Haven't seen the EcoCute (or any other CO2-refrigerant heat pump) being marketed in the US yet. Sanyo has had a pretty decent 9kw hydronic output air source heat pump good for space heating + DHW on the market in Europe (and presumably Asia) for a good handful of years now. I'm not quite sure what's holding up introduction to the North American market- perhaps it's a perceived (or real) lack of market, since most heating systems in the US are ducted hot air, not hydronic.

I wanted to resurrect this thread to get additional input as we have made some changes as we continue in design. As stated the GSHP does not pencil out. We are now planning on Misubishi Hyper heat Mini's But to really nail down the Hot water costs I want to get input on my latest plan.

I am planning on an ASHP water heater. This will be placed in the utility room next to our Freezer, as they compliment each other. There will also be a large Pressure tank, to minimize well cycling and the aforementioned Tempering tank. The 50 gallon tempering tanks constitutes about 50% of our daily water use. Most of the year any temperature change in the tempering tank will be very gradual because only a fraction of it will be replaced at a time. The exception would be if we were to hook up outside water such as garden through the tank, the increased use will cause the tank to cool substantilly, but this would only be in the summer when the cooling is desireable. Sweating is probably not an issue due to the low humidity but a drip pan is a cheap insurance policy.

We are planning a wood fireplace, about 30K BTU's maximum is the lowest we can get, so we also have the option of operating it similar to a Masonry heater, (quick hot fire then let it die down.) It will be placed in a concrete surround in the middle of the main living space. This should help store some heat in the concrete. We currently provide almost 100% of our heating needs with wood, I don't see that changing much, but will also have the benefit of increased passive solar, so wood burning will be mainly in the evening and possible early morning. So based on that the tempering tanks allows us to preheat the water, in order to lower the DeltaT of the incoming water and the efficiency would be the COP of the water heater, with a smaller delta T, adding a small amount for the heating of the tempering tank when necessary by the Mini split, but then realizing that lowered Delta T is usually supplied by Passive solar or wood heat.

Make sense? Holes in my theory?

Whirnot,
Have you investigated using a "masonry heater core" as your "fireplace"? Masonry heaters can include a "bypass damper" that bypasses the heat storage channels and makes it like a simple fireplace. With the bypass open fire viewing and oven use can occur when heat is not needed. Also have you read my post about ducting a mini split?

I suspect that a $1200 heat pump like the Fujitsu AOU9RLFC could be combined with the indoor unit of a Fujitsu Waterstage (imported from the UK) to get an outdoor air source water heat pump. But it's speculative and definitely DIY.

Posted By Liebler on 04 Aug 2013 04:04 PM
Whirnot,
Have you investigated using a "masonry heater core" as your "fireplace"? Masonry heaters can include a "bypass damper" that bypasses the heat storage channels and makes it like a simple fireplace. With the bypass open fire viewing and oven use can occur when heat is not needed. Also have you read my post about ducting a mini split?

I have investigated the Masonry heater. Oregon regulation require an EPA certification.

I see no reason to duct the minisplit, Our design provides for good peformance with a single minisplit.  Passive haus levels of sealing make this possible. My local Mitsubishi rep is very familiar with Passive haus and confirmed this.

It will be placed in a concrete surround in the middle of the main living space

Seems like a no-brainer, but you might be surprised at how much heat DOESN'T go into masonry surrounding a proper wood-burning fireplace, particularly if it is a built-in. Built-ins are designed to emit heat in certain ways; not necessarily to your enclosure. I can run my wood-fired built-in for three days straight before there is much of an increase in temperature in the masonry chase surrounding it, and even then, it's not much. Also, I'm not sure if the notion of a quick, hot fire works well in anything but a masonry heater designed to be used that way.

Posted By jonr on 04 Aug 2013 05:32 PM
I suspect that a $1200 heat pump like the Fujitsu AOU9RLFC could be combined with the indoor unit of a Fujitsu Waterstage (imported from the UK) to get an outdoor air source water heat pump. But it's speculative and definitely DIY.

Interesting concept but the economics aren't there. The HPWH costs about $500 after rebates. With an estimated cost of water heating in the high $20 to $30 per year the payback just isn't there.
Most of this is all because very low hot water use, and extremely low electric rates. Kind of changes the whole game.