Most practical hot water and home heat
I live in Wasilla Ak. Natural gas is .69c per therm or 100kBtu if I have my facts correct.
35 degree well water and NG on site. 3000 sqft twostory home, two adults no kids. ICF with FPSF slab on grade R50+ lid.
I am considering two choices of heating systems.
1. Solar collectors to preheat well water insulated storage tank through a closed loop system. Feed the tempered water to a pair of on demand tankless heaters, one or both used for dhw and radiant in floor heat.
The drawback of course is the complexity and space required for all the hardware.
2. Use a high efficiency NG boiler with a attached “boiler mate indirect tank” and use that to do both the floor and dhw.
Any guesses as to which would be the most economical?
I am leaning towards option 2.
Thanks in advance
Jim
Replies
Well, I gotta say it since someone's certain to: In Wasilla the best source of heat is probably all the hot air coming from that district.
Otherwise, assuming you're reasonably consistent with the R50 and accompanying sealing (and aren't going overboard with windows, etc) then simpler is better.
3000 sq, two adults no kids and do not have space?
Well yeah, gotta have room for my workshop and the wifes shop too <G>
You planning on tech dependency? If so, #2. Lots of defunct active solar systems here. Nobody to maintain them.
OTOH, a buddy here had a special ground source heat pump and radiant system installed. Don't know exactly what it is, but only one company in town would touch it. Mistake.
Those defunct solar systems didn't slow me down in recycling the hardware for my next place where I need to heat a large indoor pool. 480 sq ft of flat panels with 650 gal tank. Pretty simple system. Wood-fired boiler for backup, expecting to never need it.
PAHS works. Bury it.
Yeah, I'm guessing that at least 50% of residental active solar systems end up abandoned within 10 years. Just too much maintenance to be worthwhile, unless you really like to futz with that sort of thing.
There is no absurdity that human beings will not resort to in order to defend another absurdity. -- Cicero
Talisker2
Super insulation I hope, but then your choices aren't so obvious.
Solar water panels tend to be underengineered which requires more maintinace with fewer people comfortable doing the work. Hence the bad reputation.
I went a differant route after careful consideration and calculation of all the costs involved..
I built with SIP's Unlike stick building I don't have wood every 16 inches to telegraph cold in and hot out so it's at least 30% more efficent than normal stick building.. that allowed me to use in floor radiant which tends to be warmer and more comfortable than forced hot air.
Combined my heat loss calculation became surprising modest on all but the most brutally cold days (-40 and below) which could be met with a simple electric water heater.
I choose electric because in the long run here in Minnesota electric will remain competitive with Natural gas and it has the bonus of not needed an exhaust flue.
People underestimate the energy cost of an exhaust flue but that flue is allowing heated air to escape 24/7/365
since most exhaust flues exit thru the roof and heat rises you are effectively pumping heat out as fast as mother nature allows.
Not only that but since mother nature hates a vacumn. You are also drawing cold outside in to be sucked in to replace the heated air you are pumping out..
I was never able to find conclusive numbers to do the calculations to find out what the actual numbers are however in my mind it's like leaving a window open about an inch all winter..
I don't know what sort of cost comparisons between natural gas and electricity you have where you are but it's certainly worth a consideration.
Your gripe about exhaust flues doesn't hold for high-efficiency units.
There is no absurdity that human beings will not resort to in order to defend another absurdity. -- Cicero
DanH
It may not be as massive but any hole in the insulation barrier is a loss of energy.. Now granted we're talking about more modest numbers but still measurable..
MY high effecency forced air furnance (with the side exhaust) allows cold air to migrate in through the insulation envelope. I can put my hand on the pipe on a cold day and feel it.
You can insulate the pipe if you're really worried about it. But when the unit isn't running there's no air movement through the pipe (unlike a conventional flue), and hence negligible heat loss. When the unit is running there's less heat loss than in a conventional flue because only the required amount of air is supplied to the burner and no additional air is drawn in by a draft hood.
