Industrial Utility Efficiency

# Grimmway Farms Implements System Automation

### Introduction

This article presents a case study of Grimmway Farms; a carrot growing and packing firm located in California’s Central Valley that was able to improve its compressed air system efficiency after implementing system automation and making relatively small equipment and piping changes.

Grimmway Farms uses compressed air for the production and clean-up processes in their carrot packing plants.  After having been approached by the Ecos Air Program (see sidebar), members of Grimmway’s energy efficiency program realized that in addition to decreasing the continued energy use of their compressed air system while simultaneously improving overall performance, there may also be an opportunity to receive a considerable monetary incentive which could offset the cost of the suggested energy reduction improvements.

System Assessment

Where: Arvin, CA
Industry: Food Processing
Issues:   Multiple compressors are not automated and are therefore inefficient
Audit Type:  Compressed Air System

System Assessment Win/Win Results*
Reduction in Energy Use: 765,274 kWh
Reduction in CO2 Emissions: 545 metric tons
Equivalent CO2 for homes: 72 homes
Equivalent CO2 for vehicles: 100 vehicles
Approximate Annual Savings: $64,283 Investment$120,000

### Baseline Determination

Data collection took place over a 7 day period during which plant personnel indicated that the plant was operating in a typical fashion.  Compressor power and system pressure were collected via data loggers and data storage equipment, analyzed in LogTool v2 and then imported into AIRMaster+ v1.2 where various scenarios were modeled.  Estimated annual energy consumption was extrapolated from the study period to a full year.

### Control Scheme

To determine “trim” compressor loading, rate-of-change pressure is calculated and monitored at the two trim station 3,000 gallon air receivers. “Base” compressor loading is determined by downstream pressure in the plant.
From a zero flow point and compressed air demand rising, the #1 (150 hp) “trim” compressor starts and runs load/no-load until fully loaded. When system demand exceeds the capacity of the #1 air compressor (rate of decay in 3,000 x 2 gallons = negative) the #3 (150 hp) “trim” air compressor will start and run load/no-load until it too is fully loaded. When system demand exceeds the capacity of the #1 and #3 (300 hp total) compressors, the #7 (150 hp) “base” compressor will start. The #1 and #3 air compressors will respond by unloading until the demand exceeds the new #7 air compressor.  As load again increases, the “trim” compressors begin to load as described in the steps listed previously.
When the demand exceeds the capacity of the #1, #3 and #7 compressors (450 hp total), the #4 (200 hp) “trim” compressor initiates. Again, the steps listed above for the “trim” air compressors will repeat and any additional demand will initiate the #5 (150 hp) compressor and finally the #6 (200 hp) air compressor. The #2 (150 hp) “trim” air compressor will start if another “trim” compressor were to fail, any other air compressor failed and the demand was greater than the output of the operating air compressor(s), or the demand exceeds the capacity of all other air compressors.
“Base” compressors drop out when the demand expander is 100% closed, “trim” compressors are unloaded and the system pressure rises to 1.5 psig above the demand expander set-point, or 84.5 psig.

### Post Monitoring Results

Post monitoring results (Table 3 and Figure 4) were collected on the new automation system and downloaded to a computer for analysis and monitoring.

Table 3 - Post Monitoring Results

Figure 4 - Typical Post System Day Profile

### Conclusion

As a result of the above changes to Grimmway Farm’s compressed air system, compressor output more closely matches system demand and continued energy costs have been reduced by approximately \$64,000 annually. Additionally, a rebate of over \$65,000 was received which lowered the project cost by 55%.

Energy Savings Summary Calculation

3,596,788 kWh – 2,831,388 kWh = 765,400 kWh

Annual Cost Savings Calculation

$302,130$237,822 = \$64,308