How to Construct a Solar Water Heater

[nehalive]

Employing solar power to heat water symbolizes one of the most logical methods of generating hot water that you can find. Why use un-renewable resources when we have an over abundance of energy emitting from our own sun? It is rapidly becoming an acknowledged impression that the best way to diminish energy consumption is by building your own.

During the construction phase of this project, you would need to paint your water tank with flat stovepipe black paint. The paint will permit the tank to absorb as much of the sun's energy as it can. You will also need to assemble a straightforward plywood box around the water tank. Be sure to insulate the interior of the box with some fiberglass insulation, as this will facilitate eliminating any energy lost within the system.

At this point in time, you would install the painted water tank into the box and attach any of the necessary plumbing to the bottom of it. These are, of course, the pipes which carry the water from your house to the heater. Another set of water pipes will carry the water from the heater back to the houses water distribution system.

Here you have a simple home made solar water tank that is more then capable of providing a single person or perchance a couple with adequate quantities of water.

[nhmaster]

Where I live, even the best, most efficient solar panels, tank, controls etc will at best only produce 30 to 35% of the required domestic hot water. At an average installed cost of around $ 14,000.00 there is no pay back at all, but at leas you get a warm fuzzy feeling when you tell other folks how "green" you are. In India, where the sun shines more often and at a better solar azimuth, you have a much better chance of sucess.

[Alphacarina]

I can see where that would be a problem for you living in 'South Maine' . . . . that's a lot like 'Northern Massachusetts' - What little sunshine you get is from a terrible angle, especially if it's not summertime

Down here on the Gulf Coast we get more hot water than we know what to do with about 10 months of the year from a single 4 by 10 AET panel feeding a couple of 55 gallon water heaters used as storage tanks - The other 2 months, we use a timer to add about 15 minutes worth of electricity to the top element of the house tank just before we arise and that (plus the solar gain during the day) gives us plenty of hot water even in the dead of winter

I installed it all myself for less than $3K, got an 'Instant Rebate' from Uncle Sam which covered over half the cost and had it completely paid off with the energy saved in less than 3 years - It's all gravy from that point on. I guess you could say 'green gravy' because it saves us at least $50 per month ;)

I can't compute how much production he gets with a black tank in a box mounted up on the roof . . . . but I imagine it cost him so little to do that the payback will be quite short. The downside as I see it is that the uninsulated tank will give away most of it's heat overnight, leaving you to basically start all over the next day. I'd make sure the roof is capable of handling the extra weight before I began such a project though . . . . my 110 gallons of tankage might be a problem for most roofs

Don

[nhmaster]

I lived in florida for many years. Had a 40 gallon electric water heater in the car port. Hardly used any electricity at all.

[Dana]

Where I live, even the best, most efficient solar panels, tank, controls etc will at best only produce 30 to 35% of the required domestic hot water. At an average installed cost of around $ 14,000.00 there is no pay back at all, but at leas you get a warm fuzzy feeling when you tell other folks how "green" you are. In India, where the sun shines more often and at a better solar azimuth, you have a much better chance of sucess.

It's less about panel efficiency than it is about dollar efficiency. Where you have the space for more square feet of cheaper, somewhat lower efficiency collectors, DIY hackers can (and do) get a lot more than 35% for a heluva lot less than $14KUSD, even in places with cooler winter temps & higher latitudes than New England:

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

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

It takes a bit of design & measurin' skills to get away with using PEX as your tubing in a DIY collector though- pay close attention to stagnation temps, and be sure to angle steeply enough that late summer stagnation temps don't go over 200F. The melting temp of PEX is ~260F, but you don't want to deal with steam pressurization on an otherwise atmospheric pressure system like that homebuilt drainback. (Non-ferrous pumps are also important in an atmospheric-pressure system as well, since it's oxygen-rich, and will eat susceptible metals fast.)

Also key to the performance of that system is the oversized thermal storage (~180 gallons), which allows the collectors to run at lower average temps (==higher efficiency), as well as letting the system to coast through some low-input days and still have something left to deliver. Somewhat bigger storage would probably be needed to get that kind of winter performance in New England, or for hot-water hoggin' 5 person families, but more than 100gallons/person would be overkill for most.

It takes a pretty lousy designer/installer to spend anything like $14k to deliver a mere 1/3 of annual hot water needs, even in New England, IMHO. But in many/most cases there's much better ROI on drainwater heat recovery (~20% energy-use reduction for under $1k is typical). In not-so-sunny central MA the typical installed price for solar hot water systems is more like $7k (before subsidies), and deliver more than 60% of the annual hot water. That's twice the fraction, half the cost, for 4x the BTUs/$ of your straw-man system, but nowhere near the BTUs/$ performance of drainwater heat recovery.

If you're going with commercial (as opposed to DIY) solar thermal, you can buy an EnergyStar washer & dishwasher for the price of the solar thermal required to support the load difference between those and your 15+ year old clunky hot-water hogs. As with anything solar, reducing the actual load by half or more is usually more cost effective than just buying more & more solar. Once your DHW load is under 10MBTU/year, the size & cost of the solar necessary to run it becomes manageable. If you're planning on heating the outdoor hot tub with it all winter, well... (yer kinda askin' for it.)

[Peter Griffin]

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.

[Redwood]

Well I'll say you can't use PEX in a collector on the basis of UV exposure alone never mind anything else.

