Radiant makes no sense in a Green home (Dan H.)

Kevin_in_Denver_2

This "retired professional" is drawing most of his information from this article in a 2002 Environmental Building News article by Alex Wilson.

http://www.buildinggreen.com/auth/article.cfm?fileName=110101a.xml

I would consider Mr. Wilson practically unassailable. Also, I built and live in a superinsulated house with radiant floors. I wouldn't do the floors again for many of the reasons discussed.

DanHolohan

That's the case made by this retired professional


Radiant Floor Heating Challenges

Andrew Hagen_2

I have a few issues

1. The author assumes that people install radiant floor heat for of the financial payback. This is almost never the case. While a mod/con may not be the most financially appropriate heat source for an extremely low load home, radiant floor can be matched to lower cost heat sources, such as combination water heaters.

2. While the floor may not feel "warm" all of the time, it will not feel cold. Even in most conventional homes, keeping the floor at 80°F (as the author stated is required for the floor to feel warm) will overheat the space.

3. I take issue with the insinuation that outdoor reset is a complicated unnecessary patch for homes that should not have radiant floors. My opinion is that most homes can benefit significantly (in terms of comfort) from outdoor reset (and proportional flow), which, contrary to the author's statement, is not complicated.

I feel the author is attempting to apply conventional on/off single-temperature control to a high mass floor in a super insulated home. Obviously this is set up to fail. The home is high performance, and the heating system should be too.

I do agree with the last sentence of the article.

Unknown

In basic terms...

He doesn't know what the **** he's talking about. As soon as he got himself off into radiant cooling I could tell he has done no research and hasn't the foggiest idea how it works. Sad what passes itself off as an "expert". Unless he's got a hidden agenda that is. Honestly, I skimmed it and didn't finish. No sense in getting myself all worked up. LOL...

Weezbo

Dan,I enjoyed the read . *~/:)

Thank you.

i hope they publish my reply.:)

if it is thrown out like the baby with the bathwater , then i have saved a copy of the reply which will be forthcoming..:)

Perry_3

Some of the points are right - others arn't

I agree with his point that if you really build a supper insulated and properely vented house that you may not need much, if any, of a heating system.

I agree with his point that radiant floor heat is not by itself more efficient (and may be less efficient if pumping losses are considered).

Past that...

I think that if you are building a house from scratch that you should design it for solar heating and solar hot water. A superinsulated house would not need a lot of solar heat and would not need a huge storage system.

My personal prefference is for Cast Iron baseboard. Design in enough to operate at 110 F for design days. 2 pipe system with TRV's would provide the ultimate in zone control.

Perry

Dan C.

I

I would like to know who the guy is installing radiant systems for $10,000 and rinnai heaters for $1000.00 because I would like to hire him to work for me.

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Paul Pollets

Bad Advice and Commentary

The author should post his name. His arguments are very thin, and poorly quantified. The homes he's describing are rarely built in N. America, even in Seattle.

I've done several very highly insulated homes (R40 walls+) over the past 3 years and each has a heat loss of under 5 Btu's PSF. The use of a modulating condensing boiler and indirect DHW tank uses more than $100. of yearly energy. His numbers are simply inaccurate.

That he quotes Larry Drake to justify his arguments that radiant heating is too expensive, pushes the argument into just an opinion.

There are better alternatives than thru-the-wall heaters or electric baseboard. These are methods that "Air-Heads" get stuck on. I would suggest the author attend a seminar from Robert Bean or converse with Mark Eatherton, or even Siggy.



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Jim Franklin

Comment posted

I posted a long, logical (I think!) rebuttal on the article there on the website. This kind of old-school stuff comes up every now and then and is simply based on "opinions" rather than true scientific laws of physics and facts we designers can use to design better. Are the Laws of Physics different in Europe? Why is it then, that the dominant go-to home and building HVAC system is a hydronic radiant system? The science from Europe tells us that these systems save energy and provide better comfort. So why doesn't that work in North America? Because here we've been taught that efficient=cheaper, and a whole industry has been built on this concept.

The CMHC Study the author of the article references has also been widely criticized for it's lack of rigour and baselining. It was mostly a collection of opinion from homeowners, who, by the way, had digital thermostats, and what does human nature tell us- they'll dial in a number on the thermostat that they think is comfortable, rather than actually setting it where they ARE comfortable. And, oh, yeah, what do all wall thermostats measure? Air temperature. Until you can install a true mean radiant temperature sensor in a space, you CANNOT accurately measure and control radiant systems using wall mounted air temperatures!! You can get close, but close is only good for hand grenades and horseshoes.

heatboy

How can it be .......

