Bitcoin Forum

One thing I wanted to correct since quite a while:  Many people here on the forum say that electricity is expensive in summer, but free in winter.  Why?  Because it can be used for heating, which is necessary in winter anyway, and thus mining is free.

This is not universally true.

If your computer / kitchen / etc is working anyway, and produces surplus heat which you use to heat your home in winter, then this is free heat.  But when the equipment is run only for the purpose of producing heat, then it must be compared to (better) alternatives.  A computer turns electricity into heat similar to an electric resistor. 1 kw of electricity is turned into 1 kw of heat.

(Note that I'm intentionally disregarding the health aspects of the contamination with particles due to air circulation through a computer)

The myth is based on the assumption that this is the best efficieny one can achieve.  1 kw for 1 kw.  However, this is not true.  A modern household air conditioner with heat pump, can achieve an efficiency of 3 to 4.

In other words: With just 1kw of electricity, you get 3-4 kw of heat!

How does this work?  It works in the opposite way than a fridge works.  Air/gas is decompressed (making it very cold) and then warmed by the winter days' outside temperature.  Afterwards it's re-compressed (making it hot) and heats your home.  See http://en.wikipedia.org/wiki/Heat_pump#Efficiency for details.

If your home is in the mid to south area, where air-conditioners are common, and you bought yours in the last few years, then your home can probably already use this technique!

Using your computer to heat your home with electricity is 3 - 4 times LESS EFFICIENT than using such a dedicated electrical equipment.  Even if you don't already possess such an equipment, the cost of it is a fraction compared to a mining rig.

Back to the original argument, winter miners can still claim that the first 25% - 33% of their electricity bill helps heating their house.  But the remaining 66% - 75% is just "for the funs" of mining and nothing else.  Because they wouldn't spend them if they really were after the heating (and not the mining).

Conclusion:  Electricity in winter cheaper, not free.

Don't forget that if you're mining indoors outside of winter that you're also paying to cool the home. By my math, whatever electricity is consumed by my rigs I pay about 40% of that over again to remove the GPU heat from my apartment (0.41W of cooling for every 1W of mining). My rigs, combined, eat up about 2,100 W so I'm using about 861 additional W to cool them, for a total of 2,961 W. If your estimates are correct (we'll split the difference and say 28.5% is "free") then about 600 of my original 2100 W is now "free" plus the 861 W that I'm saving in air conditioning costs. Thus my new "wasted" power consumption (power spent only mining bitcoins and not performing any other useful task, like heating a house) is 1,500 W, or about 50% of my original energy usage.

I always wondered about this. The problem with those heat pumps is that they do not work when the temp is colder than I say around 45 degrees.

The question remains, is the heat thrown from a computer at the same efficiency as electrical heaters?

To also better your argument, the computer uses electric, while most people get much better heat efficiency by using gas or oil for heat.

Up north, you need a lot of heat to stay warm. Hence the preponderance of non-electrical heat sources (natural gas, oil, etc.)

Electrical resistance heating is the most expensive way to heat a house. Heat pumps are indeed 4x more efficient.

Around here (Texas) a lot of homes use electric for heat, because we only have to run the heat for maybe 1 month a year.

Also consider though, that many older homes do not use heat pumps.  I own a 1950's home, and it would cost somewhere in the neighborhood of $7000 to retrofit with a heatpump, which I simply cannot afford at this point in my life.  So, I am stuck with 1:1 electric heat.

I will use wood for heating when I can, as we have a fireplace, but I am not often home to start or maintain a fire either, which means electric must be used for heat the majority of the time.

So, for me, mining isn't "free", but it is certainly better than turning on the wall heaters and getting no Bitcoins for it!

I'll be turning my miners back on as soon as I have a proper wireless solution for them...

Yes.  An computer is essentially an electric heater.  Both have a ~100% conversion of electricity into heat.  That efficiency remains the same regardless of ambient temperature.

Gas/oil is never more efficiency (it may be cheaper but not more efficient) than electric heater.  The very best natural gas furnaces are 98% efficient.  Most sold today are 92%.  If your natural gas furnace is more than a decade old likely it is <80% efficient.


To the OP most people in US don't use heat pumps for heating they use natural gas:
Natural gas cost varies but in my area it costs (in USD) roughly half what an electric heater would require.  So that means using "miner heat" vs "natural gas furnace" is only 50% less efficient.   Another way to look at it is my mining electrical costs are cut in half because it is offset by heating (at half the cost efficiency). It isn't free electricity but it is very very very cheap given the dual use utility of it.

