Phase Transition, Expansion Valve, Evaporator, Compressor, Condenser and Air Conditioning

Posted by PITHOCRATES - April 3rd, 2013

Technology 101

We can use Volume, Pressure and Temperature to change Water from a Liquid to a Gas and back Again

Liquids and gasses can do a lot of work for us.  If we can control three variables.  Volume.  Pressure.  And temperature.  For example, internal combustion engines work best when hot.  But excessive heat levels can damage the engine.  So we use a special anti-freeze/anti-boil liquid in the cooling system.  A pump circulates this liquid through the engine where it absorbs some of the excess heat of combustion that isn’t used in pushing the piston.  After leaving the engine it flows through a radiator.  Air blows across tubes in the radiator cooling this liquid.  Ejecting some of the heat of combustion into the atmosphere.  Lowering the temperature of the cooling liquid so it can flow through the engine again and absorb more heat.

Our first cars used alcohol in the winter for a lower freezing point.  So this liquid didn’t freeze in the engine and crack the block.  Letting the coolant flow out.  And with no cooling available the excessive heat levels would damage the engine.  In the summer time we used plain water in the cooling system.  And kept the cooling system sealed and under high pressure to prevent the water from boiling into steam.  But the high pressure often caused a hose or a radiator cap to fail.  Releasing the pressure.  And letting the cooling water boil out leaving the engine unsafe to operate.

If this happened on a hot summer’s day and you got a tow to a gas station you may have sat there waiting for them to complete the repairs.  Sipping on a cool bottle of soda from a refrigerated soda machine.  Soon drops of water would condense onto your cold bottle.  The cold bottle cooled the water in gas form (the humidity in the air) and turned it back into a liquid.  So in these examples we see how we were able to use pressure to keep water a liquid.  And how removing heat from water as a gas changed it back into a liquid.  This phase transition of a material has some very useful applications.

The High-Pressure Refrigerant Liquid from the Condenser loses Pressure going through the Expansion Valve

The phase transition between a liquid and a gas are particularly useful.  Because we can move liquids and gases in pipes and tubing.  Which allows us to take advantage of evaporation (going from a liquid to a gas) in one area.  While taking advantage of condensation (going from a gas to a liquid) in another area.  By changing pressure and volume we can absorb heat during evaporation.  And release heat during condensation.  Allowing us to absorb heat inside a building with evaporation.  And release that heat outdoors with condensation.  All we need are a few additional components and we have air conditioning.  An expansion valve.  An evaporator.  A compressor.  A condenser.  A couple of fans.  And some miscellaneous control components.

We install the expansion valve and the evaporator inside our house.  Often installed inside the furnace.  And the compressor and the condenser outside of the house.  We interconnect the indoor and the outdoor units with tubing.  Inside this tubing is a refrigerant.  Which is a substance that transitions from liquid to a gas and back again at relatively low temperatures.  As the refrigerant moves from the evaporator to the condenser it is a gas.  As it moves from the condenser to the evaporator it is a liquid.  The transition between these stages occurs at the evaporator and the condenser.

The refrigerant leaves the condenser as a liquid under high pressure.  As it passes through the expansion valve the pressure drops.  By restricting the flow of the liquid refrigerant.  Think of a faucet at a kitchen sink.  If you open it all the way the water flowing in and the water flowing out are almost equal.  But if we just open the faucet a little we get only a small trickle of water out of the faucet.  And a pressure drop across the valve.  With the full force of city water pressure pushing to get out of the faucet.  And a low pressure trickle coming out of the faucet.

As the Warm Air blows across the Evaporator Coil any Humidity in the Air will condense on the Coil

As the liquid leaves the expansion valve at a lower pressure it enters the evaporator coil.  A fan blows the warm air inside of the house through the evaporator coil.  The heat in this air raises the temperature of the refrigerant.  And because of the lower pressure this heat readily boils the liquid into a gas.  That is, it evaporates.  Absorbing heat from the warm air as it does.  Cooling the air.  Which the fan blows throughout the ductwork of the house.

