Solar Hot Water / Heating...

Re: Solar Hot Water / Heating...

I installed a closed loop solar water heating system this past February. I researched what was out there commercially and the costs involved. I decided to employ commercial collectors (http://solarroofs.com/), a 12v March pump, expansion tank, 20w PV panel, and misc hardware. The kit recommended I purchase an 80 gallon heat exchange tank, but I needed more storage than that. We have a 3 year old 3100 sq ft single story house with two water heaters. We have 6 children living at home, so take lots of showers & wash the dishes twice daily by hand. I built an insulated heat storage vault housing three 55 gallon poly barrels filled with water. I put a 60' coil of 1/2 copper tubing at the bottom of each barrel joined in series to the next. The 3 12'x2' collectors heat the 50/50 mix of glycol/water and send it to the first barrel. The fluid heats the first barrel's water, then goes on to the second, then third. The water then is returned to the collectors. I find the barrels heat to within about 5 degrees of each other at the end of the day. At the top of each barrel is a 60' coil of 3/4" copper tubing that feeds cold water in from the wall to the "coldest" barrel, then to the middle one, then finally to the "hot" one, then back to the hot water heater.

I use my standard 40 gallon water heater as a backup for extended cloudy days. The preheated hot water is simply routed back to the hot water heater, then fed to the rest of the house. The 150 or so gallons of hot water is plenty to feed us hot water for at least 3 days of no sun (after a good charge of course). We have unplugged and disconnected the second hot water heater and simply run off of the one unit, if needed. We are saving about $58 per month in electricity by employing our solar hot water system.

Re: Solar Hot Water / Heating...

Frank wrote:

That sounds like a great project!  Any chance you could post some pics?

Here you go. These pictures were taken the week of the installation. Since then, I've tweaked some things to get the tanks to around 160 degrees, though I've seen the hot barrel get to 170. Hardest struggle for me was to get the air out of the system. Finally had to buy a high powered "charging" pump from Grainger to ensure enough "oomph" was put into the system to drive all the air from the barrels. That is a lot of copper, and air was not being expelled from the pipes under low pressure. I also installed an air vent (like a radiator has up north) to ensure no air bubbles made their way back to the tanks. Has been running like this for 6 months without any more problems. I used plain auto antifreeze (cheaper) that should last at least 5 years before flushing. The only other maintenance I do is to simply top off the barrels every month or 6 weeks. The heat vault box does a nice job of keeping the heat in, but some hot water vapor does escape.

Re: Solar Hot Water / Heating...

The rule of thumb is if there is one tube as a heat exchanger contacting potable water, then ethylene glycol is not to be used under any circumstances. This "one tube" concept is typical of a Rheem HE80 heat exchange type of water heater. My barrel system uses two separate tubes, so there is a "double wall" of protection. Since the cold water is under pressure, there would be no risk of contamination. Please realize also that the barrels I use simply store the heat, then impart it to the cold water piping (heat exchange). The hot water system from the roof as well as the cold water system going to the hot water tank are sealed systems. There is no direct connection between the cold water, hot water, or the barrels. There is simply a "heat exchange" taking place. I priced the other "safe" glycol when I built my system and it was absolutely outrageous. If someone were to build a system without double wall isolation, then it should be considered. The glycol is non-corrosive (does not contain silica) and has been used in the auto industry for some time, so it is long lasting under very extreme conditions. Should my pump fail, the glycol would survive a good amount of "stagnation" before breaking down.

I am using three collectors, each provides about 24 sq ft of collection. I use 150 gallons of water storage, thus divided by this total collection area (about 75 sq ft) gives me about 2:1. This does not take into consideration my 40 gallon stand by. We live just north of San Antonio, Texas. Two collectors were recommended to me, but I chose the third for extra heat collection for our larger family. The only other thing I wish I could have done is to employ additional barrels for more storage. As it is, my sweet wife gave up some of her utility room for this project. With the excess amount of heat production, she can wash in hot water and not feel like she is wasting energy producing it.

Re: Solar Hot Water / Heating...

AFWnS wrote:

I've just finished installing a system in my cabin near AngelFire NM, but still have a probelm, the circulator  is overheating, I'm told that is from air in the system.

