Solar water heater

[Stan in Oly, WA]

I'm considering installing a solar water heating panel on my roof, in line with my natural gas water heater. I haven't done any research on it yet, and I realize that when I do I'll get most or all of the answers to questions I have. Nevertheless, I enjoy the more specific and more personal information I can get here. So here are a couple of questions: How do I shut the panel out of the system when freezing conditions, especially at night, would pre-chill the water entering the water heater instead of pre-heating it? Would I need to drain the panel to keep it from freezing and breaking when it's out of the loop?

Thanks, Stan

 

[Bob]

I'm seriously considering a "heat pump water heater". Have you given those a thought?
ONE example

 

[Cliff (VA)]

I am not a solar expert, but I have a friend who is. He talks about using a "drain back valve" and a "bypass valve" in those kind of situations.

Obviously you need some kind of "smart" controller and a bunch of sensors to manage all of this.

HTH

Cliff (VA)

 

[Anonymous-0]

Its hard to make one pay out in a lifetime, even if you build it. One home design I've seen used a huge tank in the basement to hold heated water with a heat exchanger coil to the water going to the solar collector. Then it used a circulating pump and a thermostat on the collector surface that only ran the pump when sun was shining and heating the collector. It used a drain back valve to let the collector drain. Home made it cost a couple kilo bucks, for maybe $100 bucks energy savings in a year. Makes payout difficult since the hardware won't probably last that long.

There are many sources of both commercial and home built designs on line, google will find them.

Gerald J.

 

[Anonymous-0]

The heat pump scheme works better but so does grabbing excess heat from a ground water heat source pump used for whole house heating and cooling. But sometimes that's hard to justify if the house has really good insulation.

One company got put of business near here pushing a bare collector heat pump water heater that didn't work when the wind blew cold night air over the bare collector. The courts shut them down. It didn't work as well as promised.

The trouble is that the much increased cost of equipment isn't covered by the saved energy at today's energy costs within the lifetime of the equipment.

I'd think it would be most effective to combine a freezer/refrigerator and a water heater. Use the water tank to capture the heat from the refrigerator system instead of dumping that into the room air. Of course in winter that's useful house heating, but in summer it costs more to cool the kitchen because of the present styles of refrigerator. But I doubt the triple combination would pay back in energy saved before it died of old age.

Gerald J.

 

[Bob]

My utility room is always excessively warm in winter.

In the summer, I have to run a dehumidifier down there, so I think the ambient heat recapture waterheater is a GREAT idea, as it will capture the excess heat in the winter and serve as a dehumidifier in the summer.

 

[Puddles]

And where are you going to get the sun?

You know something I don’t!

 

[JDemaris]

It depends on where you live. I have solar hot water heating and it gets down to below 30F here in the winter.

Basically, there are two types of systems. Open and closed. Open runs the water you'll acutally be using up through the solar heat collector. Not something you want hooked up all year in a cold region.

A closed system usess a close-loop of antifreeze protected liguid that runs up through the solar collector. In your storage tank, it heats the domestic water via a heat-exchanger.

I'm being a bit simplistic and you can always read up on it if you want to know more.

My system has an 80 gallon storage tank. It's hooked both to water coils in my wood furance and to a heat-excanger and on to a closed-loop in roof mounted solar collectors.

The output of hot water from the 80 gallon tank runs to input of my propane tank-type hot water heater.

Watch yourself if you decide to buy. Many rip-offs out there and a lot of overpriced equipment. Even storage tanks. A used 80 gallon electric hot-water tank usually works fine. I've bought several for $50 each (just don't hook any electricity to it).

One slight caution. If you have an instant tankless heaters, they won't work correctly when hooked to solar-heated water. Not unless you buy a special version that costs a bit more.

 

[circus]

If your looking for personal experience (too much) join the yahoo group "Solarheat Solar Thermal Energy". For examples try "BuilditSolar".

Solar water heating is trickier than solar air but the payback is faster (summertime).

Perfect for a "Do it yourselfer". Not so great if contracted out.

 

[VaTom]

Bob, you"re correct. My heat pump water heater is tankless, works with a standard electric tank heater. We only use it seasonally as we don"t have your overly-warm room and I"ve found that below 70º it"s not very efficient.

But it works so well during the half year we use it that I grabbed a spare when I had a cheap opportunity recently. No idea how long they last but we"re nearly a decade into ours with total maintenance of 1 pump rebuild, a very minor job.