As the gas leaves the evaporator it travels through a tube to the condenser unit outside.  And enters a compressor.  Where an electric motor spins a crankshaft.  Attached to the crankshaft are two pistons.  As a piston moves down it pulls low pressure gas into the cylinder.  As the piston moves up it compresses this gas into a higher pressure.  As the pressure rises it applies more pressure on the spring holding the discharge valve closed.  When the pressure is great enough it forces open the valve.  And sends the high-pressure gas to the condenser coil.  Where a fan blows air through it lowering the temperature of the high pressure gas enough to return it to a liquid.  As it does it releases heat from the refrigerant into the atmosphere.  Cooling the refrigerant.  As the liquid leaves the condenser it flows to the expansion valve to repeat the cycle.  Over and over again until the temperature inside the house falls below the setting on the thermostat.  Shutting the system down.  Until the temperature rises high enough to turn it back on.  A window air conditioner works the same way.  Only they package all of the components together into one unit.

There is one other liquid in an air conditioning system.  Water.  As the warm air blows across the evaporator coil any humidity in the air will condense on the coil.  Like on a cold bottle of soda on a hot summer day.  As this water condenses on the evaporator coil is eventually drips off into a pan with a drain line.  If the evaporator is in the furnace this line will likely run to a sewer.  If the evaporator is in the attic this line will run to the exterior of the house.  Perhaps draining into a gutter.  If it’s a window unit this line runs to the exterior side of the unit.  These simple components working together give us a cool and dehumidified house to live in.  No matter how hot and humid it gets outside.

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Internal Combustion Engine, Electric Motor, Fuel Economy, Emissions, Electric Range, Parallel Hybrid, Series Hybrid and Plug-In

Posted by PITHOCRATES - September 5th, 2012

Technology 101

We started the First Cars with a Hand Crank and Nearly Broke an Arm if the Hand Crank Kicked Back

The king of car engines is the internal combustion engine (ICE).  We tried other motors such as a steam engine.  But a steam engine is a heat engine.  Meaning it first has to get hot enough to boil water into steam.  Which meant any trip in a car took a little extra time to bring the boiler up to operating temperatures.  Boilers tend to be big and heavy.  And dangerous.  Should something happen and a dangerous level of steam pressure built up they could explode.  Despite those drawbacks, though, a steam engine-powered car took you places.  And as long as there was fuel for the firebox and water for the boiler you could keep driving.

Another engine we tried was the electric motor.  These didn’t have any of the drawbacks of a steam engine.  You didn’t have to wait for a boiler to get to operating temperatures before driving.  Nothing was in danger of exploding.  An electric motor was lighter than a cast-iron boiler.  And an electric motor could make a car zip along.  However, an electric motor requires continuous electricity to operate.  Provided by charged batteries.  Which didn’t last long.  And took hours to recharge.  Giving the electric car limited range.  And little convenience.  For the heavier it was and/or the faster you went the faster you drained those batteries.  Which could be a problem taking the family on vacation.  But they worked well in a forklift on a loading dock.  Because of the battery-power they produced no emissions so they’re safe to use indoors.  They had limited auxiliary systems to run (other than a horn and maybe a light).  And when they were running low on charge you rarely needed to drive more than 20 or 30 feet to a charging station.

The first ICE-powered cars took some manly strength to operate.  They didn’t have power brakes, power steering, automatic transmissions or starters.  We started the first ICE-powered cars with a hand crank.  That took a lot of strength to turn.  And if it backfired while starting the kick of the handle could easily break a wrist or an arm.  Putting a damper on any Sunday afternoon drive.  This limited the spread of the automobile.  They were complex machines that required some strength to operate.  And they could be very dangerous.  Then along came the electric starter.  Which was an electric motor that spun the ICE to life.  Making the car much safer to start.  Expanding the popularity of the automobile.  For there was no longer a good chance that you could break your arm trying to start it.  And through the years came all those accessories making it easier and more comfortable to drive.  Today automatic transmissions, power steering, power brakes, headlights, interior lights, power locks, power windows, powered seats, a fairly decent audio system, heat, air conditioning and more are standard on most cars.  All effortless powered by that internal combustion engine.

