A simple way to increase propane expense

Winter has arrived in southern Minnesota, and with the coming of winter the realization that propane expenses will be increasing. While every production facility tries to keep the facility set point as low as possible (approaching the lower critical temperature), there are numerous other ways that propane can be wasted in production facilities.


This past week I was working with a production system at their farrowing sites. One of the unit managers said he had turned down the variable out-put furnaces in his farrowing rooms for more even heating. However, when he finished washing a room, the furnace ran almost 100% of the time during the Thanksgiving break. His question was – do I need to turn up the furnace output so it doesn’t run so long?


After further questioning, it was determined that each farrowing room had a 100,000 btu furnace installed. When the variable output valve was turned down, output now is in the range of 60-65,000 btu. Each farrowing room is equipped with an 18” variable speed fan for stage 1 ventilation. The particular fan installed in this facility is rated at 4,440 cfm when operated at 0.05” static pressure. Assuming the controller is configured correctly for this fan (correct motor curve selected), when set at 50% minimum speed, this fan is ventilating at approximately 2,200 cfm. With 24 crates in each farrowing room, this is 92 cfm/crate, well above the Midwest Plan Service recommended minimum rate of 20 cfm/crate.


When the room was empty, the unit employees kept the minimum ventilation fan operating to dry out the room prior to placement of females into the crates. Assuming a 68F shut off point for the room furnace, 45F outside air temperature and 2,200 cfm of fan exhaust, the heat loss estimate from the farrowing room due to the operation of this fan becomes:


= 1.1 btu/hr/cfm/F  x  2,200 cfm  x (68F – 45F)

=  55,660 btu/hr


Since each gallon of propane equals approximately 92,000 btu, the operation of the minimum ventilation fan was consuming 0.61 gal of propane per hour.


With the furnace output at approximately 60,000 btu/hr, the furnace had to run 93% of the time to keep up with the heat loss from the ventilation fan. The issue in this case was not furnace sizing but rather operation of a ventilation fan in an empty room.


At $1.50/gal for propane, leaving the ventilation fan operate in the empty room cost $22/day.


How many times have you done something similar in your facilities?


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