My problems started when I was initially charged the system only using a pump mounted on a drill. The pump worked to charge the system, but barely. Also because of the amount of copper tubing, it never had enough "oomph" to drive out all the air from the coils. After several attemps to purge the system, I had to invest in a higher powered water pump from Grainger. The new pump was awesome! I simply filled a 5 gallon bucket with a 50/50 antifreeze mix and let it go! I let it run for about 30 minutes to drive all the air out. It was shocking how much air actually came out. Before charging, I also installed a small vent valve (like home heating radiators have) to ensure small bubbles were purged before lodging in the coils again. It has been running for nearly seven months without a hitch. As for your circulator placement; as long as it is adequate to pump what you need, it should be fine in any placement. Some pumps don't mind being lower in the run (with a bit larger head pressure), but with the placement should not be a big deal. The real issue is getting all the air out. If they cavitate, then no fluid will move, and the fluid in the collectors will stagnate. I had an air lock early on in my installation. The temperature coming down from the roof was superheated steam that my gauge showed nearly 350 degrees! Once I got all the air out, things were fine. Summer heating is typically 180 down from the roof, and winter is about 140.

Re: Solar Hot Water / Heating...

Another consideration is to shoot for about a 3:1 ratio of solar collection square footage versus storage capacity in gallons. The idea is to heat the water quickly to get as much heat gain as possible. The multi-barrel system works very well, as the first barrel will heat up quickly, then pass the excess heat to the subsequent barrels. Multiple 400 gallon tanks will not heat quickly (unless you have a massive array of collectors), so I believe you'd be disappointed with the results. I have more than enough collector area (a bit over 70 sq ft) for my 150 gallons of storage.

Re: Solar Hot Water / Heating...

You should have enough collection for the 900 gallons of storage with that setup. Something that you may want to consider is how much you can collect and store versus the amount of loss through the radiant floor. During the winter, you will have limited sun, so you'll have to collect and store a good bit more than you'll use on cloudy days. Also, with that much storage, it will take awhile to recharge the storage, so you may want to engineer your system accordingly. You may want to drop Al Rich (RichSolar@aol.com) a note asking for his counsel. I bought my collectors from him, and he has been very helpful. He has many years of experience in solar heating, so I would certainly tap his experience to help you get a great result from your project. Happy heating!

Re: Solar Hot Water / Heating...

Interesting, and sorry to hear your results. There are many grades of antifreeze on the market. I've run one particular grade for a number of years in my vehicles without any incidents. I naturally put this into my solar hot water system knowing that it did so well for me in vehicles. Now I have not taken my system apart to see the condition of the innards. I do not see the logic in hot spots if the mixture is homogenous. Also, the mix should be no more than 50/50 depending on the climate. I too have heard that water has a better propensity to absorb heat than straight antifreeze. We have had no problems with heat transfer, but it simply provides a method of keeping the fluid in the collectors from freezing and raising the boiling point. Again, sorry to hear your horror story. Hope you find something that works well for you.

...Rick

Re: Solar Hot Water / Heating...

No Niel, not yet, but I expect to be making some changes to the system this Summer that will require partial draining of the system, so will do it then. In the meantime, with plain water in the system, there has been no more visible signs of problems - - very unlike when it has the antifreeze in.
Thanks and will update when the change is made.
Wayne

Re: Solar Hot Water / Heating...

Has anyone installed a Copperheart solar hot water heater yet. It is passive (no pumps, motors, etc.) and at about $3100 for a 40 gallon unit, it might make sense - with rebates and incentives. (Looks like $1000 AZ state credit and ~$600 Fed credit.)

http://www.solarstore.com/images/copperheart_specs.pdf

I have a remodel underway in Tucson, AZ, and am considering having one of these units installed, along with small point of use electric under counter water heaters in each bath and the kitchen.

For backup, I think the small electric heaters might be very efficient. They would only have to be turned on when solar heater can't keep up, which shouldn't be very often. I have one of these 2.5 gallon electric units in my small construction trailer at the remodel site and it works great. It runs on 120 V AC and heats up 2.5 gallons of water using 1200 watts in only 10 minutes. If you use a water saver button on the shower head, you can take a shower in 2.5 gallons of water (set at 120 degrees) and by the time you towel off and brush your teeth the next person has enough hot water to shower again.

http://www.plumbersurplus.com/Prod/Eemax-EMT2-5-Mini-Tank-Electric-Water-Heater/10414/Cat/770

With some possible future PV panels on a grid tie in the future, I think the electric back up water heaters would be a good option.
I think if the Democrats take over the White House in 2008, we might see higher federal tax incentives for solar in the future, so I am thinking of holding off on the PV panels until then. :-D