Edit - Before reading this article, you may want to first familiarize yourself with this Pool School article on Pump Basics

When building my pool, I did a significant amount of research on swimming pool plumbing and water hydraulics. I also found that there appeared to be a serious lack of understanding in the pool industry of exactly how pumps and plumbing interact. So I attempted to compile all of the information that I have gathered over the years and present it here. Hopefully this will be useful to those who frequent this site. Please provide feedback and suggestions.

Hydraulics 101 - Pumps, Pipes and Head

Pump and Head Basics

This section covers the basics of pool pumps, pump head curves and plumbing head loss.


Hydraulic Head

Head loss is another way of expressing the amount of pressure (PSI) lost in a plumbing system. In pool plumbing system there is both head gain as well as head loss. For example, a pool pump adds head or pressure to the plumbing system while the friction loss in piping removes head or decreases pressure in system. There are two basic types of head loss and gain in any plumbing system; Static Head and Dynamic Head.

Static head is the net elevation change of the water, can be positive or negative and is directly related to the height of the water. So water moving from a high location to a low location has head gain while water moving from a lower location to a higher location has head loss. In a pipe completely filled with water that rises up to any elevation and then drops down to the same location is static head neutral. The static head gain is directly offset by the static head loss. However, there can be temporary static head loss or gain during the process of priming pipes such as the pipes that go up to a solar panel on a roof. During priming, there is head loss due to the elevation lift but once the pipe is filled with water, the static head gain and loss cancel each other.

Dynamic head loss is due to the water movement inside the pipes and is sometimes called friction loss. As water travels through a pipe, the friction against the walls reduces pressure. A pool's plumbing system will experience dynamic head loss on both the suction side of the pump and return side of the pump since water is moving through pipes on both sides. The faster water moves through a pipe, the more head loss. A pool pump adds dynamic head gain to the plumbing system so as to create positive pressure and thus water flow through the pipes. The dynamic head loss in the pipes then reduces the pressure until the water returns to the pool where the pressure is 0 PSI.

So pumps and elevation drops add head to a system while elevation rises, pipes, fittings, valves, filter, heaters, etc. subtract head from a system. For a swimming pool, the total head loss is always equal to the pump's head gain since the water is returned to the same place as where it originated and at the same elevation. So the total head calculation for a pool looks like this:

Pump Head Gain = Suction Head Loss + Return Head Loss

Because dynamic head loss is dependent on flow rates, when head loss increases on the suction or return side of the pump, total head loss goes up but the opposite side of the pump experiences a slight decrease in head loss.


Pump Head Curves

Most manufactures of pumps include head curves in their pump manuals. The curves have two axes, Feet of Head vs. Gallons per Minute (GPM). Feet of head is used instead of PSI for because a centrifugal pump will always deliver the same head for any liquid while the PSI will change. So the conversion from head to PSI depends on the type of liquid.

If the head loss is known for a pool's plumbing system, then the flow rate can be determined from the head curve. Below is an example of a head curve for the Pentair Intelliflo.



The maximum head of the pump is reached when the flow rate is near zero GPM and at full RPM. This is equivalent to an equal length of open ended pipe straight up in the air. The pump will fill the pipe to the top but no water will spill out.

The chart also shows that the energy use of a pump is fairly linear with the flow rate. This is true for all residential pool pumps. The higher the flow rate of the pump, the more energy that is used. However, flow rates tend to increase faster than the energy use which is why the energy factor, measured as gallons per Watt-hr, of the pump increases with increasing flow rate effectively reducing the energy consumption. However, there is a flow rate limit that a pump can produce which is called run out but most pool installation will never reach this limit because there is always at least some plumbing head loss.

The horsepower required to turn the impeller at a specific RPM is called brake HP (BHP). The required BHP changes along a pump's head curve and reaches a maximum near the right side of the curve. A motor will typically be rated at a service factor HP (SFHP) or total HP (THP) which is greater than the maximum BHP required for the pump. The service factor of the pump is usually listed on the nameplate label. Manufactures sell pumps in up-rated and full rated versions which has caused some confusion when purchasing a pump. An up-rated pump is usually the same as a full rated pump with 1/2 HP less rating. For example, a 3/4 HP full rated pump will have the same head curve as a 1 HP up rated pump within the same pump line so their performance will be identical.


Pump Nameplate HP Ratings

Most in the industry have long understood that pump nameplates can be very deceiving. It is bad enough that manufactures have chosen to have two classes of IG pumps, up rated vs full rated, but AG pumps and combo systems add even more confusion around what the nameplate HP actually mean.

The chart below shows the flow rates of several Pentair and Hayward low HP IG and AG pool pumps from two of the CEC plumbing curves, Curve-A and Curve-C. The higher the flow rate, the more powerful the pump.



Even when comparing IG up rated pumps, there is clearly a large difference between the Whisperflo and Superflo line of pumps that have the same nameplate HP. But the difference is just as great when comparing IG to AG pool pumps with the same nameplate HP. Both the Optiflo and Dynamo are significantly smaller than even the Superflo with the same nameplate HP rating.

