I am wondering if I have understood things correctly. I am attempting to compare projected heating costs of different types of heat sources. The program I have outputs annual heating needs in therms, which I can convert into dollars for natural gas and propane without much ado. It is the geothermal I am wondering about.
If there are 100,067 Btu in 1 Therm, then it takes 29.3193 KwH to make 1 Therm. (100,067/3,413)
Then I divide by the COP of the geothermal unit right? So if using a model with a COP of 4.0, 1 Therm is 7.3298 KwH, right?
Thus if I need 1,700 Therms/year, I would be using approx 12,461 KwH.
In my area, a KwH is $0.1056; so the projected cost should be $1,315.85.
I am shocked at how much lower that is than fuel! Am I missing something such as auxillary heating, losses form the ground temp warming, etc.? Is there a way to calculate these?

Jake Vierzen
R-Value Concrete Structures LLC
www.rvaluehomes.com

Posted By rvalue on 30 Dec 2010 04:11 PM
...........
I am shocked at how much lower that is than fuel! ...

Jake Vierzen
R-Value Concrete Structures LLC
www.rvaluehomes.com

Hi,

Your basic math is right.    This is why people are willing to spend the extra for geo.

RE: auxiliary heat, we try to hit 92-98% of your requirement with geo and the rest with auxiliary heat at 1 COP. The reason for this is the last 2-8% of the requirement may take multiple tons of upsizing, larger duct work, larger ground loop etc. all to save 50-100$ a year on aux. heat.
J

Thanks guys;
That is very helpful. I wish I had upgraded to it myself while we still had the tax credit.
So I can expect to get the COP rating for the entire heating season, or is there some drift due to the ground temp changing?
Jake Vierzen
R-Value Concrete Structures
www.rvaluehomes.com

There is very little drift as long as the ground loop is sized correctly to match the heating load. The heatpump specs will tell you at what Entering Water Temp the COP is based on. If you pick the COP that goes with 30° EWT, then most of the year, the COP will be higher.

rvalue: "I wish I had upgraded to it myself while we still had the tax credit. "

rvalue,

Why do you think that you no longer have the tax credit? If you're referring to the 30% federal geothermal tax credit, it is set to expire in 2016.

Regards,

Masoud

Geo vs propane is a slam-dunk in all but the very highest cost electricity markets. Geo vs NG may need more careful analysis

Usually the heatpump are rated at 32F entering water temperature (EWT) from the loopfield. Usually, loops are designed to dip down to 30F at the peak of the winter. We see higher EWT than that during the remainder of the year, especially after the A/C season. As a rule of thumb, COP goes up by 10% for every 10F of higher loop temperature. Also the output temperature (load side) of the heatpump makes a big difference, especially applicable to radiant systems, where an outdoor reset lowers the load temperature. Same rule of thumb there. Every 10 degrees less bring about 10% for the COP.

Thank you all for your input, this helps immensely. Is the EER rating helpful for calculating energy costs?
Masoud: I had thought the tax credit expired today, but if I am wrong, then great!

As far as I know, the tax credit for geothermal is from 2009 through 2016 (with no $1,500 cap), but check with your tax professional or the IRS to be sure.

Also, as far as I know, the 30% credit capped at $1,500 for energy efficient improvements (doors, windows, and insulation) expire today (same disclaimer as above.)

So using geo, your energy costs are around $500/year less than nat gas? Sounds typical.

Tax Credit Data for Geothermal:

Here's the definitive resource for tax credits and State incentives. http://www.dsireusa.org/incentives/incentive.cfm?Incentive_Code=US37F&re=1&ee=1

Many of the State Incentives (CCEF in Connecticut for example) are not listed in the DSIRE database. So check further for State or Utility Company incentives.

Comparing various fossil fuels to the best performing DX systems shows the following - geo savings vs.:
Natural Gas 45-50%
Number 2 oil: 65%
Propane: 70-75%
Electric: 80%



Hope this is helpful.

Paul
www.TotalGreenUS.com

A new built 2500SF ranch I presented the numbers on Friday show a heating cost of $826 with geo and $1,746 with gas with one electric provider and a $1,350/yr savings on all heating/cooling/hot water. Our other local electric provider shows a heat savings of ~$575/yr and all heating/cooling/hot water for ~$900 less a year.
Percentages are obviously impacted greatly by cost of electricity and gas both.
Calling $500 in savings "typical" shows a terrific lack of research and understanding of contributing factors, or numerous qualifiers to support it. i.e.; based on this gas rate, that electric rate,that set point, this manual J load and this many people in the home typical savings would be.....
Since we are within 30 miles of one another jon, I would like to see how you are supporting this "well supported opinion". It's not like you to pull a number out of a hat and call it "typical".
joe

OP,

With your original calculations, the math is correct. I typically look a little differently at it.

Using 29.3 kWh per therm, use your cost of electricity per kWh at that point, and compare the cost per therm. With that in mind, the comparison is:

Electric resistance heating: 29.3 X $0.1056 = $3.094 per therm

Geo (4.0 COP): $3.094 / 4.0 = $0.774 per therm

Our natural gas gets billed to us by the decatherm. Right now, it is about $8.50 per decatherm. So, the rough calculation, including the efficiency of the furnace:
Nat. Gas (90%) per therm: $8.50 / 10 = therms = $0.85 cost of gas. Now, divide this by the efficiency of the appliance. $0.85 / .90 = $0.944 per therm.

