Managing propane expenses

There has been lots of press in the past 2 days about the looming propane shortage in the upper midwest. One broker was quoted this morning as saying there is only a 2-3 week supply in the upper Midwest. In the past 2 days I’ve worked with several clients on strategies to manage propane expense.

I spend a lot of my consulting time working with clients on efficient operation of their ventilation system and I commonly come across issues that waste propane. In my list of what causes high propane expense, the number 1 cause is controller settings. Too many people working in swine facilities don’t understand their controllers and have incorrect settings in the controller that result in wasted fuel.

If you have a controller that has user selected ‘motor curves’ for the variable stage(s), be sure these are set correctly. Think of motor curves as the point where you tell the controller what device is connected to that variable speed stage. If you get this wrong, the 50% minimum speed setting is meaningless and you could be operating at 90% minimum or at 25% minimum in reality while the controller says 50%. Recommended motor curves for Thevco controllers (think TC-5, Aero 2.4, Ovation) for fans are listed on a goldenrod colored sheet that came with the owners manual. All too often this sheet gets lost or thrown away. If you can’t locate your copy, contact your equipment supplier. Motor curves for Phason Supra, AP Expert, Acme, Aerotech Ultra and Elite controllers and Varifan controllers are in the owners manual.

The second mistake I commonly see is variable speed fans ramping faster following a heater on/off cycle. Variable speed fans should never increase speed as a result of a heater cycling on/off. If that occurs, you need to lower the furnace OFF setting relative to the set point.

The simplest way to tell if you have this setting correct is to go to a facility or room that is a heating mode such as farrowing, nursery or just weaned wean-finish. The daily high temperature, as logged in the controller, should never get to set point if the controller begins ramping variable stage 1 at 0.1F above set point. My target is the daily high should be 0.3-0.5F below the temperature at which the fans begin to increase speed. Adjust the furnace OFF set point accordingly if possible.

Some producers struggle with wet floors when pigs are first weaned or placed in a facility. The response is to increase the minimum ventilation to move more air. If the fans were sized correctly for minimum ventilation and the motor curve for this fan is set correctly in the controller, this is the wrong response. In many cases the floors are wet because the speed of the incoming air is too slow and air is dumping into the animal space rather than ‘jetting’ and mixing. The solution is to tighten the facility so there are fewer air inlets such as door sills, unused fan shutters, pit lid gaps, etc.

Many times I close and lock many of the inlets to make the total inlet area into the room smaller and increase the velocity of the incoming air. Correctly adjusted ceiling inlets should have air ‘shooting’ across the ceiling for 8-10+ feet before dropping into the pig space, rather than dumping into the pig space within 4-6 ft of the inlet.

Fan sizing can be an issue also. For example, if you have a 1200 head wean-finish room that is single stocked at weaning and have 2-24” fans on your stage 1 variable circuit, even at 40% minimum speed you are moving about 4 cfm/pig. The recommended ventilation rate for newly weaned pigs is 2 cfm/pig and this over ventilation is costly.

For every CFM of air removal you remove 1.08 Btu of heat per degree F between incoming and exhaust air temperature per hour. In the case of this wean-finish with 2400 cfm of excess fan operation (2 cfm/pig extra times 1200 pigs), when the temperature is 0F outside and you are heating your barn to 80F, you are removing an extra 207,000 Btu/hr of heat vs operating the system at 2 cfm/pig. With approximately 92,000 Btu/gal of propane, this is 2.25 gal/hr of extra propane expense due to over ventilation.

With speculation that the spot market for propane could go as high as $5/gal in the coming weeks, getting your minimum ventilation set correctly can have a huge economic impact.

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