Anyone heard of, or had experience with flow-reversal?

[mas985]

AG pools are only 3-4' deep so you will get even less temp difference. I really don't think it is going to matter. Also a second return probably won't give you much unless the pool is really big.

As to your last comment, AG pools are built for low cost and easy assembly, for the most part. Also, they tend to be smaller so don't need much extra circulation because they are round and avoid dead spots.

An IG pool can be built with a single skimmer and return (have seen some like this) but it doesn't take much more effort to add more returns and it can have large benefit because IG pools tend to be much more irregular so it is easier for dead spots to occur which can be alleviated by multiple returns. Usually they are done on the same side of the pool which makes it easier. Also, most IG pools only have 1 skimmer and maybe 1 main drain although the trend in the industry is to eliminate the MD. IG pools with two skimmers tend to be much larger pools >20k where the surface area is large and a single skimmer may not be enough to keep the surface clean.

So in general I don't think IG pools are over built because of the differences between the two types of pools. If anything AG pools tend to be under built because some of the equipment (e.g. Intex) is not really sufficient to keep the pool clean.

[DennisP]

Oh, I agree... I think above ground pools are way minimized compared to in-ground pools. The depth doesn't matter much, since it isn't like you see multiple returns in the deep-end alone. And average wise, it still is the same amount of water for a large above ground pool and a "normal" in-ground pool. Of course extremely large in-ground pools are much bigger, but realistically water volume is water volume...

I have been looking at pool system hydraulic designs for a few months now and it is just amazing that water turnover and circulation is taken way more seriously for in-ground pools...

I would have to imagine an above ground at 20k gallons would need a mimimum of the same type of plumbing for a comparable in-ground to be just as effective. Sure, the majority of the above-ground industry gets by with a single return and a single skimmer. But, "accepted" is far from "ideal".

That is why I am going with a dual main drain, at least two returns and 1 skimmer. I don't have trees above the pool, so a single skimmer should do just fine. The main drains are ideal to reduce the amount of time vacuuming or using an auxillary pool cleaner as well as affording for better overall "mixing". Multiple returns just make sense for the size of the pool (27ft x 54").

I mean in regards to equipment, the same argument goes for the pumps. I understand why in-ground pumps need to pull a head of water, but even for say a 1.5hp pump, the in-ground variants at the same HP rating have way more flow. Again, outside of the head of water, it doesn't make sense. It does when you figure in extra water features, multiple returns, etc, etc... So, does that mean with my setup, I should be looking at in-ground pumps and I have a way "undersized" pump at this point? (for reference I have a Pentair Dynamo 1.5hp 2-speed pump)

[mas985]

IMHO main drains are worthless and are more of a risk than benefit. They don't add much at all to circulation and just add an entrapment hazard. They do not substitute for vacuuming and have very little influence to dirt around them. In fact, if you pour a bunch of dirt directly on a main drain, it will only clean about 1-2 inches around the drain and that is it. They also easily clog with leaves. People give MDs way way too much credit. I would skip it if I were you.

Dynamo is a great pump for an AG pool and a 1.5 HP is likely over sized if anything but it depends on the filter size. You don't need an IG pump. IG pools need IG pumps because IG pumps are self priming and are above water level. Although you can use a Dynamo on a IG pool because it just so happens to be also self priming.

[DennisP]

Here is my equipment setup:

- Pentair Dynamo 1.5hp 2-speed pump
- Sta-Rite System3 cartridge filter (300sq/ft)
- Jandy Lite2 250k BTU NG pool hater (millivolt unit)
- Jandy check and 3-way valves
- all 2" plumbing from the pool to the equipment pad and at the pad
- three 2" lines installed and one 3/4" line installed for configurability

I plan on adding a 15gallon chlorine tank with Stenner pump in the future along with possibly a booster pump and pressure cleaner or a robotic or vacuum cleaner. I am installing dual main drains to comply with code and to remove any concern about "entrapment".

I talked to a few people and if you have good circulation in the pool with plenty of turbulence at the bottom the main drains are supposed to do quite a good job of minimizing vacuuming. I figure for the minimal expense (I am doing the complete install myself) it would probably be worthwhile.

[DennisP]

Pics of the equipment pad can be found in this thread: http://www.poolforum.com/pf2/showthr...065#post126065

[nefretrameses]

I heard of this with respect to solar heating panels. I don't recall where. I think their premise was the same as yours - warm water introduced at the bottom will push colder water up where it will be picked up for solar heating or something like that. But I think solar introduces a temperature delta irrespective of the input water temperature (within a relevant range). It sounds like there's not a significant difference anyway. I'd trust Mark's analysis and opinion.

[mas985]

I talked to a few people and if you have good circulation in the pool with plenty of turbulence at the bottom the main drains are supposed to do quite a good job of minimizing vacuuming.

Sorry but I think these "people" are just misguided and do not understand hydraulics very well. I have main drains and I can tell you they don't do anything. This is especially true of dual main drains with safety covers. The reduction in entrapment also reduces the force of the water in any one direction (done on purpose) so they do move anything very well. That is why they lower entrapment.

Perhaps you should read this article and watch the video if you still do not believe me:

http://www.poolinspections.com/manua...out-drains.pdf

https://www.youtube.com/watch?v=0IOUGhuKkSM