electric heater efficiency

[Josepi]

To understand your switching logic, this means you have the thermostat temp
contact and a close on high humidistat contact in series?

....and you are finding this works more human comfortable and energy
economical than just a temp. alone?

Would you set the temp. at the minimum and let the humidtstat run the show,
mostly then?

In Ontario the common item pushed is the HRV (heat recovery ventilator) for
humidity and vapour / fume control. It centrally replaces the bathroom
exhaust fan and attempts to save heat by "swapping" some of the hot air heat
for cool intake air. WE have vapour barriered out homes so tightly that we
can die from CO2 buildup from cooking and other household products,,,like
paint, formaldehyde (sp?) in manufactured goods etc....

Whie this works well there are some caveats.

In the winter, it dries your house right out and a humidifier is needed. I
got one last winter at 23% humidity...nose bleeds and sore throat get
common.
In the summer the exhausted air is replaced by high humidity / hot intake
air and is hard on the A/C energy consumption.

After attempting run on humidistat alone for a few years I have discovered
another input contact on the HRV unit. One to three contact pulses give
20,40 and 60 minutes of running the HRV and this works well in the smelly /
humid rooms in all the bathrooms, laundry and skylight windows. My hugely
expensive thermostats have some cicle control that I have tied into the HRV
and can guarantee 10-100% of each heat cycle per thermostat setback daily
quadrant. We find if the HRV doesn't tun at least 10%-20% of the time we
just don't feel alert and feel headachey...we think, so far.

More logic is required yet, when I get more time to automate this home I
have built.





I took an April-Aire humidity sensor, wired it backwards to
"make" on humidity rise instead of fall, and inserted it into
the red wire of the thermostat for my A/C. So that the A/C
serves as a whole-house dehumidifier rather than trying to
compete with that big fusion reactor about 8 light-minutes
away.

After all, a muggy 73 degrees can be far less comfortable
than a drier 83 degrees. So the thermostat is set for 73,
and we adjust the humidistat for comfort, usually at about
35%, it gets reset at higher temperature.

And after a shower, it kicks on about 45 seconds after we
open the bathroom door, runs till the humidity has been
brought down near it, and we never have a mold or
mildew issue in the bathroom.

If I come in from cutting grass and I would like it to be
running for a while, I just breathe a nice wet breath
to the humidistat, and it kicks on for a few minutes.
It has made a difference in my utility bill, and my wife does
not wake up with a dry throat in the morning.

 

[Josepi]

Nothing like a variable system you can close off for recirculate for
efficiency.

Biggest trouble is the automation of the system so you can benefit from both
methods. Need to get small percentage of fresh air when the humidity is high
and larger amounts when the outside humidity / temp is low. The house should
have enough fresh air to carry itself normally for a day at a time.



We figured that out the hard way when we tried to cool our bedroom with one
of
those one-hose portable AC units. The problem was, for every cubic foot of
hot
air that box blew out of the house, another cubic foot of saturated Florida
mugginess infiltrated from outside. The result? Cool and uncomfortable.
Never
use a one-hose portable AC in a high-humidity area! We sent that one to my
daughter in California. There, it works great.

Vaughn

 

[Josepi]

Electric blanket comes to mind there!


There is no need to heat the room I sleep in here in Seattle. I've got 3
comforters which keep me toasty all night with the house as low as 45F. The
bed
room is the last one I'd heat, except for certain special occasions. A
standard
space heater takes care of those just fine, and warms up the bed in 2
minutes if
needed when I climb in.

 

[Bob F]

Vaughn,

Even though the post I was responding to was about the efficiency of
converting electricity to heat, I think it's a valuable reminder that
there are also costs involved with production and transportation of
energy, but it in an "apples to apples" comparison, we would also have
to consider those costs for natural gas, propane, fuel oil and wood,
not just electricity.

Those cost are generally included in the price, unless you are going to pick it
up.

 

[Curbie]

Electric blanket comes to mind there!
That's what I do, 2 comforters with an electric blanket sandwiched in
between. I haven't heated the bedroom area at all so far, and turn the
heat way down in the living area at night; I'll see what adjustments
need to be made for the Nebraska winters.

 

[Curbie]

Those cost are generally included in the price, unless you are going to pick it
up.
True from a "point of use" perspective, from a "point of production"
perspective there are transmission losses which aren't included in the
100% electrical to (useable) heat conversion figure, and from a
"economical comparison perspective" all cost of goods or services sold
are reflected in the point of sale price, but from a "ecological
comparison perspective" not all costs of goods or services sold are
rolled into the point of sale price and like it or not, we don't know
what the final cost will be and although we're all going to have pick
those up.

Curbie

 

[Gordon]

Why doesn't the electricity the fan uses convert to heat?

Curbie

Well, actually it does. There is some heating of the motor
and the moving air will eventually turn to heat from friction.
But, air moving over objects and persons will have a cooling
effect as well. In any case, the standard method of measuring
efficency does not take the movement of air into account.

