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Heating and Air Conditioning I

Heating and Air Conditioning I

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Heating and Air Conditioning I

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  1. Heating and Air Conditioning I Principles of Heating, Ventilating and Air Conditioning R.H. Howell, H.J. Sauer, and W.J. Coad ASHRAE, 2005 basic textbook/reference material For ME 421 John P. Renie Adjunct Professor – Spring 2009

  2. Chapter 6 – Residential Cooling/Heating • This chapter covers the calculations for design cooling and heating loads for residential buildings. • Calculate of the heat loss and heat gain to estimate the capacity of the heating and cooling components to maintain comfort. • Based on extremes – peak loads conditions – Chapter 29 of ASHRAE Fundamentals • Residences and small commercial buildings – dominated by the external envelope (walls, roof, windows, and doors) • Large commercial building often dominated by internal gains (occupants, lights, equipment, and appliances) • All buildings need to consider energy required to heat/cool and humidify/de-humidify due to infiltration (either intentional or leakage) • Methods for commercial not applicable to residential – temperature swings • Same methods as non-residential (Chapter 7) – with care

  3. Chapter 6 – Residential Cooling/Heating • This chapter covers the calculations for design cooling and heating loads for residential buildings. • Residential buildings distinquished by: • Smaller internal gains – dominated by structural gains/losses and infiltration • Varied Use of Spaces – localized conditions tolerated • Fewer Zones – usually single zone – single thermostat – swings – moderating the peak load due to heat storage within building • Greater Distribution Losses - duct losses/gains significant • Partial Loads – systems are small (1 to 5 tons) – at capacity only rarely leading to running at partial capacity – oversized detrimental to good seasonal performance • Dehumidification Issues – only during cooling season – thermostat controlled by sensible heating – short-cycling – degraded dehumidification • Categories • Single family detached – four walls, single thermostat, open – centralized air return • Multi-family – less exposure – not same load leveling • Other – dependent on east-west fenestration

  4. Chapter 6 – Residential Cooling/Heating • Residential characteristics can lead to complex load calculations • Hour-by-hour methodology required to find peak • Different methods for heating and cooling due to simplification for heating • Heating uses worst case – no solar or internal gains and no storage – reduces to UADt calculations • Cooling methods revised due to computation speed availability – 24 hour, equation-based procedures • Cooling method based on Residential Load Factor (RLF) methodology – a simplified procedure derived from a detailed residential heat balance (RHB) analysis of buildings across the range of climates – applicable to spreadsheet • RLF Limitations given in Table 6-1 • Latitude – 20 to 60 degrees North • Date – summer peaking (July 21) • Elevation – below 6,500 ft • Climate – Warm/hot • Construction – Lightweight residential • Fenestration area/tilt – 0 to 30% total floor area • Occupancy - residential • Temperature swings and Distribution losses

  5. Chapter 6 – Residential Cooling/Heating • RLF Limitations (Table 6-1)

  6. Chapter 6 – Residential Cooling/Heating • General Guidelines. • Following guidelines apply for both heating and cooling. • Design for typical building use – meet maximum load conditions – not extreme conditions (parties, etc.) • Building code and standards – local codes take precedence • Designer judgment – prior projects, local building practices • Verification – post construction – pressure testing • Uncertainty and safety allowances – safety allowances should be added at the end to avoid compounding effect.

  7. Chapter 6 – Residential Cooling/Heating • General Guidelines. • Basic relationships

  8. Chapter 6 – Residential Cooling/Heating • General Guidelines. • Design Conditions • Indoor conditions • Cooling 75 oF db and 50 – 65% RH • Heating 68 – 72 oF db and 30% RH • Outdoor conditions • Cooling – 1% values in Table 4-7 • Wind speed 7.5 mph • Mid-summer – or early fall for south-facing building • Heating – 99% values in Table 4-7 • Ignore solar and internal gains • Several-day extreme events • Wind determinant for infiltration • Possibly use 99.6% value as extreme or 99% with safety factor • Adjacent buffer spaces • Uninsulated garages and attic – at outdoor temperature • Insulated, unheated spaces at average temperature

  9. Chapter 6 – Residential Cooling/Heating • General Guidelines. • Building Data – Component area • Gross area – outside building area discussion • Fenestration area – entire product area (framing) • Net area – gross minus fenestration • Volume – Floor area x floor-to-floor height • Building Data – Construction Characteristics • U-factors – use Chapter 25 or manufacturer’s data (under heating conditions) • Fenestration • U-factors and solar heat gain coefficient (SHGC) for entire assembly • Table 6-2 • Only and few different types of glazing • Storm window treatment • Interior and exterior shading included during cooling loads

