How to Recycle Energy

Posted: December 13, 2017
Tagged As: Climate Change, Electricity, Energy, Energy Planning

Recycling is a concept familiar to most.  Recycling paper, plastic, metal and other materials as a means of reducing waste sent to landfills has been around for decades.  However, did you know that this same simple concept can be applied to energy as well?

Basic Energy Process Model

A basic energy process has three pass-through components – Inputs, processes, and outputs. Inputs are fuels used to create a particular process such as heating, cooling or even energy storage for future use.  The unused portion of the fuel used in the process is considered waste or a by-product.
Image of a Simple Energy Model

Most of us are accustomed to singular processes like the one above, such as our stand-alone electricity grid, or the heating and cooling systems in our facilities, but how could we improve this model?  Can it be more efficient, more effective?

Optimizing the Process for Efficiency

In terms of the above process, efficiency is the ratio of useful work to the inputs required to create the desired output.  When viewing this as a single system, the non-useful outputs are simply waste from the original process.  But perhaps there is a use for this waste or by-product in other areas.
Optimizing the efficiency level of a single process will increase its overall effectiveness.  Any reduction in the energy consumption for the process simultaneously results in reduced input and/or the reduction of waste in order to maintain the balance of the equation. Therefore, improving energy efficiency occurs one of two ways:
  1. Either of:
    1. Decreasing both the input and the waste amounts, Or
    2. Increasing the utilization and decreasing the waste balance of the process
  2. Recycling (or re-using) the waste
Image showing the definition of recycling according to Collins English Dictionary

Recycling energy involves injecting the waste (better defined as a by-product) of a singular energy system back through the same cycle it just passed through, or an entirely different cycle altogether, thereby increasing the overall efficiency levels of the original inputs.

Heat/Energy Recovery Systems

Heat or energy recovery systems are a great example of passive energy recovery.  Often, there are no moving parts.  The heat in a liquid (steam, air, water) can be transferred to pre-heat or cool another liquid.  A couple of examples of this are as follows:
  • Many new homes have a Heat Recovery Ventilator attached to the furnace.  As the warm air from the home is exhausted through washroom fans, etc., the energy is transferred to the incoming air, pre-heating it so that the furnace doesn’t have to heat it as much.
  • Some arenas are able to recover the heat taken out of the ice in the refrigeration process to pre-heat the water used to flood the rink.  This is accomplished through a heat exchanger, which is connected to both the refrigeration system and the domestic water system.
  • Some industrial processes can have low efficiencies (where only 35% of the available energy in the input fuel is converted to useful energy) and high waste (as much as 65%).  Waste heat recovery technology is able to recycle the excess hot water or steam left over from the process to feed back into the original system, increasing the overall efficiency of the system (i.e. 85% energy utilization).

Cogeneration: Combined Heating & Power (CHP)

The practise of generating power for one process and then using the thermal energy from the generator for another unrelated process is called cogeneration. 

A good example of a cogeneration system is one that most of us are familiar with – the modern day automobile and its engine.  The intended purpose of the automobile is to transport something or someone from point A to point B (power).  However, both the heat produced from the engine itself, as well as the liquid coolant that runs through the engine to keep it from overheating (both of which are by-product of the process of getting from A to B), can provide heating and cooling options in the cabin to make the journey more comfortable.

Macro vs Micro Cogeneration

It is common for large industrial facilities to use cogeneration technologies to both power their manufacturing process, and provide heating/cooling within the facility itself.  It is much easier to address the electricity and thermal loads within the same facility, and the equipment required for cogeneration tends to be more cost-effective on larger-scales. 

Power-producing systems offer an abundance of free thermal by-product, particularly in large load institutional facilities such as hospitals, long-term care facilities, college and university campuses, etc.  Recreation facilities that have continual high power requirements (ice rinks) and high thermal loads (swimming pools) and/or are a designated emergency facility could benefit from on-site cogeneration.  These should be considered as viable energy efficiency opportunities when evaluating a building.

When it comes to improving efficiency in smaller facilities, the cost to re-design and install new equipment may exceed any savings offered from a cogeneration or energy recovery system.  However, as these technologies improve and energy costs continue to rise, wide scale adoption will become commonplace.

Did You Know…

The world’s first commercial electric power plant made use of energy recycling.  Thomas Edison’s Pearl Street Station began generating electricity in 1882 in the Manhattan area of New York City to produce both electricity and thermal energy, using waste heat to warm neighbouring buildings. “Recycling allowed Edison’s plant to achieve approximately 50% efficiency.

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