Agricultural Structures: Insulation and Heat Flow

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

9. What Should be Insulated?

10. Concrete Block Wall Poured Concrete 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

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

12. Insulation R-Values • 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. ½-in wood siding ½-in plywood 3½-in glass-wool insulation ½-in plaster board Air Film ExampleDetermine the R-total for the wall section shown below Inside Outside

15. ½-in wood siding ½-in plywood 3½-in glass-wool insulation ½-in plaster board Air Film ExampleDetermine the R-total for the wall section shown below 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. 4-in. glass wool ¾-in plywood Un-heated Attic 40 deg F Heated Interior 73 deg F Heat Loss Example #2 • 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. 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