Raters & HVAC

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Raters & HVAC

  1. 1. HERS® Raters & HVAC Brett DillonRESNET Conference 2010
  2. 2. ENERGYAHRI ACCA STAR® Responsibilities
  3. 3. HVAC• Comfort• Indoor Air Quality• Efficiency
  4. 4. AHRI• ARI & GAMA• Publishes HVAC & DWH data
  5. 5. AHRI Data• Region IV• 80°F indoor cooling test temperature• 67°F indoor wet bulb temperature• 90°F outdoor test temperature• 47°F outdoor heating test temperature• 17°F outdoor heating test temperature
  6. 6. System Concept Manual RS Load Calculation Manual J Air Distribution Manual TEquipment Manual SSelection Duct Size Calculation Manual D Adjust, Test & Balance
  7. 7. Heating Cooling T-stat setpoint 70°F 75°F RH 25% 40% Temp @ T-stat 68°F - 72°F 72°F - 78°FRoom-Room or Level- + 4°F + 6°F Level ∆ T Temp in any room + 2°F of set point + 3°F of set pointFloor temp over slab or > 65°F, 4” above floor unconditioned space Filtration > MERV 8 > MERV 8 7.5 cfm/person + 1 cfm/ 7.5 cfm/person + 1 Ventilation 100 ft2 cfm/100 ft2 Duct Leakage < 6% < 6% Sources: ACCA Manual RS, ENERGY STAR, ASHRAE Standard 62.2
  8. 8. ACCA Manual J• Every home is required to have a Manual J, 8th edition, load calculation –Using the 99% winter design temperature –Using the 1% summer design temperature IRC Section M1401.3
  9. 9. Oversized Furnaces Furnaces that are sized > 40% over the calculated load: • furnace & vent can cool, causing condensation and rust • airflow across exchanger can be too much, causing corrosion from condensation
  10. 10. Oversized Air Conditioners Air conditioners that are sized > 15% over the calculated load:• duct leakage increases• latent cooling capacity decreases•Blower motor uses more energy• equipment life is shortened
  11. 11. Oversized Heat Pumps Heat pumps that are sized > 15% over the calculated load: • duct leakage increases • latent cooling capacity decreases •blower motor uses more energy • equipment life is shortened • register temperatures are low during heating season
  12. 12. Undersized Furnaces Furnaces that are sized under the calculated load: • may not have enough airflow across the heat exchanger, leading to deformation or cracking
  13. 13. Undersized Air Conditioners & Heat Pumps Air conditioners & heat pumps that are sized under the calculated load: • may not have enough capacity • latent cooling capacity increases, decreasing the sensible capacity
  14. 14. Manual T• Select, size & locate • supply outlets • return inlets
  15. 15. Spread
  16. 16. Throw
  17. 17. Drop
  18. 18. Manual TSource: Hart & Cooley Engineering Data
  19. 19. Manual S Sensible Supply Temperature Room Air Heat Ratio Air Difference < 80% 54 75 21 80% to 85% 56 75 19 > 85% 58 75 17
  20. 20. Manual D• Required under IRC M1601.1 • Implies room-by-room load calculation must be performed • CFM • SHR • ΔT supply-return • Sensible load • Friction rate • Pressure drop x 100 / total effective length
  21. 21. Cooling Size• CFM = (Sensible / (1.1 x ΔT) • SHR = 0.87 • ΔT = 17°F • Sensible Room Load = 4,537 Btu/hr CFM = 4537 / (1.1 x 17) CFM = 4537 / 18.7 CFM = 243
  22. 22. Cooling Size• Friction Rate = Pressure drop x 100 / total effective length • Pressure drop = 0.10 i.w.c. • TEL = straight flex duct + fittings • 90° elbow = 30’ • 90° supply air boot fitting = 80’ • Straight duct = 20’ Friction Rate = (0.10 x 100) / (20’+30’+80”) FR = 10 / 130 FR = 0.077
  23. 23. ENERGY STAR• All cooling equipment must be sized according to latest editions of Manuals J & S, ASHRAE Handbook of Fundamentals, or equivalent procedure• Maximum oversizing is 15%• Outdoor design temps 99% & 1%• Indoor cooling temp = 75°F• Infiltration rate = Tight or equivalent
  24. 24. Responsibilities• Verify matched coils• Enter data into rating software tool• Review (verify) • Approved tool • Design values • Infiltration • Selected to meet MJ & MS
  25. 25. Contact Brett Dillon bdillon@ibsadvisorsllc.com www.ibsadvisorsllc.comDesign support by Backyard Studios www.backyardstudios.net

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