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Environmental Controls I/IG

Environmental Controls I/IG. Lecture 12 Cooling Loads Cooling Degree Hours Energy Performance Ratings Annual Fuel Consumption. Cooling Loads. Computed for worst case scenario: Late summer afternoon at outdoor design dry bulb temperature Include: Insolation from sun

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Environmental Controls I/IG

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  1. Environmental Controls I/IG Lecture 12 Cooling Loads Cooling Degree Hours Energy Performance Ratings Annual Fuel Consumption

  2. Cooling Loads Computed for worst case scenario: • Late summer afternoon at outdoor design dry bulb temperature Include: • Insolation from sun • Heat gain from people, lights, and equipment • Infiltration in residential buildings • Ventilation in nonresidential buildings SR-3

  3. Summer Design Conditions Design Dry Bulb Temperature Mean Daily Range S: p. 1496, T.B1

  4. Determine Design Equivalent Temperature Difference (DETD) Construction type Outdoor design temperature Mean daily range L: 0-16ºFM: 16-25ºF H: 25+ºF S: p. 1613, T.F.5

  5. Determine Envelope U-values Calculate ΣR and then find U for walls and roofs. Note: this method ignores floors, doors, and window U-values

  6. Determine DCLF Glazing Type Design Temperature Shading Orientation S: p. 1615, T.5.6

  7. Determine Area Quantities Perform area takeoffs for all building envelope surfaces on each facade: gross wall area window area door area net wall area 1200 sf 100’ - 368 sf - 64 sf 768 sf 4’ 12’ 4’ 8’ Elevation

  8. Infiltration S: p. 1617, T.F.7

  9. Ventilation Analysis Non-residential buildings use ventilation to provide fresh air and to offset infiltration effects. ASHRAE Standard 62-2001 (S: p. 1598, T.E.25) Estimates the number of people/1000 sf of usage type Prescribes minimum ventilation/person for usage type

  10. ASHRAE 62-2001 Defines space occupancy and ventilation loads S: p. 1598, T.E.25

  11. Ventilation—Sensible CLF S: 1617, T.F.7

  12. People — Sensible Gain Determine number of people Activity level S: p. 1617, T.F.8

  13. Lights Determine wattage of lighting/square foot • ASHRAE 90.1 prescriptive levels • Count fixture loads and add together Note: add 15% for ballasts where applicable (e.g., fluorescent lights)

  14. Equipment Determine operating wattage of equipment/square foot • ASHRAE 90.1 prescriptive levels • Count actual loads and add together Note: include a diversity factor (20-30%) if specific usage patterns are unknown.

  15. Equipment Use manufacturer’s data or other references to obtain heat gain data. Standby mode • Copiers • Monitors • Printers • CPU • “energy star” S: p. 1618, T.F.9

  16. Latent Load Not calculated separately: Apply a factor as a percentage of the total sensible cooling load Dry climates: 20% Moist/Humid climates: 30%

  17. Cooling Load Example Problem Building: Office Building Location: Salt Lake City Building: 200’ x 100’ (2 stories, 12’-6” each) Uwall= 0.054 Btuh/sf-ºF Uroof= 0.025 Btuh/sf-ºF

  18. Cooling Load Example Problem Determine Building Envelope Areas (SF) Building: 200’ x 100’ (2 stories, 12’-6” each) N E S W Gross Wall 5,000 2,500 5,000 2,500 Windows 1,000 500 2,000 500 Doors 20 20 50 20 Net Wall 3,980 1,980 2,950 1,980 Roof/Floor Slab 20,000

  19. Determine Design Equivalent Temperature Difference (DETD) Roof Construction type: Light color, vented, ceiling Design temperature: 95ºF Mean daily range: 32ºF L: 0-16ºFM: 16-25ºF H: 25+ºF DETD=31.0ºF S: p. 1613, T.F.5

  20. Cooling Loads 0.025 20,000 31.0 15,500 15,500 Insert roof values SR-3

  21. Determine Design Equivalent Temperature Difference (DETD) Wall Construction type (see given) Design temperature: 95ºF Mean daily range: 32ºF L: 0-16ºFM: 16-25ºF H: 25+ºF DETD=11.3ºF S: p. 1613, T.F.5

  22. Cooling Loads 0.025 20,000 31.0 15,500 15,500 N 0.054 3,980 11.3 2.429 E 0.054 1,980 11.3 1.208 S 0.054 2,950 11.3 1,800 W 0.054 1,980 11.3 1,208 6,645 Insert roof values Insert wall values SR-3

  23. Determine Window DCLF Glazing Type Design Temperature Shading Orientation S: p. 1615, T.F.6

  24. Cooling Loads 0.025 20,000 31.0 15,500 15,500 N 0.054 3,980 11.3 2.429 E 0.054 1,980 11.3 1.208 S 0.054 2,950 11.3 1,800 W 0.054 1,980 11.3 1,208 6,645 Insert roof values Insert wall values Insert glass values N 1,000 14 14,000 E 500 35 17,500 S 2,000 20 40,000 W 500 35 17,500 89,000 SR-3

