Assessing Options for Ventilating Adult Cow Barns Making Sense of Too Many Choices!

Transcription

1 Assessing Options for Ventilating Adult Cow Barns Making Sense of Too Many Choices! Nigel B. Cook MRCVS University of Wisconsin-Madison School of Veterinary Medicine 2015 Linden Drive, Madison, WI Natural Ventilation Principles Nigel B. Cook MRCVS University of Wisconsin-Madison Gentle Upward Movement Winter Ventilation No Wind Outside 1. Open ridge 2. Open eaves 3. Adequate interior roof slope (1:4 minimum, smooth) Slow Overturn of Air Winter Ventilation Wind Blowing 4. Free from wind shadows Assessing Options for Ventilating Adult Cow Barns Making Sense of Too Many Choices! Ridge Vent Removes Hot Air Near Roof 5. East to West orientation Summer Ventilation Sidewall Doors Open Adjustable curtain inlets Ventilation = the provision of fresh air to a building space The fresh air displaces heat, moisture, noxious gases and airborne pathogens Sometimes the wind doesn t blow! Still air 19.9% of time in July in Madison Winds predominantly from South and SW 143 July Winds in Madison, Wisconsin

2 As facilities have got larger, cows have produced more milk, summers have become warmer, producers have looked for different options to ventilate and cool cows CFD model of 2 mph wind impacting two 500 cow nat-vent barns Mario Mondaca PhD Ideal Ventilation Design Cows generate a lot of heat! Maximum Practical Ventilation Rate 7,000 Ventilation Rate BTU per hour 6,000 5,000 4,000 3,000 2,000 1,000 0 Minimum Ventilation Rate for Moisture Removal Minimum Ventilation Rate for Air Quality Control Minimum Ventilation Rate to Maintain Optimal Environment Temperature 120lb cow 40 lb cow Resting human Ambient Temperature 144 Source: Ch 14 Ventilation of Agricultural Structures ASAE Monograph no. 6

3 Designing Ventilation Reality CFD Tunnel Barn Company specific recommendations Animal heat estimations are outdated Air moves down the alleys, not over the cows! Based on a series of studies summarized in 1959! Updated physiology but not recommendations Variable speed fans, controllers, sensors Confused producers! Mechanical Ventilation Systems Fan Specification Inlet design with Air speed Increased over recent years from 2.5 mph to 5-6 mph over cross sectional area of barn In cross vent barns - air speed under the baffle used (humidity) temperature controlled Body mass/heat transfer Usually quoted ~1000 CFM per adult cow or more curtains Air changes per hour (ACH) Traditionally aimed at 4, and ACH in winter, transition and summer respectively False ceiling (usually ~18 5.5m) Potential Benefits of Mechanical Systems More control! We can orient the barn however we choose We can build facilities for more cows on less land Cows don t bunch and few fly concerns No natural ventilation option Other Considerations Noise and vibration Odor control Fan maintenance Aesthetics Ability to let the cows outside 145

4 Fans direct air over the cow resting area in tunnels CFD Cross Vent Barn Air moves perpendicular to the feed lanes Baffles likely don t help much in a tunnel barn Air also moves down the cross alleys and short circuits between fans Air still wants to go where we don t want it to go! Drags air toward the ends of the pen, away from the middle... None of these strategies solved the main problem of tunnel barns how do we get fast moving air in the resting space? 146

5 Cross-vent Baffle Problems Hybrid Barns Feed curb is a baffle too! Mechanically ventilate in the summer and transitional periods, naturally ventilate in the winter Baffles trap air between them especially a Manage the ridge opening curtain or cupola problem in the winter at lower air speeds Side wall curtains along the length of the barn (partial) Barns are specified based on air speed below Increased cost of construction over a 24/7 the baffle without enough attention to actual air changes per hour achieved Comparison of Summer Ventilation Specification Methods: 1. 1,000 CFM per cow ft/min across the cross sectional area of the barn, and air changes per hour. Cross Sectional Area wind speed (ft/min) Air Changes per Hour Tunnel Ventilation (per 500 cows) Cross Ventilation 8-row (per 1000 cows) Cross Ventilation 16-row (per 2000 cows) , mechanically ventilated barn Can let the cows outside! CFM/Cow 1,875 2,396 1,000 2,219 2,561 1,000 1,106 2,815 1,000 Cross vents without baffles! Now specify the ventilation by body mass or ACH not air speed and put fans over the stalls 147

6 Critical Elements of Ventilation Design In both types of facility, 1. FAST moving air in the resting microenvironment we have gravitated back to ensuring 2. Sufficient air changes per hour to that we have fast moving air in the remove heat and moisture from the barn resting space. using fans 3. System should work as well in the winter as it does in the summer Cows prefer fast moving air when they are hot Target ~400 ft/min (2 m/s) Air velocity & wet skin temperature Heat Stress and Resting Behavior Mean THI 120 Lying Time (h/d) THI Lying Time (Hours/Day) h/d loss in lying time in 6 days! =100 ft/m=1.1mph =400 ft/m=4.5mph =200 ft/m=2.2mph Day 30 cows followed for 6 days during a heat stress spike Berman, JDS 91:4571, 2008 Concept of Biofeedback (Atkins and Mondaca) How do we provide fast moving air? Get the cows to operate the system when they need it! Fans Tubes Baffles 148

7 Variation in fan performance Fan Diameter 0.0 per Fan Watts Used per Fan CFM/Watt per Fan Fan ,100 1, Fan , Fan ,500 1, Fan ,515 1, Fan , Fan ,379 1, Fan ,645 2, Positive pressure tube system to drive fast moving air into the lying area directly ~100 stall pen current maximum Composite Velocity Map for a 20 HVLS Fan 16 Above Floor, Spaced at 60 (Kammel et al. 2001) If we ensure that we have fast moving air over the resting space, we just need to provide sufficient ACH for the barn as a whole with the ventilation system to remove the heat and moisture. 40, 50, 60 ACH? 149

