Groton Local Energy Seminar Series # 7:

Geothermal Energy to Heat Our New Home

09-Apr-08By Lynwood Valentine Prest, P.E.

Presentation available at: http://grotonlocal.org/seminar.shtml

Email: vprest@gmail.com

Val and Wendy Prest’s New Home in Groton, MA

• Heavily-insulated• Uses Geothermal

Energy for its HVAC• Designed and

decorated by the home owners

• Builder: Shawn Boyd– Boyd Building, LLC,

Jaffrey, NH

TIGHTNESS & INSULATION• Critical, no matter what fuels & HVAC equipment used• Insulate roof or attic - R=30 or better. Ours is R=50. • Insulate exterior walls, doors and windows - R=20 or better. Ours is

about R=27.• Insulate around penetrations through roofs, attics & exterior walls

with spray-on foam• Around doors, windows, pipes, ducts, electrical items, etc.• NO fireplace so no chimney and flue• Insulate sills atop foundations with spray-on urethane foam• Obtain lowest possible Energy Star Rating. They measure air

leakage rates.• 0 to 100 w/ max at 85 to obtain Energy Star rating• Our house came in at 44

Other Factors

• VENTILATION– Necessary because house is so tight against

air leaks• LIGHTING & APPLIANCES

– Energy Star to minimize electrical usage and heat generation

HVAC with Water Filters

Geothermal Water Piping

Ven Mar Energy Economizer

Geothermal Heating System• Design: Water Energy Distributors, Inc., Hampstead, NH

– Uses their standing-well concept, a single water well that serves for both domestic use and geothermal energy.

• Furnished & installed by Bill Wenzel Heating and Air Conditioning, Inc., Merrimack, NH– Tranquility system with a 40-gallon water storage tank and a

separate 80-gallon water heater tank– Ven Mar energy recovery ventilator– 240V ultraviolet germicidal lamp– 2 separate zone-damper panels.

• Installation included:– Ductwork and grilles– Insulation of exposed ductwork.

• COST, including installation: $33,985

Water Well• Single well for both geothermal energy and domestic use

– Water line splits just inside the house.– One line goes to the heat exchanger of the geothermal system– Other line goes to the domestic water system

• Heat exchanger utilizes 35 gpm of water to obtain heat and cooling energy– Incoming water stays about 49 to 50 degrees F all year

• Well, originally designed for a depth of 700 ft., stopped at 300 ft. upon encountering a 400 gpm aquifer

• COST= $10,505

Economic Analysis - Installation -

• Cost for geothermal– Cost of system: $33,985– Cost of well: $10,505– Total cost: $44,490

• Cost of conventional alternative:– Cost of water well: $4,500– Cost of oil/gas-fired HVAC system: $19,000– Total cost: $23,500

• Additional cost for geothermal: $20,990

Other Decision Factors• Entire lot (less than 1/4 acre) is within the 100

foot buffer zone from the lake’s edge.• We did not want oil on the property, and it is

expensive anyway. • We have little to no room for a large propane

gas tank. • Coal and wood fired systems are labor intensive,

messy on cleanup, and needs waste disposal.• Electrical resistance heating is too inefficient and

expensive to operate.

Actual Operational Costs for Electricity

Month of Bill Amount of Bill *8/2007 23.149/2007 124.09

10/2007 168.2911/2007 155.5212/2007 155.251/2008 258.192/2008 346.383/2008 342.73 TOTAL 1,598.04

Supplier: Groton Electric Light

Comparison with Operational Cost for Conventional Oil Alternative

• Heating with oil:– Estimated gals. per month:253.3– Est’d $ per month at $3.46/gal: $876

• Non-heating electricity per mo.: $124• Total est’d for oil + electric per mo.: $1,000• Total est’d for oil + electric per yr.: $5,871

• Est’d total electric for geothermal/yr.: $2,278• Net savings per year: $3,593• Time to recover excess capital costs: 6 years

Bill’s