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

[fuzzy1]

Originally Posted by Shawn Clark

No, electricity is about 35% efficient overall (in the U.S.) Newer combined cycle plants can hit about 60%. You still have ~7.5% transmission losses for them though. Add to that an ~90% storage unit as compared to ~60% for natural gas and this is a no brainer. Natural gas wins.

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.

Yes, these are interesting units with interesting problems--if you are talking about the new water heaters with heat pumps mounted on top of them. You only get the 2.0 factor in warm climates...and even then you need to derate for the real thermal efficiency of electricity, which isn't pretty. ...

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?

[Shawn Clark]

Originally Posted by qbee42

The key is to use the waste heat created during electrical generation. We don't do a good job with this in our country, but places that do vastly increase the efficiency.

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

I have been pleasantly surprised by the efficiency of modern electrical generation. Given the inherent thermodynamic losses, I'm surprised it's as good as it is.

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.

[Shawn Clark]

Originally Posted by fuzzy1

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.

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.

Throw in an electric heat pump powered by the latest gas-fired electric plants, and a simple gas burner at home will lose.

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.

Some of us live in areas where the efficiency of electricity is mostly mechanical, not thermal. Hydro anyone?

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.

[fuzzy1]

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[fuzzy1]

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.

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

... 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

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.

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. ...

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.

[Shawn Clark]

Originally Posted by fuzzy1

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.

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.

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.

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.

[fuzzy1]

Originally Posted by Shawn Clark

Two problems with that:
1. The Enron ripoff was a manufacutered event by the energy traders. ...
2. That's still well short of 100% stranded. ...

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.

Haven't seen them. ...

Look at EnergyStar's list of approved products.