Animal Environment

1
Animal Environment Heat Flow

• BSE 2294 Animal Structures and Environments
• S. Christian Mariger Ph.D. Susan W. Gay Ph.D.

2
Environmental Fundamentals

• Environment is the total of all external
  conditions that effect the development, response
  and growth of plants and animals.
• Physical factors
• Social factors
• Thermal factors
• Ventilation is the method of environmental
  modification for agricultural structures.

3
Physical Factors

• Space
• Lighting
• Sound
• Gasses
• Equipment

4
Social Factors

• Number of animals to a pen
• Behavior

5
Thermal Factors

• Air temperature
• Relative humidity
• Air movement
• Radiation (one type of heat transfer)

6
Environmental Factors

• Influence
• Animal health
• Breeding
• Production efficiency
• Product quality
• Human health
• Equipment service life
• Building material longevity

7
Heating and Ventilation Terms

• Heat the energy transferred from a warmer body
  to a colder body because of the temperature
  difference
• Temperature is a measure of a bodys ability to
  transfer or receive heat from matter in contact
  with it.
• Ambient temperature - the temperature of the
  medium surrounding a body
• British Thermal Unit (Btu) the quantity of heat
  required to raise one pound of water one F

8
Heating and Ventilation Terms

• Calorie the quantity of heat required to raise
  one gram of water one C
• Specific heat is the quantity of heat required
  to raise one pound of material one F (Units
  Btu/lb-F)
• Sensible heat is a measure of the energy that
  accompanies temperature change
• Latent heat is the heat energy absorbed or
  released when a material changes phase (ice to
  water for example)

9
Sensible and latent heat to change one lb of
water from ice to steam
qs Mcv?T
10
Sensible latent heat example

• Given a 20 cubic foot water trough that was
  allowed to freeze to 28 F how many Btu will be
  required to thaw and warm the water to 40 F.

11
Sensible latent heat example

• Find lbs of water.
• ?H2O 62.4 lb/ft3
• 20 ft3 x 62.4 lb/ft3 1,248 lbs

12
Sensible latent heat example

• Find sensible heat required (Btu) to raise the
  temp from 28 F to 32 F.
• Specific heat of ice 0.56 Btu/lb - 1 F
• 1,248 lbs x 0.56 Btu/lb - 1 F 699 Btu - 1 F
• (32 F 28 F) x 699 Btu - 1 F 2,796 Btu

13
Sensible latent heat example

• Find the latent heat of fusion for the water.
• Latent heat of fusion H2O 144 Btu/lb
• 1,248 lbs x 144 Btu/lb 179,712 Btu

14
Sensible latent heat example

• Find sensible heat required to raise the temp
  from 32 F to 40 F.
• Specific heat of water 1.0 Btu/lb - 1 F
• 1,248 lbs x 1.0 Btu/lb - 1 F 1,248 Btu - 1 F
• (40 F 32 F) x 1,248 Btu - 1 F 9,984 Btu

15
Sensible latent heat example

• Sum the Btus to find the energy required to
  raise the temp from 32 F to 40 F.
• (32 F 28 F) 2,796 Btu
• Latent heat of fusion 179,712 Btu
• (40 F 32 F) 9,984 Btu
• Total 192,492 Btu

16
Types of Heat Transfer
17
Conduction

• Conduction the exchange of heat between
  contacting bodies that are at different
  temperatures or transfer of energy through a
  material as a result of a temperature gradient.

Conduction is often a heat loss factor as well as
a heating factor!
18
Conduction heat flow

• q AK (T1 T2) / L
• A cross-sectional area of the surface
• K thermal conductivity
• L thickness of the material
• T1 T2 ?T change in temperature
• q (A/R) ?T
• R thermal resistance (L/K)

19
Conduction example

• Determine the heat transfer through a wall
  composed of two sheets of ½ plywood (R 0.62)
  and 3 ½ of batt insulation (R 11).