 

[Gordon]

It especially ignores the fact BTUs directly
produced from electricity are typically damn expensive! In truth,
almost any heating method is cheaper and more efficient than
electrical resistance heating.

I think you are talking about economical, not efficent.
Think $/BTU. Then electricity is not so attractive.

 

[vaughn]

I think you are talking about economical, not efficent.
Think $/BTU. Then electricity is not so attractive.

That's exactly the point I though I was making.

Vaughn

 

[Curbie]

Jim,

I asked the question in the context of comparing different fuels for
estimating costs of space and water heating; it seems to me that heat
flow for any particular home would be about constant for any heater
regardless of the fuel. I've been planning for solar heating, but as
with anything AE, a back-up seems necessary and since reading some of
your posts, I've been taking a harder look at wood as a back-up.

Thus the 60-65% for estimations in wood stove planning question.

Curbie

 

[Josepi]

Seems like a good way to go but the bathrooms are vented through this system
also and I would be afriad of the stink being transfered.

Anybody know if this is the case? I know the recirculating ones it would
happen. That was an option I let go...and the prices were higher yet.


Enthalpy (moisture transfer) heat exchangers:
http://cipco.apogee.net/ces/library/tdew.asp

jsw

 

[Josepi]

That is the trouble with so many "green" technologies. A complete backup
system that is reliable needs to be in place and the economy gets
questionable considering, loss of income on investments and other long term
factors.


Jim,
I asked the question in the context of comparing different fuels for
estimating costs of space and water heating; it seems to me that heat
flow for any particular home would be about constant for any heater
regardless of the fuel. I've been planning for solar heating, but as
with anything AE, a back-up seems necessary and since reading some of
your posts, I've been taking a harder look at wood as a back-up.

Thus the 60-65% for estimations in wood stove planning question.

Curbie

 

[Josepi]

Air moving over objects does **NOT** cool them unless they are warmer than
the air passing over them and surroundings.

Air passing over a moist item, like a human will tend to cool them, though.


Well, actually it does. There is some heating of the motor
and the moving air will eventually turn to heat from friction.
But, air moving over objects and persons will have a cooling
effect as well. In any case, the standard method of measuring
efficency does not take the movement of air into account.

 

[Josepi]

Air moving over objects does **NOT** cool them unless they are warmer than
the air passing over them and surroundings.

Air passing over a moist item, like a human will tend to cool them, though.


Well, actually it does. There is some heating of the motor
and the moving air will eventually turn to heat from friction.
But, air moving over objects and persons will have a cooling
effect as well. In any case, the standard method of measuring
efficency does not take the movement of air into account.

 

[Josepi]

Air moving over objects does **NOT** cool them unless they are warmer than
the air passing over them and surroundings.

Air passing over a moist item, like a human will tend to cool them, though.


Well, actually it does. There is some heating of the motor
and the moving air will eventually turn to heat from friction.
But, air moving over objects and persons will have a cooling
effect as well. In any case, the standard method of measuring
efficency does not take the movement of air into account.

 

[Josepi]

Air moving over objects does **NOT** cool them unless they are warmer than
the air passing over them and surroundings.

Air passing over a moist item, like a human will tend to cool them, though.


Well, actually it does. There is some heating of the motor
and the moving air will eventually turn to heat from friction.
But, air moving over objects and persons will have a cooling
effect as well. In any case, the standard method of measuring
efficency does not take the movement of air into account.

 

[Curbie]

Jim,

I had a chat with a local tree service who pays to dump at the local
dump, that load includes both a majority (by volume) of chipped
branched and a minority of raw logs. Since I might have interest in
both (compost and fire wood logs) as long as they can come in at their
convenience and dump the whole load, the owner I talked to seemed ok
with the idea.

Curbie

 

[Curbie]

I agree there's an issue with AE technologies requiring back-up and
that certainly plays into the economics of return on investment. I
also consider thing other than ROI like security (self-sufficiency)
and "Green" (political and ecological) concerns into my "return on
investment" calculations because those notions have value to me also.

I also feel pretty comfortable in looking at supply and demand trend
lines for energy prices, instead of using current prices in "return on
investment" calculations.

 

[Josepi]

That was the point of my injection. Fans doe not cool objects unless they
are damp or warmer than the room.

Your point about elect. heater eff. is well made though.



The moving air will evaporate water and make the object cooler. However
that heat goes into the room so the net effect is no heat is gained or lost
from this process. The fan motor will heat up the room somewhat and the
friction of moving air will add some heat.
Total results is that the ammount of electricity used is still converted to
100 % heat. This is not counting the loss of the wiring in the walls.

 

[Josepi]

That was the point of my injection. Fans doe not cool objects unless they
are damp or warmer than the room.

Your point about elect. heater eff. is well made though.



The moving air will evaporate water and make the object cooler. However
that heat goes into the room so the net effect is no heat is gained or lost
from this process. The fan motor will heat up the room somewhat and the
friction of moving air will add some heat.
Total results is that the ammount of electricity used is still converted to
100 % heat. This is not counting the loss of the wiring in the walls.