geothermal vs. super-efficient boiler
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Happy Thanksgiving All–
I’m on the verge of renovating my small 1880 Victorian in New York State and I’ll have the possibility of retrofitting it with any heating/hot water system I want, the main goal being conservation of fossil fuel, but also, of course, comfort. I’m sold on radiant floor heating, having installed it in several of my projects, so I’m planning to do that, no matter how the water’s heated.
If money were no object, what would be the most efficient system? We’ve been saving for this for a long time and want to do it right. We’re even going to retrofit the existing walls with Icynene to make it as well insulated as possible and install low-e, argon filled windows. Normally, I’d do an indirect system powered by a Viessmann boiler, maybe put a few solar hot water panels on the roof to augment an already super-efficient system…..but I’ve heard geothermal has come a long way in the past few years…. are those systems really so efficient that I’m not just giving my money to the nuclear plants for their electricity instead of the oil companies for their oil? What is really the most efficient system? anyone know of any studies that have been done?
thanks everyone.
Replies
I'd think heat loss calculations would play a major factor - if your house is Icynened throughout, you're likely not running the heat very much vs a drafty place.
Geothermal is great, (ground source heat pump) but in smaller or superinsulated spaces at some point the dimishing returns argument comes into play. It sounds like you are putting the dollars toward good insulation - a smart beginning.
To get a good picture, you need to figure in size of house, heat loss, cost of running each system, installation costs and any personal biases, over time you'll live there, and make your decision.
I had a geothermal system in my last house and loved it, but my new house is ICF etc, so I don't plan to spend a lot on heat. I honestly didn't do any calculations--other than rough estimates--but the installation cost difference is significant. My personal bias was a factor too - the propane fired radiant is simpler & I can do the work myself.
Welcome to Breaktime.
I'm not sure that there's much controversy about it... If money is no object, geothermal ground source heat pumps are the most efficient means of heating a house. Tthey rob heat from the ground and put it into your house, just as an air conditioner robs heat from your house and puts it into the air (or ground, if you're geothermal). All you do is pay for the cost of moving it from one place to the next.
Standard (air-to-air) heat pumps are also very efficient, but the outdoor units do not do so well when temperatures drop below ~35 to 40°F. Wouldn't recommend air-to-air in New York State.
Comfort is also not a problem with geothermal as I understand it (wishing we had done one last year), since the ground temperature is constant.
Good luck-
>Comfort is also not a problem with geothermal as I understand it (wishing we had done one last year), since the ground temperature is constant.Comfort doesn't really relate to constant ground temp. The constant temp affects the generation of hot/cold water/air, but comfort will be a function of how that is spread throughout the house and how draft-proof the structure is, etc.
What I was getting at r.e. comfort is that people claim that air source heat pumps do not put out very hot air if it is cold outside due to the reduced efficiency. Since the ground temperature is the same all the time that should not come into play with a ground source pump.
"Comfort is also not a problem with geothermal as I understand it"
Good point Lew - we had forced air GSHP, and it was warmer out of the ducts than most heat pumps. I think radiant is still the best, however.
One issue is where to place the coil/compressor/blower. Ours was quiet, but you could still hear the hum...I'd want it in a masonry mechanicals room to stop the noise.
UrbanMyth - let us know what you do and how it works...
Treat every person you meet like you will know them the rest of your life - you just might!
Hi,
If your aim is to minimize consumption of fossil fuels (and greenhouse gases), and your electricity comes from a coal fired power plant, then I don't think there is a lot of difference between an electric geothermal heat pump and an condensing (90% efficient) furnace or boiler.
I realize that most people would say that the geothermal heat pump would burn less fuel, but here is the logic for saying they are about equal:
The heat pump uses electricity and will have a COP of around 3 (that is it has an effective efficiciency of 300%), but the electricity is generated at a coal fired plant with an efficiency of around 30%. So the OVERALL efficency is about (0.3)(3.0) = 0.9 or 90%. This is about the same as for a modern condensing furnace or boiler. It seems to me that, the only real difference is that in one case you burn the fuel at a distant power plant, and in the other you burn it at your house.