From Wikipedia:

"Note that the heat pump is more efficient on average in hotter climates than cooler ones, so when the weather is much warmer the unit will perform better than average COP. Conversely in cold weather the COP approaches 1. Thus when there is a wide temperature differential between the hot & cold reservoirs the COP is lower (worse).

When there is a high temperature differential on a cold day, e.g., when an air-source heat pump is used to heat a house on a very cold winter day of say 0 °C, it takes more work to move the same amount of heat indoors than on a mild day. Ultimately, due to Carnot efficiency limits, the heat pump's performance will approach 1.0 as the outdoor-to-indoor temperature difference increases for colder climates (temperature gets colder). This typically occurs around −18 °C (0 °F) outdoor temperature for air source heat pumps. Also, as the heat pump takes heat out of the air, some moisture in the outdoor air may condense and possibly freeze on the outdoor heat exchanger. The system must periodically melt this ice. In other words, when it is extremely cold outside, it is simpler, and wears the machine less, to heat using an electric-resistance heater than to strain an air-source heat pump."

So if you live in an extremely cold climate electric heaters are technically better to use.  Our heat pump has electric heater coils in it as secondaries. 

Also, I think most who consider mining heat as "free" electricity might be using less efficient forms of heating.  I would consider the mining heat supplemental...never free.  Mining costs go down in the winter for sure though...I have been able to turn all my box fans down...now it's to the point where I am only running one fan on low instead of 3 fans on high.  Plus, my natural gas heater in my shop remains off saving me a bit of money each month in heating costs.

True if you only look at your house. however, electric heating is inefficient if you look a the total picture, the losses on conversion and transport of electricity from the plant to your house are substantial. That inefficiency is also part of your bill.

That seems irrelevant.  It's already included in your kwh rate, so why does it matter?  What matters is how much of that kwh, post-meter, is producing heat for your house?

Well I was talking about the point of use conversion.  True efficiency outside the home is difficult to compute.  If you include the transmission energy costs you should also include the extraction, refinement, and transportation costs of fossil fuels.  Likewise any energy needed to produce the materials and equipment used in either process should be used.

Technically hydro-electric power has one of the highest EROEI even when considering tranmission inefficiencies.  Coal is the second highest (in the US) but only because we already have it by "luck".  Once coal is used up (regardless of it is is in a century or in a milenium) it is gone.  It takes billions of years to produce so it gains high EROEI only because we happened to be alive on this planet ~5 billions years after stored sunlight began the slow conversion into hydrocarbons and before humans managed to burn off all the easily extracted stuff (a pretty narrow window in time).

Well cost =/= efficiency.  

You are right from a cost standpoint you are only concerned with the efficiency beyond the point of cost (delivered kWh).

So what we really are saying is given a certain set of costs (at point of delivery) of electricity, natural gas, oil, and a set of technologies heatpump, bitcoin miner, resistence heater, natural gas furnaces what is the cost in heat produced.

If you want exact figures they can be calculated.
  
For resistance heater it is equal to a computer (or other resistance heating) and thus the heat is "free".

For other forms of heating the Bitcoin Miner has a higher cost so the heat isn't "free" but it is discounted significantly.  Anywhere from 20% to 90% depending on the technology and fuel used.

A modern high efficiency Heat Pump would be the least reduced (least close to free).
A old low efficiency propane of fuel oil furances would be the most reduced (closest to free)

On a slightly related note,

Pulling extremely cold air from outside and directing it precisely to the GPUs cooler will allow for extreme overclocks while creting positive pressure that will stop cold air from getting in through cracks elsewhere in the house.

Someone is trying to rip you off. I live in a 1960s house and it cost me NZ$300 to buy a second hand heat pump, which I fitted myself with basic hand tools (A saw blade wrapped in a towel to cut a hole in my cupboard door and floor to vent it outside).

I think we're talking about different things... I don't mean an in-wall heatpump, I mean a heatpump attached to a central air system with vents in each room of the house!  Also, heatpump capable of cooling as well...  I don't currently have any ducting, and it's a 3 bedroom, 1500 sq foot house, and part of it doesn't have any crawl space beneath.  So, bottom line is, it'd be expensive to have a brand new 4-ton heatpump + A/C, ducting throughout all the house with proper insulation, and professional installation of it all.

Yeah Central heatpumps tend to be expensive especially the high SEER (high efficiency) ones.

When we were looking to replace our furnace I looked at some combo-units.  A furnace+heatpump+AC (which is just heatpump in reverse).  The goal being to use cheaper heatpump in mild weather and then supplement that with natural gas furnace when temps get too low.  Pretty sweet rig but the price wasn't viable.  Even cutting heating costs 25% it would have taken 20yrs to pay it off.

