Brett,
I found the fossil fuel reserves equally fascinating. I could never comprehend that much organic matter could exist in one place. That is until I learned on a Nova show that bacteria that we now know causes organic matter to decay, did not exist for 100s of million of years. So all organic matter, from plants and living organisms, just lay there, until earth gobbled it up. There may be other factors, but since I learned this, it makes sense to me.
I was going to post about universe but capitulated. Anyhow, your write up is much better.
Imran
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On May 23, 2020, at 11:41 AM, Brett Wissel <Brettwissel@...> wrote: ? Electric motors (like pumps) only draw the energy from the power source according?to the amount of WORK being done. A motor idling will only draw the energy from the source through mechanical losses (friction, transmission inductance losses) and when it encounters resistance will draw more energy to meet the work required of it. E.g. a 1kW motor may idle full speed at .2A, encounter?a normal load at 10A, and be forced into temporary overloads at 20A.? If one cuts the wood, after the cut the amps return?to the lower idle rate. It's not sitting there burning 1kWh of work constantly.
A pump "deadheading" with no water flowing at maximum pressure build is essentially doing no work and as such is a much lower power draw compared to a pump running at maximum volume flow rate and low pressure. Throttling?a pump by increasing head pressure will actually lower the amps in use as the pump is doing less work. A dust collector will pull more amps with a clean filter and fully open duct system than it will with all ports but 1 closed, despite the perceived velocity and pressure changes at that one open port.
Enthalpy, Entropy, and the 0th, 1st, 2nd, and 3rd laws of thermodynamics can be counterintuitive, but essentially the entire universe is on the way to converting energy in whatever form now into.....sadly, waste heat that won't return to a higher form until the next big bang forces conversion.?
What's really trippy is thinking the waste heat you generated today was the conversion of mechanical energy from the chemical bonds in the wood from the suns photosynthesis of radiant energy transmitted from solar nuclear fusion. The path of electricity down the wires to run the saw is much less fascinating in my opinion, but still ultimately points to energy conversion from nuclear fusion in the sun.
What's this about dust collecter?closets we were discussing, Joe? hahaha! On Sat, May 23, 2020 at 10:17 AM TJ Cornish < tj@...> wrote:
Brian, yes, all electrical input is converted to heat. The force to cut something turns into heat eventually as well. The power is not all consumed by the motor, but all of that work ultimately ends up as heat. Have you ever stuck your
hand in a bucket of just cut sawdust? It¡¯s hot. How about hand sanded something with a piece of sandpaper? It¡¯s hot. Work ends up as heat. A 3KW table saw produces exactly as much heat as a 3KW electric heater (assuming they¡¯re on for the same amount of time
¨C again, see the difference between KW and KWH). The only difference is with a saw you get a board cut in the process of making heat, while the heater takes a shorter path to making heat.
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Another obvious example is drilling a hole in metal with a drill press. The chips come of hot ¨C really hot. Hot enough to change the temper of the metal (chips turning straw colored or blue). That energy to tear and deform the metal turns
into heat. It¡¯s not all friction ¨C deforming a material takes work, too.
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Unless you¡¯re storing the energy somewhere ¨C in a battery, in a flywheel, in lifting something, that energy ends up as heat. That stored energy changes to heat too ¨C just maybe not right away.
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No, not all energy to do the work is converted to heat. For example, your saw idles at say 1hp, a heavy cut is consuming 3hp, that¡¯s a 2hp or 1500W increase. Picture a 1500W heater, which efficiently converts all it¡¯s watts to heat, do
you really think you pumped out 1500W of heat into the shop taking a cut with the saw? No, you might have gotten 100W of heat in the cut, but everything else was consumed doing the actual work.
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That is where I started. At least 80% of the energy is consumed in doing work otherwise it is a pretty inefficient setup. But these guys have convinced me that the energy used to do the work is also released as thermal energy in the environment.
I have never thought of this before. It makes sense to me.
On May 23, 2020, at 10:36 AM, Brian Lamb <blamb11@...> wrote:
?You all are missing the point that a lot of the hp/watts is actually consumed doing the ¡°work¡±, whether it¡¯s sawing the wood, jointing, planing, sanding, lighting or even compressing air. It takes force to do most of these things (not
lighting of course), and the force of the blade cutting through the wood is a large percentage of the watts consumed. Yes, there is always a heat load, but it¡¯s not anywhere close to 100% of consumed power¡. even here in AZ where it will be 111? later this
week.
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I think perhaps the issue then is the usual workload of a typical shop. Although in an it system things are, I imagine, a bit more stable in terms of draw and power use, that is not the
case for most shops not in a factory environment. We tend to turn on and off equipment and not be steadily throwing plank after plank in rapid succession thorough a saw at max force leading to an actual nameplate type draw. Whereas computer fans are typically
more blunt force objects running at max 100% of the time to account for a potentially catastrophic consequence of failing to control heat in a limited space and the consequences of those failures. And so, I may allow for a total heat release into your shop
for the sake of argument, but even then, the draw is variable and subsequently the heat release. If the OP is concerned about utilizing a motor and dealing with the heat for 100% utilization, he is probably 1) not using the right equipment as Felder doesn¡¯t
spec the duty as 100%, and 2) in the wrong forum and needs to be talking to factory owners.
