Geothermal, wood boiler, radiant floor heating, oh my...

I've been doing some research on the combination of geothermal heating and cooling, outside wood boilers for heat / hot water, and radiant floor heating.

There should be a way to tie all of this stuff together that isn't totally redundant or excessively expensive, but I haven't found anything yet.

Does anyone have experience w/ this combination?

Thanks,
-Slice

Friend has an outdoor wood boiler and he did that work professionally.

He put it into a new house ~10 years ago. He taught me about it and then died.

Hooked to a genny and some more than ordinary stuff for backup in the country since he had access to stuff at low cost.

I don't know what I can tell you, he was very happy with it..

if i was going to do geothermal for HVAC i would get rid of the conventional water heater and go with either a POU(point of use) or a whole house on demand LPG water heater. of course where you live, and me for that fact you would need an add on supplement heat source because once the temp drops to 15*(might be 10*) or so the GT unit alone just wont cut it. for me cost is the big issue. the wife and i are going to be buying a new house(modular) this summer and just cant justify the $20k+ added onto the cost of the house.

A geothermal heat pump will do just fine at 15* and well below. Geothermal means it is exchanging heat with the ground, not the freezing air. If the system is using a shallow horizontal system in a climate that stays very cold for a long winter, there might be some issues due to the ground loop not being far enough away from surface temperatures. If the ground loop is a deep, vertical well, it will work regardless of outside air temperature. If your geothermal heat pump can't handle the cold temperatures vs. a gas furnace, you are dealing with a sizing issue.

The problem is air source heat pumps. They start losing noticeable heating efficiency around 40 or 50 degrees(approximately, different brands/models perform differently), and it gets worse as the temperature drops. You should always use an outside air temperature sensor to turn off your air source heat pump at around 30* or so and use your backup electrical(or other) heat. It will make your compressors last longer and save you money. Again, different brands and models behave differently so the numbers I've mentioned may vary. There are exceptions, such as some of the new commercial variable refrigerant flow mini-split systems from Mitsubishi that continue to heat down to -10 or so at least(according to the sales manager I spoke with).

ETA: If he gets a geothermal heat pump, what you suggested is perfect. Run the hot water through the heat pump, then to the on-demand water heater. Then if you use a well-placed PEX manifold with homeruns to the faucets you get hot water fast throughout the house, and your water heater gets an extra efficiency boost from the "free" heating from the heat pump.

I like what your thinking, and I have a wood boiler with radiant heat in my mud room. Radiant heat is awesome, wish I could have done it in the rest of the house.

A friend of mine with very deep pockets and a really big brain just built a house and had planned on geothermal but in the end decided to go with high efficiency propane as he would never break even on the added cost. He lives on a mountain in NH in a snow belt so he sees cold (other than this year) so it would get a lot of use. I am not sure if it was his building site that added to overall cost or what, but for him he went a different route after all of his analysis.

if you're running an outdoor furnace you will need to maintain enough electricity to run the circulation pumps. other than that you're good to go as long as you have something to burn.

now that we have an excellent heat source covered let's get into how to best use this heat:

radiant heat will be the best form of whole house heat you will find. for starters you don't need any kind of duct work, fans / blowers, air handlers, etc. (you will need that stuff for traditional cold air though) radiant heats everything in the house with what is actually a very low temperature water.

as a way to get more use from this hot water and further save on the energy bill / consumption you can use a combi core hot water heater. it's a hot water heater that has a coil of copper pipe inside. water from the furnace is a sealed system and in this case will make a trip through the water heater before continuing on to the floors. the potable water is heated by the hot water in the copper pipe. as long as you're running the furnace you have hot water for the house. going this way you can still have what looks like a traditional hot water heater, offering the benefit of extra water storage! this method works with electric and gas hot water heaters.



now let's look at making the geothermal work to cool the house:

with a simple valve system you can shut the water off to the furnace and open up the circulation to a geothermal loop. in short you would be circulating the cool water through the radiant system. this has the ability to dramatically lower the temperature in the house at a very low cost. by cooling the structure down from the core it'll make it much easier for the traditional air conditioner to do it's job... if you need it at all.



we installed a system like this in a rather large shop and it worked very well. heating and cooling bills were almost nonexistent.

on another job the customer has a large green house operation on the property and radiant heat in the house. we built a manifold system that would run the water from one of the wells through the house before it went out to water plants. his cooling bill dropped substantially after the retrofit. this isn't a good option for the average home owner as we don't use enough water to make it worth while.




i'll check back in here later....