[Alphacarina]

I don't think PEX would work well either . . . . but whatever you used in a home made collector, I'd assume it would be painted black before you closed it up and that should take care of any UV exposure

I didn't use PEX anywhere in my system largely because I just didn't trust it with 212 degree temperatures coupled with 60 pounds of pressure . . . . likely that pressure goes way up when the water starts to boil too

My tubing runs to and from the collector are soldered 1/2 inch rigid copper, insulated and placed inside 1 1/2 inch PVC pipe - I've had a couple people comment that my 1 1/2 inch lines are pretty big . . . . until I explain that there's insulated 1/2 inch copper inside them. If you can imagine how thrilling it must have been to solder on a piece, insulate it, slide a piece of 1 1/2 inch PVC over it . . . . complete with 90 degree fittings and then move on to the next connection then you're right - It was quite a challenge. I only did it after I had sweat soldered together about 200 connections without a leak when I was re-plumbing the house - Still, it was an apprehensive moment when we fired up the solar panel checking for any water running out of the end of the PVC - Fixing a leak at that point would have been . . . . problematic ;)

Don

[Dana]

Of course you can't use PEX in solar collectors...

...and yet Reysa builds his collectors with PEX tubing...

...glazes them with UV rejecting materials...

... covers most of the PEX with UV opaque aluminum...

...angles the collector so that the stagnation temps never exceed 200F (Wirsbo has sample of PEX that's been running at a bit over 200F for 25 years and counting)...

...runs them at atmospheric pressure...

...and they work.

Is it ideal? Not even.

Is it anything I'd want to support, as commercial installation? Nope!

But it works, and it's cheap. (I warned him off of using PEX the day he put the design concept on his site, but did he listen? Not much! :-) )

But you don't have to go that cheap, and you get WAY better than 30% of your hot water in New England for $14K straw-man solar price tag (unless you're a hot-water pig, of course. Don't plan on fillin' the 120gallon spa with endless solar HW.) And it shouldn't take anything like 3 panels worth either.

I refer you to figure 35 page 31 of idrionics 3.

A single 40 square foot panel with a paltry 60 gallons of storage in Boston (the closest latitude/weather to Southern Maine listed) will yield roughly a 50% fraction for 80-gallon/day users, or a ~70% fraction for the same system for 40 gallon/day hot water sippers. My family's use is somewhere in between, which means we'd more likely to see something like a 60% fraction with that minimalist system- more if we went with bigger storage to be able to run lower collector temps. This isn't rocket science.

If that costs FOURTEEN THOUSAND 'MERICAN SHEKELS installed, I'm in the wrong business. And if it's only a 30% fraction either the installer/designer fugged up, or you're not at all conservative in your hot water use. The US average is 15-30 gallons/person/day. It takes a lot less money to implement easy reductions in volume used than it does to buy more solar to support a ridiculously heavy load. (Buy a front-loading washer and check the flow on the shower heads before you buy the first panel.)

On the same page if idrionics 3 they state the obvious:

"As would be expected, the larger collector arrays and
correspondingly larger storage tanks yield higher solar
heating fractions in all locations."

Gia-normous unpressurized tanks like Reysa's are cheap, and increase the average collector efficiency by keeping the delta-Ts bounded. And with collectors as cheap as his, more square footage isn't very extravagant, nor is the sub-par performance per square foot much of an issue. Performance per dollar is pretty good. But I'm repeating myself...

But none of it has the ROI of drainwater heat recovery- couldn't imagine doing anything solar without going there first. For under a grand in hardware you get the first ~20% fraction. (This assumes national average usage, where showers are 40% of hot water used, and the flow runs at 2.5gpm or less so that the more than 50% of the heat is directly returned to the system.)

[Angelb]

Building your own would be a perfect idea but of course before you can make it possible you will need to have certain knowledge about it well don't worry too much about it the internet can be a good source for the info you will need

[johnjh2o1]

The bottom line is there is no savings on these systems. They break down long before you get any pay back. Some day there maybe when the cost comes down. As far as government pay backs, that's another big problem that I won't get into here.

John

[Scuba_Dave]

No savings on a solar system ?
That's completely wrong

I have a solar system for my pool, works great

[Dana]

No savings on a solar system ?
That's completely wrong

I have a solar system for my pool, works great

Completely wrong?

Methinks not.

Cheap plastic unglazed pool heater systems are one thing, professionally installed rooftop mounted potable systems in deep-freeze & hail/hurricane country quite another. Maintenance & damage in excess of fuel savings are common (though not the rule). It still takes a high-fuel price to rationalize the upfront costs & maintenance expense. If you're on the natural gas grid and paying $1/therm, the net present value of the fuel savings against the the cost of money isn't likely to be positive at full retail installation & maintenance. One $200 service call wipes out more than a year's fuel savings(!). But cheap DIY hacks, self-maintained can be cost effective. If it's replacing electric hot water on an isolated island power grid @ 40cents/kwh the economics of commercial systems are compelling enough.

On the commercial end, plastic flat-plate batch-solar pre-heat in the non-freeze south is usually cost effective: No pumps, no glycol loops to maintain, no heat dumping required, simple-as-pie plumbing, they just work. If you're in an area that get's baseball sized hail it could be an issue though. The Harpiris SunCache and it's ilk would probably be reasonable bets even in the Pacific Northwest (west of the Cascades, at sub-1000' altitudes, but alas not freeze-proof enough for New England winter temps.) The greater the complexity, the greater likelihood of making it a losing proposition. Any batch solar hot water (flat plate or evacuated tube) is pretty simple, cheap, & reliable relative to drainbacks & glycol loops with pumps, sensors & electronic control failure modes.