If this is faulty logic, I'd like to hear why?
I'd say take the money you save on buying a regular furnace instead of a geothermal heatpump, and use it on either: 1) adding more insulation, or 2) (if you have the site for it) adding solar space heating or solar water heating.
The COP for solar is infinity :-)
Gary
http://www.BuildItSolar.com
Logic seems sound, assuming that coal plants are only 30% efficient. Hard to believe that could be the case.
Hi,"Logic seems sound, assuming that coal plants are only 30% efficient. Hard to believe that could be the case."I searched around a bit, and found numbers ranging from 30% efficient up to 39% efficient -- depending on plant age, size, and location. So, its not quite as bad as I had thought, but pretty close.
There is and additional about 4% lost in transmission, but, to be fair, there is also energy used to transport other fuels like natural gas.Burning coal to produce a given amount of energy produces somewhat more carbon dioxide than buring natural gas to produce the same amount of energy, so coal is worse that way -- its also dirtier in a number of other ways than gas.Gary
http://www.BuildItSolar.com
Gary, Brian, Lew, everyone else thanks. That's exactly the conundrum for me, and you've helped me solve it in my head. Since our goal is really to minimize CO2 and dirt going into the air, not only to save money on monthly bills, it looks like we'll be going with the Viessmann. That was the problem with the GSHP for me, that ultimately you're burning fossil fuel by using electricity anyway, and if it all comes out in the wash ultimately in terms of how much fossil fuel we're using in either scenario, I'd rather go with the one that my plumber can fix. I had some email correspondence with Viessmann a few years ago about their boilers compatibility with Biodiesel, and they basically said that they've had good luck with it but weren't ready to actually endorse it yet--anyone else out there been running their boilers off of biodiesel? that may be subject for a different thread. If we ran it off of biodiesel then we'd be super-low on the emissions/CO2 scale.
thanks everyone. My wife and I truly appreciate your help.
I'd like to look into the biodiesel as well. I am building now and will probably avoid oil b/c of the smell issue in the basement, but if I knew I could (and would) be producing enough biodiesel for the tractors and the house, I'd go there in a heartbeat.
BTW - in some areas electricity is generated w/hydro or nuclear, so that throws a wrench in the calcs.
Treat every person you meet like you will know them the rest of your life - you just might!
you don't necessarily have to produce your own biodiesel. I pay a premium for it but I run my truck, my wife's TDI off of it right now and my mother's boiler is running off of 20% biodiesel, and it all gets delivered. It depends on where you are but you may be able to do the same. You may want to check out http://www.biodieselnow.org before you step into it just to know what you're getting into....
urbanmyth -
We run a dump truck, box truck, and a couple of pickups as well as an excavator, skid loader and farm tractor. I've heard rumors of folks collecting fryer oil and homebrewing for ~$.70/gallon. If we could get the process down, I'd switch every vehicle we own to diesel, and heat my house with it too.
If it could be delivered for less than off road diesel costs, I'd buy the tank tomorrow, but the nearest place I know of is 1 hour away, and last time I checked, prices were higher than petroleum diesel (is that the right term?)
Treat every person you meet like you will know them the rest of your life - you just might!
Brian:To your other question, yes people are running used fryer oil in diesel engines. There was a local high school student that made his own diesel to run in farm equipment for a science project! Check out greasecar.com or type cooking oil diesel into google or another search engine. Basically you can heat the used oil and use it directly in the engine, or process the oil to remove the room temperature solids and then run it in the engine. Then there is soy diesel...Waiting for fuel cells,Frank DuVal
Yeah, biodiesel does cost a fair amount more than petro diesel, but look at it this way. Kids aren't dying over your ability to drive you vehicle and the biodiesel is much better for your engine (as long as you don't drive when it's under 30 degrees). I just budget it as $3/gallon and pretend that's what gas prices are (because they'll be there soon enough anyway).
Michael
A 30% efficient electric plant is a non-issue to a home owner. The power plant pumps out "X" number of megawatts whether you use it or not. They still feed it to the grid.
