Swimming Pool Energy Consumption (S.P.E.C.)
or “What I learned on my summer vocation”
Let’s have a look at energy efficiency and consumption from the swimming pool stand point, referred to simply as S.P.E.C. throughout this discussion (swimming pool energy consumption). Such considerations may seem silly to some, an oxymoron of sorts to others. Who in their right mind, conscious of energy consumption and efficiency in their household would even consider installing or embracing a swimming pool? After all, pools are notoriously energy inefficient, expensive to own and operate and will never help reduce your consumption of energy. Although pools have been built this way with little change for the last 60 years, the conscientious homeowner can now look forward to more choices than ever in their ability to balance costs vs. the many potential rewards of pool ownership; leading ultimately to an improved quality of life. Let’s look at some ways for the savvy consumer to tip the scales in his favor and make pool ownership a prospect where the many positives can grossly outweigh the few negatives of a well designed pool.
Just because you happen to already have or want a pool doesn’t mean you should turn your back on the prospect of energy efficiency. The fact that your pool only runs for half a year or less doesn’t mean that you need not strive to have it run it in the least expensive, most efficient way possible. There are many steps you can take whether your pool is merely a pre-installation concept or you are considering a re-fit of an older pool with modern efficient equipment. For starters, we have listed some of the design parameters and equipment choices that will contribute to the lowest cost of ownership regardless of the age of your pool
Of course you can save energy by disabling your heater and reducing your filtration cycle but what good is all the effort and expense that goes into pool ownership if the pool is just too cold and dirty to enjoy most of the time? Balance is key to successful pool ownership through maximum enjoyment and minimum cost.
The most efficiently run pools would strive to incorporate:
A solar heating system professionally sized and automated.
A variable flow permanent magnet motor pump or Low E optimized single speed pump.
A multiple cartridge filter or oversized sand filter where water conservation is not an issue.
2 inch plumbing and intelligent manifolds with sweep elbows and full flow valves and check valves.
An automatic cover (for gas heated pools) or a custom cut-to-fit solar blanket (for solar heated pools).
An in-floor water return cleaning system (aids in heating and stirs bottom settling particulate in to suspension all without the need for an additional pump).
An in depth discussion as to the structural and practical elements that contribute to the most efficient overall pool designs possible such as shapes and contours, insulated sidewalls, full sun exposure, wind breaks, choice of materials for the shell of the pool and efficient plumbing layouts are beyond the scope of this discussion although not without individual and collective merit. Anyone in the planning or dreaming stages of new pool design should invest the time and resources necessary to acquire some knowledge of their proposed undertaking and make themselves aware of the different approaches, technologies and philosophies of modern pool design. Greater knowledge will precipitate your best overall chance at balancing aesthetics vs. efficiency, initial costs vs. long term savings, and mission derived design elements vs. cookie cutter pool designs.
I find it amazing that consumers will charge headstrong into a purchase and installation of a new pool doing little or no research about what the current trends are, placing their entire faith and decision making process with the pool company. Often, a swimming pool is the second most valuable purchase a homeowner makes after their home. I’ve seen pools from 20k all the way up to 300k and more. A new car purchase warrants many hours research on the internet, BBQ grill, several hours, new TV at least a few hours of research, a pool??? “W’ell just go by what the salesman recommends and my friend Joe knows something about pools too.” Maybe this is because there is so little on the internet about this topic or because it is so hard to find. I put this discussion out there to encourage readership, intelligent decision making, greener living alternatives and because I believe the internet should be a tool for humans to improve their lives and not just an advertising media.
The most efficient overall pool construction methods and designs are another matter and would better be served by a separate discussion. Suffice it to say that those in the planning stages of a new pool should be aware that there are specific choices that can and should be made in all aspects of their pool design. Different types of construction yield wildly different efficiency results. Select pool designs and wise appliance and equipment choices have the potential to save tens of thousands of dollars in operational costs, make for greater ease of cleaning and maintenance and exhibit a greatly reduced environmental impact or ‘carbon footprint’ during your pools lifespan. Choosing a contractor should be largely based upon their awareness of these choices and their willingness to implement them as you see fit, and within your proposed budget. One guarantee, universally accepted when designing and building a pool, is that smart efficient pool designs and equipment will cost more to build, up front. As one adds such energy saving measures as a variable speed, variable flow pump and controller, an automatic cover, a solar heating system and an electronic purification system your costs will quickly escalate. You can and will however, expect to offset additional expenditures for equipment specifically engineered to reduce operating costs over time. The quicker these costs can be reduced and recovered, the more efficient and sustainable your pool design will have turned out to be.
