Can anyone tell me the real benefit of a geothermal heat pump vs a High efficiency HVAC system? I am building a house in FL and want to see if it is worth it.  I have no space (plenty of land) limitation but do not have access to a pond close by. The closest water is lake Apopka which is about 700 ft away through a bunch of woods.

Thanks

It is beneficial: often.
We determine that case by case.
Factors include operating cost, installation, cost fuels available, consumer goals...........

The economics often/usually depend on the size of the peak load, but are also largely dependent upon your electricity rates, and the amount of federal/state/local subsidy. The crossover generally (but not always) occurs between 2.5-4 tons (cooling.)(Larger favoring geo, smaller favoring air source/ductless air source heat pumps) Pond loops are cheaper than trenched-slinkys, trenched slinkys usually cheaper than drilling. Most homes in FL are fairly close to the water table, which may favor a trenched in loop approach.

Of course the quality & experience of the system designer play a huge factor. Hack designers can bring the as-installed efficiency of even the best equipment to it's knees.

It's often the case that spending the money on reducing the load with better insulation & air sealing is a better investment than a scaled-up geo installation. Any time you're spending that type of money it's important to look at the bigger picture, and sharpen your accounting pencil. Even if the costs of the extra to of geo equals or even exceeds that of the building envelope improvements necessary to reduce the load by a ton, the insulation has no operating or maintenance costs, has a lifecycle many times that of the mechanical systems, and provides a higher comfort level than simply a bigger system.

While the shallow water table in most of Fla. would seem to benefit horizontal loops, the reality is that in many areas a drought (such as during 1998 and other summers) can drop the surficial water table below the tubes, leaving them in dry sand.

Our compressed design temperatures mean that in many cases, the use case for geo isn't nearly as open and shut. A popular exception is for beachfront homes whose sea breezes carry corrosive salt spray into conventional outdoor compressor sections.

Posted By engineer on 22 Jan 2013 11:03 PM
While the shallow water table in most of Fla. would seem to benefit horizontal loops, the reality is that in many areas a drought (such as during 1998 and other summers) can drop the surficial water table below the tubes, leaving them in dry sand.

Our compressed design temperatures mean that in many cases, the use case for geo isn't nearly as open and shut. A popular exception is for beachfront homes whose sea breezes carry corrosive salt spray into conventional outdoor compressor sections.

Ouch! That's got to be pretty tough for folks who didn't design for the historical min/max water table depths! (But as the climate changes that too can change- in both directions.)

We don't do horizontals owing to the above-described effect. Geo really only enjoys an efficiency premium here when supplied with open loop deep aquifer water that runs in the low 70s year round.

Can I use an Existing Deep aquifer pump that is used to supply my house water to run my HVAC? Do I need a second pump? How much water will it use and will I notice a big drop in available water when my AC is running? Can I discharge the used water into a nearby lake or use it as a sprinkler?

Open loop systems use 1.5 to 2 gallons per minute per ton. Since we don't know your requirements that's as close as we can come. In my AO a 5 ton open loop system may discharge up to a million gallons/yr.
You may discharge the water anywhere it is not a nuisance.

I personally do not like the idea of drawing water from an aquifer (well), and discharging it to a stream or other waste area ( even though its acceptable). Being a well driller, i know the importance of water below our feet. Your using it as a heat sink, while some people rely on it as a source of drinking water. I always drill a second well to the same aquifer and discharge the water back to the same aquifer that it draws from so depleting the water quantity is not an option.

The well drillers in my AO tell me that reinjection wells are to flakey around here (due to iron fouling I believe) and won't use 'em. I presume they feel a lot like you about drinking water.