Whereas with propane or ng, it isn't getting burned until you fire up your furnace, so by switching on the gas furnace, you're adding to burning fossil fuels whereas when switching on geothermal, you're just using the energy already created and sitting out there.
The only way you can make your argument is on a larger scale... say a whole community switches to geothermal or propane...at which point they are influencing demand and the output the electric company is feeding to the grid. But from the perspective of a single ho, it is a non-issue.jt8
"Do not let what you cannot do interfere with what you can do."-- John R. Wooden
Hi,"A 30% efficient electric plant is a non-issue to a home owner. The power plant pumps out "X" number of megawatts whether you use it or not. They still feed it to the grid."Electric power plants constantly adjust their output to match the load. If you don't use it they don't generate it.Gary
http://www.BuildItSolar.com
Electric power plants constantly adjust their output to match the load. If you don't use it they don't generate it.
That applies to whole areas, not to individual houses. Whether I use 5kw today or 100kw, the power company is not going to change their output unless all my neighbors increase as well. If they notice demand is increasing, they might fire up another turbine, but otherwise they're just going to pump out "X" megawatts per day.
They probably have charts of typically usage on a given day of the year for a given external temp and just make sure they produce more than that amount.
jt8
"Do not let what you cannot do interfere with what you can do."-- John R. Wooden
John:
In response to:"Electric power plants constantly adjust their output to match the load. If you don't use it they don't generate it."you said:"That applies to whole areas, not to individual houses. Whether I use 5kw today or 100kw, the power company is not going to change their output unless all my neighbors increase as well. If they notice demand is increasing, they might fire up another turbine, but otherwise they're just going to pump out "X" megawatts per day." Perhaps you missed something in science class about energy, or even how little home use generators work, or even alternators on cars....If you produce electric energy by converting another form of energy, say coal, nuclear, etc. ( and remember energy is neither created nor destroyed, just changed in form) the energy must be used or stored. The grid does not store energy, it transports it to where it will be used. If there are no users of the energy, it cannot be forced down a wire. Ohms law still applies. The grid is the wire part of a complete circuit. If you use 5kw less energy, the power plants connected to the grid converted 5kw less energy! Example: If you have a home generator for emergencies, it will produce rated KW only when there is that much load connected. The engine will consume less gasoline with less load connected. Less demand=less energy converted. Example: The alternator in my car is rated at 100 amps. It will only produce 100 amps when all the accesories are on and the battery is low on charge. It is sized for worst case, the need to power all accesories and replace the battery charge so it will start next time. Most of the time it is producing way less than 100 amps.Remember, no one repealed ohms law. Power(watts)=Volts x Amps. If you have no load, you have no amps, there is no power being used. Just because a power plant is connected to the grid does not mean it is running wide open, it can only supply the demand of the present time.Frank DuVal
Frank - So what happens when I run my generator w/ no load - where does the power go? (I know I use less diesel w/no load, but I've always wondered - and I'm running it all day most workdays)
I wish there were a quiet, portable way to carry stored electricity w/enough power to run tools - my generator is loud. Plus I wouldn't have to pay the power company to run wires down my lane. Fuel cells? Mr fusion?
Treat every person you meet like you will know them the rest of your life - you just might!
Brian:When the generator is running no load, the engine ( gasoline or diesel ) is producing enough power to spin the crankshaft and armature of the generator at 3600 rpm (two pole generator, 1800 rpm for 4 pole generator) to keep the output AC at 60 Hz. The energy of the fuel burned is equal to the losses of energy through heat output (air cooling of motor and windings ) and windage losses which is the resistance of the crankshaft and armature to move through the air. There is also some electrical energy used to keep the circuitry running, but again this results in heat output. If you have the idle down economy switch you save a lot of fuel because the engine idles down between uses, so the windage and heat losses are less. Just like your car sitting at a traffic light, the major energy output is heat, not movement. Fuel is consumed (converted to heat) but not as much as driving at 60 mph. Law of conservation of energy. Frank DuVal
Frank,
sounds like you're pretty knowledgable about generators. Can you answer this question? If you use the auto power down mode on the generator are you hurting the power tools with the startup when you first pull the trigger? we've had this discussion on the jobsite before with no answer.
