Heatsource with low energy consumption.

[Moojundai]

How do I get/make a heatsource with a low as possible energy consumption.

The powersource is 12 V "Optima" battery connected to a 200w wind generator.

I've thought about:

1) Fill a 60litre plasticcontainer with water (maybee with antifreeze as
well). Solder wires on to a 20-50 watt bulb as a heatsource (isn't it 75% of
the energy that is "wasted" as heat?). For insulation, I'd probably use a
thick layer of paint on the bulb's connections. Hereafter I'd submerge the
bulb into the water, and let it's excess heat, warm the water. Isn't the
water a good way of "holding" the heats energy?
Would it be better to use some kind of oil, and If so witch?

2) 20-50 watt bulb in an insulated box, and a small ventilator from a CPU
cooler, to blow out the heat?

3) Reuse an old seatheater from a car (how many watts do theu use?)

Isn't the best idea to use some kind of fluid like in no. 1 to hold the
heat?

 

[Steve Young]

How do I get/make a heatsource with a low as possible energy consumption.

The powersource is 12 V "Optima" battery connected to a 200w wind generator.

I've thought about:

1) Fill a 60litre plasticcontainer with water (maybee with antifreeze as
well). Solder wires on to a 20-50 watt bulb as a heatsource (isn't it 75% of
the energy that is "wasted" as heat?). For insulation, I'd probably use a
thick layer of paint on the bulb's connections. Hereafter I'd submerge the
bulb into the water, and let it's excess heat, warm the water. Isn't the
water a good way of "holding" the heats energy?
Would it be better to use some kind of oil, and If so witch?

2) 20-50 watt bulb in an insulated box, and a small ventilator from a CPU
cooler, to blow out the heat?

3) Reuse an old seatheater from a car (how many watts do theu use?)

Isn't the best idea to use some kind of fluid like in no. 1 to hold the
heat?

dood, how many Btus do you think are in 200 watts?

haven't we been through this before with your shitter?

start by putting the shitter in a thermos bottle

 

[William P.N. Smith]

How do I get/make a heatsource with a low as possible energy consumption.

Well, electrical heaters aren't going to be any more than 100%
efficient, any better than that you are going to have to use a heat
pump or something....

 

[Bughunter]

Some things to thing about.

I'll assume you are still tryng to get some heat for a small 2m x 3m
insulated greenhouse space that you posted about before. The one where we
went off on a tangent with suggestions about how to heat toilet seats.

I have heard that people use a standard electric resistance element from
electric hot water heaters as a diversion load for wind generators. A
diversion load serves the purpose of maintaining an electrical load on the
wind generator to keep it from free spinning and destroying itself. An
electrical brake of sorts. This is needed whenever the wind generators
normal battery charging load goes away (batteries are completely charged).

Concieably, that would work as a heater element in your application, and
also serve the purpose of acting like an electrical brake for your wind
generator. I have no direct experience with this myself, but I'm sure many
who frequent this group do and could supply additional guidance.

The hot water heater elements are obviously designed to be emmersed in water
and convert 100% of the electric supplied to them as heat. They are readily
available at local hardware stores, and inexpensive.

I would avoid emmersing a lightbulb in water. I do not think it would last
long.
Paint may be a poor insulator. I would not use it for that purpose, unless
it was specially designed for that purpose as stated on the label.

Another thought for a homemade resistance heater would be to use nichrome
wire. Nichrome wire is used in toasters. It's the thin silver wire, wrapped
on s-patterns across a heat resistant board. It's what you see glowing
cherry red. The same wire is used in electric hair dryers.

You could find a discarded toaster and salvage the nichrome wire. The same
thing is probably used in the seat heaters for automobiles. Discarded
toasters are cheaper, and often found discarded. I'd scan the dump for old
toasters and hair dryers.

If you have a battery in the system, you need to make some kind of circuit
that will detect when the battery is getting discharged, and disonnect the
heater. Otherwise, if you have no wind for a while, the heater will totally
discharge the battery. Eventually, this will destroy the battery.

You also have to take into consideration how much real wind you will get to
power your wind generator. This is not easy to determine. Most of the good
wind is high above the ground and a tower can be quite complex to erect as
well as being costly.

