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Author Topic: The myth about "free electricity" in winter  (Read 8340 times)
jetmine
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October 25, 2011, 05:20:56 PM
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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.
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October 25, 2011, 05:29:42 PM
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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.

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October 25, 2011, 05:30:09 PM
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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.

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October 25, 2011, 05:58:39 PM
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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.
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October 25, 2011, 06:26:06 PM
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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...
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October 25, 2011, 06:47:41 PM
 #6

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.

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.
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October 25, 2011, 06:58:08 PM
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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.
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October 25, 2011, 07:25:44 PM
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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. 

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.

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October 25, 2011, 07:28:52 PM
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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. 

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?
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October 25, 2011, 07:39:56 PM
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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.

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.

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).
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October 25, 2011, 07:46:59 PM
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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 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)
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October 25, 2011, 08:32:15 PM
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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.
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October 25, 2011, 10:43:35 PM
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  I own a 1950's home, and it would cost somewhere in the neighborhood of $7000 to retrofit with a heatpump,

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).
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October 25, 2011, 10:52:41 PM
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  I own a 1950's home, and it would cost somewhere in the neighborhood of $7000 to retrofit with a heatpump,

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.
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October 25, 2011, 10:57:27 PM
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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.
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October 25, 2011, 11:09:00 PM
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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.
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October 26, 2011, 04:39:09 AM
 #17

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.

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.

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.
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October 26, 2011, 04:48:03 AM
 #18

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  Smiley

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October 26, 2011, 05:20:38 AM
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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.

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.

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October 26, 2011, 10:25:50 AM
 #20

while most people get much better heat efficiency by using gas or oil for heat.

^this^

using electricity to heat your home is stupids.

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