Water heating options...anyone tried condensing water heater?

Discussion in 'Environmental Discussion' started by Celtic Blue, May 25, 2009.

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  1. fuzzy1

    fuzzy1 Senior Member

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    If that 35% is for the entire industry fuel mix, it cannot be compared directly to natural gas at home. A better comparison would be natural gas at home vs. natural gas in a central electric plant. Throw in an electric heat pump powered by the latest gas-fired electric plants, and a simple gas burner at home will lose.

    Thermal efficiency of nuclear is fairly low due in part to the many safety systems. But since nuclear home water heating is simply not available, its contribution to the energy industry's 'efficiency' is irrelevant and misleading.

    For similar reasons, I refuse to give credence to anything that includes coal in the 'efficiency' mix. OTOH, coal's carbon emission for a given work function is a valid metric, which usually damns it even harder.

    Not just the stand alone units. Water heating is also an option for some central space conditioning heat pumps too. If I ever do a heat pump for water heating, it will require an outdoors evaporator.

    Some of us live in areas where the efficiency of electricity is mostly mechanical, not thermal. Hydro anyone?
     
    #41 fuzzy1, Oct 17, 2009
  2. Celtic Blue

    Celtic Blue New Member

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    Fair enough, but it takes a condiserable level of integration with lower level thermal users to make this work efficiently.

    I guess we differ in that I came at it from the opposite angle, originally not appreciating how inefficient electrical generation was. That left me disappointed in it. Expectations based on first impressions are perhaps a key difference in whether one is pleasantly or unpleasantly surprised in anything.

    Nevertheless, the efficiency of electrical generation and transmission still appears to fall well short of natural gas for the very thermodynamic reasons you mention. Using the combustion of natural gas for thermal heating at the point of use makes a lot more thermodynamic sense.

    An efficiency one might get for a combined cycle plant: 60% vs. old coal plants running in the mid 30's.
    Transmission losses: 7.5%
    Storage losses: 10%
    Overall electrical water heater efficiency = 0.6*(1-0.075)*(1-0.1) = 50%.

    For natural gas I do not know the average transportation loss as a percent (would be interested in having it though.) The overall combustion and storage efficiency of the water heater are about 60%...although 80+% is acheived with various systems.

    If one compares the carbon footprint, electricity is even worse in many regions because of the coal dependence.

    Propane is better used as chemical feedstock. It is in fact a testament to the overall inefficiency of electricity that propane can be competitive with electricity for heating water/home. The advantage propane has is that it is a transportable/storable liquid.
     
    #42 Celtic Blue, Oct 18, 2009
  3. Celtic Blue

    Celtic Blue New Member

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    The electric plant loses, hands down.

    But that isn't a realistic measure even though it is the best break electric deserves. When you are setting next to an old coal plant (as I am) you really can't make this sort of comparison seriously.

    Only if you have a climate favorable to it. When I was looking at one of these units the manufacturer showed three modes: all heat pump (2.0), mixed heat pump/resistance (1.5), and all resistance (1.0). They had a graph of what likely factors were for various locales.

    If one is going to use the latest gas plant then one MUST also use the most efficient condensing gas tankless...something well over 90% efficiency. If one is in an area which is only cooling (fairly small subset of the nation) and can get a 2.0 factor then it might narrowly favor the latest combined cycle gas plant with distribution losses and such.

    Is it all stranded? If that hydro power can be sold elsewhere then you really can't take credit for it being nearly hydrocarbon free. What actually happens is that it backs out some percentage fossil fuel generation in adjacent regions.

    The same logical fallacy is used for solar, wind, nuke, geothermal, etc. to excuse inefficient use of the resource by those closest to them. If I have a humongous solar array on my grid tied home that produces 2x what I need, any that I don't use backs out fossil fuel electrical generation.
     
    #43 Celtic Blue, Oct 18, 2009
  4. fuzzy1

    fuzzy1 Senior Member

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    deleted ...
     
    #44 fuzzy1, Oct 18, 2009
  5. fuzzy1

    fuzzy1 Senior Member

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    That is why different energy sources should be compared by carbon emissions, not by meaningless 'efficiency'.

    If one MUST use the most efficient condensing gas units, then one ought to include the better HPs too, at 2.2, 2.4, and 2.5 EF.

    As we learned very painfully during the 'California/Enron' energy crisis (a misnomer, as we got hit even harder), we don't have enough transmission capacity to ship everything around to where it might be wanted. Even outside of the spring runoff.
     
    #45 fuzzy1, Oct 18, 2009
  6. Celtic Blue

    Celtic Blue New Member

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    Two problems with that:
    1. The Enron ripoff was a manufacutered event by the energy traders. They were at times shutting down local capacity to intentionally overload the grid so that they could get any price they wanted over those transmission lines. That was central to the scam. They could screw folks on both ends of the transmission lines simultaneously.
    2. That's still well short of 100% stranded. If 20% or 30% are stranded or even 50%, it still means that one is kidding themselves by thinking their energy uses is anywhere close to "carbon free." This is something that is mostly missing in the EV threads, solar, etc.

