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4.3 Capture & Use of Waste Energy

Posted September 02, 2007 8:36 AM by masu

A classic example of waste energy not being utilized is the dual duct air conditioning systems that were so common a few years back. The systems used a supply of hot and cold air that was mixed at the appropriate ratio so the temperature in a given area could be controlled in much the same way you regulate the water temperature in a shower. Not only is the process wasteful in itself, but you would often find huge chillers that produced copious quantities of hot water that was cooled by cascading it through cooling towers. Meanwhile, a few feet away hot water that was used to generate the hot air supply was heated by a boiler.

There are a myriad of examples where energy is treated as a waste byproduct while nearby another process needs to consume energy in virtually the same form. It makes sense that the waste energy be captured and used as it not only reduces costs, the consumption of fossil fuels and pollution but it reduces the impact we are having on the environment..

Since it makes sense one would think that whenever and wherever it was possible waste energy would be used productively. However, my research into the subject for this thread revealed little information on the subject or examples of it.

So, why if it makes so much sense to capture and use waste energy, is it not being done more often? I believe the primary problem comes from the way productivity is often measured by the effect on short term profitability. Put bluntly, if it doesn't increase the profitability within a few months or at most a couple of years the people making the decisions don't want to know or hear about it. Since energy recovery systems usually require the installation of some complex and expensive infrastructure and unless the cost is amortized over realistic periods of time such systems have no chance of being developed and utilized.

Another problem involves the transporting of energy and unless the process that create and use the energy are nearby, transporting the energy can be anywhere between difficult and impossible.

Energy recovery systems can be fairly complex and I think one of the more fanciful ones is the Anchored Tornado by PureEnergySystems. None the less there are many examples of wasted energy, like coal fired power stations, where twice as much energy is wasted than is eventually utilized.

It is, however, necessary for us to reduce the impact we are having on our environment and reducing wastage is always a good place to start. For the most part we live in a commercially driven society and any solution must be commercially viable, but we will need to change the way we think and calculate the effectiveness of our actions. It is no longer possible to just look at what is happening locally or within a single company or department within a company and we need to expand our perspective to take in the problems as a whole.

What have you seen? Is industry in your region of expertise and locale trying to do the right thing by capturing and utilizing waste energy or are they just carrying on as so many have done in the past? What sort of wasteful processes have you come across and what would you do to recover much of the wasted energy?

I do apologize for the lack of background material in this thread, but there is little information or examples of it being done. I will keep looking and add information on and links to anything I subsequently locate and would ask others to do likewise.

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#1

Re: 4.3 Capture & Use of Waste Energy

09/03/2007 1:17 AM

We are in a changing world, when it comes to energy $20 [bbl] oil makes different economic decisions than $70[bbl] oil. The real change should be in planning! the food processing plant needs to be next to the co-gen that should be next to the feedstock.....

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#3
In reply to #1

Re: 4.3 Capture & Use of Waste Energy

09/03/2007 5:24 PM

make copper coated roads in cities , highways , automobiles are biggest contributers apart from pollution , tonnes of heat is diposed in the atmosphere . we have previously discused such matter no of times , but application never prop ,earth itself is bigger energy conserver , we blame politics ,industries ,society , it is in the human system ,even basic physics can solve much of our day to day problems .

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#6
In reply to #3

Re: 4.3 Capture & Use of Waste Energy

09/04/2007 9:59 AM

Hi vikas,

  • make copper coated roads in cities

I'm not quiet sure what you think making the roads out of copper would achieve other than reducing the population with the increase in accidents. Are you trying to use the earth as a gigantic heat sink or what?

While the temperature as little as a metre below the surface is fairly constant this stability is due to several factors.

  1. Specific Heat: Most rocks have a fairly high specific heat and as such can store considerable amounts of energy per unit of temperature difference.
  2. Thermal Conductivity: Dry rocks, earth, soil, gravel etcetera does not have a very high thermal conductivity. This lack of conductivity severely limits how much energy can be sunk into or sourced from a given volume of rock.
  3. Heat from Mantle & Core: The Earth's core is extremely hot and as mentioned earlier the main driving force behind this is believed to be the decay of unstable isotopes of heavier elements. This energy is ultimately radiated up through the mantle and crust and eventually through the atmosphere into space. As you start to descend the temperature of the surrounding generally fairly constant at about the mean temperature of the atmosphere above it. However once you go past a certain point it starts getting hotter and depending on where you are rises to a point where rock becomes fluidic.