Current Battery Technology does not give the All-Electric Car a Great Range

The reason why an ICE can do all of this is because gasoline is a very concentrated energy source.  It doesn’t take a lot of it to go a long way.  And it can accelerate you up a hill.  It even has the energy to pass someone on a hill. It’s a fuel source we can take with us.  A small amount of it stores conveniently and safely in a gas tank slung underneath a car.  And when it’s empty it takes very little time to refill.  A ten minute stop at a gas station and you’re back on the road able to drive another 500 miles or so.  Even in the dark of night with headlights blazing.  While keeping toasty warm in the winter.  Or comfortably cool in the summer.  Things an electric battery just can’t do.  So why would we even want to trade one for the other?  In a word—emissions.

The internal combustion engine pollutes.  The more fuel a car burns the more it pollutes.  So to cut pollution you try to make cars burn less fuel.  You increase the fuel economy.  And you can do that in a couple of ways.  You can cut the weight of the vehicle.  And put in a smaller engine.  Because a smaller engine can power a lighter car.  But a smaller car carries fewer people comfortably.  And can carry less stuff.  A motor cycle gets very good fuel economy but you can’t take the family on a Sunday drive on one.  And you can’t pack up your things on a motorcycle when going off to college.  So the tradeoff between fuel economy and weight has consequences.

An electric car does not pollute.  At all.  (Though the power plant that charges its batteries does pollute.  A lot.)  But current battery technology does not give the all-electric car a great range.  Typically coming in at less than 75 miles per charge.  Which is great if you’re operating a forklift on a loading dock.  But it’s pretty bad if you’re actually driving on a road going someplace.  And hope to return.  The heavier the car is the shorter that driving range.  If you want to use your headlights, heater or air conditioner it’ll be shorter still.  On top of this short range recharging your battery isn’t like stopping at the gas station for 10 minutes.  No.  What one typically does is pray that he or she gets home.  Then plugs in.  And by morning the car would be fully charge for another 75 miles or so of driving.

To Maximize the Benefit of a Hybrid you’d want to Carry the Absolute Minimum of Batteries to Serve your Needs

So all-electric cars are clean but they won’t really take us places.  The ICE-powered car will take us places but it’s not really clean.  Enter the gas/electric hybrid.  Which combines the best of the all-electric car (clean) and the best of the ICE-powered car (range).  There are a few varieties.  The parallel hybrid has both an ICE and an electric motor connected to a transmission that powers the wheels.  The ICE also drives a small generator.  Batteries power the electric motor.  And a gas tank feeds the ICE.  The generator keeps the batteries charged.  The battery powers the electric motor to accelerate the car from a stop.  After a certain speed the small ICE takes over.  When the car needs to accelerate the electric motor assists the ICE.  The small ICE has excellent fuel economy thus reducing emissions.  The electric motor/battery provides the additional horsepower when needed to compensate for an undersized ICE.  And the gasoline-powered engine provides extended range.

In addition to the parallel hybrid there is the series hybrid.  It has the same parts but they are connected differently.  The series hybrid is more like a diesel-electric locomotive.  Gasoline feeds the ICE.  The ICE drives a generator.  The generator charges the batteries and/or drives the electric motor.  The electric motor drives a transmission that spins the wheels.  This car drives on batteries until the charge runs out and then switches over to the ICE.  For short commutes this provides excellent fuel economy.  For longer drives (well over 75 miles or so) it’s more like a standard ICE-powered car with a roundabout way of turning the wheels.

