How To Determine Water Turn Over Rate

[itabb]

How could I estimate the amount of time it takes to send all of the water in my pool through the filter one time. I have a 15,000 gallon pool, 1.5HP (1.1kW) sta-rite pump and a Sta-Rite system 3 filter. The filter says max flow rate is 125 GPM, which I guess is gallons per minute. If the filter is my limiting factor, then that is 2 hours to turn over all the water in my pool. I don't know the flow rate of the pump. I am going to assume that the sizing of pipes, holes, etc is as perfect as can be because of the installer's reputation in the area.

Furthermore, I'd like to know the minimum number of times I need to turn over the water in the pool for each 24 hour period, assuming light use and little sun (less than 1 hour exposure a day) with a SWG, FC 3-4.

Finally, if the pool is closed over night, is there any reason to circulate the water at all during the night if the water turned over enough times during the day? Or would running even a bit over night optimize sanitation because the water would not sit for still for 16 hours (or so) straight?

I'm looking for some guidance to start with which I can then tweak for my specific usage. I have a Jandy control, so scheduling is not an issue. I do factor in that I add chemicals in the evening or morning and solar heating is optimal between noon and 5pm.

[chem geek]

How could I estimate the amount of time it takes to send all of the water in my pool through the filter one time. I have a 15,000 gallon pool, 1.5HP (1.1kW) sta-rite pump and a Sta-Rite system 3 filter. The filter says max flow rate is 125 GPM, which I guess is gallons per minute. If the filter is my limiting factor, then that is 2 hours to turn over all the water in my pool. I don't know the flow rate of the pump. I am going to assume that the sizing of pipes, holes, etc is as perfect as can be because of the installer's reputation in the area.

Furthermore, I'd like to know the minimum number of times I need to turn over the water in the pool for each 24 hour period, assuming light use and little sun (less than 1 hour exposure a day) with a SWG, FC 3-4.

Finally, if the pool is closed over night, is there any reason to circulate the water at all during the night if the water turned over enough times during the day? Or would running even a bit over night optimize sanitation because the water would not sit for still for 16 hours (or so) straight?

I'm looking for some guidance to start with which I can then tweak for my specific usage. I have a Jandy control, so scheduling is not an issue. I do factor in that I add chemicals in the evening or morning and solar heating is optimal between noon and 5pm.

I suggest you post your question to troublefreepools.com and have mas985 answer your question. He's the expert on flow rates, head, pumps, etc. The way I figured it out in my own pool was to get the pump's head curve from the manual and look up the flow rate based on the pressure recorded on my filter pressure gauge. I added a little more to that to account for suction head. That's the easiest thing to do. Otherwise, you could attach a large diameter hose to a return and measure how long it takes to fill a bucket (of known size) with water. Do that for each return and add the results. It's important to use a large diameter hose to minimize the extra head (resistance to flow).

As for the turnover rate -- i.e. number of times to do a full turnover of water per day -- that is debatable. There are multiple purposes for circulating the water. One is to filter out particles. For that purpose, you only need to run your pump as long as it takes to keep the water clear. If you run your pump so short a time that your water starts to look cloudy, then it's too short. This is really a function of how much junk gets thrown into your pool. The other purpose of circulation is to prevent localized consumption of chlorine -- i.e. to evenly distribute chemicals. There is still diffusion, but if algae takes hold it can readily consume the chlorine locally and continue to grow in relatively still waters. This is a harder one to quantify, but having a somewhat higher chlorine level probably combats this. Regular brushing would also help reduce the need for as much circulation.

For my own pool, I run it 8 hours per day during the peak solar times of 9 AM to 5 PM (the sun goes behind trees in the late afternoon). I also brush all pool surfaces once a week and the water temp is around 85-88F. During the winter, I run it only 2 hours per day (and don't brush the pool) and the water temperature is around 45-55F. It would be technically better to run it over 24 hours at a slow speed, but the solar situation prevents that. After I get my Intelliflow variable speed pump, we'll see if some solar at higher flow rates (48 GPM) plus non-solar rest-of-day at lower flow rates (12 GPM) will work.

Richard