Owning a Geothermal HVAC system

I bought a house in 2012 that had a Water Furnace geothermal system in it.  The system has a geothermal domestic hot water (DHW) heating system integrated in it.  The system was installed when the house was built in 2004.  It uses vertical wells in a closed loop.  A water mixture circulated through the wells in a loop that goes to a heat exchanger in the geothermal HVAC system mounted in the basement.  There is a heat pump that uses this ground loop to transfer heat either to or from the house for heating and cooling respectively.  Heat is also added to the hot water tank when the compressor is running.  The hot water tank is just an electric hot water heat that is not connected to power.  The geothermal system pre-heats this water tank before the water enters the main hot water heater so the main hot water heater has much less heating to do.  Here is a graphic explanation showing the cooling mode:

Here it is in heating mode:

Like all heat pumps, they move heat rather than generating it (for the most part).  The actual heat comes from the ground.  The compressor does have some inefficiency so it does generate some heat as well.  Heat pumps have a coefficient of performance rating which indicates how much energy they move versus how much energy is required to generate the total heat.  In other words, you may spend $1 to get $3 worth of heat.

There are many benefits to a geothermal system.  Of course the energy savings is one.  However, there are many others.  There is no noisy ugly outside HVAC condenser for one.  There never seems to be a good spot for the outside condenser unit in a typical air conditioner.  They also collect leaves and the fans can fail.  The geothermal system has no outside unit so your yard looks nice and you don't have that noisy thing to deal with.

The geothermal system has a large cooling capacity for summer.  Since it is sized for heating, the cooling capacity in many climates is more than is generally needed so it has no trouble at all keeping the house nice and cool all summer. Also, the ground temperature it is exchanging heat to is much cooler than the outside air in the summer so the compressor has much less work to do.

Like all heat pumps, the heat comes at a lower temperature.  Most furnaces put out very hot air for a while then shut OFF.  They wait until the temperature in the house drops then they do it again.  This leads to cycling between too hot and too cold.  The heat pump (geothermal or air exchanger type) run the fan much longer but put out warm but not hot air.  This leads to a more comfortable room temperature and better circulation in the house.

The geothermal system is better than a typical heat pump since it uses ground temperature instead of trying to move heat to and from outside air.  I have owned homes with the traditional heat pump systems.  They work just like a regular air conditioner in the summer.  In the winter though, they have issues.  The outside coils, acting as an evaporator in the winter, condense moisture on them and freeze up.   To defrost the coils the heat pump must reverse and heat the outside coils back up.  This is an energy waste and interrupts heating of the house.  Also, the heat pump is always trying to push heat the hard way as the air temperature become less desirable for this.  For instance, in the summer it has to push heat outside.  As the outside temperature increases it takes more energy to achieve this.  In the winter it is trying to extract heat from outside and as the temperature drops this takes more energy to achieve.  At some temperature, it can't really heat the house anymore and backup heat is used.  This backup heat is usually an electric grid (translation: very expensive to run).  In contrast the geothermal system is always exchanging heat with the ground temperature which is much more stable. Traditional heat pumps work well in very dry climates where the coil freezing issue is much less.

So, how much savings is there.  Below is a chart showing the energy use for my house compared with typical houses in my area.  I got the data from Ameren which provides both electricity and gas for our area.  I converted the gas therms into kWh units for this comparison.

As you can see the energy savings is quite significant.  This is total energy for the house, gas and electric.  However, depending on costs of each, the dollar savings can be much less.  Here is the costs for this same period, again comparing with typical homes similar to mine in the same area.

Right now the costs savings is not that big because electricity costs are high and natural gas costs are very low in this area.  This value proposition changes with varying costs of each.  Back when the house was built in 2004 natural gas was very expensive compared to now.  For those interested in reducing carbon foot print though, the geothermal system always wins.

This comparison is for total energy used in the home and includes all energy use.  We have converted nearly all our lighting to either CFL or LED.  I run a weather station off my main PC so it is always ON and awake.  We have gas for the fireplace and oven/stove only.  Everything else in the house is electric.  Our house was built in 2004 to the standards then and is fairly typical construction. We heat and cool the whole house all the time including the basement.  We keep it about 71F in the winter and 74F in the summer.  This comparison is not between identical homes or use of those homes so there is quite a large margin of error, in the plus or minus 20% range I suspect.

