30ft AG Pool adding second return and pump sizing?

[Strictly BBB]

I will be ordering (by the end of the month) and installing a 30ft AG Pool. I was wanting to put an extra return (180 degrees apart) on the pool, to help water flow around the large circumference and help with potential algae problems around the ladder areas. I have read TFP Pump Basics and Hydraulics 101. Finally to my three questions: First, is the 1 hp pump big enough or would a 1.5 HP be needed? Second question, would the slow speed setting on the two speed pump filter as good on the Pentair SD-80 Sand Dollar Filter with ClearPro Technology with near DE filtering qualities? Second question asked another way, Do people with DE Filters have any filtering problems with a Hayward Power-Flo Matrix 2 speed pump when set on the low speed? Do you think a 2 inch suction line and a 1.5 return line would work well in this system?

The below pump,filter and system setup is what I came up with.

Hayward Power-Flo Matrix 1 hp 2 speed Link
Pentair SD-80 Sand Dollar Filter with ClearPro Technology Link
Hasa Commercial 8 gallon Liquidator Link

Other useful info about my possible system.

I plan on puting gravel in bottom of filter and using regular pool sand with a small measured amount of DE media on top.
The pump system will stay next to the pool.
I plan on hard plumbing it in with quick disconnects and 2 inch suction line and 1.5 return lines.
My automatic suction pool cleaner will be a Hayward AguaBug
I will use the Hasa Commercial 8 gallon Liquidator for my bleach dispersal unit.

All help and comments will be appreciated as I am going to start ordering by the end of the month.
Thanks in advance for the great info from the TFP Community.

 

[Guest]

My question would be why you would plumb 2" suction but then "bush down" to 1 1/2" return? Why not run 2" the entire way? That would make for even flow of water (and I would consider looping the return line to equalize the flow to both returns).

Depending on how many gallons you have, a 1 HP pump may be too much. Slow moving water filters better, and large diameter plumbing helps. You may find that you can use a 3/4 HP pump just as efficiently (or more) and save some money on electricity. There is no value in screaming fast water, so bigger is not better in this case (the biggest filter you can get, however, is the right choice)!

The Liquidator is a great choice, in my opinion. Make sure you do the upgrade kit if you really want it to work!

 

[dmanb2b]

Welcome to TFP...I'm also in the school of buying the biggest filter you can get and the smallest pump possible. If you go 1hp, makes sure it is a 2 speed...otherwise a fullrated 0.5 or 0.75 hp pump will do just fine on a AGP. If you go sand filter, with that large of a pool, I would suggest getting at least a 300lb+ filter, and the SD-80 certainly fits that bill.

Sounds like you are on the right path

 

[Strictly BBB]

First thanks for the quick responces.

My question would be why you would plumb 2" suction but then "bush down" to 1 1/2" return? Why not run 2" the entire way? That would make for even flow of water

I may be thinking of this wrong, but I thought that the 2 inch suction line may help with the total head loss from the 42 Ft of return line to the second return line 180 degrees apart from the orginal return line (30 ft dia pool circumference (94 Ft) divided by two).

(and I would consider looping the return line to equalize the flow to both returns).

I was planning on equalizing return pressure by using a PVC manifold with independent valves on each of the return lines and possibly having a short necked down section on the orginal return to keep from gating down the valve so much. I read somewhere on TFP that necking down a short section of piping on the return line (On the line that you need to reduce the most) will not reduce the head/water flow as much as gating down with a valve.

But a simple loop would be alot easier. My questions are: First, I would have 94 Ft of second return line plus the distance of the original return. What would this do to the total head, pump size, etc? Second, I guess I would have to run to the second longer distance return in the loop first, then to the orginal return next to the pump area. Third, not understanding hydraulics that well, it looks to me that the first return in the line would have to have more pressure then the second return line unless you put a valve on the first one. I like your idea because of its simplicity, I just do not understand how a loop equalizes the pressure coming out of both of the returns, plus if it makes me have to use a bigger pump because of the extra total head (94Ft of return line) my electric bill may cancel the simplicity of the loop. I am probably over thinking this, but I am installing my first and only pool and just trying to get it right the first time if at all possible.

