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Thread: How to Construct a Solar Water Heater

  1. #31
    Plumber Plumbermurrieta's Avatar
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    SOLAR HEATING Solar heating is feasible today. The average American household consumes between 1000 and 2000 gallons of number two fuel oil per year. Efficient use of the suns energy could easily cut this consumption in half or eliminate it entirely. The heating of water is perhaps the easiest, most cost effective solar project a person can get involved with.

  2. #32
    Tasha Faith
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    Be careful working with the water heater since the water and the heater parts can become extremely hot. Wear gloves and safety goggles during this project. Make sure that you read, understand, and follow all instructions that come with your equipment. Do not let children or animals near this device. The sharp edges of the metal can be coated with tool dip after using a Dremel tool on them if their sharpness is a potential issue.

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    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    We maybe should have a thread dedicated to cost/benefit analyses, but since the discussion is here, here's my $.02. I've had a professionally-installed (about $2800 after rebates, etc.), open-loop, PV-driven circulation pump, 80-gal tank, 4x10 collector system installed for about 4 1/2 years. It was installed in December, and by accident we left the backup electric power off. We didn't notice anything for about 3 weeks, during a cloudy few days. When running normally, the hot water in the tank is about 160F. Occasionally the overtemp ciruit breaker in the WH opens (set point is 180), so after a run of cloudy weather we have to reset it. So, we believe it's working. Here's the rub: I keep detailed records of my electrical power consumption, and can detect no significant reduction in consumption following the installation of the solar system. Nor for the installation of triple-glazed windows, high-efficiency AC and R-30 insulation (augmenting R-6 or so). I'm puzzled, needless to say, but mention all this to caution that, as emphasised above, you can't guesstimate savings. Get the numbers, before and after, and you can see what really happened.

  4. #34
    In the trades Dana's Avatar
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    Quote Originally Posted by Mikey View Post
    We maybe should have a thread dedicated to cost/benefit analyses, but since the discussion is here, here's my $.02. I've had a professionally-installed (about $2800 after rebates, etc.), open-loop, PV-driven circulation pump, 80-gal tank, 4x10 collector system installed for about 4 1/2 years. It was installed in December, and by accident we left the backup electric power off. We didn't notice anything for about 3 weeks, during a cloudy few days. When running normally, the hot water in the tank is about 160F. Occasionally the overtemp ciruit breaker in the WH opens (set point is 180), so after a run of cloudy weather we have to reset it. So, we believe it's working. Here's the rub: I keep detailed records of my electrical power consumption, and can detect no significant reduction in consumption following the installation of the solar system. Nor for the installation of triple-glazed windows, high-efficiency AC and R-30 insulation (augmenting R-6 or so). I'm puzzled, needless to say, but mention all this to caution that, as emphasised above, you can't guesstimate savings. Get the numbers, before and after, and you can see what really happened.
    In FL the incoming water temps are pretty high (70-75F on an annualized average), so water heating energy per gallon is typically 2/3 or less what it is in MN or the upper peninsula of MI where the average temps are 25F lower, and it'll be "in the noise" on electrical power use relative to cooling bills. If you track power use with cooling degree-day(CDD) data you'll usually find some monthly baseline number with a roughly linear CDD power use function on top. If you have older billing data with exact dates, you may be able to look up the CDD history to correlate to those exact dates. (Uncorrelated monthy numbers won't work with any accuracy but kwh/CDD for whole cooling seasons might.)

    If your window & insulation upgrades haven't been measurable in the bill I'd be looking at duct leakage & air infiltration issues. While FL does have significant sensible cooling loads, the latent loads are still typically higher. If you're dragging 1-2 air-exchanges/hr into your home with poorly implemented duct design or other air leakage issues, keeping up with the latent loads becomes the dominant air conditioning issue, not much affected by the insulation levels or the rated efficiency of the AC unit. A tight house and tigher/better-balanced ducts acn make a huge difference. See: http://www.buildingscience.com/docum...ent-loads/view

