Controlling Energy Bills In The Winter
By Dr. Mike Brumm, Brumm Swine Consultancy, Inc.
The ventilation needs for a wean-to-finish facility range from 2 cfm/pig at weaning in winter to 120 cfm/pig at market weight in summer. Designing and managing facilities to accomplish this range of needs continues to be a challenge. Ventilation mistakes are common in production facilities and these mistakes often equate to elevated and unnecessary energy expenses.
Benchmarking Expenses
Many of the wean-finish facilities built in the past 5-10 years have 1,200 pig spaces per room. Commonly constructed with deep pits, the facilities often have two 24” variable speed pit fans as the Stage 1 ventilation. While 24” fans have a range in ventilation capacity when operated at 0.05 in. static pressure, many have an installed capacity of approximately 6,000 cfm (www.bess.uiuc.edu). With 1,200 pigs in the facility, this means each 24” fan has 5 cfm/pig capacity. When there are two fans installed as the first stage of ventilation, this means the capacity of this stage when operated at 100% is 10 cfm per pig, which is 500% of the 2 cfm/pig requirement for moisture removal within the facility for the newly weaned pig.
Common Mistakes that Increase Expenses
The most common method used to reduce the ventilation rate for weaned pigs is to install the fans with a variable speed ventilation controller. At 50% of capacity (not necessarily 50% of fan speed or 50% as stated on the controller) each 24” fan provides 2.5 cfm/pig. When pigs are single stocked into a facility, a common mistake is to operate both Stage 1 fans which equates to 5 cfm/pig as the minimum ventilation rate.
Brown-Brandl et al (2004) have summarized recent research on pig heat production. When this data is combined with heat loss estimates for the building shell and the ventilation system (MWPS, 1977), it is possible to model the impact of varying ventilation rates on the heat flows within a wean-finish facility.
For example, if one combines the heat production of a 25-pound pig with the heat loss estimates from a curtain-sided wean-finish barn when the room temperature is 78 F, at 5 cfm/pig the balance point temperature is estimated to be approximately 45 F. That is, heat production by the pig equals heat loss from the building shell and ventilation system when the incoming air temperature is 45 F. At incoming air temperatures lower than this, additional heat must be provided or the room will gradually lower temperature. At incoming air temperatures higher than this, the ventilation system must gradually increase the rate of heat removal or the facility will gradually increase in temperature.
Contrast this 45 F estimate with the estimate of 22 F when the ventilation rate is lowered to 2.5 cfm/pig. Thus, when Stage 1 fans are over-sized, the result is a significant increase in propane usage as a result of over-ventilation.
Three common methods often used to correct this over-ventilation:
1. Turn the minimum ventilation speed to 20 or 30%
2. Unplug or otherwise disable one of the pit fans
3. Install a single speed 18” fan (often 3500-4000 cfm rated).
When the minimum ventilation speed is set very low for a variable speed fan (option 1), the fan’s ability to maintain static pressure is usually compromised. This means that wind effects, either when blowing into the fan, or into the attic, causes the ventilation rate to fluctuate rapidly, ranging from severe under- to severe over-ventilation.
In the case of turning off one of the pit fans (option 2), if the facility has ceiling inlets linked to the controller (often called powered inlets), operators must turn off the ceiling inlet control device or make other temporary adjustments. The controller will react as though both pit fans are operating and open the inlets accordingly which means there will be too much inlet capacity into the pig space, resulting in lowered inlet velocities and reduced air blending and cold air dropping into the pig zone in the wrong areas.
Furnaces are often oversized in swine facilities. As a consequence, when the furnaces operate, air temperatures rapidly increase. Because temperature probes for ventilation controllers are often suspended some distance from furnaces, rapid increases in air temperatures results in ‘overshoot’ of the temperature setting in the controller that turns off the furnace. In general, furnaces should be set to turn off 2 F below the temperature at which the ventilation system either increases the speed of variable speed fans or turns on additional fans.
Monitoring Energy Consumption
Most ventilation controllers capture high/low temperatures. An effective tool to monitor for ‘overshoot’ is to record the daily high temperature logged by the controller. If this high temperature reaches the temperature at which the ventilation system begins increasing output when the facility is operating in heating mode, “overshoot” has occurred and propane expense is increased.
Brumm (2007) discussed the current technology for both on-site and remote monitoring of energy consumption in swine facilities. Currently, these systems only capture temperature, fan run time, propane usage, etc. They do not relate the consumption of energy to a predictive model that is unique for the facility as sited and constructed and for the specific pig numbers and growth status of the pigs in the facility.
Many of the ventilation controllers now being installed in swine facilities log daily hours of run time for furnaces. The challenge producers and their many advisors face is comparing the logged run times to an estimate of what is “normal” for that facility. Future data capture technology will include an internal model of pig heat production, facility heat loss and energy expenditures to maintain set point conditions. The reporting from the data capture system will include process control charts documenting energy (both electric and propane) usage versus predicted.
References
Brown-Brandl, T.M., J.A. Nienaber, H. Xin and R.S. Gates. 2004. A literature review of swine heat production. Trans. ASAE 47(1):259-270.
Brumm, M.C.. 2007. Managing the growth process using real-time data. Proceedings 32nd annual A.D. Leman Swine Health Conf., University of Minnesota, St. Paul.
MWPS. 1977. Structures and Environment Handbook. MWPS-1. Midwest Plan Service, Iowa State University, Ames.
Dr. Mike Brumm is the owner of Brumm Swine Consultancy, Inc. of North Mankato, Minnesota. He was previously a professor at the University of Nebraska. Dr. Brumm's areas of expertise include management and housing of the growing pig, industry issues including production networks, contracts, cost of production and record systems.
|