Then there’s the plug-in variety.  In addition to all of the above you can plug your car into a charger to further save on gasoline use and reduce emissions (produced by the car; not by the electric power plant).  Letting you recharge the battery overnight in a standard 120V outlet.  In a slightly shorter time with a 240 volt outlet.  And quicker still in a 480 volt outlet.  If your commute to and from work is 50 miles or less you can probably charge up at home and not have to carry a charger with you (to convert the AC power to the DC power of the batteries).  Saving even more weight.  But if you plan on charging on the road you’ll need to carry a charger with you.  Adding additional weight.  Which will, of course, reduce your battery range.  Also, you can adjust the number of batteries to match your typical daily commute.  The shorter your commute the less charge you need to store.  Which lets you get by on fewer batteries.  Greatly reducing the weight of the car (and extending your battery range).  A gallon of gas weighs about 7 pounds and can take a car 30 miles or more.  You would need about 1,000 pounds of batteries to provide a similar range.  So range doesn’t come cheap.  To maximize the benefit of a hybrid you’d want to carry the absolute minimum of batteries to serve your needs.  Knowing that if you got a new job with a longer commute you could rely on the ICE in your hybrid to get you to work and back home safe again.

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Honda has New Electric Car that gets 118 Miles per Gallon of Gasoline

Posted by PITHOCRATES - June 10th, 2012

Week in Review

Honda is selling an electric car that can get 118 miles per gallon of gasoline.  Even though this car doesn’t consume a drop of gasoline to go those 118 miles (see Honda electric car gets 118 mpg, but costs add up by Jonathan Fahey and Tom Krisher, Associated Press, posted 6/7/2012 on Yahoo! Autos).

At 118 miles per gallon, the Honda Fit electric vehicle is the most fuel-efficient in the United States. But getting that mileage isn’t cheap — and it isn’t always good for the environment…

The electric Fit has an estimated price tag nearly twice as high as the gasoline-powered version. It would take 11 years before a driver makes up the difference and begins saving on fuel…

People drive an average of almost 13,500 miles a year, so a typical driver would spend $445 on electricity for an electric Fit over a year, and $1,552 on gasoline for a regular Fit…

A fully charged Fit EV can go 82 miles, meaning a daily commute could cost nothing for gasoline.

First of all the 118 miles per gallon is meaningless.  An electric car doesn’t go a single mile on gasoline.  So if you divide the miles you’ve driven by the amount of gasoline you used to go those miles you’re dividing by zero.  When you divide anything by zero you get infinity.  But 118 is NOT infinity.  So there is a formula they use to give you a comparable mpg by calculating cost per mile.  But as gasoline prices and driving distances vary this number is a moving number based on some assumptions.  And, in the end, meaningless.

And speaking of driving distances, who has ever leased a car?  I have.  My lease was for 15,000 miles per year, though.  Not 13,500.  And I went over on miles.  About 3,000 miles.  So let’s assume that the average miles people drive per year is 18,000.  If you divide 18,000 miles by 365 (the number of days in a year) you get 49.3 miles per day.  Leaving you a cushion of 32.7 miles (82-49.3).  Unless you’re running the air conditioner (or heater in winter).  If so subtract about 20% from that 82 miles.  Giving you a range of 65.6.  And a cushion of 16.3 miles.  Or less if you’re car pooling (more weight means shorter battery life).   Or if you’re stuck in rush hour traffic with the air conditioning (or heat) on.  Or run an after work errand.

Pretty soon you’ll be worrying about making it back home.  We call this range anxiety.  Also, few people own a car for 11 years.  The two-year lease is a popular lease for the car may remain under the factory warranty for the term of that lease.  But if you buy an electric car and hold it for 11 years to get your investment out of it there’s a chance it will be out of warranty when you’ll need some big ticket repairs.  Such as replacing the batteries.  It’s why a lot of people lease.  They’ll live with a car payment forever just to have a car that is no older than 2 years and will always start when they need it.  And never have to deal with the hassle of taking the car in for service.  Or get a very expensive out or warranty repair bill.

The electric car market is confusing.  Because we understand gasoline-powered cars.  We understand mileage.  How far we can go on a tank of gas.  And know that it takes only a few minutes to top off the tank.  Which feels like forever if you’re in a hurry.  Imagine having to wait an hour or two to recharge.  That will really feel like forever.  But if you never drive more than 20 miles a day and don’t care about cost savings, you can enjoy driving a car without ever having to visit another gas station.  Which wouldn’t be bad for a retiree.  But not very practical for someone who really puts some miles on a car.