Inside temp 80 F
Outside temp 20 F
Assume the cross-sectional area A is 1ft2
20
Conduction example

• Find RT for the wall
• Material 1 ½ plywood R 0.62
• Material 2 3 ½ batt insulation R 11.00
• Material 3 ½ plywood R 0.62
• RT 12.24

21
Conduction example

• Find q for the wall
• q (A/RT) x (Tinside Toutside)
• q (1ft2/12.24) x (80 20) 4.90 Btu/Hour

22
Heat conduction for a building (qb)

• Calculate the conduction (q) for each building
  component
• Ceilings qc - Windows qwi
• Doors qd - Walls qw
• Etc.
• Add all the conductions to find the conduction
  for the building (qb)

qb qc qwi qd qw q...... (in Btu/hr)
23
Conduction temperature change

• We can also calculate the temperature from one
  side to the next for each layer in the wall.
• Determine the temperatures at points 2 and 3.
• Where T1 T2 (q/A) R

R1 0.62
R3 0.62
R2 11
T1 80 F
T4 20 F
T2 ?
T3 ?
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Conduction temperature change

• Temp at point 2
• T2 T1 (q/A) R1
• T2 80 F (4.9/1) x 0.62 77 F
• Temp at point 3
• T3 T2 (q/A) R2 .
• T3 77 F (4.9/1) x 11.0 23 F

25
Convection

• Heat transferred to or from a body by mass
  movement of either a liquid or a gas

26
Convection

• Convection is often used for interior heating

27
Radiation

• The exchange of thermal energy between objects by
  electromagnetic waves.
• Radiant energy is transferred between two bodies
  in both directions, not just from warmer to
  cooler.

28
Radiation

• Here is an example of infra red (IR) radiation
  being used in an interior heating application

29
Typical Environmental Effects (dairy cattle
example)
30
Heat stress occurs in animals when their heat
gain is greater than their heat loss.
Body heat Metabolism Physical activity Performanc
e Environment Radiation (sun) Convection
(air) Conduction (resting surface)
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Heat stress has a severe impact on cow
performance and health.
Increases Respiration rate Sweating Water
intake Decreases Dry matter intake Feed passage
rate Blood flow to internal organs Milk
production Reproduction performance
32
Cows are much more comfortable at cooler
temperatures than humans.
Thermal comfort zone 41 77 F Lower critical
temperature Neonatal calves 55 F Mature cows 13
F Upper critical temperature 77 78 F
33
Animals can lose heat by sensible or latent heat
losses.
Sensible heat Conduction (direct
contact) Convection (air movement) Radiation
(line of sight) Latent heat Evaporation (phase
change)
34
As air temperatures increase, animals cannot lose
as much sensible heat, so they pant and sweat
(evaporation).
Direct radiation
Indirect radiation
Convection
Indirect radiation
Digestive heat
Conduction
35
As relative humidity rises, an animal losses less
heat by evaporation.
Evaporation (from skin)
Evaporation (respiratory tract)
36
Relative Humidity ()
80
100
20
40
60
0
72
No Stress
80
Mild Stress
90
Heat Stress
Temperature (F)
Severe Stress
100
110
Dead Cows
120
37
How can you tell if a cow is suffering from heat
stress?
Rectal temperatures Above 102.5 F Respiration
rates gt 80 breaths per minute Decreases in Dry
matter intake Milk production
38
How can heat stress be managed?
Shade Air exchange Air velocity Water
39
Shade lowers the solar heat load from direct and,
sometimes, indirect radiation.
40
Good air exchange or ventilation of confinement
housing is essential to animal comfort.
Removes Hot, moist air Increases Convective
heat loss Recommended 1000 cfm per cow
41
Cows cooling ability is improved by increasing
the air velocity over the animals skin.
Removes Hot, moist air in contact with the
animal Turbulence Disrupt the boundary layer
Recommended 220 to 440 fpm (2.5 to 5 mph)
42
Water improves animal cooling through
evaporation.
Watering locations Increase in hot
weather Sprinkling systems Wet cows
hide Increase direct evaporation Evaporative
cooling pads Cools air directly Cows cooled by
convection
43
Thermal effects on other species
44
Heat Balance
45
Heat balance

• To maintain constant room temperature, heat
  produced by the animals and heaters must equal
  the heat lost through the building structure and
  by ventilation.
• Heat gain (Qh) Heat loss (QT)
• Qf Qs Qvent Qb

46
Heat removed by ventilation (Qvent)

• Ventilation removes heat by replacing warm in
  side air with cold outside air.
• If humidity is constant we know the specific heat
  of air.
• If we also know the difference between the
  outside temp and the inside temp (?t)
• If we also know how much air is being exchanged
  in Cubic Feet/Minute (cfm)
• Then we can calculate the heat removed by
  ventilation.