If you use a battery, you need to take into consideration how long you
battery will power the system without wind energy input. The concequence of
running out of both wind and battery power are dire, if your plants die. How
will you provide heat if the system is not sized large enough to cover a
stretch of cold days without wind. Unless you system design is done well,
you should have some kind of a backup system in mind.

It would be a good idea to calculate the heat requirements for your space.
To do this, you would need to know how large a space, how well insulated,
what the temperature range is that you desire to maintain, as well as the
seasonal variations in outdoor ambient temperature ranges are. Knowing
that, somebody like Nick Pine might plug your numbers into a few formulas to
detemine what the required heating input would be.
My instinct is that 200watts is way too little to have much effect,
especially from a very variable source like a wind generator. Numbers are
better than my instincts any day of the week. Nick asked a few questions in
the previous thread, and seemed poised to provide some calculations, but I
don't think you answered his questions specifically enough to allow him to
do his job.

I do think that you are on the right track when thinking about heating a
body of water, rather than simply heating air. The reason being that the
water will act as a thermal mass to slowly dissipate the heat over a longer
period of time. That is a good thing, as plants would probably do better
with slow transitions in temperature.

Water should work fine, and I'd only add a bit of antifreeze if the ambient
temperatures went below freezing for any part of the year. I'd use
automotive anti-freeze, and follow the dilution instructions on the bottle.

I have known of people placing a 100watt light bulb in a very small
pump-house
(1m x 1m x 1m) to keep the pump from freezing in conditions that go well
below freezing. It works reasonably well in a small very well insulated
space, with a continous supply of electricity to keep the bulb burning 24x7.

One other potential source of a resistance heater element just came to mind.
They sell an electrical heat-tape designed to wrap your pipes with to keep
them from freezing. These probably use nichrome wire, and are designed for
110v AC input. They often come complete with thermostats. The might work
with DC, or you might consider a small inverter which are getting very
inexpensive these days. You would not have to worry about efficiency of the
inverter, because the losses are generated as heat anyway.
You might bury lengths of this heat tape wire eneath the soil in which your
plants live.

12 V "Optima" battery does not tell us much. You need to know the capacity
of the battery, expressed in amp-hour to have any chance of determining how
long it might power a given load.

I doubt that a single 12v battery of any type would give you much of a
buffer. You might simply the whole system by eliminating the battery
altogather, and maximizing the size of the wind generator. After all, what
you really want to store is heat, with the ability to dissipate it slowly to
maintain a stable temperature. Water should serve that purpose well.

That's just a few thoughts on the subject, and still far from a realistic
solution.

 

[Ecnerwal]

How do I get/make a heatsource with a low as possible energy consumption.

The powersource is 12 V "Optima" battery connected to a 200w wind generator.

So, you have, when the wind blows enough, 200W * 3.413 BTU/Watt, or 682
BTU. Doesn't matter what cockamamie thing you do with your 200W, it
still can only add up to 682 BTU, when the wind blows enough, or an
average of less that that, when the wind doesent blow sometimes. This is
an absurdly small heat input for any building.

If you have an 8 foot cube for your building which is insulated to R33
on all sides (7-8 inches of styrofoam), with no air exchange at all, no
door or window with lower than R33 insulation, you could keep it 58.6
degrees F above the exterior temperature. If the wind only blew 1/2 the
time, you'd only be able to do 29 degrees F above the outside, on
average.

 

[Steve Spence]

You don't produce heat with a 200 watt wind generator. Use a fuel like wood,
veggie oil, or even solar thermal.


--
Steve Spence
Renewable energy and sustainable living
http://www.green-trust.org
Donate $30 or more to Green Trust, and receive
a copy of Joshua Tickell's "From the Fryer to
the Fuel Tank", the premier documentary of
biodiesel and vegetable oil powered diesels.

 

[Steve Spence]

can't run much of a heat pump with 200 watts.

--
Steve Spence
Renewable energy and sustainable living
http://www.green-trust.org
Donate $30 or more to Green Trust, and receive
a copy of Joshua Tickell's "From the Fryer to
the Fuel Tank", the premier documentary of
biodiesel and vegetable oil powered diesels.

 

[[email protected]]

...how many Btus do you think are in 200 watts?

Bad question. Please learn the difference between power and energy.

