Electric heat 2

[ChasBean1]

I've always heard electric heat (either baseboard in home applications or electric duct reheat, etc.) is far worse than combustion based heating from a cost perspective. I tend to accept this as fact, because it seems to be widely known. What I wonder is how the costs truly compare between electric and fuel burning applications. If I have a furnace, for example, I have to pay for the fuel. I have to pay for the electricity to run my blower and/or water pumps. I have to change the filter. I know there are efficiency losses as heat escapes in the flue. I have combustion efficiency losses, heat loss from piping or air ducts, friction losses in piping or air ducts, etc. So if I use electric heat throughout (which I understand converts electricity to heat 100% efficiently) why is this a sin?

How do the costs truly compare? Tx, -CB

 

[DanTheMan]

Well, just look at it this way; the power company that provides the electricity has to burn a fuel to make electricity at less than 100% efficiency. So the direct method is the most efficient because the power company has to do very similar things to generate the electricity as you do with fans, pumps, filters etc...

 

[quark]

CB!

Electricity is high grade energy, heat is a low grade energy and conversion of high grade to low grade energy is always less efficient. And those are exactly my concerns which were raised by Dan.

But there are some exceptions for coversion from electricity to heat I experienced in my work. As far as refrigeration system is concerned, until and unless you have waste steam generated from other process, vapor absorption system is uneconomical.

In our process we have to heat the product (medicinal product) by using hot air. Here we never go for steam heating for the fear of line punctures, rusting etc.

If you have to have a separate facility for combustion based heating system right from the fuel storage, there may be a possibility that sometimes electrical heating would be cheaper.

Regards,

 

[Cooky]

Electric heating will have the lowest capital installation cost. However, due to the cost of purchasing electricity, it will probably have the highest running cost. The efficiency is 100%.

Gas heating has about average capital installation cost. However, the energy purchase price of gas is much lower compared to electricity (here in the UK). Most new combustion heaters have efficiencies of about 85%, although new condensing technology can push thermal efficiencies to 100%.

Finally.

A simple split refrigeration system would have the highest capital installation cost. Electricity prices have been mentioned above. When operating in heat pump mode, it will operate at about 300%. That is, for each kW of electrical power you put in, about 3kW of heating will be rejected into the room.

 

[TBP]

Convert all energy units into cost per BTU, then factor in efficiency the device that uses it. Electrical BTUs are typically far and away the most expensive. Then cooling BTU, then heating by fossil fuel is normally the cheapest.

By the way, ask the manufacturers of forced air furnaces and hot water heating boilers exactly HOW they calculate their eff numbers. I can't get ANY of them to say, but I suspect strongly that the numbers being tossed around are for combustion eff ONLY. They are NOT boiler eff values. (Or proper eff on forced air units, because nobody in the field actually measures the mass flow of air across the space heating side of the heat exchanger in a furnace.)

I know a heating contractor, who has actually installed a water meter to measure the thru-put on the heating boiler in his own home, and inlet/outlet thermometers. Now he knows exactly what the output of his boiler is. He always knows the inputs, as there's always a gas meter. He has all of the up to date combustion analysis tools, and is well trained, and very experienced in their use. His burner eff is 81%, which the value claimed by the manufacturer of the boiler. He is VERY puzzled by his BOILER eff, as it appears to be only 61%. I'm not puzzled at all - the manufacturer is providing a number, that while not false, is misleading. His boiler eff number is CORRECT. As is his combustion eff number. But nobody has ever explained to him (or pretty much anyone) that these are two, separate calculations. And as far as I can determine, listing COMBUSTION EFF, as opposed to BOILER EFF is standard practice among manufacturers.

 

[ChasBean1]

TBP - you're absolutely right. Everyone's told ~81-88% range. The gas company doesn't do a system calorimetric. This is just combustion efficiency because the numbers look better and it's much easier to do. The true efficiency is the difference in the heating value of the fuel versus the energy of the leaving air's temperature and flow rate at all the vents (for forced hot air). That's why I wonder how the numbers compare in actuality...

