| |
Prepared by: Stephen D Allen, B.S. Electrical Engineering
Download White Paper as printable PDF
1 | Introduction
Pool filter pumps consume a significant amount of energy in residential homes. Swimming pool pumps were ranked as the third largest consumer of residential energy in SCE’s 1993 Residential Appliance End Use Study (SCE 1993).
The purpose of this paper is to draw attention to the significant energy savings that can be attained through automatic seasonal run-time adjustment of pool filter pumps in the Southern and Western regions of the United States. Energy savings are the result of an intelligent algorithm which automatically runs the pool filter pump less in the winter, and more in the summer.
2 | Product Description
Most pool filter pumps are controlled by an electronic or electro-mechanical timer. The timer has the function of turning the pool filter “on” and “off” at designated times of the day (ideally off-peak hours) to filter contaminants from the pool water. The “run-time” is the difference between the “on” and “off” times when the pool filter motor is running (consuming energy). A “constant-duty” timer turns the filter pump on and off at the same time every day, irrespective of the season. While some consumers adjust the run time of their constant-duty timer in the winter, and again in the spring, many forget to adjust the run time, resulting in unnecessary filtering. Automatic adjustment of the timer precisely controls the pool filter run time through the year, with measurable savings. Pool pump motors consume a measured weighted average of 1.36 kW of power while running according to an ADM study (ADM-2001).
A seasonally adjusted timer automatically reduces the run time of the pool filter, to run more in the summer and less in the winter. A gradual transition between the maximum run time (summer) and the minimum run time (winter) produces optimum run time to keep the water at acceptable quality at a reduced energy cost.
3 | Contamination Sources
Contamination is introduced to the pool through four methods: Bathers, Environmental debris, Surface leaching and Algae/ Bacterial growth. Basically, the contaminants enter via the water surface, the pool structure, or arise from biological activity within the pool water itself.
3.1 | Bathers
Bathers introduce contaminants to the pool water such as lotions, perfumes, dead skin cells, detergents, ... When the water temperature is low, people do not swim in the pool. This eliminates a primary contamination source when the pool water is cold in the off-season.
3.2 | Environmental Debris
Environmental debris is introduced mainly during storms. When an occasional storm introduces leaves and dust into the pool, a manual cycle can be run to clean the water and surface of debris. The amount of environmental debris varies depending upon amount of plants nearby, and weather conditions. A short cycle each day will generally remove all environmental debris.
3.3 | Algae / Bacterial Growth
Algae/bacterial growth rate in a pool is a function of four main variables: Temperature, amount of sunlight, base algae population, and water composition. The daily cycle of a pool filter pump must be such that an algae population cannot achieve sufficient size to reproduce faster than the filtering system removes it from the water. If the size of the algae population exceeds the rate at which it is removed, the pool must be “shocked” with a chemical agent that will kill the algae in the pool. The “shock” must be followed by an extended filter cycle which will remove the dead algae from the pool.
Temperature and amount of sunlight are variables which generally track together, and are primarily a function of the season. During winter months, the water temperature decreases. Also, there is less sunlight incident upon the pool. Algae metabolism is reduced as temperature decreases.
4 | Seasonal Run-Time
Clearly, the contaminants which are introduced/generated during the winter months are substantially less than the summer months. If there is less contaminant in the pool water, the filtering system does not need to run as long in order to maintain acceptable water quality. It is a generally accepted fact among pool professionals that a pool filter does not need to run as long during cold winter months. Many pool professionals use a “rule-of-thumb” that filtration can be decreased by an hour for every 10 degrees of temperature. Pool temperature in Phoenix, AZ changes approximately 50 degrees from summer to winter. This would justify a 5 hour reduction in run-time from summer to winter.
The “TightWatt” pool filter controller uses an algorithm which slowly reduces run time twice a month beginning July 15th, and increases the run time twice a month beginning February 1st. Successive run time adjustments are made on the 1st and 15th of each month. Figure 1 (page 3) shows Pool Filter Pump Run Times as a function of the date, assuming a maximum daily run time of 8 hours, and a minimum daily run time of 3 hours. The algorithm is somewhat flexible in that it allows selection of the minimum and maximum times. For example, a maximum run time of 10 hours and a minimum run time of 6 hours could be selected. The run time selections will vary depending on the amount of environmental debris, and the climate for a given location.
The graph below show an example of the self-adjusting run schedule unique to TightWatt pool timers (click graph to enlarge).
5 | Climates which can benifit from reduced Winter run-time.
5.1 | Examination of Specific Cities
Figures 2–7 examine the average temperatures for selected cities through the western and southern United States. It can be seen that high and low temperatures generally track together and that the difference between high temperatures between July and January is approximately 45° Fahrenheit, although the difference is less in moderate climates such as Pasadena, California. It should be noted that Figures 2-6 are multi-year averages, whereas Figure 7 (Austin, TX) is a one year average. Figure 7 is not as smooth a curve as the other figures due to less averaging.
During winter months, pool water temperatures more closely follow the low (when less light is incident on the pool). Pool water temperatures rise closer to the high during the summer (when more light is incident on the pool).
Click any graph to enlarge.
Figure 2 | San Fresno, Ca Figure 3 | Las Vegas, NV
 
