Modern swine production is being challenged to reduce air emissions and energy consumption and yet remain profitable. A novel approach to accomplish these goals is to remove the hydrogen sulfide, ammonia, methane, volatile organic compounds and moisture from the air, and then recycle the same air back through the swine barn. This type of system would reduce the amount of energy used for heating during the winter months.
The objectives of the paper study included designing a practical system that would clean the exhaust air from a swine finishing barn, remove the moisture added by the pigs, and recirculate that same air back into the barn. The capital and operating cost of the proposed design would be compared to a tunnel ventilated finishing barn.
The proposed design consists of a biotrickling filter, a biofilter, a heat exchanger to condense the moisture out of the air and another heat exchanger to add heat back to maintain a constant temperature barn. Ammonia is removed by passing the air through a biotrickling filter; hydrogen sulfide and volatile organic compounds are removed in the biofilter; moisture is removed by cooling the air causing the moisture to condense; the air is then reheated and recirculated back to the barn. A heat pump system is utilized to move the heat from the cooling heat exchanger to storage tanks and then back to the heating heat exchanger. A centrifugal blower moves the air through the system and barn at a rate of 20 cubic feet per minute per pig. Depending on pig size, 23% to 36% of the air is discharged to the outside atmosphere to remove carbon dioxide exhaled by the pigs and is replenished with ambient air for oxygen renewal. Air is discharged after being cleaned by the biotrickling filter and biofilter. The make-up air is introduced in the system before the heat exchangers.
The major advantage of an air recirculating barn is improved pig performance. A literature review of published papers show that feed efficiency can be improved (reduced feed pounds per pound of gain) by reducing daily (i.e. morning to night) temperature variation and seasonal temperature fluctuation to within 2.7º F. Also reducing the air speed over the pig reduces the stress and improves feed efficiency. The expected feed efficiency would be 2.2 pounds of feed per pound of gain or less for pigs raised in an environment provided by an air recirculating system.
Other advantages of the air recirculating barn include near zero emissions for gasses and odor from the barn. Since energy consumption is increased for the recirculating barn as compared to the tunnel ventilated barn, overall emissions, including those from the power generating facility, may be effected. Improved pig health would also be expected which would result from reduced stress and airborne pathogens. Pathogen reduction could be achieved by adding filtration to the make-up air inlet.
The capital and operating costs of an air recirculating type of pig finishing barn were compared to tunnel ventilated barn. [MSOffice1] [R2] The capital cost estimated for an air recirculating barn was $590 per pig space compared to $250 for a tunnel ventilated barn. Annual energy operating cost for the conventional tunnel ventilated barn would be $1.54 per pig place. The proposed air recirculating barn of the same size has an estimated annual energy cost of $6.21 per pig place. The major increase is due to the electrical energy required for the heat pump motors. [MSOffice3] [R4]
After combining improved pig performance, increased capital cost and energy costs the projected payback period on the added investment for an air recirculating barn is 10.9 years [MSOffice5] when[R6] compared to a tunnel ventilated 1000-head finishing barn for a life expectancy of 15 yr. No additional cost benefit credit was given to improved pig health or reduced emissions but depending on the specific producer management practices these additional benefits could be very significant.
The three most sensitive assumptions used for the cost analysis are: feed efficiency, feed cost, and market price of pigs. [MSOffice7] [wl8] Payback period can vary from 6.3 years to over 16 years as depending on feed costs vary from $150 to $250 per ton, if feed efficiency changes from 2.2 to 2.0, and if market price changes from $55 cwt to $75 cwt.
Areas of further research include: verification of design component size, validation of improved pig performance, and investigate heat pump methods that use less electrical energy.
