Re-thinking geothermal

[ametcalf]

An interesting thread that I would like to add my two cents to. We built a high performance home with geothermal in 2008. Before and while we were building I went to the same seminar 5 times and learned more every time I went. I will try to compress a 3 hour seminar into a few paragraphs.
This thread has focused almost entirely on the heating system but you have to consider the whole house as a system and all the components of that system have to work together. From reading your posts I believe you did a great job of building your house to make it efficient. But things have changed since 1992. The first thing I would do before I even started thinking about what type of HVAC is to run a blower door test on the house and tighten it up. Last winter I spent a couple of weeks tightening up the house we moved from when we built our new house. It is a hundred years old and not as well constructed as your house but by using great stuff foam in every crack and opening I could find, putting foam plates behind the outlets and switches and other measures we cut the heating bills about in half and made the house more comfortable. Wish I had done it 30 years ago when we bought the place. What the blower door test on that house told us was that we had more air leaks from outlets on inside walls than the outside walls. When I went to the attic and pulled back the 12+ inches of fiberglass I saw where the air was coming from. The holes where plumbing and electrical penetrations were made were allowing a free flow of air every time the wind blew. After tightening up the house the next step I would take would be to get someone to run a GOOD J-manual calculation on what your heating needs really are. The reason I emphasis GOOD is that we had 2 contractors bid on the geo thermal on new house. One calculated that we needed a 4 ton unit and the other calculated we needed a 2.5 ton unit. The first guy obviously kept hitting the default button on his computer. The second company actually came and measured the windows, checked the type construction, (sips), looked at the north south orientation of the house, etc. They calculated that we needed a 2.5 ton unit but they installed a 3 ton unit because they said they just couldn't bring themselves to install 2.5 tons in a house this size. They didn't know how tight the house was going to be when we got done. As it worked out 2.5 tons would have been better. In fact, after living through 2 winters in this house I think a 2 ton unit would have been fine as we never go off stage one in a three stage system. The fact that your oil furnace is only running 12 to 15 min per hour in sub zero weather tells me that your present system is oversized. An oversized system is less efficient than a properly sized one. An analogy would be a car that races from stop light to stop light and waits for the next green light as opposed to a car traveling at the right speed to stay in sync with the traffic lights.
Our geo thermal uses 3-200 wells. Wells are relatively cheap here because we are sitting on solid limestone so they don't have to put casings in the wells. We are heating and cooling our 3000+ square feet for about 83 cents a day.
I hate to make this post any longer, if you are interested pm me and I will send you my phone number and I will be glad to talk to you.
ametcalf

 

[Rob-D]

If it wasn't for everything else being affected by the oil price, I'd agree with the sentiment.

Sean

Sean,
I agree, that's why I said "almost".

 

[Rob-D]

An interesting thread that I would like to add my two cents to. We built a high performance home with geothermal in 2008. Before and while we were building I went to the same seminar 5 times and learned more every time I went. I will try to compress a 3 hour seminar into a few paragraphs.
This thread has focused almost entirely on the heating system but you have to consider the whole house as a system and all the components of that system have to work together. From reading your posts I believe you did a great job of building your house to make it efficient. But things have changed since 1992. The first thing I would do before I even started thinking about what type of HVAC is to run a blower door test on the house and tighten it up. Last winter I spent a couple of weeks tightening up the house we moved from when we built our new house. It is a hundred years old and not as well constructed as your house but by using great stuff foam in every crack and opening I could find, putting foam plates behind the outlets and switches and other measures we cut the heating bills about in half and made the house more comfortable. Wish I had done it 30 years ago when we bought the place. What the blower door test on that house told us was that we had more air leaks from outlets on inside walls than the outside walls. When I went to the attic and pulled back the 12+ inches of fiberglass I saw where the air was coming from. The holes where plumbing and electrical penetrations were made were allowing a free flow of air every time the wind blew. After tightening up the house the next step I would take would be to get someone to run a GOOD J-manual calculation on what your heating needs really are. The reason I emphasis GOOD is that we had 2 contractors bid on the geo thermal on new house. One calculated that we needed a 4 ton unit and the other calculated we needed a 2.5 ton unit. The first guy obviously kept hitting the default button on his computer. The second company actually came and measured the windows, checked the type construction, (sips), looked at the north south orientation of the house, etc. They calculated that we needed a 2.5 ton unit but they installed a 3 ton unit because they said they just couldn't bring themselves to install 2.5 tons in a house this size. They didn't know how tight the house was going to be when we got done. As it worked out 2.5 tons would have been better. In fact, after living through 2 winters in this house I think a 2 ton unit would have been fine as we never go off stage one in a three stage system. The fact that your oil furnace is only running 12 to 15 min per hour in sub zero weather tells me that your present system is oversized. An oversized system is less efficient than a properly sized one. An analogy would be a car that races from stop light to stop light and waits for the next green light as opposed to a car traveling at the right speed to stay in sync with the traffic lights.
Our geo thermal uses 3-200 wells. Wells are relatively cheap here because we are sitting on solid limestone so they don't have to put casings in the wells. We are heating and cooling our 3000+ square feet for about 83 cents a day.
I hate to make this post any longer, if you are interested pm me and I will send you my phone number and I will be glad to talk to you.
ametcalf

Nice house!
Thanks for the input too.
This house is so tight that I have to open the front door sometimes to get the Tulikivi fireplace to vent properly. In fact it's mouse proof. The ceiling in the great room is over r55 and the walls are little low at r22.5 or so. The outside of the basement concrete walls are insulated also so it doesn't take much to get this place hot. The oil fired furnace I'm now using is about the smallest I could get to run the place efficiently. I know what you're saying when I called a plumbing firm to give me an estimate for a boiler they came in twice the size of the one I installed!
I'll send you a PM and perhaps we can chat a bit, thanks for your help,
Rob

 

[Rob-D]

When we build our house there was not water in the pond to speak off. The coils were about half above the ice. I measured the water temperature in the inlet of the HP to be about 26F. Nevertheless the heat was working fine whole winter. The pond water temperature is not the whole story. The pipes between the pond and the house will also extract some heat from the ground.

Ladia,
That's interesting, how far is the pond from the house and how deep are the lines from the pond?
Rob

 

[SpringHollow]

If it is that tight, it is not safe to run a combustion device, etc. You need to install an air exchanger.

Ken

 

[Kyle_in_Tex]

I've only lightly perused this thread and it got me to thinking (dangerous thing eh?). At what point in $$$ does it make sense to go to solar PV panels and forego a geothermal? It would seem a large enough solar grid tied into the main grid where the meter turns backward when consumption is low might be an answer. As the costs of PV comes down, it looks better and better. I'm not knocking the geothermal as it makes sense for some who's costs of installation are not that high.

Here in the south, our summer power needs are greater than our winter needs, mainly due to duration of season and not temp differentials. IE, my summer bills stay high for 4-5 months and my winter bills are usually high for about 2 months.

Here is a neat solar calculator link I've discovered.

Kyocera | Solar Energy Products | Products | Tech Support | Kyocera Solar PV Calculator

I will look for a solar panel re visited thread.

 

[Chilly807]

I think solar won't generate enough heat during the winter months at our latitude, when you need it the most it works the worst. I.e. short daylight hours and frigid temperatures.

If you had a big enough solar grid it would do the job, but I have no idea what it would take. No one here is doing that, to the best of my knowledge, so it's most likely cost prohibitive.

Sean

 

[DAY]

Last winter I spent a couple of weeks tightening up the house we moved from when we built our new house. It is a hundred years old and not as well constructed as your house but by using great stuff foam in every crack and opening I could find, putting foam plates behind the outlets and switches and other measures we cut the heating bills about in half and made the house more comfortable. f

Hundred year old houses (mine was built in 1781!) are not a health problem when "tightened up", but new construction can be. Reason: All the synthetic building materials, from vinyl siding to carpets, will outgas nasty stuff (like formaldehyde) for years.
Anyone recall the horror stories a couple of years ago, about Chinese drywall? Or radon? In this area (eastern PA) it comes up from underground, and in a tight house has no where to escape. It was discovered by a worker at the Limerick power plant, who set off a radiation detector on his way INTO work!
Cracking that front door proves that the house is tight- but carbon monoxide will get you if that stove can't get outside air!

As was said above, the whole picture needs to be taken into account when planning an energy efficient house. Even Jimmy Carter's advice to turn down the thermostat, and put on a sweater:laughing:

 

[ametcalf]

Hundred year old houses (mine was built in 1781!) are not a health problem when "tightened up", but new construction can be. Reason: All the synthetic building materials, from vinyl siding to carpets, will outgas nasty stuff (like formaldehyde) for years.

You are exactly right. Our heat recovery unit runs when our heat pump runs. In the spring and fall when the heat pump is not running if we don't open the windows I wake up with a headache. We have very little carpet, lo VOC paint, and Ikea cabinets which I think have about half the formaldehyde of some American built cabinets. We were aware of the dangers of building a tight house so we tried to select products that would minimize the off gasing problem and we have no combustion appliances in the house. We still need to make sure that we are getting outside air into the house.

 

[tractordog]

ametcalf

Thanks nice right up.

 

[Chilly807]

I don't know what the building codes specify in the US, but in Canada all new housing MUST have an air exchange system, most have taken it one step further and use one that has heat recovery as well.

It does make quite a difference, the house is never stale smelling, and stays remarkably cool and fresh in summer.

Sean

 

[eepete]

I think solar won't generate enough heat during the winter months at our latitude, when you need it the most it works the worst. I.e. short daylight hours and frigid temperatures.

Sean

Well, you're absolutely right on the short daylight hours. I see a big difference in the KWH output in January vs. June.

As for the frigid temperatures, the PV panels actually are more efficient when they are cold. My 7.7KW array had a peak output of 9200 watts the other day. A cold front came through, it was about 60 degrees out and very windy (so the wind cooled the panels), we were near the Zenith, and the humidity was very low.
A typical voltage change is about .08 volts per degree C, another manufactures says it is -.38 percent per degree C. And the resistance of the interconnect wire goes down as it gets cold.

Today, temps were about 68 degrees but the humidity was way up and we had little wind, and the peak output was only 8000 watts.

Regarding too tight houses, we noticed more odors when we moved into our house. We probably need the exchange, oh good another project :laughing:. One thing we did that helped was put a UV light in a duct that feeds the master bedrooms. The bulbs had a catalyst of some sort on them that supposedly gets rid of lots of VOCs. The UV lights do that on their own too. The "cat box smell" went down since uric acid (C5H4N4O3) is a VOC. The little bits of black mold at the bottoms of some windows where condensation accumulates in the winter was greatly reduced, some windows it just went away. We're trying to decide if we want to add them to the main part of the house too. It's hard to find a good place to put them where the UV won't damage the ducts and HVAC equipment.

Pete

 

[grsthegreat]

i can see that most of you like your geothermal systems.......my experience here in north Idaho have been mixed.

It must be the way they install it here, cause all 3 people that have had it installed that i have had contact with arnt happy with the systems.

The reason i have been involved is im there wiring in an electric water heater or boiler to supplement their winter heat.

There FREEZING. Maybe our subsurface temps are too cold????

 

[Chilly807]

i can see that most of you like your geothermal systems.......my experience here in north Idaho have been mixed.

It must be the way they install it here, cause all 3 people that have had it installed that i have had contact with arnt happy with the systems.

The reason i have been involved is im there wiring in an electric water heater or boiler to supplement their winter heat.

There FREEZING. Maybe our subsurface temps are too cold????

Proper design is a must if it's going to work right, and retrofits aren't easy to make work in some cases.

For example, hot water baseboard heaters don't work well with geothermal, simply because the water doesn't get hot enough. My hottest water temp at -20 C outside temp is just under 100 F. That's not hot enough for baseboard heaters to keep the house warm. It is hot enough for infloor piping, though.

If you already have infloor piping for radiant heat, what is the spacing? Mine is every 6", not 12" as is common with higher temp systems. We discussed it with the installers at the time we built the house, they were undecided if 12" spacing was going to be enough, so erred on the side of caution and went with 6" throughout, with the garage floor being the exception. It has 12" spacing, and is harder to keep warm. Mind you, it also has a 7x10 steel garage door with an R value of around 12, so that's a source of heat loss to begin with.

In my personal opinion, geothermal is a much better option for new construction than retro-fit, the cost is more reasonable since you're comparing the complete package price instead of simply adding a different thermal source. It'll never compare well with an oil furnace for initial cost.

Our costs were about $5000 more than anything else that was even vaguely energy efficient, for the whole project.

If I had to guess, I'd say there was a miscalculation when those systems you mentioned were designed, either in the size of the system, or in the application of the heat generated. Possibly in the heat loss numbers for the house.

We had three estimates, one was for a 5 ton system, the one we went with was a 3 ton. The 3 ton does a good job, so the 5 would have been overkill.

This is relatively new to most installers, I expect the knowledge base will get better with time and experience.

Sean

 

[Redneck in training]

Ladia,
That's interesting, how far is the pond from the house and how deep are the lines from the pond?
Rob

The lines are about 6 to 7 ft deep and about 200 ft from the house. My observation is that there is no point to obsess about few degrees of temperature. The overall heat gain will not change that much with greater temperature rise.

 

[Redneck in training]

i can see that most of you like your geothermal systems.......my experience here in north Idaho have been mixed.

It must be the way they install it here, cause all 3 people that have had it installed that i have had contact with arnt happy with the systems.

The reason i have been involved is im there wiring in an electric water heater or boiler to supplement their winter heat.

There FREEZING. Maybe our subsurface temps are too cold????

The heat accumulatoir in my system is also the water heater. The heater elements are wired in parallel for about 9 kW. I consider it as back up when the HP goes bad. I turned the breaker off from day one and never turned it back on.

 

[Rob-D]

Well, you're absolutely right on the short daylight hours. I see a big difference in the KWH output in January vs. June.

As for the frigid temperatures, the PV panels actually are more efficient when they are cold. My 7.7KW array had a peak output of 9200 watts the other day. A cold front came through, it was about 60 degrees out and very windy (so the wind cooled the panels), we were near the Zenith, and the humidity was very low.
A typical voltage change is about .08 volts per degree C, another manufactures says it is -.38 percent per degree C. And the resistance of the interconnect wire goes down as it gets cold.

Today, temps were about 68 degrees but the humidity was way up and we had little wind, and the peak output was only 8000 watts.

Regarding too tight houses, we noticed more odors when we moved into our house. We probably need the exchange, oh good another project :laughing:. One thing we did that helped was put a UV light in a duct that feeds the master bedrooms. The bulbs had a catalyst of some sort on them that supposedly gets rid of lots of VOCs. The UV lights do that on their own too. The "cat box smell" went down since uric acid (C5H4N4O3) is a VOC. The little bits of black mold at the bottoms of some windows where condensation accumulates in the winter was greatly reduced, some windows it just went away. We're trying to decide if we want to add them to the main part of the house too. It's hard to find a good place to put them where the UV won't damage the ducts and HVAC equipment.

Pete

Pete,
I have UV for my water purification system. The bulb lasts a lot longer than the year they specify it for but I'm waiting for LEDs to be designed that run the right spectrum, so far, no good. We're using a Berkey system now after the water filters. If any of you are interested in a simple solution to pure water yuo should investigate these. They use them in disaster areas around the world. Low tek but super good, we're finicky about our water.
I like the idea about the bulbs in your system, I'm thinking you guys are right and an exchanger is something I should definitely investigate.

Rob

 

[Rob-D]

Proper design is a must if it's going to work right, and retrofits aren't easy to make work in some cases.

For example, hot water baseboard heaters don't work well with geothermal, simply because the water doesn't get hot enough. My hottest water temp at -20 C outside temp is just under 100 F. That's not hot enough for baseboard heaters to keep the house warm. It is hot enough for infloor piping, though.

If you already have infloor piping for radiant heat, what is the spacing? Mine is every 6", not 12" as is common with higher temp systems. We discussed it with the installers at the time we built the house, they were undecided if 12" spacing was going to be enough, so erred on the side of caution and went with 6" throughout, with the garage floor being the exception. It has 12" spacing, and is harder to keep warm. Mind you, it also has a 7x10 steel garage door with an R value of around 12, so that's a source of heat loss to begin with.

In my personal opinion, geothermal is a much better option for new construction than retro-fit, the cost is more reasonable since you're comparing the complete package price instead of simply adding a different thermal source. It'll never compare well with an oil furnace for initial cost.

Our costs were about $5000 more than anything else that was even vaguely energy efficient, for the whole project.

If I had to guess, I'd say there was a miscalculation when those systems you mentioned were designed, either in the size of the system, or in the application of the heat generated. Possibly in the heat loss numbers for the house.

We had three estimates, one was for a 5 ton system, the one we went with was a 3 ton. The 3 ton does a good job, so the 5 would have been overkill.

This is relatively new to most installers, I expect the knowledge base will get better with time and experience.

Sean

Sean,
My radiant is from Radiantec(?) in Vermont. The tubes are 6 x 200 foot loops on three zones. They are about 12" apart and use aluminum plates to disperse the heat. The trouble is that the floor is 1-1/2" thick and there is a slow rise in the evenings when the sun goes down. We expected this in the design so it's not a problem and compensated for.
I designed a temperature regulator that keeps things about 108F to compensate for the extra floor thickness.
It's a very efficient system and we can keep the room temp much lower with the floor being warm.
To keep the mean temp at 108f I'm concerned that the geo won't be able to reach the 115~120f top temp to maintain the system.

Rob

 

[Lt CHEG]

I like the idea of geothermal myself, especially if I don't go with modular construction of my new house. My big problem is that I have access to natural gas on my land and it is so darn cost effective that I think the pay back time of geothermal would be too long and I'd probably benefit more from investing the extra from geothermal into another energy saving measure. By the same token I will be renting an excavator for my uncle to use to construct the foundation for my house. So since I'll already have the excavator the extra cost for excavating for the geothermal loops would likely be minimal and that may really bring the cost down too, since my uncle ( a former full time GC) is helping us for free. Since I plan on running central air conditioning this may be a real money saver in that area. I'll be keeping my eye on this thread carefully as I live less than an hour north of the Catskills and my conditions are likely pretty similar to Rob's.

 

[Rob-D]

I like the idea of geothermal myself, especially if I don't go with modular construction of my new house. My big problem is that I have access to natural gas on my land and it is so darn cost effective that I think the pay back time of geothermal would be too long and I'd probably benefit more from investing the extra from geothermal into another energy saving measure. By the same token I will be renting an excavator for my uncle to use to construct the foundation for my house. So since I'll already have the excavator the extra cost for excavating for the geothermal loops would likely be minimal and that may really bring the cost down too, since my uncle ( a former full time GC) is helping us for free. Since I plan on running central air conditioning this may be a real money saver in that area. I'll be keeping my eye on this thread carefully as I live less than an hour north of the Catskills and my conditions are likely pretty similar to Rob's.

LT,
Hi neighbor!
If I had to do my house again I would do modular. I've seen some really nice designs and I've read that you can submit a plan and have it built for you. Everything is put together in a factory , all the beams are cut on jigs and then dropped on your foundation.
The most labor intensive part of geo is running the tubes and the tubes are relatively cheap compared to the compressor. You might want to think about running in the tubes and dead ending them in the house. You could run a dual system with the gas as a backup or the geo as backup. The initial expense would be higher but it might pay dividends down the line.

Personally I like the idea of having the oil burner intact and adding the geo. After 18 years the expense of the initial system is no an issue. The other thing i would consider is radiant floor heat. It's the best system I've ever lived under. No noise, warm floors, no radiators taking up room space, etc.
Just make sure if you build hardwood floors that you keep the top lay as thin as possible. I wouldn't do hardwood again. I bought "TrafficMaster" from Home Depot for my new office and this stuff is great! Water proof, looks like wood, goes down easily and is perfect over radiant. At ~1/8" thick it keeps your subfloor under an inch thick so your radiant response time is much quicker.

Good luck with the new house, I know the excitement of building a house.

Rob