I would tie the wood boiler in with a high efficiency propane/NG boiler. Primary source of heat is the wood boiler. It supplies hot water to the radiant heat loop and indirectly heats a hot water storage tank. The storage tank could then run water through something like a Navien Combi. If the water temperature is high enough, it won't run. If you exhaust the supply of hot water from the tank and the Navien's input temperature drops it turns on to heat the domestic hot water. If the wood boiler stops supplying hot water to the radiant loop, the Navien turns on to supply the loop. The plus for this setup is that you should be able to run the would boiler or the Navien, plus the pumps and controls on a reasonably sized generator or inverter system.

You could instead use a geothermal heat pump. The heat pump alone should be able to supply all the heating, cooling, and domestic hot water you would need. You could even connect a standard gravity propane/NG water heater in as the storage tank to supply hot water when there is no electricity. To run the heat pump you will probably need a much larger generator.

You could do the geothermal system combined with the wood boiler, but I think the cost of this would be much higher than either of the options above.

Radiant cooling is becoming available. I read about it in industry journals frequently. As long as the water temperature is above the dew point it is supposed to work great, but I don't have enough knowledge about it to suggest anything. There are companies out there that specialize in this stuff. Your best bet is to contact RSES or a similar organization that would be able to refer you to companies that specialize in this particular area. There are a lot of options available, but most companies only do the traditional stuff so the challenge is finding a company that does this specific kind of equipment.

We have 4 real seasons here. Spring is nice, but humid. Fall is nice and dry. Winters can vary, but we've had record lows that I remember in my lifetime < -20*. Summers are hot and humid, w/ 100* days not abnormal. Dew points in the upper 70's or low 80's aren't uncommon June - August.

I know a couple of people at work who have geothermal, and another w/ a wood boiler. They all rave about their solution, but I don't know any of them well enough to invite myself over to see how the stuff works. From what I understand, geothermal saves a lot of $ on cooling, and does OK w/ heating.

Radiant heating sounds awesome from everything I've seen. Radiant cooling scares me a bit because of the potential condensation problems in a high-humidity environment. Ductwork for cooling seems redundant if we have tubes for heating. ugh!

Today we have a small ranch home. We heat w/ a wood stove in the basement, but have a propane furnace as a backup. In the summers we have the choice of either a $250/month electric bill, or cooking ourselves in our little oven.

We're considering building a new place, which will be a little bigger and likely multiple stories. I don't think the iron box stove in the basement will cut it in that environment. If the cooling costs are proportional to the square feet, we're looking at a 35-40% increase, which would be tough to afford.

If my math is correct, an additional $10K on a mortgage @ 3.75% for 20 years is $59/month. We'd be willing to spend the extra $10K if it resulted in > $60+ savings off the energy bill.

Whatever we do, we want to be able to run off a generator, and not have to run the genny 24x7. I think the circulating pumps could be run off a battery/inverter combo.

We have an on demand LPG water heater today, and love it. We'll probably put in another one of those, but if it were pulling water from a tank that was already warmed by wood and/or geothermal, so much the better.

I suppose what we're trying to figure out is an economical way to heat and cool that has some form of ROI in the way of reduced monthly energy costs in trade for a slightly larger up-front capital cost.

Hopefully that ramble makes sense. Please let me know your thoughts.
-Slice

PM me, I can help you out.

Creekrider

If you want the biggest bang for the buck, and a system that will pay off within your lifetime, consider a n air to air heat pump with a hot water coil in the duct work, and use either an outside wood boiler or a stoker fed coal boiler for backup. You can also use the boiler as a hot water source in addition to a propane hot water heater.

Geothermal costs a ;lot to install, and you are screwed if the system gets a leak. Radiant heat works VERY well if it gets cold and stays cold, not so good if you have an occassional mild spell. Radiant does not respond well to rapid temp changes. Installation is also pretty salty, and as mentioned, you need ductwork for AC.

Send me a sketch when you find a floorplan. Oversized cooling systems won't pull the humidity out, and poorly sized duct work will not heat/cool evenly.

Ops

Sounds like geothermal is out if you want to run off a generator. However you could get a split geothermal system and connect it to a high efficiency gas furnace. That way the furnace could be run off a generator or battery bank if necessary. The geothermal system could also use a gravity gas water tank as a storage tank that would double as a back up, no need for electricity, source of hot water.

10k financed for 20 years will probably cost 20k in the end.

