Sunland Pools :: Owner-Built Pools

"Hydraulics" is the study and understanding of the behavior of liquids at rest and in motion.
We are concerned with water, and the following characteristics of our application:

1.

How much water do we have.
(Pool Capacity)?

2.

How fast can we safely move the water.
(Turnover Rate and Water Velocity)?

3.

How much resistance will this water meet while moving through the system. (Friction Loss)?

4.

How will we overcome this resistance.
(Pump/Filter Sizing)?

Following are step-by-step instructions to answer these four questions and ultimately determine the proper size pump or filter for virtually any installation.

Below each step is a calculation based on the following example:

16 ft by 32 ft rectangular pool

3 ft to 8 ft deep 2"" suction side return side plumbing.

Existing 1 HP pump; filter gauge reads

10 PSI (clean).

Pool Capacity

To determine total gallons, we must first calculate the surface area of the pool in square feet:

A. Surface Area ____________ ft 2 (surface area)

Surface Area: 16 ft x 32 ft = 512 ft 2

Next, multiply the surface area by the average depth to determine the

appropriate volume of the pool.

B. Average Depth

(____________ ft + ____________ ft ) 2 = ____________ ft

(depth, shallow end) (depth, deep end) (average depth)

Average Depth = (3 ft. + 8 ft) 2 = 5.5 ft

C. Volume

____________ ft 2x ____________ ft = ____________ ft 3

(surface area) (average depth) (volume)

Volume = 512 ft 2 x 5.5 ft = 2,816 ft 3

Next, multiply the pools volume in ft3 by 7.5 to get the pool capacity in gallons:

D. Pool Capacity

____________ ft 3 x 7.5 gallons/ft 3 = ____________ gallons

(volume) (pool capacity)

Pool Capacity = 2,816 ft 3. x 7.5 gallons/ft 3 = 21,120 gallons

Some of the more common pool sizes are:

Above-Ground Size Gallons*

15 ft Round 5,293

18 ft Round 7,622

21 ft Round 10,374

24 ft Round 13,550

12 ft x 24 ft Rectangle 8,626

27 ft Round 17,149

*Average Depth: 4 ft

In-Ground Size Gallons*

12 ft x 24 ft Rectangle 11,861

16 ft x 32 ft Rectangle 21,086

18 ft x 36 ft Rectangle 26,687

20 ft x 40 ft Rectangle 32,947

*Average Depth: 5.5 ft

2. Flow Rate

While the actual flow rate of a pump is based on the total resistance of the system

as described below, the desired flow rate must be calculated to verify it will satisfy

Turnover Rate and Water Velocity requirements.

2A. Turnover Rate

The turnover rate for a swimming pool is the amount of time required to circulate

the entire volume of water through the system once to meet reasonably clean,

safe water standards. The minimum recommended turnover rate is twelve (12)

hours, however an eight (8) to ten (10) hour rate is quite common. Check with local

regulations for the minimum required turnover rate.

Based on the pools capacity and the desired turnover rate, the minimum rate at

which the water must be circulated in Gallons Per Minute (GPM) is calculated

as follows:

A. Minimum Flow in Gallons per Hour (GPH)

____________ gallons ____________ hours = ____________ GPH

(pool capacity) (desired turnover rate) (minimum flow,gallons per hour)

Minimum Flow: 21,120 gallons 10 hours = 2,112 gallons per hour

B. Minimum Flow in Gallons per Hour (GPM)

____________ gallons per hour 60 minutes per hour = ____________ GPM

(minimum flow (minimum flow,

gallons per hour) gallons per minute)

Minimum Flow: 2,112 gallons per hour 60 minutes per hour =

35 gallons per minute

2B. Water Velocity

The maximum recommended water velocity is six (6) or eight (8) feet per

second for suction lines and ten (10) feet per second for return lines. Check

with local regulations for the maximum water velocity for suction and return

lines. The table below lists the maximum flow in GPM based on plumbing size

and water velocity.

Pipe Size Maximum Flow

(in) 6.0 ft/sec 8.0 ft/sec 10.0 ft/sec

1 1⁄2"" 38 GPM 51 GPM 63 GPM

2"" 63 GPM 84 GPM 105 GPM

2 1⁄2"" 90 GPM 119 GPM 149 GPM

3"" 138 GPM 184 GPM 230 GPM

Maximum Flow: 2"" suction side plumbing at

6.0 ft/sec = 63 gallons per minute

2C. Desired Flow

The desired flow rate must be between the minimum flow based on the

Turnover Rate and the maximum flow based on the Water Velocity. Note that

if higher flow rates are needed, such as for water features, the maximum

possible flow would have to be increased by using larger size plumbing

(e.g. increase from 2"" to 2 "" plumbing).