Figure 4 | Pasadena, CA Figure 5 | Phoenix, AZ
 
Figure 6 | Santa Fe, NM Figure 7 | Houston, TX
 
Figure 8 | January 2000 Mean Temperature Map of United States
Figure 8 indicates January Mean Temperatures across the United States for the Year 2000 (NOAA 2005). As a general rule, pools which are in regions below 30 degrees, are drained in the winter. Seasonally adjusting run time provides little or no benefit, as the pool is filled prior to the swimming season, and drained at the end of the swimming season. On the other extreme, areas such as Miami, Florida which have warm temperatures throughout the year would benefit little. The climate will support substantial algae growth even during the winter months.
Areas which lie between 30 degrees and 60 degrees stand to benefit the most from seasonally adjusting the pool filter run time. The “TightWatt” pool filter controller (www.tightwatt.com) adjusts the run time of the filter pump as a function of date. Run time is varied between a maximum run time (set for the summer) and a minimum run time (set for the winter). The “TightWatt” pool filter controller is a drop-in replacement for the low-cost Intermatic timer mechanism.
6 | Energy Savings
Consumer energy savings for a seasonally adjusted run-time vs. a constant duty timer can be computed as follows:
Formula 1: Yearly Energy Savings
ES
Energy Savings [dollars/year]
Power Power consumed by the pool filter pump [kW]
Max Maximum run time (summer) [hours/day]
Min Minimum run time (winter) [hours/day]
.541 Savings factor (using TightWatt version 1.0 algorithm) [unit less]
EC Energy cost [dollars/ kWh]
Calculation 1: Present Value Energy Saving
Power = 1.36 kW = measured weighted average of pool pump motor power (ADM-2001)
Max = 8 hours run time
Min = 3 hours run time
EC = .931 = Life Cycle cost of $0.931/kWh, assuming 10 year Design Life (CEC-2001)
As Calculation 1 shows, energy savings can be significant, over the life of the product. This is especially true for higher wattage pumps, and in areas where energy cost is high. It should be noted that for many areas of California, energy cost is greater than 10 cents/kWh.
Assuming a 10-year life of the electronic timer, this would produce savings which would well exceed the incremental cost and well exceed the cost of replacing a functional constant-duty timer with a seasonally adjusting timer.
An automatic adjusting timer can also, by design, move more electricity usage to the off-peak hours. The “TightWatt” has a default pump turn-on time of 10:00 PM. As most people would leave the default setting, this would drive usage to off-peak hours.
7 | Incremental Cost
The TightWatt timer has a suggested retail price of $150.00, while the Intermatic T104 model has an approximate retail price of $60.00. This produces an incremental cost of $90.00.
8 | Design Life
Constant-duty timers are designed to turn the pump on and off at a designated time. Reducing the run time seasonally should directly extend the life of the pump motor, as less wear is occurring on the bearings, and other motor components.
9 | Conclusions
A pool pump timer which automatically adjusts run time with the seasons can have a significant impact on reducing energy consumption in the Southern and Western United States. Comparing energy savings vs. incremental cost, a timer such as the “TightWatt” pool filter controller offers superior value to other pool energy saving systems, such as two-speed pumps. Ease of installation is also improved, as a timer replacement and set-up should take less than 15 minutes.
10 | References
ADM-2001: ADM Associates, Baseline and Market Characterization Report (Revised Draft Version), October 2001, prepared for PG&E Contract No. 4600011448.
NOAA-2005: NOAA-CIRES Climate Diagnostic Center: January 9, 2005 http://www.cdc.noaa.gov/map/
DEG-2004: Davis Energy Group, Analysis of Standards Options For Residential Pool Pumps, Motors, and Controls for Pacific Gas and Electric Company, May 2004
NWS-2004: http://www.srh.noaa.gov/hgx/climate/iah/normals/iah_summary.htm
SCE-1993: 1993 Residential Appliance End Use Study, Quantum Consulting, Dec 1993.
WRCC-2004: http://www.wrcc.dri.edu/climsum.html |