I haven't been able to find what kind of electrical load the geo heat pumps draw. That'd be handy if anyone has it. I was thinking we could use a wood boiler vs. a HE gas (propane) furnace for the backup. I wouldn't think the circulation pumps in those draw a lot of juice?

$10K @ 3.75% for 20 yrs is $14229, or $59/month. Anything that saves me more than that is positive cash flow, no?

I'm expecting there to be some significant inflation in energy costs over the next 20+ years. Maybe not for natural gas since we seem to have hit the mother lode here in the US. Unfortunately, the only place w/ NG around here is in town, and we don't want to go there...

Locked rotor amps for some of the air source heat pumps we put in are ~180 amps. Plus fans and pumps.

If you want to be as off the grid independent as possible the wood boiler is best. But you have to think about how long you are going to be able to split wood.

Holy cow! That's a lot of juice!

You're right about wood. I don't want to have to be out splitting when I'm 85. It needs to have a "lazy" option that's relatively efficient.

That is what offspring do, split wood for us geezers.

It looks like there's a fed tax credit of 30% (no max) for installation of geothermal systems thru 2016: http://www.dsireusa.org/incentives/incentive.cfm?Incentive_Code=US37F

One of the examples I saw was for a $26K system, which is mind boggling. Is that really what this stuff costs?

It turns out that IN also offers a property tax incentive for the same thing: http://www.dsireusa.org/incentives/incentive.cfm?Incentive_Code=IN01F&State=federal&currentpageid=1&ee=1&re=1. Unclear how long this will last, or what the expected benefit is, but it warrants further research.

What size heat pumps? Start-up current is one of the things I was worried about, and hadn't checked into yet. I'll likely only need a 2.5-ton unit or so. Now I have to go talk to the parts guys, lol. I'd be wanting the ability to run it off of backup power if possible. Hmmm.

Some of the newer units are using inverter compressors and/or soft start kits that also lower start-up current, I'll have to see how much of a difference it makes.

I think that was for the last 4 ton system we put in. It is still going to be over 100 locked rotor amps. I am not aware of any geothermal systems using an inverter compressor, only the ductless split systems.

I think the estimate my friend got was MUCH higher, 100K plus if I remember correctly.

Like I said, even with deep pockets it was not for him.

That's not what it normally draws though.

Wow, that's crazy. Maybe because they had to drill down through a bunch of rock or something?

I'm sure the folks I know who have it didn't spend $100K on it..

Geothermal heat well at pretty much all temperatures. Air source heat pumps have problems at lower temperatures.

My parents did geothermal, takes a lot of electricity to run it, but no gas bill.


I have radiant, designed for low temperature solar hot water. It's wonderful.

Thinking abt the well water being pulled from one well and returned to the second, if [this isn't rocket scence so it prolly is done this way] water were pumped from one well, run though the water source heatpump and then allowed to return to the return well...

...as long as the water circuit wasn't opened to atmosphere, then the returning water would create a sort of 'siphoning' effect and much of the energy used by the well pump to lift the water would be balanced/cancelled by energy by the returning/falling flow.



That's a very efficient cycle, although, if I were doing it, I'd use a HOJO motor to pump the water and wouldn't even need electricity.

Please elaborate

ETA: color

Slice, the 'evaporator' reference temp is the temp of the well water, not ambient air that can drop to low values, like w/ a conventional heat pump.

Ground water temp is pretty stable around 50F or so.

That's why I suggest to folks who worry abt storing insuline to put it in a deep hole or well.

Even at 8 feet deep when snow is on the gnd, I measure a temp in the mid 40's F in the middle of winter.

This applies to HEATING mode:

Well, even tho the evaporator is supplied with say 50F water, the compressor still has to run to extract heat from the circulating water and dump it in the house via the compressor/condenser.

Depending on how big a house, that's the bill.

Still is a great way to do it.

I checked with the parts guys today, the 2-ton units we have draw 12 amps running @240V and call for a 20amp fuse max. That's with no soft-start setup. Even with slow-blow fuses you aren't looking at any more than 20-30 amps startup current. That means with a soft-start setup the whole thing should easily run off of a 5-6kw portable generator without maxing out the generator.

As for locked rotor amps, I had to ask what that meant. It refers to the draw by the unit when the compressor slugs/locks up. The fuse(s) would blow by then anyway, not sure why you posted that number? The unit would never draw that amount, short of mechanical failure. Also they told me inverter compressors may indeed be on the way but nothing they sell at this point. Except for the ductless mini-splits, of course.