However, it doesn't end there. If you compare the impellers used in some of the combo systems, you will find that the impeller is smaller than even the up rated version of the same pump. In the manual they call this SPL HP. The bottom line is that a 1 1/2 HP (SPL) Dynamo pump/Filter combo uses a 1 HP up rated impeller which is equivalent to a 3/4 HP full rated impeller but still smaller than 3/4 HP up rated Superflo impeller which makes the pump a very small pump, especially by IG standards.

So the lesson here is that you cannot judge a pump's power or strength just by the nameplate HP rating.



Pump Efficiency

Traditionally, a pump's wire to water power efficiency has been defined in the following manner:

Pump Power Efficiency = Hydraulic Power / Electrical Power

But this can lead to the wrong conclusion about a pump's true efficiency. According to this definition, a larger pump will have a higher efficiency than a smaller pump. That is because when using power efficiency as the definition, the larger pump will not only have a higher pumping efficiency due to the higher head curve but the motor driving the pump will also have higher efficiency because it will have larger windings and lower resistive loses to support the higher current required.

But does the average pool owner really care about hydraulic power efficiency? The short answer is no. Hydraulic power consists of BOTH flow rate and head/pressure. Hydraulic power and efficiency is lowest at the two ends of the head curve but the point on the right is a much better place to operate than the point on the left. What the average pool owners should care about is the time it takes to turnover a pool and how much energy it takes to do that. Therefore, the more important measure of efficiency is measured as gallons pumped per watt-hr consumed or energy factor. It turns out that the energy factor is somewhat opposite to that of the power efficiency. Smaller pumps with lower flatter head curves tend to have better energy factors than larger pumps with higher steeper head curves. So when talking about efficiency it is very important to understand which efficiency is being discussed.


Two Speed Pumps

Low speed of a two speed pump has 1/2 the flow rate of a high speed. Therefore, the pump needs to be run twice as long to get the same turnovers per day. The good news is that the energy used at low speed is generally less than 1/4 of high speed. So with the longer run time and lower energy use, the overall energy savings is about 50%. This will vary a bit by pump model and manufacture.


Variable Speed Pumps

Current generation variable speed pumps provide even more cost savings over their two speed counterparts. Because of the range in RPM settings, the pump can be optimized for the given pool plumbing. The flexibility of a variable speed pump assures that maximum energy factor for nearly any operation condition can be achieved. Unlike two speed pumps, variable speed pumps can maintain fairly high efficiencies at lower speeds thereby reducing the amount of energy consumed for a given head loss. A 1 HP Whisperflo two speed pump can operate at close to 6.3 gallons/watt-hr at low speed while the Intelliflo pump operates over 9.4 gallons/watt-hr for same flow rate so the Intelliflo will save an additional 30% over the 2 speed. However, a VS costs more than a two speed pump so the cost difference could be more than the energy savings of the pump. For a small pool and low energy costs, a VS may not make sense and a two speed could end up being more cost effective over the life of the pump.

There are four primary factors which determine the cost to run a pump:

1. Electrical cost ($/kwh)
2. Pool Size (g)
3. Turnovers per Day
4. Plumbing

Therefore, the following formula can be used to determine the cost savings of a VS pump over a two speed pump.

VS Cost Savings ($/month) = Pool Size (g) * Energy Cost ($/kwh) * Turnovers per Day / Table Constant

The constant in the above equation can be determined from the table below. Currently, there two plumbing types, Curve-A or Curve-C. Curve-A is closer to an AG pool or a an older IG pool with 1.5" plumbing while Curve-C is closer to a more modern pool with 2" plumbing. Also, several two speed pump sizes are shown depending on the requirement for the high speed (e.g. spa jets).

Full Rated	Up Rated	Intelliflo	EcoStar	Intelliflo	EcoStar
HP	HP	Curve-C	Curve-C	Curve-A	Curve-A
3/4	1	440	300	330	230
1	1.5	330	245	275	200
1.5	2	305	225	250	185
2	2.5	275	210	225	175

So as an example, a 20k pool at $0.10/kwh on Curve-C with one turnover per day, the Intelliflo would save about $4.55 over a 3/4 FRHP two speed pump. If the cost difference is $300, then it would take about 66 months to break even.

Other assumptions for the table are:

2500 RPM VS high speed
1000 RPM VS low speed
25% of the turnover on high speed
75% of the turnover on low speed


Pump Affinity Equations

Pump affinity equations define how a pump's characteristics will change with speed assuming that the efficiency of the pump does not change. However, since a pump's efficiency does change with RPM, these equations can only be used as gross approximations. So if the flow rate, head or hydraulic HP is known for any one speed A, it can be calculated for another speed B using the following formulas.