But in more real world situations, we don¡¯t use 100% draw even when we are using machines most of the time, turn them off between runs, have leaks under a doors, windows to radiate out,
poor insulation to not contain heat or cold, and a myriad of other issues. Sure, running motors will increase heat but it¡¯s not a 1:1 in any of our shops, and especially not at nameplate levels.
I think you just said mostly what I did ¨C that the energy turns into heat, just not entirely in the motor itself.?
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8KW of electricity into a room turns into 27,000 of BTU in that room, either directly or indirectly, unless that motor is driving a shaft through a wall where some of that energy is converted into heat somewhere else. That 8KW of heat may
not stay in the room due to diffusion through the room walls and ceiling, but it¡¯s put into the room, no if¡¯s, and¡¯s, or but¡¯s, just as if you had an 8KW electric resistance heater.
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Energy is not returned to the environment on the return leg ¨C the neutral wire in a single phase 120v world, or the other hot legs in a 240v or 3-phase world. If the energy is not needed for work output or system inefficiency losses it
is not drawn in the first place; e.g. a 5HP/3KW motor has a free-running power consumption value of maybe 1KW, and that power consumption increases when the motor is asked to do work. Only when the motor is fully loaded does it draw 3KW of power. Yes there
is voltage drop on the electrical service wiring and yes there is heat generated from that lost energy, but that¡¯s a different problem in a different room. Power distribution is sized to deliver nominal voltage at the end point, factoring in losses in distribution.
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RE designing HVAC based on electrical load ¨C yes, this is exactly how it¡¯s done. My day job is in IT, part of which includes managing a datacenter and it¡¯s power and cooling. Cooling load is absolutely sized based on power draw of computing
equipment as well as the expected environmental factors. ??
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Small spaces like workshops ¨C small closed systems ¨C will show the temperature rise of power consumption more quickly than a larger system which has a lot more thermal sinking capability.
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I agree it¡¯s complicated, and I¡¯m glad nothing is simple on the Felder forum, which I¡¯m new to. There are few things in life that can truly be expressed simply.? Learning stuff ¨C the reason I joined the group ¨C happens when the complexity
is welcomed.??
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No. While you may be correct that the differences between potential energy and kinetic reach equilibrium through heat transfer, it¡¯s not so clear cut as the statement that an 8kw input to a motor yields 8kw of heat within a workshop. Within
systems there are many components, heat sinks, and losses. So for example, the spinning motor creates heat in bearings through friction, the blade creates heat through friction in the wood and drag through air, some energy is passed through entirely in the
electrical supply and leaves the system and recovers its potential in a ground, some energy is absorbed through wood fibers/saw dust and heat sinked. Heat is lost through inefficient insulation, air drafts, radiation through windows etc. Some energy is released
slowly and muddies the results like the specific heat of cast iron and sawdust. All causes, yes, 8kw input leads to 8kw of heat. But the closed system needs to be very large which simply is out of line with a real world workshop. I don¡¯t know much about sizing
hvac but I don¡¯t think this is the way to do it.
Nothing is simple on a Felder forum :) And I¡¯m waiting for my finish to dry.
All forms of energy ultimately end in heat, so yes, 8KW of energy coming in results in 8KW of heat in your shop.
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A 3KW 5HP motor produces 3KW worth of heat ¨C electrical resistance heat in the power cord and motor windings, sliding friction heat in the bearings and air friction in parts rotating in air. Even the work output of the motor ¨C the cutting,
sanding, blowing, etc., ultimately ends up as heat ¨C if you stick your hand in a pile of just cut sawdust, it will be quite warm from the cutting tool friction and the forced deformation of the wood.
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It is accurate to say that a 3KW motor itself doesn¡¯t itself give off 10,000 BTU of heat, but if you factor all of the losses in the system and especially the work output into whatever the motor is doing, you end up with 10,000 BTU of heat
in your room as a result of the motor running. It¡¯s counter-intuitive, but it¡¯s true.
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I am not an expert but I am pretty sure this is not correct.
¡°?That's about 8KW of electric coming in that all turns to heat, either motor heat, or friction heat from cutting etc.¡±
Only a small portion of power being consumed is generating heat.
?Mark, I understand the thermal mass.? I often run the saw or shaper for an hour or two straight.? Sucking 110F air into my shop would definitely be a problem.? When running I have a 5HP dust collector and a 5HP saw, shaper, or sander running.
That's about 8KW of electric coming in that all turns to heat, either motor heat, or friction heat from cutting etc.? My lighting is another 2.3kw.? 1kw of electric is 3412btu so 10kw of electric in is about 34K btu.? Over 3 tons of AC.? If I ran machines
all the time and wanted to keep it cool when it's over 110F I would have had to have 10 tons of AC per the mechanical engineer.? That's without dumping exhaust outside.? Now if I were heating the machine heat would work for me and not against me.
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-- Brett Wissel Saint Louis Restoration 1831 S Kingshighway Blvd (at Shaw Blvd) St Louis, MO 63110 314.772.2167 brett@...
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imran