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Generator, Current, Voltage, Diesel Electric Locomotive, Traction Motors, Head-End Power, Jet, Refined Petroleum and Plug-in Hybrid

Posted by PITHOCRATES - June 6th, 2012

Technology 101

When the Engineer advances the Throttle to ‘Run 1’ there is a Surge of Current into the Traction Motors

Once when my father suffered a power outage at his home I helped him hook up his backup generator.  This was the first time he used it.  He had sized it to be large enough to run the air conditioner as Mom had health issues and didn’t breathe well in hot and humid weather.  This outage was in the middle of a hot, sweltering summer.  So they were eager to get the air conditioner running again.  Only one problem.  Although the generator was large enough to run the air conditioner, it was not large enough to start it.  The starting in-rush of current was too much for the generator.  The current surged and the voltage dropped as the generator was pushed beyond its operating limit.  Suffice it to say Mom suffered during that power outage.

Getting a diesel-electric locomotive moving is very similar.  The massive diesel engine turns a generator.  When the engineer advances the throttle to ‘Run 1’ (the first notch) there is a surge of current into the traction motors.  And a drop in voltage.  As the current moves through the rotor windings in the traction motors it creates an electrical field that fights with the stator electrical field.  Creating a tremendous amount of torque.  Which slowly begins to turn the wheels.  As the wheels begin to rotate less torque is required and the current decreases and voltage increases.  Then the engineer advances the throttle to ‘Run 2’ and the current to the traction motors increases again.  And the voltage falls again.  Until the train picks up more speed.  Then the current falls and the voltage rises.  And so on until the engineer advances the throttle all the way to ‘Run 8’ and the train is running at speed. 

The actual speed is controlled by the RPMs of the diesel engine and fuel flow to the cylinders. Which is what the engineer is doing by advancing the throttle.  In a passenger train there are additional power needs for the passenger cars.  Heating, cooling, lights, etc.  The locomotive typically provides this Head-End Power (HEP).  The General Electric Genesis Series I locomotive (the aerodynamic locomotive engines on the majority of Amtrak’s trains), for example, has a maximum of 800 kilowatts of HEP available.  But there is a tradeoff in traction power that moves the train towards its destination.  With a full HEP load a 4,250 horsepower rated engine can only produce 2,525 horsepower of traction power.  Or a decrease of about 41% in traction horsepower due to the heating, cooling, lighting, etc., requirements of the passenger cars.  But because passenger cars are so light they can still pull many of them with one engine.  Unlike their freight counterparts.  Where it can take a lashup of three engines or more to move a heavy freight train to its destination.  Without any HEP sapping traction horsepower.

There is so much Energy available in Refined Petroleum that we can carry Small Amounts that take us Great Distances

The largest cost of flying a passenger jet is jet fuel.  That’s why they make planes out of aluminum.  To make them light.  Airbus and Boeing are using ever more composite materials in their latest planes to reduce the weight further still.  New engine designs improve fuel economy.  Advances in engine design allow bigger and more powerful engines.  So 2 engines can do the work it took 4 engines to do a decade or more ago.  Fewer engines mean less weight.  And less fuel.  Making the plane lighter and more fuel efficient.  They measure all cargo and count people to determine the total weight of plane, cargo, passengers and fuel.  So the pilot can calculate the minimum amount of fuel to carry.  For the less fuel they carry the lighter the plane and the more fuel efficient it is.   During times of high fuel costs airlines charge extra for every extra pound you bring aboard.  To either dissuade you from bringing a lot of extra dead weight aboard.  Or to help pay the fuel cost for the extra weight when they can’t dissuade you.

