There are two major challenges associated with cold weather ventilation: maintaining a healthy and comfortable indoor environment; and conserving energy and keeping operating costs down.

August 23, 2017

10 Min Read
This is how to get your hog barn prepped for winter
National Pork Board

By Brett C. Ramirez and Jay D. Harmon, Iowa State University Department of Agricultural and Biosystems Engineering
Winter is coming — well, in a few months, but it’s not too early to start planning for the cold weather ahead. There are two major challenges associated with cold weather ventilation: (1) maintaining a healthy and comfortable indoor environment and (2) conserving energy and keeping operating costs down.

Thermal conditions (mainly temperature and relative humidity) and air quality (noxious gases and dust) must be maintained at acceptable levels that promote cost-effective operation and high pig performance. However, even at the minimum ventilation stage, about 80% to 90% of heat is being lost through ventilation. Poor ventilation management can reduce building integrity, pig performance, increase operating costs, and cause a whole host of problems. To overcome these challenges, this column will discuss management strategies on ventilation/heating systems and provide typical problems and possible solutions to make troubleshooting this winter a little easier.

We will start with an introduction to minimum ventilation — one of the most important concepts of wintertime operation. Then we will work our way from the impact of infiltration through the building shell, to control and operation of variable speed fans, heaters and fresh air inlets, and conclude on using the pigs as the feedback. Along the way, there will be troubleshooting suggestions.

A previous column dives into a great discussion on the difference between selecting the design MV rate and operating at the MV stage. For completeness, let’s review — the MV rate stated in MWPS (1.5 to 2 cubic feet per minute per head for pigs less than about 30 pounds) is for design, that is, the fresh airflow rate needed to select the appropriate fans to remove generated moisture.

During operation when the barn is stocked, it may take more ventilation or less, depending on many conditions and influences within the barn. Feedback on adjusting the MV rate can come from measurements of air temperature, relative humidity and/or gas concentrations. Additionally, observation of the pigs (more on that later) can be helpful, too. Therefore, it is imperative to determine if the pigs need more or less ventilation, not if the fan(s) are achieving the design flow rate value. Before we cover fan management at the MV stage, we need to discuss infiltration through the building shell and the role it plays on MV.

During the MV stage, we are extremely concerned with distribution of fresh and often colder air. Infiltration through unplanned inlets (i.e., doors, cracks, holes, etc.) makes good air distribution nearly impossible to achieve. More information on infiltration can be found here. A pressure difference between the room and outside is needed to develop a jet entering the room from the inlets (try to drink through a straw with a hole it in, it just doesn’t work). Same principle here. Air (or your favorite beverage) coming into the room (or mouth) anywhere but the inlet (or at end of the drinking straw) does not go where it was designed to and can cause drafts (very harmful for small pigs), regions of stale, noxious air, and potentially increase heating costs. For good air jet development, about 0.05 inch water across the building envelope is needed. Alternatively, this is approximately equivalent to an airspeed of about 800 feet per minute exiting the inlet.

There are several ways to achieve this, for example, seal up the unplanned infiltration locations or increase the ventilation rate. Let’s say, the design MV rate in a 1,000 head wean-finish room is 1,500 cubic feet per minute; hence, the total inlet open area should equal approximately 1.9 ft2 (1,500 cubic feet per minute/800 feet per minute). This is very challenging in a large wean-finish barn … remember this is without infiltration. In the vast majority of barns, which have a considerable amount of infiltration, when the MV stage is operational, the static pressure is typically <0.01 in. water. To achieve that 0.05 in. water for good air distribution by increasing the ventilation rate, we actually need an additional 1.5 times the MV rate. That will result in an additional 2,600 gallons of LP used per year because of over ventilation, but better air distribution.

Unwanted infiltration can be reduced by sealing the “obvious” locations. Some recommendations include a minimum 3-inch overlap on curtains, unused cold weather fans covered tightly, a sheet of plastic secured behind the shutters, shutters cleaned/fixed, pump-out covers secured and sealed with sill-plate construction foam, and lastly, doorframes weather-stripped and firmly closed. While these are more easily identified areas of infiltration and relatively simple to fix, less defined locations, such as ceiling-to-side/end wall joints, can be spray foamed in the attic to substantially reduce infiltration. In addition, corroded or damaged ceiling panels may need to be patched or replaced which presents a costlier solution to infiltration.

In addition to minimizing infiltration, management and control of fresh air inlets are also needed for good jet development and distribution of air. The opening size should be in agreement with the design MV rate and the static pressure difference across the room envelope. Openings that are too wide will decrease the pressure difference, resulting in unstable air jets (known as the cold air drop) and back draft in to the attic. Openings that are too small will restrict airflow resulting in decreased fan efficiency and possibly fail to provide enough air for moisture and contaminant removal. A certain level of static pressure must be maintained, but high levels of infiltration make this challenging; hence, infiltration must be reduced as a first step.