It is recommended to select a flow that is higher than the minimum to

account for decrease in flow that naturally occurs as the filter is loaded

with dirt and debris.

Minimum Flow (Turnover Rate): 35 GPM

Maximum Flow (Water Velocity): 63 GPM

Desired Flow: 50 GPM

Hydraulics

THE BASICS OF PUMP/FILTER SIZING

P u m p s

HAYWARD 17

Hydraulics

THE BASICS OF PUMP/FILTER SIZING

P u m p s

18 HAYWARD

3. Friction Loss

Everything that the water must pass through within the circulation system

plumbing and equipment creates resistance, or Friction Loss. The friction loss

for standard plumbing supplies such as pipe, elbows, fittings, etc. can be found

using published reference tables. Friction loss for equipment such as filters,

heaters, and chlorination systems can be found in charts and/or curves provided

by the manufacturer. The sum of all the resistance is called Total Dynamic Head

(TDH) and is typically measured in Feet of Water or Feet of Head.

A properly sized pump will have the ability to overcome the Total Dynamic Head

of the system while, at the same time, providing flow that will satisfy Turnover

Rate and Water Velocity requirements.

For new installations, it is possible to calculate TDH very accurately by using

reference tables and manufacturers data to determine the friction loss asso -

ciated with every component in the circulation system.

For existing installations, we are often unable to determine the total amount of

pipe and fittings its underground. Therefore, what follows is a simplified

rule-of-thumb means of determining Total Dynamic Head.

We will need to add the resistance from the vacuum (suction) side of the existing

pump to the resistance of the pressure side of the pump. Note this assumes

the Static Suction Lift (i.e. vertical distance from the center of the pumps

impeller to the surface of the water) is offset by the water returning to the pool.

A. Friction Loss (Vacuum)

_________inches of mercury x 1.13 ft of water = _________ft of water

(vacuum reading) (total resistance, vacuum)

Typically, however, a vacuum reading will not be available, therefore, the table

below provides Common Head Loss Factors for todays high-efficiency pumps.

Pump Size Head Loss Factor*

3/4 HP 4.5 to 5.5 ft of water

1 HP 7 to 9 ft of water

1 1/2 HP 10 to 12.5 ft of water

2 HP 13.5 to 16 ft of water

*Assumes 2"" suction line, not to exceed 40 ft long, minimal fittings, one (1) 2"" valve and full-rated pumps.

Total Resistance (Vacuum): 9 ft of water (existing 1 HP pump)

B. Friction Loss (Pressure)

____________ PSI x 2.31 ft of water / PSI = ____________ft of water

(filter pressure, clean) (total resistance, pressure)

Total Resistance (Pressure): 10 PSI x 2.31 ft of water / PSI = 23 ft of water

C. Total Dynamic Head

__________ ft of water + __________ ft of water = __________ft of water

(total resistance, vacuum) (total resistance, pressure) (total dynamic head)

Total Dynamic Head: 9 ft of water + 23 ft of water = 32 ft of water

4. Pump Sizing

We now have all the information necessary to select the proper size pump

and/or filter and then proceed based on new vs. aftermarket installations.

A pumps performance data is provided in GPM (output) vs. Feet of Head

(resistance). The specific performance data for Hayward pumps can be found

in the Pump Section, pages 7-16.

4A. Pump Sizing, New Installations

For new installations, use the desired flow rate and Total Dynamic Head

calculated from tables and manufacturers data:

Desired Flow ____________ GPM

Total Dynamic Head ____________ ft of water

Using Hayward Pump Performance Curves or Tables, identify which pumps

performance comes closest to matching the point where the Desired Flow

intersects with the Total Dynamic Head.

Desired Flow: 50 GPM

Total Dynamic Head: 32 ft of water (assume to be the same as

determined above)

4B. Pump Sizing, Existing Installations

For existing installations, use the Total Dynamic Head calculated from the

Friction Loss on the Vacuum and Pressure side of the pump.