8 Mean ± SD Fan Specifications at 0.10 H2O Static Pressure With all this variation, can we identify an economical solution? Fan Type CFM CFM/Watt kw-h N Circulation 29,837 ±5, ± ± Exhaust 27,353 ±4, ± ± Cyclone 48, Mondaca and Cook, Unpublished Fan choice has a SIGNIFICANT impact on the cost of operating each system! Core Pen Used to Create Ventilation Designs Based on The Dairyland Initiative recommendations Houses 126 cows per pen (consistent with average pen size in WI survey; Brotzman et al., 2015) Capital Building Costs Did not include excavation or manure handling, parlor, holding area, back up generator requirements Did include construction costs for barn including fans, fan installation, electrical supply and curtains Local builders in Wisconsin quoted to build each facility 7 Barn Designs Ventilation Running Costs Modeled for 7 US regions using temperature data for 6 years Activate fans using three ramping models during transitional periods and 4 air changes per hour in the winter at 40 o F and 5 different summer set-points Fan usage charged at $0.10/kwh Not included: maintenance costs of fans Ventilation Specifics Ventilation Type System Name Ventilation System per Barn Natural NAT48 26 Circulation Fans alternating every 48' over stalls Natural NAT24 52 Circulation Fans alternating every 24' over stalls Tunnel TUN60 48 Exhaust Fans (60 ACH) Tunnel TUN40 32 Exhaust Fans (40 ACH) & in. Circulation Fans every 24' over stalls Hybrid HYB40 32 Exhaust Fans (40 ACH) & in. Circulation Fans every 60 over stalls & 11 Ridge Fans Cross 8 row 8CRO Exhaust Fans (500 ft min -1 under the baffles) Cross 16 row 16CRO Exhaust Fans (500 ft min -1 under the baffles) Mechanical Ventilation Ramping Functions Air Changes per Hour Linear Linear - Discrete 10 Exponential Air Temperature F 150

9 Capital Costs Ventilation System Building Cost Ventilation Installation Cost Total Costs (+5% Fee) Total Financed Cost (4.25 % APR) Total Capital Cost/Cow/Year NAT48 2,156,432 62,860 ± 5,886 2,330,257 2,908, NAT24 2,156, ,720 ± 11,773 2,396,260 2,991, TUN60 2,145, ,095 ± 44,738 2,444,397 3,051, TUN40 2,145, ,682 ± 33,915 2,513,263 3,137, HYB40 2,309, ,732 ± 35,260 2,712,806 3,386, CRO500 2,099, ,110 ± 42,045 2,384,444 2,976, CRO500 3,611, ,110 ± 42,045 3,971,833 4,958, Loan amortized over 10 years at 4.25%. Cost per cow per year for 1,008 cows (2016 in 16CRO500) housed in barn Wide body cross vent barns are the cheapest to build and operate, but they have operating issues!! Hybrid tunnels are the most expensive to build and operate up to ~22% more than a NAT24, but have the most flexibility Cost differential between HYB40 and 16CRO500 is $121/cow/year = ~ 2.0 lb milk per cow per day ($0.16/lb) Total Operating Costs Per Cow in 2 Climates Madison - WI Jacksonville - FL Operating Cost/cow/year Cost/Cost of Nat24 Operating Cost/cow/year Cost/Cost of Nat24 NAT NAT TUN TUN HYB CRO CRO Fine tuning. Most mechanical ventilation operating systems cost ~ same in temperate climates in the US at times cost of a naturally ventilated barn (NAT24) Ventilation costs in hotter climates ~ double more temperate climates across most mechanical systems Cost savings of 16CRO500 relate to added cows with no additional fans and can be cheaper to run in hotter climates than naturally ventilated barns Summer Set-Temperature To change from 72 to 68 F (22.2 to 20 C) activation temperature costs ~ $6 per cow per year It would cost ~$4 more to reduce to 65 F (18.3 C) Costs increase significantly with fan selection Total Costs Per Cow in 2 Climates Total Cost per Cow/year Madison - WI Cost/Cost of Nat24 Jacksonville - FL Total Cost per Cow/year Cost/Cost of Nat24 NAT NAT TUN TUN HYB CRO CRO Ramping and Control Functions Variable speed fans may provide ~$7 per cow per year savings from Atkins et al. (2015) Exponential vs. Linear Ramping ~$5 per cow per year savings An Ideal system could save ~$12 per cow per year in operating costs, but how much do these systems cost to implement? The economic opportunity for biofeedback is small when electricity is cheap, but the beneficial effects on the cow may be great 151

10 Operating Costs Per Cow Per Year Madison Florida NAT48 16CRO500 NAT48 16CRO500 HYB40 HYB40 8CRO500 8CRO500 NAT24 TUN40 NAT24 TUN40 TUN60 TUN60 Choice of fan can impact operating costs by $30 per cow per year or more! 7 systems in Madison WI for average year using linear ramp and T 68 F Summary If location & orientation allow, natural ventilation is still a great option Consider mechanical ventilation where site is compromised and where wind shadows are likely Three key mechanical ventilation criteria: Air speed at the stalls 400 ft/min 4.5 mph (2 m/s) Ventilation rate (~40-60 ACH in the summer, 4 ACH in winter) Transition between hot and cold weather Cross, Tunnel and Hybrid barns have pros and cons Best to choose the optimal system for the given situation the benefits of good ventilation out way the negative impact to the cow Thank you! 152