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Factor E5 = Energy • Efficiency • Entropy • Exergy • Efficacy
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This article is part of our sustainability presentation which can be viewed online.
Green, efficient and sustainable are not the same thing: A glass building is green but not energy efficient. A million new smart cars is energy efficient but not sustainable. Sustainability – is a branch of philosophy . It is not a material but the use or abuse of material. It is not a system but the execution of a system. It is not a building but the rational to build a building.
Sustainability defines how much we consume in the present at the risk of starving the future.
Alright lets consolidate this Energy, Efficiency, Entropy, Exergy, and Efficacy thing into a sustainability discussion that everyone without a Ph.D. can understand...ready?
Energy is everywhere and we didn't create it nor can we destroy it. Energy is a fixed global resource that comes and goes in different forms yet never disappears. This is referred to as the "law of conservation" or "the first law of thermodynamics".
Energy is in the earth, water, wind, the sun, the tides, gas, goal, uranium, and the big rock sitting on the cliff waiting for an earth tremor to put it into motion - yes...energy is everywhere.
Energy has power known as potential power or kinetic power, i.e. it can do something if triggered (potential) - or is presently doing something (kinetic); and it comes in many forms such as: heat, sound, light, vibration, electrical, chemical, nuclear and gravitational.
Ok...now you're going to need to sit down for this next statement...
Since we can't create energy nor can we destroy it (are you sitting down?) - we can't save it. That's right - despite the message by just about every non scientist about how to 'save energy' - energy can not be saved.
Gulp...yes I know this might mess with your head but energy is flowing or waiting to flow in different forms whether you like it or not and regardless of what efficient HVAC system or appliance or car or whatever you plan on using...you can't save it as if its like saving pennies for a rainy day.
We can make and save pennies but we can't make and save energy.
When we use less energy we are in fact preserving its state for future use.
When we do use energy we are transforming it from one state to another like burning gas to create heat - when we do this we want to do this efficiently and effectively.
So preserving energy in its current state is a matter of human behavior that results in the use of less energy whereas energy efficiency is the use of technology that requires less energy to perform the same function.
Got it so far?
This data on energy production, self sufficiency and electrical generation by fuel comes from the International Energy Association / Organisation for Economic Co-operation and Development – 2009 Data Base. The black zone represents coal and coal for power generation. To see a larger scale of this illustrations visit our presentation on sustainability .
Alright...lets discuss electrical power generation.
Take an example using coal to generate electricity (below)...coal contains potential energy in the form of chemical energy. Burning coal changes the chemical energy into thermal energy. The thermal energy is used to change water into steam - steam pressure is then used to turn a turbine which is kinetic energy. The kinetic energy through the turbine is turned into electrical energy which is then turned into light or heat energy or back into kinetic energy (to power up a motor for example) or potential energy (battery).
Generating power at a coal plant results in waste heat from the combustion and cooling process as well as losses due to friction, noise and turbulence. Generating electricity with combustion is very inefficient contrary to the belief that electricity is 100% efficient. On the other hand, power generated by hydro has no combustion emissions and considerably less losses and is preferred over other generation methods such as nuclear.
The point is the energy is never destroyed it just changes from one form to another and it doesn't matter if we're talking about energy use at a coal fired steam turbine or you blowing on a pinwheel turbine.
In both cases energy went in and energy came out...its the first law of thermodynamics.
But as you know from blowing on a pinwheel - we didn't get to use all our energy because some of it was lost to other processes like heat, friction, and noise. That's where energy efficiency, entropy, exergy and efficacy comes into play.
A really good way to look at energy efficiency is to use your heating system as an example. Let's say today you pay $100 for gas to heat your home...but 20% or $20 worth of the potential chemical energy in the gas you paid for - is released as combustion heat into the environment through your chimney. The other 80% went into your home and made you feel comfortable - BUT (and this is really important) in the process of making you feel comfortable it eventually worked its way outside in what everybody knows as heat loss...i.e. the energy was never destroyed.
Ok...so let's ask, 'how would your attitude change towards energy if you actually had to pay more for the 20%' that went up the chimney? Put this into practice. Lets imagine utilities continue to charge you for what they supply to your home but hypothetical government environmental laws penalize you with a surcharge for the heat that was released into the environment from your chimney...instead of $20 for 20% waste you had to pay $40 or twice for something you didn't use. Then let's say your neighbour builds a high performance net zero energy home with wind or solar power generation and geothermal or solar thermal heating but your house - supplied by coal fired power generation and natural gas - is a conventional home constructed to building codes which are minimum standards not requiring mandatory energy efficiency nor conservation - see EnerGuide rating scale below.