[Scuba_Dave]

I'm also building a DIY hot water heater
I expect to only use it in the summer/warmer weather
I also expect it to pay for itself in one season

I also have (2) 4x12 panels from someone who had a solar water heater assist setup
It more then paid for itself over the years

And they didn't pay anywhere near $14k for it
That's a rip-off

[Dana]

I have 10 4' X 10' Glazed solar panels, bought used from people that needed their houses re-roofed and didn't want to pay to have them re-installed, they adveraged $100/panel.

They heat my hydronic heated house about 90% of the winter.

Maintence... not much, make sure they're still water in the storage tank, maybe replace a pump every 10 or so years.

Snake

I'd hazard that it's more than cost-effective in YOUR case then, eh? :-) (I wouldn't be surprised if there isn't more than $100 of scrap copper in each panel!)

In places with higher freeze/hurricane/hail risk with less competent/resourceful owners paying full retail it's often a quite different story.

[wallyworld]

I have 2, 3 by 8 collectors, one soft tank, and one differential controller that have been in operation since 1991. Its a drain back system with a 007 Taco bronze pump. I have had a homemade heat exchanger leak in the tank from using copper wire to tie it up. Other than that, the system has had 0 maintenance. I live in Maine, is that cold enough for ya?

[Dana]

I have 2, 3 by 8 collectors, one soft tank, and one differential controller that have been in operation since 1991. Its a drain back system with a 007 Taco bronze pump. I have had a homemade heat exchanger leak in the tank from using copper wire to tie it up. Other than that, the system has had 0 maintenance. I live in Maine, is that cold enough for ya?

You might be close to breaking even by now then, eh? :-) (Or not, depending on how much hot water you actually use, what fuels you would have otherwise paid for and how much you had to pay for the repair when the heat exchanger problem. If it's was a DIY repair to a DIY HX, this doesn't qualify as "full retail" solar, not even close.) And if you're near the coastal hurricane zones, collector-longevity might be much better some decades than others...

[Scuba_Dave]

Solat water heaters are cost effective, even in colder climates
You can deny the truth all you want

[Dana]

Solat water heaters are cost effective, even in colder climates
You can deny the truth all you want

There's no denial- it's calculable. Sometimes 'tis cost effective, other times, well... not so much.

At full-retail with fat-margins for the manufacturers & installer, $14KUSD up front for a net thermal input of ~10-15MBTU/year, maybe not... (depends on the discount rate and energy price inflation and mainenance cost assumptions in your net-present-value analyis.)

At $5KUSD- maybe- depends on the cost of energy from other sources, and the maintenance cost over the anticipatied lifetime of the equipment. It's still not a no-brainer.

But I DO want to know the truth, so show me the math. (Self-maintained DIY systems for under $2.5KUSD, no argument whatsovever, eh?) The math will set you free...

[Scuba_Dave]

Why buy an overpriced retail unit?
But payback has been proven even on those when the price is OK

A complete freeze proof system is $5k or less
No need to buy a cadillac
Warmer areas you can buy one for a LOT less, under $3k

[Dana]

Why buy an overpriced retail unit?
But payback has been proven even on those when the price is OK

A complete freeze proof system is $5k or less
No need to buy a cadillac
Warmer areas you can buy one for a LOT less, under $3k

Payback is only "proven" at some price point, which isn't necessarily the current price for what a non-DIY installation costs. At current energy prices the economic argument is pretty easy at 3k, but just fer yuks, show me where the NPV turns postive on a (non-existent in my neighborhood without subisidy), of a $5KUSD unit that deliivers 12MBTU/year output vs. heating hot water with an indirect & mod-con boiler @ $1 or even 1.50/therm. (Assume a very modest 80% average efficiency while heating water if you like, but it's probably better than that on an annualized basis.)

Seriously- SHOW ME THE MATH! In simple-payback terms it takes decades to get to zero, but ever turning positive in net-present-value terms, about never without making some dubious/difficult to support assumptions about maintenance and future costs of fuel &/or money.

Simply asserting multiple times that it's cost effective doesn't make it true. SHOW me how it's cost-effective at $5K up front, cuz' it's not so obvious to me when I run the numbers.

But recommisioning systems or panels from the '80s obtained via craigslist, DIY homebuilts for $2-3K, inexpensive commercial batch heaters, yes, that's an easy argument to make.

[Scuba_Dave]

It's been proven again & again that they pay for themselves

[Dana]

It's been proven again & again that they pay for themselves

It must be true then, since you've repeated yet again (with nothing but the bare allegation for support.)

The proof goes someting like:

1>If Dave sez so, it must be so.

2>Dave sez so.

...ergo..

3> It is so.

Q.E.D., eh? ;-)

So if it's been proven again & again, what's the problem with showing the proof (yet again)?

This doesn't take hard math, but on any investment with a term over 5 years I'd at least want to see it as a Net Present Value with reasonable discount & energy inflation rates to be able to assess the assumptions. Simple-payback calculation methods don't work- it has to be compared to investing the up-front money in something conservative and using the proceeds to offset your fuel costs with the alternative scenario.

The math matters. Heating water with diesel generated island-utility electricity at 47cents/kwh in a 0.90EF tank is very different from $1/therm NG burned in a 0.82EF tankless, and a cost-effiectiveness analysis for solar under those two scenarios is substantially different, but on different ends of the scale.

Pick something middle of the road for you analysi if you like, but use something and DO THE ANALYSIS.

Too much to ask?

