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    • HERS RATER WRITTEN EXAM >
      • Section 1 Building Science Fundamentals >
        • 1a. Basic Terms & Definitions >
          • 1. Airflow in Buildings
          • 2. Equipment Efficiencies
          • 3. Power and Energy
          • 4. Effective Leakage Area
          • 5. Area Weighted R-Value
          • 6. Baseload / Seasonal Energy Use
          • 7. Driving Forces (Including Natural and Mechanical)
          • 8. Behavior of Radiation
          • 9. Thermal Resistance / Transmittance: R and U Values
          • 10. Latent / Sensible Heat
          • 11. Total Equivalent Length
          • 12. Dehumidification / Humidification
          • 13. Convert Pressure Units
          • 14. Thermal Bridges
          • 15. Pressure Boundary
          • 16. Stack Effect
          • 17. Exfiltration and Infiltration
          • 18. Natural / Mechanical Ventilation
          • 19. Net Free Area
          • 20. Input & Output Capacity
          • 21. Peak Electrical Demand
          • 22. Permeability and Perm Rating
          • 23. Standby Loss
          • 24. IAQ (indoor air quality): Moisture, CO, Dust
        • 1b. Principals of Energy, Air & Moisture Thermodynamics >
          • 1. Thermodynamics: Conduction, Convection, Radiation, ΔT
          • 2. Factors That Affect Insulation Performance
          • 3. House Pressurization/Depressurization by Various Forces
          • 4. Heat Gain / Loss
          • 5. Power and Energy
          • 6. Moisture Transport Mechanisms
          • 7. Identify Areas of Highest Relative Humidity
          • 8. Principles of Combustion
        • 1c. Combustion Safety >
          • 1. Combustion Analysis
          • 2. Carbon Monoxide (CO) Testing
          • 3. Combustion Appliance Venting, Draft, Combustion Air & Sizing
          • 4. Understand Combustion Safety Issues
      • Section 2 Buildings and Their Systems >
        • 2a. Building Components >
          • 1. Identify basic duct configurations and components
          • 2. Identify Basic Hydronic Distribution Configurations and Components
          • 3. Identify Basic Structural Components of Residential Construction
          • 4. Thermal Boundaries and Insulation Applications
          • 5. Basic Electrical Components and Safety Considerations
          • 6. Basic Fuel Delivery Systems and Safety Considerations
          • 7. Basic bulk water management components (drainage plumbing gutters sumps etc)
          • 8. Vapor barriers/retarders
          • 9. Radiant Barrier Principles and Installations
          • 10. Understand Fenestration Types and Efficiencies
          • 11. Understand Issues Involved With Basements, Crawlspaces, Slabs, Attics, Attached Garages, Interstitial Cavities, and Bypasses
          • 12. Understand Issues Involved With Ventilation Equipment
          • Understand Basic Heating / Cooling Equipment Components Controls and Operation
          • Understand Basic DHW Equipment Components Controls and Operation
          • Identify Common Mechanical Safety Controls
          • Identify Insulation Types and R-Values
          • Understand Various Mechanical Ventilation Equipment and Strategies: Spot, ERV, HRV
        • Conservation Strategies >
          • Appropriate Insulation Applications and Installation Based On Existing Conditions
          • Opportunity for ENERGY STAR Lighting and Appliances
          • Identify Duct Sealing Opportunities and Applications
          • Understand Importance of Air Leakage Control and Remediation Procedures
          • Blower Door-Guided Air Sealing Techniques
          • Water Conservation Devices and Strategies
          • Domestic Hot Water (DHW) Conservation Strategies
          • Heating & Cooling Efficiency Applications
          • Proper Use of Modeling to Determine Heating and Cooling Equipment Sizing and Appropriate Energy
          • Understand the Use of Utility History Analysis in Conservation Strategies
          • Appropriate Applications For Sealed Crawlspaces Basements and Attics
          • Identify / Understand High Density Cellulose
          • Appropriate Applications for Fenestration Upgrades Including Modification or Replacement
        • Comprehensive Building Assessment Process >
          • Determine Areas of Customer Complaints / Concerns in Interview
          • Understand / Recognize Need For Conducting Appropriate Diagnostic Procedures
          • Interaction Between Mechanical Systems, Envelope Systems and Occupant Behavior
        • Design Considerations >
          • Appropriate Insulation Applications Based On Existing Conditions
          • Understand Fire Codes as Necessary to Apply Home Performance in a Code-Approved Manner
          • Understand / Recognize Building Locations Where Opportunities for Retrofit Materials
          • Understand Climate Specific Concerns
          • Understand Indoor Environment Considerations for the Environmentally Sensitive
          • Understand Impact of Building Orientation, Landscape Drainage, and Grading
          • Opportunity Potential Renewable Energy Applications: Geothermal, Photovoltaic, Wind
          • Understand Impact of Shading on Heating / Cooling Loads
          • Awareness for Solar Gain Reduction / Solar Gain Opportunities
          • Understand Need for Modeling Various Options For Efficiency Upgrades
      • Measurement & Verification of Building Performance >
        • Measurement & Verification of Building Performance >
          • Air Leakage Test Results
          • Understand Building Shell / Envelope Leakage
          • Apply Fundamental Construction Mathematics and Unit Conversions
          • Calculate Building Tightness Levels (Minimum Ventilation Requirements)
          • Calculate Heating Degree Days and Cooling Degree Days
          • Identify Proper Appliance and Combustion Appliance Venting
          • Ventilation calculations and strategies
          • Proper methods for identifying / testing fuel leaks
          • Blower door setup, accurate measurement and interpretation of results
          • Combustion Appliance Zone (CAZ): depressurization, spillage, draft, Carbon Monoxide (ambient and flue)
          • Carbon Monoxide (CO) evaluation: ambient
          • Proper applications and use of temperature measuring devices
          • Pressure pan and room to room pressure diagnostics
          • Recognize contributing factors to comfort problems
          • Inspect for areas containing moisture or bulk water in undesirable locations
          • Understand and inspect for basic electric safety (e.g. frayed wires, open boxes, etc)
      • RESNET HERS RATER National Standards & Project Specifications >
        • Understand applicability content and intent of BPI National Standards – Do no harm, make buildings more healthy, comfortable, durable and energy efficient
        • Recognize need for a professional local/state/national codes evaluation
        • Be able to specify appropriate materials and processes needed for building performance projects
      • Analyzing Buildings Systems >
        • Recognize need for air sealing measures and their impact on other building systems
      • Conduct and Communications >
        • Conservation strategies
        • Conservation strategies
    • HERS RATER FIELD EXAM >
      • How To Put The House Under Worst Case & CAZ
      • What's What? Pa, CFM, CFM50, CAZ, Draft, Room Pressure
      • What To Know In The Attic
      • What To Know In The House
    • BLOWER DOOR TEST >
      • Manometer Setup
    • RESNET STANDARDS >
      • RESNET Standards Decoded
  • ESSENTIALS
    • HELP, I HATE MATH!
    • AUDITOR TO CREW COMMUNICATION
    • COMMON AUDITOR / CREW MISTAKES
    • RUN LIKE HELL
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BPI Written Exam - Section 1 Building Science Fundamentals