As the rest of this web site is devoted to Solar and other alternative heating systems for the pool, we recognize that not everyone needs or desires to heat their pool, and not everyone can have an automatic pool cover. In fact less than 10% of pools built today would allow the use of an automatic cover by design which we will address later in this discussion. For existing pools, barring a complete renovation, almost no one has knowledge or control over what type of piping was used and the flow restrictions inherent in hard elbows, underground piping, and poor manifold design. We concern ourselves therefore, for the remainder of this discussion to the functional necessity of the often forgotten, often ignored stand alone swimming pool pump. Every pool needs a pump as everyone must filter their pools on a daily basis. The pump can be compared to the very heart of your pool and your piping to its circulatory system and this discussion can benefit not only some but all pool owners taking the time to read it, understand it, and implement some of the ideas and suggestions put forth toward a more ‘Healthy’ pool.. We conclude with a small discussion of the pros and cons of using a solar blanket or as we prefer to call them a “lunar” blanket, and an expose' of typical cookie cutter pool designs..
Because the pool pump is said to present the second largest electrical demand in a household after central air conditioning systems, the savings generated by understanding and implementing an energy efficient pump can be significant. You could change light bulbs until your entire household is illuminated in purple low quality light, and you are literally blue in the face, and the cumulative savings per year will not be much greater than what you will save in just a few short weeks in the summer by switching to an energy efficient pool pump. For many homeowners, particularly those not burning gas to heat their pools, switching to an energy efficient pool pump can be the single greatest home energy savings measure that they might undertake ever!. Unlike attic insulation, new windows and new central air systems costing many thousands of dollars, at well under a thousand dollars installed, the new energy efficient single speed pool pump may offer the homeowner his greatest return on investment of all the energy savings measures available or in some cases, his second greatest return on investment after first replacing a gas guzzling pool heater with an equally capable professional solar heating system, generally recognized as the ultimate green energy product available*.
*(when calculating the amount of BTU’s produced over its intended lifespan vs dollars invested or cost of ownership, nothing even comes close to return on investment or environmental friendliness as a professional solar pool heating system!)
Prior to the SPEC movement which began in California, pool owners were limited in what steps they could take to reduce the cost of running a pool. During the seventies when the oil crunch spawned the development of solar pool heating collectors, these were adapted by people with pools heated by natural gas, oil and propane. At the time, electricity was readily available and cheap. And for the most part, electrical efficiency in residential pool design simply did not need to be addressed.
This all changed after the explosive growth of the 80’s and 90’s. Precious natural gas to fuel power plant generators was becoming more expensive, coal fired energy plants were being phased out due to growing environmental awareness, and the cost of producing new energy generating facilities was growing exponentially higher due to fuel costs, land costs, environmental constraints and ever more stringent permitting processes. When it began to appear as though California may not be able to meet its energy requirements during periods of peak demand, (so eloquently phrased in this quote by filmmaker/author Michael Moore: “California didn’t have enough energy to run its juicers and execute its prisoners”,) legislators began to dream up ways to lessen this demand so as not to put the great state of California in the embarrassing predicament brought about by ‘rolling blackouts’, a common phenomena in poorly managed and third world countries.
