We are in the planning stage of a very tight, efficient, single level home in Central Oregon. This will be primarily heat load, (it can get to freezing at night, 10 to 11 months of the year.)

Originally I was thinking slab on grade with Radiant heat. Several Architects told me that Radiant is quite a bit more than a standard heating system.  I also understand it does not make sense to put a very expensive heating system in a Highly insulated home, as it just doesn't make financial sense.

We will have some passive heat as well, excellent windows, but Jan to March the cloud cover may be significant.

After reasearch we have decided to utilize a GSHP, and with Tax incentives, and a substantial rebate from the electric company, I figure my net cost for a 3 ton, GSHP Water to air, and Duct work to be about $11,000. ($20,00 initially) After energy modeling we are expectng that it will be closer to 2-2.5 ton.

We are still planning insulated, slab on grade. So I am thinking a large part of the cost of radiant heat has to be the boiler, other than that it is just the valving and Pipe correct? 

So I just can't get around the fact that the piping and valving would be more than a complete duct system?  I anticipate almost no AC need, if so we can always look and a single mini split or something along that range.  Is there any out there that do Radiant and conventioanal GSHP that can answer if my thinking is skewed?

Thanks

You're basing an awful lot of conclusions on what appears to be guesswork. Maybe you should get some bids on the different systems you're interested in so you have something to compare.

I'm up in Washington state and I selected an air source heat pump with radiant because of the high efficiency. It's easier for the heat pump to warm water up to radiant temp than it is to get air to the temp needed.

I don't see what you are calling assumptions based on guesswork. I have already gotten bids on the GSHP and know what the tax incentives and rebates are.
I merely thought someone here that is familiar with both systems would have a idea of whether the Radiant without a boiler would be more expensive than ducts.

Radiant slab on grade with an electric boiler is about as easy as it gets.
You can do most of the pipe work yourself.
How many square feet?
How many zones?
Dan

2400 sq ft. 4 zones?

whether the Radiant without a boiler would be more expensive than ducts.

Like Blueridge says, radiant in slab is about as cheap as you can get and I'll add that the efficiency can be very high, too. The cost goes up when people start making the system complex with lots of manifolds, valves and pumps. One strategy with an electric boiler is to save enough money that you can put a substantial amount into solar PV panels.

I don't see what you are calling assumptions based on guesswork.

That was where you were wondering about the component costs of radiant.

If you do go all radiant, you may need to have a ventilation system.

Radiant is nice and comfy, but if you have a very well-insulated tight home, your heating needs might go down enough such that the radiant slabs no longer "feel warm" to the touch and you might lose that if it was something you wanted.

Does your geo quote include everything? It seems lower than a lot I've seen.

You have a lot of options, but you haven't clearly laid out what your primary goals are? Efficiency? Low energy usage? Low cost? Warm floors?

Our goals are for maximum efficiency, which would be lowest energy use, but I don't want to pay a premium for the radiant. Our ultimate goal is Net Zero., if it can be done within the budget.

I will be placing premium money in the envelope. We are planning on having an HRV. The warm floors are a bonus but not a requirement.

Since we are planning on insulated slab on grade anyway, not having to do ducts makes the design easier.

Our Geo quote does include almost everything, we have an ideal location for an earth loop and I am doing the excavation, saving about $4000. As I mentioned the electric company has a pretty decent rebate for GSHP, and that makes a big difference. Doing this groundwork for this project is a little more difficult because I currently live over 1000 miles from the property, and work all over the US.

Our ultimate goal is Net Zero

That doesn't happen without substantial effort and engineering in either the insulation/conservation side or the production side or both.

Radiant slab can be very efficient in it's low-temperature forms. It gets even better from a cost basis if you use the actual slab as finished flooring through stamping or staining during concrete finishing.

I am doing the excavation, saving about $4000.

Aha. Are your costs included in the estimate, even if it is only fuel and machine wear and tear?

My recent quotes on quality Air-source minisplits ran about $7K-$8K for the whole system. Under that plan, you wouldn't even have the costs of tubing the slabs. And, you'd have the benefit of cooling if ever needed. You'd also have a few thousand towards the solar PV system, albeit not much due to your particularly low geo cost after rebates and DIY.

PS to add Don't forget passive solar.  Done right, you can get a 20%-30% improvement or more in energy consumption with very little additional cost.

remember the geo tax credit does NOT include ductwork costs, just in case you were.

You are comparing piping a slab plus HRV ductworks vs force air heat ductwork. the radiant will be more expensive. it will also be quieter, less noticeable, and most likely more efficient in distribution energy as a small pump can circulate a lot more efficiently than a central fan.

As a general rule (with many counterexamples to prove the rule) on new construction in a place as temperate as central OR, spending the money on envelope improvements and going with high-efficiency ductless reduces the power consumption more than going with only marginally higher GSHP heating.

Getting quotes for the GSHP systems in advance of knowing with higher certainty the actual heat loads isn't the best approach, and constitutes an assumption based on gueswork (even if it's educated guesswork.) Every ton (even half-ton) of geo costs, and oversizing the system to the load is an expense with no efficiency ROI. By contrast, oversizing ductless by 25-50% gives them a lower-speed/higher-efficiency average operating point, and can add a full COP to the seasonal average performance. In a place such as say, Bend OR, the mid-winter mean temp is about 35F despite a design temp of +4F. In that climate, if underdesigned or right-sized for the load a pretty-good mini-split will deliver a seasonal average COP of about 2.8, but if oversized 25% it'll be well into the 3s, which is the typical whole-system COP for GSHP when pumping & air handler power are included. (Sure, using best practices with ideally sized high-efficiency pumps and water-to-water radiant you can hit the mid-4s with GSHP, but with geo there are design risks, and betting the farm that you'll beat the "typical" numbers isn't prudent. Figure on averaging 3.5 to 4, best case.) Oversized ductless is far less expensive than oversized GSHP, no matter how heavy the subsidy.

