Val Prest Payback Calculations

HEATING my NEW HOME & RE-CAPTURE of CAPITAL COST By Lynwood V. Prest, P.E., 11 Highland Road, Groton, MA 01450

Water Energy Distributors, Plaistow, NH calculated the Heating Load = 79,847 BtuH, for a Farenheit temperature difference of -2 outside to 70 degrees inside = 72 degrees. Bill Wenzel Heating & Air Conditioning designed and built the Geothermal HVAC sytem to do that. Assume a more seasonal, average temperature difference of 25 to 69 degrees = 44 degrees Then my Heating load is 79,847 x (44/72) = 48,795 BtuH Operating 24 hrs/day for 30 days per month the total Btu = 48,795 x 24 x 30 = 35,136,680 Btu Heating oil contains 138,690 BTU's per gallon. (From kirotv.com, "The Facts About Heating Oil".) Therefore oil usage per month would be 35,136,680 BTU/138,690 BTU per gallon = 253.32 gallons/month Heating Oil costs $3.46 per gallon as of Feb. 27, 2008 according to the Energy Information Administration, (Official Energy Statistics from the U.S. Government) Therefore, if I used oil heat, its cost would have been 253.32 gallons x $3.46/gallon = $876.48/mnth This would not include electricity for lights and appliances. My new home has all high-efficiency, Energy-Star-Rated lighting and appliances, except for the radiant heating in the workshop. My largest invoice from Groton Electric was $346.38 for January, 2008 which includes everything in the house - Geothermal HVAC, ventilation system, lighting, appliances, tools, radios, stereo systems, etc. What would separate electricity cost? For August, 2007, our 1st month in the home, the electric bill that came on 9/1/2007 was Though that included some air conditioning I will ignore it and use that cost for the separate electricity. SO, assuming oil-fired heat, monthly cost would have been $876.48 + $124.09 = $1,000.57mnth for Dec., Jan. & Feb. Apply 1/2 the oil costs + electricity for Oct., Nov., March and April = $876.48/2 + $124.09 = $562.33/mnth Let us further assume that for the other 5 months there is no savings (Not quite true because AC and heating water is ignored.).

Annual cost would have been 3 x $1000.57 + 4 x $562.33 + 5 x $124.09 =

$5,871.48

Projected Actual Annual cost in new house = 3 x $346 + 4 x $155 + 5 x $124 Diff. =

$3,593/yr

Time to re-capture excess capital cost for Geothermal HVAC system = $20990/$3593 =

APITAL COST

C sytem to do that.

= 44 degrees

35,136,680 Btu

out Heating Oil".)

on = 253.32 gallons/month

nformation Administration,

allon = $876.48/mnth

all high-efficiency, e workshop. ncludes everything in the s, stereo systems, etc.

/2007 was $124.09. the separate electricity.

9 = $1,000.57mnth

+ $124.09 = $562.33/mnth e true because AC and

124.09 =

$5,871.48

+ 5 x $124 =$2,278 $3,593/yr

/$3593 =

6 years