It’s similar with cars.  To meet strict CAFE standards manufacturers have been aggressively trying to reduce the weight of their vehicles.  Using front-wheel drive on cars saved the excess weight of a drive shaft.  Unibody construction removed the heavy frame.  Aerodynamic designs reduced wind resistance.  Use of composite materials instead of metal reduced weight.  Shrinking the size of cars made them lighter.  Controlling the engine by a computer increased engine efficiencies and improved fuel economy.  Everywhere manufacturers can they have reduced the weight of cars and improved the efficiencies of the engine.  While still providing the creature comforts we enjoy in a car.  In particular heating and air conditioning.  All the while driving great distances on a weekend getaway to an amusement park.  Or a drive across the country on a summer vacation.  Or on a winter ski trip.

This is something trains, planes and automobiles share.  The ability to take you great distances in comfort.  And what makes this all possible?  One thing.  Refined petroleum.  There is so much energy available in refined petroleum that we can carry small amounts of it in our trains, planes and automobiles that will take us great distances.  Planes can fly halfway across the planet on one fill-up.  Trains can travel across numerous states on one fill-up.  A car can drive up to 6 hours or more doing 70 MPH on the interstate on one fill-up.  And keep you warm while doing it in the winter.  And cool in the summer.  For the engine cooling system transfers the wasted heat of the internal combustion engine to a heating core inside the passenger compartment to heat the car.  And another belt slung around an engine pulley drives an air conditioner compressor under the hood to cool the passenger compartment.  Thanks to that abundant energy in refined petroleum creating all the power under the hood we need.

The Opportunity Cost of the Plug-in Hybrid is giving up what the Car Originally gave us – Freedom 

And then there’s the plug-in hybrid car.  That shares some things in common with the train, plane and (gasoline-powered) automobile.  Only it doesn’t do anything as well.  Primarily because of the limited range of the battery.  Electric traction motors draw a lot of current.  But a battery’s storage capacity is limited.  Some batteries offer only about 20-30 miles of driving distance on a charge.  Which is great if you use a car for very, very short commutes.  But as few do manufacturers add a backup gasoline engine so the car can go almost as far as a gasoline-powered car.  It probably could go as far if it wasn’t for that heavy battery and generator it was dragging around with it.

This is but one of many tradeoffs required in a plug-in hybrid car.  Most of these cars are tiny to make them as light as possible.  For the lighter the car is the less current it takes to get it moving.  But adding a backup gasoline engine and generator only makes the car heavier.  Thus reducing its electric range.  Making it more like a conventional car for a trip longer than 20-30 miles.  Only one that gets a poorer fuel economy.  Because of the extra weight of the battery and generator.  Manufacturers have even addressed this problem by reducing the range of the car.  If people don’t drive more than 10 miles on a typical trip they don’t need such a large battery.  Which is ideal if you use your car to go no further than you normally walk.  A smaller battery means less weight due to the lesser storage capacity required to travel that lesser range.  Another tradeoff is the heating and cooling of the car.  Without a gasoline engine on all of the time these cars have to use electric heat.  And an electric motor to drive the air conditioner compressor.  (Some heating and cooling systems will operate when the car is plugged in to conserve battery charge for the initial climate adjustment).  So in the heat of summer and the cold of winter you can scratch off another 20% of your electric range (bringing that 20 miles down to 16 miles).  Not as bad as on a passenger locomotive.  But with its large tanks of diesel fuel that train can still take you across the country.

The opportunity cost of the plug-in hybrid is giving up what the car originally gave us.  Freedom.  To get out on the open road just to see where it would take us.  For if you drive a long commute or like to take long trips your hybrid is just going to be using the backup gasoline engine for most of that driving.  While dragging around a lot of excess weight.  To make up for some lost fuel economy some manufacturers use a gasoline engine with high compression.  Unfortunately, high compression engines require the more expensive premium (higher octane) gasoline.  Which costs more at the pump.  There eventually comes the point we should ask ourselves why bother?  Wouldn’t life and driving be so much simpler with a gasoline-powered car?  Get fuel economy with a range of over 300 miles?  Guess it all depends on what’s more important.  Being sensible.  Or showing others that you’re saving the planet.

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