Author Topic: A very silly question about heating water  (Read 6169 times)

0 Members and 1 Guest are viewing this topic.

BulletMagnet83

  • Guest
A very silly question about heating water
« on: May 17, 2015, 02:44:18 pm »
Hey guys,

A good friend has reached out to me about this. Please bear with me, I swear it's not a troll question, I just want to report back with community expertise so I can save his boss from himself.

His boss wants to get into the carwash business, and is intent on devising a more efficient method of heating water. He would like to use an electric motor (I do not know which type) to act as the heating element, running it with it's cooling fins mechanically removed...

I am well aware of how this sounds, and Dave - I'm sorry :C but this is probably the only way I can make him see sense as I've already tried to explain why this is a terrible idea. If 5 to 10 very knowledgeable members can shoot this idea down and kill it then I'm happy for the thread to be closed. Just give me something I can link my friend to to show his boss why this is an awful idea so he'll do what I tell him :C

If it helps, consider it "peer review"... go nuts. Shoot it down.

EDIT:

To clarify, said friend has only just learned the difference between volts and amps, and is currently studying what is roughly equivalent to a BTEC level 2, and is being forced to research stuff by a boss who from what I can understand, doesn't know his arse from his anode.

He's based in Portugal, so the language barrier in explaining WHY this is a terrible idea is possibly being a problem.
« Last Edit: May 17, 2015, 02:51:53 pm by BulletMagnet83 »
 

Offline tautech

  • Super Contributor
  • ***
  • Posts: 12989
  • Country: nz
  • NZ Siglent Distributor
    • Taupaki Technologies Ltd.
Re: A very silly question about heating water
« Reply #1 on: May 17, 2015, 02:54:12 pm »
Now IF one of the motors in the carwash runs quite warm, you could conceivably water cool it and REDUCE total water heating costs.
But will the outlay be recovered with lower heating costs?  :-//
Avid Rabid Hobbyist
 

BulletMagnet83

  • Guest
Re: A very silly question about heating water
« Reply #2 on: May 17, 2015, 02:56:54 pm »
Tautech, this is exactly where I was going! My suggestion was to use an off-the-shelf system, but my friend is dealing with a boss who wants to design a bespoke system and won't be told. He's a good person but lacking in technical expertise.
 

Offline tautech

  • Super Contributor
  • ***
  • Posts: 12989
  • Country: nz
  • NZ Siglent Distributor
    • Taupaki Technologies Ltd.
Re: A very silly question about heating water
« Reply #3 on: May 17, 2015, 03:00:33 pm »
A much better option would be solar.
Avid Rabid Hobbyist
 

Offline Rick Law

  • Super Contributor
  • ***
  • Posts: 2436
  • Country: us
Re: A very silly question about heating water
« Reply #4 on: May 17, 2015, 03:03:00 pm »
Hey guys,

A good friend has reached out to me about this. Please bear with me, I swear it's not a troll question, I just want to report back with community expertise so I can save his boss from himself.

His boss wants to get into the carwash business, and is intent on devising a more efficient method of heating water. He would like to use an electric motor (I do not know which type) to act as the heating element, running it with it's cooling fins mechanically removed...

I am well aware of how this sounds, and Dave - I'm sorry :C but this is probably the only way I can make him see sense as I've already tried to explain why this is a terrible idea. If 5 to 10 very knowledgeable members can shoot this idea down and kill it then I'm happy for the thread to be closed. Just give me something I can link my friend to to show his boss why this is an awful idea so he'll do what I tell him :C

If it helps, consider it "peer review"... go nuts. Shoot it down.

This is nutty.

If he is using a motor coil as heat element - ie, using it as a heating coil, why not just get a heat element directly.

Law of Thermodynamic - all your lost in efficiency is in the form of entropy dissipated as heat.  In this case, you have darn near 100% efficiency because all you want is heat.  (Assuming the whole contraption is submerged which means the water get to capture all its heat.)

Then the question is, where do you want the heat?  A motor coil will likely keep more heat inside the coil than a water heater element which is designed to spread the heat in the water.  So, a motor coil can perhaps keep enough heat within it to melt something it should not (which would not be very nice), whereas a heat element is designed to spread the heat.

