I am building a new home (6600 sq ft) in Lakeland, FL 33803. The home is tight, reasonably well insulated, energy efficient windows. I've narrowed my HVAC options to two. Each proposal is for a total of 11 tons of AC split among 4 units. 1 - Carrier Infinity ~16 SEER traditional heat pump system. $35,000 2 - ClimateMaster Tranquility 27 open loop system. $89,000 before tax credit including 2 wells. The geothermal vendor's ROI calculations show an annual energy savings of $2,212 (heating and cooling only. They have shown additional savings for decreased repair costs and hot water generation compared to a "traditional" system). If I go to the ClimateMaster site and use their simple calculator, I get annual energy savings of about $540/year. Obviously that is a huge discrepancy. So . . . from all you smart and experienced guys, what are your thoughts? What type of real energy savings do you typically observe comparing a new high efficiency traditional system with a new high efficiency geothermal? Thanks. Clark

There isn't a simple answer, but I'm not at all surprised that someone trying to sell you a system is over estimating the savings (and perhaps the size). Ask for a guarantee on the savings :-).

With a relatively large system, you can combine technologies to optimize cost effectiveness. Ie, 1+ highly efficient systems that do more of the work and less efficient ones that are only used during peak loads.

>Ask for a guarantee on the savings :-)
Well that would certainly make the decision easier! They would politely decline and I would just go with a traditional system.

At this point I'm inclined to make my decision based on the lower savings shown on the ClimateMaster calculator. You'd think they have as much incentive as anyone to show the maximum possible savings from having a geothermal system.

jonr, thank for your response.

cgal.....11 tons seems extremely high esp for geo!

Yeah, this part of my home has gone pretty much like everything else I've tried to use a little building science on (but that's a whole other story). We had an independent energy company do Manual J calcs. Their recommendation was for an 8-1/2 ton system (3+2+2+1-1/2) with consideration for going to 9 ton if we want all 2-stage units. The geothermal company and the 2 local companies with the best reputation for service all say their manual j calcs show need for 11 tons (5+2+2+2). Half the companies my builder contacted weren't even interested in bidding the system based on someone elses design. I've delayed my project 3 weeks now trying to figure out the best solution but have to move forward on Monday. Conceptually, I like everything about geothermal but don't love it enough to ignore cost justification. (sorry, long answer for a short comment.)

Hopefully "engineer" aka Mr.Kinder will be along shortly. He is the fla. resident expert and can help guide your decision with field experiance facts for fla.
Eric

Present and accounted for...(thank you, WP)

I would be quite suprised at 6600 SF of new "effiicient" construction in central Florida really needing much more than 6-7 tons. I have 2 deep retrofits under my belt and one more coming wherein adding sprayfoam (with verified infiltration performance) to conventional mass produced homes 10-ish years old gets their load down to 900-1000 SF per ton. That's with no additional wall insulation or window changes. Well-considered conventional new construction should easily come in at 1000-1200 SF / ton with reasonable care. With ICF construction and excellent (but not crazy pricey) windows, we routinely get 1300-1500 SF per ton. My own house has 3400 SF under air and heats / cools with 2-ish tons (an 038 geo locked in low stage using open loop water at 71*F). We have 48 Andersen 400 windows...nice but not ridiculously expensive.

Larger houses tend to have somewhat higher SF per ton because of increased interior square footage with very light loads relative to exterior window, wall, and door area.

Geo is a no-brainer for beachfront houses since it saves having outdoor units under constant attack from salt spray. In Florida's interior, the case is harder to make. While Florida is hot, it is not as hot as, say, Las Vegas or Tucson, so that shaves the geo advantage. Rejecting heat into 75 degree water happens at a greater efficiency than rejecting it into 85 degree air (average summer outdoor air temperature) but the efficiency gain is not huge. Lakeland has low heating load, so savings there are likely minor.

I assume the two wells mentioned are for an open loop / reinjection system. I imagine deep aquifer temps are 75-ish down there. An important consideration is how deep the aquifer water lies - that will impact pumping power. What is the plan for pump control - would calls by any one of 4 units cause a big pump to have to run flat out? That could negate some or all savings.

I cannot emphasize enough the advantage conferred by sprayfoam in typical Florida construction. Here we typically put hundreds of feet of flex duct that we try to fill with 55 degree air 8 months per year in a vented attic that often approaches 140*F. It is simply insane. Sprayfoam fixes it. By bringing ductwork into the (indirectly) conditioned envelope, duct losses that often run to 25% of total system capacity, are negated. Duct leaks become far less significant since that airflow is not lost to the house, just slightly out of position.

