Presentation on theme: "Agricultural Structures: Insulation and Heat Flow"— Presentation transcript:
1 Agricultural Structures: Insulation and Heat Flow AGME 1613Fundamentals of Agricultural Systems Technology
2 Objectives Describe methods of heat transfer Explain why structures are insulatedDescribe common types and forms of insulationCalculate total thermal resistance of a structural componentEstimate building heat lossDetermine optimal level of insulation for a structure
3 Heat TransferHeat 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 costsReduce building heat gain in hot weather.Decrease cooling costsReduce / eliminate water condensation during cold weather.Decrease repair costs
8 Condensation Process Outside Inside Cold, dry air Warm, moist air W A
10 What is Insulation?Insulation – Any material that reduces the rate at which heat moves by conduction.Insulation, including structural materials, may be:HomogenousNon-homogenousPoured ConcreteConcrete Block Wall
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 hourHeat flow through a component is calculated as:Q = Δt x A RtotalWhere, 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 FilmInsideOutside½-in wood siding½-in plywood3½-in glass-wool insulation½-in plaster board
15 Example Determine the R-total for the wall section shown below ½-in wood sidingAir Film½-in plywood3½-in glass-wool insulation½-in plaster boardR = .81R = .62R = 11.9R = .45Inside air filmR = .61Outside air filmR = .17Rt = 14.56
16 Heat Loss Example #1Assume 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. FOutside temperature = 25 deg. F
17 Heat Loss Example #2 4-in. glass wool ¾-in plywood Determine: Current R-totalTotal ceiling heat loss (BTU/hr)Amount (in.) of loose-fill cellulose insulation required to bring ceiling up to DOE recommendations.Un-heated Attic40 deg FHeated Interior73 deg FCeiling = 60’ x 40’
18 Economic AnalysisAssume 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-hr3413 BTU/kW-hrWhat is the “optimum” insulation level IF “payback period” must be < 10-yrs?Spreadsheet