Now, if he really wants efficiency, why not solar pre-heat the water (like running it through a "shallow pool" with black paint on bottom and plexi-glass on top), and/oruse a heat-exchange mechanism to recapture the heat of the used water?
« Last Edit: May 17, 2015, 03:07:57 pm by Rick Law »
 

BulletMagnet83

  • Guest
Re: A very silly question about heating water
« Reply #5 on: May 17, 2015, 03:06:09 pm »
Rick Law,

Thank you :D It's mad, I know... please keep it coming :3 I just want some backup so my friend can talk to his boss and put this idea to bed before he kills innocent motors trying to make it work.
 

Offline CatalinaWOW

  • Super Contributor
  • ***
  • Posts: 2713
  • Country: us
Re: A very silly question about heating water
« Reply #6 on: May 17, 2015, 03:12:53 pm »
Heating water is one of the few viable uses for low content "waste" heat.  Electric motors are at best around 90% efficient, so the remaining 10% could in principal be used to heat water (as opposed to the air which usually gets rid of this waste heat).

The idea falls apart in several places.  Most importantly, it is unlikely that his car wash has enough motors to supply the necessary heat.  As stated already it makes no sense to use a motor only as a heater, it just isn't any more efficient for that than a resistance wire.  Roughly a dozen 1 horsepower motors to get a kilowatt of waste heat.  Even if there are enough motors the plumbing and extra difficulty in maintenance will far outweigh the energy costs saved.  You might be able to get some green publicity credit, but no way there will be actual financial benefit.
 

Offline Rick Law

  • Super Contributor
  • ***
  • Posts: 2436
  • Country: us
Re: A very silly question about heating water
« Reply #7 on: May 17, 2015, 03:20:50 pm »
By the way, he should think about using natural gas heat - unless you want to pay big bucks whenever the sun is not out.

Cost-effectiveness (BTU/dollar) of natural gas heating is many fold that of electrical heat.  It will however depend on state and federal regulation of today and for your locale.  So he needs to look into how his state is in term of fossil fuel friendliness.
 

Offline IconicPCB

  • Frequent Contributor
  • **
  • Posts: 960
  • Country: au
Re: A very silly question about heating water
« Reply #8 on: May 17, 2015, 03:34:52 pm »
The boss has a reasonable idea. He needs to modify it ever so slightly and he will be on a winner.

He should use an electric motor interposed between clean supply and warmish waste water. He should attach a heat pump as is done in many a domestic heating system and shuffle energy between the two water flows.
In the process he can harvest motor waste heat too.

For every unit of electrical energy he will extract at least two units of heat energy.

Clever boss.
 

Offline Rick Law

  • Super Contributor
  • ***
  • Posts: 2436
  • Country: us
Re: A very silly question about heating water
« Reply #9 on: May 17, 2015, 03:37:39 pm »
The boss has a reasonable idea. He needs to modify it ever so slightly and he will be on a winner.

He should use an electric motor interposed between clean supply and warmish waste water. He should attach a heat pump as is done in many a domestic heating system and shuffle energy between the two water flows.
In the process he can harvest motor waste heat too.

For every unit of electrical energy he will extract at least two units of heat energy.

Clever boss.

He may not be thinking about capturing waste heat!

Read again and you will see it can mean he is actually thinking about using motor as heat element - not as motors to run something and capture waste heat.

...
His boss wants to get into the carwash business, and is intent on devising a more efficient method of heating water. He would like to use an electric motor (I do not know which type) to act as the heating element, running it with it's cooling fins mechanically removed...

As CatalinaWOW pointed out a couple of replies back, the pumping and the maintenance (for waste heat) will kill any saving you got.

A heat-exchange mechanism to pre-heat with re-capture heat from used water would probably be the biggest saving "low hanging fruit".

