I ran across a new (Oct. 2012) report on high-efficiency, natural-gas furnaces from the National Renewable Energy Laboratory apps1.eere.energy.gov/buildings/publications/pdfs/building_america/highefficiency_gas_furnaces.pdf (Edited to correct link.) It provides a nice summary of installed costs versus efficiency for natural gas furnaces, and discusses issues associated with condenscing natural gas furnaces.

If we use the guideline provided by DOE that we have to burn 3.34 kW of fossil fuel, on average across the U.S., to generate 1.0 kW of electricity, then for space heating with a heat pump, we need a COP of 3.34 just to get to breakeven in terms of source energy use. With electrical resisitance heating, we are "wasting" a lot of source energy. Of course there are regional variations on how electricity is generated, but the 3.34 factor is the U.S. average.

Current and projected costs for natural gas make natural gas furnaces look attractive for heating-only applications, or applications where low outdoor temperatures limit the COP for heat pumps. Installed costs for 80,000 Btu/hr furnaces estimated by NREL vary from $1040 for 78% AFUE to $3120 for 96% AFUE. I would guess that the life times for gas furnaces would be very favorable compared to those for heat pumps.

Fix the link- it's not pointing to the right place.  Is this the report you're trying for?

The thermal efficiency of fossil plants is increasing (and rapidly) with the displacement of thermal-coal with combined-cycle gas.  I'm not sure how old your DOE rule of thumb is, but on local grids where ccgas is the primary fossil source you're at about 50% net thermal efficency, not 30% (the DOE guideline cited.)  I suspect it's from dated data. When gas became cheaper per source MMBTU than coal, the financial incentive to move to higher-efficiency ccgas became irresistible. In the past 4 years wind power and combined cycle gas have dominated the new-generation coming on line, and conversion of coal plants to gas is also a booming business.

An all combined cycle gas grid would only need a wheezy old skool COP=2 heat pump to beat a 98% AFUE fossil-burner on source fuel efficiency.

Very few local grids are 100% fossil fired, and many have substantial renewable resources (especially in the PNW, where hydro power has long dominated), and the carbon foot print of condensing gas is often WAY above that of heat pumps (even low efficiency heat pumps) in those areas.

Even the smallest condensing gas furnaces out there are in the 40KBTU/hr range, and oversized for almost any high-R house (but would be OK in my 1923 antique, if I didn't already have a hydronic heating system that is radiation-constrained to about 44K max at the water temps I'm running.)  Their biggest attraction is that they're cheap- comfort takes second-fiddle unless you spend more money on ECM drive air handlers, etc., and even then it's nowhere near as comfortable as hydronic radiators or mini-splits, let alone radiant floors.

Who the hell needs an 80KBTU/hr furnace (unless you like sleeping with the windows open)? 

The average home in (not so tropical) MA- all single-family housing stock, including all of those 18th & 19th century farm houses, and barely-insulated early 20th century houses has a heat load at a 0-10F outside design condition of  ~14kw or 48KBTU/hr.  (Not that different from the ~47K assumption used in the NREL report.) The average heat load of NEW houses (we're under IRC 2009 here) is in the ~25KBTU/hr range, 'ceptin' McMansions.  Just because it's cheap to oversize hot air furnaces by 3x doesn't mean it's a good idea. Oversizing hot air furnaces may have little to no impact on efficiency or cost, but it SURE has an impact on comfort (and not in a good way.)

Smaller houses are now coming in under 20K, even at code-min, but there are NO hot air furnaces truly appropriate for those loads.  But a 1.5 ton mini-split makes it (for about $4000-4500), and comes with air conditioning, and a seasonal average COP closing in on 3 in this climate, on a local grid that is more than 1/3 (and growing rapidly) low-carb nukes &  renewables, about a 1/3 combined cycle gas, and the other 1/3 a mixture of standard efficiency fossil-thermal (with gas taking the lions-share.)  The carbon footprint of heating even with a lesser COP 2.5 mini-split is maybe half that of condensing gas (or my own heating system) here. Clearly your grid may vary. The operating costs of heating with mini-splits vs. condensing gas are comparable (at local utility rates.)

