Technology in Architecture Lecture 7 Degree Days Heating Loads Annual Fuel Consumption Simple Payback Analysis

Heating Degree Days Balance Point Temperature (BPT): temperature above which heating is not needed DDBPT= BPT-TA

Sample Calculation January TA=28ºF DD65=65-28= 37 Degree-days/day x 31 days = 1,147 degree-days M: p. 1620, T.C.19

Heating Loads

Heating Loads Computed for worst case scenario: Do not include: Pre-dawn at outdoor design dry bulb temperature Do not include: Insolation from sun Heat gain from people, lights, and equipment Infiltration in nonresidential buildings Ventilation in residential buildings SR-3

Outdoor Dry Bulb Temperature M: T.B.1, p. 1571 Outdoor Dry Bulb Temperature Use Winter Conditions RESCAN S11: T.B.1 1513

Determine Temperature Difference Indoor Dry Bulb Temperature (IDBT): 68ºF Outdoor Dry Bulb Temperature (ODBT): 13ºF ΔT=IDBT-ODBT=68ºF - 13ºF = 55ºF

Determine Envelope U-values Calculate ΣR and then find U for walls, roofs, floors. Obtain U values for glazing from manufacturer or other reference

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 12’ 4’ 4’ 8’ Elevation

Floor Slabs For floor slabs at grade, there are two heat loss components: slab to soil losses edge losses M: p. 1680, F.E.1

TI=Indoor Air Temperature TGW=Ground Water Temperature Slab to Soil Losses Q=Uslab x 0.5 x Aslab x (TI-TGW) TI=Indoor Air Temperature TGW=Ground Water Temperature

Edge Losses Method I Determine F2 based on heating degree days M: p. 1680, T.E.11/F. E.1

Select F2 based on insulation configuration Slab Edge Losses Method II Select F2 based on insulation configuration M: 1681, T.E.12

TI= Indoor air temperature TO=Outdoor air temperature Slab Edge Losses Q=F2 x Slab Perimeter Length x (TI-TO) where, TI= Indoor air temperature TO=Outdoor air temperature

Heating Load Example Problem Building: Office Building Location: Salt Lake City ΔT=IDBT-ODBT=68-13=55ºF Building: 200’ x 100’ (2 stories, 12’-6” each) Uwall= 0.054 Btuh/sf-ºF Uroof= 0.025 Btuh/sf-ºF Uwindow= 0.31 Btuh/sf-ºF Uslab= 0.16 Btuh/sf-ºF Udoor= 0.20 Btuh/sf-ºF Slab Edge: R-15 vertical insulation, 2’ deep. Degree Days = 5,983

Heating 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

Heating Loads Insert roof values Insert wall values 0.025 20,000 55 N 0.054 3,980 55 E 0.054 1,980 55 S 0.054 2,950 55 W 0.054 1,980 55 Insert roof values Insert wall values Insert glass values Insert door values Insert floor values N 0.31 1,000 55 E 0.31 500 55 S 0.31 2,000 55 W 0.31 500 55 0.20 110 55 N/A N/A N/A N/A SR-3

TI=Indoor Air Temperature TGW=Ground Water Temperature Slab to Soil Losses Q=Uslab x 0.5 x Aslab x (TI-TGW) TI=Indoor Air Temperature TGW=Ground Water Temperature Ground Water= 53ºF ΔT=68ºF-53ºF=15ºF

Heating Loads Insert floor values SR-3 0.025 20,000 55 0.025 20,000 55 N 0.054 3,980 55 E 0.054 1,980 55 S 0.054 2,950 55 W 0.054 1,980 55 Insert floor values N 0.31 1,000 55 E 0.31 500 55 S 0.31 2,000 55 W 0.31 500 55 0.20 110 55 N/A N/A N/A N/A 0.16 20,000 15 SR-3

Select F2 based on insulation configuration Slab Edge Losses Method II Select F2 based on insulation configuration Slab Edge: R-15 vertical insulation, 2’ deep. F2=0.52 M: 1681, T.E.12

Heating Loads Insert floor values SR-3 0.025 20,000 55 0.025 20,000 55 N 0.054 3,980 55 E 0.054 1,980 55 S 0.054 2,950 55 W 0.054 1,980 55 Insert floor values N 0.31 1,000 55 E 0.31 500 55 S 0.31 2,000 55 W 0.31 500 55 0.20 110 55 N/A N/A N/A N/A 0.16 20,000 15 0.52 600 55 SR-3

Infiltration Residential buildings use infiltration to provide fresh air “Air change/hour (ACH) method” or “Crack length method” Prone to subjective interpretation Vulnerable to construction defects Provides a relatively approximate result