Ended up going with a condensing ultra-high efficiency natural gas furnace and 100% efficient ventless gas logs in the living room.  Then the price of natural gas fell off a cliff.  Super woot!!!

If you don't have access to cheap natural gas a geothermal heatpump is another high efficiency option but they aren't cheap either.

I definitely might go the natural gas route when I do end up having funds to upgrade my house.  At least, having the option vs electricity is good.

Yes! This is what I'm banking on.  Right now I have electricity costs for Bitcoin mining and my miners generate heat. This is a constant.  I also have a natural gas forced air furnace.  Because the Bitcoin mining waste heat will reduce my need for natural gas heat I will save money on my gas bill which changes my Bitcoin mining profit equation.

The point isn’t that there aren’t more efficient ways to generate heat.  The point is you have heat that is a free byproduct of an activity you were already engaged in. This free waste heat reduces your need to purchase additional heat at whatever that would cost.  Nobody is suggesting that anyone purchase Bitcoin mining rigs to replace their high efficiency heaters.

99% of all households use any other source than electric power for heating so the whole thing is irrelevant.

If you are mining other than 'just for fun' turn them off already  :)

For the same exact reasons, a CFL light bulb isn't nearly as cost effective as is advertised.  An regular bulb takes about 5 times as much energy to light up a room, but it only costs about a quarter; while a single CFL can cost $6.  And they don't have nearly the longevity that is claimed on the package, either.

^this^

using electricity to heat your home is stupids.

For many parts of the country/world a high efficiency heat pump is far superior to burning natural gas and almost anything is superior to burning heating oil.

Given top heat pumps can achieve 500% efficiency even if you used natural gas in a turbine to make electricity (60% efficient) and then lost another 10% in transmission (0.55% combined).  It is 5*0.55 = 275% or 175% more efficient than a non-existant 100% efficient natural gas furnace.

Still, natural gas is much cheaper in practical use (enduser prices), transmisson losses are usally greater than 10% and heat pumps you can actually buy have less efficiency than 500%.

Still, natural gas is much cheaper in practical use (enduser prices), transmisson losses are usally greater than 10% and heat pumps you can actually buy have less efficiency than 500%.
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Actually no.  In many parts of the US a heat pump IS cheaper than natural gas furnance.  The two conditions are a) cheap winter time electrical rates and b) winters which don't have many days below 10C.   Efficiency falls off a cliff below 10C and below 0C will often require resistance heating. 

Generally areas with very hot summers need a lot of electricity in summer thus they have huge amounts of available capacity in the winter driving down winter rates.  Those areas also tend to have milder winters.  That is perfect combination for heat pumps.

Also if you are stuck on natural gas they do make natural gas powered heat pumps.  Not that common though because until recently natural gas prices were much higher relative to electricity.  With low natural gas likely in the intermediate future natural gas heat pumps may become more common.  Get >100% efficiency AND the lower cost (per unit of energy) of natural gas.

Also BTW:

Average transmission losses in the US are ~7%.
http://www.eia.gov/tools/faqs/faq.cfm?id=105&t=3 

There are 500% efficient heatpumps on the market.
http://www.mitsubishi-aircon.co.uk/default.asp?url=http%3A//www.mitsubishi-aircon.co.uk/mitsubishi_electric.asp%3Fid%3D169931
Well technically this one is "only" 433% (COP of 4.33).

http://www.waterfurnace.com/products.aspx?prd=Envision
(COP of 5.0) 5 watts of heat for every 1 watt of electrical power

Well, those are all 'up to' numbers.  Yes in some cases you are probably better of with a heat pump, but as long as power companies charge over a magnitude more for electrical power as for gas or even oil it is still cheaper to use that.

Well good thing they don't charge a "magnitude more".

1 Therm of natural gas in the US averages $0.85 delivered.
1 Therm = 29.3 kwh

In southern US winter time rates are usually ~$0.08 per kWh.
$0.08 * 29.3 = $2.34 per therm.

A heat pump achieving only a COP of 2.4 is cheaper than 92% efficient natural gas furnace.  Heat pump is simply an AC unit in reverse so buying a high efficiency heat pump has the advantage of getting a high efficiency AC unit for summer time usage in the same unit.  In a place like TX where temps are high and summers long that makes a lot more sense than buying a high efficiency furnace and using natural gas and then needing to either waste electricity in summer or spend even more getting a high efficiency AC unit.

Heating oil?  Are you kidding me.   Heating oil is insanely expensive about $2.60 per therm.

