VENTILATING AND HEATING SMALL LIVESTOCK ROOMS NEW 88:09 G.R. Bayne, C.M. Gorman, D.E. Darby, J.E. Turnbull Modern livestock facilities frequently include one or several small rooms to house the young, more sensitive animals. Examples of small rooms with critical ventilation problems include pig facilities like multi-room, all-in/all-out furrowing and nursery rooms, dairy calf nurseries designed to isolate young calves from the adult dairy herd, and small poultry buildings. In all these examples, the smallest available farm -grade exhaust fans are vastly oversized for winter ventilation. A small livestock room is hard to ventilate. The small volume of air in the room is very sensitive to changes in ventilation rate, heat supply and drafts due to uncontrolled air distribution. These problems are made more critical by the lack of fans and heaters small enough. Another complicating factor is that many small rooms house young animals that produce only a small part of the required winter heat. Therefore, using thermostats to control ventilation rate is not as easy as it is in buildings housing more and larger animals, making interaction with the heating controls more critical. Consider, for example, the typical nursery room for weanling pigs. A group of 50-60 young pigs, average weight 7 kg, is weaned and moved to a freshly-cleaned nursery room in January. Referring to Plan M-9700, the minimum (step 1) winter ventilation rate for this group is only 50 pigs x 0.4 L/s = 20 L/s (or 43 cfm). However, the same room in July must be able to handle 50-60 pigs approaching 25 kg average weight. These require a maximum ventilation rate of 50 pigs x 16 L/s = 800 L/s (or 1700 cfm). This is 40 times the 'step 1' winter rate! The summer ventilation is easy- most manufacturers can supply a fan to exhaust around 800 L/s. But there are few, if any, heavy-duty farm fans small enough to deliver a reliable 20 L/s. Another problem is that conventional air inlets do not work well in the winter. The small flow of cold, fresh air lacks the momentum to properly mix and circulate with the room air. Instead, this cold, denser air sinks to the floor, displaces the warm inside air upwards, and chills the young animals. The ideal ventilation and heating system for small rooms such as calf nurseries, swine furrowing rooms and weanling rooms should have the following features: A continuous 'step 1' ventilation for cold weather, with a manual adjustment for the operator to fine tune this minimum rate according to animal population, odors and humidity; Automatic control of the intermediate ventilation rates (steps 2 and 3) based on room temperature, and preferably interlocked with the heating (see Plan M-9701); A high-capacity, two-speed summer fan (steps 4 and 5), controlled by thermostat; A fresh air inlet integrated with a ducted recirculation fan, to ensure uniform distribution and adequate mixing of the fresh air; and A compatible system for supplemental heating, interlocked with the intermediate ventilation steps 2 and 3 so that heating is reduced as ventilation is increased. This is especially important in small rooms such as weanling pig nurseries where the animals produce a very small part of the necessary heat. The Canada Plan Service prepares detailed plans showing how to construct modern farm buildings, livestock housing s ystems, storages and equipment for Canadian Agriculture. To obtain another copy of this leaflet, contact your local provincial agricultural engineer or extension advisor.
