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112 comments on Peak Oil and the Environment - last afternoon

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TJ on May 11, 2006 - 12:08pm Permalink | Subthread | Parent | Comments top
I can't see many people going for a multi-thousand solar installation when you can get a gas water heater for $400.  You have to be convinced that gas prices will be high for ten years at least. Residential, commercial, and industrial users still believe this is a short term problem.
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tate423 on May 11, 2006 - 12:58pm Permalink | Subthread | Parent | Comments top
Check out the Rinai Tankless water heater.  No tanks, it just heats your water up as you use it.  Much more efficient and it qualifies for a tax credit.  They start at $600 and the top of the line is about $1200.  I don't know the details, but I've convinced my parents to include one in the house they are building.  On a micro scale, you will be more energy efficient.
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Donal on May 11, 2006 - 1:53pm Permalink | Subthread | Parent | Comments top
Keep in mind that Rinnai and Rheem only make NG-fired units.  We're cancelling our gas service, and are looking at electric tankless units to use in conjunction with solar-heated water.
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tate423 on May 11, 2006 - 2:09pm Permalink | Subthread | Parent | Comments top
Ok, but for the basis of heating water isn't NG much more efficient than electric?  I just read somewhere that NG costs are relatively fixed.  So the last quad of NG would take the same energy to extract as the preceding quad.  Electric, mostly coal powered, would be less energy efficient due to the increasing cost to extract.  Or am I off?
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Donal on May 11, 2006 - 4:53pm Permalink | Subthread | Parent | Comments top
You are probably correct, but we don't use the NG furnace anymore, so having NG service just for the water heater is too costly.  All the flat fees, taxes, surcharges, etc. add up.  

So we're switching from NG storage to Elec tankless.

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odograph on May 11, 2006 - 7:01pm Permalink | Subthread | Parent | Comments top
i've heard that the partial solution - a small "solar preheat" system attached to a traditional water heater, has a short payback time.  good ROI.  i was probably reading a report based on the california climate however.
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Substrate on May 12, 2006 - 12:15am Permalink | Subthread | Parent | Comments top
http://www.findarticles.com/p/articles/mi_m1594/is_3_14/ai_101763360

"The average American household spends 20 percent or more of its energy bill on hot water, and much of what's paid for is heat lost through the thin walls of the storage tank in the basement or utility room." ...

"Most solar heating units act as preheaters for conventional units. Although the installation costs are high, owners save from 50 to 85 percent annually on their utility bill, according to the U.S. Department of Energy."

I'm definitely a fan of solar hot water systems.  A lot of fossil fuel could potentially be displaced.  I tried cruching some numbers on what I assume are reasonable numbers for a pre-heating system but for some reason it doesn't seem right.  I know (and the quote above also suggests the same) that they are more effective than the numbers I got.

Assuming the pre-heater raises the temperature of the water to 90F from 55F. (32.2C - 12.8C)  Delta 19.4 C

1gal X (3.785Liter/1gal) X (1000g/1L) X (19.4C) X (4.185 Joule/gram X degC) = 307300 Joules (per gallon)

or 291 BTU (per gallon)

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and these were some numbers I crunched of a storage system I saw at a house I visited(he used this system for both hot water and to heat his house):

Assume 150*F to 80*F useable range (delta 70*F or ~39*C)

5000gal X (3.785Liter/1gal)X(1000g/1L) X 39degC X (4.185Joule/gram * degC) = 3089581950 Joules

3089581950 Joule (.00094978 BTU/Joule) = 2934423 BTU

Or... ~23.66 gallons of gasoline (based on BTU's) of storage if the tank is at 150 degrees F.

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112 comments on Peak Oil and the Environment - last afternoon

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