One such piece of legislation voted into law disallowed the continued use of single speed pool pumps on all new construction and existing pump replacements. California Title 20 states that after January 2008, you will no longer be able to legally purchase or install a single speed pump 1 hp or greater in the state of California for new or existing pools. Homeowners who had no prior knowledge of multispeed pumps would be forced to agree to have the same old inefficient pumps installed but with the more expensive dual speed capability. Because this lower speed was not optimized for any aspect of their particular system, and they didn’t truly understand the potential benefits of this additional lower speed, they would simply ignore the lower setting and continue to run the pump on the familiar high speed! This problem was exacerbated by the fact that almost none of the pools and plumbing systems were optimized for low speed operation and as such, the lower speeds were perceptively and functionally inadequate for meeting the filtration demands of the pool. The available lower speeds just didn’t seem to work as well, didn’t produce the desired results, and were thus largely ignored. In addition, although compliance was assured on new pools through the permit and inspection process, the explosive growth in internet sales proved that there was no way to force compliance in the replacement pump market, potentially larger than the new construction market each year. I believe that it has been the recognition of this loophole in noncompliance that has since spawned a whole industry wide re-examination of the role of the basic residential pool pump and the results to the industry over the last several years have been nothing short of amazing!
Engineers began to look at ways to make the pump more efficient by doing more with less. Whereas the California approach to running longer periods at lower wattage was acceptable in theory and on paper for that time period, in the real world, little or no savings were being realized. Engineers have been able to make great progress in new cooler running and permanent magnet motor designs, more efficient impeller designs, multispeed capability, and finally the state of the art pump of today which combines some elements of all these state of the art refinements. As of 2012, the variable speed, variable flow, electronic SVRS-VGB compliant, permanent magnet synchronous motor pumps have the potential to be the most energy efficient pump for many applications and are being hailed as the new revolutionary pool pumps. Because the pool pump has been proven to be the single largest consumer of electricity in a household without central air conditioning, the savings potential for the average residential consumer employing some variation of energy efficient pump designs can be immense. Of course, in households with central air conditioning, the pool pump averages a close second in overall energy consumption. But please note as these aging, inefficient air conditioning units become tired and beyond repair, the industry has responded nicely with energy efficient replacement options. You will never see an air conditioning contractor recommend a model with similar efficiencies to the one being replaced. More than likely you will get to choose from models between 50% to 150% more efficient than the ones being replaced depending upon your budget, because as is usually the case, the most efficient models, offering the greatest potential savings, garner the highest initial costs. When a household using a standard 2 hp pool pump upgrades to a super efficient AC unit, then the pool pump may move to the top of the list for energy usage in their household! And yet, when your 1.5 or 2 hp pool pump bites the dust, there is little or no talk of a more energy efficient model, no talk of kilowatt hours and savings, and generally no knowledge or discussion of the newer state of the art energy savings pool pumps amongst your average pool retailer and pool Service Company. Equally compelling is the fact that there will be very few companies and contractors who will actually recommend a smaller (lower hp) pump based upon their observations of your particular pool and equipment. In fact it is common practice to entice you to step up a notch in pump sizing from 1hp to 1.5 or from 1.5hp to 2 with the assurance that it will simply be ‘better’. The simple truth of the matter is however, that the most efficient pool pump for any application is the pump that gets the job done for the lowest purchase price and the lowest cost of ownership. One serious drawback of the latest variable speed electronic pumps has been the considerably higher cost of both stocking and retailing these pumps combined with the added costs of an electronic control module and a certified electrician to install and program all of the features and safety measures. Swimming pool companies would just as soon continue to sell and install the standard duty pumps of yesteryear due to the ease of installation and their familiarity with these proven workhorses. You can expect to pay several thousand dollars up front for the most efficient variable flow pumps to realize a savings on average of about $400 per year. This can be a difficult pill for most homeowners to swallow and pool companies to propose.
In the process of developing these new ‘revolutionary’ multi-speed pumps, the engineers went back to the drawing board and re-applied some of this new technology to the old fashioned single speed pump. This is where we see the potential for the greatest cumulative energy savings in the history of the swimming pool, the single speed energy efficient pool pump, and the shift in manufacturing that renders the California proposition 20 law virtually obsolete.
As mentioned above, according to F.S.E.C. (Florida Solar Energy Center), in the average residential household the pool pump is the largest user of electricity after the central air unit! Let that sink in. The only exceptions are households where a heat pump is used daily to heat the pool (or house). In this case the central air takes a backseat to the heat pump and the order of consumption becomes Heat pump, Central air, and then pool pump. Conversely, if you are using a super efficient air conditioner unit and a larger inefficient pool pump then this can be reversed. The point here being that running a pool for any length of time each year can be a costly proposition, and these costs remain insidiously buried in your summer or annualized utilities bills when compared to your more obvious seasonal pool purchases of chemicals and other consumables
The Case against 2 HP Pumps.