If ductless air source heat pumps were unreliable or had high maintenance/short service life Japanese & Korean homeowners simply wouldn't buy them, yet they dominate the market there. Scroll compressors and motors spending most of their operating life at mid-speed with very little on/off cycling tend to hang in there. The refrigerant volume valves may have a half-life of less than 20 years, but they're not particularly expensive.  If the thing gets hit by lighting all bets are off, but the same is true of the controls in a condensing gas furnace (which ARE considerably more complicated than those of their 78 AFUE dinosaur ancestors.)

Dana1-

The link that I provided was in error (now corrected), but you guessed the correct report.

You said: "I'm not sure how old your DOE rule of thumb is, but on local grids where ccgas is the primary fossil source you're at about 50% net thermal efficency, not 30% (the DOE guideline cited.) I suspect it's from dated data. "

I should have provided a reference for the site-to-source ratio. The 3.34 value of units of fossil energy required to generate one unit of electricity and conducted to the site comes from the March 2011 - "ENERGY STAR Performance Ratings
Methodology for Incorporating Source Energy Use"
http://www.energystar.gov/ia/business/evaluate_performance/site_source.pdf?a739-8b06.

A value of 3.365 site-to-source electricity is given by Building Science Corp. in material copyrighted 1999-2012, http://www.buildingscience.com/documents/digests/bsd151-understanding-primary-source-site-energy.

Do you have a reference that is more recent with your drastically lower value of site-to-source ratio? It is unreasonable to pick out a late-generation, natural-gas fueled, co-generation plant and assume that its thermal efficiency represents the efficiency for the average grid in the United States. It is also unreasonable to assume zero losses in the electrical lines. It is not a good assumption to pick out a local grid in Massachusetts and assume that it is representation of the average for the U.S.

Coal-fired electrical plants are designed for a long lifetime and continue to provide base load for most of the U.S. They cannot or will not be phased out quickly.

Let us stick with the 3.34 site-to-source ratio for the ratio of the fossil fuel energy required to produce one unit of electrical energy INCLUDING electrical line losses unless you have a more recent published value.

So about the only common heating technology that can beat nat gas is well designed geothermal. Perhaps combined heat and power (CHP) using nat gas.

Posted By jonr on 27 Dec 2012 06:23 PM
So about the only common heating technology that can beat nat gas is well designed geothermal. Perhaps combined heat and power (CHP) using nat gas.

It appears to me that modulating, condensing (mod-con), natural-gas fired furnaces with ECM motors are an efficient, (relatively) inexpensive, and long-lived way to get heat in a house. I think of them costing in the low thousands of dollars. I think of gound-source heat pumps as costing in the low tens of thousands of dollars, but a lot of that cost seems to be tied in the cost of the ground source loop.

I think of combined heat and power (CHP) as being applied to small commercial applications where electrical power is needed, and using the waste heat can improve the overall efficiency.

A question that I would like answered is the efficiency of a mod-con furnace when operating at low loads. I suspect the efficiency improves at low loads due to lower exhaust gas temperatures, and lower duct losses due to lower friction losses, but I have not seen efficiency curves. Does anyone have them?

Dana1 complains about comfort with an oversized mod-con furnace. I have certainly NOT experienced that problem with my oversized mod-con furnace. It is so quiet under normal operation that I have to check the thermostat to see if the furnace is operating, unless it is firing up at high power after overnight thermostat set-back. Even then, it is a stretch to hear, and certainly quieter than heat-pump A/C systems that I have had, although those were not modulating systems. Temperature control is excellent with the Honeywell thermostat, even turning on automatically ahead of time in the morning so that it just reaches the set-point at the required time. The duct work provides a convenient way to duct the HRV and the humidifier to the whole house.

When I have had combined natural-gas fueled furnace and electrical A/C systems, the problems have always occured in the A/C (heat pump) portion of the systems, and never in the furnace portion. Even the A/C systems have been fairly reliable, but after a while the compressors need a freon recharge, and then finally a compressor replacement, which usually means replacing the whole system to get the latest improvements in efficiency.

Lee, When you refer to modulating natural gas furnaces, are you referring to products such as the Carrier Infinity series which offers a dual fuel option of a high efficiency (20 series) modulating heat pump (20) along with a high efficiency (98 series) modulating natural gas furnace? Isn't this the best of both worlds ... an air source heat pump combined with a gas furnace when temps get really cold. I'm referring mainly to cold climates such as central OH (zone 5).

