solar water

if the panels (or tubes) are well constructed and insulated - easily can see temps above 120 degrees. The solar panels absorbing the heat energy is about the same summer and winter - what is very different, is the ambient temp. around the panel - thus, a well sealed and insulated panel is a must. And equally important is how well the piping is insulated - from the panel to the storage tank. The longer the pipe run, the more important this insulation is. In reality, you don't care what the temp IN the panel is, what matters is what temp. makes it to the storage tank for use.

Good luck - and keep researching.

Dave from Maine

I didn't know Virgina got 20 degrees. thought it was just us Mainers.

DaveM said:

I didn't know Virgina got 20 degrees. thought it was just us Mainers.

Click to expand...

Obviously you've never been to WVA! It gets quite chilly up in them hills...

Dangit Pook! Quit changing your name! It's getting too hard to keep track of you!

Chris

no, I don't have first hand experience - am a DIY, just starting the research - and about to hook up my panels.

I totally agree with your thoughts - everything I read, talks about Solar still needing a boost from more conventional sources. Even , in the summer, it's dumb of them to claim 100%... seems like no matter how large a storage tank you have, a week of no sun will leave you needing heat off the solar system.

good luck
dave

I have two 3x8 AET's which are flat plate collectors in parallel. The rule of thumb is 80F over ambient and I would tend to agree although my system is not instrumented with data logging. So if its zero degrees out on a sunny day when I havent been using much hot water, the system temp gets up to around 80 F. Its definitely a log curve on the temp rise where the last few degrees take quite awhile. Evacuated tubes collectors can give a higher differential but are less efficient. So if you want to collect the maximum amount of heat per square foot, go flat plate but if you want to maximize temp go evacuated tubes. Note, I have a fixed panels at 45 degrees and plan to move them up to optimize winter surface area and minimize summer surface area.

It is quite interesting to note that at times in the winter the panels will be putting out viable heat whie partially covered with snow.

Why I went with flat plates instead of evacuated tubes is that Flat plates are a lot more robust from external damage (limbs and roof rakes) and I dont have to worry about the system boiling when I dont have demand (in northern NH max ambient temp is 90 F . During the winter the solar hot water tank feeds my hot water tank (that is heated with oil or wood) so it acts as a preheater. During warm weather I valve out the hot water maker and run directly off the solar tank.

Panels are now rated by the SRCC and the ratings tend to reflect the real world so learn how to read the rating tables and factors and you can compare panels quite readilly.

80 over ambient for hot water could be right, but it's low for hot air. In the 80's I made a hot air collector for house space heating. At -20F ambient, it was 120F in the collector. The main problem at 46* latitude is that on sunny days good sun was available only for about 2-4 hours during Dec and Jan, and that in MN there is considerable cloud cover from Nov to mid-Jan (as well as other times during the year).

As I stated in the prior post the SRCC rates the majority of the panels that are sold in the US and any company you deal with should be able to supply the rating sheets to you. I suspect that you can reasonably get 80 F water whenever the sun is out in your area but cant guarantee how long the tank will stay warm. It all comes down to how much heat you need versus how much heat you can store for cloudy days. Sizing the tank relative to the size of the panels is a challenge, too small and the tank heats up quickly but doesnt carry you through over a cloudy period, too large and you get lots of warm water that may not be warm enough.

I assume that you have a clear solar window from 9 AM to 3 PM or all bets are off.

I'm interested in this too...living in MA I am really looking at ways of cutting my utilities (very $$$). PV is too long a payoff currently (hoping the next administration will fix that), but solar hot water seems a much more attainable goal. Cutting electricity is proving easier than cutting hot water usage (family of 5). I have looked around sites like masssave.com, but cannot find any links to rebates, etc. I tried national grid as well (used to be keyspan) and I am not finding any rebates/subsidies for solar water heaters.

Does anyone know where to go for any state/federal help?

Water must be kept hot enough to keep bugs from growing in it. You don't want to save 100 bucks a month in hot water costs just to spend several thousand a day per family member to the hospital. Ideally, storage would be at least 140 degrees constant, or you'd need to treat the water.

