Solar water heating systems for homes have become quite common. These systems preheat the incoming cold water for baths, kitchen and to do laundry. A correctly sized solar water heating system will supply about 40-70% of your hot water needs. In order to qualify for the currently available federal tax credits however, your system must provide at least 50% of your water demand. Combine these tax credits with the higher efficiency of today’s systems, and it has become very feasible for many homeowners to install a solar water heating systems.
Domestic solar water heating systems are either an open loop system or a closed loop system. Open loop systems are installed in regions where temperatures don’t drop below freezing and where the water is soft. The domestic water loop is open to the solar collectors in these systems, and the incoming cold water is run directly through the solar collectors and from there to the solar storage tank. In a closed loop system, the domestic water is isolated from the solar collector loop by a heat exchanger. The liquid running through the collector loop is freeze proof and is usually a glycol solution. Unfortunately, the closed loop systems required in colder areas and regions with hard water, cost more because of the added heat exchanger.
Size and number of collectors depend on the type of collector you decide to install, for a given hot water load. Flat plate collectors and evacuated tube collectors are the two most common types used. Evacuated tube collectors have a higher efficiency than the flat plates, especially in colder or foggy weather and climates. It is generally ok to use flat plate collectors in sunny and warm climates, as long as your water is soft. The more expensive, but also more efficient, evacuated tube collectors are preferred in in colder, cloudy or foggy areas.
It is essential to mention that a solar water heating system will not replace your existing domestic water heater or eliminate the necessity for installing one in a new home. The intent of the regular water heater is to make sure that you have sufficient hot water during and after a series of cloudy days. A complete solar heating system also includes a solar storage tank. This tank is used to hold the water that was (pre)-heated in the collectors. The (pre)-heated water then flows from the solar storage tank to the regular water heater where it is heated up as needed. The regular water heater will not need to run on most sunny days, if the solar heating system is designed well.
Where are you planning to put the solar collectors? I guesson the roof somewhere. The “somewhere” is critical. You have to make sure that the location you choose receives sufficient direct sunlight, all year. Numerous tools are available online to help you determine this. Some of these tools are free. Keep in mind though that some of these tools might not make allowances for trees. You can also contact a local solar heating system installer. Many will do a free analysis for you and they will include trees and tall buildings next door.
Now on to the roof itself. Will it need to be re-inforced? How exactly will the collector support system be anchored to the roof? What about the pipe penetrations? What will be required to make sure that the roof is still fully waterproof after the solar system has been installed. Talk to a trusted contractor.
Ok, let’s look what is needed in the house. Here you will need space for the solar storage tank, pump and possibly a small expansion tank, if you end up with a closed loop system. How much space? To be on the safe side, allow at least 2 1/2 times as much space as your existing water heater uses. This needs to be right next to the water heater. Allow enough space for easy access for maintenance.
All right, the collectors are on the roof, the solar storage tank is in the basement. How will you run the pipes between the two? You will need to run two 3″ pipes. That is based on 1″ pipes with 1″ insulation. Scout out which walls you can use to run the pipes up through, all the way from the basement, or first floor, to the roof. If possible, avoid having to build pipe enclosures. That can get costly and might not look very nice. Corners in built-in closets are great places to tuck a set of pipes into.
That’s it. You have done a lot of the important up-front work. Hopefully you now know enough to be dangerous, can make educated decisions and ask the right questions about how to plan, design, purchase and install, or have installed, a solar water heating system for your home.
It is critical to have the knowledge when design and build a solar water heating project. If you want to learn more about the best approach to planning, designing and installing a solar heating system for your home, visit us at www.greenandsustainablehomes.org
