New pool, pump question

[GTakacs]

Hi,

I am having a gunite pool installed soon. The pool is 30'x24' but if you look at the picture you'll see that it's actually a much smaller pool than those numbers make it look like. It also has a beach entry for the first step which is rather large. Total surface area is around 470 sq ft. Depth will vary from 3.5ft to 6ft. My designer estimated the pool to be 22,000 gallons but I just can't come up with that number any way I try. Actually it seems like he used an ellipse approximation of 30x24ft and used an average depth of 4.75ft ((3.5+6)/2). With this calculation I get 20,000 gallons but the ellipse area would end up being 565 sq ft and I already know that the pool is nowhere near that.

Long story short, based on my calculations I am estimating between 13,000 and 17,000 gallons (I am thinking it'll be a lot closer to 13,000 than 17,000 though).

The designer added a 1.5hp pump to my contract but I think it is an overkill for my application. They are installing 2" drain, skimmer (2 skimmers) and return lines (the return line get reduced to 4 1.5" returns). My equipment will be probably about 50ft away from the pool. I don't know what my total dynamic head is going to be but I can't see it being excessive. I'm going to have a salt water system (so the salt generator will add some dynamic head) and I will have a Jandy DE 60 sq ft filter which is capable of 120GPM flow if needed.

OK, so the question is: why would I want a 1.5hp pump? In worst case scenario my pool is 17,000 gallons and if I want to turn the water around in 6 hours I would need 47gpm flow rate. it seems like a 0.75hp pump would do just fine for my application as long as my THD is under 65ft.

What do you think?

Here is a picture of my pool design:
http://gregtakacs.com/dpr/pool2.jpg

[imfignewton]

Your pump could really be a 1hp if it is an uprated pump. Some pool companies quote an uprated pump to make it look like your getting more.

[duraleigh]

Hi, Greg,

I think you're on the right track on all accounts. I agree with your pool calculation.....I just placed an imaginary rectangle over the body of the pool and used 4.5 for average death....16,000 gallons.

I no engineer but most pools have a THD around 40-50 it seems...yours should be no exception. A full rated .75hp pump would be perfectly adequate for your pool. :)

[mas985]

I agree with Dave, .75 HP full rated is more than enough. For a given pool design the THD drops with the pump HP so you will get plenty of flow and save on electrical costs.

My guess is your head loss for the .75 HP pump will be close to 40 ft while it would have been up near 60 ft for the 1.5 HP pump.

[PoolDesignnet]

I traced the pic of your pool and it looks like about 15,000 gal, and mabye a shade under. The beach entry has almost no water and I took that into account. 1hp uprated or 3/4 hp full rated is all this pool should need unless there is some other waterfeatures that we don't know about.

Also, 2 skimmers is overkill for this pool. And if I may suggest, the beach entry should be a beach step instead.

[GTakacs]

The beach entry has almost no water and I took that into account.
Based on my calculations the beach entry will hold around 260 gallons of water.


1hp uprated or 3/4 hp full rated is all this pool should need unless there is some other waterfeatures that we don't know about.
There will be a 12ft x 2 ft x 2 ft cascading waterfall but it will have its own pump (the designer added in a 1hp pump for that, don't ask if it's full rated or up rated, I do not know). They were going to run the waterfall off of the same pump as the pool but I said no!


Also, 2 skimmers is overkill for this pool. And if I may suggest, the beach entry should be a beach step instead.
This particular builder builds every pool with at least 2 skimmers, other than the cost, is there another drawback to having two skimmers? For the beach entry, my wife really wanted a true beach entry so that is what we're going with. They are installing a return (a 5th one) in the middle of the beach entry with a directional jet to move the water. I hope we won't regret it. I have read the possible problems with a beach entry I just hope that my builder is familiar with building one and will overcome them.

I haven't mentioned that I'm getting Pebble Tec for the pool including the beach entry and I will have a Levolor Water Level system isntalled to keep the water level constant.

[PoolDesignnet]

Hi,

I was concerned with the size of the beach entry. Looks like it will be about 10' into the pool. About 3' of that area will be dry. That leaves 7'. With the slope of 1' in 7' it will drop 12" in depth over the remaining length. There will be a drop-off at the end of that on the right side and two additional steps on the left. While it may look nice, it's not a very functional area. Just my 2 cents....

Pebble tec is the only way to go on a beach entry pool. You may even do that in a sandy beach color and the rest of the pool in blue or what ever color you have chosen.

[GTakacs]

I was concerned with the size of the beach entry. Looks like it will be about 10' into the pool. About 3' of that area will be dry. That leaves 7'. With the slope of 1' in 7' it will drop 12" in depth over the remaining length. There will be a drop-off at the end of that on the right side and two additional steps on the left. While it may look nice, it's not a very functional area. Just my 2 cents....

I am aware of the above issues, it is what the wife wants so this is what we're getting. We're paying a fortune for nothing essentially as far as swimming area goes. Your math is correct, we're doing a 1' in 7' drop down to 12" water level then two more steps at 10" each for a total depth of 42" at the shallow end (3.5 ft). I have an 18 month old son so I hope to get at least some use of the area for a little while.



Pebble tec is the only way to go on a beach entry pool. You may even do that in a sandy beach color and the rest of the pool in blue or what ever color you have chosen.
We'd love to get a separate color for the beach entry, unfortunately they're asking a $2000 surcharge for a second color, I think it's excessive. I will double check on these numbers, but for now I think we're going with a single color.