Paul,

  I've got a full SIP shell.  R-38 in the ceiling and R-26 in the walls.  No blower door test yet, but I've made every attempt to seal it up tight.  I took advantage of passive solar design to the extent my lot allows.  Now, I certainly could have built a smaller house.  But, for the sq ft, my heating and cooling loads are very modest...  Just over 5 ton of heating and 3.5 ton of cooling for a 4500 sf house in the mid-atlantic is not bad.  Other than cutting the house in half, I don't know how I'd get those numbers much lower. 

Tech,

  Energy Star sounds like a great idea, but the execution is sorely lacking.  For instance, ES requirements for your basic ground loop GSHP are 14.1 SEER and 3.3 COP.  My choice of twin heat pumps would perform at 18 SEER and 3.4 COP.  In terms of the stated goals of the tax credit, that SHOULD qualify.  But it doesn't.  Why?  Because the rules are written to be easily enforceable, not to make any kind of sense.   If a person acheives the stated performance goals, they should receive the credit.

  Because the rules are written with so little thought, I'm going to have to buy a piece of equipment that's more complex and expensive than I require.  I'm also going to end up with a heat pump that's undersized on the heat side, forcing me to suppliment with a far less efficient source.  

  Or, alternatively, I could scrap my efficient radiant floors and use 20% more energy to heat my house with forced air, using an 8-ton Energy Star rated heat pump.

   In other words, I have to WASTE resources in order to qualify for a resource conservation incentive.  You're going to have a tough time convincing me that makes any kind of sense.

Tuff,

  I know.  But it's hard not to hope for something better. 

Seneca,

Probably possible to chain together multiple hp's.  But, again, it's hard to see how that serves any useful purpose. 

As far as radiant heat, I don't see it as that much of a luxury.  I'm tired of paying $300/month to heat my Ryland townhouse (In which, by the way, I paid extra to get the Energy Star package) and still have to stand on ice cold floors.  There's certainly an overhead cost to the distribution system.  But I think the value from that investment is much better than, say, $12k worth of marble countertops.  It's also, by all accounts I've found, more efficient than forced air.   That should be in concert with the conservation goals of the current tax credits. 

I suppose it also depends on motive.  If the intent of the legislation is to promote conservation and lessen the amount of fuel used and emmisions created, then it makes sense to reward all of those who acheive those goals by the target amount.  

On the other hand, if it's a need-based subsidy, then don't pretend to care about energy conservation or pollution.  The earth doesn't care about the income of the family that creates the emmisions.  Future generations that pay $5/KWH won't care about the income of the generations that squandered all the resources.

Joe, I know we had a lively discussion on this issue a while back, so I'll just maintain that radiant floors CAN be as efficient or more so than forced air, even if they aren't usually. If I was designing the ultimately efficient system and money was no object I'd use radiant.

Unfortunately it seems not to matter how efficient a radiant system is since to be energy star qualified the unit must be rated under ISO whatever-1 which is a forced air test. Water-water heat pumps are rated under ISO whatever-2 so it seems to me that even if the COP was 10 they still could not be energy star rated due to what I consider to be a technicality.

Joe,

  I'm not a building science specialist.  But I am an engineer that's spent the past 12 years researching residential building technology.  In that research, I have found a large volume of material that suggests radiant floors are an efficient way to deliver heat.  Given that there's an entire forum here at GreenBuildingTALK that's devoted to radiant heating, it appears that I'm not the only one who's drawn that conclusion.

  That's not to say that I've considered every variable, or that my conclusion is unquestionably correct.  But,  the reasons given to support radiant floors and thermal mass make sense to me.  I believe that I've chosen a system that is efficient for my application.  Maybe you know better than I do.  Maybe you don't.

  The real point I'm trying to make here is that none of this is considered in this conservation incentive.  The Energy Star folks don't give a damn if I blow 120,000 btu's past fiberglass insulation and leaky windows.  As long as I generate all those btu's at a COP of 3.3 or better, I'd get my 30% back. 

  But if I cut my energy usage in half - which SHOULD be the ultimate goal here - and deliver the heat through the floors, that doesn't qualify.   That makes no sense to me.

Jon 
   

Ok...if we don't debate the floors or the tax law,

I still suggest a 3.5 ton water to air unit as your "primary" system, with a 5 ton water to water "back-up". Yes this will cost a few grand more than an air handler and water coil, but it will have a higher EER serve as an excellant back-up system and likely qualify for the tax credit.
Joe

I don't know how likely that system would be to qualify.  We're all guessing at the particulars here.  My guess is that the 3.5 ton system would qualify, but the 5 ton system would not. 

I've never considered a single w2w with an air handler.  My cooling/heating loads don't support it.  Geo pumps are biased towards cooling, my loads are biased towards heating.  I've got to have dual systems.

The path I'm traveling down is not all that different than the one you've suggested.  I'm having an 18-SEER air-source heat pump installed.  That will provide the efficient AC, as well as fast-response heat during the shoulder seasons.  The downside to this choice is that it won't provide supplemental heat when I need it most - ie when it's 5 degrees outside.  Your system would excel there, but at a substantial additional cost.

To provide the heat, I'll need a 6 ton Synergy3D.  That's not the best choice, for a variety of reasons.  But it's the only choice that's government approved.  When it gets really cold outside, I'll have to fire up the masonry heater.

I wish I knew more about the field-sharing you mentioned.  I've considered this possibility, but never found any information about it.  I might have gone with dual geo pumps if I was confident in the installation details.