GPM B = GPM A * (RPM B / RPM A)

Head B = Head A * (RPM B / RPM A) ^ 2

Hydraulic HP B = Hydraulic HP A * (RPM B / RPM A) ^ 3

Also, for estimated filter pressure at different speeds, the filter height must be taken into consideration. If the filter gauge is 3' above the pump then,

Filter Pressure B = (Filter Pressure A + 3 / 2.31) * (RPM B / RPM A) ^ 2 - 3 / 2.31


Variable Speed Pump Flow Rate Approximations

The following formulas use the affinity equations to yield a very rough estimate of flow rate.

1.5" Return Line with 1 x 1.5" Suction Line:
Plumbing Head (ft)= 0.0167 * GPM^2 (CEC Curve A)
Intelliflo Flow Rate (GPM) = RPM / 48
EcoStar Flow Rate (GPM) = RPM / 49

1.5" Return Line with 2 x 1.5" Suction Lines or 1 x 2" Suction Line
Plumbing Head (ft)= 0.0130 * GPM^2
Intelliflo Flow Rate (GPM) = RPM / 43
EcoStar Flow Rate (GPM) = RPM / 44

2" Return Line with 1 x 2" Suction Line
Plumbing Head (ft)= 0.0100 * GPM^2
Intelliflo Flow Rate (GPM) = RPM / 39
EcoStar Flow Rate (GPM) = RPM / 40

2" Return Line with 2 x 2" Suction Lines or 1 x 2.5" Suction Line
Plumbing Head (ft)= 0.0082 * GPM^2 (CEC Curve C)
Intelliflo Flow Rate (GPM) = RPM / 36
EcoStar Flow Rate (GPM) = RPM / 37

2.5" Return Line with 1 x 2.5" Suction Line
Plumbing Head (ft)= 0.0074 * GPM^2
Intelliflo Flow Rate (GPM) = RPM / 34
EcoStar Flow Rate (GPM) = RPM / 35

2.5" Return Line with 2 x 2.5" Suction Lines
Plumbing Head (ft)= 0.0071 * GPM^2
Intelliflo Flow Rate (GPM) = RPM / 34
EcoStar Flow Rate (GPM) = RPM / 35


Estimating Plumbing Head Loss

The plumbing curves listed above can be used to determine the operating point of a pump by plotting the curves on top of the pump's head curve. The point at which they interest, is the operating point.

However, you can also directly measure the head loss of a plumbing system by using the following method:

Return dynamic head can be estimated from a filter's PSI reading with this formula:

Return Dynamic Head = 2.31 * Filter PSI + 3

The 3 is added because the filter gauge is usually 3' above the pump so that needs to be taken into account.

Suction dynamic head can be estimated from a vacuum gauge at the input to the pump (i.e. drain plug). Vacuum gauges can be found at automotive stores or Sears for about $20. If you have one, you can determine suction head loss with this formula:

Suction Dynamic Head = 1.13 * Inches Mercury (vacuum gauge reading)

Once the total head loss is known, the operating point of the pump can be determined by drawing a horizontal line from the measured head loss to where it intersects the pump's head curve.


Cavitation

Cavitation in general is pretty rare in pool pumps but it can happen in larger high head pumps under high suction conditions. Cavitation cannot be directly observed unless you can directly view the location of the cavitation and see the bubbles form and collapse very near the impeller inlet vanes where they occur. The flow rate will tend to move them downstream but they don't make it very far because as water travels through the impeller it gains pressure which immediately collapses the vapor bubbles. It is the collapsing of the vapor bubbles which makes the gravel sound and which also causes damage to the impeller.

The reason cavitation occurs is because the pressure at the impeller is very low and it causes the water to boil. When the pressure gets that low, it is nearly impossible for the pump lid seal to prevent air getting sucked in. So when air is seen in the pump basket, it doesn't mean that the pump is in cavitation. However, the opposite is almost always true. When the pump is in cavitation you will most always see air in the pump basket.


Advanced Hydraulic Formulas

There are a set of formulas that can be used along with a pumps head curve to determine the head loss of a pool but it is very difficult to do. In order to get an accurate estimate, every element in the pool's plumbing must be characterized including pipe, fitting, valve, skimmer, main drain cover, filter, heaters, etc. Finding the friction coefficients for all of the elements is nearly impossible but if you are still interested in pursuing this option, there are several web sites in the reference section that explain the hydraulic equations and how to apply them. Another option is to read the next section which helps the reader to choose the best pump and pipe diameters for their pool.

Hydraulics 101 - Pumps, Pipes and Head

Pump, Pipe and Filter Sizing

This section covers how to choose a pump, pipe sizes and plumbing designs.

Plumbing Considerations

Pools, spas and water features all have different plumbing requirements so using the same plumbing system to satisfy the needs of all of the pool's features can be difficult to design. Spas and water features will usually have higher flow rate requirements than a pool and since pool pumps run longer, efficiency becomes much more important.

