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Math in HVAC

Math in HVAC. Presented by Mike Veeder HVAC instructor Columbia Greene Questar. Whole House Heat Loss question #1. Determine design temp difference Find total square foot of windows and doors Find gross walls Subtract windows and doors from gross walls to find net walls

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Math in HVAC

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  1. Math in HVAC Presented by Mike Veeder HVAC instructor Columbia Greene Questar

  2. Whole House Heat Lossquestion #1 • Determine design temp difference • Find total square foot of windows and doors • Find gross walls • Subtract windows and doors from gross walls to find net walls • Determine exposed ceiling area • Find floor area

  3. Multiply each by U factor • Add all btu’s/degree Fahrenheit • Multiply by temp difference • Multiply by 15% for duct losses • Arrive at heating btu loss for house

  4. Calculate annual heat lossQuestion #2 • BTU annual = BTUH x HDD x 24hr/day x .75

  5. BTU annual = 875 x 6860 x 24 x .75 • Annual heat loss is 108,045,000 btus

  6. Propane • Determine how many gallons of propane burned per year • Gal/yr = annual btu / 92,000btu / gal • Gal/yr = 108,045,000/92,000 • Gal/yr = 1174 gal • Cost/yr = 1174 gal x $2.60/gal • Cost/yr = $3052.40 x stack loss of furnace • Cost/yr = $3662.88

  7. Electricity • Determine the amount of electricity used on a annual basis • Watt/yr = btu annual / 3.41 btu/watt • Watt/yr = 108,045,000/3.41 • Watt/yr = 31,684,750 / 1000 • KW/yr =31,684 x .14/kw • Yearly cost of electric is $4435.87

  8. Calculate BTU output of a Heat PumpQuestion 5 • BTU=1.08 x cfm x delta “T” • CFM= FPM x .66 x sq. ft of duct area

  9. Determine cfm of a Geothermal Heat pumpQuestion #4 • CFM = fpm x .66 x sq. ft • CFM = 606 fpm x .66 x 2 • CFM = 800 cfm • Btu = 1.08 x cfm x delta “t” • Btu = 1.08x 800 x (92 – 65) • Btu = 23,328 btu

  10. Geothermal loop performanceQuestion #6 • Loop filled with 20% Methanol • Btu = 485 x gpm x Delta “t” • Btu = 485 x 6 x (40 – 32) • Btu = 23,280 btu

  11. BPI Building Airflow Standard(BAS) • Living Space Area = 1500 sq. ft. • Basement area = 700 sq. ft. • Ceiling height = 8 ft. • # of Occupants = 4 • # of stories above grade = 2 • Location = Albany, NY

  12. Calculate ventilation required for building • Airflow(b) = .35 x volume/60 • Volume = 8 x (1500 + 700) = 17,600 cu. ft. • Airflow(b) = .35 x 17,600 / 60 • Airflow(b) = 102 cfm

  13. Calculate ventilation required for people • Airflow(p) = 15 x # of occupants • Airflow(p) = 15 x 4 = 60 cfm

  14. Using the higher airflow requirement • Convert cfm to cfm50 • Minimum cfm50 = airflow x N • N = LBL conversion factor • Minimium cfm50 = 102 cfm x 15.4 = 1570 cfm50

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

  16. Determine course of action for home • Cfm50 x .7 = minimum ventilation • 1570 cfm50 x .7 = 1099 cfm50

  17. If the blower door reads: • Above 1570 cfm then the house is too loose and you would recommend air sealing

  18. If the blower door reads: • Between 1570 cfm50 and 1099 cfm50, then the house is within the normal range for infiltration and ventilation

  19. If the blower door reads: • Below 1099 cfm50 then you need to mechanically ventilate the house using a hrv or equivalent device. The house is too tight at this point.

  20. My class after a math lesson

  21. Thanks for your attention !! • Any questions??????????

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