« Last Edit: May 17, 2015, 03:48:05 pm by Rick Law »
 

Offline IconicPCB

  • Frequent Contributor
  • **
  • Posts: 960
  • Country: au
Re: A very silly question about heating water
« Reply #10 on: May 17, 2015, 03:48:22 pm »
Yes Rick...

but pointing to the heat pump is a friendly way to not tell the boss he is a silly person
 

Offline Mechatrommer

  • Super Contributor
  • ***
  • Posts: 8243
  • Country: my
  • reassessing directives...
Re: A very silly question about heating water
« Reply #11 on: May 17, 2015, 03:53:39 pm »
Heating water is one of the few viable uses for low content "waste" heat.  Electric motors are at best around 90% efficient, so the remaining 10% could in principal be used to heat water (as opposed to the air which usually gets rid of this waste heat).
you havent used a motor for an air compressor, it got fin installed and if it runs for 10 minutes you are lucky if you can survive touching it for 5 seconds. the fin will undoubtedly further increase torque resistance and hence power usage, an inevitable waste for the cause. as of OP's friend's boss, if he want to recycle energy of such motor, i 110% support it, but piping and all will be something. but if he intend to use the motor to ONLY heat the water, then he have lack of knowledge, or in rough word people might easily say... stupid.
if something can select, how cant it be intelligent? if something is intelligent, how cant it exist?
 

Offline Rick Law

  • Super Contributor
  • ***
  • Posts: 2436
  • Country: us
Re: A very silly question about heating water
« Reply #12 on: May 17, 2015, 04:15:18 pm »
Capturing heat from a compressor instead of motor makes sense.  There is a lot of heat with compressors, but I am not sure if a lot of air compressors are in used for a car-wash.

A thought occur to me that you need to check into even with compressors.  If you modify it, will warranty and insurance be impacted?

If your compressor fails, you would be on your own.  If your compressor fails to a point where the building burns down, would insurance be a problem since you tempered with the equipment in use.

Your boss needs to look into that!
 

Offline cs.dk

  • Supporter
  • ****
  • Posts: 553
  • Country: dk
Re: A very silly question about heating water
« Reply #13 on: May 17, 2015, 04:31:39 pm »
you havent used a motor for an air compressor, it got fin installed and if it runs for 10 minutes you are lucky if you can survive touching it for 5 seconds.

A regular induction motor? Did some logging on my old compressor, it never came above 40C at full load. Haven't tested on my "new" (used) one, but i think it will be the same.
 

Offline C

  • Super Contributor
  • ***
  • Posts: 1345
  • Country: us
Re: A very silly question about heating water
« Reply #14 on: May 17, 2015, 04:55:28 pm »
He would like to use an electric motor (I do not know which type) to act as the heating element, running it with it's cooling fins mechanically removed...

For most motors with air cooling, the cooling fins cool the windings and rotor. Removing the fins will burn out motor or shorten it's life.

There are motors that use water for cooling.
https://www.google.com/#q=water+cooled+motor
So a water pump could use a water cooled motor in place of an air cooled motor. Need flow of water  and one quick look says 5 c rise in water temp at proper flow rates.

Non standard setup could be more trouble then the gains. It could be cheaper and easer to to use a heat pump recover waste water heat and the exhausted air from the room that contains all the heat producing equipment.

C

 

 

Offline max_torque

  • Frequent Contributor
  • **
  • Posts: 876
  • Country: gb
    • bitdynamics
Re: A very silly question about heating water
« Reply #15 on: May 17, 2015, 08:30:02 pm »
Ask your Boss how he's going to pay the insurance payouts to the customers he's electrocuted by trying to "water cool" a motor clearly not designed for such a purpose?
 

Offline timofonic

  • Frequent Contributor
  • **
  • Posts: 904
  • Country: es
  • Eternal Wannabe Geek
Re: A very silly question about heating water
« Reply #16 on: May 17, 2015, 09:17:36 pm »
He's your boss, not your friend. He gets more money than you and he's acting that dumb, right? Is he dumb in any other areas too?

 Just explain him what can happen, if not agrees obey and let the disaster happen.

That's what Dilbert would do!
 

BulletMagnet83

  • Guest
Re: A very silly question about heating water
« Reply #17 on: May 17, 2015, 10:32:01 pm »
Thanks very much for the replies, all :D I will pass them on. So I heard from my buddy, his boss is on the same beginner's electronics course as he is.... and after bringing the idea up in class, their tutor made a face like this "O___________o"

I apologise to anyone who's left a head-print on their desk reading this thread. But you know how sometimes you encounter people who treat "that's stupid, you can't/shouldn't do that" as a challenge? Well...  |O
 

Online xrunner

  • Super Contributor
  • ***
  • Posts: 3416
  • Country: us
  • hp>Agilent>Keysight>?
Re: A very silly question about heating water
« Reply #18 on: May 18, 2015, 01:32:50 am »
He would like to use an electric motor (I do not know which type) to act as the heating element, running it with it's cooling fins mechanically removed...

