Plant and Livestock Systems: Environments

• Course is titled Plant and Livestock Systems and Environmental Control Engineering
• Instructor is Engr. Azereel C. Suor
• Course is for the 1st Semester of 2024-2025

Course Description

• Course will cover environmental parameters and their relationships in plant and livestock production systems
• Microclimate control for plants and animals included
• Principles of environmental control engineering will be examined
• Analysis and design of environmentally controlled agricultural building structures

Environment: Surroundings

• Plant environment is affected by aerial and root conditions
• Animal environments are affected by physical, thermal, social and microbial considerations

Importance of Location

• Climate types vary across geography
• In the Philippines, climate types range from evenly distributed rainfall to distinct periods of maximum rain

Factors Affecting the Biological Environment

• Solar radiation
• Temperature
• Humidity
• Atmospheric pressure
• Atmospheric contaminants

Solar Radiation

• Black Body: An ideal object is a perfect radiation emitter and absorber
• Absorbs all incoming radiation without reflecting
• Re-emits radiation perfectly based on temperature following Planck's Law
• Radiates energy in a spectrum characteristic of its temperature with maximum efficiency
• Emissivity (ε): Measures the effectiveness of a material in emitting thermal radiation compared to a black body
• It's a dimensionless number between 0 and 1
• 1 signifies a perfect black body, emitting maximum possible radiation at its temperature
• 0 signifies a perfect reflector emitting no thermal radiation
• Used to quantify radiation an object emits relative to a black body under same conditions
• Several factors determine the emissivity
• Material surface properties
• Texture
• Wavelength of the emitted radiation
• Metals generally have low emissivity due to high reflection
• Polished aluminum has an emissivity of about 0.1
• Non-metals or rough surfaces have higher emissivity
• Rough blackened surfaces can have near 0.9 or higher emissivity
• Absorptivity (α): A material property describing how well the material absorbs radiation (electromagnetic, light or thermal)
• Defined as the fraction of incident radiation absorbed by a material
• 0 indicates no radiation absorption, reflecting or transmitting all
• 1 indicates absorption of all incident radiation
• Kirchhoff's Law: For a body in thermal equilibrium, absorptivity and emissivity are equal at any given wavelength
• An object that is a good absorber of radiation at a certain wavelength is also a good emitter at that wavelength
• Reflectivity (ρ or R): A material property that describes how much incident radiation is reflected
• Is the ratio of reflected radiation to total incident radiation
• Reflectivity is a dimensionless quantity that ranges from 0 to 1
• 0 means complete absorption with no reflection
• 1 means complete reflection with no absorption
• Reflectivity is dependent on the angle at which radiation strikes
• Reflectivity increases as incidence angle increases, especially nearing 90 degrees
• Transmissivity (τ or T): Material property measuring incident radiation passing through it
• Is the ratio of transmitted radiation to total incident radiation
• 0 means full opaqueness and no radiation passes through
• 1 means full transparency with all incident radiation passing through
• Material thickness significantly affects transmissivity
• As thickness increases, transmissivity generally decreases due to more radiation being absorbed or reflected
• Transmissivity depends on angle of entry
• Steeper angles have longer paths, reducing transmissivity if the material is not perfectly transparent

Solar Radiation Equation

• ρ + α + τ = 1, where:
• ρ is reflectivity
• α is absorptivity
• τ is transmissivity

Stefan-Boltzmann Law

• Describes power radiated from a blackbody regarding its temperature
• Total energy radiated per unit surface area of a blackbody per unit time referred to as the blackbody's emissive power
• Directly proportional to the fourth power of its absolute temperature
• E = σT^4, where:
• E is the emissive power or radiated energy per unit area (watts per square meter, W/m^2)
• T is the absolute temperature of the blackbody (in Kelvin, K)
• σ is The Stefan-Boltzmann constant

Stefan-Boltzmann Constant

• σ is a physical constant, approximately ≈ 5.670x10-8 W/m²K4

Wien's Displacement Law

• Describes the relationship between a blackbody's temperature and the wavelength at peak radiation emission
• Wavelength at which emission spectrum peaks is inversely proportional to temperature
• λmax = b/T, where:
• λmax is the peak wavelength in meters
• T is the absolute temperature of the blackbody (in Kelvin)
• b is Wien's displacement constant

Wien's Displacement Constant

• b has a value of approximately b ≈ 2.898 x 10^-3 m. K.

