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Technology in Architectures. Lecture 5 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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Technology in Architectures

Lecture 5

Cooling Degree Hours

Energy Performance Ratings

Annual Fuel Consumption

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

Summer Design Conditions

Design Dry Bulb Temperature

Mean Daily Range

S: p. 1496, T.B1

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

Determine Envelope U-values

Calculate ΣR and then find U for walls and roofs.

Note: this method ignores floors, doors, and window U-values

Determine DCLF

Glazing Type

Design Temperature

Orientation

S: p. 1615, T.5.6

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

Infiltration

S: p. 1617, T.F.7

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

ASHRAE 62-2001

Defines space occupancy and ventilation loads

S: p. 1598, T.E.25

People — Sensible Gain

Determine number of people

Activity level

S: p. 1617, T.F.8

Lights

Determine wattage of lighting/square foot

• ASHRAE 90.1 prescriptive levels

Note: add 15% for ballasts where applicable (e.g., fluorescent lights)

Equipment

Determine operating wattage of equipment/square foot

• ASHRAE 90.1 prescriptive levels

Note: include a diversity factor (20-30%) if specific usage patterns are unknown.

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

Not calculated separately:

Apply a factor as a percentage of the total sensible cooling load

Dry climates: 20%

Moist/Humid climates: 30%

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

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

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

0.025 20,000 31.0 15,500 15,500

Insert roof values

SR-3

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

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

Determine Window DCLF

Glazing Type

Design Temperature

Orientation

S: p. 1615, T.F.6

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

ASHRAE 62-2001

Defines space occupancy and ventilation loads

S: p. 1598, T.E.25

40,000 sf x 5people/1,000sf = 200 people

200 people x 17 cfm/person = 3,400 cfm

Design Temperature: 95ºF

Commercial Building: Ventilation

S: p. 1617, T.F.7

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

People — Sensible Gain

Determine number of people: 280

Activity level: moderately active office work

S: p. 1617, T.F.8

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

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

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

Cooling Degree Hours

Relative indicator of warmth

S: p. 1496, T.B.1

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

Performance Ratings

COP: coefficient of performance

EER: energy efficiency at full load

SEER: seasonal energy efficiency ratio

Note: SEER≈COP x 3.413

Annual Fuel Usage (E)

E= UA x CDH(BPT)

SEER

where:

CDH(BPT): degree hours for balance point

SEER: seasonal energy efficiency rating

Calculating UA

QTotal= UA xΔT

UA= QTotal/ΔT

From earlier example:

QTotal= 610782 Btuh

ΔT= 95-75=20ºF

UA=610782/20= 30,539 Btuh/ºF

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

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

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

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

Simple Payback

Cooling SystemCost Comparison

First

Cost

(\$)

System 1 500

System 2 600

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?