what you are doing. A three story house isn't going to be 60-80ft high in most situations. A sand filter is much more complex than a can full of sand. You can't restrict the inlet of the pump with a filter bed like that. You need to push water through the sand. Finally, it's likely your existing pump or another pool pump installed in its place can raise the water to the roof with no modifications to your system.

 

[Vince-1961]

JohnT, you covered a lot of ground with a few words! As to height of building, I was just guessing at # of feet, but's it's a two story building with a steep roof. As to sand filter, wouldn't the pump's suction pull the water through the sand and wouldn't that be practically the same as pushing it through? (I got the idea of using a trash can as a homemade sand filter from a YouTube video.) As to restricting the inlet of a pump with a filter bed, are you saying is that the suction won't be great enough to pull the water through the sand or that the pump won't work if it has to suck so hard? As to existing pump, do you have any clue what the max head is on an Intex 633T?

 

[JohnT]

The pump will be much happier with resistance on the outlet. If the filter gets dirty, back pressure won't bother the pump, but starving the pump for water can cause it to overheat and/or send bubbles through to the outlet.

 

[mas985]

As to sand filter, wouldn't the pump's suction pull the water through the sand and wouldn't that be practically the same as pushing it through?

It would but at a much faster rate than would flow through the filter so the filter would empty of water and the pump would be pumping air. Because the filter is open to air, it is gravity fed and gravity fed systems are much much slower flow rate than a pump system. In order for that to work, the filter would need to be 10-15' below water level so it maintains enough head so the pump will not drain it. But then the pump would also need to be that low because suction lift is limited.

As to existing pump, do you have any clue what the max head is on an Intex 633T?

I think it is less than 15'. Intex pumps have very little head lift and would not be able to lift the water to a one story roof let alone a two story roof.

 

[Vince-1961]

It would but at a much faster rate than would flow through the filter so the filter would empty of water and the pump would be pumping air. Because the filter is open to air, it is gravity fed and gravity fed systems are much much slower flow rate than a pump system. In order for that to work, the filter would need to be 10-15' below water level so it maintains enough head so the pump will not drain it. But then the pump would also need to be that low because suction lift is limited.

How much larger diameter would the gravity feed from pool to trash can need to be in order to keep the water level in the trash can even with the water level in the pool? (i.e.- to keep up with the pump) Or could it just use multiple inlets?

What is "suction lift"?

 

[mas985]

The pipe or pipes (combined area) would need to be nearly as large as the garbage can itself. Think of how a skimmer is designed, the largest part is at water level. If you restrict the flow at all near the water line, the can will will empty. Much like a skimmer that will empty when the weir door gets stuck.

Besides that, the pump will likely cavitate because you are putting so much head loss on the suction side of the pump. That is why you should never put a real filter on the suction side of a pump.

Suction lift is what IG pump's experience when they have to lift water from the pool into the pump during the priming process. This can only be done with a self priming pump.

 

[Vince-1961]

Okay, so my idea of adding a D.I.Y. sand filter to my solar heating won't work. In the meantime, I'm still in need of solar heating. So, I'll start a different thread on that subject.