In the pork industry, there are few “benchmarks” available for comparison of energy expenses by the swine enterprise. Most producers, facility managers and contract growers attempt to manage this expense by making ventilation system management decisions that impact not only the pig's environment, but the resultant consumption of electricity and propane.

The key to management of energy expenses lies in the selection and control of the ventilation equipment. In my work with pork production systems, the four mistakes I most commonly see are:

• Incorrectly sized, minimum-ventilation fans;

• Mistake # 1 - Incorrectly sized, minimum-ventilation fans

  Incorrectly managed, variable-speed fans for minimum ventilation;

• Incorrectly sized heaters; and

• Incorrect ventilation controller settings for furnaces and variable-speed fans.

Heat loss of production units occurs via the ventilation system (air exchange) and via the building shell (insulation). A common obstacle to effective management of propane expense is a lack of knowledge about the ventilation system capacities in the facility vs. the estimated requirements for moisture control.

The Midwest Plan Service recommendations for minimum-ventilation rates in cold weather are listed in Table 1. These rates are designed to remove the moisture produced by pigs and their associated activities.

While many producers can recite the values in Table 1, they often cannot translate these values into capacities associated with their production facilities.

Table 2 lists approximate fan capacities for fan sizes often associated with minimum-ventilation fans. Note that Table 2 is an approximation, as specific fan performance is influenced by fan housing design, blade design and other items such as shutters, deflection hoods and discharge cones.

Specific fan performance details are available from the University of Illinois BESS Labs testing results (www.bess.uiuc.edu) and the performance estimates of specific fans from manufacturers.

Farrowing rooms are most commonly the victims of incorrectly sized, minimum-ventilation fans. This is because of the relatively low ventilation rate required for very cold weather.

At 20 cfm (cubic feet/minute) per crate, in cold weather, a 24-crate farrowing room only needs an estimated 480 cfm of fan capacity to maintain humidity levels. Many farrowing sites that I have visited have 14-in. or 16-in. diameter fans installed as the minimum-ventilation fan. Fans of this size often have estimated capacities of 2,000-2,500 cfm. To obtain 480-500 cfm, these fans must operate at 25% of their estimated capacity. Slowing variable-speed fans to this very low percentage of capacity almost always results in fans stalling, or at best, operating very poorly. As a consequence, managers often operate these fans at speeds — 1,000 cfm or higher — for minimum-ventilation rates.

Mistake # 2 - Incorrectly managed, variable-speed fans

The net consequence of this “small” error in fan sizing is that heat loss from the ventilation system goes from an estimated 540 Btu/hr/°F to 1,080 Btu/hr/°F. This change in rate of heat loss means the furnace must come on to provide supplemental heat when the outside air temperature is approximately 10°F warmer than when the ventilation rate is correct.

If the farrowing room is maintained at 70°F, and the outside air temperature is 20°F, this mistake in ventilation rate is the equivalent of 27,000 Btu of extra energy consumption. If unvented propane furnaces are used as the supplemental heat source in the farrowing facility, this amounts to almost 7.5 gal. of extra propane usage per day.

At one site I worked with this past summer, the over-sizing of farrowing room minimum-ventilation fans, and their associated inadequate minimum speed settings, resulted in propane expenses for the past three winters that were equal to facilities in the same production system having twice as many females in inventory.