New house! Eternal heater w/ solar preheat?

Discussion in 'Tankless Water Heater Forum' started by jjwest29, Aug 24, 2011.

  1. Steve29

    Steve29 New Member

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    Aug 28, 2011
    Location:
    Sedona, AZ
    Was your $3000 estimate excluding whatever controls, pumps, manifolds, check valves, and heater that we'll need? (Shows my ignorance - I'll have to spend some time looking into radiant systems) Correct, my gyp cost of $6200 was just for the gyp. If we did gyp, we expected to tile over it, as I didn't realize there was a way to make exposed gyp look decent, and to wear OK. Is there?

    You didn't mention doing our slab downstairs. You would do that, too, right? One water heater for each floor's radiant, or one boiler for all? The calcs show a pretty high heating load. (stupid view windows!)

    I'll read some of your previous discussions from Feb 2010 on using the same heater for the radiant and domestic, as it seems odd to me right now. Seems you'd want the water for each to be at different temps.

    Great tips on the other things, too. Thanks!
     
  2. Dana

    Dana In the trades

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    A ~110-115KBTU heating or cooling loads for a 3800' house in that climate seems kinda insane, but I s'pose anything is possible with an insane amount of glazing. Are you sure you're entering the right U-values for the glass? Have you tried changing the amount & type of glass in the tool to see just how far you'd have to cut back to get it at least under 50K? (Seriously, I see bigger houses than that in places with -10F design temps and half the heating load, but perhaps not the view!) Without higher performance glass &/or less raw glazed area you probably won't be able to get there with insulation.

    With those kinds of incentives for geothermal, you might want to consider a geothermal-hydronic radiant solution rather than gas-fired, but try to cut the heat load in half first. With water-to-water and the low water temp requirements of radiant slabs you'd be able to beat the true system average COP of any water-to-air system, since hydronic pumps would use less power than the air handler(s), and with a lower temp output the geothermal heat pump itself will run at higher efficiency.

    I would NOT recommend trying to support a 110K heating load with just a condensing HW heater but an HTP Versa or Flame combi would get you there in a code-legal fashion. Some models are set up with solar-thermal heat exchangers already in place as well. Radiant & hydronic "open systems such as those recommended by radiantec are a code violation in most places (but not all).
     
  3. ballvalve

    ballvalve General Engineering Contractor

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    "retired" and still building and troubleshooting
    Location:
    northfork, california
    Check my link to passive radiant systems, there is a lot on the web. But it automatically puts cold water in the floor during the summer, extracting some heat and tempering the incoming water to the heater. Only a few valves for you to adjust a few times a year.

    I like the Polaris, its improved they say, and it has ports already installed just for the passive system, although you don't really need them. They have a fantastic recovery rate, and unless you are snowed in all winter, one is enough. The longer one unit runs, the higher the efficiency anyway.

    When you use hot water, the water entering the heater is floor temperature, so if in winter, you have a huge storage mass of warm water to extend the recovery rate - I dont have the math to calc it, buts it self evident. In summer you leave all your zone valves open, and you can pick up some btu's from that sunny slab for free. Its all about 1 top quality check valve and some simple routing of plumbing.

    If you get your hands dirty and use small screeds for the mortar upstairs, the pipe is about 30 cents a foot, ready mix mortar a few bucks a bag, and the screeds perhaps 100 bucks. Just about any kid can level out [very dry mix] mortar between sticks a foot or so apart. Thats probably $1000 dollars. And you can tile over it. The gyp crete guy was "created" to do fireproofing between floors of motels/ hotels. He's way out of work now and wants to pay his mortage on his pump with your job.

    My system works fine with the water at about 130 degrees and less. It just means cranking the hot water handle more than the cold one.

    Yes, you still need all the mechanicals to be done.

    Gyp is just basically sheet rock mud, and not very hard. Perhaps there are newer products. But I'll never part with 6 grand for it.

    I never used it. I suppose you could stain it and use a good catalyzed finish on it, but dont dance in high heels or let the German Shepherd chase the kid up there.

    As to the "code" submit the plan for the combined system. I never saw one questioned in any manner. And I see no merit to the objections at all. The "code" should be out checking meat and lettuce in the stores for listeria and bacteria, where they might actually save a life.
     
    Last edited: Sep 26, 2011
  4. Dana

    Dana In the trades

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    I don't write the code, but I'm bound by it. Open systems are allowed in combis in MA provided it's controlled with minimum circulation times per hour when not in heating mode etc. It gets to be a bit messy when it's more than a single-zone. Buying the heat exchanger and another pump, or using something with the heat exchanger built into the unit makes life with the inspector simpler.
     
  5. ballvalve

    ballvalve General Engineering Contractor

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    "retired" and still building and troubleshooting
    Location:
    northfork, california
    How about those monster homes with 300 feet of pipe dead ending in the guest bath?

    Ma. should MAKE you circulate that if they want to justify their minimum circ times.

    In any case, I don't drink a whole lot of hot tap water, and the passive system automatically circulates all zones all the time when cold water is being used, as long as the valves are partially open.

    I read about a lot of dead people that ate a melon or a sprout, but never from their radiant heat system.
     
  6. Steve29

    Steve29 New Member

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    Aug 28, 2011
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    Sedona, AZ
    Here's a breakdown for the amount of glass we have planned: of the entire exterior (vertical) surface of our house, 65% is insulated walls, 28% is insulated-glass windows and 7% is butted-glass windows. So it's 35% glass right now.