STEP 1 WINTER VENTILATION Several attempts have been made to obtain the low ventilation rate needed for step 1: 1. SMALL, SINGLE-SPEED FAN This would be ideal, but nobody makes a heavy-duty farm fan small enough for these rooms. Also lacking is a manual adjustment that permits the operator to balance ventilation, humidity and odor control against heating costs. 2. TWO-SPEED, MULTI-SPEED OR VARIABLE-SPEED FAN Attempts have been made to give the complete ventilation range with only one variablespeed or multi-speed fan. This is not possible. Special two-speed fans are available with low-speed windings to give 1/3 of full speed, but this is seldom low enough for a small room. And the typical voltage-modulated variable-speed and multispeed fans, when running at less than 30-35% of full speed, have unstable airflow characteristics. They may even fail to start at the reduced voltage (some electronic controllers give the motor a burst of full line voltage to get them started). At least three variable-speed fans would be required to give the full winter-to-summer range of ventilation rates - an expensive alternative! 3. INTERMITTENT FAN OPERATION Step 1 fans have been operated by an adjustable cycle timer (3 minutes on, 7 minutes off, for example) to give a reduced effective ventilation rate. However, this produces erratic airflow patterns, excessive temperature fluctuations and backdrafting of room air through the inlets during 'fan off' periods - not recommended! 4. RESTRICTED FAN OUTPUT This is done by choosing an exhaust fan that is only 50-60% oversized for step 1 and installing it in a throttling box with an adjustable opening from the room. The opening (usually a simple slide valve) is adjusted by trial and error. There is an element of risk here -the motor may overheat if the valve is closed too far. In any case, locate the valve opening directly in front of the motor, for air-over cooling. 5. ONE LARGER FAN SERVING SEVERAL ROOMS The step 1 fan is installed at the outlet end of an exhaust duct that runs through or under several rooms. In each room a slide valve is adjusted to balance the airflows into the duct. A change in slide valve setting in one room alters the ventilation in the other rooms, therefore some trial and error is necessary; once set up and balanced, keep the valve adjustments to a minimum. The exhaust duct may be a tunnel system below the floor, permitting the step 1 airflow to be drawn from the manure gutters below the slotted floors. 6. ONE HEAT EXCHANGER SERVING SEVERAL ROOMS A variation on system 5 - an air-to-air heat exchanger replaces the step 1 multi-room exhaust fan. Thus, heat reclaimed from several rooms preheats fresh air that is fed back to a common preheat hallway. Short lengths of insulated duct between trusses in the attic connect from the preheat hallway to the fresh air inlets in each room (Figure 4). To ensure that the 'fresh' air is not contaminated by stale exhaust air, select a heat exchanger with zero crossover leakage. Also, separate the outdoor exhaust from the inlet opening, to minimize cross-contamination of the air supplies. 7. COMBINATION EXHAUST/RECIRCULATION SYSTEM This system addresses most of the problems outlined above with respect to obtaining an adjustable, reliable and correct ventilation rate for step 1 in each room. In addition, it provides for controlled recirculation of room air to improve air mixing, control drafts and eliminate temperature stratification. It also provides enough fresh air inlet capacity to automatically handle up to the maximum summer ventilation requirements. From this discussion, systems 4 and 7 emerge as most suitable for single, small rooms, and systems 5 and 6 for multiple rooms. System 7, applicable to both single and multiple rooms, is the most innovative; the following describes it more completely. COMBINATION EXHAUST/RECIRCULATION SYSTEM Figure 1 shows the essentials of a combined exhaust/ recirculation system for a small livestock room. In principle, the recirculation fan 1 serves two purposes, recirculation and step 1 ventilation. If this fan is a little oversized, it doesn't matter because its seed can be reduced with the manual speed control 10. Pressurized warm air in the duct 2 jets out through the holes 3, as well as to outdoors through the slide valve 4. The part of the airflow that escapes at 4 determines the step 1 ventilation rate. Provided that the room has tight construction and weather stripped doors, air escaping at 4 is replaced by an equal volume of fresh air entering through the automatic inlets 14. Recirculated air jets 3 enter just below the inlets, mixing and carrying the fresh air across the ceiling, to prevent cold down-drafts. As with any negative-pressure ventilation system, doors and other openings must be sealed or weatherstripped so that the fresh air comes in through the inlets as intended. Exhaust fans not used in winter must especially be sealed with tight-fitting insulating covers (6, Figure 1) since the commercial back-draft shutters are not tight enough for small rooms. Fans that operate intermittently during winter should have additional backdraft dampers that seal better than the commercial shutters normally supplied by fan manufacturers (see 10, Figure 3).