As I mentioned before, my system has geothermal water heating.  There are some drawbacks to this.  In the spring and fall when the system is not needing to heat or cool the house, it also stops producing hot water too since the compressor does not need to run.  Hot water is only produced when the compressor is running.  This just means the main hot water heater has to produce all the hot water so your cost savings goes away.  In the summer the system is very efficient because it dumps heat from the house into the hot water.  You get a double benefit.  Even in the winter though, my geothermal hot water hits over 110F so my hot water heater barely runs at all.  Given the low natural gas prices now in into the near future, I plan to replace my electric hot water heater with a natural gas unit to further reduce my costs.  I can also install some floor heating using the hot water.  In addition, I would like to remove the electric emergency heating grid and replace it with a radiator using hot water.  Right now my system will occasionally use the emergency heat when the temperatures get below single digits (F) which seems to happen all too often here.  I have a high efficiency natural gas fireplace I use during cold ambients to prevent using the emergency heat now.

There are many other types of geothermal systems.  Mine is closed loop as I mentioned.  Open loop systems pump water through them.  For instance, you pump water out of a well, through the heat exchangers in the geothermal system, and then it flows into another well back to the ground.  You can also use a lake or river for the water source.  Each of these systems makes different trade-offs.  The optimum system varies by your area, local laws, ground water levels, drilling costs, climate, and more.

Make sure your installer does the job correctly!  Our house had an issue with galvanic corrosion of copper and brass parts because they did not put dielectric fittings on all connections with the hot water tank.  This actually caused blue coloring on the bath tubs and other fixtures.   It also ate the water tank and several heating elements. Water heaters must have dielectric fitting on all water connections!  This is required because if the different metals used in the house plumbing and water tank.

Damage from galvanic corrosion. This fitting needs a dielectric connector to isolate the water heater from the rest of the plumbing.

Geothermal tank is closest to HVAC system (right).  Valve that is missing the dielectric fitting is at the bottom.

I fixed this when I replaced the water heater.

New tank and fittings with dielectric fitting in place

Another thing people often mess up is the use of the geothermal water tank.  Its important that this tank have a water loop the the geothermal system.  I have heard about system where the installer just put the geothermal inline with the tank intake.  This does not work!  When the geothermal kicks ON, it must circulate water through the tank.  Also, do not heat the geothermal tank (do not power it).  The idea is that you are pre-heating the water before the main water heater.  If you heat it (by connecting the heater to power) you will not get much if any geothermal heating.  The heater will heat the tank up and the geothermal will just turn OFF the water heating function.  Some people do connect the heater to power for use in the spring and fall when the geothermal is not producing much heat.  You can do this if you need more hot water but remember to turn it back OFF in the winter and summer.

Make sure the water lines from the water tank to the geothermal system are well insulated.  If you don't you will get fairly significant heat loss to the room.

Enhancements

Thermostat

I recently installed a modern thermostat on this system.  I used the Honeywell RTH9580WF.  This is a programmable thermostat that supports 2-stage heating and cooling and emergency heat.  One thing you need to consider when setting this up is the heating schedule.  Make you it does not vary much.  I plan to let it drop 2 degrees at night (because it like it cooler at night).  In order to warm it back up in the morning though, you need to bring the temperature back slowly.  No more than about 1 degree per hour.  Attempting a faster rate may engage the emergency heat.   You can create any cooling schedule you want since the system can easily handle even rapid cooling changes and has no emergency cooling mode.

I tried to find a thermostat where I could better control emergency heat but have been unsuccessful.  I have also considered putting an X10 module in-line with the emergency heat wire to block it unless the outdoor temperature is below a threshold, or the inside temperature has dropped below a threshold.  I can do this with data from my weather station system.  I created a .Net plugin that reads the weather station data and can control X10 devices.  I would need to add to that project for this functionality but it would be pretty easy.