Considering the above and that I have heard that IG pumps last longer and are more energy efficient than AG pumps, would a full rated IG pump be a better choice? I would like to use Pentair and Hayward brands. Hayward dominates my local market, making it easier to find parts, but I have heard really good things about Pentair except that they cost a little more.

Depending on how many gallons you have, a 1 HP pump may be too much.

My pool size will be 21,200 gallons.

The Liquidator is a great choice, in my opinion. Make sure you do the upgrade kit if you really want it to work!

The two websites that I know that sell the Liquidator did not show the upgrade kit. What site has the kit? From searching on TFP I am guessing that you are talking about the 3/8 line conversion and using the no hole drill process?

Thanks for clearing up the bigger filter is better thing, and slower low speed filtering is just as good or better. I am all for the smallest pump size possible. I am just worried about the 40 plus foot of return line (90 plus foot in looped return). And will I have enough suction pressure on my hayward AquaBug Automatic pool cleaner?

Sorry for all the questions, just trying to get this done so I can start buying by the end of the month.
Thank you both very much for the input. I appreciate it.

 

[mas985]

A loop helps to equalize the pressure at each return by providing two paths for flow rate to each return. However, it doesn't gaurentee that the flow rate will be equal but it is better than feeding the two returns with separate pipe that is not of equal length.

However, one simple way to equalize the flow rates to two returns is to place the equipment half way between each return so the pipe runs are identical. This will save you both on head loss and pipe since you really won't need the loop. You can also go with the manifold idea as well but you shouldn't need to reduce the flow on either return as they will be nearly identical. Ideally, the skimmer would be located near the equipment so that pipe length is kept to a minimum (better to have less head loss on the suction).

Also, if you decide on an IG pump, keep in mind that the HP ratings are not equivalent. A 1 HP IG usually has a much higher head curve than an AG pump so it will create much more pressure and flow rate for a given plumbing system. Because of this, AG pumps tend to be more energy efficient as well.

 

[Strictly BBB]

Thanks mas985
I reread your Hydraulics 101 and got a little confused on the foot of head section. It seems that if the system is not already installed, I can not find my total foot of head, but without knowing the total foot of head, I can not buy the smallest energy efficient HP pump for my 21,200 gallon pool.

First, I called Pentair about the Pentair SD-80 Sand Dollar Filter with ClearPro Technology (3.5 ft of filtering surface) Link , to find out if they could give me a ballpark figure on the total foot of head on this filter when it is clean, their answer was 10 Ft of head. This sounds low to me,that would mean the filters gage pressure is (10ft*0.433=4.33 Psi)

According to this Link from hydraulics 101, the average AG pool with a pump, filter, one return and around 10 ft of 1.5 inch line should have 30 ft of head. But, I want to add a second return line, this is an extra 47 ft of 2 inch line (Half of 30ft pool circumference). Or 94 ft of line, if I decide to make a simple loop return setup.

Second, Is there a way to figure how much the extra 47 ft of 2 inch return line (94ft if looped) will change my foot of head? There will be 45 degree fittings about every 4 foot, so the pipe will go around the pool.

Could it be that the 30 foot of head on the average AG pool be caused by using too big of a Hp pump with too small of a filter and the use of 1.5" PVC pipe (Max flow of 42 GPM)? Would changing these three factors help offset some and/or all of the head change from the extra plumbing for the second return, so that the total head would remain around 30 ft?

Third, (1.5 inch Pvc max flow is 42 GPM) (2 inch max Pvc is 73 GPM) To turn over my 30 ft AG pool (21,200 gallions) one time in 8 hrs, it would take a little over 44 GPM, so would I need at least 2 inch PVC on both the suction and the return lines?

