Central heat and air unit (standard vs geothermal)

[pharmvet]

We are starting a house this fall and are considering a geothermal central heat and air system. Apparently there is a 30% tax credit with a geothermal, but even after that it is about $8,000 more that traditional system. Anyone have a geothermal meal system?

What % do you feel it lowers your monthly electric bill?

Pros and cons wanted. Thanks!

 

[japody]

There have been several threads on TBN detailing experiences with geothermal systems. Having said that, we had a horizontal system installed when we built our house 3 1/2 years ago. We are very pleased with the system and the savings. We have 2200 sq ft on the first floor and 1100 on the second. Our highest bill this summer for an all electric house has been $142 so far. We keep the thermostat at 74. Winter bills showed similar results. When all of the cost factors were considered, we figured the payback period to be 8 years. Other factors also helped in our decision - the desuperheater, which helps heat the hot water, and longer life of the unit because it is under the house, and not out in the weather. I'm a believer!

 

[TheGoose]

Geo typically is more suitable for places that have colder climates due to the difference in water temperature and heating/cooling temperatures. For instance, in the Northern US the water temperature can run in the 50's and 60's. In heating mode, the outside temperature can be from the teens to the 30's and 40's. So if you set your thermostat for 70 deg F the water that is transferring the heat is anywhere from 40 deg F and higher (10 deg outside temp vs 50 deg water). In cooling mode in Tx our groundwater temp is about 72 deg F. On the hottest day of the year for that same 70 deg F thermostat setting the groundwater is only 30 deg cooler than the outside temps. This is the extreme case as most of the time we are in 85-95 deg weather for cooling mode.

I wish I could explain this better and understand it better but this is basically the gist of it.

What I found when I researched this was that it makes much more sense in climates where the conditioning is predominately heating and not as much sense where the conditioning is predominately cooling. Of course a GSHP is many times more efficient than a standard system but by the time you calculate expenses etc. it takes a long long time to pay back.

I do know that in S. Texas you will find very little GSHP (ground source heat pumps) but as you get into the Dallas and northern Tx areas they are much more popular.

 

[Carl_NH]

Another option to consider is to solar of 5-6KW, then two Mini-Split heat pumps to take the majority of the heating and all cooling load, then a propane or natural gas for hot air heating backup and for water heating/cooking.

The solar investment less tax and local credits will be $8K or so out of pocket, and the mini splits around $3K each, but after the initial investment the heating and cooling is "free".

For the mini splits they work well in more open concept, two floor designs. If a single floor with a lot of separate rooms then traditional heating or GSHP may be better.

 

[dodge man]

We had it installed about a year ago. In our case, going by vague memory, the difference was a lot less than 8k more than a convential system, more like 4k. Just my opinion here after doing a lot of reading about geothermal, the savings all depends on your source of power and heat. In our case we were heating with propane. A couple of years ago propane got crazy high, at those rates our return on investment would be just a couple of years but the prices have dropped a lot since for propane. It seems like natural gas for heat is prettty competive to geothermal if thats available.

Then you have to look at the AC side of it. I like our house pretty cool and our last bill for just the geo was $40, pretty cheap for us. There is also an added benifit of getting some free hot water from geothermal. We got rid of our old system of both the furnace and the hot water heater, which both were propane, because they were getting old. I don't have any facts, but I'd say we are paying more for hot water in the summer and maybe about the same in the winter. You can do some research on making hot water from geothermal and decide, but it basically just requires a second tank that is for storage.

I'd also say the quality of heat and AC is better with geo, more even might be a better word. With new construction, you can also setup the house in zones, which we didn't do.

I'd say do some research for your area, lots of info out there, but for us the bottom line was a return on our investment of about 5 years.

 

[techman]

I installed geo in my house several years ago. It provides a very economical source of heating and cooling. I disagree with an earlier poster that it makes more sense in northern climes, since AC cost in the south can be as significant as heating in the north. The additional cost is a factor, but will be savings and enhanced reliability make up for it. I say enhanced reliability since the units are indoors and do not see the effects of sun and weather.

Consider the system you are thinking about. Horizontal piping (trenching) is the lowest cost, but requires 1 acre + of land and will make a mess of the area until it is restored. A horizontal slinky requires somewhat less digging but has somewhat lower efficiency due to the smaller ground contact and dissipation area. Vertical boreholes are required for smaller lots where the area is not available for a horizontal pipe system. The cost is quite a bit higher since you are effectively drilling multiple well holes at $$/foot. Water well (known as open loop or "pump and dump") offer the highest efficiency since the incoming water temp is co0nstant. These system have the disadvantage of increased power requirements (for the well pump) and potential issues with water quality (PH, solids, dirt contamination, etc), as well as higher installation cost (higher than horizontal and equal or lower than vertical boreholes).

I also added solar (electric) at my house a few years ago. My house is 2800 sq-ft + pool, all electric w/4 adults. With geo my electric monthly average was $160/month (yearly average) in NE PA. With solar I have lowered my bills to $100/month average.

I would shop around a bit. An added of $8K after 35% credit sounds a bit high. Look at options and see if you might be able to do better.

Paul

 

[Loadstar]

I have not seen too many AC units effected by weather. Unless it was hammered by hail. Compressors do better inside on geothermal because the head pressure is lower and always consistent.

 

[techman]

I have not seen too many AC units effected by weather. Unless it was hammered by hail. Compressors do better inside on geothermal because the head pressure is lower and always consistent.

Just some common service items: hi and lo temp effect on run caps, ants and other critters in contactors, rust on fans, etc, UV ageing of wires and other plastic items, and other factors related to temp extremes and weather.

Not a hugh item, but I having been doing repairs for 25 years and I would much rather work on a unit indoors as they are much "better preserved"

Paul

 

[Loadstar]

Just some common service items: hi and lo temp effect on run caps, ants and other critters in contactors, rust on fans, etc, UV ageing of wires and other plastic items, and other factors related to temp extremes and weather. Not a hugh item, but I having been doing repairs for 25 years and I would much rather work on a unit indoors as they are much "better preserved" Paul

I'd say capacitor failures are more of a quality issue than temps. Never had wires fail from sunning themselves, usually it's from being improperly secured. As far as working on indoor units verses outdoor, some of the most disgusting or heavily corroded units are found indoors. The only point here is pressures are lower on a geo unit so they have an easier life.

 

[srossman]

Something that was said to me when I was looking at different heating and cooling systems was the lifespan of the unit. It was mentioned to me that a standard heat pump was designed to last 8-10 years and then you were replacing it again. Where as the Geo units were going to last you a longer amount of time before replacing it.