Anything Geothermal won't be cheap or inexpensive. Same goes for wood boilers and in floor heat. You really don't want to go cheap in this area with your most expensive possesion. Using these to heat your house/hot water works. But the pay back period is high.

Having worked in the supply side of this field I'd suggest hiring a heating professional to do the work.

The fuses won't open, but the internal compressor overload will. It may only be in the event of a compressor failure, but the compressor will try to start again when the internal overload closes. I'm not sure what the effect on a generator or inverter would be if it gets repeated 2-3 second bursts of 100 amp draw. Maybe the generator or inverter has a protective device.

Check code in your area. An open loop geothermal system may be a no go. I know you can't do it here any more. With a closed continuous loop the circulator would not have to do much work. It's not pumping, just moving. With an open system you are going to need to add a well pump unless you have a natural spring.

I would only be dealing with a horizontal ground loop, so no need for a pump.

Still looking at the drawings, but here are my thoughts..

You have a couple of triangle shaped boxed in areas that will serve a duct chase up to the second floor. I'd strongly suggest that you have the second floor supply air registers in the ceiling along with a single central return air intake. Hot air rises, and I have fought way too many hot second floor calls that were the fault of a second floor duct design that favored heat over AC.

As far as geothermal, you probably won't live long enough to see the payback. I did one for one of my cousins, he's a builder and was able to borrow a backhoe for a closed loop system. It works well enough but he still needs electric backup when its down around 25* or so.

Have your installer size up an air-to-air heat pump for the cooling load and run ductwork accordingly I'd then install either an outdoor wood furnace or a stoker fired coal burning boiler and a hot water coil in the duct work downstream of the air handling unit. I can come up with an auto control system so that one thermostat will automatically call for the hot water coil with no intervention by you. Don't let your installer talk you out of it!! Many installers are good at ductwork but don't really understand control systems.

I'd install a propane hot water heater and leave it at that. There is no sense to firing a boiler just to heat hot water. Hot floors are nice, but the control system necessary is a friggin nightmare, and it will not work well without an insulated concrete floor. Hot floors also respond VERY slowly to temp changes outside and will leave you with either an overheated or chilly house in the event of wide temp swings outside.

I spent 20 odd years as an HVAC service mechanic, have seen a LOT of butchered up installs, and seen way too many systems that literally cannot be repaired without ripping out walls and ductwork. I have two air to air heat pumps in my house, sized up for cooling, and a hot water coil in the first floor ductwork hooked up to an oil fired boiler. I manually switch mine from heat pump heat cycle, to oil fired heat. My house is an old passive solar design, and if it's sunny outside it more or less heats itself.

In this house, I'd install an air to air heat pump with the air handler in the basement, and as above, with first floor air regeisters in the floor and second floor air registers in the ceiling with appropriate ductwork. Specify insulated stell ductowrk, not that damn ductboard. Ductboard is held together with tape and it WILL blow apart eventually, and usually where you can't get to it to fix it. Have the installer hang a hot water coil(which kinda looks like a car radiator) and hook up to either a wood or coal burning boiler. Dual fuel boilers (oil/coal or propane/coal, or wood/oil etc.) are available but costly. Given that you may want to live in this house until yo die, it may be worth it to install a dual fuel boiler. You may not want to fuck around with a wood burner as you get older, and if you have to buy anything, coal is usually the cheapest BTU that you can get. A stoker fired coal burner with a coal bin in the basement only needs periodic attention to fill the hopper. If you do oil backup also have them install the fuel tank in the basement. Propane seems to be highly effiicentt for small appliances and water heaters but seems to lose that efficiency as the burner gets bigger, and will eat you out of house and home if you try to heat the house with it. IMHO the only time wood heat is worth all the BS that goes with it is if the wood is free. having burned both wood and coal, my vote goes to coal but I am also able to drive 45 minutes to the mine and get it cheaply.

LMK how it goes. your builder is gonna have an installer that he uses and very likely b/c the installer has the cheapest price. I'd tell your builder that you are going to have your own HVAC system done and find someone who will do it as outlined above.

Good luck with the project!

Ops

See Smoklessheat.com for Varmebaronen Indoor boilers. Use radiant floor heat in the bathrooms. Baseboard radiators in the other rooms.

A/C with geothermal requires air ducts or split systems.

Use the boiler to heat when the temp drops really low or you are off grid power.

Varmebaronen makes pellet boilers to work with heat pumps, but your number one method of heating will be geothermal.

Yes, it is expensive. Less so if you stick to room A/C and wood heat.

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