Posted By Chairman on 27 Dec 2012 08:25 PM
Lee, When you refer to modulating natural gas furnaces, are you referring to products such as the Carrier Infinity series which offers a dual fuel option of a high efficiency (20 series) modulating heat pump (20) along with a high efficiency (98 series) modulating natural gas furnace? Isn't this the best of both worlds ... an air source heat pump combined with a gas furnace when temps get really cold. I'm referring mainly to cold climates such as central OH (zone 5).

Indeed HVAC systems can have great complexity and be hybrids of all sorts. What I was discussing in this case is the simplest version of modulating, condensing, natural-gas fueled, hot air furnaces. The "modulating" part of that can be described by paraphrasing from the operating manual for a Johnson Controls (York) furnace.

The process may be described as follows.
1. The thermostat signals that heat is required by the house.
2. The fan for the combustion air turns on, the igniter heats up, the gas valve opens, the furnace lights, and the circulating fan turns on at low speed.
3. The furnace fires at the 70% of full rate for 30-45 seconds, then drops to the minimum (35%) firing rate.
4. The firing rate is automatically adjusted to meet demand, increasing gradually to the maximum (100%) firing rate if the thermostat is not satisfied within a defined time. The circulating fan is powered by an ECM (electronically commutated motor, reg. trademark of GE) fan motor, which is able to run efficiently over a wide range of speeds.
5. Once the thermostat is satisfied, the burner shuts off, but the cirulating fan continues to extract heat from the heat exchanger until the supply air temperature drops to the desired level. which should take 30 to 90 sec.

The reasons for going to the complication of making the furnace modulating include the following:
(a) the furnace operates more efficiently at the lower power settings, due to lower blower loses due to a lower pressure drop, but retains the capability of higher heating rates when needed,
(b) quieter operation due to lower blower speeds and firing rates,
(c) tighter regulation of indoor temperatures for better comfort due to less cycling of the furnace at the maximum power rating.

The modulating feature is not unique to hot-air furnaces, and is used by other systems like many air-source heat pumps. The use of the ECM motors has been a key to modulating HVAC systems in general.

You asked about a hybrid system that includes an air-source heat pump and a gas-fired furnace. One potential disadvantage of this approach has to do with the fact that the heat pump is electrically powered, and creating the electricity in the first place requires, on average in the U.S., the use of fossil fuels, and the energy content of those fossil fuels is about 3.34 times the energy content of the electricity produced (see reference earlier in thread). The losses include thermal efficiencies in power generation and line losses between the power plant and the house.

Of course, increased costs and complexity must also be considered. The great advantage of some air-source heat pumps is that they can be "reversed" and operated as A/C or heaters, while a straight furnace is only a heater.

When discussing the site-to-source ratios, I should have mentioned that the ratio for natural gas is not unity, but is 1.047 in the 2011 - "ENERGY STAR Performance Ratings
Methodology for Incorporating Source Energy Use"
http://www.energystar.gov/ia/business/evaluate_performance/site_source.pdf?a739-8b06 reference.

Therefore, comparing air-source heat pumps to natural-gas furnaces, the ratio of interest should be (3.34 / COP) / (1.047 / AFUP) for the source energies. The highest efficiency natural gas furnaces have AFUP of 98%, while COP's for air-source heat pumps vary with climate, being better for mild climates.

COP's for air-source heat pumps vary with climate

Yes and even hour by hour. Unfortunately, they typically hit COP = 3.2 at the temp where you hardly need any heat.

I agree with Lee's math overall....but don't want to lose the forest for the trees. For millions of homes that are not too far north, without access to NG, HP's are far cheaper than propane or oil and nearly as cheap as NG even at current low rates. AND in many elec markets they can emit less CO2 than those other options too.

I do think lumping the whole US supply together is a bit bogus re CO2 intensity of the electrical supply. For my distributer (PECO) the carbon intensity of conventional power is nominally 1.06 lbs CO2/kWh, so my ASHP using 10 MWh/yr = 10,600 lbs carbon (@SCOP~2.3). If I still used oil at 82% AFUE, I would burn ~600 gallons for space heat, which I think is ~15,000 lbs CO2.

And with the ASHP, I can source my elec from a Wind Power supplier, and figure my effective emissions are <1 ton CO2/yr.

