A pool's plumbing system is designed to keep the water clean and hygienic. It consists of one or more suction fittings in the pool that draw water and debris in, a bunch of equipment located somewhere near the pool that processes the water, and one or more returns, where the clean water flows back in to the pool.
On the suction side, most pools historically had a single skimmer (box that draws water from the edge of the pool at the surface) and a main drain, typically located on the floor at the deepest point. This has the potential to be a dangerous setup as it can present an entrapment hazard.
Pool water pumps can be very powerful and if they are drawing water from a single drain in the pool (most pool setups typically have a valve to select between drawing water from the skimmer or the drain or a combination thereof), it's possible that someone could become trapped if their body covered the drain.
The death the granddaughter of former US Secretary of State James Baker III as a result of an entrapment incident led to the enactment of the Virginia Graeme Baker Pool and Spa Safety Act to regulate pool drainage systems. In Australia, AS1926.3-2010 regulates suction fittings.
Both sets of regulations seek to prevent entrapment by only permitting the use of approved drain covers that have been tested to not present an entrapment hazard at specified flow rates and by requiring multiple drains (with minimum spacing) to be connected via a common line. The idea being that if one drain becomes covered, water will drain via the other rather than creating a vacuum in the pipe trapping the swimmer.
The simplest arrangement on the suction side is to have a single skimmer only. The skimmer draws surface water and is great at removing surface debris. The key problem with a skimmer only setup for us is that the water at the surface is the warmest. We will be installing solar heating and for maximum efficiency, the cold water from the bottom of the pool should be used to feed it. So we need an additional suction point low on the deep end wall and an additional one to prevent entrapment. All in the design looks like this:
The returns are design to try to get the water circulating around the pool (and debris into the skimmer) and also to mix the returned (solar) heated water with the cool water low in the deep end.
Most sources recommend passing the entire volume of
water in the pool through the filtration system every day. Flow rates vary, but this typically equates to running the pump for several hours per day.
The flow rate of water through a pipe depends on two things - the resistance to flow of the pipe itself, and how hard you push it.
Pushing harder requires more power. Some time spent during the design phase to minimize the resistance can provide substantial savings over the life of the pool.
Even in a straight and level tube, friction with the pipe walls will
resist movement of the water. Add right angle bends, tee fittings, a filter, chlorinator etc, and the resistance adds up. Some of the methods we'll be employing to reduce resistance include use of an oversized filter, sweep elbows instead of sharp 90 degree bends, 50mm (2") piping (dual in most places), multiple returns, and high flow suction fittings.
I've also endeavored to keep the equipment pad (i.e. place where the pump, filter, and chlorinator will go) relatively close to the pool.
After consideration, the only reasonable location is beside the existing water tank, about 5 meters beside the pool and 1.2 meters above it.
Locating a pump above the water it's pumping is not ideal. Pumping water up a meter or two is not a big deal, but drawing water up is more challenging as the pipe will initially be filled with air. Clearing this air and replacing it with water is referred to as priming. Most pool pumps can handle some air on the suction side and will generally prime themselves, but it should be minimized as much as possible.
To mitigate any potential issues, we'll be running the pipes below water level as far as possible and then coming up a steep angle to the equipment pad. Once the system is primed, the system should (in the absence of any leaks) maintain prime until the next time the filter media needs to be replaced or until the pump is opened to clean out the basket.
Arranging the equipment
To determine the optimal arrangement of equipment prior to actually having all of the equipment on hand, I modeled the placement using the known dimensions and came up with the following:
With this layout I've tried to maximize the efficiency by keeping the water path as simple as possible. The two pipes off to the left are the solar out/return lines. These will be running onto the second storey roof once the solar panels are installed.