That being said, my favorite link discusses how to build a system that will provide pretty much 100 percent hot water year round. I plan to duplicate this setup, with improvements, but will have a backup wood heater. I intend to have enough hot water to both provide DHW and heat the house in the winter strictly off the sun, but only a fool doesn't plan ahead for the worst. My system will be a drainback with storage, and will directly interface with the house heating system for efficiency, but will also use a heat exchanger to heat any water that hits a faucet for safety.

The fellow in the link reports that the inside of his solar collectors, where the water pipes are, hits upwards to 300 degrees in 60 degree weather within 8 minutes of the sun hitting it, measured with a thermometer, so you can expect at least 240 degrees inside the collector on a sunny 0 degree day.

From the link:

"This chart shows the temperature of the inside surface of the glazing near the top of the collector. This is around solar noon. Initially all the collector vents are closed.

At minute 1, the circulation pump is turned off, and the collector temperature starts to rise. It continued to rise until it leveled off at about 205F around minute 8. At this time, the temperature of back near the absorber surface is a bit over 300F.

I opened the vents at minute 9, and the glazing and collector temperature immediately begin to drop, and eventually reach a very nice 110F. This was done under sunny conditions, Tambient about 60F, and windy.

In a later test the next day, with Tambient at about 25F, the collector reached even higher temperatures, and the glazing near the top of the collector had a noticeable inward deflection from the expansion. This did not look good to me for the long term health of the polycarbonate panels. The polycarbonate glazing is listed as having a temperature capability of 270F, and I don't believe that this was exceeded, but I don't think it would be good to routinely expose the panels to these relatively high temperatures."

The 140 recommendation for dhw comes up again. While I don't dispute that it is possible that dhw less than 140 can result in some bacterial growth, I haven't heard of a single case resulting in illness or death anywhere in a home supplied dhw system.

All sources I have found find the risk to be miniscule; that the risk as it is relates to high risk individuals; and that unless your water system is infected with legionella, there is no need to do anything special, including water hotter than 120, to prevent or minimize legionella or other bacteria from a dhw system.

Note the following from the US Dept of Energy:

"Although some manufacturers set water heater thermostats at 140ºF, most households usually only require them set at 120ºF. Water heated at 140ºF also poses a safety hazard—scalding. However, if you have a dishwasher without a booster heater, it may require a water temperature within a range of 130ºF to 140ºF for optimum cleaning.

Reducing your water temperature to 120ºF also slows mineral buildup and corrosion in your water heater and pipes."
http://www.eere.energy.gov/consumer/your_home/water_heating/index.cfm/mytopic=13090

Note the following from the Univ or Michigan:

"The following chart shows just how dangerous hot water can be.


Temperature Time to Cause
of Water a Bad Burn
-------------------------------------
150°F (66°C) 2 seconds
140°F (60°C) 6 seconds
125°F (52°C) 2 minutes
120°F (49°C) 10 minutes "
http://www.med.umich.edu/1libr/pa/pa_hotwatr_hhg.htm

Note the following from legionella.org:

"I need your advice. My condominium association has received a proposal from a company to check our water for Legionella on a quarterly basis. As far as I know, we have had no cases. My inclination is to say no, but I want to consult an expert.

The brief answer to your query is "don't culture buildings unless the building houses a high risk group of individuals (chronic lung disease, immunosuppressive illnesses, illnesses requiring chemotherapy/transplant rejection meds/corticosteroids).

The rationale is at least 2.

1. Miniscule attack rate.

Please download the article on the home page of www.legionella.org by Pedro-Botet on Coming of the 3rd Plague. We do recommend that convalescent care facilities housing a notable number of debilitated patients culture their water supply once a year (Seenivisan, J Amer Geriatrics Society 2005 in our Publications section).

2. Maintenance measures directed at water supplies colonized with legionella are not evidence-based; in fact data from our lab shows that virtually all recommendations involving maintenance do not affect legionella colonization.