..... taken seriously when the author won't sign it? 2 Btu/ft2? Not in my neighborhood no matter how you build.

I love the World Wide Web.

hb

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Unknown

\"or even Siggy\"

Why do I suddenly see radiant panels and teeny pumps in my head?

Dave Yates (GrandPAH)_2

ProSense theme created by Dosh Dosh and The Wrong Advices.

Kind of sums it up nicely! Bottom right of the web page.

Best use may well be to place a printed copy by the WC - for appropriate editorial use(G).

hot_rod

With the trend towards energy efficient

homes, sounds like Larry and many or the rest of us will be out a job in the not to distant future

I would say a radiant concrete slab may not be the best match for a building with low loss numbers AND wide outdoor temperature swings.

I guess passive solar wouldn't have a place in green homes either? Even at a low installed cost

Plenty of dry, low mass radiant floor products available. Not to mention radiant ceilings and or walls for fast acting radiant..

Panel radiators are radiant emitters. They start and stop quickly.

hot rod

singh

2 btu/hr/sq.ft ?

Are there windows in these imaginary structures? At that low of a heat loss at design day, NO heating or cooling system at all is needed. He shoots himself in the foot on that one.
I also agree, play with the amount of tubing in green home, maybe just in traffic areas (for warm feet), radiant walls, or ceilings, all of these are cost saving measure also.
My only concern would be, to find a heat source that can go that low.

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Unknown

Concrete...

I'm a big fan of heating with the concrete, and maybe cooling with it too. What Ive done so far has involved heating the slab (in the basement)and supplementing that with warmed (not heated) floors in strategic areas kitchen, bathrooms and foyers, supplementing THAT with hydro air. Now, when I heat the slab I don't think any of the hydro kicks in till ~ 30* ODT. And that's conservative. And, as many of you have heard me say several times now, I'm using 110* water throughout. So we're talking about 9000 sq ft of living space plus another 3000 ft of garage and basement. The customers, Mr AND Mrs, are ecstatic. First off, they "have never been in a house before that was so evenly heated. There are no cold or warm spots!" Secondly, in the month of Feb 07, while still under construction, finish work, they spent $347 on natural gas and ~ $100 on electricity. I expect those numbers to improve. The electric usage bugs me a bit, hence my interest in teeny pumps or variable speed pumps that reduce power usage as well as speed. One of those combined with zone valves should reduce usage quite a bit I'd say. The simple fact of the matter is, I don't care how well insulated your house is, if you design your system correctly it will never use any more energy than is necessary to condition the space. All you have to do is dial down the water temp to suit the customer and let it cruise. To spend umpteen dollars on an ultra tight house and then say, "Well, in that case, I can skimp on the HVAC." is pretty much a contradiction.

Here, this is me:

http://www.robur.it/us/pag_news_dett.jsp?id_news=268&cat=13

Mike T., Swampeast MO

Sing:

The 2 btu/hr/sq.ft. was per annual degree day.

The "super-green" house for which I'm designing the heating system [should] have less than 1 btu/hr/sq.ft annual space heating consumption in a 10,000 degree day climate.

And no, I would never have suggested radiant floors anywhere in that house except bathrooms and even there I doubt they ever would have been truly "warm" to the bare foot. And yes, there are windows and glass in the design. 21 good-sized double hung and one pair of French doors.

Unknown

How,..

are you planning to heat it? Will there be cooling?

Warm floors are a common misconception, in a tight house especially, if the floor feels warm the space will overheat. I always stress that point during the sale. They won't feel warm they just won't feel cold. Somebody else said that here a few posts back.

Mike T., Swampeast MO

Heat Source

A Bradford-White "water heater" with integral space heating coil! I looked carefully at every option and found the Bradford-White the "only" choice. My favorite part about it is the arrangement of the space heating coil. It's smooth, large diameter (at least 1") and circles the outside of the water heater from nearly the bottom to the top. Compared to other similar heat sources like the HTP "Phoenix" with a corrugated HX coil confined to the bottom of the tank, this will allow full use of the "buffer" provided by the storage tank.

No central cooling system, but I sure hope they use their windows as even normal occupancy gains might overheat this house in what passes for their "summer"!

Manual-J loss for about 2,500 sq.ft. about 19 mbh @ -20F.

