Daikin althermas are available in the US and Canada though, definitely. There are some areas still where it's hard to find a trained installer I'm sure.

That can change simply by making your interest known. My experience has been that installers will jump at the chance to put the first Daikin unit in. I was surprised to find that one I contacted took it on himself to get the training, and before I knew it he had one installed in his shop and was eagerly exploring it. They are ideal for my climate area, so I suspect it represents a significant competitive tool for them.

The Daikin solar option is simply an external heat exchanger with circulator (and control boards) that can supplement the Daikin DHW heating system. The heat exchanger allows a closed loop glycol system for the solar collection (you supply the solar panels). It's set up so that if the solar panels are unable to heat the DHW tank during the day, the Daikin unit will cut in and provide heat pump heating for the DHW by evening or throughout the night for the next morning. Of course, the Daikin DHW tank also has a resistance element to ensure demand is met.

The first question to ask might be "Is the solar unit actually available yet?". At last check, which is maybe two months ago now, several contractors said they still couldn't get a definitive price or delivery date on the system, however, at least one of them felt good enough (or eager enough) to supply a bid which included it.

My issue with the system is that your solar panel output will have to be above the temp of your DHW tank in order to be effective. If the DHW temperature has been drawn down by morning usage (or usage during the day), then you are in a better position to utilize the solar contribution.

Because solar is less consistent in my area, I have chosen to put the solar panel output into a large "preheat" tank which stores about 3 days hot water volume. This allows maximum utilization of solar capability. If the solar output is high, the tank can actually get above standard DHW temp and will reduce the temperature of the feed to the Daikin DHW tank by mixing. In these cases, the tank might represent even longer supply than three days.

If solar output is low, the preheat tank will be more like incoming water temperature, but that represents a good opportunity for the solar panels to do even a little work, boosting the temp from, say, 50F to 75F before it needs additional energy in the final DHW tank.

The worst part of all this is that the cheapest hot water is produced when the heat pump is in cooling mode which is the same season when solar input is also plentiful.....

Posted By Wedge on 20 Feb 2011 06:12 PM
Overkill in terms of retun of long term payback vs.investment for geo. Radiant is must in my book, the dog and I like a warm floor so we are not negotiating on that one. Arctitect sugested a forced air alternative may be less costly give layout.

Yes we are looking at costs closely, not just the construction phase but long term, that is the reason we will build with ICF. We like the idea of the heat pump as a heat sorce, from what I keep reading air source continues to improve, especialy with solar assist as a way to help reduce operating costs.

RRR

My unconventional heating/cooling system is working great. You might give it some consideration, if you're willing to be a little bit of a contrarian. I designed and built my 2000 sf single story ICF house in 2008/09. The roof is insulated with spray foam on the underside of the roof deck. We've been in it now almost 2 years. Our design temp for heating is 9°F. We went below that maybe 3 or 4 times this winter. My max heat load calculated out at about 34,000 Btuh. My best estimate of actual heat load is right in that area.

I have a 36000 Btuh Daikin VRV-S air-to-air heat pump. It outputs heat as low as -5°F. The air handler is in the crawl space with only short ducts to direct the air flow to all parts of the crawl space. There are registers all around the perimeter of the house so the crawl space serves as the supply plenum. I have grills in the ceiling all around the house with a return duct from the attic to the crawl space and air handler. The air handler runs constantly so we have a constant air flow all through the house. There are no hot or cold spots and no drafts. I really wanted to go with in-floor radiant for the same reason you do. By using the crawl space as the supply plenum there is warm air under all the floor. This gives me a "quasi-radiant heated" floor.

The comment about the floor in a well insulated house being not so much warm as it is "not cold" is spot on. The floor has never been cold underfoot, but neither has it been noticeably warm. The thermometer I have in the crawl space seldom, if ever has been above 85°, and usually it's only about 2 to 3° above room temp. When I've checked the floor temp it has been just above room temp. With this system I have the benefit of a heat pump and some of the benefit of an in-floor radiant heat system, all at nearer the cost of a conventional forced hot air heating system. The Daikin VRV-S has no auxiliary or backup heat strips built in. My auxiliary/backup heat source is a pellet stove in the living room. We turned it on only a couple of times this winter, and that only for the ambiance factor! The house stayed a constant 74°, with maybe a drop of a degree or two on the coldest 2 or 3 nights. I don't recall exactly.

Now, another consideration. Do you have natural gas available? When I started my house design gas was around $1.10/therm. Now it's about $0.70/therm. Electricity is about $0.09/kwhr. At the current prices the cost of heat from a 2.5 to 3 COP heat pump is about the same as from a 95% efficient gas furnace. Reportedly gas reserves are being developed that will keep gas prices down for years to come. This is a wrinkle in heating economics that should not be ignored, especially in a smaller super energy efficient home. That's why your architect is questioning pay back of the combined heat pump/radiant system. The payback may not be there for 15 to 20 years. Also, if you've read any of my other comments here on GBT you will know that I emphasize a lot that in a smaller energy efficient house the heat supply from daily living activities cannot be ignored. A significant amount of heat is generated from TVs, computer, cooktops and ovens, and even CFLs. In fact upwards of 99% of the electricity that enters the living space of your house is converted to heat that enters the living space. Your bodies also contribute significantly. If you really are committed to radiant, take a hard look at a gas boiler with solar assist. That just may be cheaper than a heat pump, both in up front costs and operating costs. I don't know.

You need to be careful that you don't end up with a heating system design akin to using a dump truck to deliver sand to your kid's playpen. You still may end up basing your decision on comfort considerations over economics. Right now, that's the overriding justification for my decision to use the Daikin heat pump in my house. In the end I just could not justify a geo source heat pump with radiant heat, and that's what I really wanted to put in. Call it a life long dream gone down the tubes!

Well done demaceld!

Your "ductwork" may be in question, but your conclusions spot on.

A condensing water heater with DX fan coil for AC if you must. Natural gas should be used where ever it is available.

Ground source heat pumps rarely make sense in residential application, a fact that will be borne out with the loss of federal tax credits.

I continue to use a lot of minisplit heat pumps for smaller homes.

we have discovered a sensor miscalibration that has thrown off our numbers. most of our COP calcs were overstated by 0.5 to 1.0 COP or so, our return sensor to the altherma was reading a degree low.

So things are still doing well: we are solidly in the COP 2.5 to 3.0 range under most conditions, but it's a little less great that we thought originally. Still pretty great though!

Sorry for the oversight and misinformation! if anyone is interested in our data, you can always email me, we're happy to share.

The thermometer I have in the crawl space seldom, if ever has been above 85°, and usually it's only about 2 to 3° above room temp.

So, help me understand this better; the crawl space is above the temperature of the living spaces due to the supply ducting and heating unit being down there? Is that elevated temperature found throughout the crawlspace or just in the vicinity of the heat plant? Is there any insulation between the crawlspace and the floor? What did you use to stop heat loss to the ground in the crawlspace?