Does this make sense?

Discussion in 'HVAC Heating & Cooling' started by mark_g, Apr 6, 2009.

  1. mark_g

    mark_g New Member

    Messages:
    23
    We're building our "forever" 2700sf home in upstate NY, and are trying to make final decisions on how to heat and cool it. It got down to -11º this winter, and hot & steamy summers are no longer uncommon. Comfort is a big deal, but we will probably occupy the house only 2 or 3 nights/week--we both travel for work.

    We have priced various methods of heating & cooling. The differences in prices--from the same contractor who has shared his open books with us--is staggering. We are trying to make an educated and informed decision.

    Oh yes, one more impt detail: our recently completed well is a flowing artesian: in January, producing 27gpm of 54º water! That has inspired us to try to make geothermal heating & cooling work, since it can be plumbed (legally) as an open system.

    SYSTEM (A) "cost x" High Efficiency LP furnace (96%) with 13 SEER air. All-air distribution system.
    SYSTEM (B) "cost 1.6x" Geothermal Heat & Cool, but with fewer units & zones than conventional high efficiency. All-air distribution system.
    SYSTEM (C) "cost 1.6x" LP High Efficiency boiler (95%) for multi-zone underfloor radiant & two-stage cooling using well-water as first stage with hydro-air coils. Radiant-floor heat and air for cooling & ventilation only.
    SYSTEM (D) "cost 2x" Similar Geothermal Heat & Cool with an additional water geo-thermal unit. All-air distribution system.

    Price differences are significant--between $10,000 and $20,000 over the "base price" System A. And that's what is making me nuts--trying to justify the premium for Systems B or D for what are essentially apples:apples air systems.

    The geo equipment mfr is trying to sell me on a projected payback over 10 years. That makes little sense to me, too. I don't believe anyone can predict costs of equipment or fuel that far out. Even if they could (let's assume that both will cost more), it seems as if there would be no payback--it would be a wash. I'm not even bringing into the equation that this is *not* a 24/7 live-in home for 4 occupants with great everyday energy demands.

    One person suggested we put the savings into the best (most efficient) insulation and other building components, which I guess means open or closed-cell foam.

    Meanwhile, our well is putting out by itself 38,000 gallons of water every day. Seems a shame not to be able to take advantage of it and reduce our carbon footprint responsibly.

    So what's your take? Is there something faulty in my thinking? Am I missing a different geo source mfr? Is this just the wrong time to invest in new technology?

    Thank you for any and all feedback. --Mark
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,313
    Location:
    New England
    Is the house still on paper (i.e., not built)? If I was going to build a house, I'd use ICF blocks and manufactured panels for the floors and roof. You can get them with very substantial insulation factors, and the structure is pretty much immune to termites, carpenter ants. Very quiet, great thermal mass, very comfortable. Air infiltration is essentially non-existent if you do your doors and windows properly. Typical lag in heat soaking can be up to three days. One school in the upper mid-west used them to build a new gymnasium...cost them $100 for the season to heat it. The people and lights provided most of it.

    Radiant heating is nice, but does not typically respond very quickly...if the house was going to be turned down for a couple of days in a row, it will take awhile to warm up. If you go with the ICF walls, once the concrete core is warm, it will stay that way a long time, but the same thing is true if it gets cold-soaked...it will be cold for a long time, too.

    The benefit is, if the house is really well insulated, it won't take much to keep it warm.

    An ICF walled house will be thicker than a typical wall. Some would like this as you could have deeper window sills for plants, etc.

    I would also consider windows from VisionWall Technologies. They do more commercial windows than residential, but their technology goes really well with thick walls. If you've ever been to Germany, you might notice similarities to how the windows operate. Turn the handle 90-degrees, and you can tip the top in. Turn it 180-degrees, and you can open it like a door. really nice, since you can open them and not worry about rain or people from getting in (unless they break them, like any window). They are really thick, but there is no seal to break and the noble gas to leak out. They're at the top of the industry in efficiency.