My calculated "heat requirement" when maintaining 72F in @ -20F out is about 9 mbh. Homeowner told me the first heating pro (a VERY old man) who computed heat loss manually came up with 9 mbh but "nobody could believe it".

By my calculations, the Bradford-White will have a maximum duty cycle of one firing per hour! Literally hours between firings (barring DHW demand) except in the depth of winter.

Only thing that bothers me a bit about this system is that the manual gas valve on the Bradford-White may have to be manually adjusted a few times a year.

The homeowner does not plan to use daily setback, but since this is a fully TRVd system occupied by two "empty nesters" unused bedrooms will likely be set back considerably. While I calculate that 130F average water temperature will be sufficient year-round, I suspect it could take days to heat a deeply setback room in very cold weather.

Unknown

Could you elaborate Kevin?

I'd like to know why you feel this way. What is it that you dislike? I would think I'd get away with nearly space temp water in the floors of something super insulated. Is the radiant the only source of heat? I'd like to hear more about the design too.

Unknown

yes,

one thing I've found is these super windows let the heat in and the super insulation doesn't let it out. So on a 70* day I might push to 80+* in a sunny, unconditioned room. I was worried at first but once I got the chilled water units dialed in everything seemed to settle out. The customer even raised cooling setting on the T'stats once the humidity came down. He started at wanting, INSISTING on 68* indoor temp for summer. Last I heard he's at 73.

I like the water heater idea. I'm not sure why you feel you'll have to adjust the gas valve?

Mike T., Swampeast MO

A part of me still has a hard time believing that a house that size in windy, -20F weather could be heated by 3 average-sized blow driers...

If my estimate of actual heat load bears out, 130F average water temp will be more than adequate and even allow for reasonably quick recovery in setback rooms.

"Conventional" wisdom (as well as my own observation) says that actual heat load is 40% - 60% less than Manual-J heat loss, but that's with "conventional" construction.

But this home is FAR from conventionally constructed:

1) Quite literally a weatherized shell (using 2 x 6 studs) surrounded by another weatherized shell (using 2 x 6 studs). Rigid exterior insulation and special insulating siding on the very outside. Double-layer (2 x 1/2")drywall everywhere including interior partitions and closets!

2) Obsessive attention to weatherization detail with the floor cavities themselves originally designed to be a huge warm-air heating plenum. The "worst" part of most houses (the rims) is likely have significantly less loss than "best" parts of even typical "green" construction and it's likely to stay that way indefinitely.

3) Insulation levels in ceilings/walls so high that adding more has negligible return.

4) "Super" windows and doors that according to the homeowner are available only in Canada.

5) Natural infiltration so low that the three-outlet HRV [should] be providing the vast majority of the ventilation. Even the commonly used entry (no attached garage) is designed to limit air infiltration. A south-facing good sized, fully weatherized but unheated entry room external to the shells surrounds the common entry door.

6) In a "good or bad depending on how you look at it" situation, the home is not well-suited for passive solar gains.

7) Highly significant occupation gains with even an "Energy Star" refrigerator sufficient to heat the kitchen for at least half of their 9-month heating season.

Put all this together and I'm not quite sure what to expect. All I know is that this will likely wind up being one of the most space-heating efficient residences in this entire country!

Unknown

Well,

I know we sure as heck didn't build a 6" shell within a 6" shell on mine, that's for sure! Wow! Right, I look at mine as using about a toaster and a half's worth of electricity on the extreme days. To heat or cool. I measured the draw with the entire system going and came up with ~ 28 amps. On most days it's less than half that. Don't forget I'm burning gas, but at a very efficient rate in the winter and at about a 14 SEER rate in the summer. It's been just about a year since I turned them on. So far so good.

Kevin_in_Denver_2

radiant floor vs. forced air

I love my in floor heat. It cost more than double what forced air would have cost.

I still had to design and install air conditioning, (pretty easy in Denver, only an evaporative cooler), air filtration and humidification (not so easy)

When the heating system is only on 5% of the time during cold conditions, to me it doesn't really matter how you deliver the heat.

Unknown

Right,

humidification is a problem with radiant. What I have is a system where we are going to use forced air to cool anyways, why not incorporate it into the heat as well? This way, even if the hydro air is not needed but the humidity is down my customer can run his air handlers on fan "On" and get some humidity into the air. Humidity hasn't been totally addressed yet because they haven't lived there during a heat season, they moved in May I think. We're on wait and see mode but I'm not overly concerned. Plus, by splitting the heat between floors and air handlers I reduce the amount of tube I need to install so I figure my set up only cost maybe 1.5 times forced air as opposed to 2.

