I contacted the well Driller and this was his answer:

The loop length(one half out of it) is 510'. There are two parallel pipes connected by a u-bend at the bottom. The total loop length is 1020'

I downloaded the 60 day hvac-calc trial - came out with a heat loss of 34K at a 72F indoor winter temp and 32k at a 68F indoor temp

Posted By sbeausol on 20 Apr 2013 06:44 PM
I contacted the well Driller and this was his answer:

The loop length(one half out of it) is 510'. There are two parallel pipes connected by a u-bend at the bottom. The total loop length is 1020'

Don't you need a mining permit once you drill below 500'?
If you run 100' of pipe out and 100' back to the heat pump (including 12 elbows), and 1000' in the borehole, you should have a flow around 8 gpm with 1 26-99 pipe and a 3 ton heatpump. No need for 2 circulation pumps.It would just double your pumping costs if you put a 2 pump flowcenter in.

Posted By sbeausol on 20 Apr 2013 08:50 PM
I downloaded the 60 day hvac-calc trial - came out with a heat loss of 34K at a 72F indoor winter temp and 32k at a 68F indoor temp

I'd look to tighten the envelope and try to drop down to a 2 ton.

Yup!

Factor in the basement insulation you have in mind anyway. Tinker with some other low to medium height fruit. Chase a few more air leaks. Include a 5 kW heat kit and / or retain a few of the baseboards just in case. Lay in a cord or so of wood for the wood stove for the 10 nights it gets below 10*F

Then go for the 2 ton and certainly just 1 pump. If the loop guy can't make a 2-3 ton system work on just one pump, find another.

Ok, after playing more with HVAC-Calc, I realized some of my settings were wrong. I noticed that about half of my heat loss was through the floor because my design was over an unconditioned space - in this case an unheated basement. The other half was through the walls/windows. That led me to consider two different options -

1) Insulate the floor between the basement and the first floor - this saves me about 85% of the loss through the floors taking the load down to about 27K

2) Insulate and condition the basement. Since I am insulting the basement walls this summer, and plan to finish half of it (1000 sqft) in the future I ran the numbers this way. Taking my basement walls to R-16 (R-3 foam board plus R-13 fiberglass), changing the floor heat loss to the rooms above the basement to 0 since they are above a conditioned space, and insulating the other half of the floors over the unconditioned part of the basement. This took the load to 24K for the first floor and 6k for the basement, a total of 30K for the whole house.



These improvements are pretty minor, likely costing about $900 to insulate the floor or some where <$1000 to put R-3 rigid foam on the walls, plus another $600 or so for R-13 to put on stud cavities. Either way it should be about $3500 less for a 2-ton well, and probably a few hundred less for a 2-ton heatpump. Is my logic correct here? Am I underestimating my heat load for any reason?

Make sure the supply ducts have matching returns in any room that will be closed off. Then have the balance adjusted. Otherwise your ACH will be much higher than expected. And of course you won't have any ducts in unconditioned space or exterior walls - right?

It all sounds about right. Your 2.5 ACH 50 blower door test and subsequent envelope improvements will be the linchpin of your success. You have the stove, you can keep a few baseboards here and there. Pocket the $4k in up front savings and rest assured the smaller system will run both more quietly and more efficiently than an oversized system. I know it is hard to overcome the local tendency to oversize.

Jonr is right, and I will expand on that and warn that for a right-sized system to work right it must be connected to properly sized and configured ductwork ideally all within the thermal and pressure envelopes. Contractors tend to oversize to compensate for shoddy ductwork, so avoid that. You may just partially condition the basement, so some of its 6k Btuh load may not be realized.

You might find that the $4k combined with federal tax credits and state subsidies could buy a fair bit of solar PV, nicely offsetting the increased resistance heating during the coldest days, assuming you have a decent solar window.

Ok, I've made the inquiry so we'll see what the response is. Here is my logic as it stands:

Scenario 1 - The load of the house as is which comes in at 32K BTU/h, consistant with a 3-ton system. I noticed, that most of my heat loss was in my walls/windows (~10KBTU/h) and floors (~15k BTU/h) since the basement is currently unconditioned.

Scenario 2 - Finish half of my basement. Now half of the first floor is over a conditioned space in which the foundation is insulated to R-16 and the other half now has the floor (basement ceiling) insulated with R-13 fiberglass batts. Interestingly, the load for the first floor came in at 19,000BTU/h (floors now only lose about 3K BTU/h), and the basement came in at 4K BTU/h, resulting in a total load of 23,000 BTU/h. The design conditions are 5F winter temps and indoor temp is set for 68F.