I now know that I need a pump with 44 GPM MIN. and not over 73 GPM MAX(This is the max of the filter and the 2 inch pipe) of flow, but again without the total head amount I am just guessing at the pump size? :grrrr:

Fourth, What is the point of a 2 speed pump with a max head of 20ft (As most 2 speed AG pump and some of IG pumps that I have found are) if my total pool system head is above that number? I thought that if a pump with 20ft of head was connected to a pipe that was positioned straight up 20ft in the air, it would fill the pipe with water, but not flow any water over the top, so a pool system with 30 foot of head and a 2 speed pump in low speed with only 20 foot of head would not flow any GPM? I am sure this is not true, just trying to understand. It looks to me that the GPM on the low speed would be way less than half of the high speed settings GPM, if the pool systems head was higher than the pumps low speed max head.

(mas985) However, one simple way to equalize the flow rates to two returns is to place the equipment half way between each return so the pipe runs are identical. This will save you both on head loss and pipe since you really won't need the loop. You can also go with the manifold idea as well but you shouldn't need to reduce the flow on either return as they will be nearly identical. Ideally, the skimmer would be located near the equipment so that pipe length is kept to a minimum (better to have less head loss on the suction).

Fifth, I would like to go this route, because it is the best to both worlds, equalizing flow and head loss, but with the location of the original factory return and skimmer holes being right next to each other, I would have to have a 24 ft suction line (1/4 circumference of pool) to get the pumping system in the middle of the two returns. Could I still do this using 2.5" suction lines and 2" returns with out hurting total head? (I may be able to plug the original return hole. Then I could do your return setup.) Or are we back to the 94 FT simple loop return setup? I do not care about the cost of the pipe just what works the best.

Finally, At this point I am getting frustrated with the whole process of finding the right pump, if you were to say that a 3/4 hp 2 speed Pentair whisperflo is the best pump for my needs. I would buy it, even though it is one of Top of the line IG pool pumps on the market. I am just wanting your best guess based on the above info. 1/2 hp, 3/4 hp or 1 hp make and model? single or 2 speed?

I am very tired of thinking about total head and pump sizing! I need to come up with a pump by the end of the month, so I can start ordering my pool.
Any and all comments welcome!
Just please help!!
Thanks

 

[dmanb2b]

Personally, I think you may be over thinking a bit, but so do we all One of the main reasons most of us found TFP Question...are you set on plumbing the returns 180 deg apart from each other? and why not maybe 10ft apart from each other? The reason I ask is on a round pool, dead circulation areas tend to be a non issue, especially if you point the returns slightly down and to the right. All of the 20K+ gallons of water will be swirling counter clockwise :compress: . I know my pool is almost half the volume, but same concept. You'll also not want to disrupt that circular flow, because as an added benefit, your pool debris will tend to accumulate in the middle of the pool, which makes for easy clean-up.

I push my water through a 250 lb sand filter, 2 solar panels and the 1/2hp IG pump has no problem trying to push the steps over if I aggressively point my single return to the right.

 

[mas985]

First, I called Pentair about the Pentair SD-80 Sand Dollar Filter with ClearPro Technology (3.5 ft of filtering surface) Link , to find out if they could give me a ballpark figure on the total foot of head on this filter when it is clean, their answer was 10 Ft of head. This sounds low to me,that would mean the filters gage pressure is (10ft*0.433=4.33 Psi)

That is only the filter, the rest of the equipment will add head loss as well. However, 4 PSI is not uncommon for just the filter but at fairly high flow rates.

Second, Is there a way to figure how much the extra 47 ft of 2 inch return line (94ft if looped) will change my foot of head? There will be 45 degree fittings about every 4 foot, so the pipe will go around the pool.

Yes but if you put the equipment between the returns, then the run length is only 24'. Each leg will have 2 45s and a 90. This will be the equivalent of 24+11=35' of pipe. Assuming the pump delivers 50 GPM or 25 GPM per pipe run, that is about 0.6' of head for the return lines.

