Bernoulli vs. the pool guy

[mas985]

One simple way to model multiple runs is to divide the length of the pipe by the square of the number of runs. Technically, you should use the Hazen-Williams factor of 1.85 but the square is close enough. So if you had three runs of 40' pipe, you would then enter 4.44' of equivalent pipe. You can also do this with the fittings since they seem to take non integer valves in the spreadsheet. So 9-90s in each leg would become just one equivalent.

If the runs are unequal lengths and/or the fittings are not the same in each leg, then you can use this following formula:

Leq = 1 / ((1/L1)^(1/1.852) + (1/L2)^(1/1.852) + (1/L3)^(1/1.852))^ 1.852

L1, L2, L3 should include the equivalent lengths of each of the fittings in addition to the actual length.

This formula is derived from the fact that the head loss has to be the same in each leg but the sum of flow rates must equal the equivalent length flow rate even though each leg's flow rate can be different.

 

[chem geek]

As was just figured out in this long thread there's a huge wrinkle to the analysis of solar systems that are put on a roof or otherwise elevated. The panels in such systems are not designed to have a pressure lower than the atmosphere (i.e. are not designed to run with a vacuum relative to air pressure outside the panel) and the vacuum relief valve (if put near the top of the panels) will prevent this from happening in addition to being used to drain the panels when the solar is off. This means that the minimum pressure for solar panels will be that of the static head from the water level in the pool to the top of the solar panels. For panels whose top is at 15' above pool water level, that's 6.5 PSI and at 20' that's 8.7 PSI. This requires the dynamic head from the top of the panel to the pool to be equal to this 6.5 to 8.7 PSI. That usually requires a flow restrictor.

So there is no point in improving the piping anywhere along the line from the top of the solar panels at least back to the pad. The lines from the pad to the pool would still benefit from lower resistance (larger piping) when the solar was off. So the savings I detailed in this post are too high for solar and would instead only be:

To Solar: (1.8-0.8) PSI/100 feet @ 75 feet --> 0.6 PSI
Half of Solar on Roof: (1.8-0.8) PSI/100 feet @ 60 feet --> 0.6 PSI

so a total of 1.2 PSI compared to the 5 PSI I had calculated (or 1.5 PSI compared to 5.8 PSI if 3" pipe is used). This makes the savings quite low and not generally worth it, but does point out that if one wants to save on pump energy costs with solar one wants to minimize the elevation of the solar panels, if possible. So the analysis of savings from piping with solar is still valid if the solar panels are close to ground level, but becomes largely a moot point if such panels are elevated onto a roof.

Interestingly, in my system I have an unusually high and unexplained flow resistance (higher than expected pressure measured at the filter) when the solar is off and I'll bet that's because the flow restrictor needed for the solar is probably put into the main line so affects flow when the solar is off. That may have been done due to the 1 HP (1.65 SF) Jandy HHP pump that expects higher pressure to operate closer to its efficiency point. Now that I have an IntelliFlo VF pump, I don't need this so could move the flow restrictor to be in the return part of the solar loop only so as not to affect flow when the solar is off.

 

[mas985]

There are some who have sucessfully run panels under a slight vacuum so I'm not sure I total agree with that statement. In fact, I had a discussion with a couple of different solar panel makers and asked if this would be a problem and most said no as long as the vacuum is not very high. The panels were designed to operate under positive pressure but would stilll hold up fine under slight negative pressure.

However, one manufacture told me that they started to install the VRV about 6' above the pad in order service the valve easier and to allow solar to work on low speed of a two speed pump. He then explained that after they had started to do that, they had problems with the PVC return pipes collapsing on certain installs. It wasn't the panels where the problem existed but the return PVC pipe. If the solar system is shut off but the water is still in the panels (i.e. pump still running), the water can get very hot and then when the pump shuts off the VRV opens and there is a high vacuum on the return side of the plumbing pull very hot water through a PVC pipe. The pipe softens and then collapses. However, according to the manufacture, this only happend in very hot locations like the central valley and since they started to install CPVC, they haven't had an issue.

I still think you can get the system to operate well at lower speeds, you just need to take some extra precautions but placing the VRV closer to the pump either on the supply side of the panels or even further down the line solves the pressure issue at lower speeds/flow rates and doesn't seem to affect the panels all that much.

 

[teapot]

With 2" plumbing, the OP would save 960 watts/turn.