Unknown

Oops...

The old double click...

Mike T., Swampeast MO

Someone here suggested that this may be the 2nd passive house in the country! I don't know that I'd go that far (given the very cold environment) but it wouldn't surprise me if the house went passive around Christmas with kids, spouses and grandkids visiting.

Unknown

LMAO...

Sounds like about my luck too...

Mike T., Swampeast MO

Must say that I find myself agreeing more than finding fault. I would have said that before becoming involved with an extremely "green" structure.

Huge emitters like floors certainly come at a rather high cost and if the homeowner is expecting "warm floors" they could be sorely disappointed. They may even resort to the "double-hung" thermostat to keep their floors warm...

Better in my mind to confine heated floors in "green" homes to hard-floored baths and perhaps the kitchen.

For the rest I would STILL consider "radiant" heating, but in an unconventional form: Tall, narrow, non-convection enhanced "flat" panels WITH TRVs on interior walls facing points of greatest heat loss designed to meet the Manual-J load at 150F - 160F average temperature.

Dave_4

I will comment later On some of the ideas posted here since advanced housing is my cup of tea.. The old adage hold true if you build the shell like a foamed in walk in freezer. It will perform like one. Hands down. In the day when Canadas R-2000 program was being pioneered and Rolled out as the standard in constuction . Other were working and building test homes in the Advanced housing program ... that was 17 years ago. they consumed I think 70% less than the r-2000. Were talking homes that burned $200 yearly heating ,1600 sq. feet. in 7800 DD. I've been in them . they simply perform as designed. Pretty impressive. Paul

Dave_4

Mike T. Some of best Superwindows are actually from the U.S. and not Canada. Paul

Mike T., Swampeast MO

Paul B:

It sounds like you're saying that extreme insulation/weatherization only increases the gulf between Manual-J heat loss and actual heat requirement. Correct?

Unknown

he makes the case....

and if you are in the situation he describes in the article, he's dead right.

as heat load drops, the way you meet it gets less and less important, until it's not important at all.

I'm a radiant fanatic, sure, but come on guys... there are limits. If you build a superinsulated house, a really superinsulated house, radiant has minor advantages over any other form of heat and is definitely not worth the premium, unless it's in a slab. In which case, it's cheap, go for it and spend a few bucks on some smart controls. Otherwise, put in 90 degree baseboard, PV electric baseboard, or a few extra canister lights.

The only way to argue that is to argue about that is to argue about what it means to have a "superinsulated" house. If you mean anything with two digit BTU/sq ft loads, then you're not talking superinsulated like the author was.

No need to burn the witches here. His points on overheating are not on the mark because you can address that with proper indoor feedback/constant circ systems. But most of this is 100% spot on. He's not even attacking radiant; he's just pointing out that there comes a time when it's not providing any real benefit that justifies its cost (though again, in a slab, it's pretty cheap, even controlled correctly).

He even references Mumma's DOAS/radiant cooling stuff that all of us at REXPO just learned about a month ago, for criminey's sake. Which is bleeding edge for the residential market outside of the SW united states, so far.

I think this was an extremely fair minded and smart assessment, with just a few weak spots that don't really affect the gist of what he was trying to say.

Tom Hopkins

Why so high?

I completely agree with everything except I couldn't see the reason to exceed 125°F or do...

It would not take much panel size under these design conditions. With the lower temps it is a better match for GSHP, solar or condensing in the future, even if they aren't being contemplated now.

Unknown

In a sense,,,

I disagree, If you are considering the bottom line only, yes, but if you are concerned with comfort, at least as much as the $, you will spend that premium. If you are going to go all out on the insulation why wouldn't you be willing to spend a few bucks on the HVAC end? My feeling is that, whether it's slab on or a basement, in a superinsulated house, you would almost never use anything but the slab. And I further believe that you'd only have to heat the water to maybe 85* to achieve that result. Now solar becomes a bit more attractive, doesn't it? And you sure wouldn't need much of a boiler to supplement. If you're going to go green, don't go half way on us. Like I said, to me it seems to be a contradiction. I would say heating the rest of the floors might be overkill but again, that depends on what you are looking for. I do feel panels have a place. Especially now that I am seriously looking at offering radiant cooling.

One other question noone has asked here. What about some fresh air?

