Washington Elementary School, Sacramento, CA

Sacramento, California - Even in the summertime, the Washington Elementary School is a busy place. The playground is bustling with activity from neighborhood kids, and the year-round children's center is alive with the sounds of small children. In the heart of this, an innovative idea is at work, quietly and efficiently providing the comfort cooling for the facility.

The Washington Elementary School utilized a pair of air-cooled reciprocating compressor chillers that were installed when the building was completed 20 years ago. The primary machine had a cooling capacity of 60 tons, and the secondary, 40 tons. The primary machine was in poor condition, and in dire need of replacement.

With the year-round children's center open from 6am to 6pm on weekdays, and interior classrooms without windows, the demand for cooling exists 12 months per year at varying loads. Unfortunately, high demand charges were being charged for peak kW usage, and regular kW consumption was also high due to inefficient operation of the old chillers.

The Challenges

• Reduce peak kW demand charges significantly.
• Reduce regular kW consumption significantly.
• Provide smooth and efficient operation at varying loads.
• Control the existing secondary (40 ton) machine with automatic lead/lag operation.
• Utilize a chiller that will fit on the existing concrete pad of the old 60 ton chiller.
• Install a quiet machine since the installation is at grade level, just outside of the Children's Center. Also, the school is closely bordered by homes in a residential neighborhood.
• Provide a machine that will operate within the existing maintenance budget, which covers the district's 77 academic and 23 administrative buildings.

The Solution

The Dunham-Bush sales representative on the project was Claude Poinski of DMG North in Sacramento, CA, who began working with American Chiller Services, the service contractor for the school. With design ambient conditions of 105°F dry bulb/71°F wet bulb, it was immediately clear to Claude that the installation would benefit from the use of an evaporative cooled machine. "I knew that the efficiency of the Dunham-Bush ECDX with its evaporative condenser and screw compressor would substantially reduce their kW consumption, and peak demand charges," says Claude. "I also knew that the School District has a 'like replacement' program, which called for me to bid an air-cooled machine by default. Therefore, I needed to prove the operational savings of the ECDX compared to a new air-cooled screw machine."

Given the load profile of the school, a comparison was generated between the Dunham-Bush ECDX-045 (evaporative-cooled chiller), and the ACDX-050 (air- cooled chiller), each delivering 45 tons at the specified design conditions. See below:

The Results

With an EER of 14.64 at the design conditions, the ECDX-045 consumed approximately 45% less kWh and peak kW than the air-cooled approach. This would result in a net operating savings of about 60% over the existing 60 ton air-cooled reciprocating machine to be replaced.

Claude Poinski provided the above comparison to American Chiller Services. Armed with this information, American Chiller Services contacted Jim Hicks, Plumbing/HVAC Foreman for Sacramento City Unified School District who was intrigued. " We have cooling towers on our other buildings in the district, but this was the first application of an evaporative condenser," says Jim. " I was out on a limb here, but Dunham-Bush provided me with the information necessary for me to understand the application and the maintenance and water treatment recommendations for the condenser section of the ECDX."

This information was factored into Jim's analysis, plus he allowed for the cost of a $3,000 automatic water treatment system. The district pays a flat fee for water usage, so it did not enter the equation.

"The bottom line is that I can reap the operating savings with the ECDX, and still work within my existing maintenance budget. This unit will pay for itself in no time," Jim adds.

The Conclusion

The ECDX-045 fit easily on the existing concrete pad from the old air-cooled chiller. With its quiet screw compressor, it handles the varying loads and the fluctuating seasonal ambient temperatures without a problem. In fact, since the condenser performance is based on the wet bulb temperature, the ECDX-045 is able to handle the cooling load for the entire school when the ambient temperature is as high as 100°F. Above this temperature, the unit's microcomputer sends a signal to the old secondary air-cooled machine to provide supplemental cooling.

"With the help of Claude Poinski, and the engineers from Dunham-Bush, we were able to specify the best unit for the application," Jim states. "They were there to give me the facts I needed to make the right decision for the district. I appreciated the quality customer service I received from Dunham-Bush."