    Blower door testing on the building envelope, and pressurized duct testing may tell you where the bigger problems are. If the air-handlers & ducts are in an uninsulated attic the "fix" can be as simple as foam-insulating/sealing the ducts, or foam insulating the roof deck (sealing the soffits), making the attic into semi-conditioned space, etc., putting the ducts & air handler inside the pressure boundary of the structure. (If you do the latter, don't let the foam installers try to convince you that you need to remove insulation at the attic floor, or than some number of inches of foam "...is all you need...", which seems to be a common misconception in the trades. ) See:

    http://www.buildingscience.com/docum...load%20florida

    http://www.buildingscience.com/docum...ealed%20Attics

    http://www.buildingscience.com/docum...ealed%20Attics

    In general, window replacement is almost never cost effective in an NPV analysis on energy use, but can be good from a comfort point of view. In cooling dominated climates exterior shading of the windows with awnings &/or operable exterior screens/shades are usually a better bet, but every house is different. Truly leaky or horribly placed single-pane uncoated windows from a solar-gain point of view can sometimes be cost-effective to replace, but they're the exception, not the rule.

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    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    Thanks, Dana. That's good advice and consistent with I've found and guessed. I'd love to do a blower-door test, but haven't found anybody around yet that does them. I did the best I could to seal everything in the attic before putting in the insulation, but never did any quantitative testing. The utility company used to, but no longer. My weak link, though, I'm pretty sure, is the walls. They're 6" "jumbo brick" with 3/4" foam on the inside. I don't know offhand what that works out to in R value, but it ain't much. Hard to fix.

  6. #36
    In the trades Dana's Avatar
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    Quote Originally Posted by Mikey View Post
    Thanks, Dana. That's good advice and consistent with I've found and guessed. I'd love to do a blower-door test, but haven't found anybody around yet that does them. I did the best I could to seal everything in the attic before putting in the insulation, but never did any quantitative testing. The utility company used to, but no longer. My weak link, though, I'm pretty sure, is the walls. They're 6" "jumbo brick" with 3/4" foam on the inside. I don't know offhand what that works out to in R value, but it ain't much. Hard to fix.
    If it's 3/4" bead-board EPS ("Styrofoam"), it's ~R3. If it's foil-faced polyisocyanurate it's ~ R5. If it's pink or blue XPS you're looking at ~ R4, none of which adds up to much, but it's way better than nothing, and the thermal mass of the brick helps even out the peak loads (but not the average.) If it's bare foam without a foil or poly facers it has very modest vapor retardency too, but vapor permeance is likely to be only a secondary factor (well behind infiltration, in most homes) for your latent loads. Add another R0.5-0.75 for the brick, and that's pretty much your clear-wall R-value.

    Hopefully it's a cavity wall with, at least a 1/2" gap between the brick and the interior foam, which would allow a good portion of the high vapor drive that occurs when sun hit's a rain or dew-wetted brick to vent rather cook into the interior. But if the brick tight up against unfaced foam, with no studwall on the interior, just plaster or drywall it can be a signficant moisture path. In either case, some amount of that type of vapor drive can be mitigated using masonry sealers on the exterior, which keeps dew or rain from wicking into the brick only to be vaporized and transmitted into the interior as the brick heats up. In some instances it might be better to use a vapor-retadent sealer, but I wouldn't recommend that without a lot of site investigation. Vapor permeable or semi-permeable sealers reject liquid water, yet still allow the brick to release moisture as vapor to the exterior (it's more forgiving, since it can't create moisture traps.)

    Plantings or shades to keep direct sun off the E,S, & W sides of the house can also make a difference. Brick is (unfortunately, in this case) a pretty good solar absorber, and surface temps can easily hit 20-40F above the exterior air temp in direct sun. When it's 90F out at 11AM the surface of sun-baked brick might already be 110F, and may hit an egg-frying uncomfortable-to-touch 120F+ in the afternoon, even if the air temps only hit 95F. A sunbaked section of 120F wall is letting in about twice the heat per square foot as a shaded section of 90-95F wall. Shrubs, trees, trellisis, fences, awnings, roof overhangs, etc all help reduce the amount of direct solar gain from both windows and low-R walls. Air-tight & shaded walls, with R30+ rafter-mounted radiant barrier (or cool-roof materials) on the roof/attic are about as much as you can do to get the cooling load down, but it's substantial.