A heatpump with a COP of <1 is cheaper.  However heatpump will never have COP of <1 because worst case scenario it will switch to resistance heating and be 100% efficient.

Well, not everybody is living in the southern US.
Here in central Europe gas comes from russian pipelines and electrical power from monopolized hydropower. I think you'd be able to know what figures this leads to...  :(

Absolutely depends on where you live.

Completely untrue.  Again, it depends where you live.  In my hometown, I'd say the majority of people heat with electricity.  Heatpumps, if their house has been properly retrofitted, but I know one guy who heats with ceiling heat still, and ends up with a bill around $300 during the winter.

Point is, a lot more than just 1% of people use electricity for heating.  It just depends where you live, and how cold it gets during the winter.

Here in Kansas I use natural gas for heating, and my water heater.  I prefer this so that when power goes out during a winter storm, I can still light my fireplace and have hot water to shower with before I go to work (since my work has a generator, I still have to go to work even if we have a city-wide power outage)

That's nice that you have natural gas for a backup and all, but you really don't need to shower every day in the winter, unless you're doing some *serious* physical work indoors...

It's actually not good for your skin, or your Vitamin D absorption.

Really?  Didn't know that... I usually end up with a shower every other day, namely because I only wake up on time that often.  :P  But I would prefer to take one every morning, just for the "wake-up" factor.

I forgot to add "for your hair" as well, though guys usually don't care about that. My hair is 1/4" long, so I obviously don't care much about it. But most women do, so we guys should spread the word to them.

Soap and hot water every day is the fastest way to dry out your skin (and hair) in the winter. And our bodies produce Vitamin D by being in the sun -- but here's the catch: you have to wait 48 hours after being in the sun for most of it to be absorbed by the body. So daily showers wipe out the lion's share of it. Vitamin D does more things than I can count, including keeping your immune system in top condition (one of the reasons more people get sick in the winter -- most people don't go outside as much, plus there isn't as much sunlight, and people are more covered up)

I agree, one always feels clean & relaxed (and awake) after a shower -- but it's good to weigh the two and strike a balance.

I think it's only America that is fanatic about once-a-day showers -- most other countries have a long tradition (of common sense?) that doesn't dictate such.
(FYI, I'm an American living in America)

Ah, yeah, I have heard the "bad for your hair" part.  Didn't know the bit about vitamin D though, thanks for sharing.  I haven't been sick for 3 or 4 years now though, which is nice.  Guess I'm getting enough D then?  :P  I own a convertible, and put the top down even in 30 degree weather though, so maybe I'm just a bit on the odd side...

Consider both mini split systems (which have install cost) as well as window heat pumps which do not if you can put them in the window/wall yourself. 

http://www.ebay.com/itm/LG-LW1210HR-12-000-BTU-Window-Air-Conditioner-heat-/160558003778?pt=Air_Conditioner&hash=item256200b642

I am not recommending this specific unit, but this gives you an idea of what is out there.  I have an 18000 BTU heating/cooling one.  These can pay off vs electric heating in less then one heating season because they are 2-4x more efficient then resistance heat. 

This post only applies to those with a card or three.  It's 26 degrees (F) outside currently and the air exiting my "mining room" is a nice 72 degrees.

Not everyone has *your* climate.  :)   It takes a *LOT* to keep a house heated here in the winter.  With my mining rigs going, I haven't had to touch the furnace.

Could someone please explain to me how somthing can be more than 100% efficient without allowing people to use its output to power the device for free?

uh yeah people have seem to forgotten the law of conservation of energy..

YOu are harvesting heat stored outside or in the ground (geothermal). If it helps you understand, imagine living in iceland next to a hot water well and pumping that water through your house. You would use a few 100W in electricity to pump the water but you would obtain a 1000x more in heat.  Doesnt violate any thermodynamic laws.  You just need a source of heat, and with a heat pump, even fairly cold outside air or water can be used as a source of "heat". All you have to do is cool your inside air to a point well below that of your heat source (by compressing it), then heating it up, and decompress it. IOW, all you need is a temperature difference.


Oh and yes, you could use that to generate electricity too, if the temperature difference is big enough. Its already done:
http://en.wikipedia.org/wiki/Geothermal_electricity

But if you can use room temperature to make the air hotter, why can't you use that generated hot air to power your air heating device?

Thats more or less what these devices do. But since it costs energy to compress and decompress, the energy is not free. But you can get > "100%" efficiency if you measure efficiency as electricity you spend for heat inside your house. You will be cooling the outside world a bit though (or warming it if you are trying to cool your house).