[Scuba_Dave]

Yer a bright boy
Do a search
People buy these & install them because they work & save $$

[Dana]

Yer a bright boy
Do a search
People buy these & install them because they work & save $$


I've been searching and analyzing the issue for quite some time, which is why I've concluded that it's not a slam-dunk for cost-effectivness in many (or even most) situations. You're the one making the assertion that this isn't correct, so I need to see your analysis to figure out where I've gone rong, eh?

The simple math on a $5K solution that delivers an 80% solar fraction with electric element backup @ 12 cents/kwh (considerably less than I pay) for the remainder, compared to a 0.58EF gas fired tank at $1/therm (what I paid, full-retail, on my last gas bill) goes something like this:

Tank capiliziation: $500 up front, $500/decade for replacement & maintenance.

Tank fuel use: 250therms/year or $2500/decade, (delivering ~15MBTU to the water/year)

10 year cost: $3000.

20 year cost $6000

Solar system capitilalizaon: $5000, assume zero mainenance for 20+ years, 80% solar fraction.

Solar backup power: 20% of 15MBTU, or 3mbtu/year, which is 3x 293kwh/mbtu= 879kwh/year, so x $0.12/kwh= $105/year, $1050/decade

10 year cost: $6050 (more than the 20 year cost of the cheapo tank)

20 year cost: $7100

But simple analysis doesn't reflect the real world in two important respects:

1> The $4500 up-front different in cost between a cheapo tank and a cheapo solar could be invested very conservatively to return 5% after taxes, the proceeds of which could be applied to the higher utility costs of the tank. The tank uses $250 (in gas), the solar system uses $105 in electricity, for a difference of $145 in operational cost. With the returns on the cash applied to the utilites that's now reduced to a ~$100/year cost difference.

2> The price of natural gas (and electricity) are not static, and some assumptions have to be made about the future costs of each if we're looking out 5+ years. With the ramping up of production in the Allegheny shale formations predictions of natural gas prices INCREASING dramaticaly over the next 20 years are very dubious indeed, and fraught with many many impossible-to-know factors. Will the US start taxing carbon emissions heavily, driving electricity production to shift from coal to gas quicker than the gas production can increase? If yes prices will indeed rise on average, but how much requires a crystal ball. If not, we could be looking at decades of lower NG pricing relative to the upramp of the 1900s and early part of this century. At the same time, if electricity is ever increasingly supplied by the same natural gas burners, the price of electricity will also rise.

This is not simple to model, and by no means a no-brainer at $5KUSD. In a net-present-value analysis the underlying assumptions for discount & fuel/electricity inflation rates are likely to have large errors, and it could fall far to either side of the cost effectiveness in a 20 year term, but there's no way it can be demonstrably cost effective in a shorter years than that without some fairly wild assumptions.

It's dead-obvious 10 years at $3K up front though.

But if you have a better analysis (or can point me to one online) let's have it. The math will tell you "the truth".

[Hardt]

Hmm...I haven't read anything about all the tax credits that come with installing a solar hot water system! My first solar system was installed in 1980, 120 gal 4 panels for $4200. After federal and state tax credits, the net cost was $2100. The cost of electricity then was about $.25/kwh. now it averages $.42/kwh (yeah, it's expensive but you gotta pay the price when you live in Hawaii). After 29 yrs of reliable service ( during which I maintained it my self, I replaced the recirculating pump, the heating element, a couple of ptr & air release valves and a spring loaded check valve with a more reliable swing check valve), I had a new system installed last May, 120 gal 2 panels for $6100. I reroofed the entire house and it would not have been cost effective to remove/reinstall the old panels/piping, etc. The electric co. rebate was $1000, then federal and state tax credits kicked in of 30% and 35% and a real property tax credit of $300 and the net cost was down to $1485. If I did not have this system, my guess is that I would spending about $60/mo on electricity for my hot water needs. I should have pay back period of about 2 yrs. which is not bad economics and besides that as a hard-core DIY person it is a fun system to maintain.

[Scuba_Dave]

Tank cost ?
I have a HW tank, I don't need another one
So that cost is out, you need to buy a tank with or without solar
Early Spring to Late fall full HW provided
Solar works as long as it is set up correctly
And 30% back of the cost

[johnjh2o1]

I find it hard to believe that the 120 gal tank lasted 29 yrs. You had to replace it once if not twice in that time period.

John

[Dana]

Hmm...I haven't read anything about all the tax credits that come with installing a solar hot water system! My first solar system was installed in 1980, 120 gal 4 panels for $4200. After federal and state tax credits, the net cost was $2100. The cost of electricity then was about $.25/kwh. now it averages $.42/kwh (yeah, it's expensive but you gotta pay the price when you live in Hawaii). After 29 yrs of reliable service ( during which I maintained it my self, I replaced the recirculating pump, the heating element, a couple of ptr & air release valves and a spring loaded check valve with a more reliable swing check valve), I had a new system installed last May, 120 gal 2 panels for $6100. I reroofed the entire house and it would not have been cost effective to remove/reinstall the old panels/piping, etc. The electric co. rebate was $1000, then federal and state tax credits kicked in of 30% and 35% and a real property tax credit of $300 and the net cost was down to $1485. If I did not have this system, my guess is that I would spending about $60/mo on electricity for my hot water needs. I should have pay back period of about 2 yrs. which is not bad economics and besides that as a hard-core DIY person it is a fun system to maintain.

It's very easy to make the math work for you when your utility rates are high, the year-round insolation levels are high, outdoor temps are moderate to high, and the capitalization is heavily subsidies. In your case you have all four, making it a no-brainer. (It's an easy argument in your case even without the subsidy!)