Tuning the step 1 rate The beauty of this system is that the operator can set any step 1 rate needed, from maximum down to zero if necessary. The problem is that nothing indicates directly what step 1 ventilation rate is achieved. Condensation on walls and ceilings and excessive odors (the 'nose test') can indicate that the ventilation rate is too low during cold periods. A more precise method is to measure the relative humidity (RH), then adjust the exhaust rate to give 50-70% RH. To change the step 1 rate, the trick is to chan a stepwise the fan speed 10 and the slide valve 4 while reading the manometer 11 indicating the duct pres sure. A duct-to-room pressure difference of 25 Pa (0.10 in. water gauge) will give 6 m/s airspeed at the holes 3. To increase the step 1 ventilation, open slide valve 4 a little, then turn up the fan speed at 10 to regain 25 Pa duct pressure. To decrease ventilation, do the reverse. To check static pressure drop through the fresh air inlets, switch to another small rubber tube 13, leading from the attic to the manometer. Supplementary heating 13 Do not place heaters close to the recirculation fan 1; part of the airflow from this fan is discharged directly outside at 4, which would waste some heat. An electric or hot water fan-forced heater can be hung at the other end of the room, aimed to discharge warmed air under, and parallel to, the recirculation duct 2. Check with smoke to make sure the heater fan is not creating drafts in the pens or upsetting the recirculation air flow from the duct holes 3. Another alternative is to hang hot water fin-tube convectors (or better still, black iron pipe radiators) under the duct 2. With recirculation, there is no advantage to putting the radiators too low where they may restrict headroom and where they can be damaged by animals or during cleaning operations. Self-adjusting Air Inlets Figure 2, item 4 shows one version. With baffles and counterweights made as shown, adjust the counterweights to 105 mm (4.1 in.), measured from the center of the counterweight to the 'hinge' (edge of 6). This lets the baffles start to open at about 10 Pa (0.04 in. of water), a pressure well below the 25 Pa pressure in the recirculation duct. Then turn on the winter ventilation, carefully observe the opening of each baffle, and fine-tune the counterweights so that all baffles open the same amount. Increasing ventilation and decreasing heat Referring again to Fig. 1, with rising room temperature, ventilation is increased to step 2 when the 2-stage thermostat 7 starts the two-speed fan 5. If a multispeed or variable-speed fan is used instead of two speed, a matching temperature controller replaces thermostat 7. Whichever control is used, it can be interlocked with the heating so that the heat is reduced when the fan speed is increased, and vice versa. One way, with a fan-forced electric heater, a two-stage thermostat and two-speed ventilation fan, 1 recirculation + step 1 fan, manually controlled variable speed 2 recirculation duct, sized for airspeed less than 3 m/s (600 ft/min) 3 recirculation air holes, sized for 6 m/s (1200 ft/min) 4 step 1 exhaust air slide valve, to outside weatherhood 5 step 2/step 3 exhaust fan 6 step 4/step 5 summer exhaust (shown covered and sealed for winter) 7 two-stage thermostat, interlocked to increase fan 5 and decrease heating on 12 temperature rise, and vice versa 8 two-stage thermostat controls step 4/step 5 fan 6 9 max/min thermometer 10 manual speed control for recirculation fan 1 11 manometer measures pressure difference, duct 2 to room 12 additional manometer tube from attic fresh air supply 13 fan-forced electric or hot water heater, or hot water convectors (black iron pipe, or finned tube) on wall below 2 14 automatic fresh air inlets, through ceiling Figure 1 Combination exhaust recirculation system for ventilating and heating small rooms