The size of the pump and pipe is going to be determined by the maximum flow rate in the plumbing. To keep head loss low, it is a good idea to keep the water velocity in a pipe below 8 ft/sec and if possible, below 6 ft/sec for very high flow rate applications. The water velocity in a pipe is determined by the size of the pipe and the flow rate going through the pipe. Below is a table of common pipe sizes and the recommended flow rates for two different velocity specifications. In general, choosing 6 ft/sec for suction pipe and up to 8 ft/sec can be used for return pipe but the lower the velocity the better. For spas, to keep the jet action strong, it is highly recommended to keep both the suction and return pipe velocity below 6 ft/sec.




Another way to reduce water velocity in pipes while maintaining high flow rates is to use multiple parallel pipes. The table below shows the equivalent diameter of pipe for multiple pipes of another diameter and equal lengths. N is the number of pipes from 1 to 10 and across the top is the diameter of each pipe. The values within the table are the equivalent diameter for a single pipe.



Ideally, the plumbing would have a suction line from the pad to the pool for each skimmer and main drain with a valve at the pad to control flow from each location. With this type of configuration, it is possible to use the pool pump to partially drain the pool by isolating the main drain on the suction and having a drain port on the return side. On the return side of the pump, multiple lines can help reduce head loss as well.


Pipe Size Impact

The size of the plumbing will have an impact on how efficient the pump will run. To visualize this impact, the following plumbing scenarios shows the relative Gallons/watt-hr energy factor for a typical pool.

1.5" Return Line with 1 x 1.5" Suction Line: 100% (Reference)
1.5" Return Line with 2 x 1.5" Suction Lines or 1 x 2" Suction Line: 105% Relative Efficiency
2" Return Line with 1 x 2" Suction Line: 115% Relative Efficiency
2" Return Line with 2 x 2" Suction Lines or 1 x 2.5" Suction Line: 117% Relative Efficiency
2.5" Return Line with 1 x 2.5" Suction Line: 120% Relative Efficiency
2.5" Return Line with 2 x 2.5" Suction Lines: 122% Relative Efficiency

As the lines get bigger, the impact diminishes because only the head loss contribution of the pipe and fittings will decrease with increasing pipe size. Components such as the skimmers, filters, heaters and even some valves do not change.


Water Velocity Recommendations

There are three reasons to be concerned about water velocity in plumbing. The first is that high water velocity means high head loss. The second is that on suction lines, high velocity can mean an increase risk of entrapment. And third, high water velocity can also mean an increase risk of hydraulic shock which is most often called water hammer. To address these issues, you will sometimes see web sites quote recommended maximum flow rates in piping usually in the range of 5 ft/sec to 10 ft/sec for PVC piping. However, it is important to understand that these are only recommendations and not hard limits. In other words, if you can find a big enough pump, the flow rate can and will easily exceed these flow rates. There is no fundamental limit to how fast water will travel in pipe.

Large pipe equals low head loss but it can be over done to some extent. 3" plumbing for a 3/4 HP pump is probably not necessary and is simply a waste of money. However, putting 3" plumbing in a spa is probably a really good idea especially if the pump is bigger than 2 HP.

The second issue of entrapment was addressed by the Virginia Graeme Baker Act and the ANSI/APSP-7 standard which states that for residential pools, you should not exceed 6 ft/sec in the piping within 3 feet of a suction port and 8 ft/sec in the line going back to the pool. This is easily accomplished with large piping which should be done to limit head loss anyway.

As for water hammer, high flow rates in plumbing have the potential to damage plumbing should a valve close suddenly. This is probably a rare event and not worth being too concerned about. Here is a quote from Haestad Methods, a leading authority on hydraulics regarding velocity:

Hydraulic shock is caused from a rapid increase or decrease in fluid velocity which causes a pressure wave that can be several orders of magnitude greater than the average steady state pressure. Repeated stress cycling of PVC pipe will eventually cause failures according to this paper. The cycles to failure is directly dependent on the average pressure of the pipe and amplitude of surge pressure in the pipe. Several charts are shown in the Uni-Bell paper which would indicate that most failures occur at very high pressures or large cycle times.


Pump Sizing

To conserve energy, the smallest total horse power (THP) pump is desired. However, several pool features may require higher THP than others. Features that can drive higher THP are:

- Spa jets usually require 10-25 GPM per jet and thus very high flow rates which are difficult to achieve with low THP pumps. Total required flow rate is the number of jets * the flow rate per jet.

- Water features are similar to spa jets and usually require high flow rates for good action.

- In floor cleaners usually require fairly high flow rates per head. Total flow rate is the number of heads * flow rate per head.

- Suction side and pressure side cleaners require high head pumps but depending on the cleaner can sometimes run on lower THP pumps.

Even if one of the conditions does apply above, the best of both worlds may be a two speed or variable speed pump. High speed can be used when needed and low when it is not. This will save money on electrical costs in the long run.

Other considerations that are very important when choosing a pump are:

- Minimum flow rate for three turnovers per day or one in 8 hours.

- Above ground vs in ground pumps. They are generally not interchangeable so stick with the pump made for your type of pool.

- Maximum GPM rating for filter size. Exceeding the flow rate specification for the filter may damage it.