This graph (credit: Natural Resources Canada) places different housing strategies on Canada's EnerGuide Rating scale. Of the 13,000,000+ existing homes in Canada, practically all fall into the conventional, upgraded old existing and existing old category. To see a larger scale of this illustrations plus the long term trends in R-2000 homes, visit our presentation on sustainability .
You both use energy (heat and power) but your neighbor actually uses less than he or she produces - in fact your neighbor - as a conservationist - is a net producer and could also be considered a micro power company and sell the power back into the system. You - as a consumer on the other hand are not supplying energy - only paying to have a non renewable resource come into your home so it can be released as light, heat, sound and work. But as we hypothesized, you get billed for not only what you used but also for what you didn't use...that being the heat going up the chimney.
In fact the more you didn't conserve and the more waste you generated the more you get charged.
Would you look at energy differently if you were charged a penalty for what you let slip past you...?
That's what energy efficiency is all about...its about using everything you paid for whereas energy conservation is needing less of what you might want otherwise.
It's kinda like the old dinner saying, "take what you need but eat what you take".
That's why we at www.healthyheating.com get bent all out of shape when people pay for high efficient heating systems when their buildings still literally suck. Why? Because no high efficiency equipment is going to prevent you from using energy...it just means while you are using energy you'll be doing it more efficiently - a good thing - but not as good as improving both...and being less bad doesn't mean we're doing good.
Aside from that, what also gets us going is when consumers get coerced into buying high efficiency equipment that never performs at or close to its maximum engineered capacity and this happens all the time when condensing furnaces, boilers or water heaters never condense or when heat pumps are operated at their lowest coefficient of performance (COP).
These are the 'potential' operating performances for heat pumps. However this equipment will never reach these hypothetical conditions if there are flaws in the installed system. As for all applications, it's not enough to install high performance equipment, the system has to enable it to reach its rated capabilities. To see a larger scale of this illustrations visit our presentation on sustainability .
Ok...lets look at why everyone in the world is so concerned about energy conservation and then we'll introduce you to entropy and exergy.
Energy - State Preservation
By far the biggest concern world leaders have is the growing demand for electrical power. There are significant parts of the world that to this day still don't have access to power and of course other areas that have an insatiable appetite. You can see this from the satellite mosaic below.
This night-time satellite mosaic nicely illustrates the electrical consumers of the world. Image courtesy of NASA.
As mankind develops the underdeveloped areas and expands its use of electrical appliances and gadgets the demand for more power generation increases - resulting in further increases in pollution from power generation plants - the majority based on combustion processes. These products of combustion occur from changing the state of energy (chemical to electrical) and contribute to greenhouse gases which destroy the very ozone layer protecting the earth from getting sun burned - that being damage from short wave ultraviolet radiation.
Look at it this way - the ozone layer in the upper atmosphere is like suntan lotion or sun block and greenhouse gases dilute it's effectiveness. So preserving the states of energy reduces what gets released into the environment (known as entropy) and reduces the destruction of useable energy (known as eXergy).
With a combination of paradox's and oxymoron's we're trying to efficiently feed our appetite for power even though the consumption is slowly eroding the safety shield keeping us alive.
Nobody said the human race was using anywhere near its intellectual capacity for making smart decisions...and from looking at the satellite mosaic - look where all those smart people live ...oy - can you see your neighborhood?
Entropy - The Energy Story of a Cooling Tower and Pile of Manure
Whereas energy cannot be created nor destroyed, it's form seeks balance. Nature is like that... pressure goes from high to low as does temperature and moisture. That's what causes the earths atmosphere and weather to change - it's Mother Nature at work - creating balance. For example energy in the form of thermal warmth will travel to thermal coolth (yes it's a real word) via conduction, convection and radiation.
Everything you need to know about heat transfer and building science can be found in a "pile of poo." Shown is manure taken from the barn and dumped onto the cold ground. Conduction is the warm manure heating the cold earth; convection is the raising of the air temperature around the pile, evaporation is the moisture in the manure being released to the atmosphere and radiation is the heat you feel from the manure even though you're not touching it....and that smell...well check out our presentation on indoor air quality .