Cost effectiveness at the national average utility rates isn't plausible without subsidy on the hardware. This is analyzed in great detail within governing bodies & utilities when trying to determine the appropriate level of subsidy to achieve a policy objective. At least until recently in CA the size of the total subsidy by the natural gas ratepayers is required to be at parity with how much that reduction in load tp the natural gas grid lowers the retail price of the gas delivered, as a matter of fairness to the ratepayer. It took a very complex economic analysis to come up a credible defensible number. This may soon be superceded by newer state policies with broader goals, with an entirely different analysis.

BTW: I'm assuming that in HI the systems can be simpler since they don't require freeze protection. Are you running potable water in the collectors, or is it an isolated loop for corrosion/scaling control on the panels?

[Hardt]

Dana, yes I use potable water in the collectors. I'm surprised that a solar hot water system would not be cost effective in Ca. I would have thought that even with marginal subsidies from the utilities, the federal and state(?) tax credits would make it viable. But I do remember when we lived in Sacramento 30+ yrs ago that SMUD & PG&E rates were extremely low! John, yes the tank was made by American Appliance Mfg. Solar Stream model, glass lining, etc... In my previous post I left out the most problematic area that I had with the tank. After about 10 yrs of use the dip tubes/anode rods gave out. I tried various plastic tubes ( I gave up trying to find replacement anode rods ) but they didn't last long. I finally put in 1/2" copper tubes and that did the trick. When the new system was installed and the installers were hauling my old tank to the landfill, they commented on how heavy the tank was and one of them said "they don't make 'em like this anymore"!! So that set my expectations that this new tank will last 10 yrs at most! Did I mention that I still use a Snapper 22" rotary mower that I bought in February 1972! I was thinking "green" before it became fashionable... ;)

[Plumbermurrieta]

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 sun’s 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.

[Tasha Faith]

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.

[Mikey]

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 160°F. 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.

[Dana]

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 160°F. 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/documents/reports/rr-0207-residential-ventilation-and-latent-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/documents/reports/rr-9801-vented-and-sealed-attics-in-hot-climates/view?searchterm=latent%20load%20florida

http://www.buildingscience.com/documents/information-sheets/hvac-plumbing-and-electrical/information-sheet-ducts-in-conditioned-space/?searchterm=Sealed%20Attics

http://www.buildingscience.com/documents/reports/rr-9801-vented-and-sealed-attics-in-hot-climates/view?searchterm=Sealed%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.

[Mikey]

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.

[Dana]

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?

[Mikey]

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

[Dana]

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.)

[hj]

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.

[AigleAntonina]

A system in which the sun’s 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

[Scuba_Dave]

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

[Dave D]

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 (Solar Shed)

http://www.builditsolar.com/Experimental/PEXColDHW/Overview.htm (1000 Dollar Solar Hot Water)

[Dana]

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 (Solar Shed)


http://www.builditsolar.com/Experimental/PEXColDHW/Overview.htm (1000 Dollar Solar Hot Water)

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.

[Dave D]

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

[Mikey]

Hey, Dave, what kind of temp datalogger do you use?

[Dana]

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


It may well work great in low-insolation ME in low-temp apps without much tweaking, but the PEX could still melt if you're not paying attention. Have you tested the stagation temp of your collector? If it runs 200+ in stagnation tests you need to adjust the angle for less summertime gain.

For space heating you'll get a lot more bang for buck out of thermal air panels (lots of examples of those on Reysa's DIY site too), than with solar hydronic. Solar air is inherently lower temp/lower loss (== higher efficiency) than domestic hot water systems, but if you had say, radiant slabs or above-the-subfloor tubing systems such as WarmBoard(tm) the temp & efficiency of solar hydronic will be similar to solar air (at 5x the cost.) Serioiusly- getting $25/month's worth of electricity at typical NE rates out of a $1000 hydronic system like Gary's at 120F+ operation isn't very likely, whereas for the same money you could build 80-100 square feet of thermal air panel that would deliver as much space heating as you'd get out of ~150-200 gallons of oil burned in an 85% combustion-efficient boiler.

Unless your datalogger tests were done on a section of thin-walled copper or brass drainpipe your temp numbers drainwater heat recovery don't mean much, and you don't have corresponding flow rates to work from, etc. Natural Resources Canada has studied drainwater heat recovery extensively. See: http://www.builditsolar.com/Projects/WaterHeating/NRCanDrainWaterHtRecov.pdf I can point you to other web resources for their test methods & data if you're really interested. 50%+ average efficiency on a 4" x 48" 3" x 60" or longer is quite realisitic at typical Maine incoming water temps. If you're heating HW with electricity at NE prices it's fairly cost effective (http://www.renewability.com/uploads/documents/en/analysis_dwhr_minnesota.pdf), if natural gas (at current prices) less so.

Also, high temperature is not a measure of efficiency or effectiveness on any of this- running systems at the lowest possible temperature that will actually deliver the heat to where it's wanted it key to keeping losses low, and efficiency high. This is true of everything from solar hot water to space heating systems. Running 140F water in a solar collector to maintain the temp in a 70F room when it's 20F outside means your collector is running at about 30% collection efficiency, but if you can still deliver the BTUs to the room with 90F water (which you probably can, if you have a slab-radiant) your efficiency will be around 50%- nearly twice as much heat per square foot of glazed area. For comfort reasons thermal air panels with active fans sometimes need to be run at 100F+ or the exit air has too much wind-chill to the nearby humans, but they don't need to run anywhere near 120F. Simple snap-disc thermosats on the heat exchanger panel that turns the fan on at 100-110F & off at 80-90F are often the cheapest & easiest way to go, and quite efficient.

