thank you very much for explaining this.... I appreciate your comments and recommendations. This being my "once in a lifetime" shot at building a home, I really want to "do it right". So many options, though! Good to know about the solar hot water -- I will cross that off the list. For south wall glass, would double pane be sufficient, given the price difference going to triple pane? Wasn't planning on any west windows, and will have to calc the south wall. Will look more into HRV..... since everything in my home will be "new", I want to mitigate off-gassing. Hubby poo-poo'd HRV (and he's a contractor) he says just open the window, haha! In his 40 yrs. of contracting, no one has asked for HRV. He also nixed the double-wall construction, due to cost, even though to me it makes sense. Still unclear about: is the electric boiler for heating the floor only or DHW, too? Is the air to water heat pump water heater -- for DHW or the hydronic or both? I do like the idea of the ductless mini-split for that instant burst of heat (hydronic floor takes a long time to raise temp.) or to cool off the house on that rare occasion when needed.

thank you very much for explaining this.... I appreciate your comments and recommendations. This being my "once in a lifetime" shot at building a home, I really want to "do it right". So many options, though! Good to know about the solar hot water -- I will cross that off the list. For south wall glass, would double pane be sufficient, given the price difference going to triple pane? Wasn't planning on any west windows, and will have to calc the south wall. Will look more into HRV..... since everything in my home will be "new", I want to mitigate off-gassing. Hubby poo-poo'd HRV (and he's a contractor) he says just open the window, haha! In his 40 yrs. of contracting, no one has asked for HRV. He also nixed the double-wall construction, due to cost, even though to me it makes sense. Still unclear about: is the electric boiler for heating the floor only or DHW, too? Is the air to water heat pump water heater -- for DHW or the hydronic or both? I do like the idea of the ductless mini-split for that instant burst of heat (hydronic floor takes a long time to raise temp.) or to cool off the house on that rare occasion when needed.

The tighter you build the house, the more important active ventilation becomes, and the up-charge for heat recovery ventilation can have a good economic rationale if you are heating primarily with an electric boiler, less so if you're leveraging the power with a heat pump. But it always has a comfort rationale in winter.

A standalone electric hot water heater is a lot cheaper to install than an indirect tank running off an electric boiler. Most heat pump water heaters take half or more of their heat from the indoor air, which costs about the same to operate as the electric tank or boiler in the winter, assuming you're heating only with an electric boiler, but would be cheaper if you're heating the space (at least partly) with a mini-split heat pump.

A 73F floor in a 68F room is pretty comfy, but is using lot of heat from the electric boiler, to the tune of 3412 BTU/kwh. A 73F floor in a 73F room is also pretty comfortable, but is using almost no power (only to cover the heat loss out the bottom of the insulated slab to the ground.) Heating the room to fully 73F with a mini-split and heating the slab to 73F with the boiler would use substantially less power than heating the room to 68F with the radiant slab and no heat pump. In your climate it would be about a 2/3 savings on the heating bill, despite keeping the room 5F warmer(!).

With mini-splits you'll get a lot WORSE efficiency if using deep setbacks, since they run at substantially higher efficiency when modulating at part load then when running flat-out at the highest speed. A better strategy is to "set and forget", pick a temp that works for you, and bump it up or down only a couple of degrees at a time to adjust for comfort. The "instant blast" of heat can be acheived, but if right-sized for the load it takes quite awhile to recover from a 5F+ setback during cold weather. See the efficiency difference at different modulation levels and outdoor temperatures in Figure 5, p10 of this bench testing on an older model 1-ton (the newer versions are more efficient, but have the same characteristic):

http://www.nrel.gov/docs/fy11osti/52175.pdf

Note that when it's 35F outside (roughly your mid-winter average outdoor temp) the 12RLS2 runs at literally TWICE the efficiency at minimum speed than it delivers at full speed. At full speed it's only a bit more than 2x as efficient as an electric boiler at that outdoor temp, but at minimum speed it's nearly 5x as efficient. If sized correctly to the 99% design load the average efficiency over a full season should be more than 3x as efficient as the boiler, but probably well shy of 4x.

