Posted By ilgeo on 20 Aug 2010 01:03 PM
Whats the the thermal efficiency of the free watt or Marathon. My point is you are getting 98% out of a Mod Con boiler in this app that will run circles around anything forced air. And I believe electricity is pretty cheap in this area of the country so my opinion is that a cogen would probably only be good for peak shaving. Need utility rate avg for past 2 years and a prediction of were they are going to be able to know for sure. And I think we might be hijacking the thread...Eric

A mod con boiler does nothing to offset the ~30% thermal efficiency of fossil-fired thermal power plants, a cogenerator does- big-time.

And for the record 98%average efficiency out of mod-con boiler only happens with radiant slabs- the return water to the boiler has to be around 85-86F to even get the raw combustion efficiency that high.  But multi-stage hot air furnaces hit the low-mid 90s pretty reliably & cheaply. I like radiant too, but it's not a shoestring budget kind of deal.  Getting a 5-8% improvement in heating efficiency might seem like "running circles around" condensing hot air, but it comes at price...


...and it's nothing compared to about a 300% improvement in source-fuel energy utilization at the power-generation end (with only ~15% of the carbon output per kwh of a coal-fired grid after the heating-benefit fraction is subtracted.)

And that's the point of micro-cogeneration. 

Micro-cogens are relatively new as a product class, but cogeneration has been around for over a century.  Micro cogens make the most sense when sized for the thermal loads, but they don't have to be perfect to be cost-effective.  The installed-cost adder to a residential heating system using the Honda is only a few grand (as any 1.2kw generator would be.)  I haven't priced the 4.7kw Marathon, but it's just a tiny grid-attachable generator at one level- what to do with the thermal output and how to control it is up to the system designer.  But these things aren't super expensive, and en-masse they're pouring more juice onto the grid at precisely the same time/rate that locally heat pumps & resistance heaters are adding to the load.  Even without smart-grid control, in a widely dispersed array they're a perfect complement to geo from a grid-loading perspective.  At national average utility rates it's easy to make the economic argument, but if you have access to 5cents/kwh electricity 24/7 it's probably not going to cut it without subsidy.

'nuff sed. (indeed we have hijacked it...)

Whats the the thermal efficiency of the free watt or Marathon. My point is you are getting 98% out of a Mod Con boiler in this app that will run circles around anything forced air. And I believe electricity is pretty cheap in this area of the country so my opinion is that a cogen would probably only be good for peak shaving. Need utility rate avg for a few years and a prediction of were they are going to be able to know for sure. And I think we might be hijacking the thread...Eric

You're absolutely NOT getting 98% out of a mod- con- you can't without resorting to very expensive radiation to achieve the low return water temps necessary. Details count.  Most mod-cons installed in the US are running in the low 90s as-implemented, and about 91-92% would be about the maximum to expect out of a system with fin-tube baseboard no matter how many miles of it you add to get the average temps down.

Total thermal efficiencies out of cogenerators WITHOUT supplemental condensing burners for the thermal loads are in the 85-90% range. (The Freewatts hit mid-90s as a system.)

Electricity may be cheap, but how cheap is cheap? (And does that really matter when looking at buying LEEDS brownie-points?)  Even a 5cents/kwh a therm of electricity (100KBTU) cost $0.5 x 29.3= $1.47, which is about 2x the current retail price of natural gas in UT, which is why most people heating with 70% efficient gas burners are still money ahead of those with electric resistance heating.

Lets do some simple arithmetic:

Assume you're paying $1/therm ($10/decatherm) retail, and 5 cents per kwh. (Most of the US is paying 2x that for electricity, and less than that for gas.)  Also assume (conservatively) that only 25% of the output energy of the system is in the form of electricity (most are about that or somewhat more), and that you're running on the low end- 85% total thermal efficiency.

Burn a therm of gas and 15% of it goes out the exhaust, and the other 85% is split 25/75 between electricity and thermal output.  About 21% of the source fuel ends up as electricity on the local grid, and about 64% shows up as heat inside the building.  At a buck a therm, that's 15 cents up the flue, but 21000BTUs ends up offsetting 21000/3413= 6.15 kwh of electricity, while the other 64000BTUs heats up the place.

At even a nickel/kwh that's 31 cents worth of electricity for which you spent 21cents in source fuel, and (0.25x15=) 4 cents in pro-rated exhaust heat, for 25cents total.  It's a 6 cent profit when accounted for that way.

