1、24.1CHAPTER 24ENVIRONMENTAL CONTROL FOR ANIMALS AND PLANTSDESIGN FOR ANIMAL ENVIRONMENTS. 24.1Cooling and Heating 24.4Ventilation 24.5Ventilation Management 24.6Recommended Practices by Species 24.7DESIGN FOR PLANT FACILITIES. 24.10Greenhouses . 24.10Plant Growth Environmental Facilities . 24.16Othe
2、r Plant Environmental Facilities. 24.21HE design of plant and animal housing is complicated becauseTmany environmental factors affect the production and well-being of living organisms. The financial constraint that equipmentmust repay costs through improved economic productivity must beconsidered by
3、 the designer. The engineer must balance costs of mod-ifying the environment against economic losses of a plant or animalin a less-than-ideal environment.Thus, design of plant and animal housing is affected by(1) economics, (2) concern for both workers and the care and well-being of animals, and (3)
4、 regulations on pollution, sanitation, andhealth assurance.1. DESIGN FOR ANIMAL ENVIRONMENTSTypical animal production plants modify the environment, tosome degree, by housing or sheltering animals year-round or forparts of a year. The degree of modification is generally based on theexpected increase
5、 in production. Animal sensible heat and moistureproduction data, combined with information on the effects of envi-ronment on growth, productivity, and reproduction, help designersselect optimal equipment. Detailed information is available in aseries of handbooks published by the MidWest Plan Servic
6、e. Theseinclude Mechanical Ventilating Systems for Livestock Housing(MWPS 1990a), Natural Ventilating Systems for Livestock Housingand Heating (MWPS 1989), and Cooling and Tempering Air forLivestock Housing (MWPS 1990b). ASAE Monograph 6, Ventila-tion of Agricultural Structures (Hellickson and Walte
7、r 1983), alsogives more detailed information.Design ApproachEnvironmental control systems are typically designed to maintainthermal and air quality conditions within an acceptable range and asnear the ideal for optimal animal performance as is practicable.Equipment is usually sized assuming steady-s
8、tate energy and massconservation equations. Experimental measurements confirm thatheat and moisture production by animals is not constant and thatthere may be important thermal capacitance effects in livestockbuildings. Nevertheless, for most design situations, the steady-stateequations are acceptab
9、le.Achieving the appropriate fresh air exchange rate and establish-ing the proper distribution within the room are generally the twomost important design considerations. The optimal ventilation rate isselected according to the ventilation rate logic curve (Figure 1).During the coldest weather, the i
10、deal ventilation rate is thatrequired to maintain indoor relative humidity at or below themaximum desired, and air contaminant concentrations withinacceptable ranges (Rates A and B in Figure 1). Supplementalheating is often required to prevent the temperature from drop-ping below optimal levels. In
11、milder weather, the ventilation rate required for maintainingoptimal room air temperature is greater than that required for mois-ture and air quality control (Rates C and D in Figure 1). In hotweather, the ventilation rate is chosen to minimize the temperaturerise above ambient and to provide optima
12、l air movement over ani-mals. Cooling is sometimes used in hot weather. The maximum rate(D) is often set at 60 air changes per hour (ach) as a practical maxi-mum.Temperature ControlThe temperature in an animal structure is computed from thesensible heat balance of the system, usually disregarding tr
13、ansienteffects. Nonstandard buildings with low airflow rates and/or largethermal mass may require transient analysis. Steady-state heattransfer through walls, ceiling or roof, and ground is calculated asThe preparation of this chapter is assigned to TC 2.2, Plant and AnimalEnvironment.Fig. 1 Logic f
14、or Selecting Appropriate Ventilation Rate in Livestock Buildings(Adapted from Christianson and Fehr 1983)24.2 2015 ASHRAE HandbookHVAC Applicationspresented in Chapters 25 to 27 of the 2013 ASHRAE HandbookFundamentals.Mature animals typically produce more heat per of unit floor areathan do young sto
15、ck. Chapter 10 of the 2005 ASHRAE HandbookFundamentals presents estimates of animal heat loads. Lighting andequipment heat loads are estimated from power ratings and operat-ing times. Typically, the designer selects indoor and outdoor designtemperatures and calculates the ventilation rate to maintai
16、n the tem-perature difference. Outdoor design temperatures are given in Chap-ter 14 of the 2013 ASHRAE HandbookFundamentals. The sectionon Recommended Practices by Species in this chapter presentsindoor design temperature values for various livestock.Moisture ControlMoisture loads produced in an ani
17、mal building may be calculatedfrom data in Chapter 10 of the 2005 ASHRAE HandbookFunda-mentals. The mass of water vapor produced is estimated by dividingthe animal latent heat production by the latent heat of vaporizationof water at animal body temperature. Spilled water and evaporationof fecal wate
