One thing to keep in mind about this idea is that air is a horrible medium for heat storage. It doesn't really hold much heat, and it readily releases and absorbs it. The heat pump would exhaust the stored heat energy in the surrounding air as quickly as it would the transfer that heat to the same volume of inside air which doesn't really count for much since it's the ambient temperature of the structure and what it contains that really needs to be affected, thus a more dense mass for storage would be far more effective.
Even so, it would have a 1 time cost, and any heat that could be pulled would be free. Was also kinda playing with the idea of a solar water heater for the house, could run the line from the solar heater through the heat pump's little hut, and have a radiator to add extra heat to it.
I know these are off the wall ideas, but perhaps from the BS I spread on this topic an actual good idea may grow .
So far as the house goes, was looking at a metal building with an inner shell house, with a ton of insulation in the middle. Now I'm kinda looking at doing a passive solar house with high thermal mass, building the place out of cement with a nice, thick floor. One thing I really like about this site's ideas in particular is building the house larger than I intended, and having an indoor garden area for year round fruits and veggies. The wife is always trying to grow stuff in the house anyway, might as well build a larger area suited for it and get some real use (and food cost savings) out of it. Would be nice to need a tomato for dinner, and just step from the kitchen's cooking area to the garden to pull one off the vine without having to go outside, or even better doing this in December. And, by doing this dry stack cinder block build method, I'd save even more since stacking blocks and filling them with concrete is something anyone can do.
If anyone wants to try this idea of enclosing their heat pump I'd be interested in hearing the results. While researching alternative heating and cooling methods, I found that another possibility would be to build a Tromb wall inside a fixed enclosure for the heat pump. A Tromb wall would provide a more stable, radiant heat for the heat pump to draw on, which would effectively make the heat pump a solar pump. From what I've found, a Tromb wall can raise the temperature inside a small enclosure to some 160 degrees or more. Surely the heat pump wouldn't be able to pump all that out of the air before the house was warm enough, and the wall could recharge between pumping sessions. A thick enough wall would also store heat during the day for night time use, for even more savings. It would require that the heat pump's enclosure be permanent and well planned though, you'd want a way to shut down the heat absorption in the summertime and just use the enclosure to supply shade to the heat pump. Best of all about this plan, there is no additional energy or expense required once the wall was installed, and really all you'd need is some cinder blocks, insulation, and the plans for a Tromb wall with a heat pump facing the south.
For myself though, I've decided to ditch the whole heat pump idea in favor of radiant heat. Been hammering the web pretty hard over the last few days, and I think I found the way forward. Looking at using an outbuilding with a solar water heater on it to heat a water/antifreeze mix, which will be stored in a heavily insulated tank. No idea on the correct sizing yet, but just for grins I'm saying 1000 gallons for now.
The water will be heated by a whole wall of heaters during the day, with a pump to circulate heat back into the house into the house's hot water heater. This should mean that my in-house water heater should effectively be just a hot water tank, although it will have heating elements inside to keep the temp from falling off too far.
The water from the heater will be pumped through a heat exchanger that will be connected to a water powered radiant water heater that will keep the interior of the house warm. This also frees up my design method. The reason for a heat exchanger is so that I can use the radiant heating system as an air conditioner of sorts as well. I still have to figure out that part of it.
Using this setup, with the pumps being run off solar panels, means I should be able to keep the whole house toasty using only the power of the sun. Of course there will be a diesel generator onsite for backup power, and the outbuilding will have a wood fired stove to heat the water when necessary, but I kinda think that it will only be necessary on the coldest days of the year. And, considering it'll cost approximately 8 grand, if not more, to install a high efficiency air exchange heat pump that will then require lots of electricity and lots of extra solar panels, I think that building a radiant heating system into the house as I go will make for a huge savings to both me and the environment. Not to mention I'll no longer be responsible for stinky coal fired power plants and brownouts!
Telco, one thing you may want to keep in mind is that if you go super-insulated then radiant heated floors might not even feel warm. They won't have to give off many BTUs and you have to consider all the parasitic pumping losses (higher electrical bills), especially if the tubing is smaller and more restrictive.
For a superinsulated home, my preference would be panel rads with TRVs (except perhaps the kitchen and baths). The TRVs allow non-electrical room by room heat control and automatic compensation to prevent solar heat gain - it's a purely mechanical control.
I'd love to do what you're doing. My outer walls would be concrete, then continuous XPS inside that and then a wood structural frame inside that possibly insulated with Roxul (no VP because the XPS is it). With high performance windows. the heatloss would be pretty low, even in the Great White North (although this design would work in suth'rn climes as well). The key idea would be to prevent thermal bridging everywhere...
I may be calling a duck a goose here. When I say radiant heat, I'm speaking of those little water radiators that go along the wall at floor level. They would be inside the insulated shell. I'm not too big on the in-floor heaters, since a pipe breaking means pulling the flooring out where a radiator simply requires turning a valve, then replacing the offending unit. Older tech, yes, but still very effective.
The pump should be covered by solar. When you look at the cost of a high efficiency HVAC system on a new install, like 10-12 grand, I'm figuring that going this way won't cost very much more even when you take the extra solar panels that would be required into account. And worse comes to worse, a diesel generator can provide the power on those few days per year when there wouldn't be enough sun to provide power. Winters in the Midwest are pretty mild overall, we usually have no more than 2 really bad weeks.
Don't let the fear of pipes breaking hold you back from the idea of radiant floor heat. In a well tested and sealed system constructed of Pex tubing, there really is no known definate lifespan. So long as you don't damage it by drilling through it or something, the possibility for a properly constructed system to leak is virtually nil.
Hmm, interesting. How well does it handle weight? My intent is Pergo-style flooring throughout the house, except in maybe the master bedroom, with large throw rugs in the living room and other bedrooms. Mater bed also will have a king size waterbed, one of the ones that looks like a regular bed but has a single bladder for the water. I'd like to do throw rugs in all rooms due to my wife's allergies since throw rugs can be either cleaned outside with soap and water regularly, dry cleaned or replaced when needed. I've heard of nasty stories where a large, heavy piece of furniture has crushed the lines under the floor causing a nasty leak, but as I say they are stories and may not be true.
Also, what happens if there is a power loss and the piping freezes? With the radiant heaters along the wall I know I have the option of draining the lines in an emergency. Would suck to take a weeklong cruise in the Bahamas to come back to no heating system. If the water bed freezes the bladder will stretch to accommodate some, and has a built-in retaining wall to catch most of the water so leakage would be minimal, if any in the event of a freeze.