High Efficiency Single Phase Air Conditioner   Customer Energy-Use Research Commercial and Residential Research >Heating, Ventilation, & Air Conditioning Research

This project was funded under Energy Commission's PIER Energy Innovations Small Grant Program (EISG), which supports the development of new technologies that are in the proof-of-concept stage.

EISG Grant Number:  99-39

Organization:  Smith & Sun

EISG Status:  Completed 2002

Contact: David Michel III, Energy Systems Research Office, Energy Innovations Small Grant Program (916) 651-9381

Project Description:

Electric power system overloads often occur during hot summer afternoons when many residential air conditioners are operating. The majority of these air conditioners are powered by single-phase electric motors. Out of concern for power reliability on these hot afternoons, power companies bring on-line their least desirable power supplies. These are the most expensive to operate, the most polluting or oldest generators. These actions are taken to minimize the probability of system degradation or a blackout. The cost to the power company and to society to supply these air conditioners at the peak load time is high, and is often higher than the rate that the customer is currently paying. Also, emissions from the older power plants are usually higher than the newer power plants. The less desirable power plants would be dispatched less frequently if higher efficiency air conditioners were widely deployed in the marketplace at reasonable prices.

One solution is to power the air conditioners with the more efficient three phase motors. The constraint is that most residences and perhaps 40% of all rural areas have only single-phase power available, and it is uneconomic to change these distribution and wiring systems. The compressors are well designed, but the low efficiency single-phase motors on the compressor shafts are much less efficient than three phase motors of the same power rating.

This project demonstrated the feasibility of using a control system that can operate high efficiency three-phase induction motors from single-phase power supplies. These control systems were originally developed for water pumping applications by the researcher in previous, unrelated efforts. These controls are trademarked under the name EnablerTM.

The use of such controls on three phase air conditioner motors could reduce the electrical power demanded by residential and small commercial air conditioners by 8 to 10 percent. Air conditioner manufacturers would design all products with three phase motors, adding the control system to those sold to market segments where three phase power is not available.

The goal of this project was to determine the feasibility of operating air conditioners with three phase motors efficiently on single-phase power. A test program to measure efficiency was very carefully designed and implemented in order to provide high confidence in the test results. The following project objectives were established:

1. Design, construct and demonstrate a control system specifically for three-phase air conditioner motors enabling them to run using single-phase power.
2. Demonstrate that residential size central air conditioning units, running on three-phase motors that have been modified with a control system to operate on single-phase power, will consume 10% less electrical energy than equivalent air conditioning units running on single-phase motors.

1. Control systems were designed and constructed to operate two different three-phase motors from single-phase power. One motor was designated a Model 48T motor, the other, a Model 42T motor. The control systems were capable of operating the three-phase motors. As expected, motor performance was improved. With the control installed on the Model 48T motor, the winding current unbalance was reduced to only one percent, compared to 7.4% with the three-phase power supply. Also, the single-phase input to the control had a power factor of 90.8% LEADING, compared to 75.2% lagging with the three-phase power. With the control installed on the Model 42T motor, the winding current unbalance was reduced to 3.2%, compared to an unexpectedly large 13.8% with the three-phase power supply. Still, the single-phase input to the control had a power factor of 88.3% LEADING, compared to 77% lagging with the three-phase power.
2. All of the objectives were achieved for the two sizes of compressors that were tested. A 48,000 BTU/hour compressor and a 42,000 BTU/hour compressor were tested at an independent commercial testing facility by the professional staff as directed by Dr. Smith. Many tests were conducted. The average Energy Efficiency Ratio (EER) for each configuration is tabulated below, the efficiency improvement is presented in the last row:

The feasibility of operating three-phase motors in air conditioners using single-phase power was demonstrated. The motor performance improvement was consistent with that observed in prior development of the controls on larger motors. Without test results from additional like units, it can not be assumed that the savings of nearly 12 % of the electricity use for the 48,000 BTU/HOUR unit with the control system will be realized on all air conditioners of this size. The 42,000 BTU/HOUR unit demonstrated nearly a 4% energy savings. The test results show that the 42T three-phase motor was significantly below average in efficiency. It was less efficient than the single phase motor. The principal investigator concluded that this resulted from low quality in the area of winding current imbalance and suggested that a motor of average quality of this size would have produced greater efficiency gains. Due to the small sample size and variability in motor quality the Program Administrator estimates the energy savings from this invention to be in the 8% to 10% range on average, but additional testing will be needed to confirm this conclusion. The impact of the tested technology on unit efficiency was significantly effected by motor quality. That quality remains an unquantified variable. If the two three-phase motors selected in this study are representative of the range in quality of commercially available three-phase motors this would suggest that the motor manufacturing industry has a quality control problem that also needs addressing.

The ultimate commercial success of the EnablerTM technology will depend on the impact this technology will have on the retail cost of new air conditioners. The researcher reported that his direct cost for the control system components (purchased at retail) was $128 per unit. The researcher projected that the equipment manufacturers could reduce the direct cost of the control system circuitry to $64 per unit if mass-produced. Based on the $64 cost estimate, the Project Administrator projects an increase of about $100 in retail price per unit of the large 48T class of air conditioner. The control circuit for the smaller units, utilizing smaller capacitors, would have a lesser retail price impact. To put this into perspective, the Program Administrator prepared a simple payback analysis. Two electric rates, $0.10 and $0.25 per KWH, were used to span a broad range of retail prices. The 48T motor tested uses electricity at the rate of 4 KW. By using the new control circuit, one could reduce demand by 10% or 400 Watts. It follows that the modified air conditioner would save 400 KWH in 1000 hours and 1000 KWH after 2500 hours of operation. A person with an electric rate of $0.10/KWH will have a simple payback in 2500 hours of operation, while a person with a $0.25/KWH rate will achieve a simple payback in 1000 hours of operation. Depending on the length of the cooling season, payback could occur in one to two cooling seasons. This supports the conclusion that this innovation offers a near term payback to the ratepayer using this control technology with three phase motors.

The researcher asserts that the direct cost of the control system circuitry could be further reduced if the manufacturers of the three-phase motors made some minor design modifications to the motor wiring. While additional research is required to bring this technology to market, air conditioner manufacturers would be able to adopt this new technology without modifying their existing manufacturing tooling.

Benefits to California:

The primary benefit to California will be the availability of higher efficiency (8-10%) air conditioners to electric consumers that are limited to single-phase power. A second major benefit is the reduction in peak loading of the electrical system on hot summer days. Many advantages accrue to the ratepayers from the reduction in peak loads. The relatively near term availability of these benefits is due to the simple, modular nature of the control circuitry, which can be a simple add-on at first, with integration in depth developed as cost cutting measures by the manufacturers.

The results of this project indicate that significant energy demand reductions can be accomplished in the relatively near term if the tested technology is deployed in California. Because of the limited funds in the grant, the researcher only tested the control system on two air conditioning compressor units. To further this technology, additional testing is needed to assess the energy savings on a full range of commercially available air conditioning units. Research is also needed to fully define the distribution of motor quality to enable a more accurate projection of average efficiency improvement. In addition, the researcher should select a major manufacturer of air-conditioners as a partner in any additional research to insure that the technology development meets all market needs.

This project is part of the research portfolio of the California Energy Commission. The Energy Commission supports energy research and development that improves the quality of life in California by bringing environmentally sound, safe, reliable, and affordable energy services and products to the marketplace.