Dan, I see your point but it could also cause me to question why I would want to repeat that process in my home. You all have good points and I understand the issues conceptually, just not mathematically yet! (I should do some homework on this).

 

[TBP]

Just on a purely non-scientific basis, I've never known ANYONE here in Ontario that has switched from electric space heating to gas/oil, and been anything less than thrilled at how much their total utility bills dropped.

 

[DouginMB]

You really need to examine climate type, building type, and local energy costs using energy analysis software. Here in coastal South Carolina electricity is still regulated. I recently analyzed a high-rise condo building that employed a water loop heat pump system. Because of the low degree-days, high solar load, and first cost of heating boiler and pumps, I found that electric strip heating was more economical than heating the loop with a boiler. In general is gas more economical than strip heat? Yes, but there are exceptions in certain cases.

 

[KenRad]

CB,

I've always operated on your original assumption as well, until I recently ran the numbers for someone who had electric baseboard, and was considering converting to propane-fired hot water baseboard. Considering what he is now paying for propane and electric in his area (over $1.60 per gallon for propane; $0.049 per kW/hr for electric), he was actually better off keeping the electric heat for the time being. I believe that the cost of propane will eventually come down as the market becomes less volatile, but until then, I counseled him against changing anything.

One advantage to the much-maligned electric baseboard is cheap and easy zone control of each room, something that cannot be said for hot water baseboard or forced air.

---KenRad

 

[quark]

Kenrad!

I would stop at easy zone control. (except that individual zones of single AHUs are to be maintained at different temperatures) Installing individual duct hot water coils may cost you much, but you will have smooth heating.

I used thyristor controlled heaters and PID looped (time base) heaters but never found any smooth functioning. This basically because of thermal inertia. What sort of technic you follow?

Regards,

 

[KenRad]

quark,

Sorry for the mix up....I was really only talking about residential applications. For commercial/industrial, I typically use hot water coils, or gas-fired forced air.

---KenRad

 

[ClydeMule]

Gentlemen,

This has been an interesting discussion. My only input is a question.

The statement has been made that electric heat is 100% efficient. But isn't this if we are only talking about the heater element? If we talk about the system as a whole isn't the efficiency much lower?

My analogy is that the heater element efficiency is what would be called combustion efficiency of the burner. As stated the overall unit effiency is much less because of losses in the entire unit. Do electric heaters more or less have the same losses.

I guess my point is that while the electric heater element is more efficient than burner, the whole system still has significant losses. It seems like the the whole efficency point is minimised and the major concerns are inital and operating cost.

Just my thoughts. Thanks for a great thread.

Clyde

 

[TBP]

I think that the cost per BTU of electricity in general, and electric heating in particular reflects the overall inefficiencies of the entire process.

If you go back all the way to the generating plant to determine the eff of electicity, should you not count all of the costs involved with other energy forms? Drilling, collection, pipelines, refining, marine, rail & tanker truck distribution, etc - should these not all be counted against each source of energy?

I think that the 2 main issues are: How much did this BTU cost me, at my meter? And - What is the total cost of using a given source of BTUs to actually heat my space?

Unless you live in an area with hydraulic power generation that is old enough to have have had the initial construction costs paid off, I think most people will find that the "100% eff" electric heat is pretty pricey, once they start looking at their electric bills.

 

[ChasBean1]

TBP, I agree and show that by a star for your thoughts. If I were to think globally, we have literally millions of combustion sources disguised as innocent brick chimneys at almost every home. By theoretically removing the combustion at every home, energy production would be greatly increased at the central plants that contribute to the grid. These plants, however, may be equipped with water side economizer, more efficient means to handle varying loads, cogeneration, or other forms of energy recovery. If we get rid of all these "mom & pop stores" of combustion to favor the Wal-Mart of energy production, would we be better off overall with respect to fuel burning and emissions?

(p.s., in the retail biz, I favor the mom & pop stores even if they cost a little more)...