You can afford to spend quite a bit on reducing the load if net-zero is your goal, because you're not only spending more for every half-ton of heat pump, you're also having to spend for more PV to run it. Yes to designing-in passive solar, yes to getting the peak load under 2 tons, then spend anything left over on more PV, if you have any room left on the roof.

Simulate the thing using DOE2 or BeOpt (both DOE downloadable freebies) to optimize best bang/buck on building envelope improvements.

Putting the tubing in the floor is cheap, and leaves you the options of going with a radiant in the future. Wood boilers, active solar etc can add quite a bit of cush to the the place in the middle of winter, even if the primary heating system is ductless or GSHP-air, but it can also cook you out on clear days of high solar gain after clear nights of severe radiant cooling, since the slab starts out the day already warmer than room temp. Running the tubing north-south has the benefit of moving heat from the high passive-gain rooms to the cooler north side rooms too.

Packages to do a system like this are fairly standard,
Pipe 12 inch OC / 4 manifolds (1 per zone)
4 zones
60,000 BTU modulating electric boiler with out door reset
prefabricated boiler/pump system on stainless steel panel
Full package would run about 6,000.00
Naturally you would need a design and pipe lay out to get exact, but this gives you an idea of what an electric boiler type system would run.
Couple this with a solar PV grid tie system and you have a affordable package.
Dan

And for about same six grand, a mini-split based heating would use about 1/3 the power, reducing the size of the array required to hit Net Zero by a comparable amount.

Resistance electric heating can work in a net-zero environment for supplementary heat situations, but I've yet to hear of any all-electric net-zero home that was achieved without the heat pump advantage. Radiant cove-heating or similar can be added to rooms if and when necessary to maintain temp balance and comfort, but use of any COP=1 heating needs to be kept to a minimum to meet net-zero goals.

Marc Rosenbaum manages to pull it off with a PV array that still fits on the house, despite lower than optimal R values, with the aid of a cooperative partner with the appropriately parsimonius attitude toward unnecessary power use, but only by relying on a 1-ton Fujitsu with seasonal COP > 2.5:

http://blog.energysmiths.com/2012/07/one-full-year-of-usage-and-production-data.html

In a higher R/lower-U house you might not need as big a PV array as his, but if you're heating with an electric boiler you'd have to be at near-PassiveHouse levels to make it work.

even passivehouse ratings score heat pumps significantly better to discourage passivehouse proponents from going COP1.

Makes sense- resistance heating is about as good an idea as the incandescent light bulb- it might have been a great idea in 1912, but a the current state of the art of heat pumps in 2012, not so much.

It's cheap to install, but it isn't generally the best way to heat your house, even without Net Zero dreams.

So I like mini splits except for the appearance, a bit cumbersome on the wall. Question is how do you keep that slab comfortable in winter when it is zero out? That warm slab is nice.
With PV hitting record low prices .85 watt plus install, a grid tie support is fairly reasonable.Central Oregon is loaded with clear days in winter.
Dan

a PV array that still fits on the house

Ha Ha, pretty funny.

it isn't generally the best way to heat your house...

Out here, you hear a fair number of people say that resistance electric is "100% efficient". After all, that's as good as it gets, right? ;-)

I think it is a consequence of our history with cheap hydro....

I love the look of mini-split heads compared to having to fill the front and side yards with PV panels, that broke the bank to meet NetZero. :-)

Seriously, if the PV required to make it net-zero doesn't even remotely fit on the house, it's a ridiculous expenditure of resources just to come up with modestly higher comfort during the coldest 12 hours of the year. It's probably cheaper to install an air-to-water heat pump like the Daikin Altherma than it is to buy the "extra" PV to make an electric boiler go net-zero, but that's also a significant up-charge over a mini-split for marginally better comfort.

Installed prices of less than $4K/peak-kw are still the thing of legend in the US (unlike Germany, where the competition is fierce). Panel prices no longer drive the system cost, true, but until the rest of the system costs crash as deeply as the panel costs, it'll continue to be expensive. From a planning point of view I wouldn't count on $2/w installed showing up in the US before 2020, ( even if that's a reasonable price-target for Germany for 2013.) Plan on $5-6/w and hope for $4.

When you have a well insulated slab the slab temp tracks the room temp. With very low heat loads (< 5BTU/hr per sq.ft.) radiant floors are barely above room temp except when at the full design condition, which usually happens while you're in bed anyway.

For a primer on getting to net-zero with a PV array that actually fits on the house, check the details on some of the houses on Erik Haugsjaa's list:

http://ehaugsjaa.wordpress.com/resources/new-england-massachusetts-passivhaus/

installed cost for PV here in maine is about $3.50-$3.75/watt.

And at that price heat pumps are significantly more cost effective ways of meeting BTU needs with PV.

Posted By ICFHybrid on 16 Jul 2012 05:41 PM

a PV array that still fits on the house

Ha Ha, pretty funny.

Funny or not, that's the reality, unless you're already at PassiveHouse levels or lower (at an incremental cost in insulation well in excess of the cost delta between a mini-split and a resistance-electric heating system.)

I don't care where you are in zone 4 or higher in the US you'll never make net zero with an array that fits on the house unless you can leverage it with heat pump technology.  It's tough enough to do even WITH heat-pump technology, but it's at least within some economic-sanity zone doing it that way.

Now, if I could just get this dang mini-thing to give me some hot & cold running water, I could radiate the heck out of this place!