A pool pump is an essential part of any swimming pool. It helps to circulate the water and keep it clean and clear. If you have a 30000-gallon pool, you’ll need to choose the right size pump to ensure that the water is properly circulated. Here are the steps to determine the pump size for a 30000-gallon pool:
1. Determine the number of gallons to be pumped per hour
The first step in determining the pump size for your 30000-gallon pool is to decide how many gallons of water you want to circulate per hour. As mentioned earlier, the industry standard for pool water turnover is between 8-10 hours. For this example, we will use a turnover time of 8 hours.
To calculate the number of gallons to be pumped per hour, divide the total number of gallons of water in your pool by 8: 30,000 gallons ÷ 8 hours = 3,750 gallons per hour
So, you would need to pump 3,750 gallons per hour to clean or remove all the water in your 30,000-gallon pool in eight hours.
2. Convert gallons per hour to gallons per minute (GPM)
Since pool pumps are usually rated in gallons per minute (GPM), you’ll need to convert the gallons per hour to GPM. To do this, divide the gallons per hour obtained above by 60: 3,750 gallons per hour ÷ 60 = 62.5 gallons per minute (GPM).
So, you would need a pool pump with a flow rate of 62.5 GPM to circulate the water in your 30,000-gallon pool in 8 hours.
However, if you prefer a turnover time of 10 hours, you can follow the same formula and divide the total number of gallons of water in your pool by 10: 30,000 gallons ÷ 10 hours = 3,000 gallons per hour
Then, convert the gallons per hour to GPM by dividing by 60: 3,000 gallons per hour ÷ 60 = 50 gallons per minute (GPM)
So, you would need a pool pump with a flow rate of 50 GPM to circulate the water in your 30,000-gallon pool in 10 hours.
A 30000-gallon pool requires a pump with a flow rate of 50-62.5 GPM for a turnover time of 10-8 hors, respectively
Total dynamic head
Total Dynamic Head (TDH) is the sum of various factors that determine the energy required by a pump to move fluid through a system. It represents the total resistance the pump needs to overcome to maintain the desired flow rate. Here are the factors considered when calculating Total Dynamic Head:
Static head (HS) refers to the vertical distance between a reference point and the water level in a fluid system, typically a liquid like water. It represents the potential energy that the fluid possesses due to its height above a specific point.
Losses due to friction in pipe length (Hf), often referred to as major losses, occur when a fluid flows through a pipe. These losses result from the friction between the moving fluid and the interior surface of the pipe. This can be done using the Darcy-Weisbach equation or empirical methods.
Losses in fittings (H fittings), also known as minor losses refer to the reduction in pressure or energy that occurs when a fluid flows through various components in a piping system, such as bends, valves, elbows, and other fittings.
The formula for calculating Total Dynamic Head (TDH) is:
TDH = HS + Hf + H fittings
Where:Top of Form
Hs is the static head
Hf is the head loss due to frictionhe
H fittings is the head loss due to fittings
Example used in the calculations
For easy understanding we are going to be using an example in all the formulars , we going to use our example in all the calculations.
The pipe length from the swimming pool to the pump and from the pump to the pool is 26 meters, the pipe diameter is 2 inch, the piping system has 6 in number 90° Standard Elbows, 3 in number 45° Standard Elbows, 4 fully open Ball Valves. Vertical distance from the lowest pool bottom to the centre of the pump is 2 meters and vertical distance from the pump’s centre to the highest discharge point into the pool is 0.5 meters.
Size the correct pool pump needed.
The swimming pool is of 30000 gallons of water, we obtained the flow rate 50-62.5 GPM for a turnover time of 10-8 hours, respectively. Here in the example we are using GPM of 50 gallons per minute hence a turnover of 10 hours.
Static head
Refers the cumulative vertical distance that water needs to overcome as it navigates through a fluid system. It is divided into two, suction static head and discharge static head.
Suction Static Head: This refers to the vertical distance between the water level in the pool and the pump’s inlet. It represents the height that the pump needs to lift water from the pool. A greater suction static head requires the pump to work harder to overcome the gravitational force and draw water into the system. Factors such as pool elevation and the height of the water column contribute to the suction static head.
Discharge Static Head: This is the vertical distance between the pump’s outlet and the highest point where the water needs to be delivered. It represents the height that the pump needs to push water against gravity to reach its intended destination, such as the pool’s return jets or other equipment. Similar to the suction static head, the discharge static head contributes to the overall resistance that the pump must overcome to move water effectively.
Pool pump static head illustration
Static head = suction static head + discharge static head
From the example
Static suction head is 2 meters
Static discharge head is 0.5 meters
Static head = suction static head + discharge static head
Static head = 2 + 0.5 = 2.5 meters
Static head is 2.5 meters
Head loss due to friction/ major losses
Hf = (f*L*V^2)/(D*2*g)
Hf is the head loss in the pipe due to friction
f is the Darcy friction factor.
L is the length of the pipe.
D is the diameter of the pipe: 2 inches = 0.0508 meters
V is the velocity of the water (V): Q / (π * D^2 / 4)
g is acceleration due to gravity (g): 9.81 m/s²
Obtain the Darcy friction factor (f)
From the example above of a pool
Flow rate (Q): 50 gallons per minute
Pipe diameter (D): 2 inches = 0.0508 meters
Pipe length (L): 26 meters
Calculate the fluid or water velocity
V = (Q*4)/(ℼ*D^2)
Given 50 gallons per minute.
