Prepared for: Pacific Gas and Electric Company
Report dated: January 1999
Prepared by Proctor Engineering Group
Contributors: John Proctor and Tom Downey
The AC2 system shows considerable technical merit. Proctor Engineering Group is extremely enthusiastic about the performance of these units, particularly at high temperatures. On the average, the analysis predicts a cooling kWh savings of 32% to 34% when compared to a SEER 10 and a savings of 20% to 22% savings compared to a SEER 12 air conditioner. These percentage savings are nearly independent of the duct system and building shell. Under peak conditions these units maintain a much higher efficiency than both SEER 10 and SEER 12 units. These units are particularly attractive for peak reduction.
The enthusiasm for the performance of the AC2 is tempered by three concerns. First, the quality of the product as delivered for this project was unsatisfactory. Second, the monitored data indicated a potential problem with the outside heat exchanger. The potential problem is lost efficiency due to scaling. Third, the training and factory documentation provided were insufficient to ensure proper installation and service of this equipment.
When the AC2 system has component problems corrected, an effective quality assurance system in place, and is installed by a well trained technician following proper installation procedures, the unit should operate with a very high efficiency. The long term reliability of the AC2 system was not tested in this project. Many of the components of the AC2 unit are identical with an air-cooled system. The evaporative cooler portion of the system adds complexity and thus potential for lower reliability. This complexity is a primary reason why better training and quality assurance are important to the adoption of this technology.
The outdoor heat exchanger is the component that requires the greatest attention to long term reliability. This study did not dispel fears that the outside heat exchanger might scale over time and that the scaling could produce a significant drop in capacity and efficiency. Key conclusions of this study are: The AC2 unit is extremely efficient, particularly at high outdoor temperatures. It is very well suited to the climate within PG&E’s service territory.
The units installed in this project all had substantial problems with their initial function. These problems can be reduced with a significant quality assurance effort at the factory.
The decreases in outdoor heat exchanger effectiveness are cause for concern. The reduced effectiveness at Davis, Fresno, and Tracy likely signals scale build up. The composition of the water at each site is likely to effect the amount of scaling at that site. AC2 installation costs should be comparable with properly installed SEER 12 air cooled units over the long term.
Air conditioners sized to meet Manual J calculated loads will produce cooling capacity in excess of the needs of the house. The AC2 manufacturer’s suggestion that the air conditioners be sized by square footage encourages oversizing and unnecessarily increases the first cost of the air conditioner as well as of the duct system. The manufacturer must increase the effectiveness of the installation and service technician training as well as printed installation instructions.
Key recommendations of this study are: Any PG&E promotion of the AC2 units should be tied to quality assurance at two levels: Manufacturer -- product function, training, documentation, and technical support; Contractor -- certifying proper sizing, brazing, evacuation, charge, and air flow.
The AC2 undergo continuous testing with both scaling water and corrosive water similar to that found in approximately 2% of the water supplies. PG&E investigate and promote lower watt draw fan/motor/air distribution systems with particular attention to inlet and exit conditions as well as low static pressure. PG&E investigate the effects of smaller refrigerant line sizes on air conditioner performance.
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