Sorry wanted to re-post this, as it got knocked to the 1st page from another one of my replies...

Another question... what, if anything are people with all electric mechanical systems doing for backup power?

Having gone through 1 week w/o power in NJ, two years in a row (granted this has not happened in VT, but it could) , a LP generator has been on my "want" list.

With the FE18 pulling max. 2,420 W to heat, it is possible we could still run off the smallest Generac Guardian (8000 watts) , leaving 5500 watts for pumps(would have to check wattage on these), refrigerator and lighting (just the basics). I know these things are the antithesis of efficiency, but will also not be used very often.

these houses have the same need for backup as any other house that relies on electricity, so a generator would be in order for long outages. However, there are new inverters on the market which will enable someone with a photovoltaic system to run one outlet in the event of a power failure. Not enough for heat and hot water - yet, but as with other technologies these are developing quickly so at some point soon you will be able to switch over to run the house on your PV system. Further, with the advent of electric cars, their batteries will have 70% of capacity remaining when they are replaced by new batteries, so the old ones can be used for in-house electrical storage.

As of right now, it looks like our heat loss will be about 17,000 BTU/hour at -13 F and 11,000 BTU/hour at 17F (roughly the average winter temperature here)   We're still pricing windows out so this could go down.

It looks like the FH15 has a rated capacity nearly exactly the same as our heat loss at 17F: 11,000 BTU/hour (input 1020 watts, COP: 3.15 - according to http://www.mitsubishipro.com/media/946493/fh_product_guide.pdf).

If we size the mini-splits slightly bigger (for example either FH15+FH9 or FH12+FH12), will that COP go up, or is it best to size it exactly to their "rated" output?

The other thing I am curious about is if we can get away with just one unit located downstairs--considering it seems that we are just about equal to the FH15's output rated and max output ratings.

Two units would give us these outputs:

FH15+FH9 would give us 11k+6.7k BTU/hour @ 17F = 17.7k BTU/hour
FH12+FH12 would give us 8k+8k BTU/hour @ 17F = 16k BTU/hour

Our 1st floor will be slightly bigger than the second, with a mudroom bump out and secondly, we like cold bedrooms (which are all upstairs) .  So having two FH12's would seem like an odd choice to me.  FH15+FH9 would give us some flexibility.   I should also mention we don't really run A/C, so that isn't a huge  factor.  

One more question.  Are the GE GeoSpring's proven in unheated basements?  How is this going to perform if it's 60F (or cooler?) in the basement for 6 months? 

Thanks

Patonbike,
Google "GE GeoSpring Problems".

I see the GeoSpring gets pretty bad reviews although I also heard  they have improved it in their newer versions.  We are certainly not married to the GeoSpring.    Interestingly,   Efficiency Vermont is really pushing these (actually any  heat pump water heater that qualifies) with a $550 rebate.

What would be a better alternative?

We can do a Rinnai RU80i (or similar) which says it will consume 156 gallons of propane per year.  I am not sure how this will do if we have hard water.

A Richmond 50 Gallon High Efficiency Condensing Power Direct Vent LP Gas 6-Year Tanked Water Heater will use 200 gallons a year. 

These are the Energy guide numbers, I am assuming that is the best way to compare apples to apples for actual usage.  Our usage obviously may be higher.  All of these are about $1300 per heater.

here are the energy guides showing 156 and 200 gallons/year = $312-400 in today's bulk propane prices for me.
Rinnai ru80i: http://www.rinnai.us/documentation/downloads/energy_guide_ru80i_kb2530ffud_us.pdf
Rheem condensing tank: http://www.menards.com/main/store/20090519001/items/media/Plumbing/Rheem/Energy_Guide_Label/6RHE50P-EG.pdf

Here is the list which Efficiency Vermont considers to be the most efficient electric heaters: https://www.efficiencyvermont.com/docs/for_my_home/eligible_products/evt-heat-pump-water-heater-qpl.pdf

The heat pumps advertise about 1800 KWH a year = $315 @ .175 KWH for me.

Thanks.

In my area, treated city water stops up tankless water heaters.  Any savings in fuel may be eaten in plumbing repairs.

How about other brand heat pump hybrid water heaters? Accelera 300?

My parents have the  newer version of the geospring 1 year old.  So far it has been flawless.  They were able to buy it with a 10 year extended warrantee (I think through GE) that covers parts and labor.
It is about right for 2 people who don't consume too much water.  They generally keep it in heat pump only mode unless guests are staying there.  It does take quite a while to reheat in heatpump only mode, does a great job of dehumidifying the basement.

Cheers,
Eric

After reading a bit more about these... I am not sure I'm convinced yet for our application. We use a decent amount of hot water (think kids taking baths!). We'd probably need an 80 gallon model to keep up, if that would even do it. I'm not sure I like the idea of cooling my unheated basement either. The Accelera has impressive numbers though, showing 1400 KWH per year per the EnergyGuide. A lot seems to depend on how cheap I can get propane.  Around $2/gal I am pretty close to the GeoSpring, basically same cost of the heater and install,  and very near operating costs, with I would have to guess,  better performance.

