Putting together solar and radiant heating is a marriage made in heaven, say some practitioners in the field, pairing a widespread, free heat source with a proven, efficient method of heating buildings. 
   Yet others in the solar and radiant fields are concerned that any solar-radiant marriage is actually in the newlywed stage, where the partners are still new to each other and unsure about their long-term future. 
   "What we're seeing is solar radiant floor heating more common in Europe and Canada," said Monique Hanis, director of communications for the Solar Energy Industries Association in Washington, D.C., "but we also see wide possibilities for its use in the United States because the temperatures coming off our rooftops are perfect for floor radiant systems." 
   Hanis pointed out SEIA is starting to see more solar and radiant pairings in industrial use, where manufacturers use such systems to heat a factory or in a manufacturing drying process. 
   "The entire system is more efficient because radiant floor heating itself is more efficient," Hanis said. "You're heating from the bottom up from fall through spring, and even on the coldest winter days you can get the temperatures you need off the rooftop with solar." 
   She noted that a solar energy collector-typically water and propylene glycol in a closed loop system-puts out temperatures between 70- and 80 degrees Fahrenheit. 
   "It's perfectly complementary for a radiant floor heating system," she said. "It's much more efficient than a boiler-heated radiant floor system, which usually heats to 120 degrees and then has to be tempered for the floor system." 
   Hanis thinks the biggest challenge to overcome in regard to solar radiant heating applications is the "cadre of plumbers and HVAC companies that are putting in traditional systems and who are not familiar with or have the technical expertise to install solar radiant heating systems." 
   She recommended they get connected with solar heating and cooler manufacturers, as well as the installer base that SEIA maintains in its solar directory. 
   "Traditional installers can get trained and certified to install solar radiant heating systems, which can extend their product line and offerings to customers," Hanis added. 
   Steve Elkin, chief executive officer for Solar U.S. in Branford, Conn. and vice chair of SEIA's solar heating and cooling division, said solar is the most effective way of deriving heat from any source, whether it's photovoltaic solar, concentrating or geothermal. 
   "Some systems are working at 85 percent efficiency in converting solar to energy," Elkin said, "and with the higher efficiency collectors, you can get into heating and cooling residential structures, and even into manufacturing where thermal is required." 
   However, he cautioned, solar-radiant systems have to be properly sized and the hydronics married to the collectors to be sure to meet the BTU heating requirements needed. 
   The advantage to using solar for heating, Elkin pointed out, especially with evacuated tube collectors, is that you can provide the heat when it's needed as long as some sunlight is available to be converted into heat. 
   "The collectors take the sunlight and convert it to heat, but when less sunlight gets through they function at a reduced level," he said. "Coupled with radiant floor heat, if the building is tight enough, once you get to the required temperature, it doesn't take all that much to maintain it." 
   Elkin said in designing such a system, one must factor in the load and the structure itself. For instance, lack of insulation or no thermal windows mean the system has to work harder, compared with a new building with state-of-the-art windows, which would be much easier to heat. 
   "In the newer building, the BTU load required might be half of that in a loose building," Elkin pointed out. "Those are considerations you have to make." 
   Elkin noted a recent SEIA survey that showed solar is the number one job growth area in the country, creating 30,000 new jobs in the past year for solar photovoltaic, heating, cooling and concentrating solar power. 
   However, Elkin said the challenge facing the industry "is getting people to understand, believe in and invest in solar and radiant heating. The banking community is starting to loan on these kinds of projects, but people have to think of solar and radiant heating as an electric, fuel oil or natural gas bill," he added. "The difference with solar is they are purchasing 30 years of energy in one package." 
   For instance, Elkin pointed out, a homeowner might spend $8,000 for a solar hot water system, which they will recover in five to eight years. 
   "That's a tough pill to swallow because the homeowner has to pay for it all at once, even with any incentives they receive," he said. "But now the banks are loaning on these systems and the homeowner can take 20 years to pay it out. And with the government tax credit coming up front in many instances, the homeowner might not be out of pocket for perhaps seven years." 
   The return on investment is even better for commercial applications, Elkin noted. 
   "With commercial installations, you have the added bonus of depreciation that a homeowner doesn't get," he said. "On top of the 30 percent tax credit, the business owner can take accelerated depreciation so that we've seen as low as a 2-1/2-year return on investment. That doesn't even take into account the fuel savings or appreciation of fuel costs." 