Nick

 

[Nick Pine]

...200W * 3.413 BTU/Watt, or 682 BTU.

Bad answer. Please learn the difference between power and energy.

Nick

 

[Steve Young]

Bad question. Please learn the difference between power and energy.

I wasn't sure he could keep it up for an hour

sounds like even fewer than I thought ))

you're something else Nick

 

[ptaylor]

Some things to thing about.

I'll assume you are still tryng to get some heat for a small 2m x 3m
insulated greenhouse space that you posted about before. The one where we
went off on a tangent with suggestions about how to heat toilet seats.

I have heard that people use a standard electric resistance element from
electric hot water heaters as a diversion load for wind generators. A
diversion load serves the purpose of maintaining an electrical load on the
wind generator to keep it from free spinning and destroying itself. An
electrical brake of sorts. This is needed whenever the wind generators
normal battery charging load goes away (batteries are completely charged).

Concieably, that would work as a heater element in your application, and
also serve the purpose of acting like an electrical brake for your wind
generator. I have no direct experience with this myself, but I'm sure many
who frequent this group do and could supply additional guidance.

The hot water heater elements are obviously designed to be emmersed in water
and convert 100% of the electric supplied to them as heat. They are readily
available at local hardware stores, and inexpensive.

True,but most are rated at 1KW+,but he only has ~200W available
anyways.Without a way to control the element,it would drain the battery
very quickly.

I would avoid emmersing a lightbulb in water. I do not think it would last
long.
Paint may be a poor insulator. I would not use it for that purpose, unless
it was specially designed for that purpose as stated on the label.

Another thought for a homemade resistance heater would be to use nichrome
wire. Nichrome wire is used in toasters. It's the thin silver wire, wrapped
on s-patterns across a heat resistant board. It's what you see glowing
cherry red. The same wire is used in electric hair dryers.

Hairdryers,toasters,electric heaters,toaster ovens,larger power
resistors?,anything with a "heating element".. Actually,A large power
resitor,or bank of series/paralellel resitors might be a good choice.
using ohms law,you can adjust the current draw,etc. and estimate how
long a given heating load will drain the battery.

Another thought I just had was to use headlight bulbs.the older "sealed
beam" types have a sealed bulb inside of a big glass housing,so the bulb
would have a bit of an air cusion between it and the water.
Of course you'll also have alot of light as a byproduct..could be good
or bad in a greenhouse. I think most are rated at 50/55 or 55/60W
(lowbeam/highbeam)
That might actually be a good way to go also.Because you have multiple
loads,you can switch from 50W up to 200+W of heat/light.

Heating a tank of water might not be a bad idea. You could get a small
pump,and some tubing and pump the warm water on the shelves near the
plants,to help spread the heat around.

200W isn't a lot of heat,unless it's a fairly small greenhouse!
You will probably want to get antoher battery or two,and maybe consider
a solar panel,or something to bump that up a bit.

I'd think perhaps a water heater element in a tank of water,and a
pump/tubing to circulate it would be a fairly simple,inexpensive way to
do it.
The simplest/cheapest way might be to put a "heater" of some type
(bulb,element,etc) in a barrel of water,connected across the wind
genny..Whenever there's more wind,theres more heat.

You could find a discarded toaster and salvage the nichrome wire. The same
thing is probably used in the seat heaters for automobiles. Discarded
toasters are cheaper, and often found discarded. I'd scan the dump for old
toasters and hair dryers.

If you have a battery in the system, you need to make some kind of circuit
that will detect when the battery is getting discharged, and disonnect the
heater. Otherwise, if you have no wind for a while, the heater will totally
discharge the battery. Eventually, this will destroy the battery.

You also have to take into consideration how much real wind you will get to
power your wind generator. This is not easy to determine. Most of the good
wind is high above the ground and a tower can be quite complex to erect as
well as being costly.

If you use a battery, you need to take into consideration how long you
battery will power the system without wind energy input. The concequence of
running out of both wind and battery power are dire, if your plants die. How
will you provide heat if the system is not sized large enough to cover a
stretch of cold days without wind. Unless you system design is done well,
you should have some kind of a backup system in mind.