I think teapot mentioned something about saving energy. Form everything i can find on the net, it takes ~ 0.04 gallons of gas to produce 1 kW of power. So for one turnover a day for a 6 month swim season, thats a savings of 8 gallons of gas for the season. I burn more than that on a one way trip to NYC from Boston.

I realised a long time ago that talking about energy saving to Americans was.......well.....a waste of energy :lol:

Looking at your journey from NYC to Boston looks about 200 miles so you get less than 22 miles/gallon? European cars are good for 45 mpg (gasoline) and diesels (turbo charged) are good for 70+mpg.

As was also mentioned earlier, we tend to have two skimmers for pools around 24ft x12ft or larger. Baring in mind the max flow rate for skimmers from manufacturers info and that generally I see bigger pumps fitted on the pools on this forum are you balancing this with the flow through the floor drain? Otherwise energy is again being wasted?

 

[duraleigh]

Teapot,

That's pretty amazing gas mileage over there. Do those European cars hold more than one passenger (110 lbs or less) and a box of Kleenex? Are all the roads downhill?

 

[bk406]

Do those European cars hold more than one passenger (110 lbs or less) and a box of Kleenex? ?

 

[Ohm_Boy]

Teapot,

That's pretty amazing gas mileage over there. Do those European cars hold more than one passenger (110 lbs or less) and a box of Kleenex? Are all the roads downhill?

They will hold at least two passengers in the back, along with a wild-eyed unshaven cab driver in the front who is evidently playing 'tag' with some other, imaginary cab driver or former/future Soviet spy all the way from Prague to Brno, and they can get there in *record* time. Ask me how I know. Or don't - and I'll just go ahead and suggest the train instead. And they will hold a box of Kleenex. Also, a Tupperware-esque bowl of some sort of pork/dumpling concoction which is too thick to worry about spilling, and a month or so's worth of daily apple dumpling remains.

The real importance of their car's small stature is revealed in how many they can pack into an intersection.

 

[dmanb2b]

All kidding aside though...not sure about 45mpg, but with the price of fuel in Europe you don't see many 5.0 liter v-8s rolling around. Most are manual trans, with 1.0-2.0L engines, I'll bet ya they get pretty darn close to 45-50mpg

Here you can see that a BMW 318 4dr gets well over 40mpg and the diesel is good for 50+mpg

http://www.bmw.co.uk/bmwuk/pricesandspe ... uk,00.html

That said...nothing like a nicely worked chevy small block on a Sunday morning to pick up breakfast and avg about 13mpg

http://www.youtube.com/watch?v=Rxo8Qyhs ... r_embedded

 

[bk406]

Can we say Vauxhall?

rubber band and 4 wheels

 

[teapot]

Teapot,

That's pretty amazing gas mileage over there. Do those European cars hold more than one passenger (110 lbs or less) and a box of Kleenex? Are all the roads downhill?

Obviously depends on the size of the box of Kleenex, Really wondering what you need all that kleenex for

A timely little story, perfect to illustrate my point:
http://www.worldcarfans.com/110100428800/vw-passat-bluemotion-sets-world-record-for-single-tank

 

[lbridges]

It's worth noting that Mahindra (Indian OEM farm tractor company to non-rural US residents) is/was planning to import pickup trucks to the USA. They have run into a snag with who they intended to use as a distributor. However, USAToday reported their truck is rated for a 2765lb load and gets 32 MPG (diesel). A considerable difference from the domestic market one & a-half ton pickups (getting what - 10MPG - downhill, without a box of kleenex).

 

[Ohm_Boy]

It's worth noting that Mahindra (Indian OEM farm tractor company to non-rural US residents) is/was planning to import pickup trucks to the USA. They have run into a snag with who they intended to use as a distributor. However, USAToday reported their truck is rated for a 2765lb load and gets 32 MPG (diesel). A considerable difference from the domestic market one & a-half ton pickups (getting what - 10MPG - downhill, without a box of kleenex).

I wish them luck. See, that's another problem - there are many very efficient vehicles that cannot be imported into the US except as 'farm' vehicles and some esoteric off-road only classifications. I'd love to get a little Kei Truck, like a Carry or a HiJet, but can I? NOOOooooooo.
In essence, we regulate against efficient vehicles, then turn around and try to regulate higher efficiency standards targets... I don't know how this is supposed to work.