How do I know if I have enough fans for summer heat relief?

While this summer in southern Minnesota has not been anywhere close to having record heat, I’ve still had quite a few discussions with growers and managers about maximum ventilation rates for heat relief. The basic question has been – how do I know if I have enough fans in my hog barn?

If you have enough fans (assuming you also have enough air inlets), the average room air temperature should be within a couple of degrees of outside air temperature. That is, if you are moving sufficient air thru your facility the temperature rise in the air should be only 2-3F before it is exhausted from the facility.

If this is happening in your facility, adding more fans won’t improve conditions for the pigs as you are already keeping air temperatures in the barn within a couple of degrees of outside temperatures. If you have 90F outside temperatures and you bring this air into your swine facility, the best you can expect is to have a temperature of about 92-93F at the exhaust fan as the air has to increase in temperature as it picks up the heat given off by the pigs in the facility. It doesn’t make economic sense to continue to add fans so the temperature at the exhaust fans only rises to 90.5F. Air temperature in the pig zone is still above 90F and alternative methods have to be used to help the pigs deal with the high temperatures in their pig zone.

If you have tunnel ventilated facilities you can monitor this by examining the readings of your temperature probes. The difference in temperature between the probe closest to the tunnel curtain and the probe closest to the fans should only be a couple of degrees at the ventilation stage that has all of the fans operating.

Note that I have a statement above about air inlets. There are still too many production facilities which have restrictions in air inlets. Adding more fans and trying to get more air thru the same inlet area may not add any air flow to the room. If you look at the performance response of fans to static pressure, as pressure rises, cfm/fan declines, with each fan having a specific response curve to pressure. It is quite possible that when you add a big fan to a starved room you in fact reduce the total amount of air moved because the increase in static pressure has lowered the performance of all fans in the room.

We see this quite often with filtered inlets. This is why farrowing sites which filter all of their incoming air talk about fan performance at 0.2’ or even 0.3” pressure. The filters on the inlets are a restriction. More filters can be added to reduce this restriction, but at $150+ per filter this can be a very expensive option.

Another ‘choke point’ for ventilation air in farrowing sites is the evaporative pad cooling system. As the pads plug with debris, algae or calcium carbonate their effective inlet area declines, meaning the fans have to pull more air thru less pad area. In this case, the exit temperature of the air from the pad rises as the air spends less time exchanging heat in the pad and overall efficiency of the pad cooling drops.

Now the temperature rise in the room may not be an issue of enough fans, but rather an issue of enough pad air so the air flow through the pad remains less than 400 fpm velocity. At velocities higher than this exit temperatures from the pad rise as the cooling efficiency becomes compromised so the incoming air into the room is warmer than intended.

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