But if in your accounting scheme you ascribe 2/3 of the exhaust waste to the electricity, that becomes a 10cent cost adder for those 6kwh and you've broken even on the electricity front, but it moves the relative heating efficiency into the 93% range, and you've also broken even over a realistic representative condensing heating system (but not an 98% efficient slab-radiant system)

If your gas is cheaper, and your electricity is more expensive, the deal gets sweeter, and conversely.  

eg.  My gas is ~1.1x that, but my electricity is more than 3x that- I'm still money ahead running a cogen if metered only at wholesale. (It's really a no-brainer here.) 

In UT commercial customers are paying closer 8-9cents/kwh, and ~70-80cents/therm. Gas prices would have to about double before you were only breaking even.

Is your electricity under 3 cents, and  gas over a buck/therm?  Then there's no future in gas fired cogeneration for you!  But I suspect even net-metered at wholesale in UT you'd get at least 4-5 cents/kwh and your gas is some of the cheapest in N. America.

But it's the net carbon footprint of a gas-fired cogen vs. the coal fired grid that you've offset that makes the biggest green-ness argument, not the raw cash flow of the investment. It's literally an 85% reduction in carbon emissions for those kwh.  If we're looking for cheap brownie points that also come with lower net utility costs, micro-cogens un-subsidized are still usually a better investment than subsidized PV, with higher reductions in carbon footprint per capital-dollar spent, delivering far more power to the grid.

Need life cycle costs with maint and repairs, life expectancy, etc. otherwise I totally agree with your equation. One of the problems I have is that I have worked in power plants and I don't see any real benefit to wind and solar in most of the country as it cannot be relied upon as a constant source of power. Because of this Peaker plants must be on stand by to take up the slack wasting huge amounts of energy producing nothing, but attributable to subsidized green energy. Now if we could harness the heat from a micro cogen continuously then we would have something....Eric

The good news is there are a number of technologies that are getting close to being cost effective. Now if the government would stop using our tax dollars to artificially push fossil fuel energy prices down.....

I'm not a fan of coal fired plants either . I would think that the latest generation of nuclear power combined with private micro generation at the local level would be a solution. At least until we have affordable electric storage Its a shame we haven't built modern nuclear power plant until now.

While the amount of dollars is very high the percentage of tax breaks is low, its just that the energy industry is huge. Don't forget the huge amount of taxes and royalties the energy companies pay. There would be a much smaller amount, I would guess 75% less; solar, wind and geothermal if it wasn't for the take breaks and subsidizing.....Eric

Posted By ilgeo on 23 Aug 2010 05:13 PM
Need life cycle costs with maint and repairs, life expectancy, etc. otherwise I totally agree with your equation. One of the problems I have is that I have worked in power plants and I don't see any real benefit to wind and solar in most of the country as it cannot be relied upon as a constant source of power. Because of this Peaker plants must be on stand by to take up the slack wasting huge amounts of energy producing nothing, but attributable to subsidized green energy. Now if we could harness the heat from a micro cogen continuously then we would have something....Eric

Putting large fleets or "swarms" of micro cogens under utility-control LichtBlick style is a means of stabilizing grid load for less-than-ideal wind places with longer heating seasons (such as northern Europe.)  It could still have benefits in UT for summertime peaking provided there was sufficient thermal storage capacity to take advantage of.  The thermal loads of a commercial space like this are small in summer, but in food-processing & other apps it could be optimized. From an annualized net grid loading/sourcing point of view a building like this might be better balanced with a combination of microcogen heating and PV solar.

In larger systems than would be suitable for this building mini-cogens have been successfully used in conjunction with absorption-chillers, running both a net surplus on the air conditioning compressor energy use, and utilizing the thermal output for chiller stages. With a bit of forethought designing systems to be net-neutral or even net sourcing to the grid under conditions associated with peak load are possible, even without full utility control over the mini-generators.

Un-controlled, simply balancing net output of fleets of mini-cogens used for space heating against the reasonably local loads of heat pump & resistance heating works too.  In places (such as MA) where regulations are trending toward requiring utility investment in efficiency at the load whenever that's cheaper than building & running more generating capacity there's a good argument that micro-cogens SHOULD be subsidized by the utilities directly, even though it's something of a middle ground in some respects. 