Emergency Heat

I would like to replace my emergency heat system.  Today it is just an electric grid.  I would like to start by replacing my main hot water heater with a high efficiency natural gas unit.  It could be either a tank type or tankless.  Then install a simple radiator in the air handler, downstream of the main coils.  Basically, just remove the electric grid and replace it with a radiator (water to air heat exchanger).    Next, connect this radiator to the outlet of the hot water heater with a circulation pump, returning the water to the intake of the geothermal tank.  When emergency heat is needed this pump would turn ON circulating the water through the radiator heating the house.  This water is heated with a combination of geothermal and natural gas which is far cheaper than the electric grid.  A similar loop can be used for radiant floor heat.

With natural gas prices low, and expected to be low for a long time, this could pay off reasonably fast.  It also depends on how big your ground loop is, and how harsh the winters are.  If your ground loop is to the small side, and you have harsh winters, this could really make sense.  It may also make sense if you really want more temperature variation in the winter.  For instance, you like to sleep at 65F but you want 71F in the morning.  

Direct Ground Loop Cooling

Another enhancement I have considered is using the ground loop water directly to cool the air in moderate seasons.  The ground loop water is about 55F .  In the spring and fall when the cooling load is low, the house can likely be cooled without even running the compressor.  Ideally a thermostat with 3 cooling stages would be needed.  The first stage would just run a circulation pump which pumps ground loop water through a radiator in the air handler.  The other 2 stages would be just as they are now.  As the cooling load increases, and the compressor is needed, it will heat the ground loop diminishing the value of this ground loop cooling mode.  It would work well in the spring, especially on days where it is cool at night (possibly even needing some heat) but it gets a bit hot in the house in the afternoon.  When the geothermal runs in heating mode, it cools the ground loop.  

The payback time for this could be long.  It would save cooling costs in the spring and late fall but the savings may not be worth the costs.

Buying and owning a Porsche Cayman S

I sold my Porsche 944S in June 2014 so I could replace it with a newer Porsche.  I started looking for a 996 (or 1999 - 2004 911 for the non-Porsche folks) or Cayman S.  My goal was to find something around $30k, hopefully under.  I don't mind miles as much as age.  The newer the better.  However the colors and features are the most important. I use several sources to find a car.

• Auto Trader.  This is one of the best used car tools there is.  Decent search capability and nearly every new and used dealer, plus private party sellers, use this site.  
• eBay.  While this has auctions, it also has classified and buy-it-now. Many dealer and private parties use this as well.  
• Car Gurus.  Not as good as the others but still useful.
• NADA.  Good to get car pricing info, specs, and more.
• Kelly Blue Book.  Another good pricing website.
• Edmunds.  Good for specs and info mostly.  Also have some listings and pricing info.
• Craigslist. Although this generally has lower priced cars on it.  I was not able to find many Porsches here. You can set up an RSS feed to capture several Claigslist sites.

I also look at local dealer websites.  Since I am always looking for a less common car, searching just the local dealers and classifieds rarely gets the cars I want (although I did find my 944S and XJ12 locally). Instead, I do a radius search.  While there are several good 996's around its hard to get the right set of features and colors.  Porsche's have so many options.  It seems that most German cars are either silver or black for some reason so finding a color I like can be a challenge.  Cayman's are harder to find.  It is the lowest volume car Porsche makes.  There just aren't all that many around.  I have always wanted a mid-engine car though and the Cayman is a fantastic one.  The 996 is also a great car and the prices are very low for what this car is.  When you look at the design where the engine is out the back, behind the rear axle, it seems strange.  However, you must drive one before judging them.  I have driven many, mostly the turbo's, and they are fantastic cars.