ASHRAE Standard 62.1-2016 (M: p. 1696, T.F.1) Ventilation Analysis Non-residential buildings use ventilation to provide fresh air and to offset infiltration effects. ASHRAE Standard 62.1-2016 (M: p. 1696, T.F.1) Estimates the number of people/1000 sf of usage type Prescribes minimum ventilation/person for usage type

ASHRAE 62.1-2016 Defines space occupancy and ventilation loads M: p. 1697, T.F.1

Ventilation Load — Sensible 40,000 sf x 5people/1,000sf = 200 people 200 people x 17 cfm/person = 3,400 cfm 3,400 cfm x 60min/hr = 204,000cfh

Heating Loads Input Ventilation Load—Sensible SR-3 0.025 20,000 55 0.025 20,000 55 N 0.054 3,980 55 E 0.054 1,980 55 S 0.054 2,950 55 W 0.054 1,980 55 Input Ventilation Load—Sensible N 0.31 1,000 55 E 0.31 500 55 S 0.31 2,000 55 W 0.31 500 55 0.20 110 55 N/A N/A N/A N/A 0.16 20,000 15 0.52 600 55 204,000 55 SR-3

Ventilation Load — Latent Determine ΔW WI= 0.0066 #H2O/#dry air -WO= 0.0006 #H2O/#dry air ΔW= 0.0060 #H2O/#dry air

Heating Loads Input Ventilation Load — Latent SR-3 0.025 20,000 55 27,500 N 0.054 3,980 55 11,583 E 0.054 1,980 55 5.880 S 0.054 2,950 55 8,762 W 0.054 1,980 55 5,880 Input Ventilation Load — Latent N 0.31 1,000 55 17,050 E 0.31 500 55 8,525 S 0.31 2,000 55 34,100 W 0.31 500 55 8,525 0.20 110 55 1,210 N/A N/A N/A N/A 0.16 20,000 15 24,000 0.52 600 55 17,160 204,000 55 201,960 204,000 0.0060 97,308 SR-3

Heating Load Total Load 469,435 Btuh 5.9 6.8 8.8 SR-3 14.5 0.3 63.8 0.025 20,000 55 27,500 27,500 5.9 N 0.054 3,980 55 11,583 E 0.054 1,980 55 5,880 S 0.054 2,950 55 8,762 W 0.054 1,980 55 5,880 32,105 Total Load 469,435 Btuh 6.8 N 0.31 1,000 55 17,050 E 0.31 500 55 8,525 S 0.31 2,000 55 34,100 W 0.31 500 55 8,525 68,200 14.5 0.20 110 55 1,210 1,210 0.3 N/A N/A N/A N/A 0.16 20,000 15 24,000 0.52 600 55 17,160 41,160 8.8 204,000 55 201,960 204,000 0.0060 97,308 299,268 63.8 SR-3 469,435

Annual Fuel Consumption

Annual Fuel Usage (E) E= UA x DDBPT x 24 AFUE x V where: UA: heating load/ºF DDBPT: degree days for given balance point AFUE: annual fuel utilization efficiency V: fuel heating value

Calculating UA QTotal= UA x ΔT UA= QTotal/ΔT From earlier example: QTotal=469,435 Btuh ΔT= 55ºF UA=469,435/55=8,535 Btuh/ºF

Determine AFUE Annual Fuel Utilization Efficiency of an electric heating system is 100% M: p. 311, T.9.4

Determine Heat Content (V) Heat content is the quantity of Btu/unit Note: Natural Gas is sold in therms (100 cf) M: p. 309, T.9.2

Annual Fuel Usage Example What is the expected annual fuel usage for a house in Salt Lake City if its peak heating load is 35,750 Btuh? UA=Q/ΔT UA=35,750/55= 650 Btuh/ºF

Determine AFUE Annual Fuel Utilization Efficiency of an electric heating system is 100% M: p.311, T.9.4

Determine Heat Content (V) Heat content is the quantity of Btu/unit M: p. 309, T.9.2

Annual Fuel Usage — Electricity E= UA x DD x 24 AFUE x V EELEC =(650)(5,983)(24)/(1.0)(3,413) =27,347 kwh/yr If electricity is $0.0735/kwh, then annual cost = $2,010

Annual Fuel Usage — Gas E= UA x DDBPT x 24 AFUE x V =1,111 therms/yr If gas is $0.41/therm, then annual cost = $456

Simple Payback Analysis

Simple Payback Heating System Cost Comparison First Electricity 6,000 ($) Electricity 6,000 Oil 8,000 Gas 8,900

Simple Payback Heating System Cost Comparison First Annual Incremental Incremental Simple Cost Fuel Cost First Cost Annual Savings Payback ($) ($/yr) ($) ($/yr) (yrs) Electricity 6,000 2,010 --- --- --- Oil 8,000 1,152 2,000 858 2.3 Gas 8,900 456 2,900 1,554 1.9 If money is available, select gas furnace system