    What is going to be backed out by reducing electrical consumption or growth in consumption? Solar? No. Wind? No. Nuke? Probably not, at least not existing. Natural gas? Yes. Coal? Probably, particularly in the form of replacement capacity or continuing to operate the oldest/least efficient. When doing project economics, one must focus on the incremental change produced on the whole system. This is a larger box than most folks ever draw, instead getting locked into parochial thinking.

    Haven't seen them. Do any exist for annual water heating requirements? It gets tricky because for me the winter time water heating duty is about 50% more than summer. And when would I be unable to use the heat pump? During winter. It would be running resistance most of the time during the highest duty.

    The problem with the arguments is that to get any case where electric wins one has to find extreme exceptions, not the rule.
     
    #46 Celtic Blue, Oct 18, 2009
  7. fuzzy1

    fuzzy1 Senior Member

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    While the Enron ripoff was manufactured, it highlighted, and was made easier by, pre-existing transmission capacity problems. The increasing supply of wind energy is adding to this problem

    No one represents our hydro as even close to 100% stranded. But some water is spilled at various times for a variety of reasons, and an unknown portion of conservation ends up as spilled water rather than reduced coal burn.
    Look at EnergyStar's list of approved products.
     
    #47 fuzzy1, Oct 18, 2009
  8. richard schumacher

    richard schumacher shortbus driver

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    The first Energy-Star ratings for gas condensing water heaters should appear in mid-2010. To request notification, email [email protected]
     
    #48 richard schumacher, Apr 13, 2010
  9. ilusnforc

    ilusnforc Member

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    I just installed a GE Heat Pump Water Heater from Lowes. I first considered solar thermal, but it still uses resistance electric backup. Gas is not an option as it is not available in my neighborhood. I had an estimate done by a solar installer, I asked him what the rated electricity consumption is on the solar thermal system (with an 80-gal tank) and he said "it saves 2384 kWh annually". My 2 year old 40 gallon water heater energy star rating was 4773 kWh and the new GE Heat Pump model is rated at 1856 kWh, a savings of 2917 kWh beating the solar thermal in electric consumption, cost and payback time.

    Hot Water Heater, Heat Pump Water Heater, Water Heater Electric | GE Appliances

    It was listed at $1,599 at Lowes and was marked down 10% the week I bought it ($1,439.10) and I had a 10% off coupon ($1,402.04 after tax). I reserved a $300 rebate from SECO, a Texas state rebate, and $75 for turning in my existing water heater for recycling, and I will claim a $300 rebate from my electric utility GVEC. I will also be able to claim a 30% tax credit ($420.61) resulting in a final investment of $306.43. The GE Heat Pump water heater is rated at $198 cost per year at 10.65 cents/kWh, my old heater was $508, this water heater should pay for itself in a year. I'm even trying to sell my perfectly good 2 year old water heater and I'd gladly trade in an older not so good water heater for recycling and the $75 rebate.

    At some point in the future I'd consider adding a solar collector and a heat exchanger tank to the heat pump water heater. The only way I can think of to beat that efficiency would be to have a heat exchange coil inside the heat pump water heater with inlet/outlet connections for a solar collector.
     
    #49 ilusnforc, May 15, 2010
  10. richard schumacher

    richard schumacher shortbus driver

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    Marathon offers storage tanks and a Solar system interface:
    Marathon Water Heaters: For Consumers

    Trevor-Martin makes desuperheaters which use heat from an airconditioner compressor to pre-heat water:
    Trevor-Martin Corporation
    They are apparently the sole manufacturer, which are all re-sold through others (Doucette, etc.).
     
    #50 richard schumacher, May 15, 2010
  11. jcgee88

    jcgee88 Member

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    You may want to check the basis you are using for the Federal
    30% tax credit. I am going through this right now, albeit for
    PV, and the rule is that the Feds consider any rebate you
    receive from the state or your utility company to be a
    reduction in your final cost.

    You are taking 30% of $1402 = $420.

    I believe it will be ($1402 - $300 - $300) * 30% = $240.

    Thus, your final investment would be $487.

    This is described in an article by Peter Parrish in SOLARPRO:

    When a rebate is available from
    the utility company, the rebate is
    treated as a purchase price reduction.
    This means that the value of
    the rebate is subtracted from the
    total purchase price, resulting in a
    net adjusted cost for the purposes of
    determining the value of the federal    ​

    tax credit.

    --

    That's still a great price!
     
    #51 jcgee88, May 16, 2010
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