There is no absurdity that human beings will not resort to in order to defend another absurdity. -- Cicero
Thanks Frenchy for your thoughts, I appreciate any and all feedback. Yes it will be as super insulated as I can afford to build. Watching my 401 circle the drain is delaying the project longer than I had originally planned. 2012 was to be the magic year but it is looking further out.
Talisker2
If I can suggest something consider using ICF's instead of even SIP's
so much easier to build with!
I suspect I could have saved some serious money building with ICF's instead of SIP's. I know I saved money over stick building.
The potential energy savings with either are high enough that you can completely ignore the durability benefit as well as the greater fire safety..
I would make one suggestion that I didn't see anyplace in the instructions.. First do one floor at a pour but before pouring your cement do all the wiring & plumbing etc.
That will save you a massive amount of time later on.. once a floor is done then go ahead and do the the flooring etc.. that way you are only pouring one floor at a time and you'll wind up a lot less frazelled.
Thanks Frenchy, that is the plan from the start. If I can afford it I would like the lid to be SIP's but because we don't manufacture SIPS up here it probably will be a truss roof.
there is no such thing as "preheat" in heating. you are either heating, or you are not heating.that's an oversimplification, but it serves a point; you can't "bump up" a hydronic system without also heating your solar tank with your on demand... some heat comes back from your emitter. heating up your solar tank with your on demand kills your solar efficiency and wastes a lot of the benefit you've got there.if solar make sense at all, use it for DHW first, with an on demand booster. that's ideal and if you have good sun and use a significant amount of DHW it can be very economical. It's pretty rare that it makes any economical sense to try to heat with solar (but sometimes it does or economics alone are not the decider). If your water temperature requirements are very low, you can tie the solar into your heating.. if not, you can use a dedicated radiator or two as a "heat dump" into the living space with basic control if you are willing to let indoor temps rise up a bit when solar is available..for heat plant itself, it depends on your heat load. I assume you have a significant number of degree days, so for anything over 20 to 25kBTUs/hr max load I would tend to think a true mod/con boiler would have payback over a less efficient water heater of any kind, and definitely over an on demand jury rigged into heating duty it was never designed for.but if your load is very low, a tank water heater can be a great choice. on demand, generally only in a single zone (or low zone count) high mass system would I even consider it, and even then you're spending more money for basically zero benefit over a tank heater in a heating application.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Thanks for the information, yes we are at 5-8K heating degree days here. Since we have such a high number of degree heating days the Idea was to temper the input water to the on demand heaters. The storage tank/s would take the cold well water in and its water would be heated by the coils from the solar panels, that in turn would be the feed to the input side of the tankless heaters.
I understand what you are saying, and I am saying you don't quite understand your plan.You have two issues.1. cold groundwater. this may require the preheat you are talking about to an on demand for domestic hot water purposes... or a larger on demand, or a sidearm on a mod/con. no problem, you've got that right.2. High heating requirements. Assuming your max load is somewhere over 20kBTUs/hr under design conditions, with that kind of degree day load you want efficiency; it will pay for itself. That means you DO NOT want an on demand for a heater, you want a mod/con boiler if you are using gas. You cannot "preheat" or "temper" for heating... you are reheating previously heated water, not raising ground water for heating.you should never use potable water for heating or vice versa. these are two entirely separate systems with two entirely separate issues.Hope that helps!-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Thanks Rob, I think I understand you. I of course would not use the same water for domestic water and heating water. Don't want a chance of bugs in the drinking water. I like the KISS system and will probably go the mod/con (by that I assume you mean the boiler w/boilermate process). I think I will preplumb the house for both PV and solar HW so if gas prices do go through the roof or if the components for solar drop enough in price will have a "easier" time installing them.