It would be a good idea to calculate the heat requirements for your space.
To do this, you would need to know how large a space, how well insulated,
what the temperature range is that you desire to maintain, as well as the
seasonal variations in outdoor ambient temperature ranges are. Knowing
that, somebody like Nick Pine might plug your numbers into a few formulas to
detemine what the required heating input would be.
My instinct is that 200watts is way too little to have much effect,
especially from a very variable source like a wind generator. Numbers are
better than my instincts any day of the week. Nick asked a few questions in
the previous thread, and seemed poised to provide some calculations, but I
don't think you answered his questions specifically enough to allow him to
do his job.

I do think that you are on the right track when thinking about heating a
body of water, rather than simply heating air. The reason being that the
water will act as a thermal mass to slowly dissipate the heat over a longer
period of time. That is a good thing, as plants would probably do better
with slow transitions in temperature.

Water should work fine, and I'd only add a bit of antifreeze if the ambient
temperatures went below freezing for any part of the year. I'd use
automotive anti-freeze, and follow the dilution instructions on the bottle.

I have known of people placing a 100watt light bulb in a very small
pump-house
(1m x 1m x 1m) to keep the pump from freezing in conditions that go well
below freezing. It works reasonably well in a small very well insulated
space, with a continous supply of electricity to keep the bulb burning 24x7.

One other potential source of a resistance heater element just came to mind.
They sell an electrical heat-tape designed to wrap your pipes with to keep
them from freezing. These probably use nichrome wire, and are designed for
110v AC input. They often come complete with thermostats. The might work
with DC, or you might consider a small inverter which are getting very
inexpensive these days. You would not have to worry about efficiency of the
inverter, because the losses are generated as heat anyway.
You might bury lengths of this heat tape wire eneath the soil in which your
plants live.

12 V "Optima" battery does not tell us much. You need to know the capacity
of the battery, expressed in amp-hour to have any chance of determining how
long it might power a given load.

Optima batteries aare intended for Automotive use.I just recently
purchased one,and it was well worth paying twice as much.
($80-90,instead of $40-50 for a conventional Lead-acid)
It's been worth it already.. No problem starting during our recent ice
storm,I did notice that on the coldest day (well below 0 with the 50mph
winds) it was a little "slower" to crank (it was being affected by the
cold) But it cranked my old small block V8 (1967 327ci) for a good 20-30
seconds till it started,so it wasn't affected too badly.
I probably would have had to "thaw"/charge the old lead-acid battery a
bit to get it to start.

http://www.optimabatteries.com/

I think the one I got is either 50,or 55AH. 650CCA?..I forget..

 

[Bob Adkins]

Isn't the best idea to use some kind of fluid like in no. 1 to hold the
heat?

I think fans. Use small fans that use about 150-200W total. There will be
resistance heating, frictional heating in the mechanical parts, and just a
tad of frictional heating between the blades and the air. Blow the air on
the most massive things in the room, such as the flower pots, or add heavy
rocks, glass, or ceramic objects. Avoid blowing the air directly on windows
or walls, and avoid intake of air from windows and walls.

The fans will also prevent temperature stratification of the air.

Bob

 

[Moojundai]

No, it's still NOT a "shitter", and unfortunately the last tread ended up
with old memories about going "where even the king goes alone", in stead of
heating ideas.

Yes, I'm aware that it's probably underpowered, but if it's not enough, I
expect that there will be bought a solar panel to help the windgen.








Yes it's still the small insulated room, of aprox 2x3 metres.
I dont know if it is insulated after R33 standards as we probably use some
other other standard in scandinavia.
It's insulated after the standard used for houses to live in. As far as i
remember its 200mm rockwool in the walls and 300mm in the cieling. No
insulation in the old original concrete floor. The windows are doubleglazed
thermowindows, also made for living quarters.

I'm not sure about degrees Farenheight, as we use Celcius here.
We usually have a few degrees above freezingpoint in the winter, with
periods of 5-15 degrees C below. This winter we havn't been below 5 degrees
C yet, and not more than a few days at a time.

So what can I do to get max out of the system?

The system will be used for illumination as well, so leaving the battery
uninstalled, and shortcuirciting the windgenerator, with a toaster, would
not be possible.

I've already ordered a "Batterywatch" that cuts the power below a voltage
not known yet, so I don't drain the batteries.