Bish
Bish:I think it depends on the tool. If the inrush current (startup current) is close to generator capacity, then maybe a problem, such as large compressors. I would try the economy mode and keep a listen for motors that are starting too slow. If it is just a second or two, the extra heating effect of a slow start up should not matter. With saws one can always double trigger to get the generator to spin up with the first pull and then trigger the saw to run full speed. There can also be a point with multiple users where the generator does not stay in idle mode very long, so it may as well be turned off. I'm sure there is no "correct" answer for all cases, and many opinions can be found. Hey equipment dealers, have any opinions based on job site reports of damaged generators or tools?Frank DuVal
From the design point that is pretty much right on. Size of the generator leads quickly to point a of diminshing return. ie. the bigger the generator the less your getting out of that power down mode. Causes a lot of stress to spin up and spin down for some that it bigger.
Finally something I know a little bit about. I lurk looking for carpentry tips but am really a mechanical engineer.
A coal fired plant hitting 39% is very good. The 30% qoute is pretty good as a rule of thumb.
The temperature of the ambient air can swing that up or down a couple of percent. I have read their is a couple of plants that can some times get their effeciencies up into the 40s if things work just right. They mostly use what is called fluidized bed reactors (pulverize the coal into dust, mix it with hot air and ignite).
One of the biggest things is the quality of the coal. Has a huge effect on effeciency.
People kind of freak out when they hear our coal plants are only 30 something percent effecient. What you have to keep in mind is that the US has massive coal reserves. One of the few natural resources where we are one fo the world leaders.
BTW your car/truck engine is not much better.
Hi,
Good to have that confirmed.
The other point that seemed to be in question is whether the generators at the coal power plants react to changes in load. That is, if the power demand goes down a bit, do the generators automatically reduce their power a little bit. Seems to me they would have to, else where would the extra power go?The thing that concerns me about coal is the carbon dioxide emissions. One scenario that is really bothersome is that as oil and gas go up, more people will heat space and water with electricity. It seems to me that this will result in a net increase in carbon dioxide emissions, in that you are replacing 80 and 90% efficient gas/oil water heaters and furnaces with 30 to 40% efficient electricity generation, and getting a corresponding increase in greenhouse gases.The scale of the whole thing is mind boggling. I read that 65 loaded coal unit trains leave the Powder River coal mining area in Wyoming every day bound for power plants all over the country. Each train is 130 cars, 5 engines, and carries 19,000 TONS of coal -- the heavist trains on the rails. One large power plant can consume an entire unit train of coal in 8 hours -- addeding another 50,000 tons of carbon dioxide into the air. It seems a bit out of control to me.Gary
http://www.BuildItSolar.com
Gary- that's the thing that gets my wife and I about biodiesel (not to sound too much like a broken record)--this may be completely wrong, but we figure that the carbon molecules being released during the combustion of biodiesel were molecules that that plant breathed in from the atmosphere anyway---thus it's truly a renewable fuel, it's not reintroducing carbon from a million years ago to the atmosphere.
Hi,"we figure that the carbon molecules being released during the combustion of biodiesel were molecules that that plant breathed in from the atmosphere anyway---thus it's truly a renewable fuel, it's not reintroducing carbon from ####million years ago to the atmosphere."Yes -- I believe thats true. And, I guess it works for wood burners and corn burners as well. Gary
http://www.BuildItSolar.com
They do match output to demand as best as possible. There are some big issues with spinning up and down turbines so they try to do it as little as possible.
There are some pretty unique solutions so keep a constant load on the pland but "store" energy. One that is used here in Virginia is that during the night when load goes way down they pump water into a resevoir on top of hill. then during the day they flow the water down the hill thru a hydroelectric setup to handle the daytime peak load. It is a really simple solution to a complex problem.
