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Raters & HVAC
- 1. HERS® Raters & HVAC Brett Dillon RESNET Conference 2010
- 2. ENERGY AHRI ACCA STAR® Responsibilities
- 3. HVAC • Comfort • IndoorAir Quality • Efficiency
- 4. AHRI • ARI &GAMA • Publishes HVAC & DWH data
- 6. 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
- 7. System Concept Manual RS Load Calculation Manual J Air Distribution Manual T Equipment Manual S Selection Duct Size Calculation Manual D Adjust, Test & Balance
- 8. Heating Cooling T-stat setpoint 70°F 75°F RH 25% 40% Temp @ T-stat 68°F - 72°F 72°F - 78°F Room-Room or Level- + 4°F + 6°F Level ∆ T Temp in any room + 2°F of set point + 3°F of set point Floor 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
- 9. 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
- 11. 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
- 12. 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
- 13. 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
- 14. Undersized Furnaces Furnaces that are sized under the calculated load: • may not have enough airflow across the heat exchanger, leading to deformation or cracking
- 15. 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
- 16. Manual T • Select,size & locate • supply outlets • return inlets
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- 20. Manual T Source: Hart& Cooley Engineering Data
- 21. 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
- 23. 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
- 24. 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
- 25. 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
- 36. 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
- 39. Responsibilities • Verify matched coils • Enter data into rating software tool • Review (verify) • Approved tool • Design values • Infiltration • Selected to meet MJ & MS
- 40. Contact Brett Dillon bdillon@ibsadvisorsllc.com www.ibsadvisorsllc.com Design support by Backyard Studios www.backyardstudios.net