47
Heat removed by ventilation (Qvent)

• Qvent (1.1)(Fan rate cfm)(?t)

48
Ventilation (Qvent) example

• A building is ventilated at 1,200 cfm. The inside
  temperature is 65 F and the outside temperature
  is 15 F. Determine the rate of heat removal.

49
Ventilation (Qvent) example

• (Qvent) (1.1) (fan rate) (Ti To)
• (Qvent) (1.1) (1,200) (65 15)
• (Qvent) 66,000 Btu/hour

50
Heat lost through the structure (Qb)

• We have discussed heat lost through structure in
  terms of thermal resistance (R) and thermal
  conductivity (K).
• Q AK (T1 T2) / L
• A cross-sectional area of the surface
• K thermal conductivity
• L thickness of the material
• T1 T2 ?t change in temperature
• Q (A/R) ?t
• R thermal resistance (L/K)
• Qb qc qwi qd qw q......

51
Heat gain (Qh)

• Heat gain in an animal structure comes from two
  major sources
• Supplemental heat (Qf) the heat provided by
  various heaters.
• Animal sensible heat (Qs) the heat the animals
  give up to the environment.
• Conduction
• Convection
• Radiation
• Evaporation (latent heat of vaporization)

52
Animal sensible heat (Qs)

• Assumptions
• air velocity 20-30 fpm
• humidity 50
• surface temp of walls are equal to air temp

53
Forced ventilation example

• Fifty (50) pigs in the growing stage (100 lbs)
  are housed at a temperature of 60 F. The cold
  weather ventilation rate (To 20 F) is 7 cfm
  for each animal. The total heat loss for the
  structure QB 14,000 Btu/hour and the animal
  sensible heat Qs 375 Btu / hour / head. Will
  supplemental heat (Qf) be required for this
  structure, if so how much?

54
Forced ventilation example

• Find the required ventilation
• ( animals) x (cfm/animal) fan rate
• fan rate (50) x (7 cfm) 350 cfm

55
Forced ventilation example

• Find the heat removed by ventilation (Qvent)
• Qvent (1.1) (fan rate) (?t)
• Qvent (1.1) (350) (60 20)
• Qvent 15,400 Btu/hour

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Forced ventilation example

• Find the total heat loss (QT)
• (QT) Qvent QB
• (QT) 15,400 Btu/hour 14,000 Btu/hour
• (QT) 29,400 Btu/hour

57
Forced ventilation example

• Find animal sensible heat (Qs)
• (Qs) ( animals) (Btu/hour head)
• (Qs) (50) (375) 18,750 Btu/hour

58
Forced ventilation example

• If Qf Qs Qvent QB then
• Find the supplemental heat (Qf)
• (Qf) Qvent QB Qs
• OR
• (Qf) QT Qs
• (Qf) 29,400 Btu/hour - 18,750 Btu/hour
• (Qf) 10,650 Btu/hour

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Moisture Balance
60
What about moisture?

• As ventilating air moves through a structure it
  evaporates moisture from the floor, pits and
  other wet surfaces.
• As animals breath, moisture is lost from their
  respiratory system to the air.
• To maintain a desirable temperature, enough
  moisture must be removed to keep the relative
  humidity below 70

61
Moisture balance

• To maintain a constant rate of moisture
• Moisture Loss Moisture production
• The moisture holding capacity of air nearly
  doubles with each 20 F increase in temperature!

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Where does the moisture come from?

• Incoming air
• Animal waste
• Animal respiration
• Feed and water

63
Swine ventilation rates
64
Air tempering systems

• Tempering warms or cools air before it enters the
  animal housing portion of a structure.

65
Air tempering systems

• Tempering systems include
• air make-up systems
• air blending systems
• heat exchangers
• solar collectors
• earth tubes
• evaporative coolers

66
Air pre-heating
67
Air blending
68
Heat exchangers
69
Solar collectors
70
Earth tubes
71
Evaporative cooling