- Minimum GPM rating for heater. Most heaters require at least 30-40 GPM or the flow switch may prevent it from starting. This usually only happens for the low speed of a very low HP pump so if you want to use the heater on low speed, double the minimum flow rate to determine the high speed flow rate as minimum.

When designing a new pool, it best to first determine the maximum flow rate required for all of the features and then size the pipe and pump to that flow rate requirement. This will ensure the most energy efficient design for the requirements of the pool.

Once you have determined the minimum and maximum flow rates desired, the best pump for the job is the one with the closest best efficiency point (BEP) to the maximum required flow rate. Unfortunately, not all manufactures show the best efficiency points on the head curves. However, in most cases it is around 2/3 of the maximum head of the pump.

Below is an example of a head curve for the Hayward EcoStar complete with a series of overlaid plumbing design scenarios (A-D). The chart shows how the plumbing system head will change with different flow rates and pumps. The points where the plumbing system intersects the pump head curve are the operating points.



The plumbing scenarios are defined by the California Energy Commission and represent different plumbing pipe sizes and designs. Curve B represents the worst case plumbing and most plumbing should perform better. Curve A represents 1.5" plumbing with quite a bit of head loss. Curve C represents 2" plumbing with an average plumbing design. Curve D represents 2.5" plumbing with a very good low head loss design.


SPA Pump Sizing

The first step in designing a spa is to settle on the number of jets, size of jet and how strong you would like the jet to feel. Once this is determined, the following table can be used to determine the proper pipe size and the resultant operating point for the pump.



NOTE: The head loss numbers in this table assume a dedicated jet pump without any pad equipment.


The following example will help the reader understand how to use the sizing table:

Jet Design: 6 x 3/8" Jets @ 15 GPM/Jet

Total Flow Rate = 90 GPM
Minimum Recommended Pipe Size = 2.5"
~ Head Loss = 55' (assumes 100' of pipe and typical fittings for a spa)
Desired Pump Operating Point = 90 GPM @ 55' of head

A few 1 HP full rated pumps and most 1.5 HP full rated pumps would work well for this setup.

Also, note that for designs requiring more jets than a pipe or pump can support, multiple plumbing loops with multiple pumps can be used to achieve the necessary flow rates.


Solar Pump Sizing

If the solar panels are on the ground, most any pump can handle the extra dynamic head. However, when placed on a second story roof, a pump must overcome the initial static head of the panel's height during the priming phase of panels. After the panels are primed, the static head going up to the roof is cancelled by the static head dropping from the roof.

A pump should have at least twice the maximum panel's height as its maximum head loss. This ensures quick priming of the panels and the closing of the vacuum release valve at the top of the panel. So if the peak height of a panel is 25 feet, then the pump should handle a minimum of 50 feet of head @ 0 GPM. Most full speed pumps will handle this fairly easily.

However, most two speed pumps at low speed will not have sufficient power to prime panels on a high roof since the maximum head at low speed is usually below 25 feet. The water may reach the top of the panel but there will not be enough pressure to close the vacuum release valve. If the valve does not close, then the static head loss will remain, total head loss will be high and flow rates will be near zero.

In addition, even when the panels are primed and the pump is switched to low speed, there may not be enough pressure at the top of the panels to ensure that the vacuum release valve stays closed. So it may not be possible to run solar on low speed of a two speed pump. It may be possible for panels on a single story house but probably unlikely for a two story house.

Also, solar will increase the head loss on the return side due to the additional pipe and the panels themselves. Whenever return side head loss is increased, flow rates are decreased and the head loss on the suction side is decreased because of the lower flow rate. Therefore, total head loss can be increased by as much as 80% of the PSI rise in the filter.


Filter Sizing

The following table is derived from the ANSI/NSF 50 Specifications for public pools and shows the minimum recommended filter size based upon the specifications maximum GPM/Sq-Ft for each filter type. These requirements are shown in the APSP-15 standard a nd are now being adopted as regulations by many states for both public and residential pools.



In some cases, the minimum filter size will be dictated by the pump maximum flow rate rather than the pool size so both must be taken into account. The filter sizes are determined from a 6 hour turnover so even if an 8 hour turnover is targeted, the filter sizes would still be appropriate and have an extra 25% margin. Also, increasing the size of the filter beyond what is shown in the table is generally a good idea and will minimize the number of cleanings per season.


Filter Types and Efficiency

One thing to consider when choosing a filter is that not all filters are energy efficient. In general, a cartridge filter will have the lowest head loss of any filter and the backwash valve in both sand and DE filters can be a very large contributor to head loss. Below is a table of different filter configurations with their associated head loss.




Which filter is best for you depends on your situation:

Cartridge Filters: Most energy efficient and don't require back-washing. Best suited for areas with water restriction, high electrical rates and/or pools that use a SWG.

Sand Filters: Easiest for algae clean up. Best suited for areas where the pool is closed for the winter and/or high algae potential.

DE Filters: Best filtration. Best suited for owners that really want their water to be as clean as possible.