If you meant why these systems cant work autonomously; in order to produce electricity you have to make water boil. to achieve that kind of concentration of heat and achieve a positive energy return, you need large and expensive devices and large enough temperature difference. Like those geothermal generators linked above; they exist and they do produce electricity, its not impossible, but its not really something thats economically feasible in a house :)

A heat pump doesn't CREATE heat.  If it did it could never have more than 100% efficiency.  A heat pump MOVES heat.  There is significant heat outside the home.  Even in 0C air there is thermal energy.  The only temp that has no thermal energy is absolute zero.

If a heat pump burned fuel or turned electricity into heat via resistance its max efficiency would be 100%.  You can't get more heat/energy than what existed in the fuel/electricity to begin with.

However as a pump it can pump in huge amounts of outside energy for a small amount of energy and thus achieve >100% efficiency.

The theoretical max efficiency for a heat pump varies by the difference is desired source (outside) & sink (inside) temperatures.  For 10C outside and 35C inside is ~1200%.  The highest efficiency units available for purchase are ~500%.

As energy becomes more scarce/expensive expect heat pumps to replace furnaces.  With technology we potentially could have 600%, 750%, 800% efficiency heat pumps someday.  A furnace simply can never be more than 100% efficient (due to law of conservation of energy).

As for why couldn't you use that energy to power the device.  the thermal energy in your house is not very concentrated.  The less concentrated an energy form is the more difficult it is to convert into another form.  For example a thermalcouple can directly convert heat into electricity but it is usually less than 1% efficient.  For 100 units of heat energy = 1 unit of electrical energy.

BTW:
Air conditioners, refrigerators, freezers are all heat pumps they are simply one way heat pumps.  A residential "heat pump" can pump heat into or out of the house.



Some people don't understand the law of conservation of energy.

If you have 100 units of energy outside the home and 10 units inside and I move 20 of those units inside via a "pump" (a energy/heat pump) then the end state is 90 units of energy outside and 20 inside.  No energy was created or destroyed.  Energy was simply moved.

Converting heat into electricity is difficult and inefficient.  There are a couple different methods but generally efficiency INCREASES when the difference in temps between input and output is very large.

This is why for example we super heat steam by heating it, putting it under pressure, and heating it more.  The higher the input temp and the lower the output temp the more energy which can be converted into electricity. 

The heat in your house while it may feel warm is very very very low.  It is cooler than the exhaust of a car for example.  With low input temp and only slightly lower output temp you wouldn't get much efficiency (maybe 1% or less).

Concentrating heat would require more energy and thus a heat pump can never be a perpetual motion machine.  You could however use a heat pump as a "battery".

Take a storage area that hold temps well (say crushed granite) and surround it with an insulator.  When you have electricity to store use heat pump to pump heat (form atmosphere) into your "heat battery.  When you need electricity allow that heat to flow out of the "heat battery" into a turbine to produce electricity.

If you can get the round trip efficiency of electricity -> stored heat -> turbine -> electricity close to 100% then you have a battery.  The problems are
1) some heat will be lost.  better cheaper insulation will help
2) turbines are at best 60% efficient that can be compensated by a heat pump which is 500%+ efficient
3) turbines are most efficient when input temp is VERY HIGH so you would need a specialize heat pump designed to concentrate a lot of thermal energy into the granite.

I see, people say it's over 100% efficient because the device isn't working alone, the Sun or the Earth's molten core (or some other factor that is already there anyway and doesn't need humans to keep it going) is also participating in the process.


That's like saying a fan pointed at a wind turbine in a windy day is more than 100% efficient, right?

Yes.


No.  That is a bad example.  Neither the fan nor the turbine are >100%.  Neither are 100% either.

No, not really, no.

By nature, the wind would blow into the turbine whether you had a fan pointed at it or not.
By nature, the heat would stay outside of your house unless you used a heat pump to get it inside your house.

what about this point.

It does not matter about the efficiency of the miner rig producing heat.  If the bitcoins are sold to pay for the electric, then the electric is free, hence the heat is free. period.

Just so long as you generate enough bitcoins to cover the cost of the heat.  With the recent difficulty drop, and price hovering around $3.00/coin, I'm finally back in the black.  So free electricity + some more!

The question remains? Damnit guys, don't you learn physics at school??? Like, that energy DO NOT disappear? If something use 1kw guess what, it will spit out 1kw of heat, be it a computer or a heater.

Well that statement is equally wrong.  An electric car (or any other non-resistance load that does actual work) that pulls 1kW won't generate 1kW of heat.