I'll be very interested to watch how the LichtBlick system works in practice- they're dedicated to building a few gigawatts of peak capacity in their subsidized micro-cogens, but conceptually it works, and works well.  A nukes-worth of highly-reactive highly controllable output at their disposal can't hurt, eh?  It sure beats a fleet of mid-sized peakers idling away at 0% efficiency on the thermal output, hitting maybe 30% net at full bore.

My point is most places we are applying wind and solar are meaningless. We should have much more stringent uptime regulations in green power generation as the way it is now is little more than window dressing as you need to have peakers idling on standby for when the wind doesn't blow or the sun doesn't shine.This is not allowed in any other form of utility power generation. I would even say that until PVs are much improved and we have some type of storage that allows for peak generation to align with peak usage, wide scale deployment serves little actual purpose in most of the country. Off grid and other special applications aside....Eric

Your point seems to be drifting (but I'll allow that you may have more than one point... :-) ) You kept insisting on my explaining the point of cogens + condensing forced air vs. just condensing boilers, but now you've moved on to PV & wind, OK fine...

In many places the correlation of PV output and peak air conditioning loads isn't too far out of phase- close enough to be useful in grid-balancing, if less than ideal. The less responsive the base generation is, the less valuable random intermittent sources are, to be sure. But in decently sized regional distributions the output of PV & solar are quite predictable- those peakers don't need to be idling away needlessly, but do add the total capital cost of a grid with a large fraction of PV & solar. (The Danes, Germans, and Spanish are getting to be experts at this now, and there will be more to come.)

But the balancing of even non-utility-controlled micro-cogen output against power use related to other heating systems is in PERFECT phase inherently, and should be encouraged over mere condensing burners. It's really too good a deal to pass up from the utility operator's point of view: The cogen operator capitalizes it, and pays for the fuel, and delivers predictable amounts of power that lowers their cost of peaking & standby. Subsidizing micro cogens will often be more cost effective for the grid operator than building or operating peak generators to deal with heating load peaks. (The economics of that will be very dependent on local circumstances, of course.) But there's very little down side here, not to the utility, and not to the cogen owner/operator. Of course a full lifecycle analysis is warranted when making the investment, but it's generally a clear win at national-average retail electricity & NG prices for the cogen owner/operator even without subsidy, and the utility gets the benefit as well. In places where it needs a bit more to make it work financially for the cogen operator, where the utility benefits they should be willing/able to kick in something. But local regulations will often make other projects more profitable for the utility than subsidizing micro cogens- it's not universal (nothing is, really.)

Utilities are used to making investments that are only NPV+ in a 10-20 year financial analysis, whereas building owners have shorter time horizons, and home owners typically have RIDICULOUSLY short time horizons. To the extent that the utility can nudge the rest to make the investment, it's usually a win all the way around.

LichtBlick's approach of grid-hardening the variable output of wind & solar with a large fleet of distributed micro-cogens under utility control isn't a bad one, but won't be possible everywhere- it really requires a reasonable year-round thermal load and a lot of buffering to make a go of it. But that approach could work well enough in cool parts of the Pacific Northwest or coastal British Columbia, where peak heating loads aren't super-deep, and the heating season is relatively long. In residential apps you at least get some summertime benefit out of domestic hot water heating. It only works in the summer when smart-grid controlled, allowing the utility to use the thermal tank reserve capacity for peaking, but with that control it works.

Posted By William Hickman on 18 Aug 2010 01:22 AM
I would like to build a leed platinum building on a shoe string budget? Do you think that it is possible? I am looking to build an 18,000 square foot building on a 9,000 square foot footprint.  Two floors with office space on the second floor and warehouse space on the first floor.I intend to use Solar and geothermal for power and heating. The building will subdivide into 4 tenant spaces. I would like to get a Leed platinum certification. Any ideas on how I can achieve this an a limited budget.

I re-read your original post and focused on the fact that you will divide it into 4 tenant spaces.  Is this a totally spec building?  If it is a spec building and the tenants will do their own tenant improvements, you might do better under LEED CS (core and shell) than under LEED NC.  If you are doing a "turnkey" buildingout (everything ready for the tenant to move in), you will need to use NC.  Your LEED AP should be able to advise you on the + and - of both.

The level of improvements the owner/landlord provides varies greatly by location, so do a bit of benchmarking to determine what your "competition" offers.

Bruce