Now let's look at LP. LP requires 1.09 gallons to get a therm (roughly). So, at $2.60 per gallon (our price here) the calculation is: (1.09 X $2.60) / .90 = $3.419 per therm.

I don't know the fuel oil stuff, as it's not used in my area. BTW, my area has electric rates of $0.056 per kWh. So our cost per therm is $1.641 for electric resistance, and $0.41 for Geo.

After having the cost per therm, just multiply the required annual therms to show the total cost.

Another side note... my area has a tiered electric rate. So for the first 800 kWh, it's $0.062 per kWh, the next 700 is at $0.056 per kWh, and anything above that is $0.037 per kWh. These are year-round rates. So geo looks good here. Just need to get the word out better.

Here is a link to a handy calculator for comparing costs. For geothermal I just throw 300% in for efficiency to get comparable numbers.

http://www.hearth.com/econtent/index.php/articles/fuel_cost_comparison_calculator/?id=47_0_1_0_M7

It is pretty amazing that people are paying that little for electricity. I pay 0.196$/kwh plus a fixed fee.
Resistance heat 1,000,000 btu/3412(btu/kwh)= 293 kwh * 0.196 = 57.44$
Geothermal 1,000,000 btu/3412(btu/kwh)= 293 kwh /3 * 0.196 = 19.14$
Propane 1,000,000 btu/9300BTU/gallon)*93% efficiency= 11.56 gallons * 1.83$/gallon = 21.15$
Geothermal would be 11% cheaper. Considering I use about 18 million btu’s per year for heat, geothermal could conceivably save me almost 37$ a year. I am guessing the payback would be about the ½ life of californium.
I am firmly of the opinion that for new construction you work to get the heat load very low, and then don’t worry about the source of heat too much.
In older buildings, where the yearly heat requirement is high, and electricity costs are low, geothermal can be a bargain.
With electrical costs in the northeast, geo seems like a very hard sell to me.
Cheers
Eric

Posted By eric anderson on 10 Jan 2011 09:35 AM
It is pretty amazing that people are paying that little for electricity. ......save me almost 37$ a year. I am guessing the payback would be about the ½ life of californium.
I am firmly of the opinion that for new construction you work to get the heat load very low, and then don’t worry about the source of heat too much.
In older buildings, where the yearly heat requirement is high, and electricity costs are low, geothermal can be a bargain.
With electrical costs in the northeast, geo seems like a very hard sell to me.
Cheers
Eric

Eric,
It is true that geo isn't a good fit everywhere for everybody. I think it is fair to say the pros here do a good job of stating that.
The only thing you said I can't agree on regards new construction. In most cases, if geo makes sense for existing homes it works for new ones. As you noted our electricity is darned cheap here making electric baseboard cheaper than propane. There are few new propane homes that would not benefit from geo as well (in my AO). Though I quoted nat gas numbers, the house I used to make my points above is a new build with very high insulation values and possibly propane (nat gas far enough away that several thousand dollars are required to bring it to home). Imagine the savings against propane. The geo payback is just fine.
j

Joe,
I usually agree with what you post on the board and you have a great knowledge of geo that you willingly share. I like reading your posts. My only point is that, I think if it is done correctly, new construction can be built with such a low heat loss that geo does not make sense financially. Yes, I agree that per BTU generated, geo is usually 15%-300% cheaper then other sources of heat. If you build a house that is under 1 btu’s/sf/hdd which is doable today without resorting to crazy stuff, a 2500 ft^2 house in a 5000 hdd climate consumes 12.5 million btu’s per year, or 3665 kwh assume 0.10$ kwh = 366.6$ per year with resistance heat. Geothermal would save 2/3-3/4 of that or 250$ per year. On the other hand it would not matter, as most people would be happy with 367$ per year.
The question is it cheaper to do a much better job of insulation, or is it cheaper to add geothermal. I think with the knowledge and emphasis on insulation increasing, insulation is a better deal (usually). The end goal is the lowest utility bill achievable for the smallest initial cost, I think we share that mindset
Cheers,
Eric

What Eric said- or more succinctly:

High efficiency high cost heating systems like geothermal are best suited for low-efficiency building envelopes.

In most of the US, good design and best-practices on the insulation & air sealing is a better investment than that first-ton of geo, and results in lower operating & maintenance costs than running geo on a code-minimum house. Taken to the PassiveHouse extreme mechanical systems become quite spartan- supporting extremely light loads their efficiency becomes fairly irrelevant. In-between, it's, well, in-between.

Building a code-minimum house and buying geo to heat/cool it is only the better deal in rare instances. You can buy a LOT of building-envelope efficiency for $20K, when designed in from the get-go.

For retrofits on houses that don't need a complete overhaul, and where all of the low-hanging insulation & air-sealing fruit has been taken, upgrading heating system efficiency is more cost effective than a chainsaw rehab with a fat rigid-foam overcoat & a high-efficiency window & door swap. In some instances (particularly homes in need of siding, windows and roofing all at the same time) a chainsaw rehab is sometimes/often more cost effective than geo + minimalist rehab.

It would be great to see how a 2400 sq ft. cape or colonial gets from $8-11 btu/sq ft. to 1. Any articles or homes that have been documented for insulation techniques and materials? I don't think there is a lot of interest in igloos made of closed cell foam or geodesic domes in New England. And you are correct about retrofits. Geo does make sense.