For insulating the basement walls you'll need at least R5 (and not R3) in foam on the wall prior to the studwall to both meet code and avoid a mold/rot problem in the studwall. (MA is based on IRC 2009, which spells it out in black & white.) It won't change the heat load calc much, but it'll bump the cost up a hair. You could skip the studwall and use 2" reclaimed roofing iso instead (available cheap, even delivered. Check the local craigslist for "rigid insulation"), held in place with 1x furring through-screwed to the foundation 24" o.c. with 4" TapCons instead. If you do a studwall, using unfaced batts will make it more resilient than kraft-faced, so long as you have the requisite R5+ as foam between the studs and concrete. With kraft-facers on the interior side and foam against the concrete it still has the potential to trap moisture in the studwall, though it still retains at least some drying capacity.

The sub-25K heat load number is in fact credible, which again points me more toward ductless solutions when loads are that tiny, since the design risks and upfront costs are so much lower. I'm sure with the right geo contractor you could beat ductless somewhat on efficiency, but the cost delta is high, as is the design risk should you end up with a not-so-right geo contractor.

The MA & federal subsidies for PV could probably get you close to Net-Zero with ductless + PV for the $35,000- ish quotes you've been seeing for just the geo. Pre-subsidy costs in the $4/watt range have been showing up in MA in the past year, so even if you went with 4 heads of un-subsidized ductless/mini-duct at about $10-12K the "extra" $20K+ would buy you at least 5kw of rooftop power, and after the tax credits and local MA perks for the PV roll in you'd still have some cash to spend before you'd hit the pot-tax-credit ~$25K price tag for the geo.

If you can find somebody who can trench it in on the cheap rather than drill, coming in under $20K on the geo it might work favorably. You'd have to sharpen your pencil and look at both price/performance and subsidy carefully, but in rough terms that's about where it would need to be to be competitive in the current subsidy climate. That price point seems only the stuff of legends in MA, but keep working it- I'd LOVE to actually see one of those! It would give me at least some hope for a GSHP future in MA post-tax-credit subsidy. At the moment it's hard enough to make the numbers work even with the tax credit.

The cost/benefit of desuperheaters may not be very good at your low-loads & low duty cycles. It's more of a slam-dunk in places with long and steady cooling seasons than it would be for a house in a heating dominated climate with a sub-2-ton heat load, and (probably) something like 1-1.5 tons of peak cooling load. The average cooling load is pretty tiny for most houses in eastern MA, (and it's often almost all latent-load.)

I get the affinity for ductless - what HVAC guy wouldn't want to sell and install 15 pound air handlers, bend nothing larger than 3/8" copper tube, and install outdoor units weighing under 100 lbs with SEER > 20 and HSPF 10 and up? I wish I could install many more of them than I do now.

So many houses simply aren't open enough to support a reasonable # of heads. My own home, 3400 SF, 4 beds 3 baths, 3 floors, chugs along with a 3 ton, 4 zone geo, costing about $30 / month to operate, on average. It would need 10 minisplit heads to deliver the same comfort we enjoy today. If the minisplit industry had some 2-3 kBTUH heads it might be worth another look, but that's a lot of plastic hanging off the walls and 10 separate condensate drain lines to maintain free of clogs and leaks. I could throw some ducted minisplits into the mix, but their energy ratings are not so hot and retrofitting would be a bear. I'm singularly unimpressed with the air filter options and TESP available from ducted minis.

A Carrier Greenspeed with Infinity zoning might be more cost-effective than the geo.

Florida is admittedly a special case, so let's set it aside for a few minutes - my Mom's house, also 3 floors, roughly 3500 SF, is located about 4 miles from our OP, Sbeausol. it was built in the 1960s on high ground in sight of the ocean overlooking the town. I've glanced at a load calc done by the oil furnace company...55 kBtuh heating. That's probably more like 45 kBtuh today owing to improved windows. Summer cooling, rarely (though more and more often with each passing year, it seems) needed, is probably around 20 kBtuh, and is now done with window shakers just in bedrooms.

Her house would need at least 10 minisplit heads for effective heating and improved cooling. I've mulled a Mitsubishi 4 ton 8 zone system for Mom, but even that would fall short. Again, too much wall plastic, too many drain lines.

So many houses simply aren't open enough to support a reasonable # of heads

Better insulation helps, as does supplemental heat of some type. But it's the right point.

The Passive House folks feel head count can be managed by superinsulating and superglazing. Then smaller perimeter room loads can be met via ventilation / circulation. That's probably true...for heating.

Throw a bit of window solar gain or latent load into the mix and it's bye-bye comfort.

I agree on solar gain, east and west side rooms might always need their own head. Not clear to me that good air sealing and a small amount of internal air circulation wouldn't address the humidity balance issue. One advantage of warm climates is that the delta-T (indoors to out) is low and this helps significantly with room to room balance.

I agree that low cost, low output, hidden in the wall heads would be nice. Being in the wall, they could probably serve two rooms (both sides).