We use these methods of heat transfer in keeping us comfortable when we heat our homes in cold climates and cool our homes in hot climates and why we have to be careful about moisture in dry or moist climates. This need for balance or order describes the process of a cold glass of water in a warm room eventually coming to an thermal equilibrium with the surrounding environment and why it will eventually evaporate in a dry room due to an equilibrium with vapor pressures.
But lets go back to power generation, heat energy balance and the word entropy by looking at a cooling tower.
As you can clearly see in the side photo of a cooling tower at coal fired power plant - there is nothing cool about a cooling tower when viewed with a thermographic camera . Heat from the cooling tower is released into the atmosphere which diffuses (spreads) away from the power plant...but that heat broadcasted into the atmosphere is now unavailable for use; the word "entropy" is a measure of its unavailability. Other examples of loss of usable energy can be friction in a mechanical system, resistance in an electrical system, turbulence in a fluid system or noise in a communication system. If entropy were an emotion it would be defined as "dazed and confused".
When we discuss the principles of energy (conserved) and entropy (unavailable energy) and power generation, it is easy to see with the power plants cooling tower why there is absolutely nothing energy efficient about using the combustion of coal, gas or oil to generate electricity - yet that's how much of North America's power is produced as well as many other countries in the world. (source IEA World Energy Outlook, 2009). That's also why engineers and energy environmentalists get all steamed up when the myth that electrical heat is 100% efficient gets rampantly spread across the worlds largest social network called - you got it - the internet.
Reality is - on a good day electrical generation efficiency with combustion might be between 20% and 35% whereas hydro generated power is up around 82%. Furthermore in Canada, like other countries; of the potential energy in non renewable resources - when converted to other forms such as electrical power - approximately 56% is lost or unusable due to various "entropy" processes - yes fifty-six percent! For practical discussions we may as well state that we have to release one unit of energy for every one that we need.
Now take that information and imagine every fourth family in North America increased their electrical use due to further increases in plug loads from more and bigger TV's, computers, entertainment centers and other stand alone electrical appliances (ask the folks in California about this problem). Then hypothesize global temperatures do rise as anticipated by the International Energy Association say by 1 deg C or 2 deg C ... then ask yourself what impact will that have on the use of cooling systems? Then take that scenario and add in the growth in China, India, and Africa who have all increased their acquisition of North American lifestyle.
Shown above are the energy flows in Canada - includes nuclear, hydro, biomass, coal, oil and gas. Shown in the circle is more than 6 Exajoules (EJ) of energy lost, unrecovered or unusable. So how much is 1 EJ? Well 1 (one) EJ is equivalent to 160,000,000 barrels of oil. To see a larger scale of this illustrations visit our presentation on sustainability .
Are you seeing the magnitude of the challenge we face as an inhabitant of earth and the problems created by those who spread the myth that electricity is 100% efficient? We must educate the public to differentiate between source efficiency and site efficiency likewise with appliance efficiency and system efficiency as these are most definitely not the same thing.
What should this mean to you and I?
It means that even if we build the most perfect energy efficient home but use non renewable energy to generate electricity for heating, cooling, lighting or otherwise to condition us, the home and anything in the home...we are ultimately contributing to global waste and pollution through combustion emissions (see CO2 emissions side graph). So while you're choking on that - consider what happens if you and I don't incorporate efficiency or sustainable principles into our day to day decisions making. Now what happens if everyone was like us and ignored these energy, efficiency and entropy principles...how does it look to you now? Gulp!
Imagine everyone in this photograph represented the worlds population (2010 = 6.7B). Then image that everyone in the pool represented the population of the United States and Canada, 2010 = 0.34B). Now let the water represent coal, oil and gas and then ask yourself - if the rest of the world jumped into the pool and used these resources like we do...would the world be a better place? What happens in 2030 when the world population is at app. 8.3 billion? To see a larger scale of this illustrations visit our presentation on sustainability .
Alright lets set aside that ugly thought and discuss e-x-e-r-g-y.
Exergy - is not a spelling mistake
Exergy is a cool word (pun intended) and describes the quality of heat and how effective we are at using that heat. Generally speaking the higher the source temperature the higher the quality and vice versa. Exergy efficiency occurs when the supply and demand temperatures are closely matched.
In a very simple example take the space heating of a home using natural gas. In a cold climate we need to maintain operative room temperatures of around 20 deg C or 72 deg F. This allows us to maintain relative skin temperatures between 85 deg F and 95 deg F (30 to 35 deg C). We do this by burning natural gas which has a flame temperature of around 2700 deg F (1500 deg C).
