Math in HVACMath in HVAC

Presented by Mike VeederPresented by Mike Veeder

HVAC instructor HVAC instructor

Columbia Greene QuestarColumbia Greene Questar

Whole House Heat LossWhole House Heat Lossquestion #1question #1

Determine design temp differenceDetermine design temp difference Find total square foot of windows and doorsFind total square foot of windows and doors Find gross wallsFind gross walls Subtract windows and doors from gross Subtract windows and doors from gross

walls to find net wallswalls to find net walls Determine exposed ceiling areaDetermine exposed ceiling area Find floor areaFind floor area

Multiply each by U factorMultiply each by U factor Add all btu’s/degree FahrenheitAdd all btu’s/degree Fahrenheit Multiply by temp differenceMultiply by temp difference Multiply by 15% for duct lossesMultiply by 15% for duct losses Arrive at heating btu loss for houseArrive at heating btu loss for house

Calculate annual heat lossCalculate annual heat lossQuestion #2Question #2

BTU annual = BTUH x HDD x 24hr/day BTU annual = BTUH x HDD x 24hr/day x .75x .75

• BTU annual = 875 x 6860 x 24 x .75BTU annual = 875 x 6860 x 24 x .75

• Annual heat loss is 108,045,000 btusAnnual heat loss is 108,045,000 btus

PropanePropane

• Determine how many gallons of propane Determine how many gallons of propane burned per yearburned per year

• Gal/yr = annual btu / 92,000btu / galGal/yr = annual btu / 92,000btu / gal• Gal/yr = 108,045,000/92,000Gal/yr = 108,045,000/92,000• Gal/yr = 1174 galGal/yr = 1174 gal• Cost/yr = 1174 gal x $2.60/galCost/yr = 1174 gal x $2.60/gal• Cost/yr = $3052.40 x stack loss of furnaceCost/yr = $3052.40 x stack loss of furnace• Cost/yr = $3662.88Cost/yr = $3662.88

ElectricityElectricity

• Determine the amount of electricity used Determine the amount of electricity used on a annual basison a annual basis

• Watt/yr = btu annual / 3.41 btu/wattWatt/yr = btu annual / 3.41 btu/watt

• Watt/yr = 108,045,000/3.41Watt/yr = 108,045,000/3.41

• Watt/yr = 31,684,750 / 1000Watt/yr = 31,684,750 / 1000

• KW/yr =31,684 x .14/kwKW/yr =31,684 x .14/kw

• Yearly cost of electric is $4435.87Yearly cost of electric is $4435.87

Calculate BTU output of a Heat Calculate BTU output of a Heat PumpPumpQuestion 5Question 5

• BTU=1.08 x cfm x delta “T”BTU=1.08 x cfm x delta “T”

• CFM= FPM x .66 x sq. ft of duct areaCFM= FPM x .66 x sq. ft of duct area

Determine cfm of a Determine cfm of a Geothermal Heat pumpGeothermal Heat pumpQuestion #4Question #4

• CFM = fpm x .66 x sq. ftCFM = fpm x .66 x sq. ft

• CFM = 606 fpm x .66 x 2CFM = 606 fpm x .66 x 2

• CFM = 800 cfmCFM = 800 cfm

• Btu = 1.08 x cfm x delta “t”Btu = 1.08 x cfm x delta “t”

• Btu = 1.08x 800 x (92 – 65)Btu = 1.08x 800 x (92 – 65)

• Btu = 23,328 btuBtu = 23,328 btu

Geothermal loop performanceGeothermal loop performanceQuestion #6Question #6

Loop filled with 20% MethanolLoop filled with 20% Methanol

Btu = 485 x gpm x Delta “t”Btu = 485 x gpm x Delta “t”

Btu = 485 x 6 x (40 – 32)Btu = 485 x 6 x (40 – 32)

Btu = 23,280 btuBtu = 23,280 btu

BPI Building Airflow StandardBPI Building Airflow Standard(BAS)(BAS)

Living Space Area = 1500 sq. ft.Living Space Area = 1500 sq. ft.

Basement area = 700 sq. ft.Basement area = 700 sq. ft.

Ceiling height = 8 ft.Ceiling height = 8 ft.

# of Occupants = 4# of Occupants = 4

# of stories above grade = 2# of stories above grade = 2

Location = Albany, NYLocation = Albany, NY

Calculate ventilation required for Calculate ventilation required for buildingbuilding

Airflow(b) = .35 x volume/60Airflow(b) = .35 x volume/60

Volume = 8 x (1500 + 700) = 17,600 Volume = 8 x (1500 + 700) = 17,600 cu. ft.cu. ft.

Airflow(b) = .35 x 17,600 / 60Airflow(b) = .35 x 17,600 / 60

Airflow(b) = 102 cfmAirflow(b) = 102 cfm

Calculate ventilation required for Calculate ventilation required for peoplepeople

Airflow(p) = 15 x # of occupantsAirflow(p) = 15 x # of occupants

Airflow(p) = 15 x 4 = 60 cfmAirflow(p) = 15 x 4 = 60 cfm

Using the higher airflow Using the higher airflow requirementrequirement

Convert cfm to cfm50Convert cfm to cfm50

Minimum cfm50 = airflow x NMinimum cfm50 = airflow x N

N = LBL conversion factor N = LBL conversion factor

Minimium cfm50 = 102 cfm x 15.4 = Minimium cfm50 = 102 cfm x 15.4 = 1570 cfm501570 cfm50

When we read the cfm50 from the When we read the cfm50 from the blower door, 1570 is what is blower door, 1570 is what is recommended for infiltration for this recommended for infiltration for this househouse

Determine course of action for homeDetermine course of action for home

Cfm50 x .7 = minimum ventilationCfm50 x .7 = minimum ventilation 1570 cfm50 x .7 = 1099 cfm501570 cfm50 x .7 = 1099 cfm50

If the blower door reads:If the blower door reads:– Above 1570 cfm then the house is too loose Above 1570 cfm then the house is too loose

and you would recommend air sealingand you would recommend air sealing

If the blower door reads:If the blower door reads:– Between 1570 cfm50 and 1099 cfm50, then the Between 1570 cfm50 and 1099 cfm50, then the

house is within the normal range for infiltration house is within the normal range for infiltration and ventilationand ventilation

If the blower door reads:If the blower door reads:– Below 1099 cfm50 then you need to Below 1099 cfm50 then you need to

mechanically ventilate the house using a hrv or mechanically ventilate the house using a hrv or equivalent device. The house is too tight at this equivalent device. The house is too tight at this point.point.

My class after a math lessonMy class after a math lesson

Thanks for your attention !!Thanks for your attention !!

Any questions??????????Any questions??????????