    The bigger air-infiltration holes in most homes are generally easy to fix: Dryer vents, fireplace & furnace flues, bathroom vents without backdraft control, etc.. Then there's the PITA leaks to fix, like recessed lights, flue chases, plumbing, & electrical penetrations into the attic, etc, which can be time consuming to fix (or even find, in some cases.) Rare is the home where window & door weather tightness is the primary air leak. Crawlspaces & full basements can also have large air leaks, but I'm assuming you're slab on grade?

  7. #37
    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    Yup, slab on grade, mostly. I discovered the slab was sinking a while back, and a company came in and pump some kind of magic foam underneath through holes drilled in the slab all over the house. It was magic -- the slab rose up to nearly where it belonged. Long story. Anyway, some of the slab lies on an insulating layer of foam of unknown and varying thickness.

    The foam in the walls was sprayed on, some kind of closed-cell urethane, it looks like, ca. 1973. It's brick-foam-gypsum board only. With large shading trees, large overhangs, and general orientation, I don't think the solar-absorption aspect of the brick is a major factor, but I will look into sealing it -- I know interior humidity is higher than I'd like it, but the sprayed-on foam (I thought) should be impervious. There may be leakage around the 1x2 nailers, though.

    The garage used to have a no-brainer problem: a west-facing uninsulated steel 18' door. In the late afternoon, the door was a 120 radiator. I replaced that door with a the latest & greatest hurricane-proof insulated model, and the difference is as dramatic as you'd expect. Its 4 walls are the door to the W, uninsulated brick to the N, and the house (3 1/2" fiberglass in the studwalls) to the E and S. It's bearable year-round in the garage.

    Laundry room is outside the AC'd envelope, between the house and garage. It has its own source of makeup air for the dryer, but that source exits right next to the dryer intake, so it doesn't affect the room much, which stays moderately comfortable just from traffic to and from the house exchanging conditioned air.

    Fireplace flue is an interesting issue. Some days when the AC is on, I can smell the air coming into the house via the chimney. That tells me there's negative pressure in the house, which could mean too many registers are restricted, or duct leakage in the attic (which I doubt). I haven't looked into this any further, but intend to go around and check & open up all the registers for starters.

    Leakage into the attic may be a big deal. As I said, the ductwork should be pretty tight, and I sealed all the electrical penetrations that were easy to reach (maybe 30% of the total), but there are several can lights that are IC but not AT. Even so-called AT lights were a long way from airtight, I found, so I sealed them up with 3M fireblock caulk. Those suckers are AT now. Plumbing is overhead, and all penetrations are sealed.

    The bottom line, though, is that we keep ourselves cool in the summer and warm in the winter, and it apparently costs us. But for now, it's worth it. Our bills relative to our neighbors' are better, in some cases significantly, but I still want to do the best I can on general principles. It's definitely our fault, though -- when we were both away from home in February, our bill was cut in half. Maybe we should just stay away.

    Thanks again; sounds like you do this sort of thing for a living, and are good at it. I appreciate the comments.

    Mike

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    In the trades Dana's Avatar
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    It sounds like you've taken on quite a bit of the PITA air-sealing work, but if you have detectable air flows coming down the flue, there are still more leaks to plug, possibly some big ones. Top closing fireplace dampers are much tighter than old-school steel flappers at the firebox, and may be worthwhile here- but that's only a start. (There are inflatable "chimney balloons" too, but they're a pain to swap in/out seasonally when you might want to use that fireplace.) But the flue is the return path- there has to be a big supply to get much flow, but it may be 20 smaller supplies. Pressuringizing/depressurizing the house with a big window-fan and running around with a smoke pencil, can of foam, and labels for marking the bigger leaks can be as effective at this "rat-killing" of leaks as a calibrated blower door test that actually measures the volume.

    Closed cell polyurethane foam from the '70s is about R6/inch, so you're at better than R4. But while it's waterproof to liquid water, it's semi-permeable to water vapor. At 1" thickness it's permeance is about 2 perms, and higher at 3/4" compared to 6-mill polyethylene sheet's ~0.05 perms, or kraft paper facer on fiberglass batts ~0.4 perms. It is passing in on the order of 40-50x the diffusion that poly sheeting would(!).

