New house HVAC -- reviewing choices before too late

cpackerNovember 15, 2012

In our 2800 sq ft one-story new house in southern Maryland,

we're planning to have geothermal heat (horizontal

loop) using in-floor radiant technology.

One third of the house will have a slab foundation,

so it will use embedded piping. The

remainder will be over crawlspace, so there we're going

with engineered wood (tile in the bathrooms) above

Warmboard, which was our architect's recommendation.

For AC, I thought mini-split looked like a good

solution, but the architect favors central, in

essence telling me that the HVAC contractor will

know how to do it right. So I'm deferring more

pointed questions to ask prospective builders when they

submit bids. I presume that details can be

considered more fully at that time.

We're going to live in this house forever, so

long-term efficiency is more important than

initial cost. However, our architect, I noticed,

tends to be biased toward deluxe materials.

So, anything above not to like? Another thing that's

making me nervous is whether the contractors in our

area have sufficient experience in installing some

of this technology.

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fsq4cw

"So, anything above not to like?"

YES - mini splits! Why would you combine this with geothermal?

Better options would be either triple function geothermal or full function water-to-water geothermal heat pump (hot & chilled water) with Multiaqua fan coil units for A/C - WITHOUT ducts!

Copy & Paste these links:

Triple Function Geothermal Heat Pump:

http://www.nordicghp.com/images/stories/PDFs/tf-series/tf-series-features-examples.pdf

Liquid-To-Water Geothermal Heat Pump:

http://www.nordicghp.com/images/stories/PDFs/w-series/001031slb-01-w-seriestwo-stager410a60hz.pdf

Hydronic Fan Coils (wall, ceiling, hi-wall):

http://www.multiaqua.com/products.htm#MHNCCW

SR

Here is a link that might be useful: International Ground Source Heat Pump Association

    Bookmark   November 16, 2012 at 1:03AM
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david_cary

While geo doesn't help as much with a/c, it still helps particularly with horizontal loops. The problem is hydronic heat makes it complicated. If you were just doing forced air heat, you would have a simple system. Of course it all can be done but you can't go the easy way out.

    Bookmark   November 16, 2012 at 5:18AM
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fsq4cw

"While geo doesn't help as much with a/c, it still helps particularly with horizontal loops."

That requires an explanation...

SR

    Bookmark   November 16, 2012 at 9:26AM
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cpacker

I looked at the links. One of the ads didn't make it clear how heating is done and the other didn't make it clear how cooling is done. I know what we want: heating from the floor and cooling from above (cold air descends). Therefore I'm willing to have the two systems be completely independent, if necessary.

    Bookmark   November 16, 2012 at 11:25AM
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fsq4cw

Again, see the link below for the triple function unit. This one unit does EVERYTHING you want, hot and cold forced air for heating and air-conditioning, full capacity hot water for in-floor radiant heating and desuperheater for pre-heating domestic hot water. See drawing # 1 minus the Pool & Ice Melt. âÂÂRAâ = Return Air, âÂÂSAâ = Supply Air.

SR

Here is a link that might be useful: Nordic Triple Function Geothermal Heat Pump

    Bookmark   November 16, 2012 at 7:30PM
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fsq4cw

Resending because it came out weird.

Again, see the link below for the triple function unit. This one unit does EVERYTHING you want, hot and cold forced air for heating and air-conditioning, full capacity hot water for in-floor radiant heating and desuperheater for pre-heating domestic hot water. See drawing # 1 minus the Pool & Ice Melt. 'RA' = Return Air, 'SA' = Supply Air.

SR

Here is a link that might be useful: Nordic Triple Function Geothermal Heat Pump

    Bookmark   November 16, 2012 at 7:34PM
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david_cary

Geo doesn't help with a/c as much because the temp gradients with a typical air source a/c are not that great.

The energy use for the pumps on a geo system really eat into that marginal benefit as compared to air source. The vertical pumps may eat into this even more than horizontal.

    Bookmark   November 16, 2012 at 8:45PM
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fsq4cw

David, you're in error on all accounts.

Geothermal is in fact more efficient than air-source in the A/C mode in that it's easier to sink the extracted heat from an envelope into the ground at a temperature of about 43ÃÂF than the air at about 75ÃÂF and above.

Secondly, geothermal heat pumps often have desuperheaters so that the heat extracted first goes into a domestic hot water buffer tank to assist in the production of virtually free hot water rather than just being expelled into the outdoor air and wasted.

You mention geothermal heat pumps have circulating pumps. Just as the condenser fan (that doesn't exist in a GSHP) is taken into effect for the efficiency rating of an air-source heat pump or air-conditioner so too is the circulating pump taken into account for the efficiency rating of a geothermal heat pump with regard to a closed loop vertical borehole. You can verify this yourself by reading ARI/ISO 13256-1 Performance Ratings sections 4.1.4 'Power input of liquid pumps'.

Furthermore, closed loop horizontal ground loops or vertical boreholes of any length or depth are balance systems requiring minimal pumping power due to lower head when compared to deep/long open loop systems.

The point of least efficiency differential would be in heating mode when outdoor ambient air temp would be the same as ground temperature.

SR

    Bookmark   November 17, 2012 at 5:55PM
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david_cary

I didn't say geo wasn't more efficient than air source it just isn't that significant. Ground temp of 43? - not where you usually need a/c. Of course the lower temp the better but the air is right there and the water needs to move around.

Geo believers are hard to argue with because the idea is very sound. The practical reality is not always so great.

Energy audits around me compare geo to basically a seer 18 ASHP for operating costs. Maybe they are wrong but either way, it is rarely worth the cost.

They make great sense in cold areas when no NG is available. Great Great sense.

    Bookmark   November 17, 2012 at 9:33PM
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energy_rater_la

"Another thing that's
making me nervous is whether the contractors in our
area have sufficient experience in installing some
of this technology."

this would make me nervous also.
hiring a company that has little experience in geo systems
is a bad idea. if things start out wrong..they only get worse. hiring anyone that has minimal experience is always
a red flag for me.
here in La. geo systems are very expensive.
I've been doing energy
ratings for almost 15 years now. of all the homeowners
who started out with geo systems as their choice..
only 3 actually did this install.

reasons are:
1-cost..at almost 6K per ton & higher..not cost effective

2-lack of experienced installers. one company does
the loops another the equipment..none are local
to this area. travel time adds to costs and to
problems down the line for life of system.

3-high efficiency of air source heat pumps
cost effective. or high efficiency ac with high efficiency
gas furnace. more cost effective, companies are experienced
in these installs, performance is comperable to ground source heat pump fo affordable costs.

you should consider hiring an independent energy rater
to advise you as to your efficiency choices based on
your budget, location, personal perfrences and what is
specific to you.

check with www.resnet.us for an experienced rater
in your area.

invest in foam insulation in floor of the part
of the hosue with the crawlspace. foam rim & band
joists.
make sure that vapor barrier covers all dirt in
the crawlspace and is well sealed when installed.

best of luck.

    Bookmark   November 18, 2012 at 2:04PM
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