How crazy would it be to combine two small low load appliances, a conventional dehumidifier and a heat pump water heater to get what you are looking for? I'm no mechanical engineer, so critique as needed.

Dehumidifier pulls humid air from living spaces, pulls the latent heat out and produces condensate, then passes the hot sensible air stream to the room with the heat pump water heater, which extracts the heat from the air and dumps in the HW storage tank.

I have a Daikin mini-split with a dehumidification cycle that works very nicely. 

Bruce

Jesse - from a physics perspective, brilliant. You could use the low grade waste heat from the dehumidifier to help the efficiency of the hot water heater. We will have solar hot water, though, so it's not clear what we could do with the waste heat.

Bruce - I'm very interested in a mini-split for the application. Do you have any idea what the Sensible Heat Ratio (SHR) is in dehumidify mode? Most AC units are from .8 to .95, ideally I would like something .5 or below since half of our load will be latent cooling. Another problem with mini-splits for us is the challenge of distributing the air to the entire house.

The difference between an ERV and an HRV is the dessicant/humidity exchange system- the Pinnacle IS an ERV- a big 'un to boot. And WAY overkill for a superinsulated house compared to a normal household sized ERV (even a 2-3x oversized PassivHaus.) But a 300W whole house ERV still beats a 500-800W dehumidifier (which would work, is cheap upfront, and would still be very cheap to operate in a tight house with proper vapor retarder in the foundation, etc.). What would be nice to have (and SFKAIK, doesn't yet exist) is a smaller-scale ERV capable of utilizing solar heat on the exit stream to super-recharge the dessicant when even more dehumidification is desired. (Could turn into a real Rube Goldberg contraption, but aren't they all? :-) ) But as with a heating/cooling systems, when you reduce the load sufficiently, the efficiency of the dehumidification system becomes less of a concern, and it may be silly to spend a whole lot up front to save less than 100kwh/year. (~100kwh/year is about what my 500W dehumidifier in the basement uses in central MA. This is in a not-as-tight-as-I'd-like ~2400' house with a sub-grade basement and no vapor retarder in the slab 1' above the water table. With a tighter house, an HRV, and better sub-grade vapor pressure control I'd bet it would go to zero in my climate, but let's say 50-100kwh/year in Philladephia if you don't have 8 people taking 20 minute showers every day.)

Anxiety about condensation issues with radiant-cooling are overblown, especially with the very-low loads (providing you've sufficiently killed the solar gains) of a superinsulated building. Condensation issues only become a problem if you need to super-chill the panel to remove the heat- might be a problem if you're trying to cool an office in a glass tower with a small retrofit ceiling panel. But in a low-solar-gain super-insulated building of significant thermal mass using a whole-ceiling or wall as the radiant panel that would be rare. To get a condensation problem the panel needs to stay below the room-air's dew point for a period of time. But in a superinsulated low-solar gain bulding you absolutely never need to be even 15F below the setpoint-temp if you're using a radiant ceiling or wall, or a decent sized panel. If in the dog-days of summer with an RH below 60% (which you'll need to maintain by some method to avoid mold), and with a cooling setpoint temp of 75F, a quick read of the psychrometric chart sez you won't see condensation until the panel gets below 60F. If a large surface area in the room is ACTUALLY 60F, it's not gonna stay 75F in there for long unless some other surface in the room is well OVER 75F (which should never happen in a superinsulated building unless you leave all the burners running on the stove or something.)

The same radiant panels could be used for heating as well as cooling if desired- that's a plumbing & control problem. In superinsulated buildings full radiant floors are overkill and don't provide the same "cruisin' in yer socks" cush anyway, since even on the coldest days of the year it's barely above the temperature of the other room surfaces (if the radiant floor ever needed to be over 80F on the floor it would have to be -100F outside. :-) )

Using high volumes of ventilation in earth-tubes as a primary cooling strategy may have a dismal COP, but earth-tubes on the HRV/ERV intake could still cut the cooling load (including the latent load)- don't discount that standard PassivHaus feature completely. It's a low-energy/passive strategy for reducing both heating & cooling loads. It may take a large volume of ~60-65F air to remove a bunch of BTUs from an 80F building, but by not simply dumping necessary-ventilation volumes of humid 90-100F air into the building you've lowered the cooling load for minimal (or no) additional energy expenditure, simply by not adding to it. Earth-tempering the incoming ventilation airstream is a good thing, with or without the heat/humidity exchange of an HRV/ERV.

Jetgraphics- I'd be curious to read that antique New Shelter article about the Conservation House- is it archived/available online somewhere? (That DID look like an over-kill array of solar thermal for a truly superinsulated house.) I'm not surprised that cooking heat was a bit much to bear too. Thermal mass is essential for maintaining comfort in a superinsulated building. Many 1970s versions of solar houses had WAY too large a glazing/thermal mass ratio to cook the occupants with, even at much lower insulation values.

In Passivhaus buildings, the cost savings from dispensing with the conventional heating system can be used to fund the upgrade of the building envelope and the heat recovery ventilation system. With careful design and increasing competition in the supply of the specifically designed Passivhaus building products, in Germany it is now possible to construct buildings for the same cost as those built to normal German building standards, as was done with the Passivhaus apartments at Vauban, Freiburg. On average, however, passive houses are still up to 14% more expensive upfront than conventional buildings.

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I'll see if I can find some data...all my papers are in Italian (a person who speaks three languages is trilingual.......two languages is bilingual.....and (drum roll), a person who speaks only one language is usually an American). 

Air distribution is no problem.  While I have wall units in my flat (retrofit..no ducts), Daikin and Mitsubishi both make indoor units that can be mounted above a ceiling, in the attic, a closet, etc and ducted where ever you need and can be integrated with OA heat exchangers. I am pretty sure thay are availabale in the USA.

We have used air cooled VRV units in small office buildings (both new and renovations) with good success and have investigated water cooled units where groundwater is available.  One of the two companies (maybe both now) also have a "heat pump boiler" that will make hot water for radiant.

Bruce