5. Understand area weighted R-Value

The area weighted R-value is for finding the R-value of a series of materials together as one.  It is most often used when calculating a walls R-value because it considers multiple materials such as drywall, vapor barriers, siding and wall studs, not only the insulation in the walls.  This may be a problem you see on the BPI test, so here is what you need to know.
Terms: 

  1. R-value - the measure of a materials thermal resistance in units of ft²·°F·h/Btu.  Insulation properties are described in terms of R-values.  The higher the R-value, the greater the thermal resistance.
  2. U-value - the overall heat transfer coefficient.  U-values are a measure of conductance a material.  
  • It tell us how much heat conducts through a 1 sq ft area in 1 hr when there is a 1 degree F temperature difference.  
  • The smaller the U-value, the better the object is at reducing heat transfer.  
  • U is the “total” heat transfer through an object such and takes into account convection and radiation.  
  • Window properties are addressed in terms of U-value. 


Relationship between U-value and R-values

U-values are the fraternal twins of R-values, meaning that to find a U-value for a material, simply put 1 over the R-value = U-value. The opposite is true also, to find the R-value of a material given the U-value, take 1 over the U-value = R-value. 
  • 1 / R-value = U-value 
  • 1 / U-value = R-value


The difference between R-value and U-value

  1. R-values can be added together, U-values cannot
Practice Problem:

Find the R-value of this made-up, all-insulation and no stud wall, given the following:

R-values
–Brick = R-0.10 per inch
–Sheet rock = 0.90 per inch
–Batt insulation = 2.6 per inch
–Outdoor air film = R-0.17
–Indoor air film = R-0.68
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First create a table of 4 columns of material, R-value per inch, Thickness and Total R-value.