[Dave D]

It may well work great in low-insolation ME in low-temp apps without much tweaking, but the PEX could still melt if you're not paying attention. Have you tested the stagation temp of your collector? If it runs 200+ in stagnation tests you need to adjust the angle for less summertime gain.

For space heating you'll get a lot more bang for buck out of thermal air panels (lots of examples of those on Reysa's DIY site too), than with solar hydronic. Solar air is inherently lower temp/lower loss (== higher efficiency) than domestic hot water systems, but if you had say, radiant slabs or above-the-subfloor tubing systems such as WarmBoard(tm) the temp & efficiency of solar hydronic will be similar to solar air (at 5x the cost.) Serioiusly- getting $25/month's worth of electricity at typical NE rates out of a $1000 hydronic system like Gary's at 120F+ operation isn't very likely, whereas for the same money you could build 80-100 square feet of thermal air panel that would deliver as much space heating as you'd get out of ~150-200 gallons of oil burned in an 85% combustion-efficient boiler.

Unless your datalogger tests were done on a section of thin-walled copper or brass drainpipe your temp numbers drainwater heat recovery don't mean much, and you don't have corresponding flow rates to work from, etc. Natural Resources Canada has studied drainwater heat recovery extensively. See: http://www.builditsolar.com/Projects/WaterHeating/NRCanDrainWaterHtRecov.pdf I can point you to other web resources for their test methods & data if you're really interested. 50%+ average efficiency on a 4" x 48" 3" x 60" or longer is quite realisitic at typical Maine incoming water temps. If you're heating HW with electricity at NE prices it's fairly cost effective (http://www.renewability.com/uploads/documents/en/analysis_dwhr_minnesota.pdf), if natural gas (at current prices) less so.

Also, high temperature is not a measure of efficiency or effectiveness on any of this- running systems at the lowest possible temperature that will actually deliver the heat to where it's wanted it key to keeping losses low, and efficiency high. This is true of everything from solar hot water to space heating systems. Running 140F water in a solar collector to maintain the temp in a 70F room when it's 20F outside means your collector is running at about 30% collection efficiency, but if you can still deliver the BTUs to the room with 90F water (which you probably can, if you have a slab-radiant) your efficiency will be around 50%- nearly twice as much heat per square foot of glazed area. For comfort reasons thermal air panels with active fans sometimes need to be run at 100F+ or the exit air has too much wind-chill to the nearby humans, but they don't need to run anywhere near 120F. Simple snap-disc thermosats on the heat exchanger panel that turns the fan on at 100-110F & off at 80-90F are often the cheapest & easiest way to go, and quite efficient.

My goal all along has been to reduce my electric bill for hot water as we have an electric 80 gallon tank. Its already runng about 125 degrees insulated and has a time clock. My electric bill has been tweeked to about as low as i can get it. If i can preheat water and not rely and cut down my electric needs that would be fantastic. Oil heat in our home is forced warm air and I dont want to add propane as a hot water source.

My collector has been vented and sun shadded all summer and has not expereinced any deterioration. I would rather a copper colector than the pex but fear the hot cold cycle may fatigue the sweat joints and the panel may fail. Its also set at 70 degrees from horizontal for low summer gain and max winter gain. It takes no time at all to heat up a 20 gallon tank of water to 120 degrees, Im actually considering installing an old cast iron radiator in my basement to pump the test collector water thru for added heat benifit, again more experimentation.

[Dana]

Timers buy you practically nothing with electric tanks since the stanby losses are so low. Turning it off overnight may result in a 5F drop in temp, which doesn't make a huge difference in the average heat loss, and you spend 98-99% of the energy lost overnight bringing it back up to temp.

Insulating the near-tank plumbing (including temp & pressure outflow and cold-water feed) within 6' of the tank with 3/4" walled closed cell foam pipe insulation would buy you much more than the timer. (It's not availale at box stores, try Grainger or your plumbing supply house, or online sources. Box-stores only carry 3/8" walled stuff.). It'll cut standby losses in half, for low-mid single-digit percentage savings.

Insulating all of the distribution plumbing with 3/4" walled stuff will buy you even more. Surveys by PG & E in CA show that between 15-20% of all hot water heating energy gets abandoned in distribution plumbing, mostly on short-draws. Insulating the pipes reduces the mix of hot in the flow on successive draws (within the first 30-50 minutes, anyway), and the energy savings are typically in the high single digit percentages.

Combined with near-tank insulation expect at least a 10% drop in water heating energy.

Low flow shower heads (or throttling the flow back to a practical minimum with a tiny "shower cutoff (http://www.amazon.com/Danco-89171-Shut-Off-Shower-Chrome/dp/B000JFNPJE)" ball valve) can make a big difference sometimes. In showering households showers account for 40-50% of all hot water use, and a 20% reduction in flow can mean a 10% reduction in HW heating energy use.

Similarly, in those housesholds drainwater heat recovery typically cuts total HW heating energy by 15-25%.

Only after those measures does even DIY solar become the next-most-cost-effective thing. (Unless you can find some $100 Craigslist recycled flat panels from the '80s to refurb & recommission, which is well worth keeing an eye out for.)

On the cast-iron radiator front, it's a worthy experiment, and if it's a big 'un you can get most of heat into that basement. You can't run it at atmospheric pressure Reysa-style or you'll have serious rust & scale issues clogging your pumps. It doesn't have to be high pressure though- 12psi (measured at the highest point in the system) is more than sufficient to limit oxygen infiltratino into the system (unless your PEX isn't an oxygen-barrier type, in which case all bets are off.)