IIRC, the carbon intensity of recent vintage NG electrical plants are all well under 1 lb CO2/ kWh, so that seems to suggest that national average Lee is using is skewed to significantly higher carbon intensity than most new generation in the US. IOW, the CO2 intensity of the US grid is decreasing, while the CO2 intensity of a NG burner is not.

Posted By woodgeek68 on 28 Dec 2012 11:49 AM
I agree with Lee's math overall....but don't want to lose the forest for the trees. For millions of homes that are not too far north, without access to NG, HP's are far cheaper than propane or oil and nearly as cheap as NG even at current low rates. AND in many elec markets they can emit less CO2 than those other options too.

Yes, if natural gas is not available, and the location is not too far north, heat pumps can be an excellent and efficient choice. Maybe even more significantly, if both heating and A/C are desired from the same HVAC system, then "reversible" heat pumps may be a good choice.

I do think lumping the whole US supply together is a bit bogus re CO2 intensity of the electrical supply.

I disagree with your term "bogus." This forum is read by folks all over the U.S. (and Canada), so conclusions should apply to all, or specific qualifiers need to be added for specific geographic areas. Coming up with site-to-source ratios is difficult requiring lots of calculations and analysis, and those ratios are not available for different specific grids in the U.S. (as far as I know). Some general feelings for specific areas can be used, such as, "we have a lot of hydro in my area, so our site-to-source ratio for electricity should be lower than the national average." But cherry-picking the latest high-efficiency generating plant added to your grid and using that as representative of the grid site-to-source ratio while ignoring line losses and the long-lived coal generating plants that make up the majority of the grid in the U.S. is inaccurate.

IIRC, the carbon intensity of recent vintage NG electrical plants are all well under 1 lb CO2/ kWh, so that seems to suggest that national average Lee is using is skewed to significantly higher carbon intensity than most new generation in the US.

The averages that I reported were from a March 2011 report. The authors of that report did not skew the data toward any particular conclusion. New generation capacity does have a lower site-to-source ratio than older capacity, but not that much old capacity has been removed from the grid. Coal generating plants are designed for a long lifetime. Averages change slowly.

You have chosen heat pump technology, and I imagine that it was an excellent choice for your application. However, on average for the U.S., if the application requires heating only and natural gas is available, then a high-efficiency natural-gas fueled furnace should be considered as one potential viable option with a minimal carbon footprint, along with air-source heat pumps, ground-source heat pumps, etc. Better yet, folks should be encouraged to try to include passive solar heating which is the cheapest, lowest carbon footprint possible, along with active solar PV, and solar hot water. Net-zero source energy is not that difficult or expensive to achieve in some geographic areas.

Not sure where to begin here...

Most condensing furnaces out there are not mod-cons, they're either fixed-output, single speed, or 2-stage where the low-stage output is about 70% that of of the high-fire rating. 3x overizing is still going to be a comfort issue, except in homes with exceptional thermal mass (such as passive solar homes.)

Local grids DO matter, and it's just silly to blindly apply some national average thermal efficiency for the calculation at any particular site. A gas-fired furnace (even a code min 82%er) is a HUGE improvement in carbon footprint over COP=4 ground source heat pump in 30% efficiency coal-fired Wyoming/Utah. But even a 98% AFUE modulating furnace is dead-heavy carbon footprint compared to COP=1 resistance electric heating in the massively hydro Pacific Northwest.

I wasn't cherry-picking when I applied the numbers to MY local grid (of which I have fairly intimate knowledge of the grid-mix) where the majority of the gas-fired power is from combined cycle plants. But I also explicitly pointed out that your grid WILL vary. In no way did I imply that ccgas was the new US average, only that 30% average grid efficiency from thermal plants is already old news, and getting staler every year with the current boom in ccgas powerplant construction.

Dana1,
How would I calculate the operating costs for the heating and cooling following options:
Some background:
Zone 5 ... central OH ... cold climate
Heating degree days - 5391
Cooling days - 906
Home ... 3360 sq. ft. 2 story
Some basic specs ... very tight home with Zip-R6.6 exterior sheathing covered in Obdykes Hydrogap for "outie" flashing, dense pack cellulose-filled walls 2x4, closed cell spray foam of rim and band joists @R13, R-49 cellulose in a ventilated attic, Marvin Integrity double pane fiberglass windows, basement walls R7.5 exterior and R10 subslab.

