mam pls. clear some thing about pyroelectric, I suggest thermometric will may prove better

It is a question of diminishing returns. At on time in the USSR they built tractors that used thermoelectrics on the exhaust to provide electricity to the ignition system.

It worked, but it is a very expensive way to get there. And that is usually the issue. You can never recover enough energy to pay for the devices. So unless you are where power is non-existent it is difficult to justify this approach.

I agree with Ed Blessman the technologies are not cheap,in the end is it worth it?how much do you benefit from the system?

Although speaking from a research point of view,once a technology is embraced with more research in the area cheaper alternatives can be developed. And i think i would go with pyroelectric, it is less complex than the others.

It is a classic case for economic feasibility. In most of thermal power plants mechanisms already exist for waste heat recovery and recycling. Because recovered amounts are substantial and increase the over all efficiency of Systems. Where as waste heat recovery from Vehicle exhausts may be considered for cold climates. But I doubt if enough heat can be recovered to heat the vehicle cabin.

As regards thermocouples and other such fancy schemes one should also consider life cycle energy costs of such schemes. Considerably more energy is required to make a thermocouple than the amount of waste heat recovered. I hope some one has actual calculations for energy budgets.

An new and probably expensive(now) way is use of "nantena" - i.e. rectifying electromagnetic infrared waves by antenna and rectifyer

Dear Georgi Mladenov, could you please explain more about nantena, thanks indeed.

Nantenna is an electromagnetic collector designed to absorb specific wavelengths that are proportional to the size of the nantenna. Currently, Idaho National Laboratories has designed a nantenna to absorb wavelengths in the range of 3–15 μm. These wavelengths correspond to photon energies of 0.08 - 0.4 eV. Based on antenna theory, a nantenna can absorb any wavelength of light efficiently provided that the size of the nantenna is optimized for that specific wavelength. Ideally, nantennas would be used to absorb light at wavelengths between 0.4 – 1.6 μm because these wavelengths have higher energy than far-infrared (longer wavelengths) and make up about 85% of the solar radiation.

See :

www.inl.gov/pdfs/nantenna.pdf or

www.nrel.gov/docs/fy03osti/33263.pdf

Waste heat recovery for energy, this is an interesting topic (this is continuously looked at by my students in relation to Microgeneration & services) & really if you look at it economically the manufacturers of equipment and plant pay attention to this. Why? Because they want their equipment to be as efficient as possible, this is the selling point to the end-user. Piggy-backing additional equipment to recover "waste heat" is often economically foolhardy. Like the MVHR, heat recovered by the equipment can never economically pay for the installation, maintenance, repairs & end-of-life disposal.

S Gupta "computer generated heat", perhaps more people should drive the Smart DC initiative to eliminate so many transformers and power converters that are wasting energy & link the Microgenerated electricity to the local Smart Hubs to become more energy efficient in relation to waste heat.

Could we consider our 'body heat' as watse heat and heat recovery in this case is most attractive to economically invest?

Covering the whole or part of the body for themoelectric recovery is being looked at with incorporation of new fabrics, as far as I would see the problem it is the temperature difference between the closest layer and the furthest. Peltier devices are quite effective with large temperature differentials, 37C is a very low starting threshold.

One other area that may be worth considering with respect to the best way to utilize waste heat, is the original process. The fact that so much waste heat is available from these process may suggest that there is an opportunity to look at redesign of the process to more efficiently utilize the heat it uses. I recognize that there are many constraints to this approach; however, even if a portion of the potential opportunity is recovered there may be significant value.

As a simple first pass approach, I believe that eliminating the amount of waste heat in the initial design should be the first priority, then looking for ways to reuse or recover this heat next in line.

The use of waste heat is difficult and expensive activity due to very small temperature difference of source body with environment and thermodynamics principles.

In case of success to take off waste heat of a machine, this will be cooling of this equipment, which will be a positive action. But in the case of harvesting heat from human body- the result in mamy cases will be negative, because we need of a optimal temperature for normal life and hypercooling is not desired!!!

Waste heat of a machnine to be taken off for cooling is very interesting and should be promoted. . Should we include taking off waste heat from some chemical reactions?

Dear Dr.Natakan Muensit.

I suppose that harvesting of waste heat from some chemical reactions could be more perspective, if cooling will not change results. Between chemical reactions there are enough high-temperature ones and harvesting of waste energy will be more successful!

Dear All,

Thanks a lot for relevant and convincing discussions, which would certainly be beneficial to concerns.

Heat dissipated is a heat left unused in creating physical change. It shows that a system is less than 100 percent efficient. Take for example a car, gasoline creates heat which makes the engine work hence it makes the car do the physical work by moving itself from position A to position B. Since the car needs a radiator to keep the engine cool, it shows that engine is not very efficient heat converter. It is equivalent of having a bucket of water sitting on a paddle and pouring water in it makes the paddle go. Unfortunately, bucket has many holes in it. Therefore not all of water is used to do the work.

Scavenging or harvesting is a good idea and useful to power some less demanding systems but it does not solve the original problem which is poor efficiency.

This idea is worth investigating! 

The Blue Lagoon -"spa" in Iceland runs on waste heat from the power plant, but it maybe a unique situation.

I recall a mine in Sweden that used the factory waste heat to heat up the homes, so this was (maybe still is) a one-chimney town (or no-chimney town).