1 rectangular duct made from 12.5 mm (1/2 in.) plywood 2 bottom s ecured with cornice hooks; for cleaning duct, turn hooks 1/2 turn and remove bottom 3 recirculation air holes; see text for size and spacing 4 counterweighted inlet baffle; cut two from 38 x 600 mm (1.5 x 24 in.) styrofoam SM shiplap; 3 x 3 mm saw kerf secures 4 to J-strip 6 5 25 x 100 mm (1 x 4 in.) styrofoam insulation strip 6 prepainted steel Jstrip hinge for4 7 counterweight; concrete-filled 341 ml aluminum beer can with 5/16 in. plated threaded rod 450 mm (18 in.) long; use one counterweight for each 1200 mm of inlet 8 plated washer brazewelded to slot in head of stove bolt, plywood washers glued top and bottom 9 slot extends hole 3 to allow free swing of baffle 4 and counterweight 7 10 end stop of 25 mm (1 in.) Styrofoam and nailed in place Figure 2 Details of recirculation duct and integrated self-adjusting fresh air inlet
is to wire for full heat with ventilation fan 5 off, part heat with the fan on low, and no heat with the fan on high speed. This will require wiring modifications inside the heater, and special inspection and approval from the power authority. Another promising heat control option is to use one of the new electronic pulsing thermostats, such as the Honeywell TC-900. It measures room temperature every 12 seconds; if the room is below the set point temperature, it energizes the heater for the next 12 seconds, then checks again. This gives a fully-modulated heat control that can almost eliminate tem perature fluctuations. There is a complication, however; the 12-second cycling is no problem to the heater element, but the heater fan motor could not stand this. This motor must be electrically isolated from the heater element and hard-wired to run continuously; this also requires special inspection and approval by the power authority. If using a variable-speed or multi-speed fan controller, it can be wired to a wall receptacle so that either the winter or the summer fan can be plugged into the same controller, for warm weather. This requires a slightly larger summer fan but it is cheaper than buying two expensive controllers. Recirculation Fan 1 and Duct 2 The recirculation fan in this system serves a double purpose, so it is sized for recirculation plus 1.5 times the minimum step 1. For recirculation use 1.33 L/s per m3 (or 0.08 cfm per ft³) of room volume. For rooms with pen floors raised above the alley, calculate only the room volume above the pen floor level. For rooms with sloping ceilings, use the average ceiling height in calculating the room volume. For step 1 ventilation, Table 2 gives some typical rates for animals in small rooms. Choose a variable-speed fan that will deliver the required recirculation plus ventilation rate at a static pressure of 25 Pa (0.1 in. water gauge). For example, select a combined recirculation + exhaust fan for 64 weanling pigs, 7-25 kg, continuous housing, in a room 4.8 m x 4.5 m x 2.4 m = 52 m³ (or 16 ft x 15 ft x 8 ft = 1920 ft³). From Table 2, the step 1ventilation rate is 0.7 L/s (1.5 cfm) per pig. In metric, recirculation rate, Qr = 52 m3 x 1.33 L/(s.m³) ventilation rate, Qv = 1.5 x 0.7 L/s x 64 pigs total fan capacity Qr + Qv, @ 25 Pa static pressure = 69 L/s = 67 L/s = 136 L/s The recirculation duct may be round perforated polyethylene plastic tubing (cheap, but hard to clean), or rigid plastic pipe (more expensive, more durable, but still hard to clean), or rectangular plywood. Cheap poly tubing has the advantage of allowing some inexpensive experimentation with ducted recirculation. Figure 2 shows details of the rectangular duct com bined with counterweighted fresh air inlets. Plywood ducting seems to collect less dust than plastic, perhaps because of static charges that attract dust to plastics. Assuming a rectangular plywood duct, make it the same width as the fan frame so that the tapered transition part is easier to build. To save cutting and waste, make the duct panels of widths that can be cut from 1220 mm (48 in.) plywood width; for example use panels 240 mm (9.5 in.), 300 mm (12 in.) or 400 mm (16 in.) in width. The minimum duct depth is 240 mm (9.5 in.) to allow for the counterweights to swing free. Typical duct dimensions, corresponding cross-section areas and maximum air flows for each duct size are given in Table 1. Next check that airspeed along the duct is less than 3 m/s (600 ft/min). Table 1 also gives the maximum air flows, at a