While it is 9 days until the official end of summer, many producers and contract growers are already planning for winter management of production facilities. This planning includes contracting of propane supplies. At recent meetings, I’ve had producers quote $1.71/gal up to $2.20/gal as the price they have pre-paid for this winter’s estimated needs.
At every meeting, one topic of concern was the estimated impact of these higher propane costs on overall energy expense. For contract growers with a fixed payment, the increase in propane expense has a large impact on their overall cash flow.
Whether the production unit is a breed-wean site, a nursery site, finishing site or wean-finish site, I see several common mistakes repeatedly that result in higher than necessary propane expense. The biggest source of mistakes is ventilation controller settings. Producers, advisors, fieldmen, growers and managers often don’t have an understanding of how their ventilation controller really corresponds and controls the variable speed fan often used for winter minimum ventilation. This often results in the minimum speed setting in the controller being wrong, resulting in overventilation. This is especially true when the variable speed control is set by ‘listening’ to the fan and setting the speed so the fan ‘sounds’ right.
I recently bought a digital tachometer over the internet. With delivery charges, it was less than $40. I am using this tool to measure fan speed. As a rule of thumb, variable speed fans have 50% of their full speed rated output when the fan rpm is 65% of the full motor speed. This means a 24” fan that has a rated speed of 1050 rpm and 5800 cfm at 0.05 sp will have approximately 2900 cfm at approximately 680 rpm.
A second common controller error is to have the OFF setting for the furnace too close to the set point at which the variable speed fan increases speed. In general, the larger the furnace size relative to the space being heated, the greater the difference between the OFF setting for the furnace and the set point. Keep in mind that the perfectly sized furnace is one that turns off occasionally on the coldest day of the year. If it shuts off occasionally, it is keeping the facility heated, and there isn’t much temperature variation associated with the furnace turning on/off. However, if the furnace is greatly over-sized, it only runs for a short burst of time, with a corresponding large burst of temperature. This often results in the variable speed fan increasing speed shortly after the furnace shuts off. If this is happening in your facility, decrease the OFF temperature setting for the furnace relative to the set point. If your furnace has a variable output valve, turn the valve to the low setting. Leave it at the low setting until the furnace no longer can maintain temperatures.
I often see facilities poorly winterized. If large fans will be unused in cold weather, seal the shutters or replace the shutters with an insulated insert. This not only stops cold drafts, but also reduces or prevents condensation at the fan. I’ve seen a number of producers seal shutters effectively using a bubble-wrap insulation material.
Curtain holes need to be repaired. In a 1200 head wean-finish facility, if it is double-stocked at weaning, the total inlet area needed to meet the minimum ventilation needs of the newly weaned pigs is 7.5 ft2. If there are 5 6”x6” holes in the curtains, this amounts to 17% of the total inlet needs, making temperature and draft management difficult.
Finally, don’t forget to verify the setting on the emergency mechanical thermostats. These thermostats are intended to operate heating and cooling devices in the event the ventilation controller is disabled from such things as lightning strikes, electric line surges, etc. The thermostat for the furnace should never be set closer that 5F to the controller set point. It may even need to be set more than 5F below depending on location of the mechanical thermostats within the animal space. I’ve seen instances where these were incorrectly adjusted and the furnaces were operated an entire heating season by these thermostats, with the variable speed fans often increasing speed to remove the excess heat produced by furnaces that were running too much.