air. There are three slight variations on how this is accomplished: ⢠One site utilizes air handlers in the attic and the air conditioned air enters through the same ...
Filtration and air conditioning Darwin L. Reicks, DVM, BS Swine Vet Center, St. Peter, Minnesota
Introduction
In the field, air filtration has been adopted by a number of farms.1,2 Dr. Scott Dee and Andrea Pitkin have shown us that the aerosol transmission of PRRS virus can be repeated experimentally and it is becoming widely accepted as a common route that PRRS negative farms become re-infected.3,4 One challenge for implementation of air filtration is the number of filters needed to maintain adequate air flow through a barn during summer time ventilation. Air conditioning systems greatly reduce the number of filters needed because summer time ventilation needs don’t really exist anymore. Since the air comes in cool year round, the ventilation needs are similar to those used during the winter.
Types of air conditioning systems
We have implemented the use of air conditioning in five boar studs and 100% filtration using the MERV 16, 95% DOP filters over the last three years. In all cases we use ceiling inlets and negative pressure ventilation for the cooler times of the year, just like a normal swine facility would. All of these systems have filters above each air inlet. As we transition into late spring where winter time ventilation rates become inadequate to meet the moisture and heat removal needs of the barn, the air conditioning system begins to operate. There is some variation in systems as to how this transition from cool weather ventilation to air conditioning occurs.
Recirculated air system
We have one farm that recirculates the air within the room into an air conditioning unit. As the temperature outside rises into the upper 60’s to low 70’s Fahrenheit, the air conditioner turns on, recirculates, and cools the air that is in the room. Fresh air continues to come in through the filtered ceiling inlets.
Fresh air systems
The other sites all use fresh air rather than recirculated air. There are three slight variations on how this is accomplished:
the air conditioning ducts year round. As the temperature warms up, the blowers come on first to push outside air through the ceiling inlets. As the temperature in the barn continues to rise, the condensing units come on and air condition the air. The air handlers are in the attic but the condensing units sit outside so that the heat is released to the outdoor environment. • Two sites have a similar system to the one described above, except that the air conditioning unit and air handlers are all positioned outside the building and push the air in through the side wall rather than through ceiling inlets. This seems to be a simpler system because it avoids having all the air handling equipment and duct work in the attic. Even distribution of air within the room becomes more of a challenge with this system. • Another site also has air entering through the side walls, but uses an evaporative cooling pad in front of the air conditioner and air handler. With this system, as the temperature rises, a blower comes on to help push air through the filters. As the temperature rises further, water circulates through the evaporative cooling pad to cool the air as a stage prior to the condensing units of the air conditioner coming on. The purpose of this is to delay the condensing units coming on until the upper 70’s Fahrenheit rather than coming on with temperature in the upper 60’s. This method is applied to save electrical costs.
Filter and air conditioning needs
Because the air conditioned facilities control the temperature of the incoming air, the ventilation rates can be set similar to winter time rates year round. All of the facilities operate in the range of 6 to 20 cfm per animal year round. This means a minimal number of filters is needed which greatly reduces the overall cost of filters. Normally a 24” × 24” filter would supply only 2 adult swine under maximum summer ventilation. With air conditioning operating under 20 cfm/animal year round, the same filter can supply 30 adult swine.
A rule of thumb in air conditioning needs is 5.5-7.0 ani• One site utilizes air handlers in the attic and the air mals per ton of air conditioning. The number of animals conditioned air enters through the same ceiling in- that can be supplied per ton of air conditioning is higher lets as before. In this site, the air is pulled through 17 American Association Of Swine Veterinarians, 2008
for a unit that recirculates the air. This air can be hard on equipment however. Farms using fresh air are in the range of 5.5-6.25 animals per ton of air conditioning.
Costs
The costs of implementing an air conditioning system with filtration have varied widely. We have seen a range of $300-$600 per animal. The reasons for this wide range have primarily depended on: • Whether 3-phase electricity is already on the site or needs to be either brought in or a converter installed. • The existing capability of the generator on site. • Whether using recirculated air or fresh air. The recirculated air system is less expensive but will require more maintenance. • New construction or retrofit. The new construction will be less expensive because one can avoid all the fans, cool cells, inlets, etc. that would normally be needed for summer ventilation. • The type of air conditioning system. We have seen a range which includes the use of household type systems to large commercial systems
Summary
Air conditioning is obviously a more expensive way to ventilate a swine building. However, when implementing a filtration system, some of this cost is offset by the large savings in the number of filters needed. Also, the overall reduction in the volume of incoming outside air should, in theory, reduce the risk of PRRS virus leaking into the system.
References
1. Reicks, D.L., Alternative filters for boars. 2006. Proceedings from the 2006 Allen D. Leman Swine Conference p. 99-100. 2. Reicks, D.L. Field experiences with air filtration. 2007. Allen D. Leman Swine Conference: Carlos Pijoan International Symposium on Swine Disease Eradication. p. 23-26. 3. Dee, S., Area spread of PRRSV: End of story? Proceedings from the 2007 Allen D. Leman Swine Conference p. 3-11. 4. Pitkin, A., Deen, J, Dee, S., Aerosol transmission of PRRSV: Application to the field. Proceedings from the 2007 Allen D. Leman Swine Conference p. 85-88.
Operating costs have run around $20-30 more per animal for the warm weather season.
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American Association Of Swine Veterinarians, 2008