Thanks
Jim
rob...i went back and read every post 2x.... but i still don't have a clue what a "mod/con boiler"is......
help a guy out, huh ?Mike Hussein Smith Rhode Island : Design / Build / Repair / Restore
ah, sorry Mike, that's a common acronym in hydronics these days.it means "modulating/condensing", and it's typically used to indicate a certain class of boiler.. one that modulates its gas valve, and condenses additional energy out of its flue gases when run at a low temperature. strictly speaking all boilers can condense.. just that most of them rust out if you let it happen. these boilers are built to do it for the added efficiency.hope that helps!-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
i'm getting ready to talk to a customer about RFH again......i still lean to super insulation and electric HW boilers...
but i don't have any numbers for proprly sizing the n boiler..i lean to bigger tanks because of the higher wattage coils
but i have a sneaking suspicion that i am practising overkillMike Hussein Smith Rhode Island : Design / Build / Repair / Restore
luckily that won't hurt you much with electric, at least.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Yeah, with electric there's no great harm in having oversided (wattage-wise) units (within reason). There's no startup/shutdown efficiency loss. You do pay more, of course, both for the units and the electric service install.
There is no absurdity that human beings will not resort to in order to defend another absurdity. -- Cicero
so... if i was undecided on a 40 gal vs a 50 gal i can go with the larger with no falloff in performance ?
here's the next one :
last time i had two large zones, so i chose a separate HW heater for each zone
i wonder if i would be better off with one heater for all zones ... since each zone has it's own circulating pump anyways
i still keep the DHW in it's own heaterMike Hussein Smith Rhode Island : Design / Build / Repair / Restore
All electric water heaters/boilers have essentially 100% efficiency. The only inefficiency you have to deal with is heat loss through the insulating jacket (which is a non-issue if the unit is inside the heated building envelope, and which is pretty negligible for modern units anyway). A larger unit will have a lower % "duty cycle", but that doesn't affect operational cost.I'd say one unit vs two is a question of layout and cost to install, vs operational cost.
There is no absurdity that human beings will not resort to in order to defend another absurdity. -- Cicero
Mike,
Look at the heating element in that 40 gallon versis 50 gallon water heater, chances are the 40 ga.,50gal., and even the 80 gal. electric water heater have the same element(s) it's simply a matter of the size of the tank..
If you use the 40 gal for heating you'll get a quicker rise time than the 80 gallon. Another words if you dual purpose the heater you want the smaller tank size for more BTU output and the larger tank size for more water output at a given temp..
I cross connected my water heaters to enable me to have a dual role.. on chilly days I can use both water heaters for in floor radiant. In the morning when I get up we can all shower or bathe and the large thermal mass won't chill the floors untill after we're all up and away. It then has all day to recover. In the summer I simply close the 40 gal. tank and shut if off completely.
If we should ever be reduced to 2 in the house for an extended period I can select the 40 gallon heater and shut off completely the 80 gallon heater..
Flip a switch, turn a value, it takes maybe 45 seconds. Saves dramatically on energy use..
interesting project... existing '80's house ... well insulated for then
new owner wants an addition on each end
i'm not the architect .... so i can only offer advice
slab... full basement... or........ full basement on one end ... slab on the other
heating..... cooling
we'll see where this one ends upMike Hussein Smith Rhode Island : Design / Build / Repair / Restore
I'm not an expert, but I would be very tempted to try and heat the house with 1 or 2 hot water heaters.
You get out of life what you put into it......minus taxes.
Marv
Thanks Marv the only real problem up here with that is the well water is so cold the through put to the tankless is pretty low. (inlet temp to output temp delta is very large and there for the flow is a fraction of the flow at say 50-60 degrees or better).
Drawing on tempered water from the collectors would raise the through put considerably. I have to do more home work on this, the possibility is in the dead of winter (3 months here) is my solar system will not be able to provide enough heat to raise the tank up to a decent temp to make it practical. The NG furnace w/boilermate will work all year around at the same efficiency. Now it becomes a question of how much that system will A cost up front and B how much it will cost to run year around? I do plan on building a super insulated home so plan B the afore mentioned heat system would probably work fine and be the least amount of trouble to maintain.
The problem living here with any solar system is we get all our light when we least need it.
The problem living here with any solar system is we get all our light when we least need it.