    In CA under Title 24 building efficiency laws ducts have to meet both design-balance and pressurized leakage tests. To pass the leakage test usually requires mastic or FSK tape on every seam & joint, and sometimes even the air handler panels need to be taped. Very few ducted AC or heating systems elsewhere in the US would actualy pass, but the Title 24 provisions all went through cost-effectiveness vetting as part of the process (efficiency measures that were a net economic burden to the homeowner were cut from the code.) There are many companies there that now offer duct leakage test & remediation services, but I don't know of any operating to that spec in FL.

    Evening out room-to-room air pressure via transom grills or jump ducts can often have huge positive effect on reducing air infiltration related to duct imbalances, now ensrhined in FL code for new construction See: http://www.baihp.org/casestud/return_air/index.htm Partition-wall stud cavities can often be used as jump ducts with less light sound transfer by putting a grill on the bottom of the cavity on one side of the wall, and at the top on the other. In new constrution or as retrofit jump ducts are often a U of flex duct at the ceiling. But lowering the overall resistance of the supply & return paths internal to the house reduces the volume of air-handler induced infiltration.

    Ducts & air handler in the attic are far more suscetptible to radiated heat from a superheated roof deck than the insulated attic floor, and need to be insulated for best efficiency. Radiant barrier (the aluminized fabric type) stapled to the rafters can cut the heat gain at the ducts roughly in half, even if they're already insulated. Duct insulation must be air-tight, or you can end up with substantial condensation on the duct it self in a ventilated attic. (An inch or two of closed cell foam or foil-faced rigid-board with mastic/FSK-tape sealed seams is good. Unfaced fiberglass wrap, not so good.)

    Don't feel guilty about using the AC- it's necessary for both health & comfort when living in a hot humid climate- it's what you have it for, eh?

    I'm currently working as an electrical engineer, I'm not a building pro. (My degrees are in math & physics.) But building practices & energy efficiency stuff has been of personal interest for decades now. My father was in the constuction biz (general contractor- mostly commercial & industrial stuff) in the Pacific Northwest during '60, '70s & '80s. I've seen a lot of construction practices come & go, and a lot of half-understood vapor retarder & insulation stuff mis-applied, even by the pros. A lot of stuff previously enshrined in code based on best-guesses or best practices in one climate zone mis-applied to another has slowly been tossed out since the mid-'70s, but there's still more work to be done. There's still a wealth of ignorance in the biz about moisture control regarding proper use of vapor retarders (or even what is/isn't waterproof vs. vapor retardent vs. air barrier.)

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    Moderator & Master Plumber hj's Avatar
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    I am not about to try to read everything that has been posted, but a solar system depends on a ration "radiation area" to water surface to absorb the energy efficiently. A large tank will have a very low ration since the only water in the tank which is absorbing the solar energy is that which is in contact with the tank's surface. The rest of the water is draining that temperature away. The best collectors have large radiant "fins" attached to small copper tubes, which results in a very high efficiency. DIY panels can use "finned baseboard radiators" painted black and installed in parallel manifolds to absorb the heat and transfer it to the storage tank. A serial manifold could result in overheating the water before it arrives in the storage tank.

  10. #40
    AigleAntonina
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    A system in which the suns heat is gathered by a solar collector and used to increase the temperature of a heat-transfer fluid which flows through the pipes in the collector

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    Extreme DIY Homeowner Scuba_Dave's Avatar
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    I've been heating 450g of water in my hot tub since May
    I changed my saltwater aquariums setup at the same time (less water to heat- one less pump), so not sure of exact savings
    But my electric bill dropped $100 1st month (May), $110 the 2nd month
    Hot tub will exceed 110 degrees with one 4x12 panel
    I've actually had to turn it off after 3 hours instead fo letting it run 7-8 hours
    DIY Handyman (not 4 hire)
    I have enough to do to my own house

  12. #42
    DIY Junior Member Dave D's Avatar
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    Quote Originally Posted by Peter Griffin View Post
    I am going to go gentle with you here.

    1 - You absolutely can not use pex in a collector and anywhere else in the high side of the system for two reasons. within the panel, Pex is an bad conductor of heat so it's efficiency would be just plain awful and typical temperatures can run well over 300 degrees which puts it twice what pex is rated for.

    2 - If you can get a 3 panel set with tank and controls for under 7 grand without subsidies then you need to PM me and give me the name of your supplier because I can't buy the equipment for that price.