Solar is really coming along. there are a lot of promising technologies out there to break out of the petrochemical reliance. GM has just built a prototpye fuel cell pickup for the Army where the only emissions are water and oxygen. Pretty amazing. Admittedly you won't see one on the lot real soon.
When you account for everything 30% for plants over 20 years old, is optomistic. 20% might be more realistic.
Happy Thanksgiving, I was going to use a GHSP system with air, not radiant (all hardwood floors, dont want the hassles) well went 900' at 1 Qt/Min, had it fracked the well went up to 1.5Ga/Min. I was planning on doing a pump and dump (open loop) GSHP. When I didn't hit the GPM I needed I went and talked to a very knowledgeable HVAC Contractor who has convinced me to go with an LP fired, Viesmann variable BTU output condensing furnace.
After talking to him and doing some more research I found out a couple of things about the GHSP system that my well driller never told me, like depending upon water quality an open loop system could corrode the exchanger and a closed loop sysem loses efficiency over time as the ground temperature adjusts to the return loop. Getting service for the unit also was also factor, who do I call when it breaks, the well driller?
The HVAC Contractor is a friend of mine and he is passing along the equipment at cost, I pay the invoice right to the supply house, so that was a major deciding factor also.
>a closed loop sysem loses efficiency over time as the ground temperature adjusts to the return loopCertainly not if you run heat in winter and ac in summer. Balances out. We've measured at beginning of season vs end of season, and the temp diff is so little as to be insignificant. In fact, it was so small that installer concluded that there must be some underground streams helping to level the temps.
Please check out this site: http://www.nordicghp.com/mg/pumps/dx_series.htm
This is a Canadian company that ships world wide. The DX series doesnt use water but small drill holes as the heat exchanger source.
Very good equiptment.
If fossil fuels are an issue, why not alternative fuels?
http://www.grainstovesinc.com/products.php
I just finished our project, which was re-birthing a 132-year old Victorian near Boston. We insulated the walls as best we could, within the straightjackets imposed by historical considerations. Corbond or eqv. closed-cell polyurethane foams are ideal for older, thinner walls, along with someone who can refinish/remanufacture your old window sashes and frames to their original fit and finish. Then top those with Harvey Tru-Channel or eqv. storms and you have a weathertight and relatively energy-efficient wall/window structure.
Foam the roof, forget about vents, make the whole shell as impermeable as possible, then add a HRV and a heating systems to suit. The more you insulate, the smaller and less obtrusive the heating/cooling system can become. This is a real issue in older homes where there are no wet-walls, shafts, or other means of getting utilities from the basement up and back. We ended up with RFH and an oil boiler that is fed B5. Gas is very expensive up here and I prefer the service that the oil companies provide.
Depending on who generates the power and with what fuel source, GSHP's can make a lot of sense. In my neck of the woods, the potential savings are so low compared to the insane cost of getting the loops installed that I sent with two regular condenser/AH combos for cooling that are achieving comfort at less than 1ton of capacity per 1000 sq ft.
Edited 11/27/2005 3:23 pm ET by Constantin
Hey Constanin--
did you retofit the corbondl, ie blow it in? or did you take the plaster and lathe off the walls? I wanted to blow in the icynene without ripping out the plaster but I've heard different stories about the success of that procedure. I'm with you on the no vent thing, especially if you live where there's driving snow and rain...
Due to the severity of our job, we gutted the whole place. Thus, retrofitting a closed-cell foam was not as difficult as it would be if we were retrofitting it into a closed cavity. It can be done, by the likes of Foam-Tech, but the numbers of contractors who are willing to risk busted plaster is low indeed. Pouring/spraying a low-density foam is safer, though any closed-cavity application benefits from a check with a thermal camera to ensure that all the cavities have been filled. This is particularly true in homes with bracing and other elements that do not run paralell to the rest of the studs. For example, our baloon-frame had braces running into each corner, and we also discovered a whole lot of empty cavity behind the baseboard on the stairs, for example.An IR camera on a cold day is a very good friend indeed. Perhaps you can borrow one from the FD or have a pro come out and show you where the issues are... Good luck.