Waste heat recovery is one of the measures you can take to improve energy efficiency. For example, a large kiln can collect waste heat and use that to dry the feedstock before it gets fed to the kiln. This way you don’t have to use additional energy for feedstock drying, can make the burning process more efficient and clean, cut your energy bill and reduce greenhouse gases at the same time.  Waste heat recovery is a viable, win-win solution.

Then what about us?

We eat food, burn it inside our body and generate energy that can be used for various works.  We are a small scale energy generator.  And similar to all other energy sources, our body follows the second law of thermodynamics and keeps letting out heat.  When the ambient temperature becomes substantially low, we lose warmth and feel cold if not protected well.  We use large amount of fuel just to keep ourselves warm.  If we review our own energy efficiency measures, we could reduce our fuel consumption, probably significantly.

As far as waste heat recovery goes, our traditional first order system is clothing.  We typically add layers of clothes to recover heat that tries to escape from our body.  Especially in winter, we put a sweater on top of a shirt, and a coat/jacket on top of the sweater.  Then a scarf, a beanie and earmuffs.

Then, once we arrive at a destination that has a heater, we take off most of our heat recovery system. We are ready to outsource the job of protecting our body from losing heat to external energy-fueled heat sources.

Because external energy is so powerful and warms us efficiently,  we easily forget about our own heat recovery system.  We end up burning extra fuels even when it’s not needed if our own system is mobilized.  But this can be corrected easily, and if changed collectively, would save substantial amount of fuel.

We can revisit our first order waste heat recovery system: clothing.  One of the ways to improve its efficiency is to place the system closer to our body.  As is the case with industrial heat recovery, recovery becomes increasingly difficult and uneconomic once the heat starts dissipating.  In order to avoid it, our system should be right on top of our skin to preserve the least dissipated heat from our body.  Socks do that job. But there are more items that can be added to the list.

Japanese traditional strategy is Haramaki.  It means tummy-wrapper.  Our tummy is where our digestive system is concentrated, so Haramaki was devised to keep this area warm, rather than cold, to make sure it functions efficiently.  Not only it recovers wasted heat from our body, it also improves the functionality of our digestive system.

However, Haramaki has been considered outdated and out-of-fashion for a long time.  It’s understandable, because it’s not sexy at all.  In addition, fuels and technologies for heating became cheap.  People felt they didn’t need Haramaki anymore as a measure to recover heat.  But it’s changing again.  There has been a “new wave” of Haramaki lately.  By realizing the effectiveness of keeping our tummy warm, many people and businesses invested some resources to come up with more efficient, more versatile and a bit sexier Haramaki.  It’s been regaining its popularity in Japan. You would be surprised how much this small item helps to keep you warm, healthy and feeling fit. 

A state-of-the-art version of a waste heat recovery system is a very thin, almost skin-like undershirt or inner shirt.  For example, Japanese retail Uniqlo, popular for low-price and high functional items, offer a line called Heattech. Heattech is developed to drastically improve heat retention by combining a couple of synthetic fibers that excel in absorbing/retaining heat. It’s also woven to leave more void in order to maximize the amount of warm air trapped inside the shirt.

Functional clothes are what MUJI is good at.  They are focused on natural fiber, rather than synthetic fiber.  MUJI’s cotton-wool-stretchy shirt (middle picture below) employs dual structure where wool fiber is enveloped by cotton.  This method maximizes heat retention (and even enhance it) while offering soothing texture realized by cotton used on the surface.  It also excels in absorbing sweat because it uses wool inside.

You can see that inner shirts can come in different materials, different weaving techniques and different designs.  Three shirts above come in different materials, weaving method, neck design and sleeve length.  Since an inner shirt directly touches your skin, small details would really affect your comfort level.  You may want to compare to see which one you would fit your needs.  Then put those items on top of your skin, before you put on a shirt.  Even though they are incredibility thin and flexible they are unbelievably effective. You will even forget that you are wearing it while you are keeping your body warm much more efficiently.

Consider those thin, super efficient inner linings as your insulator.  Your heat recovery efficiency will increase tremendously.