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 UA  t 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 o F db and 50 – 65% RH Heating 68 – 72 o F 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/in 2

16. Chapter 6 – Residential Cooling/Heating General Guidelines. Infiltration Driving Force (IDF) in cfm/in 2 – H = V/A cf

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 1.Through opaque surfaces (wall, floors, ceilings, doors) 2.Through transparent fenestrations 3.Caused by infiltration and ventilation 4.Cause by occupancy. Peak Load Computation – sum of all rooms Opaque Surfaces –  t and solar gains incident

19. Chapter 6 – Residential Cooling/Heating Cooling Load Methodology. Opaque Surfaces –  t and solar gains incident OF factors represent construction-specific physical characteristics If OF less 1 (buffering affect of attics and crawlspaces) OF b incident solar gain OF r 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 –  t 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, FF s 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, FF s

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)