So, what should the residents of your condominium association do to prevent Legionella infection? 1) Smokers should quit smoking. 2) High risk groups should not drink tap water (Singh, Transplant Infect Dis 2004 on the home page of www.legionella.org). Tap water should be boiled, then cooled and refrigerated for drinking for high-risk patients."

http://www.legionella.org/general_public.htm

All publications I have seen recommending 140 water are hospitals, VA facilities, or other facilities where there exists an actual, reasonable risk of Legionella.

Is anyone aware of the incidence of Legionella resulting from dhw systems in homes?

I'm not too worried about the water temp/bacteria issue; from what I've seen (and someone correct me if I'm wrong) most solar DHW setups excel in the summertime and require little of any `boosting' of water temp (let's say for argument's sake 140 F) due to the long hot days. During times of the year when 140F is not sustainable, the lesser temp water (let's again say for argument's sake 80F) is then fed to a proper water heater where the amount of energy required to raise the water from 80F -> 140F is far less than 55F town/well water -> 140F. Therein lies the savings. And as for the bacteria, the water leaving the solar/standard water heater combo would always be at 140F (using the example above). Too simplistic?

And where would the bacteria get into a sealed system? Point of use? Not common. Once installed, flush the system with >140 degree water and go from there, do 5-10% bleach if you're really concerned. I have not heard of Legionella being related to sealed DHW systems, more of an AC condenser tray type of bug.

jebatty - Cool! The only stuff I found on it after several searches showed the links I pulled up, and it was a concern to me. You never know when bugs are going to get in, or from where, but the stuff you put in makes me feel better about it. Been wondering if a solar hot water system with NO booster, as I hope to have (will still build in a provision to add one if necessary, shoot for the stars with feet on the ground sort of thing) would be able to keep the water hot enough to stay safe. 140 degrees seemed like it would be hard to get to, especially in the wintertime, without some sort of booster but 120 degrees should be attainable in my area.

karl said:

Does anybody here heat their water with solar panels? Which type do you have? Flat panel or evacuated tube?

I'm curious as to how hot it gets in the winter time. I have read alot online about solar panels and I can see where they would easily heat water to 120 plus in the summer, but it seems as though some are claiming 120 in the winter time.

If its 20 degrees out I can't see how you're going to raise the temperature 100 degrees.

Click to expand...

I've read this thread and would like to add few comments. There are a lot of variables to contend with such as square footage installed, etc.. To just generally say "it will raise the temp of the water to 120" is misleading. The question of which is better-evacuated tube or flat plate will go on forever. The temperature required for the heat load should dictate what style to use. Lower temperature loads can use a flat plate and high temp loads should use evacuated tubes. Flat plates seem to be more efficient at the low inlet temperatures but the curve drops off quickly whereas evacuated tube collectors have a "flatter curve". The economics of then trying to achieve the end result may switch based on this. Pretty much you can achieve any temp you want at anytime if you just keep adding panels though it doesn't make sense economically to oversize any system. It only makes sense to carefully analyze heating needs and solar potential before doing anything.

Also, solar radiation can be intense in the winter but you have to accept less hours of sunshine. Trying to design for 100% winter heat load would could cause problems in the summer. The cost of the installation would be much higher for less gain.

One thing to remember is that it takes 1 btu to raise one lb of water from 55 to 60 deg or 119 to 120 deg. Just preheating water makes a big difference. Its all money in the bank.

I am installing a 120 tube system at my home though I had some flat plate panels available. I may install them and do data logging. I was thinking I could get the most heat gain at anytime. I sure know what my wife would think about any more panels going up on the roof.

My take on the bacteria issue is that you use DHW and it is flushed through continually in a closed system. If I felt strong enough about it I would consider some kind of purification but I don't see it as an issue.

Let us know what you end up with.

Mike

Legionella is overrated, IMHO. All the outbreaks that I have heard about have been in the commercial/institutional world and most of them can be traced to groups of people that are immunocompromised as well as less than ideal situations. I think there is a greater concern with e-coli and salmonella in well water than legionella. It does make for very bad press, however.