An IRC 2015 code minimum window in your location (US climate zone 5B) would be U0.32, which would be a pretty good argon filled low-E double pane. If you're looking for the south windows to provide a bigger fraction of the heat you might get a more favorable solar gain heating gain coefficient (SGHC) sufficient to balance that out going with U0.36 but less window area, or a U0.28 window and more window area to make up for the lower SGHC. To know for sure you'd have to run some simulations on different options based on weather data, site orientation, construction, etc. The DOE's freebie BeOpt isn't perfect, but it's way better than a WAG for figuring this stuff out. The newest version even takes a stab at the energy use when heating with mini-splits:

https://beopt.nrel.gov/downloadBEopt2

Really appreciate your time and input on my project, Dana1.... very helpful! Leaning toward electric boiler, and standalone electric hot water, since I might not install the mini-split at the get-go. First see how the passive solar/hydronic perform (cost to heat) and see if any AC actually needed (with proper overhangs!) Another nice aspect about mini-splits are that if I ever travel, and rent out my house (airbnb) it would be easier to leave the hydronic set at 50, and have guests use the mini-split to bring house up to temp, rather than mess with hydronic and time lags. (realize that's not the most efficient way to run it) Also, some guests may "require" A/C -- whereas I'm never too warm in this climate! Another concern is space req. for all the mechanical. My mech. room/laundry room is only 7'x 9'. Would that be enough space for HP water heater + indirect tank + boiler?

Two quibbles with Dana's world view:

Solar hot water has twice the lifespan of heat pump hot water heaters and typically qualifies for more state, federal and utility incentives. Ergo, solar hot water COULD be more cost effective on a life-cycle basis. The wild card is comparing the expected btu shortfall of hot water with the kW shortfall of PV. The average rooftop PV home is not self sufficient, and the more showers required each morning the less likely it is to be so. On the opposite usage pole, a pair of retirees could be better off with plain ole electric in combination with rooftop PV. In short, your mileage will vary.

Nor is it given that overheating in a passive solar design is inevitable. Yes, it's difficult to calculate how much mass you'll need to soak up excess insolation, but it isn't hard at all to add more mass than you'll ever need. In my house, which has super-aggressive glazing, the highest winter temperature to date is 78, and that was a mistake on my part. (Began a 61 degree January day with a radiant slab on grade at 75 degrees.) The trick is to use window treatments that adequately insulate that glass at night. Super-efficient windows are usually a bad bargain in a passive solar house because they reduce solar heat gain.

Rooftop solar has twice the lifecycle and lower maintenance than active solar thermal. Depending on the $/watt installed price post-incentives (federal tax rebates), even if you're including the cost of a couple of standard electric tanks and a replacement inverter in year 15, the 25-30 year economics will usually favor expanded PV + standard electric tank. Heat pump water heaters (HPWH) tend to make more economic sense in locations with higher latent cooling loads than eastern OR, but local incentives on heat pump water heaters in OR have often tipped the balance in favor of HPWH. It's not clear if the subsidies in OR will be renewed, but until very recently there was $600 in rebate money to offset the higher upfront cost of HPWH in that state.

But a 7' x 9' room is not large enough to support an HPWH, so take that off the table.

Also there's no point to installing both an indirect and a standard electric tank. An indirect may or may not outlast a $300 standard electric water heater, and costs more than twice as much, and the efficiency is still the same.

And thanks to Dana for addressing an argument I did not make. Yes, PV has a longer lifespan than solar hot water, but that is not the case for hot water vs heat pump, which was the point I made.

And ignoring one I did. The average home would require about 10kW to completely cut your friendly neighborhood utility out of the household budget. At roughly 100SF/kW that would require 1,000 square feet of unobstructed south facing roof. When that's not possible -- in Nevada where the value of rooftop PV recently became a keen issue, the average system covered about half the kW required -- it behooves energy conscious homeowners to explore what loads they can remove from PV. And solar hot water can remove 20ish percent of average energy consumption with a fraction of the roof space required by PV. Whether heat pump hot water does it more economically is not as obvious as Dana's solar-hot-water-is-history.

The real question is whether it is worth it. For the 6 in 10 homes heating water with natural gas, the answer almost surely is 'no.' In a goodly number of the remainder, the answer is likely to be 'no' as well. But if your net-zero ambitions are bigger than your roof, solar hot water is alive and well.

