Summary

Energy usage in swine barns and potential energy conservation measures were evaluated in this study. A survey of 28 swine facilities showed large variability in energy used per hog produced between barns. Energy audits conducted in four selected barns identified the various areas, equipment, and practices in the barn that contributed significantly to the total overall energy consumption, thereby aiding in prioritizing areas for intervention. Using computer simulation, various potential strategies that can be applied in a barn in terms of lighting, creep and space heating, fans, feed motor, and heat recovery were examined. Simulation results for a typical 600-sow operation showed that potential annual savings up to 47,391 kWh electricity (79 kWh/sow) or 88,404 cubic metres of natural gas (147 cubic metres/sow) can be attained.

Introduction

Swine production in temperate regions like Canada requires substantial energy input. With the recent upward trends in energy prices, the cost of energy input to swine operations have been steadily rising such that for many operations, utilities now represent the third largest variable cost component of the total cost of production. The goal of this work is to assess the current energy usage and examine energy conservation measures that can improve the energy use efficiency in swine production operations, thereby reducing overall energy costs.

Experimental Procedures

A survey questionnaire was developed and sent out to various swine producers to collect pertinent data from each operation over a three-year period from 2004 to 2006 to be able to calculate the average monthly utility cost per animal marketed ($/pig marketed) for each operation.

Based on the survey results, two barns which used the most energy per hog produced and two which used the least energy were selected for energy audits and monitoring of actual energy consumption during winter and summer seasons. Following the barn monitoring, a mathematical model which simulated the energy use in a typical barn operation was developed based on fundamental principles of heat transfer, thermodynamics, and other engineering concepts. The model was applied to a typical 600-sow operation to simulate the theoretical energy consumption in the barn based on the building properties, climatic factors, barn management and practices, number and growth stage of animals, and equipment used in the barn. The baseline model was validated by comparing the predicted energy consumption in different operations within the barn with actual values obtained from barn monitoring. Finally, a number of potential energy conservation strategies were incorporated into the model and the projected energy savings resulting from each measure were calculated.

Results and Discussion

Benchmarking results
Table 1 shows the range and average values of utility cost per animal marketed ($/head) based on the three-year information obtained from the survey. The average utility cost between types of barns were significantly different (P<0.05) for all comparisons except between grow-finish and farrow-wean barns (P>0.05). The survey results also showed almost four times the difference in energy consumption (per head) between the lowest and highest energy user barns. This indicated significant opportunities for improving energy use practices in some barns in order to reduce overall energy costs.

Monitoring of energy use in the four selected barns showed that the grow-finish rooms had the highest contribution to electrical energy consumption in the barn during summer months followed by farrowing, nursery and gestation. The high energy consumption in the grow-finish area can be explained partly by the relatively larger footprint of this part of the barn compared to the other production stages in a typical farrow-to-finish operation and to the lower temperature set-point in grow-finish rooms (which meant all fan stages were operating almost continuously at full capacity during warm months). During winter, the highest natural/propane gas consumption was observed in nursery rooms followed by the grow-finish and farrowing rooms. This can be attributed to the high temperature set-point in nursery rooms relative to other production rooms. The gestation room had the lowest gas energy consumption because the heat generated by the sows was adequate to maintain the room at its set-point temperature.

Ventilation plays an important role in keeping the environment of the pigs at a level where production performance is optimised. The results of this study showed a medium to high negative correlation (i.e. -0.6 to -0.9) between the fan energy consumption and concentrations of ammonia (NH3), hydrogen sulphide (H2S) and carbon dioxide (CO2) gases, which are indicators of indoor air quality. This correlation indicated the need for careful consideration of conservation measures to reduce energy cost so as not to compromise the health of workers and animals in the barn.

Simulation results
Simulation of the baseline case and the cases in which energy-conservation strategies were applied showed that significant energy savings can be attained in the areas of ventilation and heating as shown in Table 2. Using higher efficiency fans can reduce electrical energy consumption by 21 per cent, while the natural/propane gas consumption can be reduced by 70 per cent using a heat recovery system, i.e. air-to-air heat exchanger. Furthermore, replacing conventional space heaters with gas-fired radiant heaters can reduce the gas consumption by 40 per cent. Applying conservation strategies to other areas such as recirculation fans, feed motors, lighting and creep heaters can reduce energy consumption by 12 per cent and 20 per cent, 26 per cent and 39 per cent, respectively.

Conclusion

Benchmarking showed that the average utility cost (electricity and gas) per animal marketed is about $6.80/head but can be as high as $12.0/head for some types of operations. Energy audits identified areas and operations in the barn such as ventilation and space heating in the grow-finish and nursery rooms as significant contributors to the overall energy consumption in the barn.

Examination of a number of energy conservation strategies using computer simulation quantified the potential impact of the application of each measure on the overall energy use. Simulation results also identified the most promising measures that would merit further evaluation under actual swine barn conditions.

Overall, the findings from this study would aid pork producers in focusing on specific areas and practices in the barn and in prioritising conservation strategies to be considered for implementation, which would result in the most significant energy savings.

April 2010