The problems with using the Earth as an energy sink or source is the poor thermal conductivity. What often happens is that the rock that is immediately surrounding you heat source/sink rapidly approaches the temperature in the heat source/sink.

Now, don't get me wrong. For small systems like home heating/cooling where the amount of energy involved can be very efficient and work extremely well. However, if you scale thins up you rapidly reach a point where the system becomes ineffective.

There are however places that lend themselves to this sort of heat source/sink and there are technologies both in existence and under development that increase the thermal conductivity of the surrounding rock. As a result the size of such systems has been increasing but unless you are in an area that has plenty of geothermal activity going on the capacity is still limited.

This article on the Birdsville Geothermal Power Plant discussed many of the problems that had getting their 80 kW plant on line. A point to not is they do not source or sink energy directly into the surrounding rock but rather use artesian water that has been heated by the rock.

  • automobiles are biggest contributers (sic) apart from pollution , tonnes of heat is diposed (sic) in the atmosphere .

While it is indeed true that most motor vehicles are no more than 20% to 30% efficient at converting chemical energy to mechanical energy it is not the wasted energy nor the used energy that is the problem. It is the pollutants like CO2 that are opaque to Infra Red, IR, radiation that are causing the problems. The more IR opaque substances there are in the atmosphere the lower the rate of IR radiation into space becomes.

It all works like a bucket with a hole in it. If you keep adding water at exactly the same rate that it is leaking through the hole the level of water in the bucket will remain constant. However, if you obstruct part of the hole and reduce the rate the bucket is leaking it will soon fill and overflow.

Now, getting back to the atmosphere, if we dump a whole load of IR opaque gasses into the atmosphere it is going to reduce the rate that this energy can be radiated into space. Since the amount of energy coming from the Sun is fairly constant as is the energy coming from the Earth's core, the reduced radiation into space can only mean a rise in the energy that is stored in the atmosphere.

So, it's not the wasted energy, although reducing the waste can only help, but rather the pollution that is being created by the burning of fossil fuels.

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#7
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Re: 4.3 Capture & Use of Waste Energy

09/05/2007 2:05 AM

What is the effect of the several billion people, converting carbohydrates to heat & exhaling co2?

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#2

Re: 4.3 Capture & Use of Waste Energy

09/03/2007 2:15 AM

There is no doubt in my mind that this is an area ripe for development. As commented, this will be brought about as a result of fuel and/or power costs, as well as (hopefully) environmental conscience.

I once toured the physical plant area on the roof of a highrise building I used to live in, and marveled at how the A/C was kicking out huge amounts of heat from the rooftop, while cold water was being heated separately to supply the building's hot water requirements, with no exchange between them. It made no sense to me at all.

I don't know if it is any different today (this was about 15 years ago), but if not, it would be a practical place to start, as it would apply to virtually every commercial building in existence.

I'm sure that short-sighted planning mentality hinders investing in waste heat reclamation technology. But buildings are among the biggest energy wasters on the planet, if not THE biggest. This should go beyond short-term bottom line analysis, and be government mandated.

They have already made "smart meters" mandatory for individual high-rise condo units here, which is a good start (as usual, pick on the citizens at the bottom of the ladder first), but I'm sure more can be done (further up the chain).

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#4
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Re: 4.3 Capture & Use of Waste Energy

09/03/2007 10:36 PM

Higher prices for energy would certainly drive the search for improved efficiency. I agree that it will probably bite the people at the bottom first, unless of course there is an election in the near future. On second thoughts it would probably happen six months after an election.

Do you think that is being just a little too cynical or is it realistic?

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#5
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Re: 4.3 Capture & Use of Waste Energy

09/04/2007 12:55 AM

Absolutely cynical! The HVAC PhD University instructor promised to flunk anyone that could justify installing insulation in homes with electricity available at 2c/KwH. After presenting him with the calculations, he stated he was preparing us for Thermo III. After showing him I already Aced Thermo III, he never backed off. Home insulation, according to him, could not be cost effective.

Obviously he was not raised where I was born. We fed chickens through knot holes in the floor, counted stars through the holes in the tin roof, watched after household pets visually between the warped siding, and woke up to frozen water pails in the kitchen. NO professor could convince me that home insulation was not cost effective.

All scientist agree on global warming in defiance of NASA data that may support global cooling. Political correctness is a required subject in all state supported institutions of learning. Unfortunately, science and engineering are not exempt.