    3 - Try this web site www.caleffi.com and download idronics 3. Read it and get back to me.

    4 - Been installing solar systems since the early 70's Not much I don't know about them and believe me, I've seen it all.

    5 - Guys that build their own stuff will always tell you how wonderful it is. People that spend a lot of money to have it installed will always tell you how wonderful it is. That's because they have an investment in it. It's just human nature.

    The performance curves and case studies from all over Europe are on the web and available to you. I strongly recommend that anyone considering solar, take a few days and do the research.
    Tell that to Gary who heats his house in a harsher climate than Maine or Mass with all kinds of collectors including Pex-al-pex collectors. The lates project linked below is amazing with all the charted graphed info you can fit in your brain.


    http://www.builditsolar.com/Projects/SpaceHeating/SolarShed/solarshed.htm

    http://www.builditsolar.com/Experimental/PEXColDHW/Overview.htm

  13. #43
    In the trades Dana's Avatar
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    Quote Originally Posted by Dave D View Post
    Tell that to Gary who heats his house in a harsher climate than Maine or Mass with all kinds of collectors including Pex-al-pex collectors. The lates project linked below is amazing with all the charted graphed info you can fit in your brain.


    http://www.builditsolar.com/Projects/SpaceHeating/SolarShed/solarshed.htm


    http://www.builditsolar.com/Experimental/PEXColDHW/Overview.htm
    That post is popping to the top again? (Dude, that post is almost a year old!)

    Don't be mean to Peter- he's actually a pretty nice (and very bright) guy. :-)

    BTW: Gary's solar shed is an all-copper flat plate design, not PEX, but his DIY water heaters use PEX.

    Note that Gary Reysa is an engineer, and is capable of designing around the deficiencies of PEX where a commercial panel manufacturer or installer would have a hard time guaranteeing performance & longevity. To be as successful as Gary at it you DO need to pay attention to the details, measure stagnation temps in-situ, and adjust other factors accordingly, which a typical commercial installer just wouldn't have the time to do. Peter is totally correct that a 300F pressurized design using PEX would blow up in your face.

    But for the DIY crowd the atmospheric-pressure low-tech low-temp approach that Gary uses works just fine if you pay attention to the particulars.

    But for the amount of fuel it actually saves, in most homes investing the money elsewhere would deliver more substantial reductions in fuel use. eg. If your house scores higher than 3.0 on an ACH/50 in a blower door test you'd be better of spending the cash on air-sealing rather than a ball o' PEX and related hardware for DIY solar collectors, as kewl as all that stuff is. Thermal air heating panels are also A: less hardware and B: lower temp/higher efficiency than any solar hot water heater, delivering better return in heating-dominated climates. A DIY-installed $600 drainwater heat recovery system is less work, delivering as much or better return per dollar than a DIY solar hot water system if your shower runs more than 20 minutes/day. Any active-solar (even thermal air panels) is typically well behind air-sealing & insulation upgrades for most homes.

  14. #44
    DIY Junior Member Dave D's Avatar
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    Doesn't matter how old his Pex project is, it works, and it works well. Its also very easy to reproduce and up size or down size depending on ambition. Ive built a test panel like Gary's with Pex with the exception, I use a flat sheet of poly carbonite. I will be tesitng it thru the winter this year and if it works as I expect, similar to Gary's, I will be building a full size unit like his. I live near Portland MAINE. There is no down side to this and it certain works and works well form what I have discovered. As for the waste water recovery, I have done some tests on that as well. I wrapped an insulation blanket around my waste line and installed a temp data logger, the temps are minimal at best seeing the pipe only heat up to around 75 +/- degrees for very short periods of time, certainly not the 120-140 you get from a solar system. My house is as good as its gonna get for insulation and sealing, solar is the next step. Currently I burn 200 gallons of oil and two chord of wood a year for heat. The goal of solar is to lower my electric bill from 100 to around 70 a month on average. So if the solar costs me 1000 to build and I average $25 a month savings for electricity thats a 40 month payoff so three or so years.... Sounds like solar works and so does PEX.....

    Dave D AIA

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    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    Hey, Dave, what kind of temp datalogger do you use?

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