Preplanning is an effective cure for many of the problems like that you might bump into. At long last, there are going to be some issues that you just can't avoid due to design issues, lifestyle choices or something else. Those are the things that help drive the final system, such as putting larger heads in the rooms getting the solar gain.

Of course, that's assuming you have considered landscaping, roof overhangs, window sizing, proper glazing and sunshades to control the solar gain problem in the first place. The nice thing about problems with the sun is that they are 100% predictable.

Posted By engineer on 24 Apr 2013 07:47 AM
The Passive House folks feel head count can be managed by superinsulating and superglazing. Then smaller perimeter room loads can be met via ventilation / circulation. That's probably true...for heating.

Throw a bit of window solar gain or latent load into the mix and it's bye-bye comfort.

Almost all the seasonal cooling load even in code-min houses in sbeausol's eastern MA location are latent- nobody can count on running an air conditioner at a sufficient duty cycle to handle it completely. In higher-R houses & PassiveHouses latent load management is an even greater issue.

Solar gains aren't that tough to deal with in new construction here. Not sure how difficult it is in sbeausol's house, but in general peak cooling loads in this region aren't huge, even WITH some amount of west facing glass.

The notion that "most houses" or particularly THIS house can't be managed by a reasonable number of ductless heads is an unproven thesis. There are as many existence proofs of those that can as there are existence proofs of those that can't.  A ~2000' single story rancher w/ full basement (like this one) will usually fall into the "can" category, whereas a 4000' 3 story Victorian would probably never make it.  Some arts & crafts bungalows can, others not so much. Same with 19th century New England farm houses. It's clearly not a "one size fits all" retrofit solution, despite the economy & efficiency of where it does work. 

But in new construction it can almost always be made to work, on middle-sized houses (~2400' of conditioned space for new construction, according to 2010 US census data.)  I suspect that the average house heated & cooled by GSHP falls above the 1-sigma mark on US house sizing, which would make sbeausol a real outlier, should he actually pull that trigger.  Do any of you pros keep statistics on the house sizes of your installations? 

I similarly expect that houses heated primarily with ductless heat pumps trend toward the small side of average, if not below the first standard deviation.  Most (but not all) that I've seen personally fall under 2000' of conditioned space, perhaps the small side of average, but only one is (barely) under 1000'.

Someone needs to make software where you enter the house layout, insulation, weather, heads, etc and it produces the expected range of room temperatures. OTOH I did a rough calculation manually for a single room and it wasn't bad. After that, it gets subjective - do you care if a bedroom warms up during late-morning if you aren't in it from 7am to 7pm? Is +/- 3F OK? Do you always need to have the door closed?

I know- unless you have monster solar gains, it's tough to call it a real comfort problem. Most houses in sbeausol's neighborhood are completely devoid of central AC in the first place, and don't really need it. Homes with crummy insulation & high solar gains usually get by fine with crummy window-shakers, and don't need to run them every day. This isn't the southeast, or even the mid-atlantic. I have some better-off in-laws in central MA who built a $1MUSD+ house 8-9 years ago with nice radiant floors, yet NO air condition, at barely better than code-min for R values & U-factors. That just wouldn't happen in SC or TX or FL, and rarely in MD or NJ.

A higher-R house with reasonably managed gains is WAY ahead of typical southern New England housing stock on comfort, even without benefit of a head or duct register in every room. In some ways running with Daikin Quaterity series splits can be more comfortable in a higher-R house in this neighborhood than GSHP, since they can dehumidify to an RH setpoint independent of the sensible cooling or heating setpoints. They're the only heat pump techology currently out there that can dehumidify even in heating mode- they can dehumidify while holding the air temps steady, which is a real virtue here during the many not-so-hot or sunny but way-muggy days.

On the DER I was involved with last year in Worcester MA the only comfort issues reported so far is the east facing third floor bedroom, by students who want to sleep in until noon on weekends. With the bedroom door open it isn't an issue (though it might be for the girlfriend. :-) ) The similar bedrooms on lower floors have greater AM shading factors.

I heard someone recently credit BSC's Joe Lstiburek with a statement along the lines of, " About five percent of all people will never be comfortable.", so I s'pose trying to sell those folks on the concept of going high-R with point-source heating & cooling would never fly- a delta of +/- 3F would be tragic, but so would steady temps of their choosing. The few people I've met who live in near-net-zero homes heated with a single mini-split per floor seem to love 'em, and talk about how even the room-to-room temps are, but they are probably a more committed class of people than the 5%ers too.

For the record, HVAC-calc is claiming a heat gain of 9,000 btuh for my house. I am also having a helluva time finding someone to install Geo. I have yet to find anyone in my area knowledgeable about mini-splits... the wife also wants the electric baseboards to go....

Yikes! really? Are you going to outlive the cost of one of these systems????