Sorry, but I just got to dis agree with that statement. Sure ya got one heck of a winter heating load, but don't forget your summer heating loads. Maybe not everyday, but still plenty of them and the water to be heated is still real cold. Lots of potentiel (sp) for solar maybe, sorta,kinda , possibly.
Too bad there isn't a real storage system out there.
Thanks for the reply Tim, hopefully the SI home will have fairly low heat demands, again everything is completely up in the air at this point as to size, construction materials etc. depending on a whole lot of variables beyond my control.
One thing we will do though is have aux. heat via free standing wood heater. We are hoping to be able to afford a Tulikivi masonry fireplace in the main room, again we may be dreaming about that and reality will be a Hearthstone stove or something of that ilk.
Heck if the economy tanks since I own the property outright I might be living in a tent on it. <G>
Thanks Marv the only real problem up here with that is the well water is so cold the through put to the tankless is pretty low
Using water heaters to heat the house would only require bringing the temp up once. Then it is a closed loop. Our you could use a liquid that wont freeze in the loop. With a ICF house, heating it would be a breeze. You don't need the super heated water of a hot water boiler system.You get out of life what you put into it......minus taxes.
Marv
But a mod/con does not "super heat" the water and has about double the efficiency of a standard water heater and about 10% more than an on demand.
Here's a pipe layout we're using this week on a house that incorporates solar and a single demand water heater with a exterior wood burning water furnace. Simple it ain't but should be pretty efficient. the house is passive solar with 8" spray foam in the roof and 5" in the walls and this is all a bit of overkill for North Carolina but would probably work swell in Alaska.
If not the above the side arm boiler with solar pre-heat tank gets my vote.
One of these days I'll figure out how to draw these things in Sketch-up and be able to post prettier pictures.
Note: the electronic controllers are mostly omitted for clarity, that three way valve is energized by a relay that is powered by the juice going to the taco 009 which is energized by the t-stat in the tempering tank but the controller for that relay is a differential temperature controller that only allows the three way valve to be energized if the solar tanks are hotter that the outflow from the tempering tank.
Hope that is intelligible.
Be well
M
------------------
"You cannot work hard enough to make up for a sloppy estimate."
Thanks SN
Looks fairly complex but do able. My instructor at the last class I took had something like that set up and he used a small PV collector to drive the circulating pump, that way it was autonomous (didn't require any special circuity to circulate the water from the solar collectors to the storage tank.
I'm in a climate here in northern Ontario Canada that enjoys about 5 or so months of winter. I've built a few homes and the one we are in now has a pretty successful heating system. First, when I built this house I made the walls extra thick and bought alot of insulation.
I use a slant fin victory 120 boiler and copper lines to all the rooms with a 3 zone system. For the first few years I used an aertherm storage tank off the boiler for domestic hot water but the municipal water is a little hard so it was pretty tough on the heat exchanger. I took it out and put in a rheem 40 gallon gas heater and it is okay. The next change will be a takagi instant tankless.
The moral of the story is I have the same gas bill as my buddy who lives close with 2 by 6 construction and a gas forced air furnace. I heat twice the square footage.
Have a good day
CLiffy
We live in similar climates, I can appreciate your interest in well insulated home. I hope to build a ICF home and should be able to heat it fairly cheaply, I don't know how hard the well water will be there but I can appreciate you comments about the lime build up in your tank. I had the same problem years ago with the system I had here and pulled it out and put in a 50gal gas hotwater heater. I am leaning towards removing it and going back to the new style tanks that are less susceptible scale build up and possibly putting a filter upstream of my boiler to help cut down on the scaling. We are on city water here and it is fairly hard.
the high efficiency indirects for both domestic and radiant are really popular, it is quite an investment but i don't think the efficiency is matched with any other product. The last two basements we did both got the shebang, wall mounted and it is a beautiful thing. The heating guys love them, they informed me that on long runs between appliances they beat ondemands water heaters.
Take everything with a grain of salt I guess. I would go with option two.
Thanks, looking like that. Appreciate all the feedback.