Then you can multiply all the R-values by their thickness to get the total R-value for each material. Before going further, try it on your own an see if your number matches mine.

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In homes and buildings, walls are not all just insulation.  We need to account for the studs and other materials as well.
On the test:

What BPI will give you:
  1. All the materials that make up a wall (air film, siding or masonry, insulation, wall studs, etc).
  2. The thickness of all the materials.
  3. The wall area.

What you need to assume:
  1. You will need to account for the wall studs, which are not 100% of the wall area.
  • 16-IOC (inch-on-center) studs account for 20-25% of the wall area (just use 25%) OR 75% of the wall area is an open cavity
  • 24-IOC studs account for 15-20% of the wall area (just use 20%) OR 20% of the wall area is an open cavity


Approach:
  1. Keeping in mind the assumptions above, calculate two sets of R-values, one for the wall cavity (where we just have insulation and no studs), the cavity column, and one for the frame (where we have studs), the frame column)
  2. Make two sets of columns, one for the cavity, one for the frame
  3. List all the materials out on the vertical axis and fill in their R-values
  4. The cavity column will be blank for the wood frame
  5. The frame column will be blank for the insulation type
  6. Add the R-values for both columns together
  7. Convert to U-values by taking 1/R
  8. Multiply the cavity column U-value by 75% or 80% depending if you were given 16 IOC or 24 IOC respectively.  
  9. Multiply the frame column U-value by 25% or 20% depending if you were given 16 IOC or 24 IOC respectively.
  10. Finally, add #8 and #9 U-values up for your total area-weighted U-value.
  11. Convert to R-values by taking 1/U
Here is another sample problem you may see on the BPI test to find the R-value of the wall composition.  Follow the approach above with your 4 columns.  Once you've added the total R-values for all the wall components, remember to multiply the cavity and frame by 75% and 25% respectively.
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Next Section

1a. Basic terms and definitions
  1. Understand airflow in buildings / ducts: CFM, CFM50, CFM25, ACHn, ACH50, FPM
  2. Understand equipment efficiencies: AFUE, SSE, SEER, EER, HSPF
  3. Understand power and energy: watts, BTU/hr, ton of refrigeration  watt-hours, BTU, therm, decatherm
  4. Understand effective leakage area
  5. Understand area weighted R-Value
  6. Understand baseload / seasonal energy use
  7. Understand driving forces (including natural and mechanical: Pressure, temperature, moisture differential
  8. Understand behavior of radiation: emissivity, reflectivity, absorbtivity
  9. Understand thermal resistance / transmittance: R and U Values; including conversions
  10. Understand latent / Sensible heat: evaporation, condensation / specific heat, heat capacity
  11. Understand total equivalent length
  12. Understand basics of dehumidification / Humidification as well as measurement equipment
  13. Understand and convert Pressure units: Inches of Water Column (iwc), Pascal (Pa)
  14. Understand, identify thermal bridges
  15. Understand pressure boundary 
  16. Understand/define stack effect 
  17. Understand and define exfiltration and infiltration 
  18. Natural / mechanical ventilation 
  19. Understand net free area 
  20. Understand input / output capacity 
  21. Understand peak electrical demand 
  22. Understand permeability and perm rating 
  23. Understand standby loss 
  24. IAQ (indoor air quality): moisture, CO, dust
1b. Principals of energy, air & moisture
  1. Thermodynamics: conduction, convection, radiation, ΔT including air movement due to temperature gradients
  2. Factors that affect insulation performance: density, installation, moisture
  3. House pressurization/depressurization by various forces
  4. Heat gain / loss: internal, solar, heat transmission, air leakage 
  5. Power and energy: BTU content of fuels, capacity of combustion appliances and electrical appliances 
  6. Moisture transport mechanisms: bulk water, air leakage, diffusion, capillary action 
  7. Identify areas of highest relative humidity 
  8. Principles of combustion: combustion analysis, CO 
1c. Combustion science
  1. Combustion analysis: oxygen, flue-gas temperature, carbon monoxide 
  2. Carbon Monoxide (CO) testing of combustion appliances 
  3. Basics of: Combustion appliance venting, draft, and combustion air including identification of proper sizing/vent tables 
  4. Understand combustion safety issues: Combustion air, draft, worst case / baseline depressurization, spillage, backdrafting, unvented combustion appliances 
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