1. Agricultural Structures: Insulation and Heat Flow
                                                                                                                                                                  
AGME 1613
Fundamentals of Agricultural Systems Technology

2. Objectives Describe methods of heat transfer
Explain why structures are insulated
Describe common types and forms of insulation
Calculate total thermal resistance of a structural component
Estimate building heat loss
Determine optimal level of insulation for a structure

3. Heat Transfer
Heat moves from area of high concentration to area of low concentration.

4. Methods of Heat Transfer
Conduction – heat transfer where there is direct contact between the hot and cold surfaces.
Other examples?

5. Methods of Heat Transfer
Convection – Fluid (air or water) transfers heat from the hot surface to the cold surface.
Other examples:

6. Methods of Heat Transfer
Radiation – Heat transfer between non-contacting surfaces without change in air temperature.
Other examples:

7. Why do we insulate structures?
Reduce building heat loss in cold weather.
Decrease heating costs
Reduce building heat gain in hot weather.
Decrease cooling costs
Reduce / eliminate water condensation during cold weather.
Decrease repair costs

8. Condensation Process Outside Inside Cold, dry air Warm, moist air W A

9. What Should be Insulated?

10. What is Insulation?
Insulation – Any material that reduces the rate at which heat moves by conduction.
Insulation, including structural materials, may be:
Homogenous
Non-homogenous
Poured Concrete
Concrete Block Wall

11. Commercial Insulation Products
Materials
Cellulose
Vermiculite
Glass fiber
Polystyrene
Polyurethane
Forms
                                                                      
Loose-fill
                    
Batt-and-Blanket
Rigid

12. Insulation R-Values Q = Δt x A Rtotal
R-Value is the rating system for insulation.
Higher R-values = greater thermal resistance.
Heat flow is measured in BTUs per hour
Heat flow through a component is calculated as:
Q = Δt x A Rtotal
Where, Q = Heat flow (BTU/hr)
Δt = Temperature difference (degrees F)
A = Area of component (ft2)
Rtotal = Total thermal resistance of component

13. Determining Total R-values
Determine the composition of the building component.
Determine the R-value for each component (Table 14, p. 84 of Engineering Applications)
Add all the R-values together to determine Total R-value.

14. Example Determine the R-total for the wall section shown below
Air Film
Inside
Outside
½-in wood siding
½-in plywood
3½-in glass-wool insulation
½-in plaster board

15. Example Determine the R-total for the wall section shown below
½-in wood siding
Air Film
½-in plywood
3½-in glass-wool insulation
½-in plaster board
R = .81
R = .62
R = 11.9
R = .45
Inside air film
R = .61
Outside air film
R = .17
Rt = 14.56

16. Heat Loss Example #1
Assume that a house has a total wall surface area of 2000 ft2.
Given the R-total just calculated, determine the total heat loss (BTU/hr) through the walls if:
Inside temperature = 72 deg. F
Outside temperature = 25 deg. F

17. Heat Loss Example #2 4-in. glass wool ¾-in plywood Determine:
Current R-total
Total ceiling heat loss (BTU/hr)
Amount (in.) of loose-fill cellulose insulation required to bring ceiling up to DOE recommendations.
Un-heated Attic
40 deg F
Heated Interior
73 deg F
Ceiling = 60’ x 40’

18. Economic Analysis
Assume that a contractor will “blow in” the insulation for:
$.25 / ft2 (first 2-in.)
.15 / ft2 (each additional 2-in. increment.)
You heat with electricity:
$.075 / kW-hr
3413 BTU/kW-hr
What is the “optimum” insulation level IF “payback period” must be < 10-yrs?
Spreadsheet