18、r must be included in the estimates of latent heat pro-duction within the building. The amount of water vapor removed byventilation from a totally slatted (manure storage beneath floor)swine facility may be up to 40% less than the amount removed froma solid concrete floor. If the floor is partially
19、slatted, the 40% max-imum reduction is decreased in proportion to the percentage of thefloor that is slatted.Ventilation should remove enough moisture to prevent conden-sation but should not reduce the relative humidity so low (less than40%) as to create dusty conditions. Design indoor relative humi
20、dityfor winter ventilation is usually between 70 and 80%. The wallsshould have sufficient insulation to prevent surface condensation at80% rh inside.During cold weather, ventilation needed for moisture controlusually exceeds that needed to control temperature. Minimum ven-tilation must always be pro
21、vided to remove animal moisture. Up toa full day of high humidity may be allowed during extremely coldperiods when normal ventilation rates could cause an excessiveheating demand. Humidity level is not normally the controlling fac-tor in mild or hot weather.Air Quality ControlContaminants. The most
22、common and prevalent air contami-nants in animal buildings are particulate matter (PM) and gases. Inanimal buildings, particulate matter originates mainly from feed, lit-ter, fecal materials, and animals. Particulates include solid particles(or dust), liquid droplets, and microorganisms, can be depo
23、siteddeep within the respiratory system. Particulates carry allergens thatcause discomfort and health problems for workers in animal hous-ing facilities. They also carry much of the odors in animal housingfacilities, for potentially long distances from the facilities. Conse-quently, particulates pos
24、e major problems for animals, workers, andneighbors. Particulate levels in swine buildings have been measuredto range from 0.028 to 0.43 mg/ft3. Dust has not been a major prob-lem in dairy buildings; one two-year study found an average of only0.014 mg/ft3in a naturally ventilated dairy barn. Poultry
25、 buildingdust levels average around 0.057 to 0.20 mg/ft3, but levels up to 0.51to 0.82 mg/ft3have been measured during high activity.The most common gas contaminants are ammonia, hydrogensulfide, other odorous compounds, carbon dioxide, and carbonmonoxide. High moisture levels can also aggravate oth
26、er contami-nant problems. Ammonia, which results from decomposition ofmanure, is the most important chronically present contaminant gas.Typical ammonia levels measured have been 10 to 50 ppm in poul-try units, 0 to 20 ppm in cattle buildings, 5 to 30 ppm in swine unitswith liquid manure systems, and
27、 10 to 50 ppm in swine units withsolid floors (Ni et al. 1998a). Up to 200 ppm have been measured inswine units in winter. Ammonia should be maintained below25 ppm and, ideally, below 10 ppm.Maghirang et al. (1995) and Zhang et al. (1992) found ammonialevels in laboratory animal rooms to be negligib
28、le, but concentra-tions could reach 60 ppmin cages. Weiss et al. (1991) found ammonia levels in rat cages ofup to 350 ppm with four male rats per cage and 68 ppm with fourfemale rats per cage. Hasenau et al. (1993) found that ammonia lev-els varied widely among various mouse microisolation cages;amm
29、onia ranged from negligible to 520 ppm nine days after clean-ing the cage.Hydrogen sulfide, a by-product of microbial decomposition ofstored manure, is the most important acute gas contaminant. Duringnormal operation, hydrogen sulfide concentration is usually insig-nificant (i.e., below 1 ppm). A ty
30、pical level of hydrogen sulfide inswine buildings is around 150 to 350 ppb (Ni et al. 1998b). How-ever, levels can reach 200 to 330 ppm, and possibly up to 1000 to8000 ppm during in-building manure agitation. Odors from animal facilities are an increasing concern, both inthe facilities and in the su
31、rrounding areas. Odors result from bothgases and particulates; particulates are of primary concern becauseodorous gases can be quickly diluted below odor threshold concen-trations in typical weather conditions, whereas particulates canretain odor for long periods. Methods that control particulate an
32、dodorous gas concentrations in the air also reduce odors, but control-ling odor generation at the source appears to be the most promisingmethod of odor control.Barber et al. (1993), reporting on 173 pig buildings, found thatcarbon dioxide concentrations were below 3000 ppm in nearly allinstances whe
33、n the external temperature was above 32F but almostalways above 3000 ppm when the temperature was below 32F. Thereport indicated that there was a very high penalty in heating cost incold climates if the maximum allowed carbon dioxide concentrationwas less than 5000 ppm. Air quality control based on
