Pump Sizing Question

[BigDave]

I'm planning to install a small new AG pool. in a couple years, I'd like to get a larger AG or maybe an IG. I want to size / buy a sand filter and pump to support the larger pool. I will also be installing a solar heating system that will be on a roof 25' above the pump. How do I calculate the appropriate size of pump / filter? how much pressure is lost to the filter, piping, etc? Any assistance greatly appreciated.

[PoolDoc]

With a sand filter, optimum performance is to filter at 12 GPM per sft or less and backwash at 15 GPM per sft. So for a 30" filter, maximum (optimal) filter rate is (1.25^2) * 3.14 * 12GPM/sft = 60 GPM. Optimal backwash would be 72 GPM. So, that's one constraint.

If you select an 8 hour turnover rate for your ultimate pool, than a 60GPM system would match a pool up to 28,800 gallons. If you use a 24" sand filter, your filter SFT is (1^2 * 3.14) or 3.14 sft, and 38 GPM. That matches a pool up to 18,000 gallons. I wouldn't go smaller than that, if you want high quality water results.

With the solar unit, you'll need to find out if you have to install a suction relief valve are not. If you do, your pump & filter have to maintain a pressure of at least 10 psi at the filter discharge, at all times. Without a suction relief, you can start on high, but then switch to low once the lines are filled with air.

Given the changes you're planning, I think you may find it hard to calculate all your flow losses.

I'm not really in love with the electronically complex multispeed pumps like the Pentair Intelliflo (link), but I think in your circumstances, that might be the most practical and effective choice. Installing a few gauges and a flow meter, like this one, Blue White 2" flow meter - (Manufacturer info) , would make it easier to adjust flows once everything is in place.

[Poconos]

The only thing to clarify is the 10 psi at the filter discharge assumes ALL the water goes through the solar. Many times this is not the case as you just need to flow a few GPM through the solar. People divert around the solar to maximize the total circulation flow. So, that 10 psi must be at the pipe leading to the solar panels if you intend to divert some water around the solar. In my setup I have a homebrew solar in a back field and a 4x20 foot mat inside the pool fence. The filter output is split 3 ways. One to the returns directly and the others to each of the solars with each of them dumping into the deep end through their individual hoses. To get the one in the back field purged of air since it is about 10 feet higher I need to manually divert all the water until I blow the air then cut it back. As long as the system doesn't leak air back in I'm OK to shut the pump off until next running.
Al

[CarlD]

My pool has some similar and different characteristics than Al's. Not better, not worse, just different. I have a FantaSea pool where the decking around the pool are solar panels. Heats the water and keeps the deck cool under your feet!
I Tee the return flow to the return and to the solar panels. I then Tee to the solar panels (I have two circuits) and each solar circuit has its own ball valve, along with a master cutoff for both. I do NOT have a ball valve on the return as forcing all the flow to the panels will blow the FantaSeas apart--they are somewhat limited as to the pressure they can stand. I don't have the purging question Al does--they purge nicely with very limited pressure.

Carl

[mas985]

A couple more things to consider. 10 PSI at the solar pipe input does not include dynamic head loss which will drop the pressure at the VRV even further so you need to add a couple of PSI for that as well. As an example from my system, When the filter pressure is 15 PSI, the VRV pressure on top of the panels is about 2 PSI. I have a bypass in my plumbing system and when I bypass enough water to lower the pressure in the filter to 14 PSI, the VRV is about 1 PSI which is about a low as I would want to go. In fact, if I bypass any more water, the panels will not prime. So I would target 14-15 PSI at the filter.

Also, most IG pumps have enough lift to prime solar panels but not all AG pumps do so you have to be careful about looking at the pump's head curve to make sure the pump has enough flow at high enough head for priming. Based upon my own system, the pump needs to produce at least 45 GPM at 50' of head to prime 25' high panels.

[BigDave]

Thanks to all of you, Mark I've been through most of the links in your sig - Thanks loads!
I'm going to try to estimate the static and dynamic head of my proposed system. I've emailed Hayward asking for pump curves for the 1 and 1.5 HP Power flow Matrix AG 2 speed pumps. Haven't heard back yet. It seems to me that the sweet spot would be a two speed pump with enough head on high to prime the solar and enough head on low to maintain the solar's flow rating (accounting for system dynamic head and psi required for vacuum check valve) and turn over the pool in eight hours (without the solar). Clearly this could all be achieved with a variable speed pump of sufficient capacity but those critters are pricey.
Does anyone knoe of a solar control system that will start a pump and run it on high to prime the panels and then on low (after staic head is returned).

[mas985]

You will have a hard time running a solar system on low speed of a two speed pump. In order to do that, you will need to plumb the vacuum release valve at a low elevation right above the pad. However, I would not recommend this as it will also the require the panels to run under a slight vacuum. Plus you will also lose efficiency running the panels at lower flow rates. With a two story house and recommended VRV placement (i.e. top of panels), you will need to run a pump at high speed or a variable at fairly high speed in order to keep the pressure up and the VRV closed. This is why I have such a low HP two speed pump. I use high speed for solar and low speed when I don't need solar.

[PoolDoc]

BigDave, if you get those charts, would you mail them to me?

I'm working on project that hopefully will be visible next spring, and will publish ALL of the pool info I've gotten over the uses, plus stuff I've found with Chem_Geek's help, plus all of HIS stuff he'll let me put up, plus all the chem MSDS I have, PLUS the old PacFab pump & hyrdraulics training manual (with the only detailed PacFab curves I've ever seen), etc.

My hope is it will be a reference we can all use to upgrade the information available to general pool users, by upgrading the information the 'answerers' have.

Already got the domain name, and with the advent of EPB Fiber here, bandwidth is no longer an issue. Which is a good thing, since the folder I have for that stuff is already almost a gigabyte, and I'm just getting started.

[BigDave]

Thanks Mark, that makes sense.
Does anyone know(knoe) of a solar control system that will switch the pump to high speed when calling for heat and back to low when it's not needed?

[mas985]

I think most controllers that control solar will switch to high speed by default. I know for sure that mine, AquaLogic, will definitely do that.

As for head curves, is the pump you are considering on this page?

The single speed and two speed versions will have the same head curve on high speed. Low speed is simply a scaled version. But looking at these pumps, I would like to see a little more flow rate at 50' of head. But you might ask the forum if anyone is using one of these pumps for a two story solar install. But if you want to be safe, I would go with an IG pump. Something like a 1 HP SuperPump, I know would work.