In our business, we constantly come across homeowners shopping a new pool and deciding which company to use. Let’s have a look at some hypothetical proposals for your new pool installation and the variables that might drive your decision making. Company A is offering a 1 hp standard duty pump, cartridge filter, an in-floor automatic cleaning system and all 2 inch piping and valves for a 550 square foot 20k gallon pool. Company B is offering a built in appliance type cleaning system (with additional ¾ hp standard duty motor), a 1.5 hp pool pump, Sand or DE filter and no discussion of pipe size (generally meaning cheaper 1.5 inch pipe) and Company C being the last to show up trumps the others and offers to install a 2 hp pump, a self contained electric (robotic) cleaning system (i.e. Dolphin, Aquabot), and a set of “Jacuzzi style” spa jets to liven up the step section along with a low maintenance sand filter (again no discussion of pipe size). All companies are around the same price offering the same basic pool design. All are offering the choice of filter types. The salesman of company C gets the deal. Who could refuse Jacuzzi style jets, a low maintenance filter and a pump that is twice as big and twice as ‘good’ as the first companies’ contract proposes. The point is that companies will give you or tell you or sell you whatever they need in order to get a deal and they are constantly building pools with 2 hp pumps when a 1 hp pump or less is all that is needed. Right out of the gate, you will spend greater than twice as much on electricity every year with package C as you would have done with a more responsibly designed and equipped pool and even as much as 150% more with prolific use of an electric pump dependent cleaning system!
None of the above examples are perfect but Company A provides the best SPEC design and therefore the most sensible investment for you. The simple substitution of an energy efficient ½ hp pump would have made the deal even sweeter and cut the cost of electricity by 75% or more over deal C! Unfortunately, it is difficult, almost impossible to sell a package to the average consumer based upon a ½ hp pool pump when another company is offering a 2hp pump for the same price. No one wants to feel ‘shorted’ and the average consumer will almost always opt for the larger model ‘just to be on the ‘safe’ side. This is the dilemma of the pool contractor and the reason for the unnecessary proliferation of 2 HP and now even 2-1/2 HP Pumps! (I kid you not. Even the aboveground pool retailers are offering 2 and 2.5 HP aboveground pool pumps to ‘enhance’ their packages insisting that they are simply ‘better’ or that you are getting ‘more for your money’ compared to other companies offers. Imagine, a filter with a 40-50 GPM flow rate that is pushed to the limit with a standard duty ¾ hp pump now being paired with a 2 HP pump!). Why anyone would want to spend 2 or 3 times as much as they need to on electricity for their pool pump is anyones guess. Maybe a macho thing! And yet,our customers laugh at the prospect of a newer energy efficient ½ HP pump but believe me when I tell you they are not a joke! We Install half horsepower pumps all the time (our largest seller) and see flow rates approaching 85 GPM. The new energy efficient half horsepower pumps are capable of delivering flow rates far greater than older 1 HP pumps and rates approaching standard duty 1.5 HP pump designs. All but the largest pools with demanding water features can be run on a half horsepower, high flow rate, energy efficient pump. On paper, the half hp pump can do 90 GPM with no head pressure loss! 90 GPM is more than the maximum flow you can pass through 2 inch piping, regardless of design so there is little or no benefit to a larger pump meaning all that most residential pools need is an energy efficient ½ or 3/4 horsepower pump! Whereas any pool utilizing 1.5 inch piping, multiport, or filter interconnects can and should be run on an energy efficient ½ hp pump, the use of a larger unit will not result in any real world increase in performance (flow rate or filtration capability)! We would hope to see this trend continue in the future with the development of 60-80 GPM 1/3 or even ¼ hp pumps! We find that unless the homeowner has complete and total confidence in the contractor or can be convinced to compare published performance curves, they are quick to discount the smaller pumps. Similar to when they do not know anyone personally using and enjoying a solar heated pool, they don’t know anyone successfully using a ½ hp pump and they remain skeptical as to how well it may work. A recent meeting with a customer seeking a solar heating estimate and building a brand new pool was productive in that I convinced him to exchange the 2hp “Superpump” they were about to install with one of the energy efficient models. I showed a comparison of the performance curves which places the EE 1HP pump as the nearest replacement to the standard duty 2hp. Where the 2 hp was just too much flow and energy use, so was the EE 1HP! If I had recommended a perfectly adequate ½ hp or even a ¾ hp pump I would have been met with major skepticism from both the homeowner and the pool contractor. I felt in this case a drop of 50% in energy costs was adequate even though a 75% reduction would have yielded similar results. Look at the published performance curves and match pump size (flow) to filter and pipe size. You will be shocked at the results!