It always ends up as heat, no matter how you complicate the route it always becomes heat in the end. If you keep running circles in a closed (and insulated) room with that electric car the room will warm up, no doubt about it.

1kw of "work" I think is what he meant. If heat is the "work" you are trying to achieve then you will get 100% eventually, as long as no chemical reactions take place to absorb heat. Movement->friction->heat. Even the sound from the fans becomes heat eventually.

It is just a matter of directing the heat to where you want it, and making sure that it is contained as desired.

You're wrong.  Movement has friction (even if it is just friction between air molecules), and 100% of it is turned into heat as soon as movement has ceased.

When you stop your car, tons of heat builds up in your brake rotors, because all of the energy that your car was moving with is turned into heat via friction.

I'd take this a step further.  Bitcoin mining is something I am doing anyway.  The heat is a byproduct.  The fact that I can use this byproduct to reduce (or eliminate) my heating costs is where the "free heat" comes into play.  It does not matter that the bitcoin miners cost money to run as long as the heat is a unintended byproduct it is "free".

I think the problem some people are having with the 100% efficiency thing is they are comparing the efficiency to the conversion factor.  That is not what the 100% is being compared to.  It's being compared to other heat generating activities.

What is the baseline comparison that is factored at 100%?  Then whatever you are using to provide the heat if requires less energy to produce X amount of heat than the baseline, it's > 100% efficient.  If it uses more energy to produce X amount of heat, it's less than 100% efficient.

The baseline for any electricity-based device is what using that amount of electricity would generate in heat, if it were sealed in a closed container.  For example, a 1000w air conditioner "creates" cool air for the indoors, but at the same time, creates the same amount of heat + 1000w outdoors.  The net effect, if you sealed the whole air conditioner unit in a box, is that it would be creating 1000w.  The air conditioner would be 100% efficient at creating heat.  In fact, if sealed in a box, ANY electrical device would be 100% efficient at generating heat equal to its wattage.

Regarding fuel sources, like natural gas and heating oil, efficiency depends on percentage of the fuel burned.  If you burn 70% of the fuel, and the other 30% is wasted through exhaust as unburnt fuel, then the device is 70% efficient.  I don't believe there would be a way to make a natural gas or heating oil device more than 100% efficient.

That's why automobiles are now fitted with EGR valves - it actually recycles some of the exhaust gases in an effort to burn even more of the fuel that may have been left unburnt during the previous burn cycle.  A typical modern internal combustion engine is around 30% efficient at moving the vehicle - the rest of the energy from burning gasoline is wasted as heat, with a tiny percentage wasted as unburnt fuel.

It isn't just unburnt yet.  Even if you burn natural gas completely some of that heat will escape outside the building (via combusiton vent) and that means efficiency will be <100% although they are getting close.  It is possible to buy 96% efficient furnances today.

As far as >100% efficience.  Through combustion (furnace) you are right it can never be >100% however there are natural gas heat pumps which can achieve a COP of >1.  Yes that means it is alos possible to cool a house with natural gas.

http://www.energysavers.gov/your_home/space_heating_cooling/index.cfm/mytopic=12680

Well, yeah, that's true.  Always going to have some heat loss through the exhaust, since you can't vent the burnt natural gas air directly into your home.  :P

Whoa, didn't know they even made natural gas heat pumps!  That's pretty neat...

Well you can have 100% efficiency however you need to just vent it into the living space to ensure no heat escapes.

Like this:
Gas logs are just fancy gas burners (like on a stovetop).
http://www.fastfireplaces.com/media/catalog/product/cache/1/image/306x306/5e06319eda06f020e43594a9c230972d/v/f/vfd-32-fb0f.jpg

Here is a less fancy version which does the same thing:
http://www.amazon.com/gp/product/B000KKO4WA/ref=pd_lpo_k2_dp_sr_2?pf_rd_p=486539851&pf_rd_s=lpo-top-stripe-1&pf_rd_t=201&pf_rd_i=B000J011N6&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=0DK64RJY3X5SBS3T7KCG

They never really caught on and since less are made tend to be more expensive.  They also are noisier than electric heat pumps.  The fact that natural gas is so cheap is increasing interest in them again.  Anything that uses a compressor can be made to run on natural gas (or any fuel source).

You can't vent natural gas fumes directly into a living space... and that's not what that gas log burner does.

EDIT:  That open gas burner still vents into a chimney or pipe.  You'll kill yourself from carbon monoxide (or carbon dioxide?) poisoning if you don't vent it at all.

Yes you can. Google "ventfree gas logs" or "natural gas IR heater".

