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Electric Baseboard Efficiency?

Discussion in 'Home Power and Microgeneration' started by Richard, Sep 2, 2004.

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  1. Richard

    Richard Guest

    I work in a hardware retail store in an area where several hundred people
    (from cottage owners to year round residents) live off solar and wind
    generated electricity. I had a question posed to me by one of them and it
    has me stumped. Would replacing a thirty year old 2000 watt electric
    baseboard heater with a new 2000 watt baseboard heater be more efficient.
    Of course you are still paying for the 2000 watts, but would you be
    receiving more radiant heat from it?

    I've been asking around and the sales people and electricians say yes. Any
    other comments?
     
  2. Guest

    I'd say no. They are both 100% efficient.
    Maybe, if the new heater had exposed coils or a reflector or insulation
    on the side towards the wall, but as you say, they both make 2kW of heat.

    Nick
     
  3. Dave Hinz

    Dave Hinz Guest

    Nope. By definition, electric heat is 100% efficient. All of the
    energy gets converted to heat.
    They're lying or ignorant, possibly both. Efficiency rating means "how much
    of the energy going in is converted to the desired output", and the
    remaining is what is lost as waste heat. Since you're making heat as the
    desired output of the device, there is no waste heat. By definition.

    Dave Hinz
     
  4. ( see my additions at end... there was no easy way to quote and snip
    and keep this clear )

    Dave, you're being a bit too fast here. While you're technically correct
    in that the final temperature in the room wll be the same, there *is* a
    difference in how people are going to feel.

    An electric heater (for that matter, all warm objects) heat up the
    surrounding area via those three things we learned back in kindergarten,
    namely radiation, convetion, and conduction.

    Now eventually all of this (in a sealed room) will stabilize out exactly
    the same way, BUT in the process there's a hefty difference.

    The electric heater will be providing a big amount of the (initial) output
    courtesy of infra red radiation. This not only goes directly via
    line-of-sight to the person's skin, making the people feel warmer than the
    "air temperature" would suggest, but also does a credible job of bouncing
    off the walls and then hitting the people.

    So yes, a new and reflective (as opposed to old, dirty, and grimy)
    electric heater will make people feel warmer - and sooner. The older one
    is dumping more of the (initial) heat directly into the air via
    convection, so the people don't get that "radiant" warmth but have to wait
    until the air temperature creeps up.

    In other words, you'll feel warmer at 65 degrees with a new unit that's
    aimed at you (plus a bit of wall bounce) as compared to an older unit.
    With the dirty one you have to wait until the air temp gets to 75 or so.

    Note that these are very approximate numbers. Actual mileage will vary a
    great deal. Cars are closer than they appear in the mirror.
     
  5. Ecnerwal

    Ecnerwal Guest

    Given, as snipped above, that the original post asked about replacing
    electric baseboard with electric baseboard, and all the electric
    baseboard units I've ever met make every effort to be completely
    convective in their design, Dave has it exactly correct. The sales
    weenies and electricians only make money if they sell you new stuff, and
    some are quite happy to lie about what they are selling to get business.

    Repacing a convective baseboard with a radiant heater might fit your
    argument, but if you put the sort of high temperature refeclting radiant
    electric you appear to be discussing in where a baseboard unit was,
    you'll probably have a furniture fire in short order - which is one
    reason that electric baseboard does not try to take that approach (and
    I've seen scorched furniture even with regular electric baseboard, since
    it runs a lot hotter than hot water baseboard).
     
  6. Dave Hinz

    Dave Hinz Guest

    Well, the question was about efficiency, not the angle at which it's
    reflected into the room.
    Right, (well, not the kindergarten part, but yeah)
    OK, that could be, but as you say, technically they're both 100% efficient.
    Do not taunt Happy Fun Ball.
     
  7. Guest

    An electric baseboard heater is a resistor, producing heat. As such it
    is 100% efficient, with all power consumed being turned into heat.

    If the old heater is clean it will be as efficient as a new heater.
    There may be small differences in the design that produce better
    convection flow, as baseboard heaters are not, strictly speaking,
    radiant heaters. This MAY reduce heating costs marginally - but from
    what I've seen, most baseboard heaters sold today are substantially
    unchanged from those sold 30 years ago - and in some cases appear to
    be much more poorly constructed.
     
  8. Richard

    Richard Guest

    I know, but most of them are pretty sharp when it comes to energy
    consumption and the guy who asked this also asked it out of curiosity. He
    uses biomass (firewood) for his heating and may go DSHW to supplement it.
    I'm glad I asked the question here. *Of course* it was sales persons who
    recommended that the baseboard heaters should be changed out for newer ones.
    With my own knowledge of electricity I couldn't see how you could get more
    heat but thought maybe technological advances would provide more BTU output.
    Actually, I still can't figure out how you can wire two hot leads (2 x
    120volt) to the baseboard and not have a return path except for the ground
    wire? Anyways, thanks all for the info! And now that I look at it, I see
    that I do have one baseboard of my own that is rusty and has been painted
    over. Guess i'd better change it....
     