Let me state again in case you didn’t fully understand “all that most residential pools need for adequate circulation is an energy efficient ½ hp or ¾ hp pump!” Here is our explanation why and we encourage you to also click the link to the left which addresses similar concerns entitled:
“What Size Pump Do I Need for My Pool?”
Residential pool design guidelines call for a once turnover of water in a 24 hour period as the minimum standard for circulation. For instance if you have a 560 square foot pool holding about 20k gallons, your pump (and filter) must be able to turn over 20,000 gallons in 8 hours or 2500 gallons per hour or about 42 gallons per minute as the absolute permitted minimum. Ignoring published minimums it has become common practice to design for a twice turnover of water in that same 8 hour period, in the above case calling for 83 gallons per minute flow rate. At 12 hours per day of filtering the above example would only need 28 gpm flow for a once and 56 gpm flow for a twice turnover of water. All these facts are relative to the pool that is being designed or SPEC’d and some exceptionally efficient pool designs will be well suited to stick to the published minimums. With a flow rate of about 85 GPM which can be coaxed out of a ½ hp pump with good pipe and manifold design, our sample pool need only run 4 hours per day on ½ HP to achieve the desired filtration specification! As far as pools go, this configuration will literally sip the electricity off the grid and will be hardly noticeable in the grand scheme of things. On the average, this pool will consume about 1/10th of the electricity of a similar pool using a 2hp pump running 8-10 hours per day! If you knew you could run a pool on less than 100 dollars worth of electricity per seasons use, how many more people would then seriously consider adding a pool to their American Dream. How many pool companies would be able to increase sales? How many new high flow low horsepower replacement pumps do you think we would all be able to sell?
All these facts are relative to the pool that is being designed or diagnosed. When sizing a pump one must take into consideration pool size in gallons, number of hours per day that the filter will run, and the amount of head pressure loss for the pool which can be calculated by adding all the linear feet of 1.5 and 2 inch pipe, numbers of elbows and fittings of each type, and knowing the values of head pressure loss in feet for all the valves, filters, skimmers, returns, cleaners, check valves, pipe, fittings and multiport valves! Sounds daunting doesn’t it? In most cases a SWAG (scientific wild ass guess) based estimate of head pressure loss will have to do. We find that using an average figure of 20 to 30 feet of head pressure loss yields acceptable results when it comes to sizing a pump and filter combination. These values may increase to 40 feet of head when a roof mounted solar heating system is in use. Precise values are difficult if not impossible to determine. For a lengthy explanation of the pioneers of this science and the formulas they contributed visit this link:
A quick look at this web site or Wikipedia entry will convince you that this is more voodoo than science and any reasonable engineer or designer must learn to rely upon educated estimates based upon prior research. In short, gravitational lift and length of pipe are of primary importance in the estimate of head pressure loss with fittings, valves and individual water features being less significant to the overall equation. We see so many filters and pump combinations in the field thrown together seemingly willy-nilly with no reasonable attempt to match or optimize anything. As an example, I met with a customer recently who complained of poor suction from the skimmers. An examination of the filter system indicated a standard duty 2hp pump capable of 110 gpm, a 48 square foot DE filter with a design flow rate of 96 GPM, a 1.5 inch multiport valve and 1.5 inch filter interconnects. Let’s take a look at these individual components and see if we can diagnose the problem.
