By Brett C. Ramirez and Steven J. Hoff, Iowa State University Department of Agricultural and Biosystems Engineering
Indirect (feed efficiency) and direct (fuel/electricity) energy usage are a large fraction of production costs. Properly managing the ventilation system can be a route to conserving energy by reducing fuel/electricity consumption and increasing feed efficiency. To reduce energy usage, an understanding of the ventilation system and its impact on the pigs is needed to determine the best strategies for balancing indoor environment and production costs.
A facility needs to provide the optimum environmental conditions to maximize production efficiency while conserving energy. If both these goals are accomplished, the result can be reduced operating costs for the producer. However, a “complete” ventilation system is one that is designed, installed and managed for the specific animals, climate and needs of the producer. Beyond design and equipment selection (such as fans, air inlets and heaters), excellent management and operation are also equally crucial. While today’s controllers automate much of the process, it is still important for facility managers to understand the ventilation process basics and where adjustments can be made to maximize effectiveness.
Energy usage in swine facilities can be split into indirect energy (i.e. feed efficiency) and direct energy (i.e. fuel consumption or electricity usage). While feed energy is not often considered, it does substantially impact productions costs at about 60% to 70% of total and more importantly, is directly related to ventilation management. Direct energy is the energy used to operate fans, lighting, feed handling, supplemental heaters, brooders, heat lamps, etc., and is only about less than 10% of production costs. It should be noted that most ventilation systems were designed to use energy to reduce management and provide a more stable environment. Attempts to reduce direct energy usage can negatively impact pig performance resulting in increased indirect energy costs through reduced feed efficiency. Careful monitoring of pigs and environment is needed to ensure ventilation system management changes result in positive outcomes for indirect and direct energy usage.
Fans are exchanging the desired amount of fresh air by creating a pressure gradient across the building envelope. In a traditional negative pressure system, fans exhaust stale or “dirty” air from the building and bring fresh air into the room. Selection of rated fans is important, and verified ratings indicate airflow rate at certain static pressures and also provide an energy efficiency reported as an airflow rate (e.g. cubic feet per minute) per watt. Current data from BESS Labs at the University of Illinois Urbana-Champaign shows for all 50- to 53-inch diameter fans (n = 200; single phase 230V; 60 Hz) tested in the database, an average capacity (at zero inches H2O) equals 25,834 CFM with a standard deviation of 2,735 CFM; minimum of 17,322 CFM; and maximum of 33,343 CFM. In terms of efficiency (at 0.1 inch H2O), the following was found: average, 18.7 CFM per watt; SD, 2.3 CFM per watt; minimum, 12.0 CFM per watt; maximum, 26.6 CFM per watt. The higher the efficiency, the more efficiently a fan uses electricity. Careful selection of a rated fan is needed to ensure good energy efficiency at the needed airflow and static pressure.
Maintaining the desired static pressure is key to good ventilation system performance and minimizing energy usage. Successful ventilation system operation requires a slight negative pressure (i.e. 0.05 to 0.1 inch H2O). The level of static pressure can have serious and opposite implications for minimum and maximum ventilation.
Specifically, during minimum ventilation, when outdoor temperatures are less than the desired room temperature, enough static pressure is needed to provide an ideal rotary airflow pattern from the inlets to create a uniform, well-mixed environment. A poor environment due to temperature stratifications, drafts from cold air dropping immediately from inlets, or elevated contaminant concentrations, can also negatively impact feed efficiency and daily gain. Further, weak sufficient mixing can increase energy costs by causing heaters to operate more frequently, if feedback sensors are located in an area that receives the poor, colder environment (i.e. a temperature not reflective of the room average). The building shell must also be reasonably “tight” to prevent unwanted infiltration through unplanned inlets (i.e. cracks).
The opposite scenario is true for maximum summertime ventilation. As static pressure increases, fan efficiency decreases. Therefore, it is critical when maximum ventilation fans are operating, that there is an appropriate amount of open area to ensure airflow is not restricted. If the airflow is restricted, static pressure will increase, airflow capacity and efficiency will decrease. The lower airspeed can result in less cooling and reduced feed intake.
Fan maintenance is also critical for ensuring energy efficiency. Mainly, fan shutters not appearing to be fully open (i.e. fluttering or slightly cracked) can be a signal for elevated static pressure resulting in lower fan airflow capacity or dirty shutters that need cleaning. A 40% reduction in airflow can be observed from dirty shutters. For belt-driven fans, loose belts have also been shown to significantly reduce fan airflow capacity.