In a suitable analogy of bad exergy - based on getting from point A to point B - burning gas for home heating is like using a blow torch on your skin to stay warm.
Good exergy would be to use the 2700 deg. F. from the combustion of natural gas to create steam to turn a turbine for power generation and then use the condensate to heat various elements in a building with heat exchangers until we cascade the temperature down to where we can use it for space heating. That's why low temperature radiant heating systems have good exergy potential when connected to high quality energy sources and why they also have good exergy effectiveness when directly connected to geothermal or solar thermal systems... if you don't know anything about radiant cooling and heating and why researchers and industry leaders are looking at its exergy efficiency benefits, you can begin by studying radiant's history going back to the neoglacial period.
The illustration below describes the exergy principles and how the traditional approach of using combustion for occupant comfort is poor exergy.
This graph illustrates the exergy principles based on high quality versus low quality heat. Good exergy either takes advantages of the temperature differentials or matches up the source and load temperatures based on thermal simalarities. To see a larger scale of this illustrations visit our presentation on sustainability .
In the best of all worlds the best exegetic solution is to connect low temperature heating and high temperature cooling systems to sources of heated and cooled fluid of like temperatures without having to employ the use of combustion or compression equipment. This is possible with high performance buildings using radiant cooling and heating systems connected to solar thermal or geothermal systems (yellow area) and where wind or photovoltaic's is used to run the fluid circulators.
Thermal Efficacy - the diffusion of heat
Efficacy is a word that is used little in energy analysis but we think it's important enough to include it...for our purposes we define thermal efficacy as the quality of heat diffusion measured by its homogeneity or uniformity. Why is this important? Well lets say we're talking about a single forced air heating system serving three levels of a conventional home. Due to air pressures on the outside of the home as well as internal pressures due to stack effects and pressure differentials developed by mechanical systems like exhaust fans, dryer vents etc all which influence infiltration and exfiltration...its virtually impossible in standard construction practices to have thermal uniformity in air temperatures from the bottom basement level to the top floor. Occupants respond to these inconsistencies by manual controlling the thermostat leading to frequent cycling and thus system inefficiencies.
Using a wood or gas burning fireplace or stove is another example. The thermal efficacy using a single point heat source without some means of distributing the heat from the fire creates hot and cold spots which can lead to discomfort. It can also lead to dew point considerations in spaces not conditioned by the heat - which potentially results in condensation on windows and moisture problems within wall and ceiling cavities. Occupants unaccustomed to this form of space conditioning compensate by burning more fuel for longer periods of time which only exasperates the discomfort due to increases in short and long wave radiation, radiant asymmetry and poor thermal efficacy not to mention the increase in emissions.
Unlike systems known to have thermal inefficacies (and outside the world of academia), radiant based HVAC systems do not heat the interstitial air directly rather the air is warm because the interior surfaces are warm. Consistent and controlled surface temperatures throughout the home minimize the motive differential temperatures necessary to change the air density and thus its buoyancy - minimize the buoyancy and you minimize the risk of having poor thermal efficacy. But note, high performance homes (less than 10 Btu/hr/sf) conditioned with furnaces can have similar thermal comfort characteristics as mid to poor efficient homes (20 to 30 Btu/hr/sf) conditioned with mechanically based radiant systems such as floor heating.
Energy is not like pennies, we can make pennies but we can’t make energy so we can’t save it, but we can preserve non renewable energy in various forms for future generations.
Efficiency says take what you need but use all that you take – waste is not an option.
Entropy is energy dazed, confused and unavailable. When you use non renewable energy you create entropy and the more energy you use the more entropy exists.
Exergy says find a supply close enough to your demand but nothing more…you don’t need a sledge hammer to pound a finishing nail.
Efficacy says be effective with your energy use…distribute energy so it doesn’t create inefficiencies elsewhere…if you need to rob Peter to pay Paul …Peter will won’t let you forget.
HVAC systems don't have to be represented by big roaring beasts for heating nor nasty frosty freezing blizzards for cooling. They can be whisper quiet mellow low power systems that are earth and human friendly . But to get there - we need to first fix the inventory of buildings that have these nasty hot and blizzard cold HVAC system because ( wait for it...) bad buildings are like big open energy sores that will never heal or repair themselves. We can build all the new high performance buildings we like, but until we stitch up the old stuff...we will not have solved our problem. The scope of that problem is illustrated below defined by systems in the unsustainable category.