Pool plumbing and plant room: how should they be built?

A 5x10 metre pool with an average depth of 1.50 metres holds 75 cubic metres; for a 6-hour turnover, 75 divided by 6 gives a required flow rate of 12 to 13 cubic metres per hour. The pump must deliver this flow against the pressure loss of the plumbing.

The filter is selected for this flow rate. In sand filters the filtration rate is kept below a set limit per square metre; for 12 cubic metres per hour, a Ø600 mm tank is the typical solution. An undersized filter leaves the water cloudy, while an unnecessarily large one wastes extra water during backwashing.

With a variable-speed (inverter) pump, the difference shows up on the electricity meter. A single-speed pump is either at full power or off; a variable-speed pump spends most of the day at low speed and consumption drops accordingly. The upfront cost is higher, and the payback shows up on the electricity bill.

A narrow pipe increases the water velocity; as velocity rises, friction loss and noise increase, and the pump has to work harder to deliver the same flow. That means the small amount saved during installation is paid back every month in electricity.

At a flow rate of 12 cubic metres per hour, a Ø50 mm pipe is at its limit, while Ø63 mm runs comfortably. The suction line is chosen one size larger than the discharge line; a pump that struggles on the suction side suffers cavitation and a shorter service life.

The number of elbows is also taken into account. Each elbow adds some pressure loss; the further the plant room is from the pool, the more pipe length and elbows there are. Placing the plant room close to the pool therefore also lowers running costs.

This space fits the pump, filter, dosing unit, control panel and, if there is one, the indoor unit of the heat pump. The clear height should not drop below 1.80 metres; there must be enough headroom to open the filter lid and change the sand.

In an overflow system the area grows because a balance tank is added. The balance tank is sized at 60 to 80 litres per square metre of pool surface area; for a 50 square metre pool, that means a volume of 3 to 4 cubic metres, which sits inside or next to the plant room.

The location rule: do not go further than 8 metres from the pool edge, and stay below the pool water level if possible. Having the pump below the water level makes suction easier. In installations above the water level the pump has to self-prime, and that does not always go smoothly.

Without ventilation, condensing moisture corrodes the panel and the motors. For natural ventilation, two vents are placed on opposite sides, with a fan added if needed.

Floor drainage is a must. Water released during filter backwashing, a possible leak or maintenance has to go somewhere. In plant rooms without a floor slope and drain, the first fault lets water get into the equipment.

If chemical storage and the electrical panel share the same space, keep a distance between them and store chemicals in a closed cabinet. Chlorine fumes quickly eat away at metal parts and electronic boards. It is a cause of failure we see often, and preventing it is as simple as a cabinet.

An automatic dosing system measures pH and chlorine levels and doses only as much as is needed. The result is more balanced water and usually lower total chemical consumption.

The second benefit of automation is the pump running schedule. Instead of a pump that runs at fixed hours, a control unit that schedules operation according to temperature and use reduces electricity consumption. Systems with remote monitoring let you see the state of the pool while you are away from home.

For hotel and residential complex pools, automation is not an option but a necessity. Heavy and changing use cannot be tracked by hand, and systems that keep records also help you during inspections.

A heater connected before the filter collects dirt. A bypass valve is fitted on the heater line so that when heating is off, water does not pass through the heater and there is no unnecessary pressure loss.

The outdoor unit of the heat pump draws heat from the air and blows out cold air. Do not point this airflow towards seating areas or the neighbour's boundary. Space must be left around the unit for air circulation; a unit squeezed into a narrow recess loses efficiency.

The capacity calculation is based on the pool surface area, not the volume. Most heat loss happens through evaporation from the surface. If a pool cover will be used, the calculation can be reduced; include the cover from the start, because a cover bought later means you will have chosen an unnecessarily large heat pump.

The pipes get longer, elbows increase, the pump gets bigger and the bill goes up. Two: choosing too small a pipe diameter. Three: placing the return inlets at random and leaving dead zones in the corners.

Four: a plant room without floor drainage. Five: chemicals and the electrical panel in the same cabinet. None of these five mistakes can be fixed cheaply once the pool is finished; four of them are decided at the excavation and shell construction stage.

That is why you should ask for the plumbing design together with the pool design. A quote with pool drawings but no plumbing diagram is telling you that half of the job will be improvised on site.