My search took months.  I kept expanding my radius.  I drove a 2004 C4S in Chicago but the condition was not so good.  Drove great though.  I drove a Cayman S in Indiana but the color and feature set was just not quite compelling enough.  I had a long email exchange with a guy in Ohio but his car was more than I wanted to pay.  We came close to a deal but never made it happen.  The farther you go the more risky the deal is.  Pictures and video just are not even close to seeing the car in person.  Pictures are 2 dimensional so its hard to tell shadows and reflections from damage.  There is so much you just don't see.  The sellers almost always leave out the important shots.  You don't get pictures under the car, or in the areas where rust could be an issue. I have traveled for hours before only to be greatly disappointed.  I found a few good prospects only to find they sold by the time I contacted the seller.  After months of searching, I finally found what I wanted.  One was in Florida and another in Virginia.  By the time I checked on the Florida car, it was gone.  Realizing I need to act fast or loose it, I called on the Virginia car.  It was at a used car lot in Manassas.  Not exactly the best place to buy a car.  I checked CarFax and found the history.  It was clean but the car had several owners and had been through auctions more than once.  Not good.  Cars are usually sent to auction when the dealership where it was traded in feel it is not good enough for their lot.  There are many reasons a car might not be good enough.  Many new car dealers only carry cars they can certify pre-owned or the car is in exceptional condition.  When you are looking for a $30k Porsche though, you are likely not in the certified pre-owned category anyway.  Those start in the $50k range usually. So, back to the 2006 Cayman S.  It had so many things right with it.  It was Guards red (my favorite) with black interior.  It had a 6-speed manual, Sports Chrono package, heated seats, power memory seats, premium sound, rain sensor wipers, and bi-xenon headlights.  It did not have the navigation system which I did not want. It also had a CD changer which I am sorta neutral on.  I asked the dealer for more detailed photos and videos.  They complied, although they shot them with an iPhone and compressed them for email so the quality was not very good.  It was hard to tell for sure the condition.  I finally just took a chance, bought a on-way plane ticket to Dulles airport (about 15 miles from the dealer), and hoped for the best.

I got to Dulles and took a cab to the dealer.  At this point I was fairly committed to this purchase.  Sure, I could back out, get a cab back to the airport, and hope for a flight home.  As we drove up I saw the car and from the cab, it looked great.  The lot was not much.  A gravel lot with a small building.  No shop.  However, it did have many nice cars.  There was an Audi R8 parked next to the Cayman and there were mostly Mercedes and BMW's.  The salesman came out and greeted me.  We went to the car and he handed me the key.  I hopped in the car and fired it up.  It cranked slowly but started fine.  It sounded good, no noises, smoke, or leaks.  I took off for a drive.  The car felt fantastic.  When I came up to a cloverleaf I took it with a bit of speed.  Cayman's handle fantastic, like no other.  I knew right then I had my ride home.  Acceleration was also great, as was everything else about the drive.  These cars just feel very tight and connected.  I get back to the car lot and noticed that the heated seats did not work.  The key also had a damaged non-functioning remote.  The cosmetic condition of the car was very good though considering its many owners and trips through auction.  I figured I can fix the other stuff.  I also shut the car off and started it up again.  It cranked slow again. I took off the battery cover to find an original Porsche battery.  So, I attempted to negotiate a price drop based on the things I found.   I said the car needed a new battery, the heated seats were inop, and there was only 1 key and it had a bad remote.  The dealer stuck to their price stating they had other buyers lined up.  Sure, this could very well be a lie.  This dealer did not always tell the truth.  They also claimed the battery was new and that Cayman's always crank slow.  I thought it over for a few minutes (which was all I had since the dealer was closing soon).  I finally decided to just go for it.  I paid for the car.

After the deal was done, the dealer was closing as I left.  I hopped in the car and off I went.  I had an 800 mile trip ahead of me.  Just a few miles down the road the "check engine" light came ON.  Oh great I thought.  Knowing how OBD works I figured they had cleared the DTC's just before I got there, likely by disconnecting the battery. 2 trip DTC's take 2 drive cycles to complete.  My road test was the first trip.  My trip home was the 2nd.  I did not feel any drivability issues so I decided it was likely a catalyst or O2 monitor so I could just ignore it for now.  Going back to the shady dealer would be pointless, especially since they were now closed.