|Standard Hayward 2hp Super pump||flow rate||110 gpm (@30 feet of head)|
|Hayward 4800 DE filter||design flow rate||96 gpm|
|1.5 inch Hayward multiport valve||design flow rate||60 gpm (@20 feet of head)|
|1.5 inch filter interconnects maximum||flow rate||44 gpm less with elbows|
This example demonstrates the lack of thought that goes into the design of these filter systems. A pump wanting to push over 100gpm encounters a multiport valve allowing only 60gpm flow and this flow encounters a further more significant bottle neck as it must travel through 1.5 inch pipe and several elbows to get from pump to filter and then back to the pool. The number of elbows really doesn’t matter in this design because we end up with reduced flow rates of less than 40 gpm. This example shows that this particular pool can be served equally as well with a ¾ hp standard duty pump or a ½ HP energy efficient pump because you are just not going to get over 40 gpm without other significant changes. Perhaps the initial design called for a 1 hp pump when the filter interconnects were simple and new. As aging plumbing was replaced with flex pipe and more elbows, these restrictions rendered the flow rate unsatisfactory. Over the course of time, pool service companies have convinced the homeowner that a 1.5 HP pump would ‘magically’ restore their flow. Sometime later enters pool company xyz who is called to replace this second pump and further diagnose the problem and recommends a 2hp pump “to increase your flow rate”. So you went from spending $400 per year on electric to spending $800 per year generating nothing but friction and heat while your flow rate remains virtually unchanged. Believe me when I tell you that I see similar setups in the field every single day in this business and would like to fix them all. Unfortunately this would take up all our time and leave none for our core business of installing efficient and high performing solar systems to heat pools and make them more comfortable. Somehow, high energy consumption or cost of operation becomes more palatable as long as the pool is warm, comfortable and enjoyable most of the time. But there is a whole other dynamic at work that needs to be addressed and exposed. In the above example, the first pump, a 1 hp standard model lasted for 10 years due to the balance that was inherently designed into this system. During year 9, the pool/filter piping was ‘fixed’ for whatever reason(possibly an expired gass heater disconnect) and this ‘fix’ resulted in the addition of several more 1.5 inch elbows thereby restricting the flow and ushering in the failure of this pump during the next season. The next 1.5 hp pump only lasted 3 seasons due to the enormous strain of trying to push 90 gpm through a filter and piping layout that would only allow about 40gpm. You can guess how long the newest ‘recommended’ 2hp pump will last. Not long at all since it would be under unacceptable levels of strain and pressure trying to push its design flow rate of over 110 gpm through a poorly designed filter system. This has been a common problem we have encountered in the field. Almost always, the addition of a larger pump, without other significant changes to this system, will lead to shortened pump life because the pump is never able to relax and achieve its design flow rate. The larger the replacement pump, the shorter the lifespan without addressing the real problems of limited flow through pool manifold design, unnecessary elbows in the filter interconnects and the reliance upon poor flowing 1.5 inch valves, interconnect pipe, multiport valves and older clogged and tired filters.
In the above example, the simple change from 1.5 to 2 inch filter interconnects and adding a 2 inch multiport valve would bring the flow rate up to 73 gallons per minute and result in a real increase in filtration capacity. Total cost: about $250 while leaving the pump untouched.
