How did your ventilation and heating system perform yesterday?

Yesterday I was at a new nursery site that went into use last summer. With the extreme cold weather, the owner was having difficulty keeping temperatures stable in the pig zone.

When I arrived at the site there were 1400 pigs/room that had been weaned 3 weeks. Outside temperatures were below 0F and the wind was blowing. In the pig rooms, temperature swings of 6-8F several times an hour were occurring and the owner was very frustrated in his attempt to maintain pig comfort.

At this site, there were 3 – 225,000 btu/hr variable output furnaces. The stage 1 variable speed circuit in the controller had 2 – 24” pit fans operating at 50% minimum speed and the inlet velocity was low from the actuated inlets, resulting in cold air dumping into the pig space.

Even with the extreme outside conditions and over ventilation at minimum, the furnaces had only run 7 hours on the previous day and by 3 pm in the afternoon had run less than 4 hours at the visit.

It turns out the solutions were relatively simple to implement and immediately resulted in improved conditions in the pig space.

Solution 1 – there was too much furnace heat output for the size of the room and the owner had to shut off the furnace 4+F below the set point to keep the variable speed fans from ramping after every burn-cycle. We unplugged the middle furnace and turned the variable valve down on the remaining furnaces. The burn-cycle was now increased 2-3x so temperature uniformity in the room was better and the probe temperature only went up 0.5F after the furnaces turned off. The furnace off temperature could now be set to 1.5F below the room set point. Even with the severe conditions of yesterday, the burn-cycle was less than 50% so we had more than enough heat out-put capacity with 2 furnaces at a lower output. In the spring, the plan is now to unplug the 2 outside furnaces in the room and use only the middle furnace to keep the burn-cycle extended. Remember the rule – a furnace is big enough if it shuts off and the goal should be a very long run time on cold days.

Solution 2 – unplug one of the 24” fans so the minimum ventilation got closer to 2 cfm/pig. At 0F incoming air temperature, this resulted in a 3 gal/hr reduction in propane use. When the stage 2 variable begins to operate the stage 1 fan will be turned back on.

Solution 3 – the controller didn’t know one of the 24” fans was off so we manually locked up alternate ceiling inlets plus a few more. This resulted in an increased inlet speed – still not 800 fpm but closer than it was. Now the air moves further into the room before dropping and is warmer when it does enter the pig zone. When the stage 1 24” fan is turned back on the inlets will be unlocked.

Solution 4 – the controller had a 2F differential between the on/off furnace settings in the controller. We lowered this to 1F which reduced temperature variation by 1F for every burn-cycle.

By making these relatively easy corrections to the controllers and inlets, the temperature variation in the rooms went from 6-8F every burn-cycle to less than 3F. In addition, fuel use was decreased by over 3 gal/hour and pig comfort increased. Without changing the set point in the controller we effectively raised the room temperature 4-5F and reduced the variation in temperature.

Yesterday was a severe test of heating and minimum ventilation systems – how did yours perform?

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