# Agricultural Structures: Insulation and Heat Flow

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

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

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

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

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

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

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

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

What Should be Insulated?

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

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

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

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.

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

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

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

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’

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