If you go with a loop, the analysis is more complicated and it depends on where you put the equipment in relation to each return. Loops work much better when you have a lot of returns to deal with in a small area such as with spas. With only two returns, it makes much more sense to just have equal length returns. So again, I think a loop in this application is not necessary and would just complicate things.

Could it be that the 30 foot of head on the average AG pool be caused by using too big of a Hp pump with too small of a filter and the use of 1.5" PVC pipe (Max flow of 42 GPM)? Would changing these three factors help offset some and/or all of the head change from the extra plumbing for the second return, so that the total head would remain around 30 ft?

Yes, in plumbing higher flow rates result in more head loss so if you try to force too much water through a small pipe, head loss increases and efficiency decreases. This is another reason to go with as small a pump as possible.

Third, (1.5 inch Pvc max flow is 42 GPM) (2 inch max Pvc is 73 GPM) To turn over my 30 ft AG pool (21,200 gallions) one time in 8 hrs, it would take a little over 44 GPM, so would I need at least 2 inch PVC on both the suction and the return lines?

Not necessarily. If you have two return lines, half the flow goes through each so you could go with 1.5" plumbing (See below for head loss). Also, those recommendations on flow rates are not really hard limits and more or less guidelines to keep head loss low.

I now know that I need a pump with 44 GPM MIN. and not over 73 GPM MAX(This is the max of the filter and the 2 inch pipe) of flow, but again without the total head amount I am just guessing at the pump size?

Yes but I don't think it matters much. If you error on the side of too low a flow rate you will be ok. Nobody really needs 3 turns per day so you can go down to as much as a 12 hour turnover and be ok. Plus I think that even the smallest pump available will give you more than 40 GPM.

Fourth, What is the point of a 2 speed pump with a max head of 20ft (As most 2 speed AG pump and some of IG pumps that I have found are) if my total pool system head is above that number? I thought that if a pump with 20ft of head was connected to a pipe that was positioned straight up 20ft in the air, it would fill the pipe with water, but not flow any water over the top, so a pool system with 30 foot of head and a 2 speed pump in low speed with only 20 foot of head would not flow any GPM? I am sure this is not true, just trying to understand. It looks to me that the GPM on the low speed would be way less than half of the high speed settings GPM, if the pool systems head was higher than the pumps low speed max head.

Static head and dynamic head are treated differently. While it is true that low speed would not be able to lift the water 30’ in the air (static head), in this application, you don’t need to lift water. Dynamic head is dependent on flow rates so on low speed, the flow rate is ½ as much and head loss is ¼ as much so all is good. A two speed pump on low speed will always produce approximately half the flow rate of high speed, assuming there is no change in elevation.

Could I still do this using 2.5" suction lines and 2" returns with out hurting total head?

Yes, that is fine. The objective is to minimize the run lengths and maximize the pipe size. However, you can over do the pipe size but certainly 2" on the returns and 2.5" on the suction is more than enough and you could probably go a bit smaller. Note that these are very short runs and pipe itself does not add that much head, it is everything else that adds head loss. Also, with two return lines, you are splitting the flow so head loss goes down by a factor of 4. Here is a comparison of head loss with line size assuming you have a ¾ HP Pentair Dynamo, cartridge filter, minimal pad plumbing and with ¾” return eyeballs.

With 1.5" returns and 2" suction/pad piping, you will have 60 GPM @ 21' of head and an efficiency of 3.84 gallons/watt-hr.

With 2" returns/pad and 2.5" suction, you will have 64 GPM @ 18' of head and an efficiency of 3.97 gallons/watt-hr.

So there is only a 3% difference in efficiency going with the larger pipe. Also, you can see that even with the smallest pump, you will get quite a bit of flow rate.

So the bottom line is that you can pretty much go with as small a pump as you can find and still be ok. Also, I would not lose sleep over the pipe size as that does not matter much either.