50GPM = (50/60) Gallons per second = 0.8333 GPs
1 gallon = 0.0037854m³
0.8333GPs = 0.8333 x 0.0037854 = 0.0031545 m³/s
Q = 0.0031545 m³/s
V = (Q*4)/(ℼ*D^2)
Substitute in the formula V = (0.0031545×4)/(𝝅 x 0.05082)
V = 1.556m/s
Having got the velocity of water, now let’s obtain Reynolds number
Calculate Reynolds Number (Re)
Re is used to determine the type of flow pattern as laminar or turbulent while flowing through a pipe.
Re = (ρVD)/μ
ρ is the density of the water
V is the fluid velocity
D is the diameter of the pipe
μ is the dynamic viscosity of the water
Re is Reynold’s number
A table that provides Darcy friction factors (f) for different Reynolds number (Re) ranges in various flow regimes:
Reynolds Number (Re)
Flow Regime
Darcy Friction Factor (f)
Re < 2000
Laminar
16 / Re
2000 < Re < 4000
Transitional
Transition Zone
Re > 4000
Turbulent
Empirical correlations
Density of water (ρ) is 1000 kilograms (kg/m³) The dynamic viscosity of water at room temperature (around 20°C or 68°F) is approximately 0.001 kg/(m·s)
μ = 0.001 kg/(m·s)
lets substitute in the formular for Re
Re = (1000*1.556*0.0508)/ 0.001 = 197612
Re = 79,045
So from the table above Re > 4000, the flow regime is turbulent, therefore use Empirical correlation to obtain the Darcy Friction factor (f)
Express the Reynolds number Re obtained in scientific form
Re = 79,045
Re = 7.9×104
Now use the moody diagram to obtain the friction factor (f)
To use the moody diagram, you have to be with the Reynolds number (Re), and the type of material of the pipes used for example plastic, steel etc. Relative pipe rougness varies depending on the material used as shown in the key of the moody diagram
In the example of this article we used plastic pipe (PVC)
Look for where the Reynolds number (Re) meets with the relative Roughness of your pipe on the moody diagram
In the example Re is 1.97X105 and the relative roughness for plastic (PVC) is is 0.0025
Draw a straight line from their meeting point to the side of friction factor and read off the friction factor (f)
In the example friction factor (f) is 0.027
moody diagram
Now calculate the head loss due to friction
Hf = (f*L*V^2)/(D*2*g)
All the parameter in the above equations have been obtained and some given, i.e.
F = 0.027
L= 26m
V = 1.556m/s
D = 0.0508 meters
Hf = (0.027*26*1.5562)/(0.0508*2*9.81)
Hf = 1.7 meters of water.
There head loss due to friction is 1.7 meters of water.
Head loss due to fittings (Hfitting) or Minor losses
Refers to the reduction in pressure or energy that occurs when a fluid flows through various components in a piping system, such as bends, valves, elbows, and other fittings.
Hfitting = (N*K*V2)/2g
Where
Hfitting is the minor head loss due to fittings ie valve, bends, tees etc
N is the number of fittings
V is the velocity of water
g is acceleration due to gravity
K is the friction factor. The fiction factor is different for various types of fittings
Friction Losses in Pipe Fittings Resistance Coefficient K
Friction Losses in Pipe Fittings
Resistance Coefficient K (use in formula hf = Kv2/2g)
Convert the total dynamic head (TDH) into feet because the performance curves for various pumps are in feet
1 meter = 3.28084 feet
4.7626 meters = 15.6253 feet
TDH = 15.6 feet
Total dynamic head is 15.6 feet, using data from the example given above
Choosing pool pump for your pool
Having got the total dynamic head has 15.6 feet and flow rate of 50 gallons per minute, we can now easily choose a pump that suites this pool using performance curves of different pumps.
These values of TDH and GPM vary according to the design of your pool and your specifications, so make sure that you have calculated the TDH and GPM of your pool, don’t just use the values we have calculated in our example.
Using pool performance curves to choose a pump involves matching the calculated Total Dynamic Head (TDH) and the desired flow rate (in GPM) to a point on the pump’s performance curve. Here’s a step-by-step guide:
Calculate Total Dynamic Head (TDH) and Flow Rate: You’ve already calculated the TDH as 15.6 feet and the flow rate as 50 gallons per minute (GPM). These two values represent the key factors in determining the appropriate pump for your pool. Let me hope you have also calculated the TDH and GPM of your pump.
Collect Pump Performance Curves: Obtain the performance curves for the pool pumps you’re considering. These curves are provided below. These curves are usually provided by pump manufacturers and show the relationship between flow rate and head loss (TDH) for specific pump models. Below are these performance curves for various pumps and models to choose from. Each performance curve is linking to that specific pump.
Locate the Intersection Point: On the performance curve graph, find the value on the x-axis (flow rate in GPM) that corresponds to your calculated flow rate in the example it is 50 GPM. Then, find the value on the y-axis (head loss or TDH in feet) that corresponds to your calculated TDH in the example it is 15.6 feet.
Choose a Suitable Pump: Identify the point where the flow rate and TDH intersect on the performance curve. This point represents the specific operating conditions of your pool. Now, look at the nearest pump curve available.
Select a Pump Model: Choose a pump model whose performance curve passes closest to or slightly above the intersection point you found. This indicates that the pump can provide the necessary flow rate and head pressure for your pool’s specific conditions.
Check Efficiency and Power Consumption: Alongside the performance curve, manufacturers often provide efficiency and power consumption information. Ensure that the pump’s efficiency aligns with your energy efficiency goals.
Pool pumps to choose from
1. Pentair 348190 SuperFlo High Performance Single Speed Pool Pump
performance curve for
Pentair 348190 SuperFlo High Performance Single Speed Pool Pump
2. Pentair SuperFlo® VS Variable Speed Pool Pump, 342001
Performance curves for Pentair SuperFlo® VS Variable Speed Pool Pump, 342001
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