Considering the following options:
1. Carrier Infinity greenspeed heat pump (up to 20.5 SEER, 13 HSPF ... http://www.carrier.com/homecomfort/en/us/products/heating-and-cooling/heat-pumps/split-system-heat-pumps/product---split-system-heat-pumps---25vna0/ ) combined with an Infinity 98 natural gas furnace (up to 98.5% AFUE ... http://www.carrier.com/homecomfort/en/us/products/heating-and-cooling/furnaces/product---furnaces---59mn7/ )

vs.


2. Carrier Infinity 21 air conditioner (up to 21 SEER, http://www.carrier.com/homecomfort/en/us/products/heating-and-cooling/air-conditioners/split-system-air-conditioners/product---split-system-air-conditioners---24anb1/ ) combined with the Infinity 98 natural gas furnace as above

In other words, when considering operating costs, does the heat pump in this central OH climate offer any substantial benefit over the straight high efficiency AC/furnace combo alone)

Appreciate your thoughts ... please let me know if additional information might be required. Thanks.

I suspect that every kwh from a hydro plant that you don't use is a clean kwh that gets sold to the neighboring areas with dirtier power, thereby reducing pollution about the same as if you had dirty power in your own area.

Posted By jonr on 28 Dec 2012 02:04 PM
I suspect that every kwh from a hydro plant that you don't use is a clean kwh that gets sold to the neighboring areas with dirtier power, thereby reducing pollution about the same as if you had dirty power.

Only where there's transmission line capacity, and contracts in place.  In an ideal world that would be the case, but with vastly different regulatory structures from state to state, sadly, that ain't happening.

The PNW is currently fairly tapped out on their legacy hydro, and efficiency programs to move resistance-electricity space heating over to heat pumps (and in particular mini-split retrofits, as a low cost high efficiency upgrade) are being heavily subsidized in WA. (Not sure about OR or ID.)  The transmission capacity out of the Columbia Basin to the power markets on the western slope of the Cacades is also being challenged (and slowly upgraded.)  The amount of PNW hydro power being shipped to dirty-grid WY and UT is pretty miniscule- the real money is in shipping it to power-hungry CA, but even that has grid-infrastructure limitations.

To figure out roughly what the local grid-sources are in your state (if not your exact local grid, which will vary by utility within the state) this is a good place to start.  Click on your state, then the "Energy Statistics" link on the upper left column, then to "Electricity Generation" about mid-page, and you get to something like this.  At the bottom of the generation page is a pie graph of grid source fuels by source-fuel TeraBTUs.  It doesn't break out the thermal efficiencies of the various options, only the energy input.

Mind you, it's not fully updated to the minute- most of that data is 3+ years old , and in many areas the grid sources are changing at blinding speed, where cheap natural gas has the pipeline capacity, or where the wind resource is being tapped heavily.  In IA the wind power alone accounts for a bigger slice than the combined "renewables" slice shown, and much of that wind resource has been built since 2009.  Some of the breakdown can be found on other links under the state pages.

mjurich: This is not a simple thing to figure out via web forum. If you have a fairly accurate heat load calculation it would be only slightly simpler, but as-used HSPF is climate and user-input sensitive, and the crossover point from heat pump to gas can be set up to be either at the financial crossover or at the point where the heat pump can't carry the load etc. And we don't even know your utility rates/structure. Any WAG we might make on a web-forum napkin could undershoot reality by half or overshoot by 2x. I haven't looked at engineering specs for the Greenspeed, have no idea how it would perform in an OH climate, but with tight ducts in a tight house you'd probably hit 2 or a bit better.

An HSPF of 13 implies a COP of 3.8 @ 47F outdoor temps- ductless systems rated north of HSPF 10 hit the high 2s for seasonal average COP in similar climates. The duct design could make or break it's actual operating efficiency though- undersize the ducts and never change the filters and it would struggle to break 1.5.

Every good heating system design starts with a room by room heat load calculation using realistic inside and outside design temperatures. If the HVAC contractor isn't taking the time to run those numbers (and this is not a 5- 15 minute process), find a different contractor. The 99% outside design temps in central OH are in the mid to high single-digits F- don't let anybody run a calc based on 0F or -3F just because it got that cold at least once in the past decade.

http://www.energystar.gov/ia/partners/bldrs_lenders_raters/downloads/Outdoor_Design_Conditions_508.pdf

And make sure they use U-factors that are correct for your actual construction, not those of a "typical" code-min house.