When the tank is ready for replacement a tank-top heat pump hybrid will make a serious dent in the HW heating costs for1/2- 3/4 of the year, but will add somewhat to the winter wood/oil consumption. It's roughtly half the electricity use, but since it draws heat from conditioned space that heat has to be made-up by the heating system during the heating season. Overall it's still a net win.

[Mikey]

My goal all along has been to reduce my electric bill for hot water as we have an electric 80 gallon tank.

That was my goal as well. Following the installation of the solar system, in January 2006, we inadvertently left the water heater circuit breaker off. In early March, following a week of dreary weather, we noticed the water wasn't very hot, and quickly remedied the situation by turning the power back on. The effect of this experiment on our electric bill? Undetectable.

Now, during the summer, the overtemp breaker in the water heater trips regularly, so we are often "off the grid" for extended periods, but still see no difference in the electricity consumption. I'm not sure what this means, other than the solar system will reach payback about when I'm 172 years old.

[Dana]

Yabbut, to be fair, in FL the incoming water is warm, relative to ME (you only need ~2/3 the energy that Dave does to raise incoming water to 120F) and the cooling bills kinda swap the signal when looking for a difference in the electric bill. The total annual bill for electric hot water heating for two average people is going to be under $500, under $250 for those who take short showers and have water sipping appliances. Even if you cut that in half it's not going to be the lions-share of most people's electric bills. Your refrigerator likely uses as much or more electricity as your hot water heater- it could easily be 2x your hot water heating bill if built before 2001 when the most-recent efficiency standards went into effect in the US.

Still, unless he lives on an island with diesel-fired powerplants for electricity, if Dave is burning through 200 gallons of $2.50/gallon oil + a few cords of wood, thermal air panels would be a better place to put the solar resources. A grand's worth of material in solar-air panels WILL show up on the heating-fuel use in a meaningful way. Before that, doing a blower-door test & air-sealing & spot-insulating the place would probably be a better use of the first $1000 of energy investment.

The only thing cheap about solar is the fuel cost. It's usually far cheaper to reduce the thermal load than to build or buy the active-solar resources to support that load. Once you've reduced the load by well over half you eventually get to where active-solar can pick up a sizeable fraction of the rest. If your appliances aren't all Energy Star variants, and your lights all high-efficiency, with occupancy sensor switches/daylight sensors/ timers, etc, you'll get better ROI spending more on the conservation & efficiency end. I pass a house on may daily commute with a ~ 3kw photovoltaic on the roof, with typically 500-1000 watts of incandescent yard lighting on during a bright sunny afternoon. What's with that? $30K was spent to WHAT end?

[Scuba_Dave]

I connected the 2nd 4x12' panel about a week ago with colder weather
Now with 2 panels its still heating the hot tub to 110 f
I have 4 panels approx 3x6' that I need to connect for hw

With solar heat I had my ~20,000g inground pool up to 88 in July

[Dave D]

When the tank is ready for replacement a tank-top heat pump hybrid will make a serious dent in the HW heating costs for1/2- 3/4 of the year, but will add somewhat to the winter wood/oil consumption. It's roughtly half the electricity use, but since it draws heat from conditioned space that heat has to be made-up by the heating system during the heating season. Overall it's still a net win.

Ive done a lot of researcha and spoken to local Mech Engineers we consult with and the concensus is tehy just don't perform in our climate UNLESS you have a serious amount of byproduct heat you are trying to deal with and can use. There is a building here in Portland that uses the mechanical room heat generated to make heat pump hot water - or a portion of it and its been successful. My basemnt is in the 60's all winter because i just use residual heat from my oil burner as heat. I am convinced if I can preheat the incoming 50 degree water form my well to 80 or 90 thru the use of DIY solar and or gray water recovery it would cut my electric bill substantially.

[Scuba_Dave]

I've measured my incoming water temp as low as 35 f
I've been thinking of connecting a pre-heat tank in the basement
Just having another 40-50g of water at the basement temp would decrease the water heating bill

[Dana]

Ive done a lot of researcha and spoken to local Mech Engineers we consult with and the concensus is tehy just don't perform in our climate UNLESS you have a serious amount of byproduct heat you are trying to deal with and can use. There is a building here in Portland that uses the mechanical room heat generated to make heat pump hot water - or a portion of it and its been successful. My basemnt is in the 60's all winter because i just use residual heat from my oil burner as heat. I am convinced if I can preheat the incoming 50 degree water form my well to 80 or 90 thru the use of DIY solar and or gray water recovery it would cut my electric bill substantially.

It's a matter of what your relative per-btu costs are for your differing space-heating vs. water heating fuels as to whether a tank-top electric heater buys you anything. In most colder places it's not buying you anything, may even cost you more if you're switching from cheap natural gas to expensive electricity. With oil it may even cost you more, but if you're cutting your own wood and thus sort of "free" it may make sense. To be sure it's not a no-brainer in your case- it's trading expensive electricity for expensive oil. I only made the recommendation due to your focus on reducing the electricity (not the oil or wood) bill. In general I don't recommend them either- the money is better spent on other efficiency measures in most cold-climate homes. That "residual heat" from the boiler isn't "byproduct", it is heat you've paid for (and dearly) in oil. And unless you foundation & rim joist are sealed & insulated, you're throwing away a substantial portion of that heat. (15-20% of the total would be typical, but it varies by quite a bit on house-by-house basis.) Odds are pretty good that the boiler is 3x oversized for your design-day load too, and some amount of boiler-tweaking (or boiler-control tweaks) can probably reduce your fuel use by double-digit fractions (TBD.)