The voltage regulator will be mounted in the room, so that the heat is
utilized as well.

Ive got a larged 155 litre plasticbarrel with lid, and a couple of old 55W
headlights from cars.

I expect it'll be 150 litres of water/antifreeze in the barrel with a
headligt mounted.

(Got a plastic headlight and a few old glass ones, witch is best?)
(Is it a good idea to paint the glass black, to utilize the heat best
possible?).
(Shall the glass touch the water or hang above it?)
(Skal the glass point into the water, or the lid?)

My guess is plastic in water won't crack???

If there is added a 100W solarpanel it'll be two 55W lamps.

I've thought about a backup system that kicks in via a relay. This could be
an other battery charged by a a 240V/12V charger. But we want to be off the
grid, so rather buy an extra solarpanel.

I tried to answer Nick, I don't know if I gave him enough?

I'm afraid that I don't know how much insulation there is, but it's enough
to convert intp living quarters. My guess is that the window is aprox. 6 m2
(double glazing)

The temerature seldolmy goes below 10 degrees of frost, for more than a
month at a time.

The wall faces south

We are using the same trick in our stable with a bulb keeping a tap
frostfree.
Here it's enough with a 60W (240V) bulb, covered with an insulated blanket
and a bucket to keep the distance between the lamp and the blanket.
Works fine, but that too is "grid power" so we hope to turn that onto 12V
(not a part of the frostfree room project).

The "Optima battery" is of this type:
http://popularmechanics.com/automotive/auto_technology/1998/12/optima_exide_battery/
and it is a 85AH battery.

I like the "sealed beam" bulb idea. This is utilized in the lamps above,
where I'd use existing lamps to hold distance between the bulb and the
water.

I've got a few sprinkler pumps, that could pump the fluid around the plants,
copper pipes must be best?

What is a BTU???

How about the fan idea?
Iv'e got a lot of 12V fans from some old computer PSU's, how much heat do
they generate?
Or maybee I should mount them all on a rack, and hang them up besides the
generator ;o)

OK, sounds like I'm joking. If the fans can create heat, as well as
distribute it in the room, then it's brilliant )

Did I miss any questions?

 

[William P.N. Smith]

Yes, I'm aware that it's probably underpowered, but if it's not enough, I
expect that there will be bought a solar panel to help the windgen.

Umm, it's not that it's underpowered, it's that it'll have no
measurable effect. You are better off packing more people into the
room (anyone remember the power output of an average human?) and
keeping it warm that way.

Try this: Run an extension cord to the nearest power outlet (or
borrow a generator), plug in a 1500W electric heater, and let it run
24x7 for a day or so. If this works, you know you need about 1.5KW,
and your 200W wind generator and 100W solar panel (which will net out
another 20 watts running 24x7 as a SWAG) aren't going to cut it.

Or you could "Just Forget It". You seem to want something for
nothing, and everyone's telling you you can't get there. If you have
200W of wind generated electricity, how do you expect to get more than
200W of heat out of it?

 

[Ecnerwal]

Yes it's still the small insulated room, of aprox 2x3 metres.
I dont know if it is insulated after R33 standards as we probably use some
other other standard in scandinavia.

In Metric R-value, that's 5.81 square meter Kelvins per watt (m**2*K/w).
Since a Kelvin degree and a Celsius degree are the same size, the unit
makes calculating what 200W input will do rather simple, without having
to do any of the conversions needed to get the same simple information
in the units we use. For a Metric R of 5.81, 1 watt will maintain a
difference of 5.81 degrees (K or C) across a 1 square meter chunk of
wall - or 1 watt will maintain a difference of 1 degree (K or C) across
5.81 square meters of wall. U-values (both metric and "english") are
just R values divided by one.

It's insulated after the standard used for houses to live in. As far as i
remember its 200mm rockwool in the walls and 300mm in the ceiling. No
insulation in the old original concrete floor. The windows are doubleglazed
thermowindows, also made for living quarters.

Ignoring framing members, which is not a very good thing to do for
accuracy, but simplifies the assumptions and results in an optimistic
calculation, about Metric R 7.3 on the roof, and 4.8 on the walls (R42
and R27 to the US reader, any anyone else, if there is anyone else,
still using the units we use). So, you have 6 square meters of roof at R
7.3, and some square meters of wall at R 4.8, and some square meters of
window, which is probably R 0.53, but might be as good as R 1.76 if
using the most expensive sort of krypton-filled windows. I'm ignoring
the floor for now.