Planck's Law

• Describes the spectral distribution of electromagnetic radiation emitted by a blackbody in thermal equilibrium
• Provides the formula for radiation emitted at each wavelength (or frequency)
• Planck's Law: The spectral radiance, or the amount of energy emitted per unit area per unit time per unit wavelength

Planck's Law (In terms of Wavelength)

• I(λ, T) = (2hc^2/λ^5) x (1/(e^(hc/λkBT)-1)) where:
  • I(λ, T) is the spectral radiance, or the amount of energy emitted per unit area per unit time per unit wavelength, at a given wavelength λ and temperature T
  • h is Planck's constant (6.626 x 10^-34 Js)
  • c is the speed of light in a vacuum (3 x 10^8 m/s)
  • kB is the Boltzmann constant (1.381 x 10^-23 J/K)
  • T is the absolute temperature of the blackbody in K
  • λ is the wavelength of the radiation

Planck's Law (In terms of Frequency)

• I(v, T) = (2hv^3/ c^2) x (1/(e^(hv/ kBT)-1)) where:
  • I(v, T) is the spectral radiance at a given frequency v and temperature T
  • v is the frequency of the radiation

Planck's Law

• E = (3.74 x 10^8)/ λ^5 (e^(1.44x10^4/ λT) - 1)

Factors Affecting Solar Energy Receipts

• Latitude & Season
• Time of day
• Altitude
• Atmospheric conditions
• Topography
• Surface albedo
• Distance from the sun
• Local weather conditions
• Day length
• Solar activity
  • Solar constant
  • Angle of incidence

Solar Constant

• It measures the amount of solar radiation received per unit area at the outer edge of Earth's atmosphere on a surface normal to the sun's rays
• It represents the intensity of sunlight arriving at Earth
• Esun (w/m²) x SA_sun (m²) = Solar Constant (w/m²) x SA_orbit (m²) ≈ 1,361 W/m²

Angle of Incidence

• Angle between incoming light ray and the normal (perpendicular line) to the surface
• Affects the amount of solar radiation a surface received
• At 0 degrees (light directly perpendicular), maximum solar energy is absorbed
• As the angle increases, the effective area exposed to the sunlight decreases, resulting in less energy being absorbed

Atmospheric Turbidity

• The degree to which particles and pollutants affect the air clarity and sunlight transmission
• Measures light scattered or absorbed by aerosols like dust, smoke, and water vapor

Temperature

• Is a measure of warmness or coldness of an object or environment
• Measured in Celsius (°C), Fahrenheit (°F), or Kelvin (°K)
• Is a measure of a body's ability to transfer heat energy

Sensible Heat

• Is the amount of heat energy that causes a change in temperature of a substance without changing its phase
• Transferred through conduction, convection and radiation
• Q = mcp∆T where:
  • Q is sensible heat (J)
  • m is mass of the substance (kg)
  • cp is specific heat capacity of the substance (J/kg-°C)
  • ∆T is change in temperature (°C or °K)

Latent Heat

• Amount of heat energy absorbed/released by a substance while phase changes (transition from one state of matter to another)
• Latent heat of fusion
• Latent heat of vaporization
• Latent heat of sublimation
• Q = mhfg, where:
  • Q is latent heat (J)
  • m is mass of the substance (kg)
  • hfg is latent heat of the phase change (J/kg)
• Latent heat of fusion means energy is required to change a substance between states of solid⇄liquid
• Latent heat of vaporization means heat energy required to change a substance through states of liquid⇄gas
• Latent heat of sublimation means a substance is converting between substance of solid⇄gas

Humidity

• Measures the amount of water vapor present in the air

Absolute Humidity

• Actual amount of water vapor in the air (g/m³)
• It varies depending on temperature and pressure
• Higher temperature means more water vapor
• Higher pressure and density means more water vapor

Specific Humidity

• Is the mass of water vapor per unit air mass (g/kg)

Relative Humidity (%)

• Is the ratio of partial pressure of water vapor to equilibrium water vapor pressure
• Expressed as percentage

Mixing Ratio

• The amount of water vapor in the air relative to the mass of the dry air
• Mass of water vapor per unit mass of dry air (g/kg)

Atmospheric pressure

• Also known as air pressure, is the force exerted by the weight of air molecules above a given point
• Force exerted at any given point on the Earth's surface by the weight of the air above that point
• Decreases with increasing altitude
• Commonly measured using a barometer
• Standard atmospheric pressure is 101,325 Pa

Atmospheric Contaminants

• Substances in the atmosphere that are harmful to health or the environment
• Can be natural or human-made

Types of Atmospheric Contaminants

• Particulate Matter (PM)
• Dust, soot, smoke, liquid droplets
• Gaseous Contaminants
• CO, NO2, SO2, O3, VOCs
• Heavy metals Lead, mercury, cadmium
• Greenhouse Gases (GHGs) CO2, CH4, N2O

Sources of Atmospheric Contaminants

• Natural
• Volcanic eruptions, wildfires, dust storms
• anthropogenic
• Transportation, industries, agricultural activities