34、carbon dioxideconcentrations was suggested by Donham et al. (1989). They sug-gested a carbon dioxide concentration of 1540 ppm as a thresholdlevel, above which symptoms of respiratory disorders occurred in apopulation of swine building workers. For other industries, a carbondioxide concentration of
35、5000 ppm is suggested as the time-weighted threshold limit value for 8 h of exposure (ACGIH 1998).Other gas contaminants can also be important. Carbon monoxidefrom improperly operating unvented space heaters sometimesreaches problem levels. Methane is another occasional concern.Control Methods. Thre
36、e standard methods used to control aircontaminant levels in animal facilities are1. Reduce contaminant production at the sources.2. Remove contaminants from the air by air cleaning.3. Reduce contaminant concentration by dilution (ventilation).The first line of defense is to reduce release of contami
37、nants fromthe source, or at least to intercept and remove them before they reachworkers and animals. Animal feces and urine are the largest sourcesof contaminants, but feed, litter, and the animals themselves are alsoa major source of contaminants, especially particulates. Successfuloperations effec
38、tively collect and remove all manure from the build-ing within three days, before it decomposes enough to produce largequantities of contaminants. Removing ventilation air uniformlyfrom manure storage or collection areas helps remove contaminantsbefore they reach animal or worker areas.Ammonia produ
39、ction can be minimized by removing wastes fromthe room and keeping floor surfaces or bedding dry. Immediatelycovering manure solids in gutters and pits with water also reducesammonia, which is highly soluble in water. Because adverse effectsof hydrogen sulfide on production begin to occur at 20 ppm,
40、 ventila-tion systems should be designed to maintain hydrogen sulfide levelsEnvironmental Control for Animals and Plants 24.3below 20 ppm during agitation. When manure is agitated andremoved from the storage, the building should be well ventilated andall animals and occupants evacuated to avoid pote
41、ntially fatal con-centrations of gases.For laboratory animals, changing the bedding frequently andkeeping the bedding dry with lower relative humidities and appro-priate cage ventilation can reduce ammonia release. Individuallyventilated laboratory animal cages or placing cages in mass air dis-place
42、ment units reduce contaminant production by keeping litterdrier. Using localized contaminant containment work stations fordust-producing tasks such as cage changing may also help. Forpoultry or laboratory animals, the relative humidity of air surround-ing the litter should be kept between 50 and 75%
43、 to reduce particu-late and gas contaminant release. Relative humidities between 40and 75% also reduce the viability of pathogens in the air. A moisturecontent of 25 to 30% (wet basis) in the litter or bedding keeps dustto a minimum. Adding 0.5 to 2% of edible oil or fat can significantlyreduce dust
44、 emission from the feed. Respirable dust (smaller than10 m), which is most harmful to the health and comfort of person-nel and animals, is primarily from feces, animal skins, and deadmicroorganisms. Respirable dust concentration should be keptbelow 0.0065 mg/ft3. Some dust control technologies are a
45、vailable.For example, sprinkling oil at 0.12 gal per 1000 ft2of floor area perday can reduce dust concentration by more that 80%. High animalactivity levels release large quantities of particulates into the air, somanagement strategies to reduce agitation of animals are helpful.Methods of removing c
46、ontaminants from the air are essentiallylimited to particulate removal, because gas removal methods areoften too costly for animal facilities. Some animal workers wear per-sonal protection devices (appropriate masks) to reduce inhaled par-ticulates. Room air filters reduce animal disease problems, b
47、ut theyhave not proven practical for large animal facilities because of thelarge quantity of particulates and the difficulty in drawing particu-lates from the room and through a filter. Air scrubbers can removegases and particulates, but the initial cost and maintenance makethem impractical. Aerodyn
48、amic centrifugation is showing promisefor removing the small particulates found in animal buildings.Ventilation is the most prevalent method used to control gascontaminant levels in animal facilities. It is reasonably effective inremoving gases, but not as effective in removing particulates. Pock-et
49、s in a room with high concentrations of particulate contaminantsare common. These polluted pockets occur in dead air spots or nearlarge contaminant sources. Providing high levels of ventilation canbe costly in winter, can create drafts on the animals, and can in-crease the release of gas contaminants by increasing air velocityacross the source.Disease ControlAirborne microbes can transfer disease-causing organisms amonganimals. For some situations, typically with young animals wherethere are low-level infections, it is important to minimize air mixingamong animal groups. It is espec