That cool dry air byproduct is something most don"t understand. It"s what made our payback in less than 2 seasons" use. FREE dehumidification along with the very low cost water heating. Our house doesn"t need AC but everybody needs to dehumidify here. The heat pump water heater does a great job except for the few worst weeks of summer, when we give it help. I expect you understand you need to distribute that cool dry air during the summer.

 

[VaTom]

Good idea Stan.

Any defunct solar systems available for salvage in your area? There have been lot here. Left over from the last go-round with tax credits. When they expired, so did the solar installing companies, leaving no one available for maintenance.

I picked up 480 sqft of collectors cheap, including a pile of plumbing parts. Repairs amounted to replacing ruptured copper pipe, happened when the antifreeze wasn't maintained. This system uses a liquid/liquid heat exchanger to run antifreeze, rather than automatic drain-down or reverse flow.

I did run into a soldering problem, but T_Bone was gracious enough to help me out. Seems this copper was originally welded and had a peculiar coating I had to deal with to get solder to flow. BTW, he mentioned that the best performer he ever knew was a truck radiator under window glass. I had my hardware, and a few more sqft of collector was already available. Not yet in place, I'll have 64 sqft. The remaining panels will be used for year-round pool heating.

If you want to figure how what your collector will do, don't forget to look up your climate cloudiness.

 

[Stan in Oly, WA]

Thanks, everyone. Great information.

 

[WA-Hal]

Lots of non-sunny days in Olympia, I'm afraid the payback time would be pretty long. Copper pipe is expensive!

Over here on the Eastern side of the state, solar water heating makes some sense. I don't have one, but have spent a bunch of time thinking about building one.

The most simple and probably cheapest system is just a tank (like a uninsulated hot water tank or something similar) painted black and put into a glassed in box on the roof. The supply water to the gas fired or electric tank first goes through the roof tank, where the supply water gets preheated. This can work great some times of the year, but must be fully drained if there is any chance of the upper piping freezing. But it also can produce water that is much hotter than you want in your home, especially in the late afternoon in the Summer when you have not used much hot water all day. But other than having to drain the system some of the time, these are easy systems to deal with. The water moves through the tank and piping by normal water pressure--no pump would be needed. If I built one of those, I would definitely include a pressure/temperature relief valve into it.

Another general type of solar water heater would involve a kind of flat plate collectors in a flat, black box, simply copper piping covered with glass or maybe some kind of greenhouse plastic. I would build the collector up off the roof, so some air can circulate under it, because I would be worried about the collector damaging the roof underneath without it. A pump would be needed to circulate either water or antifreeze through the collector and back to a tank in the basement with a heat exchanger to heat the regular water heater's supply line. Such a system could be designed so it would self-drain using regular water, or not need to be drained if using antifreeze. I don't think it would be difficult to rig automatic controls that would turn on the circulating pump when sensors in the collector show that there is heat to be gained. The controls could also turn off the pump when the collector was cooler than the heat exchanger tank. It would be important that antifreeze not ever be able to mix with supply water. And I sure would not install such a system in a room without a good working floor drain. If something broke, it could get really messy.

I have looked at several systems locally, that were put up years ago. One very elaborate system had collectors that moved to track the sun. Of course it wore out quickly and now just looks like a mess on that house roof. I hate to think how much that cost 35 or so years ago. Another system that uses a batch tank has been in use for more than 20 years, and seems to work fine, although they only use it about 6 months of the year. A third system uses a flat plate collector, and is much newer. I don't know if they use antifreeze or water in it, as I don't know those people. I think they had to replace some glass a couple of years ago when it got damaged somehow. It would be interesting to know how well that system works and how much it cost them to build it.

This Old House had a project in the last year where they added a solar water heater to a house they were working on. I didn't pay enough attention to the specifics, but if I remember correctly, the collector used evacuated glass tubes for very high efficiency. Unfortunately, I also bet it was very expensive, but it might be worth investigating. I am sure there are other commercial systems for sale.

I have thought about building one last house, on some nearby property we own, and selling our present house. If I did build a new house, I would certainly install the piping through the structure for a solar water heater system. It sure would be easier to do it then, rather than retrofitting later...I just keep dreaming. Good luck!

 

[Stan in Oly, WA]

Thanks, Hal. Very good stuff.

Stan