Swimming Pool Sweep Technical Performance Assessment Offering Major Energy Savings

Swimming Pool Sweep Technical Performance Assessment Offering Major Energy Savings
Introduction

Few residential appliance technologies offer the energy savings of robotic pool cleaners.

Typical robotic cleaners are directly powered by 24 VAC transformers, and draw an average of 200 Watts, while common booster-pump-powered hydraulic cleaners demand over 1 kW.

Major cost-effective energy savings are identified and program opportunities are presented by replacing hydraulic cleaners with robotic cleaners.
Hydraulic cleaners are powered by moving water under pressure. This hydraulic power is provided by swimming pool filtration pumps or by additional booster pumps dedicated to serving the cleaners. While these cleaners do not use electricity directly, they affect the power demand and energy use of the filtration and/or booster pumps that power them. In particular, they limit the extent to which filtration pumping can be accomplished at lower flow rates over a longer period of time, using two-speed or variable speed pumps.
A relatively new type of cleaner, the “robotic cleaner”, operates directly from an independent low-voltage power source, which eliminates the need to increase pump speed during cleaning cycles. This allows pool filtration pumping to be accomplished at the lowest flow for the longest time to achieve maximum energy savings.

Summary

The pool cleaner study was developed to determine the difference in the demand and energy requirements of different types of pool cleaners. To conduct the evaluation, a test method was developed. The measured power demand and energy use was converted into common units, as hydraulic cleaners are water powered and robotic cleaners are powered directly by electricity.
Pool cleaners are made in four different designs:

  1. Powered by dedicated booster pumps (booster pump cleaners)
  2. Powered by pool filtration pump suction (suction side cleaners)
  3. Powered by filtration pump discharge (pressure side cleaners), and
  4. Powered independently of the filtration pump with low-voltage electricity (robotic cleaners).

While the design and operation of each cleaner type is different, they often look similar (except for robotic cleaners, which are powered through a low voltage cord serving an integral pump and motor).

Figure: Illustration of Different Types of Cleaners
  

While there were differences in performance among various cleaner models of the same type, as well as differences among the three types of hydraulic cleaners, significantly greater savings may be achieved by replacing hydraulic cleaners with robotic cleaners. This is because hydraulic cleaner operation requires greater flow than filtration alone, adding to the minimum total flow rate and pump speed that could otherwise be utilized. This increase in flow is more significant than it seems, as pump power increases proportionally to the cube of the flow. Adding the hydraulic cleaner to the filtration often requires double the flow, which results in 8 times the power requirement for the duration of the cleaning cycle. Conversely, replacing the hydraulic cleaner with a robotic one allows the filtration pump power to be reduced dramatically during the time the cleaner is operating. The savings opportunity is even more significant for cases where the robotic cleaner replaces a hydraulic cleaner powered by a booster pump. In this case, the energy use of the booster pump can be entirely eliminated. 

 
Table 1. Comparative Cleaner Power Demand and Energy Use

Cleaner Type

Cleaner Hydraulic Input Power (HP)

Cleaner Hydraulic Input Power (kW)

Motor Mechanical Rated Power* (HP /THP)

Incremental Motor Electrical Input Power* (kW)

Hours of Cleaner Operation

Daily Energy Use (kWh)

Annual Energy Use** (kWh)

Robotic

N/A

N/A

N/A

0.2

3

0.6

219

Filtration Pump (Suction)

0.02

0.015

2.0 / 2.6

1.53

3

4.59

1675

Filtration Pump (Discharge)

0.09

0.067

2.0 / 2.6

1.53

3

4.59

1675

Booster Pump required

0.07

0.052

0.75 / 1.125

1.53 (filtration)*** + 1.2 (booster)

3

8.19

2989

*Assumes cleaner power is incremental and represents marginal values using California Energy Commission Appliance Database pump
** Assumes cleaner runs 365 day per year
*** Filtration pump runs on high speed when booster pump is running
Test Objectives
The objective of the pool cleaner study was to determine the power demand and energy usage of the different types of pool cleaners; i.e. robotic self-powered, hydraulic booster pump powered, and hydraulic pressure or suction side filtration pump powered. The project specifically intended to:

  • Identify the most efficient pool cleaner types
  • Determine potential energy savings of more efficient pool cleaners relative to a base case
  • Discover and evaluate other related factors, such as the effect that pool cleaners have on the overall pool operation and energy use

 
Methodology

There were no existing test procedures for determining swimming pool cleaner energy efficiency performance. Therefore, the project team needed to develop a test procedure.
Assessing cleaners on the basis of energy efficiency alone, in the absence of any measure of cleaning effectiveness, did not seem like a rational performance measure, so a test procedure was developed that attempted to measure energy use as a function of pool floor area covered. The term “energy factor” was adopted and defined as Watt-hours of energy consumed per square foot of pool floor area cleaned. The test protocol was intended to determine this figure of merit for each category of cleaner tested.
For the robotic cleaners, the electrical power and energy were measured directly. For the hydraulic cleaners, flow and pressure were measured, the water power was calculated, this value was then converted to pump brake HP and electrical power using assumed efficiencies of 0.60 for the pump head and 0.75 for the motor. This conversion was not direct, but was incremental or marginal with respect to pump motor power and energy. Since cleaner flow and power is additive to other pool needs, such as skimmer, main drain, or direct return flows, it is similarly additive to pump power. The pump affinity law finds pump power directly proportional to the cube of the flow. Where the time is the same, the energy is also proportional to the cube of the flow, so the marginal effects of adding the cleaner are not linear with respect to increased energy use.

Results

As expected, robotic cleaners as a class were found to demand the least electrical power and use the least energy of any of the products tested, as well as provide excellent cleaning performance. Average power demand for the class tested was 0.2 kW. Daily operating hours were assumed to be 3, for an average daily energy use of 0.6 kWh.
Simply stated:

  • Filtration pump powered and booster pump powered hydraulic cleaners, as well as robotic cleaners, have wide variations in cleaning performance depending on their ability to deal with pool pluming, geometry, in-pool plumbing fixtures, sizes and types of debris.
  • All cleaner categories tested in this project have similar direct power requirements, where the power comparison is made between robotic cleaners’ electrical input power and hydraulic cleaners’ hydraulic input power. Differences in power demand, and savings, result indirectly from the hydraulic system effect, where two speed filtration pump motor power increases exponentially when operating at high speed to power the added load of a hydraulic cleaner.
  • Filtration pump powered hydraulic cleaners have lower system energy efficiency because they are powered by pool pumps where their water supply is shared with other pool functions, making it more challenging to optimize filtration pumping speed and flow for maximum efficiency, and requiring that cleaner flow be supplied incrementally at exponential cost in power and energy.
  • Booster pump powered cleaners are generally utilized with massively oversized standard efficiency pumps. Since booster pumps are typically connected to filtration pump’s discharge, filtration pumps operate at full speed whenever booster pumps are running, reducing the likelihood that filtration pumps will run a larger percentage of the time on low speed.

In conclusion, the test result show that pool cleaner power demand and energy use can be reduced using a robotic cleaner while operating the pool pump at low flow and speed, for optimum filtration efficiency.
Given the complexity and cost of setting up hydraulic cleaners to operate at maximum efficiency, and the relative simplicity of adding a robotic cleaner while operating the pool pump for maximum filtration efficiency, robotic cleaners are recommended, with selection for maximum cleaning performance in individual pools left to pool professionals.
The Table below shows the following data for a Robotic Cleaner: Cleaner suction width, linear distance traveled, average power demand and linear velocity.

Table 2. Summary of Test - Robotic Cleaners-Test Duration 10min

Cleaner Model

Cleaner Suction Width (in)

Linear Distance Traveled (feet)

Average Power Demand (kW)

Required Motor Electrical Energy (kWh/Day)

Linear Velocity (ft/min)

RoboPhelps

13.38

430

0.20

0.6

43

Robotic cleaners are the most energy efficient automatic cleaning option, as they draw an average of 0.2 kW, do not require a separate booster pump drawing 1.2 kW, and do not add incrementally to filtration pump power demand and energy use in any non-linear, exponential way.

