Pool cleaners and energy use
In drought-stricken California, the humble backyard pool is under attack. From water wastage to excess energy use, pools are in the firing line from every direction. One power company decided to set the record straight with respect to commonly used pool cleaning systems and their energy use.
Back in 2009, Pacific Gas and Electric Company (PG&E) decided to conduct an evaluation of available pool cleaning systems as part of its Pool Pump Energy Efficiency Program, which sought to improve the power demand reduction and energy savings opportunity for residential pools.
This seemed to be a logical connection as many of the cleaners on the market rely on hydraulic power from the filtration pump, or a separate booster pump connected to the discharge of the filtration pump. PG&E recognised swimming pool pumping system interactive effects between the pool cleaner and filtration pumping, where maximum efficiency of pool filtration pumping is limited by cleaner operation.
It is a requirement in California for two-speed pumps to be used for residential filtration applications of one total horsepower or greater. Hydraulic cleaners therefore add incrementally to the pool pump power and energy because they are most commonly run on high speed to operate effectively.
The report references non-incremental power and energy required, as well as incremental power and energy required. Non-incremental is the actual hydraulic power and energy needed to run the cleaner. Incremental power and energy is the additional power and energy used to run the two-speed filtration pump at higher speed, as is common practice for cleaning. Due to the pump affinity law, the incremental power and energy is much greater than the non-incremental power and energy.
New to the market at time of investigations, self-powered robotic cleaners operating via a power cord and connected to a low-voltage power supply were assessed. As these cleaners are independent of the pool pump filtration system and do not require booster pumps, PG&E expected to determine that they offered an energy efficiency and demand reduction opportunity in residential settings.
Testing the water
The first issue for PG&E was that there was no test procedure or measure of energy performance for these devices. Initially, the team approached the problem by pursuing a cleaner energy factor, derived from the area of pool floor covered (in square feet) per unit of energy consumed (measured in kWh). They soon abandoned this approach as the simple measure provided to be an inadequate indicator of cleaning performance due to the idiosyncrasies of individual cleaners relative to pool plumbing, geometry, in-pool obstructions and debris load. The team determined that no simple measure of cleaning performance could be developed for all pool types and felt it best left to the judgment of pool professionals.
The team expected to find robotic cleaners performed more efficiently than other available options. This opinion was formed based on observation and measurement in several pools which found booster pumps typically drew 1.3 kW and that filtration pump-powered cleaners required increased pump speed and extending pumping time to filter the equivalent volume of water than would be needed if cleaning were provided by an independent robotic cleaner.
As suspected, robotic cleaners were found to use an order of magnitude less energy than hydraulic cleaners when the incremental cleaning-related energy use of two speed pumps was measured. The robotic cleaner's electrical power demand and energy demand proved to be quite similar to the hydraulic cleaner's hydraulic power and energy, but significantly greater incremental input to two speed pumps was needed to power them. When hydraulic cleaners were used, the actual system performance was significantly compromised by interactive effects with the pool filtration pump.
Pool skimmers and main drains for suction-side cleaners, along with pool returns and other features for filtration pump pressure-side cleaners, share the waterflow with the cleaners and prevent either from operating at optimum energy efficiency performance.
The report assumed three hours of operation per day to be consistent with typical robotic cleaner operation and allowed for a better comparison.
The following table outlines the comparative cleaner incremental power demand and energy use, converted into Australian dollars.
|Cleaner type||Energy use (daily)||Energy use (annual)||$0.01 per kW||Annual cost|
|Filtration pump (suction) cleaner||4.59||1,675||0.3||$ 503|
|Booster pump cleaner||8.19||2,989||0.3||$ 897|
|Manual vac (domestic)||1.53||558||0.3||$ 167|
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