Multiport valves used with filters vary widely in their flow rates. Great gains in flow and efficiency can be had with the simple addition of a 2 inch multiport and 2 inch filter interconnects. Take a look at the accompanying chart from Hayward Pool Products engineering department and you will get an idea of the difference a half inch can make upon overall flow rates and performance as it passes through the different varieties of multiport and slide valves. As you can see, the 1.5 inch multiport valve is not suitable for anything but the smallest pools running less than a 1hp standard efficiency pump. And yet, probably 90% of the pools we encounter in the field will be setup with the 1.5 inch multiport valve regardless of pool size or pump size. Whether this is because they are a few dollars cheaper than the 2 inch designs or because ‘that is the way we’ve always done it’ is anybodies guess. Granted, there are some companies that are installing a 2 inch multiport valve or slide valve with new pools sometimes with the purchase of a 2 inch pipe upgrade and on occasion just because it is the right thing to do and it offers a competitive advantage for the wary shopper. As most of our work heating pools are done on an existing pool as a retrofit, vs. maybe 10 to 15% of our contracts a year on brand new pools, we most often encounter older piping, older plumbing, older technology and older inefficient filters and pumps. It is in ours and your best interests for efficient solar heating to have the best allowable flow rate based upon the design flow rates of your major components. If there is an obvious bottleneck, we may simply correct it when installing the solar heating system or we may recommend any number of upgrades to increase your flow rate, increase solar heating efficiency and decrease energy consumption, a win, win, win for you as a conscientious homeowner. The lesson here is that bigger pumps do not increase flow rates without other, often less expensive upgrades. Adding a larger pump with the hopes of increasing flow rate and filtration/solar heating capacity is usually an exercise in futility and more often than not the additional expense to run these larger pumps buys only increased heat, pressure and friction while substantially shortening pump life, a vicious cycle and an incredibly bad deal.
So how much pump do you really need? First start with an accurate calculation of pool capacity.
To calculate pool gallonage: one should multiply surface area of the pool by average depth by 7.5 or 5.9 depending upon the shape of your pool.
Rectangle pools simply multiply length x width x average depth x 7.5
Example 16 x 32. 16x32 = 512 x 4.5’ (avg of 3-8 feet) x 7.5 = 17,280 gallons
Example 16 x 32 Grecian cut corners 16x32 = 512 x .95 (minus 5%) = 486 x 4.5’ x 7.5 = 16,416 gallons
For free form pools (oval, kidney, Mountain Lake, lagoon, round) or any pool with rounded ends, the multiplier becomes 5.9. Multiply length x avg width x avg depth x 5.9 to estimate gallon
Example 19x22x37 mountain lake: (average 19 and 22 to 20.5) 37 x 20.5 x 4.5’ x 5.9 = 20,138 gallons
So go ahead and calculate the gallonage of your pool. Most formulas will work out very close to manufacturer’s specs with an average dept of 4.5 feet. Large areas at 3 feet and smaller areas at 8 feet average to about 4.5 depth. Pools with a smaller shallow end and a larger deep end might use an average depth of 5 feet or 5.5’
Once you have the gallonage you must decide if your pool would benefit from a twice turnover of water in any one filtration cycle. Square corner pools and pools with many bottom angles might need this extra filtration capacity in order to stay clean whereas rounded bottom pools such as fiberglass pools, round and oval aboveground pools and many concrete pool designs without visible bottom angles can usually stick to the published minimums of a once turnover of water in one filtration cycle.
One filtration cycle is the number of hours per day that you set your filter to run. Some people have adapted the habit of running the pool at night due to somewhat decreased energy kilowatt costs, even after these savings have been largely discontinued by the servicing energy company. People with solar heating systems must run their filters during the ‘standard solar day’ in order to accomplish the dual tasks of filtering their water and heating their pools without any additional electrical usage. It makes no sense to run your pool at night to filter and then again during the day to heat even if there is a small savings to be realized in the overnight electric rates.
Another consideration is to match your desired filtration cycle to the needs of your pool. For instance, if you are running a 1hp energy efficient pump or a 2hp standard duty pump and able to achieve design flow rates of 110 gpm, then smaller, efficient pools might need only 2-4 hours per day for their filtration cycle. If you are using a solar heating system you would probably want to use the entire solar day to maximize heating potential. 10 am to 5pm or even 9 am to 6pm results in 7 or 9 hours of filtering each day. In such a case, it would be best to drop back to a smaller 1hp standard duty pump or an energy efficient ½ hp pump and you can have your 7-9 hours of filtration/Solar heating per day without increasing your cost of electricity, an ideal and efficient scenario for this particular pool. For the most part, 80% or more of solar heat gains for any particular day will be had between the hours of 10 am to 4 pm. With a high capacity solar heating system and the proper pump and filter combination, one need only run their pool 6 hours per day. Using an energy efficient ½ hp pump for only 42 hours per week can result in immense savings, often enough to offset the amortized cost of the solar heating installation!