Hydraulics 101 - Pumps, Pipes and Head

California Energy Commission Pump Test Data

The California Energy Commission supports a database which contains the test data for nearly any residential appliance including pool pumps. The data may be loaded from this web site and contains the energy efficiency of many different pool pumps. However, because of the way the tests are performed, you cannot expect more than about 5% accuracy in the measurements so pumps that are closer than that in efficiency should be considered as being the same.


CEC Test Documents
http://standards.nsf.org/apps/group_pub ... %20CEC.pdf
http://standards.nsf.org/apps/group_pub ... nt_id=8332
http://www.energy.ca.gov/2010publicatio ... 10-012.PDF

A pump cost comparison spreadsheet may be obtained from this web site: Energy Efficient Swimming Pools


Pump and Motor Definitions

Nameplate HP (NPHP) - This is the HP rating on the motor nameplate but is pretty much meaningless without the service factor.

Full Rated HP (FRHP) - Similar to nameplate HP and sometimes used when the pump is full rated.

Up Rated HP (URHP) - Similar to nameplate HP and sometimes used when the pump is max rated or up rated.

Nameplate KW = NPHP * 0.7457 - This is the KW rating and is similar to the nameplate HP and is generally used outside the US. Note that this is not the input power to the motor only the rating for the output power of the motor.

Service Factor - This is an overload rating for motors which states that the motor can be safely operated over the NPHP by the service factor for short periods of time. However, for pumps, this overload rating is typically used as the maximum load that a motor would need to deliver to the wet end. Because the load on a pump does not rapidly change over time, the service factor load is often used as the maximum design point for the pump.

Total HP (THP) or Service Factor HP (SFHP) = NPHP * Service Factor – This is the maximum load that can be safely driven by the motor and must always be greater than the maximum load from the impeller. A motor can be driven above the THP but will likely fail in a short period of time.

Electrical Horsepower (EHP) = watts / 745.7 = Volts * Amps * Power Factor / 745.7 - Electrical power input delivered to the motor

Brake Horsepower (BHP) = EHP * Motor Efficiency - Power delivered by the motor shaft to the impeller. This is not the same as THP or SFHP. BHP is a function of the load on the motor shaft and will change with Head, GPM and RPM.

Hydraulic HP (HHP) = BHP * Pumping Efficiency = Head (ft) * GPM / 3960 - Power delivered to the water. Sometimes called water HP (WHP) or pumping HP (PHP).

Motor Power Efficiency = BHP / EHP - I2R, magnetic and mechanical losses in the motor only.

Pumping Power Efficiency = HHP / BHP - Recirculation and internal friction losses in the wet end only.

Total Pump Power Efficiency = Motor Efficiency * Pumping Efficiency = HHP / EHP (note this is why total pump efficiency approaches 50%).

Energy Factor - Gallons/watt-hr = GPM * 60 / Watt-hr; A CEC definition used to measure a pump's true pumping efficiency.

Service Factor Amps - The amp draw when the motor is loaded to the service factor. Also, multiplying the SF amps by voltage should also give a good estimate as to the upper limit for power draw. However, sometimes the motor is over dimensioned for the pump so it will not always be an accurate measure of input power.

Full Load Amps - This can mean several things depending on the motor manufacture. It is either the amps at the NPHP or it can be the amps at the THP. I have seen it both ways so unfortunately, there is not a good standard for this one.

There are others but I think that the above definitions are the most important.

For further reading on this subject, I strongly recommend a web site put together by Joe Evans, a PHD from Pentair: http://www.pumped101.com.

Hydraulics 101 - Pumps, Pipes and Head

Troubleshooting

Air in the pump basket and/or lower than normal filter PSI:

Pump lid not sealing properly
Suction valves may be set improperly or partially off
Blockage in the suction side piping or valves
Clogged impeller
Undersized suction side pipe

Higher than normal filter PSI:

Dirty Filter
Return valves may be set improperly or partially off
Check for return side blockage
Oversized pump
Undersized filter
Undersized return side pipe

Pump motor will not start:

Shaft turns manually but motor hums and will not turn - Bad start capacitor, replace capacitor
Shaft is frozen and motor trips breaker - Frozen motor bearings, replace motor

Excellent.

Thanks Mark.

WOW! I always read a "mas985" post! Just wish my PB knew this data. It took me 2 years to get my PB to finally change my pump from a 2hp, TOO POWERFUL, to a 1hp.

Joe

Thanks for all the info, Mark.

I've been wanting to calculate my pump/pipe needs, but haven't, primarily due to not having all the resources in one place. At least you have all the instructions to determine it in one place.

Based on your basics, and another thread that you just posted (on pvc velocity issues), I'm thinking that 2.5" suctions lines and 2" discharge lines will work good. I'll figure it out based on your info, and post for your review.

I'm in the middle of a build, and spec'd out 2.5" and 2" pipe, and my builder agreed. Not surprisingly, evidently he forgot to mention this to his plumbing guys of the day... so as we speak my pool is plumbed with 2" and 1.5" pipe. If he would've maintained some pace at all, I was going to let it slide, and force some compensation later... but now I've pretty much decided that I'm going to have him re-do it. My preliminary calcs indicate too much of a difference to overlook... and he's going to be slow, he might as well slow and right.

