Reduction of emissions is one of the many benefits of geothermal temperature control systems. Typically heating and cooling in today’s homes uses carbon based fuel. When we burn something, the products of combustion are spewed into the atmosphere. Carbon dioxide, nitrous oxide, sulfur compounds, particulates and others change the composition of our air. Without getting into the global weirding/climate change debate (because I’m of the opinion no one truly understands all of the complexities involved), it just seems prudent to me to minimize activities that most likely have negative consequences we don’t fully grasp.
We have many examples of products or activities once deemed safe that were shown at a later time to be quite hazardous. Asbestos, PCB’s, leaded gasoline, DDT, nuclear tests, Agent Orange etc. are just the tip of the iceberg. Given our lack of a solid understanding of the ramifications of using our air as a sewer, shouldn’t we try to do it less? We have a proven ability to alter the spaceship we live on, and often not for the better. The best description of the ‘status quo’ stance is ‘reckless’. Let’s focus in on carbon emissions and how different choices for HVAC compare.
A comparison of the options
Calculating the level of reduction involves a fair number of steps to be taken to compare various fuel options. We need to know the carbon emissions for each fuel per common unit of heat content. The unit commonly used is called a “therm.” A therm is 100,000 btus. I used data from a website:
The raw data for carbon content and then the final value (after several conversion factors) of pounds per therm for each fuel is:
Oil- 10.15 kg/gallon or 16.24 lbs/therm
Natural gas- .005 tonnes/CCF or 11.02 lbs/therm
Propane- 5.74 kg/gallon or 13.32 lbs/therm
Electricty- 0.728 lbs/kwh or 21.33 lbs /therm
The carbon emissions for electricity is a New England average. Regional differences are significant depending on the makeup of the electricity sources (fossil fuel, nuclear or renewable). The national average is 1.22 lbs/kwh with the lowest, Vermont at .0055lbs/kwh and the highest, North Dakota at 2.069 lbs/kwh. As you can see, New England is below the national average. At first glance, electricity is the highest carbon emitter, but that would apply for using electric resistance heat. Geothermal temperature control systems run at an annual average efficiency of 400%. The carbon emissions associated with a geothermal system would be only a quarter of the above listed carbon emission, or
Geothermal heat pump- 5.33 lbs/therm
The percentage of carbon emissions reductions achieved by going geothermal for heat is as follows.
Natural gas- 51.6%
Electric resistance- 75%
On the air conditioning side, things are much simpler. Since conventional air conditioning and geothermal use the same fuel source, the carbon reductions are a matter of efficiency. For existing units, SEER ratings (cooling efficiency) of 8 to 12 would include most units. For new construction, SEER ratings of 16 would be for high quality conventional equipment. An average SEER for a geothermal system would be 20. Carbon reductions achieved by going geothermal:
Retrofitting older equipment- 40% to 60%
New construction with high quality equipment- 20%
A representative example
We are just in the final stages of a good size geothermal retrofit. The home had an oil boiler that fed four remote air handlers and provided domestic hot water. Each air handler also had a conventional condenser for air conditioning, total capacity 12 tons. The home used 1928 gallons of fuel oil last year. The picture below was taken by the very excited lady of the house since she wanted a record of the oil system being unceremoniously evicted.
The carbon emissions for 1928 gallons of oil are 43,823 lbs of CO2. The geo system will achieve a 67.2% reduction, saving 29,449 lbs of CO2. A 12 ton air conditioning system running at a SEER of ten for 800 full load operating hours would consume 3375 kwh emitting an additional 2,457 lbs of CO2. The new system will save 50% of that or 1,229 lbs of CO2. Total CO2 reduction is from 46,280 lbs to 15,603 lbs, or 66.3%
As for monetary savings, if we assume oil at $3.75 and electricity @ $0.18/kwh, we expect first year annual savings on heating, cooling and domestic hot water of $4,573.75. These savings will increase with the ever increasing cost of energy.
Great for both the environment and the savings account!