Lee, if you're insisting that you use some national average thermal efficiency, you also have to look at the national average grid mix.  As of 2011 42% was from coal, only 25% was from natural gas, 1% was from oil, the rest (about 32%) was from nukes and renewables:

http://www.eia.gov/energyexplained/index.cfm?page=electricity_in_the_united_states

But even in the past year coal has fallen to about 1/3, and gas has risen to about 1/3, and the new-gas really IS mostly combined cycle gas.  The October YTD numbers had coal at 37% of the total (and falling.)  The speed of conversion to gas and wind (the majority of the more than doubling of "other renewables since 2012) has been truly astounding, which is why I question any raw statements about the average thermal efficiency of the fossil fired grid, which was ~30% even 20 years ago, and a large fraction of the thermal gas plants have been replaced or upgraded during that time to take advantage of the large efficiency increases that are possible.

When comparing home heating appliances have greater "greenliness", one also needs to view the grid as it's likely to evolve over the lifespan of the equipment, not how it averaged over the past decade or quarter-century, especially at this point of rapid evolution.   Even without a carbon tax cc-gas is far cheaper per kwh than antique coal or single-cycle gas, and utility-scale wind is neck & neck with cc-gas when looking at long term gas contracts between gas suppliers and grid operators (rather than spot-market gas pricing.)  Thermal coal electricity in the US is toast- done (stick a fork in it, recent IL plant opening notwithstanding), but the retired coal plants aren't being replaced by similar-efficiency gas, they're being replaced by wind and cc-gas, at a furious pace (by grid evolution standards.)  Any environmental regulation or tax on carbon emissions would only speed up the change.

Yes, those legacy coal plants are built to run 40-50 years or more, but that's not to say that is economic to do so. The thermal efficiency averages are changing far more rapidly than any point in the past 70 years (faster in some local grids than in others.)

Posted By Dana1 on 28 Dec 2012 01:36 PM
Most condensing furnaces out there are not mod-cons, they're either fixed-output, single speed, or 2-stage where the low-stage output is about 70% that of of the high-fire rating. 3x overizing is still going to be a comfort issue, except in homes with exceptional thermal mass (such as passive solar homes.)

In considering the purchase of a new HVAC system, many of the new high efficiency natural-gas furnaces are modulating, condensing furnaces. As pointed out in http://apps1.eere.energy.gov/buildings/publications/pdfs/building_america/highefficiency_gas_furnaces.pdf,
"The key advantage of step modulating burners and variable speed blowers is realized during periods where the required capacity is less than the design condition, i.e., the outdoor temperature is greater than -11°F in the Minneapolis example. The modulating furnace will vary its capacity to 30% to 40% of maximum input and reduce the fan speed accordingly to avoid rapidly overheating the space. A secondary advantage to modulating systems is that furnace fans will operate longer in each cycle and provide more even air temperatures in the home."

This is also exactly how my furnace works, with a minimum input rate of 35% of the max., and that is where it operates most of the time except during recovery from thermostat set-back. My personal experience is that this is a quiet, comfortable heating system. Does anyone on this forum with a mod-con, natural-gas fired furnace, oversized or not, have comfort complaints?

Local grids DO matter, and it's just silly to blindly apply some national average thermal efficiency for the calculation at any particular site. ...snip...

As a starting point, the national average is a place to begin. Then if there is something exceptional about the local grid, then account can be taken for that. It looks like the carbon footprint for conventional electricity generation is lower than national averages in Washington, Oregon, Idaho, Nevada, New York, the New England states, and Florida. That means, watch out in other states, like Ohio that is 84% coal for electrical generation.

I guess the best bet is to make your local, LOCAL grid solar PV like I have. Now that is low carbon footprint!

Dana1: No problem ... thanks for the advice. I should be seeing a Manual J shortly on the new build and will be sure to confirm all of the design values used in the calculation. Probably a simple matter for the dealer at that point to plug in various scenarios of equipment.

The PNW is currently fairly tapped out on their legacy hydro,

Exactly, and the unmet incremental need gets met with something dirtier. Unless they are throwing away hydro power somewhere, one should use the higher cost/dirtier methods of incremental power production when doing comparisons regarding avoiding environmental damage at the personal level. Transmission losses should be accounted for but they are minimal. Power is fungible and transportable.