    Geothermal, like any heat pump, will have only warm air coming out the vents. If you use it to heat water, since that is normally cooler, it may be more comfortable. Heat pumps, like radiant heating (however you heat the water), both work better if you don't set back, or if you do, not by much.
    Last edited: Apr 6, 2009
  3. Bill Arden

    Bill Arden Computer Programmer

    Messages:
    584
    Location:
    MN, USA
    I would suggest investing your money in things that would be really hard to change latter.

    1. Under floor insulation and in floor PEX tubing. (you don't have to buy a boiler, just add it for latter)

    2. large low E windows facing south.

    3. lots of foundation, wall and attic insulation.

    4. plenty of soffet and ridge vents to keep the attic cool.

    5. Large ducts for efficient heating and cooling. You can always turn down the fan power. and you need ducts for moisture control anyway.

    Then add a High Efficiency LP furnace since you will want it latter even if you get a Geo system since having both lets you buy cheaper off-peak electricity.


    After all these... Then look at open loop Geo.
    If you still have money left over look at closed loop Geo to reduce maintenance.

    Edit:
    PS: Foam is not the highest R per $. The highest R per $ is a combination of fiberglass and cellulose.

    Also you are better off adding the Geo after the house is built since that way you can use the fuel usage numbers to size the Geo unit better. I am guessing the contractor is overestimating the size needed. A open loop Geo system combined with Off-peak and Dual-fuel should have a payback in the 2 to 5 year range.
    Last edited: Apr 6, 2009
  4. Dana

    Dana In the trades

    Messages:
    3,022
    Location:
    01609

    I'm mostly with you on 1-3, (some issues with how large "large" is on number 2) but

    "4. plenty of soffet and ridge vents to keep the attic cool."

    With the kind of delta-Ts they need to operate to get any amount of flow, "cool" wouldn't be the correct descriptor. Ridge & soffit venting sometimes provides enough flow to DRY the space, but provides very very little in the way of cooling.

    And unless there's a perfect air-barrier on the attic floor it tends to suck moist air up from the conditioned space all winter (sort of a "solution-problem".) Current thinking amongst building science types is that it's usually easier/more reliable to insulate & seal the roof decking from below, making the attic semi-conditioned space. See:

    http://www.buildingscience.com/documents/digests/bsd-102-understanding-attic-ventilation/ (click the link on that page to download the article.).

    As for 5- it's pretty-well documented that unless you take great pains to design the ducts to ACCA Manual-D standards, mastic-seal all seams & joints, and insulate the ducts, equivalent-efficiency furnaces will generally run 15-20% LESS efficient than low-temp hydronic boilers. If embedded PEX & manifolds for radiant floor is too rich for ya, panel radiators or even extra-length baseboards can get you the same efficiency for less money. Ducts take space, make noise and air handlers are power-pigs compared to pumps. Size your ducts only for air-conditioning- and don't oversize ANYTHING, heat with hot water if you can. The perfect duct system has yet to be built, and the imperfect ones rely on perfect pressure-boundaries on the building envelope to keep from using the great-outdoors as the pressure-equalization path. (Did I mention that the perfect building envelope ALSO has yet to be built? :) )

    But if the wall systems aren't yet fulling specified, DO look into Larsen Truss wall designs. Compared with high performance SIPs, dense-packed cellulose in Larsen Trusses can deliver 2x the R value per $. And whether full-basement or crawlspace, building the foundation with insulated concrete forms is cheaper and at least as effective as insulating the foundation after the fact. (you can add more foam-board on the interior after pouring, if you need/want more R-value.)

    Putting the extra money into the building envelope is usually more cost-effective than going for higher efficiency heating systems. But low-temp (any that can deliver the full load with water temps under 140F) hydronic heating systems can be built & retrofitted with any number of heat sources/fuel types (including solar.) No matter what type of heating system, if you build a true high-performance building envelope the size of the heating/cooling systems shrink dramatically (as does the importance of their efficiency.)

    High performance building envelopes shrink all heating systems equally. With true R40 walls, triple-pane windows, R20-R30 foundation and R70+ attic (all of which can be done cost-competitively when the relative sizing of the HVAC is calculated in), it's pretty clear where the longer-term benefit lies. Insulation doesn't break down or need replacement/maintenance NEARLY as often as mechanical systems.
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