Laura, if you find an adventurous hvac contractor you might consider a solar assisted heat pump. It pipes the refrigerant up to the panels, using them as sun boosted evaporator, and then moves the heat to a storage tank, which serves as condenser. It's newish thing and Canadian. solarheatpump.org

Again, the bigger the storage tank the greater the efficiency because you're shifting the conditioning load from nighttime peak demand to optimal daylight hours. That said, you will be standing in your house on a second, very large storage medium -- the slab. Mine is a thousand square feet, four inches thick and well insulated. In a typical winter day, averaging perhaps 30 degrees, it cools overnight about three degrees without additional heat. If you can accept some variation, you could use a diurnal setback to charge the slab during the day and let it coast overnight. (This assumes that solar assisted heat pump gives you enough btus over a short winter day. ) If you do this, you'll want a separate zone and thermostat for the slab area capturing passive solar to avoid overheating.

Unfortunately, in our small rural area, the HVAC people are not quite up to speed on the latest technology. When I ran my ideas (hydronic, PV) by them, they looked mystified and tried to talk me into a forced-air furnace instead. Not much hydronic heat here, and most here are propane fired, not electric. Since my mechanical/laundry room is only 7'x 9', my space is limited for storage tanks. Could you explain the diurnal setback in more detail? Exactly how does it work -- in the winter on a cold sunny day? (I'm not planning on solar hot water at this time, just PV panels)

How much space would HPWH take? Just curious. Not a lot of wiggle room in my small house floor plan, but at this early phase, possible. Also, curious what you'd recc. to deal with potential power outages in the winter?

If you want to operate a HPWH in a small room, design it without a door.

Posted By toddm on 14 Mar 2017 04:26 PM
Again, the bigger the storage tank the greater the efficiency because you're shifting the conditioning load from nighttime peak demand to optimal daylight hours. That said, you will be standing in your house on a second, very large storage medium -- the slab. Mine is a thousand square feet, four inches thick and well insulated. In a typical winter day, averaging perhaps 30 degrees, it cools overnight about three degrees without additional heat. If you can accept some variation, you could use a diurnal setback to charge the slab during the day and let it coast overnight. (This assumes that solar assisted heat pump gives you enough btus over a short winter day. ) If you do this, you'll want a separate zone and thermostat for the slab area capturing passive solar to avoid overheating.

Precisely and very well stated too! Passive solar and hydronic radiant are very complementary when done properly. So is a masonry heater...which makes more sense to me as a backup and immediate heat source than using mini splits. In a low humidity diurnal climate, there is no need for AC in a well insulated/sealed home. A whole house fan is way more cost effective for cooling than mini splits and also far less prone to failure and high maintenance expense.

Laura, diurnal setback simply means that you set your thermostat back when the sun sets. But alas it is mainly a thing with heat pumps. Because they effectively move heat from the outdoors in rather than generating it, efficiency and output depend greatly on how warm it is outside. In optimum conditions, heat pump output can be two or three times its equivalent use in electricity. Because you can use your slab to store heat, you can spend a whole lot more time in this sweet spot than the fellow whose heat pump is idling at 4 pm and flat out at 4 am. Solar assistance gives it an extra bump. (Canada is ground zero for cold-weather heat-pump research for the obvious reason.)

You'll still benefit because your slab will store passive solar heat gain. In fact, I wouldn't do anything with HVAC until you have a design and can model how much of your heat will be free. You can get a quick reading of it by using ClimateConsultant. http://www.energy-design-tools.aud.ucla.edu/climate-consultant/request-climate-consultant.php It asks you to download historical weather data from a nearby weather station and then shows you how many hours in a typical year that strategies like passive solar will keep you comfortable.
I'm in Pa, where ClimateConsultant told me to forget passive solar. So I heat with a mix of passive solar, a wood stove boiler, solar hot water and eventually -- when the ax gets too heavy -- an air-to-water heat pump.

Even in Pa, passive solar is a money-saving strategy; you'll want windows and a floor no matter what you build. Line them up facing south, buy uncoated inexpensive double-pane glass for maximum solar heat gain, assuming the building code permits it, and spend your money on thermal shades.

If I choose a whole house fan, do I still need HRV? Being mono pitch, my roof will have no trusses or attic. Where do I install the whole house fan?

Yes, if you build a well sealed home, you will benefit from having HRV. A whole house fan is only used during Summer evenings and does not negate need for HRV. Google Tamarack whole house fans to learn more about them including installation requirements.

I downloaded the weather data, but it is in file formats that I am unable to open: .ddy, .epw and .stat Your wood stove boiler heats the hydronic, correct?

It's been a long time, but as I remember, you launch Climate Consultant and tell it where on your computer to find the weather data files. The raw numbers won't do you much good without CC, which crunches them and presents them in a (mostly) comprehensible format. One guesses that Weatherspark.com's through-the-year averages use the same data. Eyeballing passive solar, you'd want minimal cloud cover and minimal humidity.

Yes, the wood stove boiler heats the floor indirectly. It heats a 200 gallon storage tank through a coiled copper tubing heat exchanger mounted in the bottom. The hydronic system uses the tank to heat the floor, operating on five thermostats and moving pressurized water through a second copper coil in the top of the tank and then through the loops in the slab. A 10kW tankless water heater takes over when the tank drops below 95 degrees. It's sunny and 46 at the moment and heading for 30 overnight -- weather that typically requires a fire every two or three days. Single digits on gray days, rare around here, require a banked fire at bedtime and relighting the next morning. Recognize that vigilance is only necessary if you are a cheap b*stard like me.

Posted By Laura Diane on 15 Mar 2017 01:48 PM
How much space would HPWH take? Just curious. Not a lot of wiggle room in my small house floor plan, but at this early phase, possible. Also, curious what you'd recc. to deal with potential power outages in the winter?

It's not the physical size of the HPWH that's the issue, but rather the amount of air it has to work with, since it's getting half or more of the heat from the room air. Stuff it in a closet and it'll bring the closet down to frost levels pretty quickly, and it won't be very efficient. Simply leaving the door open won't always work either, unless it's a large door to a large room. The paradigm installation is an open basement room, no partition walls.

Ah, yes...must launch the program first! That worked, although I'm not sure what to do with the data.... ;-) Thanks to all the replies I've gotten here, I'm getting closer to choosing my system: Electric boiler (NextGen) with electric water heater (not sure what brand yet, suggestions?) for the hydronic, with floor thermostats added. For back-up heat, (when power goes out) considering a gas fireplace. (no more wood chopping for me!) For HRV and AC: Whole-house fan and something like the Lunos e2 units.. After a year or so of evaluating the passive solar and hydronic heat, I may consider adding a mini-split. Thanks again for all your help with this!

Hello -- am here to report that my new house is finished and I'm in, all except for the in-floor heat still not functional. Based on reccomendations on this forum. I went with a Chiltrix (CX34) and I'm not sure if it's my electrician's inexperience or what, but he has been calling the manufacturer for a month, trying to troubleshoot why it's not working. Initially, my electrician was super impressed with the Chiltrix specs, saying it was the most efficient heat pump he'd ever seen. Now he's saying I should've never bought something off of peoples opinions on the internet! What seemed like a reasonable deal buying the Chiltrix is turning into a very expensive installation and after a month, we're still not there yet. Now Chiltrix is saying we need to purchase an additional pump to go from the heat pump to the storage tank -- wondering why they didn't suggest that from the get go? My house is not that complicated.... a basic rectangle, 1400 sq. ft., slab-on grade facing south. Anyway, I haven't talked with Chiltrix personally, just letting the electrician handle it, but I'm frustrated by how long this is taking. Fortunately I have a gas fireplace that puts out enough heat to keep me warm, otherwise it would be way worse, having NO heat at all, with night temps in the teens ( I'm in zone 4)
Anyone have any suggestions for me? I'm struggling with having to pay for all this "learning curve" and "troubleshooting"? I may have chosen another heat pump, had I known that Chiltrix was not an easy installation. I had great faith in my electrician, he's been in business 30+ years, so I figured it would be a no-brainer for him. Not the case.