Thanks again for your work. Our world needs people like you... to help the non-focussed ones like me.

Much like the book burnings and witch hunts of times past, I think we should consider banning Mas985 for being too smart, too thorough, too practical and well, you know, all that other stuff.

I gotta run.......Jerry Springer reruns are on and I never miss an episode.

Hi Mark and Anyone else who might care,

I'm back. And as you state in your post above, calculating the head loss on a future pool is nearly impossible... especially when the estimator..... ain't too smart.

So in my quest to determine if its important enough to make my PB re-do the pipes that we agreed on, I did the following rough calculations, and it seems to be a fairly large difference... I'll let y'all comment on my calcs, and if the difference seems significant or not.

Background: I specifed 2.5" suction (drain) lines, and 2" return lines. (This seemed to be 1/2" larger than his "normal", but he agreed... no problem... and certainly put $$ to do so.) Weeks ago they did the plumbing, and haven't done anything since. I was going to "overlook" it, point it out later, and get some $ back one way or another. Now, since he's still dragging his feet, I'm thinking I might as well make him do it right (and slow), rather than wrong (and slow.)

I think the difference in JUST the RETURN lines justify re-doing all of it. My calcs don't even include the suction lines, although I'll have him re-do those also.

Spa return: 2" 60' long
Spa return: 2" 60' long
Pool return: 2" 60' long
Total return length: 240 feet

Head loss due to friction, schedule 40 PVC pipe (http://www.plumbingsupply.com/pluminfo.html)
2" pipe 35 gpm: 2.21 feet per 100'
2.5" pipe 35 gpm: 1.66 feet per 100'

2" pipe 50 gpm: 2.4 feet per 100'
2.5" pipe 50 gpm: .88 feet per 100'

50 gpm: 2" pipe: 4.17 feetloss x 2.4 = 10.008 feet loss in my return lines (due to pipe only)
50 gpm: 2.5" pipe: 1.66 feet loss x 2.4 = 3.984 feet loss in my return lines (due to pipe only)

35 gpm: 2" pipe: 2.21 feet loss x 2.4 = 5.30 feet loss in my return lines (due to pipe only)
35 gpm: 2.5" pipe: .88 feet x 2.4 = 2.11 feet loss in my return lines (due to pipe only)

Ok… so how do you convert FEET to PSI… and is that a big enough difference to care about?

I will be using the Pentair 4x160, so I should be able to adjust it to pretty much what I need, assuming I can figure that out one day. My best guess is that pool will be about 24,000 gallons. Pretty odd shaped. Hard for me to calculate.

Thoughts??

First,

Filter PSI = Return Head Loss / 2.31

But the pipe is not the only contributor to head loss. The fittings and rest of the equipment actually add much more than the pipe runs.

I happen to have an Intelliflo model and for a typical pool with 60' runs, here is what you can expect


RPM 3450 2500 2000 1000
2.5"/2.0" Head Loss 74 39 25 7
2.5"/2.0" GPM 104 74 59 28
2.5"/2.0" Filter PSI 25.2 13.4 8.6 2.2

2.0"/1.5" Head Loss 87 46 29 7
2.0"/1.5" GPM 72 51 40 19
2.0"/1.5" Filter PSI 30.2 16.0 10.3 2.6

Sorry about the fomatting. Hopefully you can read it.

Now this is just an estimate but it gives you a feel to what it might be.

However, you may have an option which would not require removing what he already has laid. Have him add at least one additional line for the suction and return. So for the suction, have one 2" line for the main drain and each skimmer. Have at least two lines for the return and have him split them into two sets of eyeballs. How many skimmers and return eyeballs were you planning?

Thanks again, Mark.

Here's the pipe (and how it's labeled) at the equipment pad:

MD Pool 2"
Skimmer 2"
Skimmer 2"
MD Spa 2"
MD Spa 2"

Pool Return 2"
Spa Return 2"
Spa Return 2"
Spa Jet 2"
Air 2"

Polaris 1.5"

Here's what I see in the pool:
(2) Main Drains
(2) Skimmers
(3) Returns
(1) Autofill
(1) Polaris?

SPA
(6) Jets?
(2) Returns?
(2) Drains

Thanks for the comment on the other equipment causing head loss. The only thing i have to hang my hat on in the contraact is the "pipe size." Not even the number of suction/returns is specified (my fault), therefore, the other equipment I have to assume is the same, for either pipe size.

If you think that adding a suction and/or return would be just as beneficial, I can certainly give him that option, if he'd prefer to do that than replace existing pipe. For what its worth, the pipe is laid, but there is no concrete over it.

Also, maybe worth mentioning, my spa has a relatively large spillover (about 5 feet wide.)

Thanks,
Steve

It's a little hard to tell how he is planning to plumb everything but this is what I think he is trying to do. It may be a good idea to get confirmation from him. See bold inserts:



In general, I think he is on the right track but without seeing the schematic, I cannot say for sure.