Even more heat can be generated if the first electric motor is used to run a generator (with any cooling fins removed), and that generator's output to run a second motor. The more you connect like this the more heat you will produce.
I am a Test Equipment Addict (TEA) - by virtue of this forum signature, I have now faced my addiction
 

Offline Rick Law

  • Super Contributor
  • ***
  • Posts: 2436
  • Country: us
Re: A very silly question about heating water
« Reply #19 on: May 18, 2015, 08:33:54 am »
He would like to use an electric motor (I do not know which type) to act as the heating element, running it with it's cooling fins mechanically removed...

Even more heat can be generated if the first electric motor is used to run a generator (with any cooling fins removed), and that generator's output to run a second motor. The more you connect like this the more heat you will produce.

Entropy is just like tax - VAT tax.

Should try that on motors with bad bearings, the axle will be a "hot rod" as well.
 

Offline Dave Turner

  • Frequent Contributor
  • **
  • Posts: 434
  • Country: gb
Re: A very silly question about heating water
« Reply #20 on: May 18, 2015, 09:54:19 am »
I got the impression that you're in Spain.

If so and there is enough land area available then bury enough pipework to extract ground heat to a central insulated tank. Supplement this with roof mounted solar panels to power the required pumps.

Car wash for one maybe. Company jacuzzi more likely.
 8)
 

Offline miguelvp

  • Super Contributor
  • ***
  • Posts: 5549
  • Country: us
Re: A very silly question about heating water
« Reply #21 on: May 18, 2015, 11:04:09 am »
OP is from Wales, maybe he is on vacation or planing to go on vacation to Spain to catch some sun :)

I know I am!
 

Offline Jay_Diddy_B

  • Super Contributor
  • ***
  • Posts: 1668
  • Country: ca
Re: A very silly question about heating water
« Reply #22 on: May 18, 2015, 12:06:00 pm »
Hi group,

Time for a little physics.

The specific heat capacity of water is 4200 (J/(kg * K))

1 kW = 1 kJ s-1

 1 Imperial gallon = 4.546 litres

density of water = 1.00

1 minute = 60 seconds.

so with a flow rate of 1 gal / minute and 1 kW dissipation the temperature rise will be:

Trise = 60 x 1kJ / 4200 x 4.546 = 3.1oC

Water is pretty good for cooling, but it requires a lot of energy to raise the temperature.

Regards,

Jay_Diddy_B


 

Offline max666

  • Frequent Contributor
  • **
  • Posts: 367
  • Country: at
Re: A very silly question about heating water
« Reply #23 on: May 18, 2015, 12:46:05 pm »
Heating water is one of the few viable uses for low content "waste" heat.  Electric motors are at best around 90% efficient, so the remaining 10% could in principal be used to heat water (as opposed to the air which usually gets rid of this waste heat).
you havent used a motor for an air compressor, it got fin installed and if it runs for 10 minutes you are lucky if you can survive touching it for 5 seconds. the fin will undoubtedly further increase torque resistance and hence power usage, an inevitable waste for the cause. as of OP's friend's boss, if he want to recycle energy of such motor, i 110% support it, but piping and all will be something. but if he intend to use the motor to ONLY heat the water, then he have lack of knowledge, or in rough word people might easily say... stupid.
At the air compressor it isn't the motor that's getting that hot, it's the cylinder where the air is compressed. Partly because reciprocating compressors have friction, but mostly because gases heat up when they are compressed --> Thermodynamics.
 

Offline CatalinaWOW

  • Super Contributor
  • ***
  • Posts: 2713
  • Country: us
Re: A very silly question about heating water
« Reply #24 on: May 18, 2015, 01:29:40 pm »
Nothing inconsistent here.  Compressing air is less efficient than running an electric motor.  Don't know the number but suspect it is not that far above 50%.   Using 50% and 90% as bounds on the number says that a 1 HP compressor (~750 W) will be dumping between 75W and 325 W as heat.  Don't know anyone here that would want to grab either an incandescent light bulb or a soldering iron of those wattages.  But as the prior poster says, it won't heat much water.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf