Need technical pump help- Sizing, electrical use, etc.

[Rangeball]

You can get a flow meter for under $100. See for example this site. You need to have a couple of feet (pipe diameter * 14) of horizontal (or vertical with a different model) pipe with no other fittings to install the meter.

Pools should come with flow meters!

Jason, I was actually considering posting the other night to see if there would be any interest in a group buy that we could share. Get enough interested, and it would be pretty cheap to know your flow. I had thought of plumbing something so it could attatch to my return so I'd not have to mess with my other plumbing.

 

[Rangeball]

Rangeball,

Jason is correct in that without additional measurements it is pretty much guess work but I suspect that you are closer to 40 feet of head than 30 feet of head but again it is based on how other pools operate.

From the pump curve, I read the Dynamo at about 45 GPM @ 40 ft. while the Whisperflo will be about 53 GPM @ 66 ft. and I believe that the Whisperflo draws less current than your current pump. So your total power savings is close to 20% which about as much as can expect when upgrading to a high efficiency pump.

You will get much more benefit on low speed where the energy use is about 1/3 while flow rates are only 1/2.

So at low speed with the Whisperflo, you are likely to save close to 50% over your current pump.

Thanks Mark. Even more of a reason to consider the 2 speed when you through flow increase to DHL into the mix.

 

[Rangeball]

Mark, one last thing (I hope )

I was looking at the chart for the whisperflow, and there seems to be a good deal of difference between the 3/4 hp you modeled for my pool and the 1 hp. I assume the 1 hp will increase DHL, but I wonder by how much?

My filter can handle up to 90 gpm. You have the 3/4 HP WF at 53 gpm. That leaves me quite a bit of room to turn my pool over quicker and I'm wondering if it would possibly reduce energy consumption even more.

What do you think DHL would be on my pool with the 1hp WF?

 

[Rangeball]

BTW,

Head loss changes by this formula:

New Head Loss = Old Head Loss * (New GPM / Old GPM) ^ 1.852

What function does the "^" denote in the above formula?

And new GPM is based on old head loss rating?

 

[mas985]

First, higher HP pumps will have lower GPM/Watt so your flow rates do go up but the energy use goes up much faster. So you are always better off with a smaller HP pump if you don't really need the flow rate which I don't think you do.

Also, ^ is power so ^ 1.852 is the quantity () taken to the 1.852 power so here it is with more formating.

New Head Loss = Old Head Loss * (New GPM / Old GPM)^1.852

 

[Rangeball]

I put a new gauge on my filter. Long story short, last summer the quick air relief valve assembly that the gauge went on snapped off, I simply plumbed a valve into the top of the filter. I had always planned on getting some fittings to attach the PSI gauge to it, and finally did this last weekend

It read 8 psi, which is lower than the 10 I reported earlier in this thread. I think the reason is is that the 10 number was what it consistently read at for the past several years, when I was dumping in DE until I got to 10 as that's what it was after the pool guy fired it up years ago. Looking back, he just dumped some DE in, don't know if or how he measured.

Anyway, last summer I got a dedicated DE measuring scoop. Now I know EXACTLY how much DE to put it per my filter recommendations. This is the first psi reading I've taken since using this scoop. Likely before, I was adding too much DE, which is why I'm now getting the slightly lower measurement.

So, 4 x 8 psi = 32 for DHL. With my Dynamo this puts me right at 60 gpm. If I'm understanding things correctly, the 3/4 hp whisperflo should be 52 DHL with a 68 gpm flow.

Sound about right?

 

[mas985]

Probably as about as close as you will get without a suction measurement.

As a point of reference, the PSI to head loss fudge factors could be as high as 5x for 1.5" plumbing so you can always use that as a worse case (highest head and lowest GPM) to get a range.

 

[Rangeball]

Thanks. 5x would put me about 45 gpm with the dynamo.

Another potential wrench is comparing a non-self priming AG pump's DHL to a self priming IG model.

My dynamo is about 15" above the surface of my pool water. With the skimmer basket and line dry, it won't self prime. With the basket and line full, it will stay primed with the skimmer line open, but not the main drain line. With ony the main drain line open, it has problems pulling and flow in the basket reduces to about half. It's likely I'm getting more suction DHL with the dynamo than I would with the whisperflo, so even if I measured with a suction gauge it's likely not to be relevant.

I guess in summary, I've learned an energy efficient full rated 1/2 hp 2 speed pump would probably be perfect for my pool, but since this is hard to find (northstar? for some reason I'm thinking they didn't have this), the 3/4 hp 2 speed whisperflo is probably as good and efficient pump as I can expect to get for my pool.

Thanks Mark

 

[Rangeball]

New Head Loss = Old Head Loss * (New GPM / Old GPM)^1.852

Mark, I'm still confused on this formula.

Assuming I know my old head loss, how are you determining New GPM to insert in the formula, since that is what we are trying to determine by getting to New head loss so we can look at the flow chart?

3rd grade level explanation would be great

 

[mas985]

Basically that equation is your plumbing curve that you must overlay on top of the pump head curve. The two curves are somewhat orthogonal so where they intersect is your operating point. So what you have is two equations (pump head curve & plumbing head curve) with two unknowns (head loss & GPM). Both must be solved simultaneously.

It is easier to solve both graphically than numerically. So enter a set of GPM values that span most of the pump head curve into the plumbing equation to get several Head, GPM value pairs that you can then plot over the pump head curve. Connect the dots and find out where the two curves intersect.

I tried to model your plumbing the best I could and here is what I come up with for the Dynamo:

Suction Head: 13 ft
Return Head: 19 ft
Total Head: 32 ft
Flow Rate: 63 GPM

I had to reduce the return head significantly in order to get 8 PSI and I am not sure why.

Changing the pump to the 3/4 HP Whisperflo:

Suction Head: 18 ft
Return Head: 27 ft
Total Head: 45 ft
Flow Rate: 76 GPM

The only other reason that the PSI is so low could be that your current pump is damaged in some way and is not generating the flow it should. If I make that assumption, then the results of the two pumps are a bit different.

Dynamo (25% derated):

Suction Head: 4 ft
Return Head: 19 ft
Total Head: 23 ft
Flow Rate: 34 GPM

Whisperflo:

Suction Head: 11 ft
Return Head: 51 ft
Total Head: 62 ft
Flow Rate: 59 GPM

So you can see depending on what you really have going on, you can get different results.

Sorry I can't be more specific but without the suction measurements, it is somewhat of a guessing game.

 

[Rangeball]

No need to apologize, I need to apologize for continuing to hound you about a topic I just can't seem to get my head around...

I don't think my pump is damaged, but who knows. I'm certain the lower pressure reading is due to applying the proper amount of DE where before it was overloaded somewhat.

I think my BIL might have a vacuum gauge. If he does, I'll try to get the measurement asap.