Designing swimming pool calculations involves several crucial steps to ensure the pool is structurally sound, hydraulically efficient, and safe to use. These calculations cover aspects like pool volume, hydraulic loading, turnover rate, chemical dosing, and structural integrity. Here's a breakdown of the process:
1. Determine Pool Volume
Calculating the pool volume is fundamental for various aspects of pool design, including chemical dosing, filtration system sizing, and turnover rate calculations.
- Rectangular Pools: Use the formula:
Pool Volume = Length x Width x Average Depth x 7.48(7.48 gallons per cubic foot) - Circular Pools: Use the formula:
Pool Volume = πr² x Average Depth x 7.48(where r is the radius) - Irregular Shapes: Divide the pool into simpler geometric shapes, calculate the volume of each section, and then add them together. Alternatively, use 3D modeling software for precise volume determination.
Example:
A rectangular pool is 20 feet long, 10 feet wide, and has an average depth of 5 feet.
Pool Volume = 20 ft x 10 ft x 5 ft x 7.48 = 7480 gallons
2. Calculate Turnover Rate
The turnover rate is the time it takes for the entire volume of water to pass through the filtration system. A faster turnover rate generally means cleaner water. The required turnover rate depends on the type of pool (e.g., residential, commercial, spa). Local regulations often dictate minimum turnover rates.
- Formula:
Turnover Rate (hours) = Pool Volume (gallons) / (Flow Rate (gallons per minute) x 60)
Example:
If the pool volume is 7480 gallons and the desired turnover rate is 6 hours:
Required Flow Rate = 7480 gallons / (6 hours x 60 minutes/hour) = 20.78 GPM (Gallons Per Minute)
3. Hydraulic Loading Rate
This refers to the flow rate of water through the filter per unit area. It's crucial for ensuring efficient filtration. Filter manufacturers provide recommended hydraulic loading rates for their products.
- Formula:
Hydraulic Loading Rate (GPM/sq ft) = Flow Rate (GPM) / Filter Area (sq ft)
Example:
If the flow rate is 20.78 GPM and the filter area is 2 sq ft:
Hydraulic Loading Rate = 20.78 GPM / 2 sq ft = 10.39 GPM/sq ft
Check that this value is within the filter's recommended range.
4. Chemical Dosing Calculations
Accurate chemical dosing is essential for maintaining water quality and preventing the growth of algae and bacteria. Factors like pool volume, bather load, and environmental conditions influence chemical demand.
- Chlorine Dosage: Determine the required chlorine level (e.g., 1-3 ppm). Calculate the amount of chlorine needed to achieve this level based on the pool volume and the available chlorine concentration of the chemical product being used. Follow manufacturer's instructions and local regulations.
- pH Adjustment: Calculate the amount of acid or base needed to adjust the pH to the ideal range (7.2-7.8). This depends on the water's alkalinity and current pH. Use a pool water testing kit and consult a chemical dosage chart or pool professional.
5. Pipe Sizing Calculations
Proper pipe sizing is critical for maintaining adequate flow rates and minimizing friction losses in the plumbing system. Use the following considerations:
- Velocity: Keep water velocity within recommended limits (e.g., 6-8 feet per second) to prevent excessive friction loss and potential damage to the pipes.
- Friction Loss: Calculate friction loss using the Darcy-Weisbach equation or Hazen-Williams formula. This will help determine the required pump head.
- Material: Select appropriate pipe material (e.g., PVC, CPVC) based on water temperature, pressure, and chemical resistance requirements.
6. Pump Selection
The pump must be capable of delivering the required flow rate at the necessary head (pressure). Consider the following:
- Total Dynamic Head (TDH): Calculate the TDH, which includes friction losses in the pipes, fittings, filters, and other equipment, as well as the elevation difference between the pump and the highest point in the system.
- Flow Rate: The pump must be able to deliver the required flow rate for the desired turnover rate.
- Pump Curve: Select a pump whose performance curve meets both the flow rate and head requirements.
7. Structural Calculations
These calculations are performed by structural engineers to ensure the pool shell can withstand the pressure of the water and the surrounding soil. They involve:
- Hydrostatic Pressure: Determining the hydrostatic pressure acting on the pool walls and floor.
- Soil Pressure: Analyzing the soil pressure acting on the exterior of the pool shell.
- Reinforcement: Calculating the required amount of steel reinforcement to resist these forces.
Example Calculation Summary:
| Parameter | Calculation | Result |
|---|---|---|
| Pool Volume | Length x Width x Average Depth x 7.48 | 7480 gallons |
| Turnover Rate | Pool Volume / (Flow Rate x 60) | 6 hours (Target) |
| Required Flow Rate | Pool Volume / (Turnover Rate x 60) | 20.78 GPM |
| Hydraulic Load Rate | Flow Rate / Filter Area | 10.39 GPM/sq ft |
These calculations are a starting point. Consulting with qualified professionals (engineers, pool designers) is highly recommended to ensure a safe, efficient, and compliant pool design. Remember to always follow local building codes and regulations.