  10. Chapter 6 – Residential Cooling/Heating • General Guidelines. • Building Data – Table 6-2

  11. Chapter 6 – Residential Cooling/Heating • General Guidelines. • Load Components • Below grade surfaces – zero for cooling – non-zero for heating • Infiltration – significant portion of heating and cooling loads (see Chapter 5) – evaluated for entire building • Leakage rate (Q or ACH) • Caused by building effective leakage area • Driving pressure caused by bouyancy and wind

  12. Chapter 6 – Residential Cooling/Heating • General Guidelines. • Caused by building effective leakage area • Leakage area – measure AL by a pressurization test, or

  13. Chapter 6 – Residential Cooling/Heating • General Guidelines. • Unit leakage area (Table 6-3)

  14. Chapter 6 – Residential Cooling/Heating • General Guidelines. • Evaluation of Exposed Surface Area (Table 6-4)

  15. Chapter 6 – Residential Cooling/Heating • General Guidelines. • Infiltration Driving Force (IDF) in cfm/in2

  16. Chapter 6 – Residential Cooling/Heating • General Guidelines. • Infiltration Driving Force (IDF) in cfm/in2 – H = V/Acf

  17. Chapter 6 – Residential Cooling/Heating • General Guidelines. • Load Components • Ventilation – whole building ventilation – need to be included • Distribution Losses • Can cause substantial equipment loads in excess of building requirements • Dependent on location of duct runs, length, surface areas, surrounding temperature, duct wall insulation, air-tightness

  18. Chapter 6 – Residential Cooling/Heating • Cooling Load Methodology. • Determines the total sensible cooling load from heat gain • Through opaque surfaces (wall, floors, ceilings, doors) • Through transparent fenestrations • Caused by infiltration and ventilation • Cause by occupancy. • Peak Load Computation – sum of all rooms • Opaque Surfaces – Dt and solar gains incident

  19. Chapter 6 – Residential Cooling/Heating • Cooling Load Methodology. • Opaque Surfaces – Dt and solar gains incident • OF factors represent construction-specific physical characteristics • If OF less 1 (buffering affect of attics and crawlspaces) • OFb incident solar gain • OFr captures heat storage effects by reducing the effective temperature difference • Old technique – CF = U x CLTD

  20. Chapter 6 – Residential Cooling/Heating • Cooling Load Methodology. • Opaque Surfaces – Dt and solar gains incident • Roof Solar Absorptance

  21. Chapter 6 – Residential Cooling/Heating • Cooling Load Methodology. • Slab Floors – slight reduction in cooling load – or ignored

  22. Chapter 6 – Residential Cooling/Heating • Cooling Load Methodology. • Transparent Fenestration Surfaces - nondoor

  23. Chapter 6 – Residential Cooling/Heating • Cooling Load Methodology. • Peak exterior irradiance – with shading

  24. Chapter 6 – Residential Cooling/Heating • Cooling Load Methodology – primary exposures

  25. Chapter 6 – Residential Cooling/Heating • Cooling Load Methodology – for any exposures.

  26. Chapter 6 – Residential Cooling/Heating • Cooling Load Methodology – transmission of exterior attachments.

  27. Chapter 6 – Residential Cooling/Heating • Cooling Load Methodology. • Shaded fraction – 1 if adjacent building or …

  28. Chapter 6 – Residential Cooling/Heating • Cooling Load Methodology • Shade line factors.

  29. Chapter 6 – Residential Cooling/Heating • Cooling Load Methodology. • Solar load factors, FFs • Value of FFs corresponds to fraction of transmitted solar gain that contributes to peak cooling load.

  30. Chapter 6 – Residential Cooling/Heating • Cooling Load Methodology. • Solar load factors, FFs

  31. Chapter 6 – Residential Cooling/Heating • Cooling Load Methodology. • Interior attenuation coefficient, IAC

  32. Chapter 6 – Residential Cooling/Heating • Cooling Load Methodology. • Interior attenuation coefficient, IAC

  33. Chapter 6 – Residential Cooling/Heating • Cooling Load Methodology. • Internal Gains – effect of occupants, lighting, and appliances

  34. Chapter 6 – Residential Cooling/Heating • Cooling Load Methodology. • Total Latent Load • Caused by three predominant moisture sources, outdoor air (infiltration and ventilation), occupants, and miscellaneous sources (bathing, cooking, etc.) • Summary of RLF Cooling Load Equations (Table 6-14) … see next slide

  35. Chapter 6 – Residential Cooling/Heating • Cooling Load Methodology. • Summary of RLF Cooling Load Equations (Table 6-14)

  36. Chapter 6 – Residential Cooling/Heating • Cooling Load Methodology. • Summary of RLF Cooling Load Equations (Table 6-14)