I'm a big fan of zoning vs multiple systems. My cost of my favorite zone board and 4 dampers is a bit over $1k. Cost of a high end heat pump is $5k. A five ton system typically costs only a bit more than a 2 or 3 ton. I'm not saying your 6600SF house could be managed by 1 system, but I'd bet (sight unseen, of course) that two could be made to fly. Everyone knows the sun rises in the east and sets in the west. Cooling loads follow the sun. Zoning, done right, clues your HVAC system in on that fact.

Desuperheaters / hot water preheaters can be added to air source heat pumps. I do it on all my deep retrofits. It works well in north Florida; likely even better in Lakeland.

There is an independent company out there doing Man Js (at ridiculous expense) from afar. They treat the house as one single humongous room and come up with a whole house tonnage number. It is a poor substitute for a proper room-by-room Man J that drives system, zoning, and duct design.


This could be a $1M + house, and while three weeks of indecision are frustrating, don't let haste drive you to a decision you could regret for decades. I do geo, I do air source. Both are effective in Florida. I'd like a crack at rethinking your options, but I don't think I can get it done by Monday.

Curt,
The company that did my Manual J calcs and system and duct design are located down here (about 100 miles from me). They've made a couple of site visits and have been very interactive in working to accomodate my needs. In all accounts they seem to be reputalble and qualified. They performed room by room calcs, entered in my house orientation (front faces northwest), glazing parameters (u=0.27, shgc=0.17), construction/insulation (block first story with core fill and 3/4" blue styro; 2X6 2nd story with 2" CC, stucco outside, concrete tile roof with 3" CC under deck, unvented attic). They did two sets of calcs - one regular and one showing "entertaining" loads (45 extra people in the house). They proposed an 8-1/2 ton, 4 unit system with a couple of additional zones and supplemental dehumidification and run-time-vent for fresh air.
We're certainly no where close to being super insulated, but have tried to be pragmatic. I took some of my practical advice from the "2008 Building America Prototype 'ICI Showcase House'" in Dayton Beach. In that project they concluded in our climate it was cost prohibitive to upgrade R-value of the roof and that the most important energy efficient characteristic to pay attention to was glazing. My house does have higher than average cu ft for the sq ft because the great room (32' X 25' has an 18' vaulted ceiling. Otherwise one half of the house has 9'4" ceilings and one half 10' celings. The upstairs is two descreet (unconnected) chunks at each end of the house. Yes, the 2 wells are for an open loop system. They proposed a VFD pump. I've only found one company in this area (about 70 mi away) that is really committed to geothermal. They are a ClimateMaster dealer. They appear to have a good reputation, mostly doing high end residential (larger than mine - one was a 30,000 sq ft home with a 50 ton, 17 unit system). EarthLinked is based in Lakeland but they don't have a local presence. The traditional companies I've received bids from are local to Lakeland and have a good reputation for quality and service but seem to have varying interest in building science trends. I also have a 21,000 gal pool and planned to get double duty from the well by using it for irrigation (could save me about $1500/yr). Of note, I've already had plumbing roughed in for 2 gas demand hot water heaters. If I go geothermal, I'm guessing at least an additional $2K to run extra plumbing to add in hot water storage tanks to feed these. I'll also have to find a gas demand HWH that can properly handle preheated input (GE?). Any additional thoughts you have are greatly appreciated.
Clark

If you are a person who entertains a lot then the consideration for the added people load is definately something that should not be overlooked. The latent heat load from the added people could contribute as much as 2 tons of additional cooling. The other point is during large parties, doors are often left open, kitchen is constantly cooking food adding to the heat load, bathrooms are exhausting more air, etc. We have done plenty of large scale homes over the years and being able to have diversification in the hvac system will allow for extremes.The 21,000 gallon pool , i am a little confused at how you want to use this. I would have looked into VRF such as Mitsubishi or Daikin with multiple zoning as an alternative to geo.

We do expect to entertain regularly. The Manual J calcs that the energy company supplied did show a little over a 2 ton difference between the regular and "entertaining" loads.
The only reason I mention the pool is that the geothermal company has proposed water-water GSHP for pool heating. 3X more expensive than the air source pool heat pump we were looking at but will probably allow true full year use of the pool?
I had never heard of VRF until just now. No one has suggested it until you. Although it is an intriguing approach (and may be great for my home), I'm pretty sure my builder will just kill me if instead of calling him tomorrow with a decision I ask him to find someone who will quote a VRF system.
Thanks for your input.
Clark

Im out here in Calif.Geo systems are not very common and a tough sale. The primary reason is the drilling costs and the density of the homes.Your home is in the mid-size range as custom homes go.Typically the homes we like to get envolved with have radiant floors, hydronic heating, chilled water or VRF for cooling.The nice feature of VRF is the cooling and heating demands along with the domestic hot water is precisely met by inverter technology in the compressor. The other advantage is less ductwork, or no ductwork which equates back to higher system efficiencies.IMO you would be better off heating the pool with solar and a natural gas boiler.