Geo-Thermal heat pumps

[Diamondpilot]

Be glad to talk about the cost of a Geo system DP. At $1.76 a gallon for propane thats = 2640 a heating season for 1500 gallons. Just to heat the house not water also. Which would be minimal. There is no grantee that propane will stay at $1.76. My Geo system cost me 21K, with rebates and tax credits, my system ended up costing me 13K. Not to mention the hot water as a free by product. It was a no brainer for me. Do you think people just go out and spend 20+ grand for a heating system and not figure the payback? Your not the only person on here that files fight plans.

My home is 2,400 SQ FT. I have strait propane on the hot water heater and furnace. Both 90+. I use 2 tanks, about 800 gallons of propane a year. I am locked in at $1.69 plus 7% tax per year. So $1.80 to my door. My home has Andersen Windows and good doors and plenty of insulation, over 30" in the attic. It was built in 1997. I was figuring a $20,000 installed charge when I looked into it a few years ago and it just did not make dollar and cents for me.

By the way the heat is keep at 70 deg from 6am to 11pm then drops to 66 deg at night so we are not freezing by any means. I do build a fire in the fireplace about 2 nights a week and usually have one going all day on Sundays but its just a normal fireplace, no wood burners or anything like that.

Chris

 

[eepete]

On payback times: With the understanding that some of this is a SWAG scenario, I'm looking at 8-10 years. When we did our house in 2006, we made a lot of decisions with that payback period. It seems that a lot of the construction world goes for 2-3 year paybacks. I have lots of ideas why that is, I'll not waste time on it here.
I do think you have to look at your HAVC choices from a systems perspective. Windows, where they are (north facing, west facing, etc), insulation, duct sizes all play into these decisions and trade offs. The idea that you can just change one part of the picture and have great results is probably flawed. An example of this is all the houses that were designed for forced air heat (where the air from a furnace was at 180 degrees) that had small ducts. Changing out the furnace for a heat pump to get air conditioning didn't work well.

Stuff we did that helped get the best out of our HVAC was foam insulation in 6" walls, 12% widow area (fenestration ratio), overpriced but good windows, every duct size proposed by the HVAC guy was increased by 2", dampers for zoning and insulation in interior walls so zoning worked (also good for sound deadening), and a return duct with filter in each room (none of the under the door return stuff). The attic is conditioned space and we have a metal roof. All this adds to the price of the system, but the results are good. Most spec houses I've visited have problems when the weather is at an extreme.

It was sad to see that many houses built during this last building boom, when money was "Free", were so poorly constructed. They will have a 30 year life before they fall apart or just cost too much to maintain at all levels. At any rate, the OP wanted to know about how geothermal worked for people, that's my story and I happy. You must look at payback analysis. You must treat the house as a system. I was very lucky that I was at a point where I could do new construction and make all these great technologies work together.

Pete

 

[forester2]

Just as a note , a sold a home a few years back here in WNY that DID use the pond as a heat sink for the coils and it worked exceptionaly well. Pond was 13-14 ft deep & spring fed. I'm by no means an expert, but I wonder if our weather difference from North Carolina and potentially deep winter frosts (48" depth for footings is code) makes using a pond a more viable option here. Also, how small are units availible for lower sq. footages; for example, radiant floor heat in a 20x30 shop.

 

[galen1115]

My house is right next to a large Midwest lake, the the water table is very high which produces high yielding wells. These highly promoted Geo systems are expensive and only make sense if the numbers are right. Which they were in my case. Without the rebates from the local coop and tax credits, I would not have had my system installed. But were I live most of the time in NW Missouri my neighbor just installed the same system in his new house he is building on 20 acres. But his is a closed ground loop. I will be interested in how efficient his system is for what he spent. It's a fairly large home.

 

[eepete]

galen: great pix! I would guess that the water from the deep well would be just a bit warmer than the water from a ground loop.

forester: I had two identical units (3 ton). One on a ground loop, one in a pond about 8' deep. Pond is small, about 1/2 acre. The temperature of the water from the ground loop was 51 degrees, the temperature of the water from the pond was 40 degrees. This temperature difference was directly reflected in the temperature of the air coming out of the unit. On the pond, I got 79 degree air, on the ground loop I got 90 degree air. Rooms (i.e. intake air) were at the same temperature (62 degrees) when I made the measurements.

My HVAC guy measured a 13 acre pond at 13' deep, the water was 42 degrees. So a big pond does a little better.

So if the outside air temperature is less than 40 degrees, the pond is better but the ground loop was even better. Either works fine, but as you might guess the unit putting out 90 degree air would run for a shorter time and thus be less costly / more efficient.

So the cost of a pond (cheapest to install) vs. ground loop (middle range of cost) vs. drilling wells (most expensive) and the relative performance all have to be weight against each other and the size of the bank account. In colder areas, the pond will absolutely shine compared to any air heat pump. It cost me $7K to do the loops in the pond, and $14K to do the loops in the ground. BTW, those were for an 8 ton load, there was another 5 ton unit on them. I changed over and did the loops in the ground so I have one of the very few systems with a backup loop (just left the one in the pond, I can valve and switch it in if the ground has problems). This moved my payout period for the system by about 4 years .

Just one datapoint, just one test, YMMV.

Pete

 

[Diamondpilot]

If you are there at a lake why not just take the water out of it? That is what they do at the summer home I rent in Tennessee on Lake Norris. It just sucks it out and dumps it back in. Never been there in the winter but they do not get much below 30 but it does do a great job for AC in the summer.

Chris

 

[wedge40]

As I read this, I keep thinking about the ground loop systems.
I've read that you need about 400 to 600 ft loop for a 3 ton system. I'm assuming that would be 600' of tubing buried approx 4'-6' deep. Just how big of and area is required or should I say what is the smallest area this can be accomplished in. I'm talking ground loops not vertical loops. Do they put the pipe in trenches or do they bury a big loop of pipe. Is there a limit of how far from the house the loop can be? Since this is a tractor site, why couldn't someone get the parts, dig a 30'x40'x5' hole an lay the pipe?

Wedge

 

[eepete]

The 3 ton unit I have on a horizontal ground loop (and it's a 3 ton loop) has the following dimensions:

The ground loop is two trenches 250' long. They are in theory 5' deep so that you don't need a trench collapse device to be in there. In practice, they may have ended up a little deeper . An excavator dug the trench and the trench width is 3 feet wide (so it's easy to work in). In each trench, on each side, there is a 3/4" pipe that runs along the bottom, turns at the end of the trench, and then comes back about 2' above the bottom. It is held in with large "staples on steroids" devices hammered into the clay ground.
So there are 4 500' loops, one on each side of two trenches. Note that the 500' pieces of pipe are pre-cut, and they do not get cut again. The total loop lenght is therefore 2000'.

The feed from the house, which is about 100' long, is a 1.25" pipe (all these pipes are black HDPE). It feeds into a buried manifold that connects to each of the loops. Since the loops are the same length and same topology, the flow divides between them evenly.

Everything gets covered up, and then it takes a year for the trench to settle. A pile of dirt is left over and gets used to cover it. Eventually, it's a bit of a depression that I'll have to smooth over to get everything flat again (this is a seat time thing not a problem thing).

BTW, the 8 ton loop is 4 trenches, 300' long for 4800 feet of pipe in the ground.
There is methanol added to the water in the loop to make sure it doesn't freeze and to help keep crud from growing in it.

So, wedge40, I don't see a big limit on how far it is from the house and if it was "too far" you'd just go up a pipe size on the main feeder pipe. You could dig your own trenches, that's a time and money thing. For me, my poor little B21 backhoe and I would be at it for over a month, the bucket is too narrow, and I'd probably have to dig twice the trenches, and it would be hard to work in. Hiring the excavator was a big win.

All the Geo guys I talked too were not keen on having the homeowner dig and create the horizontal field loops. I think it's an ownership thing. If anything goes wrong, there are two people to point fingers at not one. Yeah, this is more money for the HVAC guy but this was a consistent theme.

I've heard of other schemes, this is just what happened here.

Pete

 

[LD1]

Just now ran across this thread.

To answer the OP's question directed at me: I was actually talking about and airsource heat pump. The kind that is just like you air conditioner outside your house, with the fan, and the condenser. The air to air heat pump works the same way, just in reverse. They they work on the same principal as a geothermal, with the compressing and uncompressing or the refrigerant. But instead of moderating the temperature of the compressed/uncompressed freon with ground water(geothermal) they use the fan and the ambient outside air.

As far as efficiencys are concerned, geothermals are about the same all winter long due to ground temps remaining a constant 40 degrees (in my area). The efficiencies of an air-air heat pump vary with outside temp. The colder it gets, the less efficient. But on the milder days of 50-55 degrees, it is actually more efficient than a geo unit which is using 40* ground water. But geo takes the cake in the summer. Using that 40* water instead of 90* air.

As far as payback is concerned, it depends on many variables. What you currently use to heat, where you live, utility rates, size of home, etc. I have a air-air heat pump, which is set to switch over to propane @ 17 degrees, and I heat a 1350SF house with a full basement. I am currently on my 4th winter on the current tank of propane and still @30%. My electric is about 100 per month higher in the winter on average. With the cost of propane and electric combined, I am heating my house for $800 per winter. It would take almost 20 years to payback a $15000 geothermal system, Provided I didn't have any issues with the ground loop, which would be a lot more expensive to repair than an above ground air-air unit. In my case, it is not worth it. But someone who heats entirley with propane, or electric resistance, it may be a different story. But then again, an Air to air is only about 3500 installed.

On a last note, geothermals do not prvide "FREE" hotwater but only in the summer when you are expelling the heat outside. In the winter, it is NOT free. It is simply just cheaper than your water heaters heating elements. In the winter, a geothermal has the capibility to produce more heat than your house needs. You are simply just using it to also heat your water. It is still more efficient, because the heatpump can be between 3:1-5:1 more efficient than resistance heat, which is what a water heater is.

 

[buckeyefarmer]

In general pond loops are the best for a closed loop system, but the pond has to be big enough and the loop sunk deep enough (over 10' deep). The length of the loops per ton depends on several factors such as the soil type, depth, number of pipes in each trench, pipe diameter, your climate area, etc.. The quality of the install, loop and unit are very important. You have to have good thermal conductivity between the soil and the pipe. You can't just bury a big loop of pipe in a big hole, you have to spread it out. The pipe used is HDPE, High Density PolyEthelyne. All connections underground must be fused. You can manifold either outside as EEPete described, or bring each loop inside and manifold there. There are benefits to each method, but most installers today will manifold outside and bring just two pipes, typically 1 1/4" into the house. the loops are typically 3/4" and can be 200-600' per ton.
Pump and dumps introduce other problems, but are the cheapest to install. A lot of lakes won't let you do it though, unless you own the lake.
Payback is different for everyone. A large factor is how well your house is insulated, obvious the better the insulation the smaller the system required and lower costs all around. They are very expensive systems, but with more volume and competition the price should come down some. Retrofit is also more expensive than new construction. And the units rely on higher airflow velocity, so ductwork may have to be modified.

I hope to install mine this spring, course I said that last spring... I plan on using horizontal slinky at 5' deep, each 500' per ton.

some things to look for in a system:
1. Get a manual J done on your house to determine the actual size unit required. Don't let the contractor assume based on existing AC and HEAT sizes, they are probably oversized.
2. Get a unit with 2 stage compressor, they are the most efficient.
3. Get a unit with variable speed ECM blower motor, most efficient.
4. A reliable installer, ask around
5. Get a lot of prices.