We usually have a few degrees above freezingpoint in the winter, with
periods of 5-15 degrees C below.

6 square meters of roof, at metric R7.2, requires 0.83 Watt to maintain
a 1 degree Kelvin (or Celsius, since they are the same size degrees)
difference. 12.5 watts are needed to keep the roof at 0C when the
outside is -15C.

Since you don't mention the window/wall layout, I'll guess 6 square
meters of window (one 3 m wall, 2 m high). 169 watts for 15C difference
for typical double-glazed thermopane, 51 watts for fancy krypton windows

That guess leaves 14 square meters of R4.8 wall, which needs about 44
watts for a 15C difference. I suspect that there is a 1.5 to 2M door
with insulation values more like a window in there someplace, but
perhaps not.

So, given the most optimistic assumptions, you might just be able to
keep it from freezing with 200W input. Given typical windows, you'll
come up short. Given framing reducing the effective insulation of the
wall, and non-zero losses to the ground, shorter yet. If you can
quantify all the parts in terms of the Metric R-value, you can determine
more precisely what your real power needs are - you can also make an
experimantal observation, by running a heater or lights of a specific
wattage, and measuring indoor and outdoor temperatures - when they have
stabilized, the wattage to maintain the temperature difference tells you
what the overall R value of the building as a whole is.

As I said before, it really does not matter what you put the 200W into,
it's still 200W no matter if it's feeding a car-seat heater, a
soil-heating cable, a computer, a fan, a lightbulb, a waterheater, or a
waterheating lightbulb.

If you're actually trying to keep plants alive/growing, somewhat more
than 0C inside would be good, but that takes more power yet.

A BTU is a British Thermal Unit. The heat needed to raise 454grams of
water 5/9 of a degree C. You won't need it for this post.

 

[Gordon Richmond]

What you are trying to heat is commonly known in English-speaking
countries as an outBUILDING, not an outHOUSE, otherwise known as a
privy.

Outbuilding is a generic term that is often used to refer to any small
building on a homestead or farmstead, other than the home itself.

My own feeling is that 200 watts of wind-generated electric would be
inadequate as a heat source for your greenhouse. And using solar PV to
run resistance heaters is akin to feeding gold to chickens. You would
be much better off building a solar thermal collector, and using the
wind electric to drive a circulating pump for the heat transfer fluid.

What is the reason for the objection to a combustion heater?

Gordon Richmond

 

[Bob Adkins]

No, it's still NOT a "shitter", and unfortunately the last tread ended up
with old memories about going "where even the king goes alone", in stead of
heating ideas.

Yes, I'm aware that it's probably underpowered, but if it's not enough, I
expect that there will be bought a solar panel to help the windgen.

Don't get discouraged! Unless you are in very cold climes, it's quite
do-able.

What is being ignored is heat absorbed during the day, and temperature
differential. The temperature in the outbuilding will not suddenly drop to
the outside temperature. It's more like a slow leak. On many days, it may
take until well after midnight until any heating is needed. Then, the
temperature rise needed will not be that great. It takes only a little bit
of heat to raise the temperature in such a small area by 5 Deg. In many
cases, that may be all you need. There will be extended cold spells with no
sun, for which you will have to plan. The foundation and ground will act as
a heat sink, so it's important to keep the floor warm and keep the pots on
the floor. Installing a false ceiling of foam insulation or plastic sheet
can greatly reduce wasted heat.


Bob

 

[Ecnerwal]

[email protected] (Nick Pine) wrote in message


200W * 3.412 BTU/Watt-hr, or 682 BTU/hr.

I also cringe when BTU/hr is abbreviated as BTU, but it is
unfortunately common to do so. I cringe worse when amp-hrs is
abbreviated as amps or mangled as amp/hrs.

In point of fact, it was just a typo, as was _obvious_ from the rest of
the calcualtions based on it. Though it is certainly true that a wood
boiler I recently moved was stamped 180,000 BTU with no "/hr", so
grasping the meaning in context is a useful skill anyway. Nick _should_
have been able to figure that out, given that we've been hanging around
the same newsgroups for over 7 years; but he does love to turn a typo
into an opportunity to prove that he's more perfect than the rest of us.
Yawn...