Unless you're filling a huge soaking tub every day or regularly showering until the water runs cold, or have 4+ people living there hot water isn't likely to be even as much as half your electricity bill. If it's a 1-2 person household who take 5 minute showers it could even be less than your refrigeration, if your refrigerator was build before 1991. If yours is new enough to have a yellow EnergyGuide label on it, what's the label on your HW tank say? Then consider whether you fit the 4-person household water-chugging appliance profile on which that power use was estimated and adjust the estimate accordingly. If you're a 2 person household with EnergyStar appliances an bath with 2.5gpm showerheads a ~4800kwh/year pig of a tank (per EnergyGuide) is actually using less than 3000kwh/year, maybe less than 2000kwh/year (166kwh/month, on average.) Drainwater heat recovery in a "typical" house would reduces that by about 20%, but if you have water-sipping appliances and take 10 minute showers with a 3gpm gusher it'll return a much larger fraction. (But a lower flow showerhead would be a better investment. ;-) )

Scuba_Dave: 35F would be a mid-late winter incoming temp- in summer (when you'd be getting the most benefit out of a solar preheat) it's probably north of 60F already- measure it now- it's probably not much cooler than peak summer temp. The shallower your mains are dug into the street the bigger the seasonal swings you get. In Worcester it'll get down to the 35-40F range in winter but on average it's closer to 50F. A few weeks ago it even made the low-mid 60s, after a much warmer than usual summer. I assume roughly 40F as my winter average for estimation purposes, even if I occasionally get slugs of cooler water.

But a tempering tank in the basement isn't going to buy you much, since it represents a heat load on the house. Those BTUs have to be made up by the heating system. Drainwater heat recovery would raise your 35F incoming water to well over 60F during showers though, and that's heat that was literally going down the drain.

[Scuba_Dave]

Actually peak summer we have close to 70 degree water if not higher
A tempering tank would buy me a lot in recovery time/longer showers
I can easily run our 50g tank cold in the winter

With a child in the house & older faucets/showe valves I do not keep the tank at 140+
But even when I did we I could still run it cold

[Dana]

I s'pose I should have said "...isn't going to buy you much..." in the way of fuel savings (which I had sort of presumed, since we were talking about what it takes do reduce the water heating bill.) Recovery time is a different performance parameter.

Drainwater heat recovery will buy you more of both (fuel savings + reduced recovery time) for showers. In fact, a 50%+ drainwater heat recovery heat exchanger turns a typical gas-fired tank heater with a ~35KBTU burner into pretty much an "endless shower" heater at 2-2.5gpm, winter or summer. It won't buy you anything for tub filling though.

The amount of capacity gained by going from 120F to 140F isn't huge, but the difference in standby loss is pretty significant.

[Scuba_Dave]

Unfortunately my WH is on the opposite side of the house as my drain
To run some copper around it I would probably lose any heat gained in the added distance
I do shut the drain while taking a shower to let the water heat the tub 1st
Then I let it drain

[Scuba_Dave]

My drain also exits at the back of my house...where my greenhouse is located
So drain water helps keep my greenhouse warm thru the winter
Once I have my 4 solar panels setup for HW I will have almost 100% solar hot water from April thru at least September
I spent $500 6 years ago on solar heat for my pool
Pool topped out at 88 degrees this past summer.....just dipped below 70 recently, mainly because I shut the solar off
It would cost more then $500 to heat my pool each year
So payback period is 1 year

[Dana]

Unfortunately my WH is on the opposite side of the house as my drain
To run some copper around it I would probably lose any heat gained in the added distance
I do shut the drain while taking a shower to let the water heat the tub 1st
Then I let it drain

Huh?

If 50-100 feet of copper could lose 30 degrees we'd all have to run our water heaters at 160F to be sure it was warm enough at the furthest tap!

Serioiusly- insulating it with the cheap R2 pipe insulation from box stores would be MORE than enough to keep the distribution loss down to the "indetectible while flowing" range. We're talking maybe a minute's worth of flow in the round trip- how many degrees do you think 80F water in a copper pipe is going to give up to a 65F basement in 40-70 seconds, even without insulation? And if insulated?

And what temp is the tub when you let it drain (presumably to retain some of the heat for space-heating?) I'm guessing it's still well above room temp, and WAY above incoming water temps, even after it's passed through the greenhouse. With drainwater heat recovery heat exchanger the greywater exits the house at temps several degrees above the incoming cold water temp, but well below room ambient in mid-winter. The total amount of heat recovered is much higher.

Pool heating is an ideal solar application- always low-temp low delta-T from ambient, for highest collector efficiency, and used primarily during the seasons when the solar resource is greatest, collector losses lowest- it's a no-brainer kind of investment if you have the space to install it. But add another 30-40F on the collector side, and drop the operating ambient by 30F, for a shoulder-season DHW application and you're working less efficiently, and with a smaller seasonal solar resource.

[Scuba_Dave]

I'm really not interested in running 100' of copper pipe to the opposite side of the basement
And then insulating it
I'd much rather use that 100' of copper & build a solar system to heat my house

[rogerd]

I understand from this discussion that solar heating is not suited for all locations. In some parts of the world it doesn't pay-off to have solar panels when you hardly get sun light. Investing thousands of dollars of hard earned money to try and save a few dollars isn't worth it. It would be better to use that money to better insulate the home reduce energy loss and generally conserve energy. The energy saved through such measures will bring in more savings than solar heating will ever do in certain parts of the world.

[artthink]

Well, if you really want to construct a solar water heater, this link might help you: