More calculating on our future build in Central Oregon is shooting down another technology.

We are planning on very efficient, possibly passive haus.

We are planning on GSHP which is probably overkill, but with the rebates and incentives it is attractive and there will be no concerns with minimum temps nor need for Backup, like MiniSplits

Originally I was planning on a desuperheater, but since we will also have a very efficient fireplace, and we like to use it a lot, aand a lot of passive solar, this would greatly reduce the amount the GSHp will run. Since we anticipate almost no cooling need with natural ventilation and a good envelope, and then factor in the shoulder seasons, which are neither heat or cooling, the DSH just doesn't make sense.

Then I went back to solar hot water.  We are very frugal with water in general, and especially hot water. Our current gas usage with a 62% efficient water heater is 7CCF per month. If it were 100% like an electric water heater then the usage would only be 4.64 CCF per month.   This converts to 127 KWH of electricity per month.  Then using a ASHP water heater will increase that efficiency and drop that usage to 48.26 KWH per month. or 579 KWH per year

With an extremely low rate of .06125 per KWH my total water heating bill looks to be about $35 per year.  That eliminates solar hot water heat as well.

But wait, I think I can go lower.....  Since the biggest reason to use a tempering tank is to preheat water and lessen the load on the water heater, it would seem to make sense to me that if you put in an UNinsulated tank ahead of the water heater, and the frugal use of hot water would mean a long time in the tank, you could bring the water up to ambient, say 70 which only gives you a delta T of about 55 degrees from WH output rather than the approximately 75 degrees you would have without it.  All this with minimal cost up front and zero operational cost. That could save another say 15 to 20%?

These numbers seem ridiculous but you have to remember,  two person occupancy and a frugal HW lifestyle, extremely low electric rates, Well built tight envelope, and very sustainable power supply.

A gas water heater that tests at 0.62 EF isn't running more than about half-that at your volume of use. The standby losses are about the same, but for a lower used volume, ergo lower net efficiency over time. Figure on no better than 35% efficiency as-used. That still makes the financial argument against solar hot water compelling, but you'd need to adjust the electric numbers too.

Electric tank heaters aren't 100% or even close- they're 90% after standby at 62-64 gallons /day use (the EF test volume), and if you're using only 20-25 gallons/day (or less) the standby doesn't change, but it's applied over a much lower volume. A WAG would be that an electric tank is no better than about 70-75% efficient at your usage levels, and it may be less than 50%. But it's still a small number.

Electric tankless heaters ARE pretty close to 100% efficient, and if you're pre-heating with a large tempering tank or desuperheater that's always 70F it may even work for you, despite relatively cool incoming water temps. A tempering tank still has an operating cost, at least during the heating season, since 100% of the heat going into the tank has to be made up by the heating plant or the house will get cold. So if GSHP, it's heating it at GSHP efficiency. The same is true for the ASHP water heater, assuming it's a tank-top type, not a mini-split style. During the cooling season the operating cost is net negative, since it's lowering the cooling load by moving conditioned space heat into the the water, but the rest of the year it's space heating load.

If subsidized sufficiently there may be a financial argument for a tanktop-heat pump water heater or an electric tankless, but probably not at the unsubsidized market-rate prices of the equipment.

Wiring the place for photovoltaic in hopes that the installed $/W will drop to the levels currently seen in Germany or lower in a reasonable time frame probably an OK bet though, and net-metered it could offset your GSHP operating bill pretty substantially. But in the land of 6 cent retail electricity even $2/W-pk PV is a tough sell without other incentives.

at 0.061$ kwh very few things make economic sense. At near pasive house levels of insulation and air tightness, I would think a Mini split or two coupled with a well insuluated electic water heater, marathon or similar are probably economicaly the most logical, Personaly I would go with a high effeciency small wood stove instead of a fireplace I am sitting by one right now. One thing you will find is that a tight well insulated home can be a problem to heat int he shoulder seasons. It seams like as soon as you fire it up the house is too hot. Good Luck Eric

Dana,
I realize that the efficiencies of both water heaters the gas and the electric are not as stated on the nameplate due to tank loss, but assume that to be a wash. If I drop the gas usage due to the efficiency loss then the KWH goes even further down meaning my replacement would be even lower. I had to look at it closely to believe it with these levels. When I stated 100 percent efficiency with electric water heater that would be the energy transfer not the storage losses accounted for. So as I said, I think it is a wash. As far as the water heater itself, I am planning on a GE geospring, which you can now buy for $1000. The subsidies amount to about $300. so the payback on that versus a subsidized Marathon is 4 years.

There is the cost of heating the tempering tank, but between passive Solar, the fireplace and then limited GSHP I feel it is pretty negligible. I really do appreciate your input. I fell if I can convince you it is pretty solid.

Eric, The Mini splits do make more financial sense, but in this case the subsidies are huge. That narrows the gap substantially. This is one of the few areas that I may be overkilling slightly but am pretty sold on the technology. My calculations show that the ASHP water heater will lower use of about 60% over the marathon. Efficiency rating of 2.4 Vs .94

As far as the fireplace, we currently have a Quadrafire 7100 fireplace and really love it. It is burning as we speak. One of the advantages over a stove is that it is capable of remote heat delivery through ducts. Since we are basically building a L shaped ranch this can be a real advantage. This is one place where Architecture has some priority as well, and a fireplace wins here.

You are right about the shoulder season's, that can be a challenge, that is where we are counting on the Passive solar as our area, has good shoulder sun numbers, and coupled with good windows and design, should perform well. I appreciate your comments as well.

I'm surprised that heating/cooling using GSHPs makes any kind of financial sense for a residential structure built to PassiveHaus standards, even with rebates and tax credits (unless the structure is just huge in size).

Surely there are less expensive heating/cooling options than GSHPs when down in the fractional to 1+ ton range, net of rebates and tax credits.

GSHPs really start making sense when you start at about the 2+ to 3 ton point, and go a lot higher (i.e. many school districts are converting all of their building to GSHP).  Now you're delivering a lot of heat at COPs higher than 5.0, getting excellent return on the investment.

Best regards,

Bill

No it isn't huge in size,2600 sq. ft., But L shaped, and as I said this area is a little overkill, but the generous rebates, having a lot of room for a loop and the ability to do the excavation myself really does make it closer. Any other loads we apply such as the ASHP WH, is supplied at GSHP Efficiencies, and since we will travel during some below Zero conditions, there is some piece of mind that no backup is required.

I have no doubt that the cost of operation of a tempering tank is very low with a GSHP- just pointing out that it's a non-zero number, (You did claim "..zero operational cost.") In most PassiveHouses the annual hot water heating energy exceeds the space heating- if you have that kind of house even at low water use the tempering tank could add up to a double-digit percentage of the total duty cycle on the GSHP during the heating season.

You might have days when it "sweats" a bit of condensation after a larger than average draw, so if you go with a tempering tank to pre-heat at GSHP efficiency it's worth putting it on a drip-pan.

The heat pump water heater will use less energy than the Marathon, but I'd like to see the calc that comes up with a net 60% reduction! When you get into the penny-accounting you have to also account for the increased the duty-cycle on the GSHP in winter, and the lowered duty cycle on the GSHP during the cooling season (which may be longer than you think at PassiveHouse insulation levels.) The the heat pump water heater doesn't run at GSHP efficiency the way the tempering tank does- only the portion of the heat extracted from the room is at GSHP efficiency, which is only about half. The EF of a heat pump water heater also has to be derated for the low-volume use- anything over 2 is unlikely for sub-30 gallons/day use. During the heating season any better than a 25-35% net reduction in water heating energy use relative to a Marathon is unlikely, even if you assume the GSHP is hitting a COP of 4. But the cooling season offset in load may more than make up for it. Or not- it just depends.

Bottom line- you have to model this carefully against your actual heating & cooling loads & anticipated GSHP efficiency to come anywhere near a real number, and it may turn out that it's better than a 60% reduction, or maybe it's only a 20% reduction. But even a 90% reduction of nearly-nothing is still nearly nothing.

The notion that a mini-split needs "backup" or that freeze up is even possible at PassiveHouse levels of insulation should the power go off or the heat pump fail is a bit silly in your neighborhood. Even a couple 1500W (5100 BTU/hr) space heaters can handle design-day heat loads, and in a passive solar house you'd only risk freeze-up if an earthquake took a few windows out during a cold snap while you were trekking in the Andes or something, (in which case a right-sized GSHP wouldn't necessarily cover the difference.) There are MANY NetZero Energy houses and PassiveHouse examples out there heating with mini-splits without backup in places colder than central OR. They're pretty simple & reliable, well-evolved systems.

Any Mitsubishi H2i series is still running and putting out something at -13F, which is never a sustained daily temp at any central OR location other than at some of the higher mountain peaks. Daikins and Fujitsu with specified -20C rating are still putting out too (the output is just unspecified at -25C.)