  25. ASHRAE 62-2001 Defines space occupancy and ventilation loads S: p. 1598, T.E.25

  26. Ventilation Load — Sensible 40,000 sf x 5people/1,000sf = 200 people 200 people x 17 cfm/person = 3,400 cfm

  27. Ventilation Load — Sensible CLF Design Temperature: 95ºF Commercial Building: Ventilation S: p. 1617, T.F.7

  28. Cooling Loads 0.025 20,000 31.0 15,500 15,500 N 0.054 3,980 11.3 2.429 E 0.054 1,980 11.3 1.208 S 0.054 2,950 11.3 1,800 W 0.054 1,980 11.3 1,208 6,645 Insert roof values Insert wall values Insert glass values Insert outdoor air values N 1,000 14 14,000 E 500 35 17,500 S 2,000 20 40,000 W 500 35 17,500 89,000 N/A N/A N/A 3,400 22.0 74,800 74,800 SR-3

  29. People — Sensible Gain Determine number of people: 280 Activity level: moderately active office work S: p. 1617, T.F.8

  30. Cooling Loads 0.025 20,000 31.0 15,500 15,500 N 0.054 3,980 11.3 2.429 E 0.054 1,980 11.3 1.208 S 0.054 2,950 11.3 1,800 W 0.054 1,980 11.3 1,208 6,645 Insert roof values Insert wall values Insert glass values Insert outdoor air values Insert people values N 1,000 14 14,000 E 500 35 17,500 S 2,000 20 40,000 W 500 35 17,500 89,000 N/A N/A N/A 3,400 22.0 74,800 74,800 200 250 50,000 SR-3

  31. Lighting Load Lighting load: 1.5 w/sf Equipment load: 0.5 w/sf

  32. Cooling Loads 0.025 20,000 31.0 15,500 15,500 N 0.054 3,980 11.3 2.429 E 0.054 1,980 11.3 1.208 S 0.054 2,950 11.3 1,800 W 0.054 1,980 11.3 1,208 6,645 Insert roof values Insert wall values Insert glass values Insert outdoor air values Insert people values Insert lighting values Insert equipment values N 1,000 14 14,000 E 500 35 17,500 S 2,000 20 40,000 W 500 35 17,500 89,000 N/A N/A N/A 3,400 22.0 74,800 74,800 200 250 50,000 40,000 1.5 204,780 40,000 0.5 68,260 323,040 SR-3

  33. Cooling Loads 2.5 0.025 20,000 31.0 15,500 15,500 N 0.054 3,980 11.3 2.429 E 0.054 1,980 11.3 1.208 S 0.054 2,950 11.3 1,800 W 0.054 1,980 11.3 1,208 6,645 1.1 Sensible Heat Gain: 508985 Btuh Latent Heat Gain (20%): 101,797 Btuh Total Heat Gain: 610,782Btuh or 50.9 Tons Tons=Q/12,000 N 1,000 14 14,000 E 500 35 17,500 S 2,000 20 40,000 W 500 35 17,500 89,000 14.6 N/A N/A N/A 12.3 3,400 22.0 74,800 74,800 200 250 50,000 40,000 1.5 204,780 52.8 40,000 0.5 68,260 323,040 83.3 508,985 16.7 101,797 100.0 610,782 50.9 SR-3

  34. Cooling Degree Hours

  35. Cooling Degree Hours Relative indicator of warmth S: p. 1496, T.B.1

  36. Cooling Degree Hours Balance Point Temperature (BPT): temperature above which cooling is needed CDH(BPT)= ODBT-BPT If temperature (ODBT)=91ºF CDH74 =ODBT-74 =91-74 =17 cooling degree-hours

  37. Energy Performance Ratings

  38. Performance Ratings COP: coefficient of performance EER: energy efficiency at full load SEER: seasonal energy efficiency ratio Note: SEER≈COP x 3.413

  39. Annual Fuel Consumption

  40. Annual Fuel Usage (E) E= UA x CDH(BPT) SEER where: UA: cooling load/ºF CDH(BPT): degree hours for balance point SEER: seasonal energy efficiency rating

  41. Calculating UA QTotal= UA xΔT UA= QTotal/ΔT From earlier example: QTotal= Btuh ΔT= 95-75=20ºF UA=610782/20= 30,539 Btuh/ºF

  42. Annual Fuel Usage Example Compare two systems to determine what is the expected annual electrical usage for an apartment in Salt Lake City if its peak cooling load is 12,000 Btuh? UA=Q/ΔT UA=12,000/20= 600 Btuh/ºF

  43. Determine SEER Obtain SEER from manufacturer’s data or Convert COP to SEER SEER: 5-15 For this example: SEER1=6.8 SEER2=10.2

  44. Annual Fuel Usage — Electricity E= UA x CDH74 SEER E1 =(600)(9,898)/(6.8) =873,353 wh/yr =873 kwh/yr If electricity is $0.0735/kwh, then annual cost = $64

  45. Annual Fuel Usage — Electricity E= UA x CDH74 SEER E2 =(600)(9,898)/(10.2) =582,235 wh/yr =582 kwh/yr If electricity is $0.0735/kwh, then annual cost = $43

  46. Simple Payback Analysis

  47. Simple Payback Cooling SystemCost Comparison First Cost ($) System 1 500 System 2 600

  48. Simple Payback Cooling SystemCost Comparison First Annual Incremental Incremental Simple Cost Fuel Cost First Cost Annual Savings Payback ($) ($/yr) ($) ($/yr) (yrs) System 1 500 64 --- --- --- System 2 600 43 100 21 4.8 Payback exceeds 3 years, select system 1 Other factors?

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