 

[daestrom]

In Metric R-value, that's 5.81 square meter Kelvins per watt (m**2*K/w).
Since a Kelvin degree and a Celsius degree are the same size, the unit
makes calculating what 200W input will do rather simple, without having
to do any of the conversions needed to get the same simple information
in the units we use. For a Metric R of 5.81, 1 watt will maintain a
difference of 5.81 degrees (K or C) across a 1 square meter chunk of
wall - or 1 watt will maintain a difference of 1 degree (K or C) across
5.81 square meters of wall. U-values (both metric and "english") are
just R values divided by one.


Ignoring framing members, which is not a very good thing to do for
accuracy, but simplifies the assumptions and results in an optimistic
calculation, about Metric R 7.3 on the roof, and 4.8 on the walls (R42
and R27 to the US reader, any anyone else, if there is anyone else,
still using the units we use). So, you have 6 square meters of roof at R
7.3, and some square meters of wall at R 4.8, and some square meters of
window, which is probably R 0.53, but might be as good as R 1.76 if
using the most expensive sort of krypton-filled windows. I'm ignoring
the floor for now.


6 square meters of roof, at metric R7.2, requires 0.83 Watt to maintain
a 1 degree Kelvin (or Celsius, since they are the same size degrees)
difference. 12.5 watts are needed to keep the roof at 0C when the
outside is -15C.

Since you don't mention the window/wall layout, I'll guess 6 square
meters of window (one 3 m wall, 2 m high). 169 watts for 15C difference
for typical double-glazed thermopane, 51 watts for fancy krypton windows

That guess leaves 14 square meters of R4.8 wall, which needs about 44
watts for a 15C difference. I suspect that there is a 1.5 to 2M door
with insulation values more like a window in there someplace, but
perhaps not.

So, given the most optimistic assumptions, you might just be able to
keep it from freezing with 200W input. Given typical windows, you'll
come up short. Given framing reducing the effective insulation of the
wall, and non-zero losses to the ground, shorter yet. If you can
quantify all the parts in terms of the Metric R-value, you can determine
more precisely what your real power needs are - you can also make an
experimantal observation, by running a heater or lights of a specific
wattage, and measuring indoor and outdoor temperatures - when they have
stabilized, the wattage to maintain the temperature difference tells you
what the overall R value of the building as a whole is.

As I said before, it really does not matter what you put the 200W into,
it's still 200W no matter if it's feeding a car-seat heater, a
soil-heating cable, a computer, a fan, a lightbulb, a waterheater, or a
waterheating lightbulb.

If you're actually trying to keep plants alive/growing, somewhat more
than 0C inside would be good, but that takes more power yet.

A BTU is a British Thermal Unit. The heat needed to raise 454grams of
water 5/9 of a degree C. You won't need it for this post.

Some nice calcs.

IF his -15C is the overnight low (warmer during day) *AND* he is able to
cover the windows at night with some type of thermal blanket, then it sounds
like the 200W should be fine.

I think he was looking for whether to use the 200W to circulate air through
a ground tube or some such to try to bring up some air from the ground.
Since he's just trying to stay above freezing, air warmed from a few large
pipes buried well below the frost-line might be more than enough. Just use
the 200W to run some circulating fans. Problem with that is the amount of
excavation he would need for a whole heating season's ground tubing is
probably more than the cost of using the most expensive commercial energy he
has available to him.

daestrom

 

[Moojundai]

Or you could "Just Forget It". You seem to want something for
nothing, and everyone's telling you you can't get there. If you have
200W of wind generated electricity, how do you expect to get more than
200W of heat out of it?

I don't want to get something for nothing, and i don't want to get more that
200W of heat.
I've been talking about using 55-110W.

We all have to start somewere, and I'm trying to make som eksperiance by
experimenting.
Getting as much as possible out of what you've got must be one of the most
important things when talking about alternative energy?

So yes, we have started with two wind generated sets, with each it's 200W
windgenerator, and probably by time the project will gro with solarpanels,
and larger windgens.

As of now 200W is "watt" we have, and now we dont expect to be able to run a
small town on them.