point just downstream from the fan. The duct size is usually determined by a width to fit the fan frame and a depth to clear the counterweights, rather than by the maximum airspeed. An oversized duct with lower duct airspeed is not a bad thing-the lower the duct airspeed, the more uniform will be the airspeed through the holes. Next, the holes. Bigger holes increase the throw of the jets of recirculated air, and vice versa. The objective is to choose a hole size consistent with the distance from the duct to the opposite wall. Table 3 gives general guidelines for hole size. The number of holes is based on obtaining ajetvelocityof6 m/s (1200 ft/min) and an effective jet cross-section area of 0.75 times the actual area of the hole. A formula for calculating the number of holes, N, is: in metric, in imperial: N = Qr N = Q, 4500 Ao 900 Ao where Qr = recirculation rate, L/s (or cfm) Ao = actual hole area, m² (or ft²); see Table 3 In imperial, recirculation rate, Qr = 1920 ft3 x 0.08 cfm/ft³ ventilation rate, Qv = 1.5 x 1.5 cfm x 64 pigs total fan capacity Qr + Qv, @ 0.1 in. water gauge = 154 cfm = 144 cfm = 298 cfm TABLE 1 TYPICAL PLYWOOD DUCT SECTIONS AND MAXIMUM AIRFLOWS Width x Depth Area Max. duct airflow mm x mm (in. x in.) m² (ft²) L/s (cfm) 300 x 240 (12 x 9.5) = 0.072 (0.79) 216 (470) 300 x 300 (12 x 12) = 0.09 (1.0) 270 (600) 400 x 240 (16 X 9.5) = 0.096 (1.05) 288 (630) 400 x 300 (16 x 12) = 0.12 (1.33) 360 (800) 600 x 240 (24 x 9.5) = 0.14 (1.58) 420 (950) 600 x 300 (24 x 12) = 0.18 (2.00) 540 (1200)
TABLE 2 VENTILATION RATES FOR SMALL LIVESTOCK ROOMS Step 1 Steps 2-3 Summer Livestock continuous maximum L/s (cfm) L/s (cfm) L/s (cfm) Sow and litter 7 (15 ) 20-40 (43-85) 144 (300) Weanling pig, 7-25 kg all-in/all-out 0.4 (0.9) 2-5 (4-11) **16 **(34) continuous housing 0.7 (1.5) 3-6 (6-13) **12 **(25) Dairy calf, 45-135 kg all-in/all-out *5-10 *(11-21) 15-30 (32-64) 80 (170) continuous housing *7.5 *(16) 15-30 (32-64) 60 (128) * But not less than 4 air changes per hour ** But not greater than 1 air change per minute Note that the hole spacing should be adjusted to one that divides evenly into 2440 mm (8 ft) so that all the duct side panels can be stacked up and drilled together. Typical hole spacings are 102, 152, 203, 244, or 305 mm (4, 6, 8, 9.6 or 12 in.). Never space the holes at greater than 305 mm (12 in.). Following the previous example (page 5), design a recirculation-plus -exhaust duct for 64 weanling pigs, recirculation rate Qr = 69 L/s (154 cfm). The duct is at the ceiling centerline, with holes 2.1 m (7 ft) from the two side walls. Table 3, for a throw of 2.1 m (7 ft), suggests 22 mm (7/s in.) diameter holes, with each hole area Ao = 0.00038 m2 (0.0042 ft²). Calculate the number of holes, N, as follows: in metric, N = Qr = 69 = 40 holes 4500 A0 4500 x 0.00038 (20 each side of duct) in imperial, N = Qr = 154 = 40 holes 900 A0 900 x 0.0042 (20 each side of duct) TABLE 3 RECIRCULATION DUCT HOLE SIZES Distance from duct Hole Area of to opposite wall diameter one hole, Ao m (ft) mm (in.) m² (ft²) 1.8 (6) 19 (0.75) 0.00028 (0.0031) 2.1 (7) 22 (0.875) 0.00038 (0.0042) 2.4 (8) 25 (1.0) 0.00051 (0.0055) 3.0 (10) 32 (1.25) 0.00079 (0.0085) 3.6 (12) 38 (1.5) 0.00114 (0.0123) 4.2 (14) 45 (1.75) 0.00155 (0.0167) 4.8 (16) 50 (2.0) 0.00203 (0.0218) 6.0 (20) 65 (2.5) 0.00317 (0.0341) corresponding to the number and size of animals in the room. To estimate a trial setting of the slide valve at a duct pressure of 25 Pa (0.10 in. water gauge), assume the exhaust flow wili be about 4800 L/s per m2 (6.7 cfm per in.2) of opening area. FRESH AIR INLETS Allowing space for the recirculation fan at one end of the duct, the duct length is 4.1 m (13.7 ft). The hole spacing is 4.1 m/20 holes = 0.205 m = 205 mm; use 203 mm (or, 13.7 ft/20 holes = 0.68 ft. = 8 in.). Next, size the duct for the 136 L/s (298 cfm) total airflow. From Table 1, a duct 300 x 240 mm (12 x 9.5 in.) will easily handle this flow, but increasing the duct width to 400 mm (16 in.) will make the fan-to-duct transition a simple one-way taper, as shown in Figures 1 and 3. Step 7 exhaust slide valve 4 This slide valve should slide freely and be able