Unknown

But that's the thing; the comfort differential *isn't there* in a superinsulated home such as he's talking about. Your heat loss is so low that all surfaces can get their MRT up by FHA, if you like, or any other method; it might take a few days on startup, but if you skip the setbacks, it's quite comfortable. Sooner or later the mass soaks up the heat and as long as it can soak it up faster than it's losing it, you've got a good MRT.

The arguement is why not spend the bucks you would have spent on HVAC on still more insulation? You still get comfort, and insulation as we all know is the ultimate efficiency appliance.

Further, ANY HYDRONIC heat in a superinsulated house like that becomes low temp. If it's slab... that's still the cheapest, fine, go for it. If it's suspended though, you'd be far better off with some panel radiators, maybe a little radiant ceiling, maybe even 90 degree baseboard if hydronics are to be used. Electric starts to make a lot of sense though... even if it's pricier per BTU, there is no auxiliary equipment, and you're not running it enough to care about fuel costs.

but when you've got a tiny heat load, it makes no sense to waste money on a 95% boiler that will rarely turn on when that $6k+ could have purchased better windows, or more insulation. I mean really... I understand purity, but it's just not a smart decision. I just designed a passive solar house with true double wall construction. I am 100% convinced that the heating system will almost never turn on. When it does, it will be satisifying a tiny load. They wanted a mod/con for backup. There is nothing WRONG with that, if you have the money, but it's not necessary, nor that much better than any lesser backup heat they could have put in, because it will be used so little.

It certainly makes no sense to spend $5 to $20/sq ft to heat the floor to 3 degrees over where it would stabilize if it weren't heated.

If you actually need cooling, then with a small load you could work out the heating/cooling through the radiant, ok, then it's more feasible. But, I wouldn't expect to need much cooling in most areas with a house like this and the ones that did wouldn't need much heat, so I dno't know if dual usage is THAT big of an advantage to a true superinsulated home. it might be in some areas, sure.

Fact is thus: for the *serious* Green consumer, the HVAC contractor becomes practically unnecessary beyond the V. As you note... what about some fresh air? Humidity control? That's where you can help.

GMcD

Exactly

Rob: What you've concluded and stated is exactly the logical approach. The typical Euro "Minergie" low Exergy designs are based on exactly that logical progression- it's all about the envelope, and using climate adapted envelope design, so the building envelope becomes the de-facto "comfort system". The only quibble I have is that it's still a better micro-efficiency approach to use hydronic heating/cooling as tha primary energy transfer system versus air, but the need for an HRV/ERV and humidification/de-humidification in many climate zones says that you have to have an "air system" anyway, it's a lot cheaper to add duct coil(s) for added comfort control as required. The Euros are generally using TRV low temp panel radiators for heating only, and either natural/cross-ventilation (in mild climates), or HRV/ERV as required in the harsher climates (Sweden, Denmark, Switzerland, etc.)

Unknown

Ok,

I see what you're saying, don't get me wrong, but in the case of a tiny load, the resultant tiny boiler necessary will (or should) not approach the $6,000 mark. Then when we DO add fresh air, are we not adding to the load? What about kitchen exhaust, bathroom exhaust, the clothes dryer, things like that. If you seal the house air tight and give it 12" of insulation all around, sure, it will use minimal amounts of fuel but as soon as you introduce fresh air some of that literally goes out the window. Also, how is makeup air going to be introduced to the structure? If it's airtight like we are talking a kitchen exhaust, for example, will draw the airtight space into a negative pressure and at some point effectively stop working. Now if you add one of those fresh air exchangers that capture the heat and send it back in well, now you're getting into big bucks again. Perhaps the heating industry needs to look at designs for high efficiency boilers small enough to work properly and be cost effective for these new green homes.

Unknown

What's the cheapest you could get a mod/con in to do heat and hot water, assuming reasonable DHW load, since this is a green house, no 12 GPM spa showers.

Whatever that is, is more than needs to be spent with electric heat, and probably more than a small furnace and water heater, yes?

You use an HRV/ERV in these houses. That is in place of having to reheat all that lost area. You size it reasonably so it's not a stupendous amount of wasted heat. That's needed no matter what the heating system is, so it's a non issue, except that as geoff notes, if you already have a duct system, why not just put coils in the ductwork?

Unknown

How,

are you planning to heat the hot water to begin with?

