How long does the pump really need to run?

[nefretrameses]

Interesting. I too was advised to run the pump basically for as long as the sun was on the water. That's about 9 hours in summer and 6 in winter. Since I read the article, I have been running my pump 2 1/2 hours and the water looks great. It will be interesting when it warms up to see what happens. Right now there is no bather load. (Water is 68 degrees)

Mark points out that longer run times may be needed for SWCG systems. I suppose the same is true for solar heat at times. During times when you want to get the most heat into your pool, you will want to run the pump for as long as you get a temperature differential (of some minimal amount).

[Anonymous [GDPR] European in the UK]

But water clarity has little to do with pump run time. Clarity is more about chemistry. What makes a pool cloudy is usually algae and not debris. Most debris either floats and can be cleaned by the skimmer or sinks and can be cleaned by a sweep. Pump run time is basically for these two things and for the distribution of chlorine, which takes only about 30 min for a manual dose. So pump run time is more about aesthetics than anything else which is why it can be significantly limited to meet only the cleanliness needs of the pool owner.

Now that is what I also believed early on, howerver although chemical balance is important and customers who have poor circulation I usually recommend running a higher chlorine level to try and improve the water quality/clarity. From my original experiments and from studying other people work I now believe that clarity is also very much about pump run time.
Leaves spend only a certain amount of time floating before becoming water logged and starting to sink. This means there is an optimum time to make sure they are removed by the skimmer/s. Like wise other dirt that ends up in suspension, colloids etc which are the cause of turbidity in water. If you push the water around for a few hours some is removed and after the pump is switched off, some sinks, as you say for manual removal. Manual removal however isn't that easy as small particles easily get stirred up and back into solution as most pool owners will admit. They start with a clear water but after manual cleaning the water loses that clear look for a while until the dirt settles again only to be stirred up by swimmers etc.


http://en.wikipedia.org/wiki/Turbidity

Running the pump for 24h constantly as we know from the water dilution principles means that 98% of the water has passed through the filter after 4 water cycles and that means far more dirt and small particles are removed and if the filtration is good enough colloids can also be removed. This greatly improves the water clarity and means chlorine can last longer and there is a lot less manual cleaning to be done and when it is needed there is no dust cloud to make the water cloudy. When your pump is off everything that enters your pool ends up on the bottom and stirred up when the pump starts.
I have tested this on my own pool and the requested customers to carry out the same test and the same results were observed. From the wiki link and average pool water is around 5 NTU's and a poor pool 10+ after several weeks of running my pool 24/7 which I now do for the whole summer the level of 1 NTU was obtained on my tester. The chlorine consumption fell although the sun still takes it's toll and the pH became more stable.

The reason we don't run our pumps for 24h? Cost and with the correct setup that issue can be put to rest too at least for domestic pools. I realise with the wide variations in pool water and temperature you have in the USA are different from Europe but I am sure that the pools will benefit form the extended run time. It is better to move the water constantly but slower than to move it rapidly for shorter time. Filters work much better with a slower flow so remove more but the downside of the 24h running is more frequent visits to empty the skimmer baskets proof that it works.

[mas985]

According to this web page collides are generally smaller than 1 um.This document also confirms that particles > 2 um will settle out in a few minutes but anything less than that will remain suspended indefinitely. At best, DE filter can only filter down to 5 um so any particles that are actually suspended in water, will not be filtered out anyway.

[Anonymous [GDPR] European in the UK]

Yes Mark, I agree and I said if the filtration was good enough. I don't want to get into the area of colloids yet but the point was more that continuous running of the filtration but at a slower rate will improve the the water quality by removing more suspended solids because they are suspended and so can be skimmed and filtered and not just sinking to the bottom once the water has calmed. I have vaccuumed too many pools only to see small clouds created by dirt if you move too quickly or make sudden moves. Running the sysytem continuously has removed that problem. That said, I wonder if removing too much from the water would cause a greater loss of chlorine to photodegredation as the suspended matter may shield chlorine from the sun's UV in the same way as bacteria and algae can be shielded from chlorine as stated in your second link.

It is a fact that DE can remove Ocyst of Gardia and Crypto providing the grids are intact but DE is just a mechanical filter to go to the next level we need adsorption to draw particles to the surface of the filter media.

As you have a large cartridge filter and a good sized 2 speed pump, I would be interested in your flow rate and system pressure at normal running conditions if you wouldn't mind passing on that information please?
Regards
John

[mas985]

On high speed without solar, flow rate is around 68 GPM and with solar around 58 GPM. On low speed, flow rate is half of 68 GPM or about 34 GPM.

[Anonymous [GDPR] European in the UK]

Thanks Mark, What sort of pressure shows on the gauge at those flow rates? I usually fit sand filters but have a customer who specifically needs a cartridge filter and to get my system to run well the system pressure doesn't want to be too high.

Regards
John

[mas985]

High speed filter pressure is about 10 PSI without solar and 14 PSI with solar.

But I don't understand what you are trying to say here:

and to get my system to run well the system pressure doesn't want to be too high.

Cartridge and DE filters have about the same head loss independent of filter size. Only sand filters, because of the small area, have a head loss dependency on size.

Also when sizing a filter, you really should use the APSP-15 specs and don't worry too much about pressure. APSP-15 specifications use a rate of 0.375 GPM/sqft for cartridge filters.

[Anonymous [GDPR] European in the UK]

Happy new year Mark and thanks for the update. Yes with sand filters they only present a small surface area ( pi x r2 of the filter size) as the depth of the bed isn't considered for some reason so I would have expected the pressure to be lower with the large surface area of a pleated cartridge or DE grids. You say the headloss is about the same regardless of filter size, therefore they are very poor performers hydraulically speaking which doesn't surprise me as the pool industry designers are pretty lazy/useless/untrained?

Helpful to know though thanks, On your slow speed I would have expected the headloss to drop quite a lot especially as your filter is quite big.

[mas985]

You say the headloss is about the same regardless of filter size, therefore they are very poor performers hydraulically speaking which doesn't surprise me as the pool industry designers are pretty lazy/useless/untrained?.

Actually it means just the opposite. Cartridge and DE filters have the lowest head loss so are are very good performers hydraulically. The head loss doesn't change with size because even the smallest size is "large". What causes the head loss in these types of filters is just the internal fittings and for DE, the backwash valve adds a lot of head loss but the media does not add much to the head loss. I can take the cartridges out of my filter and the pressure does not change which means they don't add any head loss. Only the internal plumbing fittings add head loss which is why it is so low. However, for sand filters, the sand area is quite small and that does have an impact on head loss but only for filters smaller than about 5 sq-ft.

Here is a table with several different types of filters and filter sizes (sand only). For a given filter line with cartridge and DE, the head loss does not change with size but as you can see, the cartridge has the lowest head loss and by quite a bit of margin.



Also, I didn't post the low speed pressure because it doesn't actually read a pressure. But theoretically, it is about 2 PSI.

[Anonymous [GDPR] European in the UK]

Many thanks for that Mark, Chart saved for future reference.

What you have said about cartridge having the lowest head loss is what I was expecting. As you say the internal fittings are where the head loss occurs which is why I said the "designers" are lazy etc because it could easily be improved and needs to be given that we are going Eco. I have fitted a 15 PSI gauge to my filter as I needed to see the 2 PSI I run at also. I notice the almost exponential graph as the flow increases, which fits with my empirical data and is where I am investigating the head loss. Is it through the media or bad plumbing? Not an issue in the past as a powerful pump always makes sure the water gets where it's going but reducing the power brings on new challenges.

Thanks for you help on this, it's appreciated.

Regards
John