    Yes, I entered into Taco real glass U values of .355 (Cardinal low-E 366, as an example). (The ACH is .5/hr.) I have not tried changing the amount of glass yet, but I will - it will be interesting to see what it takes, even though we won't be able to lop much glass off when it gets right down to it. But I did try a few things: 1) increasing the walls from the current R18 to R24 reduced the load only ~2K, 2) decreasing the glass U value from .355 to .27 saves 3K cooling and 6K heating, 3) dropping the U to Taco's lowest allowable of .24 drops another 1K cooling and 1K heating. So that last effort takes us from the original numbers of 115K cooling/109K heating down to 109K cooling/100K heating - not very compelling.

    I'm pasting a jpeg of the Taco result page below, but since I'm not sure it will display I'll say a couple things about two big numbers that are biting us, one for cooling and the other for heating:

    You probably are used to looking at their results table, but I'm not. a) The window solar contribution to the cooling load is 40K, but as far as I can tell Taco isn't taking everything into account (for instance, we have a lot of ENE glass, but we'll have exterior shades for summer mornings - I accounted for that in Taco by putting in huge overhangs but saw no change in this number. Also, our south glass has proper overhangs to mitigate solar gain in summer. West glass area is minimal.). b) The ventilation contribution to the heating load is 40K, a really big number, but I don't understand what it is - there's already an infiltration number of 9K. (Ventilation adds 8K to the cooling load.)

    Taco base case_R18 walls U35 glass_100%.jpg
     

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    Last edited: Sep 27, 2011
  7. ballvalve

    ballvalve General Engineering Contractor

    Joined:
    Dec 28, 2009
    Occupation:
    "retired" and still building and troubleshooting
    Location:
    northfork, california
    Do a passive and adjust the valves and temp of the water to the REALITY of the built house.

    I would'nt get tied up in programs details very deeply. You have already identified many flaws.

    Do a whole house fan at night, and you might never use your air cooler. I have one 100$ window AC to cool my 3rd floor bedroom, and a ton of mass inside. Never even used the AC this year, with some 100' days.

    If I want to really cool off, I tunnelled a wine cave in the mountain about 100' and it holds around 50-60' F.
     
    Last edited: Sep 28, 2011
  8. Steve29

    Steve29 New Member

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    Sedona, AZ
    I love the wine cave! We live in a passive solar house of our design, also with tons of mass (including a small earth-coupled wine room) so, like you, we appreciate mass and nighttime cooling. And yes, for this new house in Sedona we are planning for a whole-house fan. We just don't have much mass in the design other than the downstairs slab. Hence my interest in gypcrete and tile with radiant, but as you pointed out that's not cheap mass by any means. We'll do 5/8" drywall everywhere, but are told a double layer would cost too much. Not sure how else to get mass.

    Re messing with the program, I wanted to get a handle on the cooling load, too. Our (somewhat conventional) architect immediately spec'd three big AC units on the drawings. We've never lived in a house with cooling so that made us nervous.

    Not sure what you mean by doing "a passive". I had no luck with googling it.
     
  9. ballvalve

    ballvalve General Engineering Contractor

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    "retired" and still building and troubleshooting
    Location:
    northfork, california
    Thats the type of system shown by 'radiantech' or such on line. I believe I left a link somewhere above.
     
  10. brennl

    brennl New Member

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    me too i did not expect it that the singles vs a multi - tanks ..this is awsome
     
  11. Dana

    Dana In the trades

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    Steve29 (if you're still looking here): I played around with the Taco tool a bit and if you kick the ventilation & infiltration numbers down to 0.1 or even 0.05 to account for moderately air tight construction and heat recovery ventilation (HRV) I think you'd get a bit closer to reality. Doing a quick model of my home with it against measured reality it's hitting ~20% above measured reality, even with 0.1ACH. Watch out for the cubic feet per square foot ventilation entry, as the tool will use the greater numbers in the calc. (You'll note that on the results page it looks like they're calculated 2.0 ACH, not 0.5.
     
  12. ballvalve

    ballvalve General Engineering Contractor

    Joined:
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    Location:
    northfork, california
    You want warm air on your FEET, not the top of your head.
     
  13. Dana

    Dana In the trades

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    Naw, you want warm SURFACES at your feet- the air temp at your hardly matters. Radiant floor is the top of the food chain from a wintertime comfort point of view.

    But radiant ceiling in a well-insulated building is the next-best thing and a close second at that. A radiant ceiling heats up the objects below, including the floor, (just not to temps that matter to bare feet.) Radiant ceiling never gives off that oppressive "under the heat lamp" feeling that even halogen down-lighting can, but the chairs/couches/tables/floors are all directly heated by the radiant ceiling- it's air contact with the warmed up stuff in the room that raises the air temp. In hot air/tepid-air systems the heat transfer is the other way around, from the warmer air to the cooler object. As a result it takes a few degrees higher air temp to hit similar comfort levels as radiant ceiling/floor or low-temp flat panel radiators (or even big clunky old-school higher temp radiators.)

    Low-temp low-speed air and constant room temps using ductless heat pumps isn't bad though- it's a noticeable comfort-improvement over ducted-air systems, but where you might be just-plain cozy at 68F with radiant you'd need to keep it at 70F or more to be as-cozy with low-temp low-speed air. But any kind of high-speed ducted stuff adds a wind chill and noise factor- to be avoided if you can.
     
  14. ballvalve

    ballvalve General Engineering Contractor

    Joined:
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    "retired" and still building and troubleshooting
    Location:
    northfork, california
    And take a look inside that 20 year old flex duct. Scary!
     
  15. Dana

    Dana In the trades

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    Reason number 177 why ductless is a better solution than ducted, when tepid-air it the heat transfer medium, eh? ;-)

    Flex duct is an abomination- I'm surprised it's even legal. It's only positive aspect is vibe-isolation when tying into a cheap noisy air handler.
     
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