The route from Dulles to I70 was not a simple one.  I turned On Google Maps and trusted it to take me the best way.  As it turns out, there was traffic issues on some of the main highways so I ended up on small 2-lane roads going through West Virginia and Maryland.  At one point I was going over a one-lane bridge on Gaston Road in West Virginia.  The road was fantastic!  It seemed like one continuous piece of perfect new asphalt making a tight winding path through the mountains.  The Cayman and I loved it!  I have never owned a car quite like this.  I can't explain it with words, you just need to experience it yourself.  While many cars seem to complain when you push them, the Cayman taunts you for more, almost as if to say "is that all you got".  The level of confidence it inspires is probably dangerous but is absolutely intoxicating and addictive.  I was amazed at the power too.  The Cayman S has a 295HP flat 6.  295HP these days is not that much.  The car is light though, about 2900lbs.  The 6-speed drivetrain is set up to optimize for performance, like all Porsche S cars.  The gears are evenly spaced and 6th gear redline is also the cars max speed of 173mph.  I was never that impressed by the sound of Porsche flat 6 engines actually, until now.  From inside the car you get a different experience. The Cayman has the intake right behind the driver, through the side grille behind the door.   The induction sound is fantastic.  At WOT you can hear the cams change angle as the revs increase until you get this beautiful wail near redline. At idle it does not really make that much sound.  Very different from an old-school American V8.  You really need WOT and high rpm to enjoy the sound of European cars like this Porsche.

Once I got to Ohio, the rest of the drive was on boring flat, 4-lane divided freeways.  We really need autobahn style unlimited zones here in the states.  I stayed the night in Washington Pennsylvania.  I got up early the next day and drove home.

I checked DTC's when I got home to find P0421 which is intended to detect the catalyst not storing oxygen properly.  This is usually caused by a bad catalyst (no longer converting).  I swapped the 2 downstream O2 sensors and confirmed that the issue stayed with the catalyst and not the sensor.  When I modified the exhaust later I also moved the sensor on that back to the muffler (after the 2nd catalyst) and the DTC and light are now fixed.

I tried to program the himelink system for my garage door but I found it too did not work.  Nice.  One more thing wrong with this car.  I searched the web for the heated seat and Homelink issues.  This is always a good first step as most problem have been experienced by someone before.  Knowledge based troubleshooting is how it is done in the real world.  Anyway, sure enough, I found numerous posts on multiple forums for this exact complaint.  It turns out that Porsche have some problems with their body control.  To be honest, the software has a defect where a low battery condition can cause the module to reset to factory defaults and disable several features including heated seats, homelink, and rain sensing wipers function (wiped work but don't respond to rain).  The fix is to have the dealer perform a "hand over" procedure.  This procedure was intended for new cars.  The dealer just has to connect the service tool (a special Porsche tool, not a generic OBD tool) and configure the cars features.  Once this was done, all the features worked.

The key was expensive!  From the dealer, it cost about $400 for the key and remote.  It had to be ordered and then programmed at the dealer.  The new key head has been updated though and it is much nicer than the original.

At this point I had $28,500 into the purchase price plus $70 to get the hand over procedure done, and $400 to get the key and remote, and have it programmed.  Still under $30k and now everything works.  I also changed the spark plugs and oil.  I have been driving the car for months now and it is fantastic. I have put about 5k miles on it since I bought it (800 in the first 2 days).  Every day I drive it, it puts a huge smile on my face.  Strange how a car can do that.  Every other car just feels boring and unrefined now in comparison.  I have never had a car handle so fantastic before.  This design where the weight is all down low and centered in the car is ideal.  There is a very low moment of inertial about the center of the mass so very little effort is require for the car to change direction.  You can feel it right away.  Here is a great article explaining it. The weight is also down low because the engine is a flat 6 and not a typical V or inline configuration. This means the car stays flatter in corners even without over stiff suspension. The force stays on all 4 wheels more than most other cars.  There is never any under-steer.  You can get over-steer by applying heavy throttle in a corner but it is controllable and very fun.  The PSM will keep you in control while still having fun.  In sport mode, you get even more fun.

Cayman S 3.4L engine and trans assembly

Cayman versus 911 Carrera

My car has the smaller wheels and tires on it. These wheels are usually used for winter only.  They are 17" diameter and 30mm narrower than the original wheels.  They had installed new summer tires on them though.  Even with these the car still has good grip.  I look forward to upgrading back to the original size after I wear these tires out.  I figure a few track days will delete most of that tread.  I like the wheel style better than the lobster claw so many of these cars came with though. So far I have only had the car to one autocross.  

Update 2016: Replaced the wheels with 2010 Cayman S 18" and Pilot Super Sport tires.

Engine speed versus vehicle speed in each gear

After I upgraded the wheels and tires

Shot from Garmin Virb Ultra 30 mounted on custom camera bar

Here are some YouTube videos from other owners and reviewers of the Cayman.