  9. Ecnerwal

    Ecnerwal Guest

    You just need to understand power as delivered in US/Canada a tiny bit
    better. Each leg is 120V to ground (the nuetral conductor is tied to
    ground at the main breaker panel, and only at the main breaker panel) -
    the two legs are opposite, so there's 240V between them. The "return
    path" is the other hot wire - ground is _never_ a return path except in
    the case of a fault. A pure 240 volt appliance (such as a baseboard
    heater) has no need or use for a neutral conductor, as it would carry no
    current. A device or circuit which has some 120V and some 240V loads
    needs the neutral to carry the return current from 120V loads, but if
    two similar 120V loads are run on opposite legs (each 120V to neutral,
    but 240V to each other) the current in the neutral wire will be only the
    difference between the two loads.
     
  10. Dave Hinz

    Dave Hinz Guest

    Please explain how you're going to get better than 100% efficiency
    using hydronic heating? I _use_ hydronic heating, and like any other
    electrically heated hot water system, it is again 100% efficient. Just
    like inductive/resistive electric heating.
     
  11. ....
    Just because a lot of people read this and may not know better, 100%
    efficient conversion of electrical energy into heat applies to the filament
    of a light bulb at 1500C or thereabouts. The process of mixing this with
    cooler surfaces to get a comfortable average temperature is a huge, huge,
    waste of energy. The only way to do this efficiently is to run a heat pump.
    Much more complex, expensive, prone to failure. But it produces as much as 5
    times as much heating value for the energy (depending on where you get the
    heat it pumps, of course).
     
  12. Perhaps not more efficient but it allows the use of a wide variety
    of fuels to heat the water. You can have a solar water heater with
    a propane backup, for instance. If you used a ground source heat
    pump you could conceivably get more than 100%.

    Anthony
     
  13. daestrom

    daestrom Guest

    Simple. Don't use electricity to heat directly. More heat can be collected
    from a given surface area directly as heat than can be had from PV. But
    even if you *do* want to use electricity for heating, use it to run a heat
    pump instead of resistance elements. Most climates, heat pump can deliver
    *more* than the electricity it consumes.

    daestrom
     
  14. Guest

    I _use_ hydronic heating, and like any other
    Ho do you use hydronic heating??

    Do you have hydronic baseboard?

    Or is your's buried in the floor itself?
     
  15. What are you talking about, Fred? If I put a watt of energy into a
    resistive heating element at 25 degrees C, please tell me how much
    heat energy I'll get out of it, and where the inefficiencies are.
     
  16. daestrom

    daestrom Guest

    "watt of energy"?? You know better William. One watt of power into a
    resistive element will generate 1 Joule of heat energy *every second*. (1
    Joule = 1 watt-second).

    But getting back on track, still not all electric baseboard heaters are
    necessarily equal. All will convert the electrical energy into thermal
    energy with 100% efficiency. But what happens *after* it is converted to
    thermal energy can be just as important. Poor air circulation and an
    uninsulated back-side can mean that a lot of the heat energy goes into the
    wall behind it. This just raises the temperature drop across the wall's
    insulation and thus puts more of that thermal energy outside. Good air
    circulation with fins in good condition and a thermal barrier on the back of
    it so more of the heat goes into the room.

    All the electrical energy gets converted to heat. But not all the heat
    necessarily gets to where you want it.

    daestrom
     
  17. I am talking about Entropy.
    You put a joule of energy (a watt second) into a heating device. The most
    you can get out of it is, by conservation, a joule. You can't get around
    this, but you can change the problem. The heat pump changes the problem.
    Instead of asking how much heat you can turn a joule into ask how much heat
    you can deliver to the room at 75F. I can deliver around 5-8 joules, if the
    outside/heat source is around 40-50F, around 2-3 joules if the source is
    less than 30, and 1 joule if I use a resistive heater. This is 100%
    conversion of available energy into heat energy at a large increase in
    entropy, (which can be regarded as 100%, but should very much not be
    confused with efficiency). You pay for that increase in entropy, and not so
    much for the heat itself, which is mostly just laying around anyway.
     
  18. Dave Hinz

    Dave Hinz Guest

    I've got the tubing encased in the concrete floor in my basement, and in
    the concrete 4" (10cm) skim coat on top of the Spancrete which is the
    floor of my kitchen/sunroom. I heat this with a water heater which gives
    me a 1 degree (f) of temperature rise per hour given the thermal mass of
    the concrete in the system, and because my electical rates are on time-of-use,
    I run the electric water heater during off-peak rate times which generates
    enough heat for what I'm trying to do. In summer, I re-route the circulation
    so that the heat from the sunroom/kitchen floor is dumped into the basement
    floor slab.

    I'm not sure what your question actually is, but does this answer it?


    Dave Hinz
     
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