to open to almost the full size of the duct 2. When tuning the exhaust rate for winter conditions, mark the wall to indicate valve settings that give satisfactory ventilation rates Figure 2 shows the fresh air inlets combined with the recirculation duct. The objective is to introduce the fresh air just above, and as close as possible to, the mixing jets of recirculated room air. With recirculation it isn't necessary to make the fresh air inlets continuous. Each 1220 mm (4 ft) inlet unit can adjust automatically from a trickle of air in winter to over 300 L/s (640 cfm) in hot weather. Two or four inlet units spaced at 1/4 and 3/4 of the room length can easily handle the typical small room. As stated previously, it is essential to adjust the counterweighted inlets for equal openings. With new construction, the easiest way to supply fresh air to the inlets is to use an insulated attic with a white roof and screened perimeter slots all around (Figure 3). Close the perimeter slots to about 25 mm (1 in.) for winter; for summer,
1 recirculation fan 2 recirculation duct with air holes 3 fresh air inlets from attic 4 step 1 exhaust slide valve 5 outside weatherhood, to below midheight of wall, 100 mm (4 in.) from wall 6 supplementary heating 7 white roofing and insulation 8 perimeter attic vent slot, bird screen; 150 mm (6 in.) flaps, open for summer, 25 mm (1 in.) slot in winter 9 thermostats and max/min thermometer 10 exhaust fan (steps 2 & 3), winter backdraft control box is removed in summer Figure 3 Inlet and recirculation duct arrangements drop the flaps to give about 150 mm (6 in.). Insulate under the roofing with inexpensive 40-50 mm (1.5-2 in.) plastic-faced roll blanket insulation to prevent excessive increases in attic temperature due to the summer sun. With existing construction, it is probably easier to build big, short insulated attic ducts leading from a ventilated hallway (see 5, Figure 4). With moderate winter climates and a well-designed recirculation sys tem, it is not necessary to preheat the hallway if there is enough controlled heating in each room. However, where winter temperatures sometimes remain below -30 C for extended periods (as in the prairies), the inlet flaps can ice up and fail to control the fresh air flow. In this case, use the hallway or another space as a preheat chamber, adding enough heat to maintain it above freezing. exposed to the inside humidity and manure gases. Therefore, an extra backdraft enclosure is needed for the step 2/step 3 fan. Make an airtight box from 38 mm (1 1/2 in.) extruded polystyrene foam board, glued together with a suitable waterproof adhesive (e.g., Stix-A-Foam). A gravity-closed bottom trap door is hinged on a strip of plastic clamped along one edge. Make the trap door opening at least 75% of the fan opening area. Check to make sure the trap door comes up against the motor or fan guard so that it doesn't stick open. This enclosure will restrict the fan too much in warm weather. For winter, clamp the cover tightly over the fan using screw-eyes and a rubber hold-down strap, but remove and store it for the other seasons. ICING OF FANS As mentioned previously, the step 4/step 5 summer exhaust fan can be readily sealed for winter. However, the step 2/step 3 fan must be ready to start at any time. The factory-made backdraft shutters don't seal tightly enough; they leak in some cold air whenever the fan is off. Also, exhaust fans are susceptible to icing and rapid corrosion when constantly
1 exhaust air pipes from manure gutter to 150-200 mm (6-8 in.) duct under feed alley 2 slide valves adjust and balance the step 1ventilation rates in each room 3 main collector duct, 300-450 mm (12-18 in.) rigid plastic pipe. Ducts may be under concrete floor 4 air-to-air heat exchanger provides step 1 exhaust, heats incoming fresh air to preheat hallway 5 ceiling opening with 12 x 12 mm (1/2 x 1/2 in.) rodent screen to insulated attic duct between trusses 6 automatic fresh air inlets from attic duct 7 recirculation fan and duct with air holes 8 summer air inlet to hallway, remote from 4, with bird/rodent screen Figure 4 One heat exchanger serving several small rooms