Total Dynamic Head ____________ ft of water

Using the manufacturers performance curve for the existing pump, find the

flow that corresponds to the Total Dynamic Head. This is the actual flow at

which the pump is currently operating, which may or may not meet Turnover

Rate and Water Velocity requirements. Verify the actual flow rate is between

the minimum flow based on the Turnover Rate and the maximum flow based

on the Water Velocity.

Total Dynamic Head: 32 ft of water (assume to be the same as

determined above)

If the actual flow rate does not meet the Turnover Rate and Water Velocity

requirements, you must either modify the system to add or remove restrictions

(e.g. use less restrictive plumbing fittings and/or equipment) or vary the flow by

changing size of the pump.

If you increase or decrease your flow for any reason, your resistance will

increase or decrease respectively. You cannot read horizontally across

the curve at the same Total Dynamic Head to choose another pump.

You must create a system curve based on the following relationship:

_________ft of water x (______ GPM ______GPM)2 = ______ft of water

(current friction loss) (new flow rate) (current flow rate) (new friction loss)

Choose the minimum and maximum flow rates based on Turnover Rate and

Water Velocity and calculate the corresponding friction loss using the formula

above. Plot each combination of friction loss and flow to create the system curve.

Current Flow: 70 GPM

Current Friction Loss: 32 ft of water

New Flow Rate (per Turnover Rate) = 35 GPM

New Friction Loss = (32 ft of water) x (35 GPM 70 GPM) 2 = 8 ft of water

New Flow Rate (per Water Velocity) = 63 GPM

New Friction Loss = (32 ft of water) x (63 GPM 70 GPM) 2 = 26 ft of water

The point where the performance curve for a particular pump intersects the system

curve determines the flow and Total Dynamic Head where that pump will operate.

Saving Money by Saving Energy

Depending upon utility rates, pool characteristics, and equipment selected,

it is possible to recoup the premium cost of an upgrade from a standard pump

to an energy efficient pump in the first year of operation.

For example, a system featuring an energy efficient high performance pump

drawing 5.34 amps at 230 volts where the local utility rate is $0.12 per kWh

will cost you approximately $1.78 over a 12 hour period per day. A standard

pump drawing 7.0 amps will cost you approximately $2.32 per day or an

extra $197 annually!

Use this worksheet to help determine your energy savings:

A. Motor Amp Rating A

B. Voltage (e.g. 115 volts or 230 volts) B

C. Local Energy Rate ($ per kWh) * C

D. Approximate Power Usage (Watts) = A x B D

E. Kilowatts = D / 1000 E

F. $ per hour = E x C F

G. Hours of Operation G

H. Cost per Day = F x G H

J. Monthly Cost = H x 30 J

K. Yearly Cost = H x 365 K

*Refer to your utility bill to determine locate rate

4B. Filter Sizing

A filter, be it DE, sand, or cartridge, has a Design Flow Rate in GPM as

well as a Turnover Capacity in Gallons. See the table below, for example.

The specific performance data for Hayward filters is provided in the

Filter Section, pages 20-35.

Select a filter that meets or exceeds the desired flow rate and turnover

capacity in gallons.

Model Effective Design Flow Turnover Capacity

Number Filtration Rate (Gallons)

Area 8 Hours 10 Hours

S180T 1.75 ft 2 35 GPM 16,800 21,000

S210T 2.20 ft 2 44 GPM 21,120 26,400

S220T 2.64 ft 2 52 GPM 24,960 31,200

S244T 3.14 ft 2 62 GPM 29,760 37,200

S270T 3.70 ft 2 74 GPM 35,520 44,400

S310T 4.91 ft 2 98 GPM 47,040 58,800

S360SX 6.50 ft 2 131 GPM 62,400 78,000

Desired Flow: 50 GPM

Turnover 21,120 gallons in 10 hours

Select S220T (minimum)

One additional factor to consider in filter sizing is bather load. Busier pools

require larger filters. Also, larger filters provide longer cycles, reducing

everyday maintenance required by the consumer during the pool season.

Summary

Using the information calculated above, you can properly size the pump,

filter, and corresponding equipment, assuring you meet Turnover Rate and

Water Velocity requirements while eliminating the electrical waste and

potential damage to other system components associated with a needlessly

oversized pump.

Hydraulics

THE BASICS OF PUMP/FILTER SIZING

P u m p s

HAYWARD 19
"

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