However, if the barn cannot be sealed tight and increasing the MV rate is not an option, another possible alternative is, if the facility has two rows of bi-flow inlets, the side of the inlet facing toward the curtains can remain open and the side that pushes air to the middle tightly closed. This keeps the lying area warm with good rotary airflow in the outside areas — it’s not ideal, but can be a solution. Furthermore, inlet control equipment, such as cables, springs, actuators, etc., should be checked regularly. Inlet opening size should be uniform across all the inlets, if not each one needs to be firmly adjusted.

Coming back to MV, the configuration of the fan(s) greatly impacts performance and the resulting airflow. Inspect the guards in front of fans, keep shutters clean and free of dust, maintain the integrity of discharge cones, maintain proper belt tension, and inspect fan blades for any issues. Since many MV stage fans are pit fans (and are rarely cleaned), it is critical the pump-out cover and intersection between fan housing and pump-out cover are very well sealed.

The use of variable speed fans during the MV stage has increased in popularity, but the following must be kept in mind to ensure successful MV with variable speed fans. To remain effective, a fan can only be slowed down so much using a variable speed drive. The most important thing to remember is that half voltage does not yield half airflow. For example, a 24-inch diameter fan at full voltage (230 volts) and 0.05 in. water will deliver 7,200 cubic feet per minute, but at 120 volts, only about 1,900 cubic feet per minute is delivered.

Also, fans should be protected from prevailing winds because fans operating at low speeds cannot operate against much pressure. This means, when setting up your variable speed fans, pay close attention to the motor curve (if available) and remember relation between voltage percent and airflow, they are not equal.

Proper management of equipment such as LP-forced air furnaces and brooders is also key for successful wintertime operation. Location of the temperature sensors for brooders should be in accordance with the manufacturer. If the temperature sensor is not in the correct place, being too close or not directly under the heat, this can result in false measurements and excess usage of LP. Make sure the brooder temperatures are reasonable and similar if more than one sensor is used. Both propane brooders and furnaces should be tested prior to winter to make sure relays, pilots, flame switches, etc., are all in good working order. In addition, the orifices should be cleaned per manufacturer’s instructions, typically with compressed air. Cleaning improves efficiency and ensures safe operation. When an orifice is cleaned incorrectly, and the hole becomes larger, excess carbon monoxide is released and propane is wasted. This can create an unsafe environment for both pigs and workers. Backup thermostat settings should also be inspected and modified to ensure heaters do not compete with the ventilation system and will function reliably when needed.

Now for some simple analysis and solutions for some common problems.
• Room is too cold: check and adjust temperature settings, ensure the temperature sensors are located in an area reflective of the conditions the pigs experience, seal uncontrolled infiltration sources, check required supplemental heat requirements, reduce MV rate.
• Cold drafts: adjust air inlets’ openings, seal exterior infiltration sources, and increase static pressure, verify with manometer.
• Excessive relative humidity can cause condensation on building surfaces (adjust room temperature, increase MV), near air inlets (could be improper mixing of cold fresh air with room air, so check inlet insulation), and lastly, near exhaust fans (install covers around fan and seal fan perimeters).
• Odor can be noxious and undesirable. Typically, improving air distribution/mixing or increasing the MV can reduce gaseous concentrations.
• Low static pressure: ensure infiltration locations are well-sealed and increase MV rate while simultaneously reducing inlet opening size.

The pigs can be a valuable source of feedback to help identify/troubleshoot many common problems associated with wintertime ventilation. Dirty pens in the winter can be caused by cold drafts in the sleeping area; hence, pigs may sleep in the dunging area. To avoid this, the combination of inlets, fan and static pressure need to be adjusted to ensure no cold air falls directly into the sleeping area and airspeed at the animal level does not exceed 25 feet per minute. Conversely, an environment that is too warm can cause dirty pens, which can be remedied with adjustments in the setpoint or setpoint differential temperatures between stages. Huddling pigs can indicate the room is too cold. Inspect room temperature and heaters — drafts and poor air distribution can cause pigs to huddle to get away from undesirable places. Frequent observation of the pigs’ patterns and behaviors can be extremely useful for improving the environment inside the room.

With winter just around the corner, it’s important to get a head start and put cold weather ventilation management on your mind. There are major economic, energy and performance consequences of poor ventilation in the winter. It is up to you to correctly inspect, test and operate equipment and controllers to ensure the best possible environment is provided to the pigs while minimizing costs. One of the most important things to emphasize this winter is sealing possible sources of infiltration (fans, holes, doors, curtains, pump out covers, joints, etc.) to achieve the static pressure needed for good air distribution, prevent drafts and properly ventilate. In addition, fans, heaters and inlets must also be tested and inspected throughout before and during winter to iron out any potential problems.

Lastly, always keep the pigs in mind and use them to help address problems. Successful wintertime ventilation can be tedious, often requiring numerous repetitions to get equipment, and controls working in harmony — but, the results are worth it.

More information and some of the reference material used for this column can be found at the following sources.
Farm Energy Initiative — Iowa State University Farm Energy Conservation & Efficiency. (2017). Retrieved from
MWPS. (1983). Structures and Environment Handbook. Ames, Iowa: Iowa State University Press.
Zhang, Y. (1994). Swine building ventilation: a guide for confinement swine housing in cold climates. Saskatoon, Canada: Prairie Swine Centre Inc.

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