I didn't mean an natural gas IR  eater works exactly the same. I mean it is also 100% efficient and can be used to heat a home without venting heat outside.  A 30KW ventfree gas log and a 30KW natural gas IR heater will both put 30KW of thermal energy into the room at 100% efficiency.  Gas logs look nicer but are more expensive.

I have been using ventfree gas logs for 10 years now.  Natural gas when burnt completely produces only CO2 and water vapor.  I would recommend a CO dectector but I would also recommend that for any gas appliance.  It also may be against building code in some parts of the country which don't understand science.


No it doesn't.  There is no vent in that firebox.  CO is dangerous which is why you should have a CO detector.  Vent free log will only produce CO if it doesn't have sufficient oxygen (incomplete burning) but then again so will your natural gas stove or oven.  Gas logs have a ODS (oxygen depletion sensor) which should cutoff when oxygen level drops.  Always good to have them checked and cleaned (just like a furnace).   
Here is a link:
http://www.fastfireplaces.com/empire-breckenridge-deluxe-vent-free-firebox.html

I stand corrected again.  Maybe I'll just shut up now...  :P

Again, this is why there is some confusion.  You're making a disparate comparison between a device using X amount of electricity and generating X amount of heat and a device using X amount of electricity and outputting X amount of heat.  The device is still =< 100% efficient by your definition (and can never be more than 100%).  If you are comparing the amount of heat output (X) for the amount of electricity consumed (Y), then you can achieve more than 100% efficiency.  I'm not saying your basic premise is wrong in any way, I'm just trying to clear up the confusion (but perhaps now I'm adding to it).  

The output of a device can be > 1:1 efficiency when compared to another device, but the consumption to generated ratio can never be greater than 1:1 for electricity used vs heat generated.*


* Unless we are talking about cold fusion or something exotic.

That is true but heat pumps work by generating heat they achieve efficiency by moving heat from outside to inside or in reverse.

So yes a heatpump w/ 1 KW load running for an hour will convert 1kWh of electricity into heat @ 100% efficiency but that isn't really material to practical use of the heat pump.  In operating a heat pump w/ COP of 5 would add 5 kWh of heat to the air inside the home (by removing 4 kWh* of heat from the air outside) at a cost of 1 kWh of electrical power.

Yes it is impossible to generate 5kWh of heat from 1kWh of electricity (law of conservation of energy) however it is possible to move 5kWh of heat from one place to another.  The person heating their home doesn't really care if the heat they feel is heat moved from the outside or heat converted from electricity.    The net result is still 5 units of heat from 1 unit of electricity.





* Why 4KWh?  Law of conservation of energy.  The heatpump "used" 1 kWh of electricity thus it must have converted that to another form of energy, heat. Net-net if the thermal energy inside the house rises 5kWh then the thermal energy outside the house must have declined 5kWh but the unit dumps its waste heat outside so +1 -5 = net 4kWh being removed from the outside air.

Yeah, this is a better way of putting it - generation vs output.

my mistake :)

In the end, yes it will.

Go study physic

Yes it will, just not in any place or form that is usable.  In the case of the electric car, heat will be produced in the batteries, wiring, motor and braking system.

Come on guys it is called law of conservation of energy not the law of everything become heat.

Take an electric car drive it up a hill.  It now has potential energy, all of it's energy didn't become heat.

If car has potential energy it by definition can't have converted all of its energy into heat otherwise you just created energy from nothing.
1kWh electrical potential -> 0kWh electrical potential + 1kWh heat + xx kWh potential energy (did we magically create energy from nothing)??

vs

1kWh electrical potential -> 0kWh electrical potential + <1kWh heat + <1kWh potential energy

Vent free used to be illegal in Baltimore but just in the past few years code was changed (harmonized?) to a more national standard and they are now allowed.  Vent free is in most places 5x cheaper then heating with resistance electric heat due to the low cost of natural gas and the near 100% efficiency.  Vent free does have other drawbacks besides the CO2 risk, it puts a lot of humidity in the air, actually enough to do damage to items in the long term.

I have a vent free gas heater in a bathroom, which would be humid anyhow. 

Don't forget the wheels, all that weight deforming them as they roll definetly make lots of heat (and of course even if the wheels were rock solid they would still be moving against the ground)


edit: and of course, unless the room is completly evacuated there is also air friction.

This is where the old maxium "what goes up (the hill) must come down again" applies.  Eventually, it will be heat, even if that car sits at the top of that hill until the heat death of the universe.  Probably.

Moonshadow is right, when you bring a weight to the top of the hill or pump air into a can, you're creating the potential for movement. You're essentially creating potential energy that once released will produce heat+movement. After each fall, you will have less useful kinetic energy to bring it back up to same height.

