“Do-It-Yourself” Solar Water Heating Systems?
I came across a video yesterday touting the benefits of a “Do-It-Yourself” solar hot water system for homeowners. As a life-long scientist and inventor, I applaud anyone’s efforts to create a better mousetrap. I have learned in my three decades of experience in the solar industry that some ideas are better than others. “Better” doesn’t always mean cheaper. We all know this. Few people would build their own car and drive it to work just to save money. Likewise, few homeowners possess the plumbing and electrical skills to effectively pull off a task like building their own solar water heater.
In areas where the climate is mostly warm, like California and Florida, DIY solar hot water is more popular because of the mild winters. Hard freezes are not common. But in areas where the temperatures often dip or stay below freezing, these homemade systems seldom last a few years. They can also cause a lot of headaches at the wrong time.
From a thermodynamics perspective, homemade systems are significantly less efficient and in many areas of the country they will not meet code. Plus, a lot of the incentives that make solar hot water so economically attractive require a certified professional to perform the installation.
For those super-handy and intrepid do-it-yourselfers, I say the following: If you want to have fun and learn about solar, but don’t care if it works very well, then go for it. It is a great learning experience.
But if you don’t want a lot of hassle, and you want it to work well, you need factory made equipment and professional installation.
Dr. Ben
2 Responses to ““Do-It-Yourself” Solar Water Heating Systems?”
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This is our vacation home, retirement home in 10 years. Existing 220v
electric heat in ceiling, built in the ’70’s, wood floor with crawl space.
Main priorty is to install a flat plate collector drain back radiant heat
system, DHW to tankless water heater if conditions exist. Have approx. 144
sq. ft. of collector area on South side of home (receives 100% sun from
9:30am to 2:30pm in January.)to supply crawl space tank. Can install more
collectors on roof if required. Heating 1100 sq.ft.-3 zones-4 loops @ 120′
per zone. I’m thinking I need 500 gal. storage tank, 3-1″x300′ pex coils
for exchangers (one for each zone) and if possible a smaller diameter
exchanger set inside the 1″ pex for DHW. Would like to run circulation
pumps from PV collectors. Am I anywhere close?
Craig,
Let’s see, you have a 1100 ft2 house built in the ’70s,. At this point, there is no way to tell what your heating requirements are without doing a professional heating load analysis.
So, the first thing I would recommend is to check the insulation in the attic and under the floor. You need to max that out first. Recommended R values vary by region, but R30 in the ceiling and R19 in the floor are a good start. Then add double pane windows. These improvements could cut your energy bill up to 50%.
Now you add solar to that. The performance of the solar is intimately related to you location and available sunlight. That is, the weather conditions, both in terms of heating your home and available solar radiation.
You have 144 ft2 of collectors. That is not a lot. I recommend increasing the number of collectors as much as you can afford. Put the PV money toward that and use regular AC pumps.
A typical tank gallons would be 1.5 x (collector ft2). Round that up to the nearest tank size. You can go bigger, but there are diminishing returns on cost vs performance. The tanks needs to be out of the weather and insulated well.
I never recommend using plastic for exchangers, or any part of a solar collector system. This is one place where you can destroy the durability and efficiency of your system very quickly.
You will need some detailed system design, which I am not able to give in this type of situation. Let me just say this, you need a steel tank and copper exchangers.
There are designs that have no exchanger between the tank and the collectors, i.e., a drain back system. There are also ways to use no exchanger between the tank and the space heating. This depends on vertical distance between tank and radiant floor loop and whether the pumps can purge air out of the loops. If you could get the tank on the same level as the floors (or slightly above), this would be a good option. No exchangers for collectors and space heating would be the highest efficiency and lowest cost, but you can see it is too complicated to cover in this note.
Domestic hot water always requires an exchanger, though.
Plastic piping will work OK for the radiant slab floors. Radiant slab design and installation requires detailed planning of the size of the pipe, the layout in each room, pumping horsepower, and controls.
I hope this helps.
Ben