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Geothermal or AirSource Heat Pump

I'm trying to make a decision on which type unit to go with. House is approximately 1665 sq foot ranch with equivalent walkout (daylight basement). See plan here: http://houseplans.co/house-plans/1236/

We got rid of the small crawl space and opted to make full basement. Everything caulk and sealed, 2x6 walls w/owens corning propink r23 insulation. r50 blown in fiber in attic. r5 externally insulated basement in conjunction with r5 eps insulated interior (rim joists included). The basement slab is insulated as well. The house is located in (zone 4) Shelbyville, Kentucky. I have multiple geo quotes and air source heat pump quotes. Got decision down to two quotes. First is for a 3 ton single stage 5 series waterfurnace geothermal unit w/desuperheater and 40 gallon preheat tank; and a heat recovery ventilator. There are three 185 foot vertical ground loops. The unit also has intellistart, axb controls, and touch screen thermostat (consequence of the 1500 rebate deal) Initial istall would be $24132; would end up costing $15800 after rebate and 30% tax incentive. The quote for air source heat pump would be 4 ton 16 seer rheem 2 stage heat pump and a heat recovery ventilator. The price for this unit installed w/duct work would be $11500. Which option would you choose and why? Thanks.

Asked by Aron Robinson
Posted Sat, 11/24/2012 - 21:02

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5 Answers

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Can someone give me some insight here. I have to implement this in a couple of weeks and I'm trying to make the most educated decision. Given the aforementioned costs which direction do you think would be the best way to go? My main priority is ensuring the best environmental control with the best cost savings. If I would get equivalent energy consumption costs from both systems, I'd go air sources. If the geo provides me with better energy conservation and can be justified, I'd obviously go that way. I don't have enough experience with this two systems to make an educated decision either way. And by the way, I priced mini splits in Kentucky, and it was ridiculously expensive....$34000 for 6 units.

Answered by Aron Robinson
Posted Tue, 11/27/2012 - 09:56

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Aron,
It's hard to answer this question over the Internet -- there are just too many factors.

I've always felt that if a single-family home needs a $24,000 heating and cooling system, that's a sign of a bad design. In general, it's better to invest in envelope improvements than in a very expensive heating and cooling system. But it may be too late for your project to think of a simpler house design or a better thermal envelope.

One thing is for sure: your HVAC equipment will need servicing and replacing some day, so it makes sense to keep it as simple as possible.

Answered by Martin Holladay, GBA Advisor
Posted Tue, 11/27/2012 - 10:06
Edited Tue, 11/27/2012 - 11:51.

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Ground source. Only because of rebate makes the cost right. And your location is better than mine as to ground temperature.

Use a very experienced contractor!

Answered by aj builder, Upstate NY Zone 6a
Posted Tue, 11/27/2012 - 10:30

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The notion that it would take 6 mini-splits to heat & cool this place is a bit ridiculous, even though it's not high-R house. A room-by-room heat load calc would probably show that more than half the heating & cooling load is the Great Room and Game Room, and upgrading the windows on the doored off bedrooms could be upgraded to something higher-performance it could be made pretty comfortable winter & summer with just 2 heads, even if it meant you had to slightly over-cool and over heat the Great Room and Game Room zones to keep it super-comfortable in the doored-off rooms at the temperature extremes. A pair of 1.5 or 2-tons plus some pricier glass could be what it takes.

I'm with Martin- for the kind of coin you're talking for a 3 ton GSHP system you could have taken it to higher performance the building envelope and gone with a couple of 3/4 ton mini-splits or a 1.5- 2 ton multi-split, using even less annual power than the proposed GSHP. The dense-packed fiberglass is pretty good and all, but no matter what R you put between the framing it's performance is robbed by the thermal bridging- two inches of rigid iso between the sheathing & siding would cut the wall-losses by half. You have a lot of glass in that house, and upgrading to triple-panes might break the budget, but a very careful analysis of the glazing and heating/cooling requirements of each room using RESFEN or similar might find the right balance of glazing cost vs. mechanical systems costs. Better yet, simulating the whole house with BeOpt would point you to the best places to look for further load-reduction.

3 tons is about the tipping point/sanity-break between going GSHP vs. ductless, and if the place isn't built yet it should be pretty straightforward to bring the actual loads under 2 tons for less than the upfront price difference between the full on-ducted GSHP or ASHP designs and a judicious (rather than the 1-head per room micro-zoned approach) ductless design using the HRV flow & jump ducts to condition/temperature balance the low-load rooms.

Answered by Dana Dorsett
Posted Tue, 11/27/2012 - 18:43

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Thanks for the advice all. Sorry Dana....I forgot to mention that the 2x6 stud wall will be covered in with a solid layer of osb, 1 inch foam board, and hardiplank siding. I've also cut down on the amount of windows from the original plan and I've given up two of the doors leading out of the master and family room. I'm only putting in a single door from the dining room.

Answered by Aron Robinson
Posted Tue, 11/27/2012 - 20:40

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