Radiant heat
I am building a 3,100 sq. ft. 2-story home and am considering using radiant heat to heat the entire home. I am a residential framer and so have much experience in energy efficient building. I plan on using 8 1/4 SIPs with insulated headers with an R-value of 33 for the walls and R-50 in the roof.
I am going to do in-floor in the basement slab as well as the 1st and 2nd floor. On the 1st and 2nd floor I am going to lay the tube on top of the plywood. This where my first question comes in. Some contractors are telling me to not do an over-pour since the house is extremely tight. Others say I would be wasting my money not doing that.
My 2nd question is, Can I get away with running the system off my hot water tank only without a boiler?
Finally is the question of air conditioning. Some people are telling me that I won’t even need air conditioning in a house that is so tight. I have trouble believing this. If I do need an air conditioner, what is the most recommended for this application? I have read a little on the ductless minisplit units and also the high-velocity units, but I could use some direction.
I have trouble spending $8,000 on duct work for an air conditioner that will run for 5 weeks of the year. I know I have to duct my HRV, but the duct work is minimal.
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Check out Radiantec and give them a call. http://www.radiantec.com/systems-sources/best.php They can help you with the installation details, and I would guess the limited cooling their open direct system offers by pushing your domestic cold water through your floor in summer will be enough for your house. Which climate zone are you in?
Lukas,
What is your climate zone or your HDD and CDD? What is your estimated maximum hourly design heat load and what is your expected domestic hot water consumption?
What do you mean by an "overpour" - a thin lightweight concrete slab over floor sheathing? 2", 4"?
It's hardly likely that you can heat a house that size and provide sufficient hot water with a tank DHW heater. You'll almost certainly need a mod-con boiler with indirect water tank and heating zones for each floor.
If you're heating the basement slab, make sure it's well insulated both underneath and at the edges. And make sure the tubing layout and flow and temperature for each loop and zone is properly engineered for your heat losses and floor coverings.
i don't see what an "overpour" has to do with the house being extremely tight. You are either going to install tubing using a product like Quik-Track, or your going to pour gyp or lightweight over it. In my opinion you ought to review your choices of floor coverings and see which way that pushes you. I personally like gyp but it's harder or impossible to install some types of flooring over it.
You might be able to heat with a water heater, but the real question is, how many BTUs do you need for space heating and how many for water heating? I tend to like boilers a lot more than water heaters for radiant, but ultimately what you need is someone highly skilled to design and install the system, and should probably ask their opinion. Anyway, it all starts with a heat loss calc.
I would skip the duct work and AC. Those five weeks a year of hot weather will go by real quick in your nicely insulated house, and long as you don't have huge windows facing right into the sun. Your friends with the hot attics and R-13 fiberglass will want to come hang at your place. Ductwork is almost always a real hassle IMO.
Heat Transfer (maker of the Munchkin Boilers) offers a line of Phoenix gas fired hot water heaters (120gal) that have a 95% eff modulating ss boiler with a peak output of 166,000 btu. This is the type of "water heater" that you could look at using. They also come with an optional solar heat exchanger in the lower half if you wanted to add thermal solar panels later.
For those of you who are wondering what heat zone i am in I think it is 7a I am in southern ontario. As far as the over pour what I mean is an 1 12 gypsm product. I have also considered geo but I have gotten prices from about 5 different contractors and the price tag is about 30gs and that is without in floor. Radiant sounds like nicer heat and hopefully cheeper
Lukas, what are electric and gas rates in your area?
Around here, we have semi-mild winters and semi-cheap (for now) electricity, and air-to-water heat pumps such as Daikin are a great choice for radiant heating. There's no way you would burn propane, even at 95% efficiency, when you could use electricity to move BTUs from outside to inside at 200%+ efficiency.
Air source heat pumps are ineffective and inefficient in cold climates.
I have no gas and electricity is at .064
Lukas,
Your electricity is very cheap. I think that a ductless minisplit system would make sense for you, providing both heating and cooling at a much lower energy cost than propane-fired hydronic heat.
Lukas;
A good option with your cheap electric rates would be a ductless mini-split, as Martin mentioned, which would take care of AC as well as heat during the "marginal" seasons (spring,fall).
An electric boiler would take care of the radiant (winter) as well as domestic. Ductless mini's are great, but be aware that they are limited when it comes to very cold winter temp's. At least here in Vermont.
Bob,
Mitsuibishi makes a minisplit that performs at -13°F, without using any electric resistance elements.
