"Americanizing" solar thermal, settling on products and practice for "the big push"

Solar thermal, with a likely big push from the new Obama administration, has a huge opportunity ahead. Now that energy dependence is an obvious national security issue, many of us believe that this is the time for the big push for solar thermal and, along with it, integrated hydronics. The challenge is to “do it right” or to suffer the consequences of squandering this epic opportunity. As solar thermal products go through an inevitable evolution to the North American market, products, practices and price points will change. Products are evolving very rapidly. This has happened before; radiant floor heating went through a similar evolution.

I have been in the hydronic heating industry since the mid-1980s, first as a hydronic contractor, later as president of a national distributor of hydronic radiant heating and now as a product designer and inventor. I have shared in the excitement as waves of new products and methods were introduced into the North American market. Typically, high quality, expensive products from Europe that are introduced into North America are based on the methods and practices that work in the European market. When American contractors get these products they need to be adapted to our practices, methods and pricing.
The first wave of hydronic radiant floor heating from Europe included: European threads on the ends of manifolds, brass manifolds with adjustable flow meters, manifold mounted actuators on every loop, and Euro-style fittings with an insert, split ring and nut. These products are still used and are very high quality, but this way of doing things can be expensive. Many American contractors and suppliers looked around for other ways to do things, using materials they were familiar with. Soon, copper manifolds, standardized American fittings, zoning by manifold rather than by loop and balancing by using digital thermometers instead of flow meters became common. All of these changes reduced costs and made radiant heating systems available in a variety of price ranges.

Sometimes these changes from European practices went too far and, combined with the lack of specific product training, could and did produce some really bad systems. Many of us recognized this as a threat to the growth of radiant floor heating. Those of us who were early members of the Radiant Panel Association stepped in and produced “Standard Guidelines for the Design and Installation of Radiant Heating Systems.” I was the chairman of the RPA Standards Committee that produced this document.
It is logical that solar thermal will go through a similar evolution here in North America. I am an inventor and product designer for a company that builds modular hydronic products, primarily for the residential market. I try to strike a workable balance between adapting to, and influencing, American practices with the products I design. Here are some thoughts on the near future of this evolution:

1. There will be many more solar pump stations to choose from, many of them made in North America. They will have North American threads, fittings, piping and components.

2. In the use of evacuated tubes, a complex competition is developing between U-tube and heat pipe-based designs. U-tubes are simple and inexpensive to produce, but they are difficult to drain back. This means that they should be designed to closely match the load and should have a mechanism to “dump” extra heat, since they can’t be easily drained back to turn off the production of hot fluids. Typical strategies involve running some fin tube in a crawl space or under the collectors, with a changeover valve that is temperature activated. Future U-tubes will likely have heat dump capabilities built into them or will have self-regulating adaptive coatings. These will make them extremely easy to use.

Evacuated tubes using heat pipes are more complex than the U-tube design. The top of each heat pipe is usually fitted into a copper “well,” which serves as a receptacle that is built into the manifold. The fit between the heat pipe and the well must be maintained over time or efficiency declines. Some products do this better than others do. Many good and proven products exist. Most heat pipe designs allow for the use of drainback systems.

Think about how practices should and will settle out between these two evacuated tube technologies if we get the “big push.” Think about thousands of new installers. These will not be the knowledgeable, “artisanal” installers we have today for high-end custom homes. They will be volume installers. They will want predictable, repeatable, get-in-get-out fast and profitable products. Is it more foolproof to rely on installers doing a heat pipe drainback system with the correct slope and installation components or a U-tube system with a correctly operating heat dump? Which way will result in the fewest failures? Will economics drive one over the other? Will it be driven by region or by who has the most convincing training? Those of us who really care about the future of this industry will have to speak up.

3. For hydronic heating to take advantage of this will require components that easily assemble into a system that integrates with solar thermal. This means that pump stations will work as solar pump stations, while also serving as the connection point for backup heat, for injecting solar heated fluids directly into the heating system, for distributing heat to heating zones and for distributing to or drawing from solar storage, as necessary. These forms of combined hydronic heating and solar thermal systems have been variously called SDI, solar direct injection or, in recent excellent articles, Bristol Stickney referred to them as direct active solar heating.

As an inventor, I have been happily working on centralized products to solve this problem. I am sure that others are also. In order to optimize efficiency, we are going to need inexpensive but sophisticated controls that can direct the thermal traffic of all these many choices. So, for example, we need a control that can predict which use is best at which time of day and that prioritizes the different components to achieve this. If the control can predict that foregoing backup heat might only result in a small temperature drop, many people might choose to save this energy. A number of controls currently do a lot of these things. The good news is that a lot of smart people are working on it and that programmable devices have come down in cost. Each of us needs to think through the choices such a control should be able to make and to demand controls that make those choices from the manufacturers. If manufacturers don’t respond, contractors may resort to open source programmable IP-based controls and switches with widely varying results that may not be good for the industry.

4. Finally, for this “big push” to be successful, we need to eradicate the certification delays that are barriers to adopting the best products and practices. The long backlogs for testing and certifying solar thermal products need to be rectified. Solar thermal manufacturers are innovating at a faster rate than can be certified.

 

* Editor’s note: We would encourage installers and designers to review all the products available and base their decision on what is best for their client and application.

 

Hoyt Corbett is an inventor and consultant. He has designed new solar pump stations for Precision Hydronic Products of Portland, Oregon. His new solar pump stations and combined solar/hydronic heating appliance, the Allcan Sol-Center, may be seen at www.phpinc.us and is sold by www.hydronicworkshop.com and by Next Generation Energy of Lafayette, Colorado. He may be contacted at inventivedevelopment@yahoo.com.