I'll check with some people tomorrow and do a little research on smallest mod con and price. I'll agree most mod cons I've seen so far are a bit pricey. The thing I want to make clear though is, if there's only a 2btu/ft load, the system would be designed to that spec and the results would be things like less/smaller tube, smaller pumps etc. all equaling less $ outlay. In the case of siggy's ideas crossed with a green designed house I see a radiant panel in each room, each run by a teeny weeny pump pumping minimal water temp. I think that would be a fabulous way to heat and cool the place you're talking about. You would HAVE to include some forced air for humidification AND dehumidification purposes but it too would be smaller and cheaper. Anyways, the guy is arguing about radiant not having a place at all in green design, not what heat source we should be using. I say he's wrong, I say a carefully considered and designed radiant system definitely has a place in a superinsulated home. But only if you consider comfort and a reasonable bottom line as at least being equal in desire.

Yes, HRV and all that is great but, it costs! The house I use as an example was supposed to have one, until the owner got a look at the price. The house has no fresh air makeup at all right now. I don't like it but I didn't design the duct, I was a sub on the mechanicals. He's got some massive kitchen exhaust too. 600 CFM on high if I remember correctly. I haven't been around when he's frying up burgers with the house closed up.

I figured it out while I was at it too. This house has 6" walls, all sprayed in, the roof is insulated underneath with spray in between the roof joists. No insulation between attic and ceiling. So the attic area stays cool in the summer and warm in the winter and acts like a buffer. Plus he's got the super windows. I come up with ~ 12 btu/ft on Horgan's Omnicalc set for "tight" when I include the exhausts. Or 108,000 btuh for 9,000 sq ft. and 8.5 tons for cool. I had people, engineers and the like, shaking their heads saying it would never work, there's not enough. Guess what? It works just fine!

Unknown

You could use a regular water heater to do DHW; hydronic heat at all in a real superinsulated house is probably unnecessary. Electric duct coils or baseboard would do the job and again, if you aren't running it much, opearting cost doesn't matter.

And, you forget again, in the superinsulated house there is no comfort difference here. This comfort difference you are trying to sell *does not exist*.

It doesn't matter that the HRV is expensive. It's required in a superinsulated house, period. You have to bring in air. We all learned this thirty years ago, and people trying to skip it now will re-learn it again. the HRV has no impact on what kind of heat you need, except it sets a minimum base load of from the air movement modified by the exchanger efficiency and air temp dT.

You're not talking about a superinsulated house. Well insulated, yes, but not superinsulated. 9000 sq ft houses with regular insulation are typically around 15 BTUs/sq ft... lots of floor space, less wall/ceiling proportionately, lowers the PSF number; unless they are built like poop! and a lot of them are. But if they are actually built to regular standard, the 15 number is good.

superinsulated is single digit loads only.

Radiant and hydronics can be used, definitely, and if you want to use solar hot water you need to. But comfort, efficiency, and economics are not reasons to use them in true superinsulated homes. The insulation takes care of all of that already.

Unknown

Yep,,,

I did some asking around today, I agree the DHW heater would be the best idea for heat only. Like what Mike T is using. (whoops, reread says that's not what you said) I'm also hearing of houses in Switzerland(?) that have no heat, the humans are the heat source. I'd have to see this and hear what the owners have to say about living in it. Let's take a 9,000 sq ft super insulated house. At 2btu/sqft you still need 18,000 btuh. How would you deliver that evenly over 9000 sq ft? I don't agree with the use of electric. You're spending umpteen dollars on being the most efficient house there is and then throwing in the least efficient way to heat it. I keep coming up contradiction. And again, if you must cool, (which I must) there's a whole different aspect to the thing. I have found that to cool with water you need roughly 2.5 to 3 times the flow as with heat. My thoughts are, if you're going to cool, why not rig it so you can deliver heat as well? It's already there. What I see is a small geo to water heatpump that delivers both hot and cold and could probably make DHW too when it's not doing other things. Radiant panels sized for cooling will be more than adequate to provide heat and require very low temps. BTW, smallest mod con I could find was 46,000 btuh. Price wasn't too bad / seemed almost reasonable but I'll agree it's restrictive in terms of what you are describing. You could use it for DHW too but then it gets into why not just use a high recovery water heater and pull heat from it when needed, much simpler. Unless you're going to cool that is.

Have you actually lived in a superinsulated home? Same story here, I'd like to see a few of these and listen to what the owners have to say about them.

Another thought, what about warm side cool side like when the sun is beating on the west side in the afternoon. You're confident the entire house will be the same temp throughout without any special considerations?