Energy Savings

Energy savings and demand reduction calculations are based on the field observation that for the 3 hours of typical operation, hydraulic cleaners add to the filtration system flow requirements.
In the case of filtration pump powered hydraulic suction and discharge side cleaners; as the flow doubles to accommodate the cleaner needs, the power demand increases by a factor of 8.
This additional use minus the energy use of the robotic cleaner represents the savings that could be realized if filtration pumps are run at optimal speeds for filtration, and robotic cleaners are used to accommodate pool cleaning needs.
For booster pump powered cleaners, the additional energy use is calculated by multiplying the power demanded by the booster pump by the amount of time it operates. The energy savings that could be realized is this value minus the energy use of the robotic cleaner. It is common practice to run the filtration pump at full speed while the booster pump is operating, compounding the savings opportunity. The increased power needed to run the filtration pump at full speed was 1.53kW. (See Table 3 below)

Table 3. Demand and Energy Savings

Cleaner Type

Base Case Demand (kW)

Measure Case Demand (kW)

Net Demand Savings (kW)

Typical Hrs of Operation

Annual Energy Savings (kWh)

Robotic

N/A

0.20

0

3

Base Case – N/A

Filtration Pump Section

1.53

0.20

1.33

3

1456

Filtration Pump Pressure

1.53

0.20

1.33

3

1456

Booster Pump

1.2 (booster) + 1.53 (filtration)

0.20

2.53

3

2770

Annual Cost of Operation

The annual cost of operation is shown in Table 4 below. The assumptions are listed below the table. This report assumes that filtration is done on the low speed pump, but adding the additional flow needs of the cleaner requires that the pump operate on high speed.

 
Table 4. Annual Cost of Operation of Cleaning and Filtration with Different Cleaner Options

 

Cleaning Energy/year

Cleaning Cost/year

Filtering/skimming energy/year

Filtering/skimming Cost/year

Total Cost/year

Robotic

0.2kW*3hrs*365= 219 kWh/year

219kWh*₹18/kWh= ₹4,000/yr

0.415kW*6hrs*365= 909 kWh/year

909kWh*₹18/kWh= ₹16,350/yr

₹4,000/yr+ ₹16,350/yr= ₹20,350/yr

Hydraulic

1.53kW*3hrs*365= 1670 kWh/year

1670kWh*₹18/kWh= ₹30,000/yr

0.415kW*3hrs*365= 454 kWh/year

454kWh*₹18/kWh= ₹8,200/yr

₹30,000/yr+ ₹8,200/yr= ₹38,200/yr

Hydraulic with booster pump

(1.2+1.53)kW*3hrs*365= 2989 kWh/year

2989kWh*₹18/kWh= ₹53,800/yr

0.415kW*3hrs*365= 454 kWh/year

454kWh*₹18/kWh= ₹8,200/yr

₹53,800/yr+ ₹8,200/yr= ₹62,000/yr

  1. Assumes cleaner power is incremental and represents marginal values using California Energy Commission Appliance Database pump
  2. Assumes cleaner runs for 3hrs and filtration/skimming takes another 3hrs and both run 365 day per year
  3. Filtration pump runs on high speed when booster pump is running
  4. Assumes a rate of ₹18/kWh, since this is typical for residential pool owners

Conclusion

Robotic cleaners should be encouraged, as they demand less power and use less energy than the pumps and motors that supply hydraulic cleaner needs in addition to basic filtration needs.

As shown in Table 3, estimated power demand reduction and annual energy savings by replacing the following cleaners with a robotic cleaner are:

  • 1.33 kW and 1,456 kWh for filtration pump powered discharge (pressure) side and suction side cleaners as a baseline
  • 2.53 kW and 2,770 kWh for booster pump powered cleaners as a baseline