I'll once again second Martin on the Mitsubishi mini splits. I have a 1-ton Mitsubishi mini split heating my 1900sq/ft house in CT. As of January 12th Ive spent $170 heating it this season and thats with CT's ridiculously high electricity rates. The coldest outdoor temp Ive experienced with it so far is -4f and it had no problem keeping the house at 70f. Its supposed to get down to -10f Sunday night so I will keep a close eye on it to see how it performs.
But with negligible output. The problem with air source heat pumps is that they put out less heat when more output is needed as the air temperature drops.
So some sort of backup heat has to be installed to pick up the slack.
Lukas, depending on where exactly in Southern Ontario you are, your climate zone will be either 5A or 6A.
Robert,
I disagree that the heat output is negligible. The Mitsubishi Mr. Slim Hyper-Heat unit (model PUZHA36NHA) has a nominal heat output rating of 38,000 Btuh at 47°F. According to the manufacturer, at an outdoor temperature of -13°F, its heat output drops only 21%, to 30,000 Btuh.
That's enough to heat a well insulated house in a cold climate.
Martin,
It's frustratingly difficult to locate anything on the Mitsubishi website, but the spec sheet for that model lists a 37,000 btu/hr rated capacity at 47°F and a 25,000 btu/hr rated output at 17°F (both at 70°F indoor).
It is apparently able to crank out full 38,000 btu/hr capacity at any temperature down to -13°, but the efficiency suffers. According to the spec sheet, the COP at 47° is 3.3, at 17° it's 1.85 and at 5° it's 1.65. At -13°, I suspect it operates with no more efficiency than resistance heat - COP = 1.
So, you're correct that this unit can maintain output at very cold temperatures, but it trades output for efficiency - which makes it inappropriate for very cold climates with little to no AC requirement.
Robert,
I think a COP of 1.65 at 5°F is excellent -- making the Mitsubishi unit a perfectly reasonable choice to heat a cold-climate house in a location with low electricity costs.
Also, say you have an "overkill" Passive House where the peak heating load is around 6000btu/hr. At 5°f the Mitsubishi MSZFE12NA has a COP of 3.4 when producing 6500btu/hr. Of course when the output increases the COP will decline, but if you have really small loads, a COP of 3.4 @ 5°f is impressive. While I don't have any data for the PUZHA36NHA other than whats on Mitsubishi's website (I do for the MSZFE), I'm willing to bet that its COP is much higher than 1.65 @ 5°f when your heating demand is lower than its rated output of 38,000 btu/hr.
The Mitsubishi specs are great, but any problems with a ductless unit over a 3100 sf house?
"Superinsulated homes tend to be isothermal"
Meaning you don't need ductwork or pipes in gypcrete for the heat to be distributed evenly throughout the house.
"tend to be isothermal" I get, but still I've never risked proposing ductless on anything larger than 1200 sf. I'd very much like to feel confident with larger installations but I don't like to put my clients on the bleeding edge. These high-performance units are pretty new. Anyone care to share their experience?
If you share your load calc this would be easier to discuss. Solar exposure will be really important to heating as well as cooling in a super-efficient home.
Also, how do you plan to operate the home? Do you need/prefer to setback the temperature when you sleep? By how much?
James,
Here's anecdotal evidence of a 2700 ft2 isothermal building envelope:
"During construction, we were able to heat the house with one of those little 1,500-watt ceramic heaters," he said. "One day I remember, it was about seven below outside. Just really, really cold. But all your interior surfaces, floors ceilings windows walls, were all within about a degree and a half of each other."
http://thetyee.ca/News/2011/01/26/HouseWithNoFurnace/
Anecdotal evidence like this can be verified through computer modeling.
To save your clients from the bleeding edge, put tiny resistance heaters (baseboard-type ones are only $20 each) in the rooms you may be worried about. They won't be used, but at least you spent very little money on them.
NLEHTO,
"a COP of 3.4 @ 5F is impressive"
That's VERY impressive, and stats like that should make everyone think twice about ever doing a ground source heat pump.
Kevin,
Marc Rosenbaum has predicted the withering away of GSHPs as a residential option -- because the Asian ductless minisplits are getting so good.
I read somewhere that in labs they have heat pumps working well down to -60 degrees.
So if we build a massless home superinsulated, we just buy a small split and back up with small pellet stove and done.
In other words, spend the most money on insulation and low ACH
Thanks Kevin. Cooling season would be my remaining concern here in NC. We're about to try a minisplit with hi-lo room-to-room fans on a small guest house/home office addition. Work our way up from that.
Martin, good point about the perhaps waning of the GSHP trend. I was never happy about the extent to which it has been promoted through tax credits.
I'm with you on that James. Shocked to see that tax credits are also available for fuel cells.
We've done the mini-splits and found the t-stat to be overwhelming. Clients ended up hiding it to keep their guests from damaging the system by randomly mashing buttons to try to get the thing to turn off so they could sleep.
The aqua-chiller air to water heat pumps Ted Clifton and others are using in the pacific north west are very compelling. I got to interview him on video after he won the Energy Value Housing Award at IBS this month and hope to get it edited down so I can post it here for folks to see what he's up to.
I would like to see that post Chandler.
Another idea for a large well insulated home. Large solar tube collector, really large site built storage tank, combined with water to water heat pump. Seems like the efficiency of both the solar and the heat pump systems could be increased via this combination.
My idea is for a heating only climate. I have to ponder the cooling ideas a bit more, I like the heat pump water heaters for someplace where cooling dominates... hmm... help me with cooling area ideas. Maybe cool the water storage during the coolest 6 hours per day then reverse heat pump and use water instead of 100 degree outside air to run AC. That's the idea.
Another goofy idea. Run Pex a few inches under slab gravel, etc. say a foot or two below slab insulation. Insulate slab fairly well and run Pex in the slab. Use Michael's three way valves to switch where heat and cool move to between these two zones, a storage tank, and the solar tube array, making 4 zones to push or pull heat from.
Seasonal efficiency increases is the idea. For my area, use the subslab zone to cool the slab zone during the few times we need cooling. When the cooling season ends, start pumping solar zone heat into the subslab zone since it will have excess. Once the excess is seasonally not available the heat pump works with the solar to provide heat.... Back up could be anything, pellet stove to cooking more hot meals per day and baking up a storm.
OK... I said goofy. So improve upon it and point me to systems that are out there today.
And yes, I think the 30% tax credit for GSHP should be axed yesterday. At the least, install invoices should come with a complete breakdown of actual costs. You want free money, show me where it is going. No hidden rebates, kickbacks, annual sales volume payments. Once free money is involved the scams are everywhere.
Mr. AJ, I don't think your ideas are goofy but they are hard for me to understand. I'll keep trying though.
Thank You for help.
would I be crazy to forget the in floor and go geo. My biggest problem is the no air cond. It just seems that 30 grand is a little steep
In floor radiant for the slab is a no brainer. In a superinsulated home, myself and some others like the idea of limiting the rest of the in floor radiant on your other floors to bathrooms, kitchens and entry areas. That alone may heat a well insulated home almost all the time.
The radiant can be run off of a water heater, and air conditioning and other minor heat could come from a Mitsubishi split system.
We don't have cheap electricity in Ontario. Lukas is right that the cost for electricity is $0.64 but he didn't include delivery, regulatory charges and debt retirement charges of at least $0.54. Some of these additional charges are fixed meaning that for the non-winter seasons, we can pay more in delivery charges than we pay for actual electricity used (I know this because I heat with electricity).
Is electricity $.64/ kw (VERY EXPENSIVE) or $.064/kw (VERY CHEAP)?
N Lehto,
I think you mean "kWh," not "kW."
Obviously, 64¢ a kWh would be VERY expensive. I'm guessing that Mica239 meant 6.4¢ a kWh, not 64¢ a kWh.
yes I do mean KWH
I am having problems sending this post and not sure if it show it as being from Mica239.
Sorry, I should have checked my KWH reference before sending my first post.
Ontario is introducing new electricity rates. There will be 3 different time of use rates for each day and different schedules for winter weekdays and summer weekdays. The off-peak rate will be 5.1 cents/kWh (from 7pm to 7am); mid-peak rate will be 8.1 cents/kWh; and on-peak rate will be 9.9 cents/kWh (plus add on the delivery and regulatory charges).
I am planning on building a well-insulated house and using electric heat (in my rural/remote location natural gas is not available; oil would be inconvenient; and our local electrical power utility generates 100% renewable energy).
I was thinking of using in-floor radiant heat but now I am thinking of using an electrical thermal storage heating device(s) sized to take advantage of the 12-hour off-peak rate period (I don't need air conditioning where I live, so heating is my only concern).