Thank for your thoughtful reply, Mark.

Getting a schematic from the PB might be possible. That's a BIG might. I wonder how much he really knows about anything, and I certainly wonder about how much he knows is actually going on at any particular build. His regular plumber didn't run these lines.. his dig crew (who seemed very pretty knowledgable) ran the plumbing... I think they had some free time that day. The plumber showed up the next to pressure test, looked it over, didn't say too much, got interrupted by rain, and hasn't been back since.

Now that I think about it, he did seem to know a little about it, because when I mentioned that they didn't run the deck jet lines, he said "I wasn't told about any deck jets." So he may have drawn up what they laid.

So adding to above piping, there will be 2 deck jets. We will have an extra pump to run either the deck jets or the spa... I'm not sure of the exact plan there. Again, plumber didnt know about the deck jets when he "designed" the system.

Nothing like have an absentee PB who keeps the design a secret.

The spa jets are Waterway Poly Storm Gunite Jete (210-3710). It looks like the heads available for it demand 10-12 gpm each.

I appreciate your comment that this should work. What are thoughts about how much it may cost me in the future in energy due to his decicion to use 2" returns rather than the 2.5" we agreed upon?

Thanks again for your help.

Steve

There are so many variables involved that I don't think it's likely anyone could come up with a truly accurate figure. If you run the pump "x" hours per day, any restriction in the return lines will actually reduce your operating cost (but at the same time reduce the number of gallons pumped). Are you installing a flow meter? If not, how were you going to decide how long to run the pump? My guess is that the real difference will be pretty small, bordering on neglible.

If you run at the lower speeds, it will have little impact and even at full speed, the turnover time will only be about 10% more.

ok.... I'll consider other alternatives...


Thanks again for all your work.

Steve

All,

this is really great material in this thread - here is another great chapter of a book I found online and I wanted to share the link

http://www.apsp.org/docs/chapter_4.pdf

Enjoy !

Patrick

Awesome thread, have a thought to sum things up for existing equipment owners who want to know minimum HP needs if they are wanting to make a change or go for a more efficient unit. If you are new to the basics, the cliff notes and one realworld example:

On your existing equipment you can find out your head loss by using a pressure gauge on the pressure side (a port on sand filters is already there).

Read the value and multiply by 2.31 to get the feet of head. Then add roughly 5 for the suction side loss....This will get you the head loss (which most struggle with) and from there you can use the manufacturers chart to figure out what HP system you need for the number of turns you are trying to acheive per day (usually 1-3).

My Pool as an example:

21000gal pool
3 turns a day this equals 21000x3 = 63,000gallons pumped per day
63000 gallons / (60x24) = 43.75 gallons needed per minute [60minutes an hour x 24 hours]
My pump pressure shows 28PSI thus 28x2.31 + 5 = 70 for head pressure

- Look at a pump manufacturers chart for something with 70lbs head pressure and a GPM of 44, for my needs around 3/4HP
- If I wanted the most energy efficient it would be around 1Hp but then I would get 65GPM so I would only need to run my pump (21000/(65*60)) = 5.4 hrs day for one turn.

I got both of these values (3/4HP and 65GPM) from the chart in the start of this thread. You will need to specifically reference the pump makers chart for more exact numbers.

I had covered head estimates in the first section:



Simply adding 5' of head for suction head tends to underestimate head loss for small diameter plumbing. For most pools, suction head is highly correlated to the filter pressure (without solar) since filter pressure is primarily determined by pump HP (i.e. flow rates) and plumbing design. These two factors will affect return head and suction head proportionately.

One more thing to add. I have since updated some of the approximations and probably should change the original post. Here are average suction head to return head ratios for different pipe combinations:

Suction head = 75% of return head for 1.5" suction and 1.5" return pipe
Suction head = 50% of return head for 2" suction and 2" return pipe
Suction head = 30% of return head for 2.5" suction and 2.5" return pipe

Other combos I didn't cover before:

Suction head = 22% of return head for 2" suction and 1.5" return pipe
Suction head = 22% of return head for 2.5" suction and 2" return pipe
Suction head = 17% of return head for 3" suction and 3" return pipe
Suction head = 14% of return head for 3" suction and 2.5" return pipe

You information is dead-on just thought I could try to simplify it for non mechanical folks reading your posts with a realworld example. Perhaps my gauge was off or something the day I got the "5" for suction side....

But I do have to ask if your schooling me here how did you get the 25%-75% values? If your multipliers are correct that means my head pressure is 65 + 65*.7 = 110 head. I have 1.5" pipe all around and am running a Hayward Superflow with a 3/4HP motor.

I'm off your example chart and would flow 0GPM. My pumps flows are very strong on the pressure side at the pool for my 3/4HP motor setup and 28psi on the gauge (unless my gauge is broken it does go to zero when the pump is off) ....What am I missing trying to use my real world example and our agreed upon taking PSI*2.31 then adding in your multiplier for that value for head suction?