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**Environmental Controls I/IG**

Lecture 11 Degree Days Heating Loads Annual Fuel Consumption Simple Payback Analysis

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

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**Sample Calculation January TA=28ºF DD65=65-28= 37 Degree-days/day**

x 31 days = 1,147 degree-days S: p. 1524, T.C.15

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Heating Loads

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**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

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**Outdoor Dry Bulb Temperature**

Use Winter Conditions S: p. 1496, T.B.1

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**Determine Temperature Difference**

Indoor Dry Bulb Temperature (IDBT): 68ºF Outdoor Dry Bulb Temperature (ODBT): 8ºF ΔT=IDBT-ODBT=68ºF - 8ºF = 60ºF

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**Determine Envelope U-values**

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

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**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

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Floor Slabs For floor slabs at grade, there are two heat loss components: slab to soil losses edge losses S: p. 1583, T.E.11

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**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

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**Edge Losses Method I Determine F2 based on heating degree days**

S: p. 1582, T.E.11

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**Select F2 based on insulation configuration**

Slab Edge Losses Method II Select F2 based on insulation configuration S: 1583, T.E.12

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**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

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**Heating Load Example Problem**

Building: Office Building Location: Salt Lake City ΔT=IDBT-ODBT=68-8=60ºF Building: 200’ x 100’ (2 stories, 12’-6” each) Uwall= Btuh/sf-ºF Uroof= Btuh/sf-ºF Uwindow= Btuh/sf-ºF Uslab= Btuh/sf-ºF Udoor= Btuh/sf-ºF

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**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, , Doors Net Wall 3,980 1,980 2,950 1,980 Roof/Floor Slab 20,000

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**Heating Loads Insert roof values Insert wall values**

, , ,000 N , ,895 E , ,415 S , ,558 W , , ,555 Insert roof values Insert wall values Insert glass values Insert door values Insert floor values N , ,600 E ,300 S , ,200 W , ,400 ,320 1,320 N/A N/A N/A N/A SR-3

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**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

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**Heating Loads Insert floor values SR-3 0.025 20,000 60 30,000 30,000**

, , ,000 N , ,895 E , ,415 S , ,558 W , , ,555 Insert floor values N , ,600 E ,300 S , ,200 W , ,400 ,320 1,320 N/A N/A N/A N/A , ,000 SR-3

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**Edge Losses Method I Determine F2 based on heating degree days**

S: p. 1582, T.E.11

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Heating Degree Days Salt Lake City HDD65=5983 S: p. 1524, T.C.15

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Edge Losses Method I Interpolate to find F2 at 5983 DD 0.50 F2? 0.56 S: p. 1582, T.E. 11

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Interpolate to Find F2 Find difference in Degree Days: = =2083 Find difference in F2: F2?-0.50=x =0.06 Set up proportion, solve for x: 633/2083=x/0.06 x=0.018 F2?-0.50=0.018 F2?=0.518

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Edge Losses Method I Interpolate to find F2 at 5983 DD 0.50 F2= 0.56 0.518 S: p. 1582, T.E.11

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**Heating Loads Insert floor values SR-3 0.025 20,000 60 30,000 30,000**

, , ,000 N , ,895 E , ,415 S , ,558 W , , ,555 Insert floor values N , ,600 E ,300 S , ,200 W , ,400 ,320 1,320 N/A N/A N/A N/A , ,000 ,648 42,648 SR-3

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Infiltration Residential buildings use infiltration to provide fresh air “Air change/hour (ACH) method” (see S: p.1601, T. E.27) or “Crack length method” (see S: p. 1603, T. E.28) Prone to subjective interpretation Vulnerable to construction defects Provides a relatively approximate result

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**ASHRAE Standard 62-2001 (S: p. 1597-99, T.E.25)**

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

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**ASHRAE 62-2001 Defines space occupancy and ventilation loads**

S: p. 1598, T.E.25

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**ASHRAE 62-2001 Defines space occupancy and ventilation loads**

S: p. 1598, T.E.25

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**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

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**Heating Loads Input Ventilation Load—Sensible SR-3**

, , ,000 N , ,895 E , ,415 S , ,558 W , , ,555 Input Ventilation Load—Sensible N , ,600 E ,300 S , ,200 W , ,400 ,320 1,320 N/A N/A N/A N/A , ,000 ,648 42,648 204, ,320 SR-3

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**Ventilation Load — Latent**

Determine ΔW WI= #H2O/#dry air -WO= #H2O/#dry air ΔW= #H2O/#dry air

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**Heating Loads Input Ventilation Load — Latent SR-3**

, , ,000 N , ,895 E , ,415 S , ,558 W , , ,555 Input Ventilation Load — Latent N , ,600 E ,300 S , ,200 W , ,400 ,320 1,320 N/A N/A N/A N/A , ,000 ,648 42,648 204, ,320 204, SR-3

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**Heating Load Total Load 504551 Btuh or 505 MBH 5.9 7.6 8.4 SR-3 14.7**

, , ,000 5.9 N , ,895 E , ,415 S , ,558 W , , ,555 Total Load Btuh or 505 MBH 7.6 N , ,600 E ,300 S , ,200 W , ,400 14.7 ,320 1,320 0.3 N/A N/A N/A N/A , ,000 ,648 42,648 8.4 204, 204, , 63.1 SR-3 504551

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**Annual Fuel Consumption**

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**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

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**Calculating UA QTotal= UA x ΔT UA= QTotal/ΔT From earlier example:**

QTotal=504,551 Btuh ΔT= 60ºF UA=504,551/60=8,409 Btuh/ºF

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Determine AFUE Annual Fuel Utilization Efficiency of an electric heating system is 100% S: p. 258, T.8.7

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**Determine Heat Content (V)**

Heat content is the quantity of Btu/unit Note: Natural Gas is sold in therms (100 cf) S: p. 255, T.8.5

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**Annual Fuel Usage Example**

What is the expected annual fuel usage for a house in Salt Lake City if its peak heating load is 39,000 Btuh? UA=Q/ΔT UA=39,000/60= 650 Btuh/ºF

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Determine AFUE Annual Fuel Utilization Efficiency of an electric heating system is 100% S: p.258, T.8.7

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**Determine Heat Content (V)**

Heat content is the quantity of Btu/unit S: p. 255, T.8.5

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**Annual Fuel Usage — Electricity**

E= UA x DDBPT 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

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**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

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**Simple Payback Analysis**

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**Simple Payback Heating System Cost Comparison First Electricity 6,000**

($) Electricity 6,000 Oil 8,000 Gas 8,900

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**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, Oil 8,000 1,152 2, Gas 8, ,900 1, If money is available, select gas furnace system

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