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#8
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Re: 4.3 Capture & Use of Waste Energy

09/05/2007 2:45 AM

I think you'd agree that even in a comfortable climate lack of insulation can make for an uncomfortable home. When I had the roof replaced about 10 years ago, I insisted on an "Anticondensation blanket". This is foil backed fibreglass directly contacting the iron. The back of the iron doesn't trap condensation at night and induce rust and the daytime heat transmission is drastically reduced.

I ordered the iron in plain Zincalume for reflectivity and the roofers when installing it told me I should have ordered Colorbond Classic Cream as it is cooler in the long term.

The iron is now sufficiently weathered for me to conduct some experiments with thermocouples and a data logger. I'll post the results.

While the roof was off I added steelwork to support a Solar system but as technology developed I elected to go for a heatpump unit which turns waste heat into hot water.

It is a good thing at less than 20% of the running cost of gas. The water is reliably hot unlike gas and there are no longer products of combustion around under the house. The dehumidification the unit provides is also an added bunus. Mackay humidity on a dry day is 75% and rises to close to 100% in the wet season.

The problems encountered mostly revolve around build quality cost cutting issues. For instance they (Rheem) used a cheap copy version of a Klixon type non adjustable thermostat (Derwent) to control the inductive load of a 1kw compressor. It doesn't last, the contacts weld or wear over centre to a higher cut out range and trip the protection thermostat. Rheem won't honour any warranty on the thermostat and the part is non standard as well as overpriced (you can't fit a Klixon or Robertshaw due to bodgy hole centres). Bypassing it with a contactor won't work as the heat due to current flow is part of the calibration. Eventually I settled for a Bain Marie adjustable thermostat and the contactor.

As you can see waste heat is recoverable but design issues remain. Rheem deserve top marks for trying but also deserve a raspberry for product support.

Our you beaut populist communist Queensland government are setting out to ban electric hot water systems. They have absolutely no understanding of grid operation let alone "new" technologies such as heat pumps.

The only way to get sense out of politicians is to vote them out each three years...NAH that won't work. There is no way. A useful politician is rarer than a working perpetual motion machine.

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#9
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Re: 4.3 Capture & Use of Waste Energy

09/05/2007 9:21 AM

Hi Emjay4119,

Many a good idea has fallen at the first hurdle due to somebody in production cutting corners in order to save a few miserly cents. Personally the attitude of idiots like this really gets up my left nostril and I hope their pubic hairs turn into rusty fish hooks.

One thing that nearly everybody overlooks with domestic HVAC and utilities is having a centralized control system. For decades now large buildings have utilized sophisticated integral computer systems that utilize a mass of data to dramatically reduce the energy consumption. The important thing is you need to have control over and feedback from as many control loops as possible. The more diverse and extensive the data gathering the greater the integration and savings.

Now, complex control systems like this used to cost an arm and a leg and were usually built with proprietary operating systems that were confidential and could only be worked on by the equipment supplier. However, the steady increase in complexity and reduction in price of electronics means that what used to take a whole computer system can now be done on a single μ controller that costs a few dollars.

Ok, getting back to the problem of domestic HVAC and utility supply, it is now possible to do the same thing domestically. You can now get a small Programmable Logic Controller for around US$100.00 that can be used as an interface and control system. The more you connect the more you can integrate the control loops and the greater the savings.

An example of what I am talking about is security and heating/cooling. Many houses have an alarm system that is used to detect unwanted intruders. However, it can also be used to detect the presence of anybody and by integrating the information form the security system with the heating/cooling system you can shut down the heating/cooling where it is not needed. You can also add even more intelligence by allowing the system to monitor you needs and develop patterns of behavior that allow the system to anticipate your needs.

The savings and reduction in energy consumption are dependent on your imagination and how much information you can feed such s system the more you systems can interact rather than fighting against each other.

The only draw back of systems like this is it is usually way beyond the average domestic electrician, but I'm not talking to electricians here I am talking to engineers and I would hope that the majority of CR4 participants would not have too much problem realizing such a system.

The integrated control of HVAC and utilities in large buildings has been going on for well over two decades and the limitations of the systems available 20 years ago was the imagination of the engineers utilizing them rather than hardware. I can also guarantee that anybody reading this post is doing so on a system that is thousands of times faster and more complex, yet we rarely use it for anything more than an electronic note pad, post office or gaming companion.

The key is to use one integrated control system rather than a myriad of individual control loops and the power to do it is sitting right there in front of you, so there is really no excuse for not doing it.

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