Geo-Thermal heat pumps

[eepete]

Great summary buckeyfarmer!

LD1: If your ground water is 40 degrees, then the "ponds are worse than buried horizontal loops" claim that I made is wrong, and that should be a call made by region. When discussing those options with an installer, ask what the temperatures are for ponds and the ground in your area.

Pete

 

[galen1115]

When I got into this Geo thing, I found I needed a big learning curve. At Lake of the Ozarks, the dealer said the deeper the better. After 33 feet, the water is much more stable in temperature. You have to take in consideration that the arm I'm on is really a river flowing into the lake. So temperatures change quickly. As for taking the water out of the lake DP, it's just too dirty. It causes problems in the unit even with filters. The big resorts there tried it and was too much maintaining. There is a lot of crap that flows down the arms and into the main body. You have got to get the exchanger below the thermocline to be effective. At least thats what they told me. The well was really less money than the lake loop and more efficient. I would have had to protect it from fishermen that troll. The well driller was hurting for business at that time and gave me a good deal. 4800 verses 5800. He said that big rig sat too much and needed to keep it running. He did an excellent job. A lot of it is being in the right place at the right time.

 

[fish6942]

We built a house in '08 and strongly considered a Geothermal system. This what I can pass along:

1) There was no energy credit that year.
2) We have plenty of land for horizontal loops but both companies we spoke with suggested using wells.
3) There is a significant jump in system cost when you start talking about having it supply hot water (either domestic or for radiant heat).
4) We ended up going with a super high efficiency air source heat pump. We are on natural gas and the payback to go from what we ended up with to geothermal was 15 years.
5) Had we been on propane we probably would have gone with geo due to a payback of 7-8 years.

 

[newbury]

One of the things i don't see discussed here much is the temps inside.

At my house in Northern Virginia we heat it up to 63 deg F during the day, and it drops down to 58 deg at night during the winter. During the summer we cool to 75 deg. This keeps my bills so low that it would take forever to pay back proposed savings for about any energy mod.

 

[JackMentink]

I know everybody is into the alternative building types and high tech insulation sytems, but most I've seen are not real cost effective and have very long paybacks.

When I built our new house three years a go I went with 6" stud walls, r-19 blown in cellulose, r-48 blown in cellulose in the ceiling, and Anderson 200 series low-e windows (lots of them as my wife is a sunshine fanatic. I paid attention to the house wrap to get it sealed on the outside, and put my energies in the heating system.

I installed a ground source heat pump with a open loop system that use my well that supplies water to the home to supply a geothermal source. ( I upsized the well pump to a 2 HP and put a variable speed drive on the pump).

I discharge the geothermal water into two 1500 gallon tanks that I use to irrigate my two acre lawn. The heat pump has a variable speed fan and four zones with four thermostats to keep the house perfectly temperate in all areas. The house is the most comfortable I have ever been in it cost less than conventional system as my electric cooperative gave me a $1700 rebate for the system.

I also have a desuperheater attatchment on it that preheats all my hot water.

The house is 4400 square feet finished with all of it heated and cooled to 73 year round.
It is about 2800 foot ranch over a full walk out basement. I live in Missouri and we have winter with lows of 0 and summers over 95 for weeks.

The best part is the utility bills. The largest heating portion of the electric bill we have ever had was $65/month, with the largest summer cooling bill of $40/month.

Do the design properly and get a good quality system (Water furnace) it is worth it.

My unit had a zero year payback as it cost the same as a high efficiency gas furnace plus High efficiency A/C. No long paybacks here. We have abundant Groundwater here and I was drilling a well anyway for the house so only had to pay an additonal 1700 for deeper well with bigger variable speed well pump.

I estimate that I save $1500 + per year and dont have fool with wood or ashes or any of the other messes that come with wood or pellets.

Ground source heat pumps rock.

 

[galen1115]

I like what you did Jack. The storage tanks and zone heating. You have a near perfect system.

 

[Stimw]

I've had a Geothermal since 1980 when I put one in (self installed) the house I owned. I sold that house in 1999 with it still working great.
I put one in (self installed) the house (doublewide) I have now 2 years ago replacing an Air to Air (POS) system. The A to A would run all night in the winter below 40* and kick in and out of heat strips. Register temp was a few degrees above ambient.
Both units are installed using wells, my ground water is 65*, I either water my grass or dump it in ditch. My water table here is 2-4' , I put this well down 30' just washing it.
I keep my Tstat at 75* rooms are 70-73* in the winter. 80* in the summer. Register temp runs 20* higher or lower than ambient.
The first unit, 2.5 ton cost me $1000. including simple duct work. This unit 3 ton cost me $2300. for unit and well parts.
I'm very happy with them.

 

[buckeyefarmer]

When installing horizontal loops, deeper is better, but once you get past 5' deep the difference really gets minimal. Plus, as you go deeper you have to worry about trench safety issues. You can get the heat transfer with a little more pipe (longer loop) instead of going deeper. As an example from my geothermal design software, If I use a 4 ft horizontal slinky, at 5' deep I need 1219 ft of pipe in a 315' trench. If I install 6' deep instead, I need 1158' of pipe in a 289' trench. I dig a foot less and use only 61' more of pipe to achieve the same entering water temperature. These numbers are for clay soil in my area.

You do need antifreeze in the loops, and you can use either pressurized or non pressurized flow centers, each has their advantages.

eepete, what size flow centers do you have on those loops?

 

[ModMech]

Because we live in East Texas where you spend 8 months cooling your home, 40* water temperatures from a lake or pond would be a very significant improvement over 95*F air temperatures for heat exchange.

We have a pond and well that could be tapped for a Geo system, or I could go the low-buck method and simply drip water over the condensor coils allwing it to run off and water the yard, at least the portion that does not evaporate in the process.

 

[AHNC]

I prefer closed loop systems. One way I used to install ground loops (78-83) was using a product called Solaroll. It is or was, don't think it is still made, a plastic solar collector that you could make to any length. Of course you had to keep an eye on pressure drop in the loops. We'd trench the length and install the solar collector on edge, backfill with sand, put a drip irrigation system over it to keep up the heat transfer and fire it up.

I also did large diameter closed loops in the bottom of the pond. most however we did with swimming pool water. Glazed solar collectors heated the pool. A good insulated cover is essential. WE used the Don Drysdale model cover, for those old enough to remember him standing on the cover in the middle of the pool. The pool became the heat sink. These worked very well. In the summer we would reject heat to the pool and not cover it at night so the pool would radiate the heat at night. The problem with this cooling side is athat your chemical costs go up as you are heating the pool with rejection heat and cooking off the chemicals. I had one system that the pool couldn't handle the heat of rejection and we put in a small cooling tower. These systems were installed in the Napa Valley where the heating and cooling degree days are about the same. I think an indoor pool could do very well, but you would need the cooling tower or some method of rejecting the heat gain in the summer.

One thing I like about the GSHP's is if you have a water to water unit you can also do radiant heat.

Again, I want to emphasize that air to water heat pumps are being introduced by assorted Japanese manuf that equal the output of todays gshp's. Daikin is the first and just doing so this year. I prefer to wait a year to so to see how things go.