Posted By Bob I on 30 May 2014 10:19 AM
yes. Mitsubishi will have a model out shortly which will work with a minisplit compressor. Basically the refrigeration line from the outside compressor will go through the hot water tank on it's way to the minisplit.

Sounds like something I have been looking for, but the refrigeration line I would rather it end at the water tank. Not sure how well the VRF perform in dual mode where they can cool and heat at the some time?

Would love to have a Hot Water tank which can be heated by the outdoor HVAC compressor. The reason I would find this method more appealing than lets say the GE GeoSpring HPHW is that you have a higher COP and it should be more reliable.

I have seen units marketed and installed in Europe, but they where designed for hot water usage and for heating the floors. In Georgia we don't really need radiant floor heating.

Would love to hear more on this topic if anyone knows a bit more of whats coming or what available in the US.

If price isn't reasonable, I wont consider it.

I don't think you will find that a single heat source heats the entire house evenly enough, even if it is super insulated.

If this home does not end up "super insulated", just "well insulated and air sealed", is there any reason NOT to use air source heat pumps, as long as the heat loss numbers work?

I've come up with about 18k BTU/hour loss @ -13 F, and 11K @ 17F.   With 2 FH15's we can put out 2 * ( 62% of 18k) @ -13 F = 22320 K BTU, that is a 25% fudge factor... and when all else fails there is a wood stove.  Thoughts?

Specifications are looking like 2.5" thermax (R15) in the basement walls/slab edges, dense cellulose in 2x6 walls (R21 in the cavity), R50 roof, .29 windows, very good air sealing.

But the builder seems to think we need to go super insulated for the ASHP to be effective.

"But the builder seems to think we need to go super insulated for the ASHP to be effective."

If we are talking a single head mini split then I agree with your builder. If we are talking a ducted ASHP that would be rubbish.

I was thinking 2 separate single head Mitsubishi FH15 units.  One up and one down. 

The way people are getting a single head to heat a whole floor of the house is by super insulating the envelope. So what you plan would not work very well.

R21/2x6 & U0.29 windows isn't even IRC 2012 code-min construction in VT, not a high-performance building envelope.  R13/2x4 + R10 c.i. would be code min, and have good dew point margin for being able to skip interior vapor barrier, as would R15/2x4 + R10c.i.. But that isn't anybody's definition of "superinsulated"

Rather than using vague terms like "super insulated" regarding point-source heating, let's put a number on it:

If the heat load of an individual bedroom anything over ~1500 BTU/hr you'll run into pretty significant comfort issues on colder nights, unless you keep the bedroom door open all the time and even then you may need to run auxilliary heating (maybe some baseboards to back-stop the room temp for the coldest nights) if you like to sleep at 68F or higher.

But at 1000 BTU/hr or less, not so much. At 1000 BTU/hr you may have to use some auxiliary heating or leave the door open to keep it at 68F on the very coldest of nights but most of the time it won't matter.  If you're fine letting it drop to 62F while you're sleeping you won't need to prop the door open even on design-day.

At a room loss of 500 BTU/hr a pair of sleeping adult humans (or one human and a large dog or a goat :-) ) covers the load entirely.

USDA climate zones are somewhat meaningless in this context. The relevant zone map to use for energy use & HVAC purposes are the DOE climate zones (VT is entirely zone 6):

For clarification, the original plan was a VT "Gold" home, now we are looking at "Silver" which is basically code + better lighting , and appliances and HVAC , and in our case windows and doors ( which are not required by the program).   The levels are in the rnc tier comparison chart below.

The R21 cavity (in this case dense packed cellulose, and no vapor barrier) meets VT energy code. I am not sure why this differs from IRC 2012, but here's some specs on VT energy code:
https://www.efficiencyvermont.com/docs/for_partners/rnc/rnc-tier-comparison.pdf

On this doc, page 30 shows different methods to meet code. If you have R38 ceiling, you need the R20+R5 value on the wall (which is what IRC 2012 says, at least with regard to the walls), but if you have R49 ceiling then you do not:
https://www.efficiencyvermont.com/docs/for_partners/rnc/2011-VT-Energy-Code-Handbook-V3-1.pdf

In terms of sleeping temps,we sleep pretty cold (much lower than 68--probably 58) and are not big on closing doors.

But when we wake up and go downstairs, we like it reasonably warm. The living, dining and kitchen will all be open to one another though.

I have never met anyone that regretted using extra insulation(or air sealing). The decisions you make today, you or someone else will be living with for the next 50+ years. Every generation realizes the previous one did not use enough.

No way in heck I would condone R38 ceilings in new construction in VT. The cost basis to increase insulation in the new construction realm is not that high, especially with cellulose. It is much more costly to do it retroactively. The lifespan of the envelop is a lot longer than that of the appliances or HVAC, so if you are going to trim costs, the shell is the last resort as far as I am concerned.

Just food for thought
Eric

"meets VT energy code"
Keep in mind that "code" is the MINIMUM allowed by law. It is NOT the ideal amount, nor is it the best amount, it is the least amount allowed.

"At a room loss of 500 BTU/hr a pair of sleeping adult humans (or one human and a large dog or a goat :-) ) covers the load entirely."

What about a caribou?......or bison? LOL