FWIW: There is a certified PassiveHouse 5 crow-miles from mine (design heating temp= +5F, usually gets down to -10F at least once/decade) heating & cooling with a 2 zone 2.5 ton Mitsubishi (one head per floor), and it's usually running in cooling mode even in winter. (Teenage kids with multiple game machines & big screen TVs for bigger than presumed average plug load.) But you could kill the power to the house and leave for the winter and it would NEVER freeze up, not even close! The peace of mind comes from the high-R building envelope, not the rightly or ronglee presumed reliability of the equipment (or the power grid, which strands a GSHP as easily as any other grid-dependent heating system.)

Some details on that house and it's measured performance:

http://www.passivehouse.us/phc2011/2011%20Presentations%20PDF/Panish,%20Paul%20-%20Ad-Hoc%20Passive%20House%20-%20The%20Beaton%20Residence.pdf

http://www.passivehouse.us/project_detail.php?id=1025

http://www.deapgroup.com/Beaton_poster-s.pdf

OMG. You have a fireplace, too?

Do the minisplits and with the money saved put in a solar hot water tempering system and lots of solar PV.

Are you in love with the idea of digging a hole for geo, or what?

Somehow missed the part about the fireplace- which is not the greatest fit at PassiveHouse levels!

Finding an sealed combustion non-catalytic EPA rated fireplace with sufficiently low output to no roast you out of the place by the time it got hot enough for the secondary burners to kick in is a problem in very high-R houses. But there are a few tiny high-mass woodstoves and wood boilers that can throttle back to ~10KBTU or even less. Something as big as the Quadrafire 7100 won't run in low-pollution mode at anything under ~25-30KBTU/hr or so, which would turn a high-R house into a sauna unless it's high-mass house with good convective air movement.

A woodstove/boiler/fireplace with a MAX rating of ~25-35KBTU would be about the biggest that makes sense in the house you're describing. They'd still be able to run in high-efficiency/low-pollution secondary-burn mode at about half the full rated output or maybe a little less (depends on the model.) I know of very few wood burning fireplaces rated under 50KBTU/hr max, which would correlate to a practical min at high-efficiency combustion of about 20-25KBTU/hr, which can be more than the design-condition heat load. A better choice would be a tiny high-mass woodstove.

From a cuteness point of view the Hearthstone Tribute (or Bari, if you like the Euro-modern look) , which can throttle down to ~12KBTU out and still maintain secondary-burn mode in an all-night burn, but it takes pretty tiny wood. The specs say 16" logs- figure on 14" since it doesn't have a side-door to assist in loading. But smaller logs aren't always a show-stopper, and it's a very decent performing and good looking li'l stove. It's not cheap, but it has some thermal mass- won't give you hot-flashes the way a cast iron or steel woodstove would.

There are smaller-output cast iron woodstoves out there, but they often tend to be under 70% efficiency (vs. 80%+ for better high-mass wood burners), and some, like the classic Jøtul 602, have no options for ducted combustion air, which is important when building to anything like PassiveHouse tightness. The Vermont Casting Aspen or Intrepid-II might work, but they're cast iron. Ceramic or stone stoves with some thermal mass would be more comfortable, and building small but hot fires you can probably avoid the overheating flash yet still burn mostly at high efficiency/low-pollution.

Digging the hole for the GSHP is the least of it. The system designs are all custom (and carry some risk of lower than expected system efficiency) and a good system design can (one might argue SHOULD) cost as much as a well-engineered & tested 1.5-2 ton mini-split. The hardware for GSHP is also fairly low-volume production which carries higher cost compared to the literally 10s of millions of mid-sized mini-splits sold every year. There are only ~150,000 GSHP systems installed in the US every year (2011 figures) and that's including all commercial & industrial applications, not just tiny-load high-R single-family house systems. The design risk of going with a mini-split is miniscule, and the efficiency in a central OR climate is approaching that of middle of the road GSHP systems that cost several times as much. See:

http://neea.org/docs/reports/ductless-heat-pump-impact-process-evaluation-field-metering-report.pdf?sfvrsn=16

It's a big document, but look at the performance numbers in Table 24 for the Eastern Idaho cluster, which is comparable to the coldest central OR climates. The mean field-measured COP was over 2.8. If you went with a Daikin Quaternity (or any other mini-split with a 12+ HSPF, of which there are several) your average would be in the 3s. Yes, you can hit 4+ with a better-class GSHP and a good design, but "typical" implementations in the real world measure in the 3s with all pumping power factored in, and unless you have a better-class designer, don't count on breaking 4.5. In a PassiveHouse type house in 6 cent electricity land the efficiency delta will NEVER pay off the upfront cost delta (even with the generous subsidies for GSHP) with effectively no heat load. And the cooling efficiency of a mini-split will likely exceed that of GSHP in a PassiveHouse.

Bill (a0128958, who is in the GSHP biz) draws the sanity line for GSHP somewhere between 2-3 tons of peak load, which is about right at average US electricity prices, but yours are about half the US average which pushes up the number at which it makes any sense, even with subsidy, even with DIY diggin'. PassiveHouse (and most NetZero) house loads are nearly always under 2-tons, many under 1-ton, which is the sweet spot range for single-head mini-split technology. A mini-split (maybe two small ones, if the wings of the house are too remote from one another) plus a tiny high mass woodstove are probably ALREADY overkill for the house you're conjuring.

Posted By Dana1 on 09 Nov 2012 04:19 PM
...Bill (a0128958, who is in the GSHP biz) draws the sanity line for GSHP somewhere between 2-3 tons of peak load, which is about right at average US electricity prices, but yours are about half the US average which pushes up the number at which it makes any sense, even with subsidy, even with DIY diggin'. PassiveHouse (and most NetZero) house loads are nearly always under 2-tons, many under 1-ton, which is the sweet spot range for single-head mini-split technology. A mini-split (maybe two small ones, if the wings of the house are too remote from one another) plus a tiny high mass woodstove are probably ALREADY overkill for the house you're conjuring.

Dana, we're aligned.  And you bring up two additional good points: at half the kWh rate, even with a cut rate DIY cost, GSHP stuff just doesn't make sense to me when you're spending a lot of money elsewhere (PassiveHaus standard and still with a fireplace).  PassiveHaus + GSHP just strikes me as overkill in almost all situations.

Down here in Dallas, when someone's ready to replace their HVAC equipment (or needs to), in an existing not so energy efficient structure, my counsel is to get on with GSHP and then look later at windows, doors, insulation, radiant barrier, etc.  Most will find it's not cost effective to pursue windows and doors particularly after switching to a (well engineering installation) of GSHP.

Best regards,

Bill

Bill- we couldn't agree more. Retrofitting high R/low-U in to an existing occupied home can far more expensive than building it into new construction. That makes the economics of highest efficiency mechanical systems more attractive than deep energy retrofits, unless the place is nearly a complete wreck needing extensive rehab from a siding/windows/roof point of view. In a bigger-deal rehab the high-R/low-U economics vs. high-performance mechanical are based on the cost differences between code-min & higher-performance building elements rather than functioning-existing vs. whole replacement, and it's rightly viewed over a much longer time horizon.

Well, that is why these discussions are here. I guess I will take another look at the minisplits.
Thanks.

In the case of retrofits we typically confine our envelope improvements to spray foam insulation (brings ducts into conditioned space) and window film on west glass. The rest goes into higher eff HVAC, hot water, lighting, pool pumping.

Dana,
I had thought about reassessing the fireplace, and you are correct, our 7100 does put out a bunch of heat. What I hadn't thought of was the loss of pollution control at low burn rates.
Initially we had steered away from wood stoves, because they did not fit the Contemporary/ Modern look we are designing for. However after your information, I took a look at the Bari,
As well as the Rais, Wittus, and Morso. I think we may find something we like at the heat levels that make more sense.

I can then look at moving some of the air with different methods.

About the minisplits, with one side of an L shaped house having several rooms, Bedrooms, Bathrooms, laundry, I am assuming I will have to have a ducted minispit?
The other side is pretty open.

Whether it has to be a ducted minisplit on the wing with the doored-off areas depends a bit on the heat loss out of the rooms when the doors are closed, and whether the doors would stay open most of the time. With just ~10-15 square feet of ~U0.20 or lower window and high-R wall/roof it's possible to get pretty reasonable temperature balance using the HRV system, with the ventilation pulling exhaust air from the doored-off rooms, supplying the ventilation air from the space with the mini-split head.

In a typical Net-Zero 2-story with the bedrooms and bath upstairs using that strategy, even putting the mini-split head in the hall can work. But if you have a master bedroom with a big view window + a bunch of smaller rooms along the hall it may be somewhat more difficult, and short runs of ducted mini-split may be better. But in a house with PassiveHouse type U-factors the room to room balance issues are very small compared to typical houses.

There are quite a few nice sealed-combustion tiny Euro-modern woodstoves & wood boilers out there nowadays. I'm sure you'll find something suitable. It's a bit tougher if you're looking for a tradiational old-school 'merican or Skandahoovian-cabin stove sort of appearance.

Posted By Dana1 on 09 Nov 2012 04:19 PM
The design risk of going with a mini-split is miniscule, and the efficiency in a central OR climate is approaching that of middle of the road GSHP systems that cost several times as much. See:

http://neea.org/docs/reports/ductless-heat-pump-impact-process-evaluation-field-metering-report.pdf?sfvrsn=16

It's a big document, but look at the performance numbers in Table 24 for the Eastern Idaho cluster, which is comparable to the coldest central OR climates. The mean field-measured COP was over 2.8. If you went with a Daikin Quaternity (or any other mini-split with a 12+ HSPF, of which there are several) your average would be in the 3s. Yes, you can hit 4+ with a better-class GSHP and a good design, but "typical" implementations in the real world measure in the 3s with all pumping power factored in, and unless you have a better-class designer, don't count on breaking 4.5. In a PassiveHouse type house in 6 cent electricity land the efficiency delta will NEVER pay off the upfront cost delta (even with the generous subsidies for GSHP) with effectively no heat load. And the cooling efficiency of a mini-split will likely exceed that of GSHP in a PassiveHouse.

.

I, of course, read the whole document. Although this study is actually  all based on the ASHP being a Supplement to existing ER heat, it does in fact show the high efficiency of some ASHP's. I was not aware they were quite that high. I will of course do a complete cost study after final design and energy modeling, but will give ASHP's a new look.  It will be interesting to see where the final numbers come out.

Basically If I can get a cop of 3 with ASHP and a 4 with GSHP, The GSHP has to come within $2000 to have a reasonable payback period. (based on a 1 ton system) Probably not going to happen.

If your load analysis shows that all you need is one ton for a 2600 sf structure oriented and designed to PassiveHaus standards, you can skip all of the analysis time you might spend trying to figure out which one has a faster return on investment: 1 ton geo versus 1 ton mini-split.  There's just no comparison.  I'd get on with spending the time figuring out which mini-split serves you best - at the one ton level geo's just not going to be close to being cost competitive.

Best regards,

Bill

Yes, the NEEA document only covered retrofits in standard-construction houses, but there is a lot of hard-data on efficiency you can expect in relevant nearby climate zones. Also note that most of the units monitored in the field were a few years old with an average nameplate HSPF under 10, which will underperform this year's latest-greatest. There are now several 3/4 ton and 1 ton units on the market rating an HSPF of 12 (!).

There are quite a few examples of heating PassiveHouses and Net Zero houses in New England heated with 1 & 1.5 ton mini-splits.

http://uphillhouse.wordpress.com/2011/07/28/air-source-heat-pump-installed-part-1/
^^1.5 ton Mitsubishi here, the local heating design temp: -5F.

http://blog.energysmiths.com/2011/03/out-with-the-old-in-with-the-new.html
http://blog.energysmiths.com/2011/12/living-with-point-source-heat.html
^^ 1 ton Fujitsu here, not a super-insulated house but better than code, outside design temp: +10F.

http://www.mass.gov/eea/docs/doer/zero-net-energy-buildings/townsend-case-final.pdf
^^IIRC this house is heated with a pair of 3/4 ton Mitsubishis (one per floor), outside design temp: +6F.

The same guy who built the last one is doing a development of Net Zero houses heated with 1-ton mini-splits (again, one per floor on the multi-story houses):
http://transformations-inc.com/press/PDF/Solar_Today_Nov-Dec-2011.pdf
interviewed here: http://www.zerohomes.org/2012/08/02/affordable-zero-energy-home-construction-an-interview-with-carter-scott/

The rapid improvement of ductless heat pump technology over the past 10-15 years represents a real sea change for heating well-insulated houses even in fairly cool climates. I doubt the end of the efficiency curve improvements has been reached yet- there's still a gap between measured efficiency and the absolute theoretical maximum dictated by the laws of physics, plenty of room to improve.

Why not do a ground source water heater instead of an air source water heater or gas/electric. This may be a bit overkill but if you are already installed a loop its very easy to add the extra capacity. Second in central oregon a heat pump water heater will not work well in your garage because the garage will drop below the operating temps and you will just be using a very expensive electric water heater at that point. If the heat pump water heater is in the conditioned space then you have to worry where you will vent the cold air from the heat pump water heater and where the makeup air will come from. If it is in the conditioned space and you are using the ground source to heat the space, you might as well just make the ground source heat the water and take out the middleman(the heat pump water heater that uses air that is heated by the ground source heat pump)

SkyHeating, do you know who makes a "ground source water heater"? I have not found one yet. Another reasonable option would be a split air source heat pump water heater. Those are ubiquitous in Japan (called eco-cute), and getting popular in Australia.