The absolute most efficient pump designs in use today employ some variable speed capabilities and the highest efficiencies can be coaxed from these pumps particularly when using a solar heating system. Pump speeds are pre-set for solar/on and solar/off. During periods of solar/off such as cloudy mornings, rainy days or times when the pool is holding temperature, these pumps speeds must be manually set based upon a physical observation of the skimmer weirs. (The weir is the one way gate that floats in the skimmer allowing bugs and debris to enter into the skimmer but not float out) The slowest possible speed at which the skimmer weirs are working is the optimum low speed setting. When the demand for solar heat presents itself then these pumps are designed to ramp up the flow to another higher, yet optimized flow rate to match both the filter and flow capacity of the solar heating system. Aside from the increased cost of installing these pumps and control units and programming them to work together, this is the single most efficient way to run a solar heated pool. In my own case I have the pump set to 1850 rpm with solar off, and this is just enough to get the skimmer weirs working and then it ramps up to a still very efficient 2850 rpm when the solar system kicks on. 2850 rpm yields approx 75 gpm and since I use 2 inch pipe for the solar system with a max flow rate of 73 gpm, this is the optimal speed and power level for my particular application. Single speed energy efficient pumps can be used which will present savings close to but not quite as much as the variable speed pump. When one looks at the cost difference of purchasing and programming a variable speed pump vs. an energy efficient single speed pump, the difference in savings per year would require in excess of a 10year period to recover the additional costs of a variable speed pump. So as much as the variable speed variable flow and programmable pumps are the state of the art in operational efficiency, in real world analysis, the single speed, optimized energy efficient pump is the hands down winner of this contest due to the greatly reduced cost to purchase these pumps and the fact that they do not need any special programming inputs or electronic controls.
The newest development in energy efficient variable speed/variable flow pumps has been the addition of onboard controls. Not having to purchase, install and program a separate pump controller narrows the playing field a bit. Powerful VSVF pumps are now less expensive to purchase and easier to setup. Almost anyone can now purchase, install and program their own VSVF pumps. But without real world knowledge of the intricacies of a filtration system and no training in hydraulics, I suspect that these do it yourselfers will not see any real energy savings by tending toward higher pump speeds and flow rates than their filter and manifolds can handle and by not optimizing their flow for any one intended purpose. The case against 2HP pumps has a new kid on the block.
Several inexpensive upgrades that most any pool and especially a solar heated pool can benefit from are:
1. Replacement of inline chlorinators with similar offline designs.
2. Upgrade filter interconnect piping to all 2 inch and replace ‘hard’ 90 elbows with ‘soft’ 2 in sweep elbow designs
3. Incorporate 2 in full flow ball valve, multiport valve and check valve designs and eliminate unnecessary bends
4. Install an optimized energy efficient single speed pump, increasing flow while reducing electric use 50% or more
5. Employ an inexpensive solar blanket (without the elaborate and unsightly reel systems) during spring and fall on cooler nights (below 65) to prevent potentially unrecoverable heat loss. This can be one piece or cut in half or thirds for odd shaped pools. Of utmost importance is to cut the cover undersized so it lays directly on the surface of the pool with no air space or overlap.
Conclusion: The way they used to build and run pools was based upon cheap sources of energy. Now that energy has become an ever increasing part of our household expenses, we cannot continue to run our pools the way our daddy did. If you are reading this and have gotten to this point, then I think you have realized that you need to change a few things, within reason, of course about how you view your pool.. A few intelligent dollars invested can go a long way in decreasing your costs while increasing your pool use and enjoyment. Solar pool heating is a quality of life investment while energy efficient pumps are an energy/money savings investment. It is not unusual for our company to offer a solar heating system and then demonstrate that the savings generated by intelligent manifolds and an energy efficient pump installation can offset the cost of the solar installation! The choice is yours: a 2hp pump that burns itself up every few years on an ice cold pool or a naturally heated pool and an energy sipping, long lasting pump at a lower monthly cost of operation.
Make sure you check out our newest page about swimming pool energy consumption. Some of the information there will shock and surprise you. This page is recommended reading for anyone owning or contemplating a pool, should take only about 15 minutes to read, and can result in thousands of dollars in savings and an increased overall quality of life for your family.