I work in a lot of hospitals and some of them are starting to test for it, but not all. Some have taken steps to reduce the chance of it happening by replacing old horizontal water heaters and upping their water temps to 140F before mixing it down to 110-120F. The problem is more likely to happen in a cooling tower than anywhere else and many of us have been working around them for years. Bleach and Zithromax knocks it right out; one is for the plumbing and the other for you.

It would seem to me that using the solar for a preheat to the main water heater (140F) would pretty much wipe out any nasties in the pipe and be most efficient. I do periodically run my water heater up to 160F to wipe out anything that may be in there, but we're on chlorinated city water, so it really isn't a great concern.

Just offering my $.02

Chris

soooooo...coming full circle on this thread, does anyone have a recent experience either with contracting or a DIY job for solar DHW? I've found as much as $3K in tax rebates and roughly $1500 from my local utility (national grid) so that might help make the decision, but I'm looking for some more concrete examples...ideally with payback/savings numbers if possible.

Anyone wanna boast about their setup? I'd expect to find evangelists here!

Sorry about the thread seizure, didn't expect it to take off like that. I wouldn't have thought that I'd be faulted for bringing up a very real concern for someone contemplating a DIY install. Sorry I have no system design to crow about (yet) but aside from ensuring your design doesn't provide safe harbor and breeding grounds for the nasties you also want to make sure that there's no potential for water hammer action or flow direction problems. It would be worthwhile in my opinion to hire a plumber as a consultant if nothing else, once you work out what you want to do. Might also put any proposed designs up here, there's some sharp folks here that should be able to point out any potential problems.

I know my postings tend to be on the negative side, but I'd much rather bring up all the negative points BEFORE the concrete sets and the fix goes from moving a line on a blueprint to jackhammering a line out of the ground.

I did a DIY flat panel collector (6' x 3') with 1/2" tubes (8 of them). On a 70deg F day was able to raise the temp of a 20gal barrel from ambient to 140deg F in 3hrs.

This will be the first year that I use it during the winter, as I built it this spring. Will be cycling the fluid (probably antifreeze) through a radiator in my basement to provide some additional heat there as we spend some time there. The Lopi's job is to heat the main floor and the upsairs (when it can).

Erik

got wood? said:

soooooo...coming full circle on this thread, does anyone have a recent experience either with contracting or a DIY job for solar DHW? I've found as much as $3K in tax rebates and roughly $1500 from my local utility (national grid) so that might help make the decision, but I'm looking for some more concrete examples...ideally with payback/savings numbers if possible.

Anyone wanna boast about their setup? I'd expect to find evangelists here!

Click to expand...

I've posted many times on this in the past - search my ID. Lots of details on our system in NY.

Relevant to this thread, I would say that the winter production can be a challenge unless you are willing to position the system at a steep angle with direct southern exposure. In our case, we put the panels on a part of the roof that faces west at about 30 degree tilt that is also rather hidden from street view. In the dead of winter when it is zero and sun is at lowest point, we do not get 80 degree water - they often don't come on. If we installed them on a south facing roof, and angled them up off the roof more, then we could probably squeeze some extra days out in winter. The rest of the year, they do great. Even with our non-ideal location, I shut down the oil burner 7-8 months a year, with very rare use of the electric backup in shoulder periods. In Nov/Feb, we get limited preheating out of it, and in Dec/Jan it is not often that we hear it run unless we have abnormally warm days. By March, the sun is high enough again that it starts running nearly every day, and by late March, I can shut down our boiler.

As for payback - if you have a oil system with tankless coil as is common in the northeast, shutting that system down during summer and relying on solar saves a ton. If you have natural gas, you won't save as much because they're not as wasteful to start. Do a search - there is a lot of info on here. In our case, I calculated a long-term tax-free ROI of 13% with an assumption of oil at $2.50/gallon and 5% energy inflation. At $4/gallon, this jumps to 19% for us. I've run the same calculation for friends with natural gas and it comes out in mid single digits.

-Colin