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Published byCaitlin Cunningham Modified over 7 years ago

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**Agricultural Structures: Insulation and Heat Flow**

AGME 1613 Fundamentals of Agricultural Systems Technology

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**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

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

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**Methods of Heat Transfer**

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

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**Methods of Heat Transfer**

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

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**Methods of Heat Transfer**

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

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**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

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

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**What Should be Insulated?**

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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

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**Commercial Insulation Products**

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

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**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

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**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.

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**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

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**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

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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

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**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’

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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

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