Not to mention the heat generated to get it there in the first place.

Seriously. I was sweating my balls of by the time I got that weight up there.

i wasnt thinking outside the box..i thought someone meant how a simply heating coil could magically be a better convertor of electrical energy into heat energy compared to a gpu..damn studying medicine has sucked the physics out of meehh..cant believe i got a 97% in my alevel physics :(

I have a bucket that weighs 0.2 kg and contains 1 kg of boiling water. The thermal energy of the water in my bucket is mass * heat capacity of water * temperature in Kelvin = 1 kg * 4.2159 J/g/K * 373.15 K = 1.573 MJ (http://www.wolframalpha.com/input/?i=1+kg+*+4.2159+J%2Fg%2FK+*+373.15+K&a=*C.g-_*Unit.dflt-&a=UnitClash_*g.*Grams.dflt--&a=UnitClash_*J%2Fg%2FK.*JoulesPerGramKelvin--&a=UnitClash_*K.*Kelvins.dflt--). Now I lift this bucket with boiling water 1 meter straight up, the labour I need to do this is mass * gravitational field strength * distance = 1.2 kg * 9.81 N/kg * 1 m = 11.8 J (http://www.wolframalpha.com/input/?i=1.2+kg+*+9.81+N%2Fkg+*+1+m). I moved 13330000% more energy than I used energy to move it, but I did not create any energy.

This example demonstrates the difference between moving energy and using energy. This example is not a heat pump though, since there is no transfer of thermal energy between masses, the mass itself is moved instead. The "efficiency" of a heat pump is expressed in how much energy it moves between masses compared to how much energy it uses to do so. Note that using energy just means transforming energy from one form (e.g. electricity) to another (e.g. heat), not making energy disappear.

My own house is not heated by heat pumps but by a central heating system, where various gas burners at the top floor of the flat heat water and pump it through mostly unisolated metal tubes to radiators inside the apartments. I cannot answer whether I have "free electricity" in winter, because while gas is cheaper than electricity in my country, I don't know how efficient the central heating system is (definitely lower than 100% when counting only the heat that ends up in my home) nor what gas-price the landlord charges me per kWh of heat brought to my home. There is no singular answer to the "free electricity"-question because it depends on the specific prices and efficiencies of the various heating systems available in a region. Comparing the price-ratio and efficiency-ratio between GPU-heating and other heating, will determine whether you save or spend more money when mining compared to other heating. Even when spending more, since you also get Bitcoin rewards, you may still come out with profit.

A very popular solution to heating here is ground heat and it is very energy efficient. Drill a hole about 100m down or so and pump around water in it when the water comes up it is about 4-5C and you can extract one degree each time in a heat pump to heat a hot water tank and pump it around your house. Is very efficient.

However at least in my parents house there is a backup electrical heating of the water that usually kicks in when the outdoor temperature goes below -15C or so for long periods. So I guess there are still a couple of days in winter where mining would not be a complete waste with such a setup :)

My heat however comes from garbage incendiaries and is included in the rent and so is the electricity so that makes calculation very easy for me :)

What?  Really?  Do you have a source for this?

Where I live, we call that "summer".  :D

Winter temperatures rarely go over -10C.

Just pointing out, EGR valves primary purpose is not an effort to use unburnt fuel in the exhaust, although that is a desirable effect as well.

Their purpose is so that under light load conditions (crusing along at highway speeds, going downhill, etc..) the engine can use less fuel to maintain your momentum. The exhaust gas contains very little useable oxygen, so that instead of filling the cylinders with a full charge of fresh highly oxygenated air and the matching amount of fuel, you can instead partially fill the cylinder with fresh air, and partially with exhaust gas, thereby requiring less fuel to achieve a proper mixture. Engine continues turning at the same speed, still produces enough power as required at that time, and saves fuel.

EGR was strictly introduced to improve fuel economy.

Edit to add, recent engine designs with variable valve timing which allows control of intake and exhaust timing independently no longer have EGR valves. They simply use the valve timing to close the exhaust valve sooner and delay opening of the intake valve. This actually traps some exhaust gas in the cylinder between cycles. Still works like EGR, but instead of an external bypass it does it all with cam timing. Reverse this, and hold the exhaust valve open longer and open the intake sooner, introduces a concept called "scavenging" whereby the flow of exhaust out of the cylinder helps to draw in fresh air more efficiently, and they can achieve much closer to perfect volumetric efficiency. This would be the performance side of the VVT system vs the economy side which replaced those EGR valves.