By Paul Hackett
If a vehicle can only go either 0 or 40 MPH, it really does not need a Speedometer – little is gained from knowing either speed. The same argument could be made for not using a Flow Meter on a pool, spa or water feature with a single speed pump. While knowing the flow may be interesting, if you can’t change it (other than by means of a flow control valve), why spend the money installing a flow meter?
Although control valves can be used to adjust the flow rate to water features, adjustments are typically made more from an aesthetic point of view – such as giving a waterfall a desired appearance. Unlike reducing the speed of a pump, throttling a control valve back has minimal impact on reducing electrical energy.
When deploying a variable speed pump, knowing the flow rate becomes essential if you are going to achieve the desired turnover rate and maximize the energy saving potential for your customer, as this is after all, the primary reason they will invest in this type of pump.
It’s a different story when it comes to commercial pools such as hotels, apartment complexes, theme parks and schools; in all but two States, all commercial pools and spas are required by local codes to have a working flow meter. This allows visiting Health Department officials to verify that minimum turnover rates are being achieved.
Up until 2011, the accuracy of flow meters used in the pool industry was not verified by a third party, and no standard even existed for testing these devices. Even though an NSF 50 Flow Meter Standard has existed since 2012, only two products (the F 300 from Blue White Industries and the FlowVis from H2flow Controls), are certified to this standard. It’s important to note that variable speed pumps with a flow readout are flow ‘estimates’ and not flow ‘meters’.
Variable speed pumps are reported to be today’s fastest growing product segment in the residential pool market. On July 19th 2021, the Department of Energy will issue a new law whereby most in-ground single speed pumps will fall out of federal compliance. While this event may cause some heartburn with certain customers, the objective of the law is based on solid ground and has the potential to save tens of millions of dollars in energy costs here in the US. As an example, reducing the speed of the pump by just 20% will save close to 50% in energy costs.
So how can you stand out from your competitors when it comes to installing one of these soon-to-be-mandated variable speed pumps?
Simply installing the pump and setting it to one of its preset speeds will save energy, but will almost certainly not maximize the potential savings. The preset speeds are a good starting point, but there is more energy saving potential to be gained by explaining to your customer that you will be fine-tuning the pump’s speed to exactly what is required for their specific pool.
Without knowing the system head loss (TDH), it is impossible to calculate the flow rate based on the pump’s speed or power used; integrated flow readings within the pump can be off by as much as 30%.
Several years ago, my colleagues and I ran an ‘estimate the flow’ competition at a popular trade show. We had a plumbing configuration with a variable speed pump, a large tank of water, many different fittings (all visible), long straight horizontal pipe runs in 2-inch Schedule 40, with vertical up and down sections – overall, not too different to what one might expect on a 20,000 gallon backyard pool. We told people what we were setting the pump’s speed to and asked them to estimate the flow rate. There was a nice prize for whomever got the closest each day! After three days and 260+ attempts, the closest anyone got was +/-10% to the actual flow rate. The average error was more than 20%.
Let’s take a look at an example of the additional energy savings from ‘Knowing the Flow’.
• A 38,000-gallon pool located in CA has an annual usage of 10 months per year;
• A 3.0 HP (2.2 kW) variable speed pump is installed;
• The cost of electrical energy is $0.1984 per kWh;
• The pump’s full speed energy costs are $3,142 per year;
• The pump’s full speed is 3450 rpm;
• The pump’s installer selects preset speed #4 (3100 rpm);
• At 3100 rpm the annual energy costs are reduced to $2,280 (a saving of $862 per year);
• Installing an accurate, reliable flow meter shows that the turnover rate could have been achieved at 2900 rpm, which would have reduced the annual energy costs to $1,867; • Knowing the Flow resulted in additional savings of $413 per year from lowering the preset speed by just 200 rpm.
As can be seen from the above, even a small adjustment of 200 rpm can recoup the cost of a high quality, accurate flow meter in less than six months. An adjustment of even 100 rpm would have reduced the energy cost by $214 — still paying for the flow meter in less than one year.
With such compelling savings from relatively small adjustments in speed / flow, it is imperative that the flow meter being used has a third party verified accuracy – such as the NSF 50 Flow Meter Standard. Flow estimates, or devices that imply that all pools are built the same, could result in significant lost energy savings.
To utilize H2flow’s ‘Know the Flow
™ ’ energy savings calculator, visit h2flow. net/flowvis-calculator.
The calculator will allow you to enter data such as the pool size, its location, and whether there are water features. Once entered, the calculator will show the likely Preset Speed that would be chosen and how sliding the pump speed bar left or right will result in additional energy savings. This tool could be helpful in explaining to your customer that you want to not only install their new pump, but also fine tune its speed to save them the most money – after all, this is what it’s all about!
About the author: Paul Hackett is the Chief Executive Officer of H2flow Controls, Inc., and has over 40 years of experience in Control and Measurement technology for electrical and mechanical applications.