   Robert Cooley, training manager for Heliodyne in Richmond, Calif., is excited about using solar as the heat source for radiant floor systems. 
   "As a heat source, solar has the advantages that it's free and it's not going to go up in price," Cooley said. "Electricity, natural gas or propane, you can get in any quantity when you want it, but they are not free and they will go up in price over time. Any time you can take advantage of a free fuel source with a fixed price, you should do so." 
   Cooley recommends tying additional systems into a solar-radiant heating loop because in most climates, the demand for heat is 100 percent in the middle of winter and zero in the summer. Using solar in a comprehensive system to heat domestic hot water would provide approximately 80 percent of a home's needs year-round. Adding a seasonal pool to the system would use the extra BTUs produced by the solar collectors in summer to help even out the use and make the entire system more cost effective. 
   "The only time it makes sense to collect energy is when you can use it to replace energy that you would have to buy," Cooley observed. 
   Cooley said he's seen installations that use a heat store-an underground mass of rocks with hydronic tubes running through them. 
   "The ground temperature stays pretty constant year round, so you can run the BTUs into the ground in the summer and use them in the winter," he pointed out. "Another way of exploiting this heat source is to use a heat pump. A ground mass heat pump will dramatically reduce the amount of energy needed to heat a space." 
   Cooley noted as fuels become more expensive, solar and radiant heating installations will become more popular. 
   "In a geographic sense, these installations already are popular in areas like Denver," he said, "as well as in California's Sierra Nevada mountain area where there are clear blue skies, cold weather and costly fuel." 
   While snow melting is another use for the BTUs produced by a solar radiant heating system, Cooley believes its best use is in heating a house. 
   "Radiant is the highest quality way to heat a house because it is so very comfortable and efficient," Cooley said. "And it makes a lot of sense to combine the attributes of solar-it's free and there's no scarcity-with radiant heating." 
   Cooley said he thinks solar thermal is a growth industry. 
   "In the future, as we see prices of conventional fuels go up rapidly, it will make the solar-radiant connection much more attractive and viable," he said. 
   Bob Ramlow, a member of the American Solar Energy Society whose history in the solar business goes back to the early '70s, is the author of "Solar Water Heating: A Comprehensive Guide to Solar Water and Space Heating Systems." He thinks solar and radiant heating go together very well. 
   "Solar and radiant hydronic is a marriage made in heaven in a lot of ways, especially in small commercial and residential applications," Ramlow said. "Solar is a heat delivery system that operates at a lower temperature and radiant hydronics use lower temperatures too, typically at 100- to 120 degrees, compared with baseboard heat or radiator heat at around 180 degrees." 
   Usually two types of solar systems are used when coupled with radiant heating, Ramlow noted. 
   "The most common today is the hydronic system where the collectors have a liquid, commonly an antifreeze solution, that directly transfers heat to some type of storage system, either liquid like a large water tank or a large mass like sand," he said. 
   The other type of collector is an air collector, Ramlow said, where the sun heats an area of air, which is then blown directly into a building. It's a system with no storage, which Ramlow noted is very popular. 
   "With an air system, you also could run the air through ducts in a sand or gravel bed that's directly under the building," he said. "As the sand bed warms up, it gets warmer than the room above it and the heat radiates out of the sand bed and into the building." 
   It's also possible to put tubing in the sand bed and run solar fluid in the hydronic system to take the heat out of the sand, he added. 
   In warm climates, it is possible to use re-heat on an air conditioning system, Ramlow pointed out. 
   "In large systems for an entire building, the air is cooled off and run around like a doughnut of ductwork and when a particular room or area needs more cooling, a damper opens in the ductwork to deliver cold air to that room," he said. "Some rooms have to be colder than others, but they might be next to a small room that doesn't need much cooling, so they run a boiler to warm the air back up for that room that doesn't need as much cooling." 
   Solar can play a part in such a re-heat system, Ramlow believes. 
   "You can do the re-heat with solar, which would show a huge savings in energy in a very large building," he said. "It seems counter-intuitive, but it is fairly efficient." 
   "These systems (solar-radiant heating) lend themselves to every climate on the planet," Ramlow said. "Solar heating can do a number of different things, with the most popular being to heat domestic hot water. But it also can do space heating or the type of heating that is used in many commercial applications where the water doesn't have to be super hot." 
   Ramlow noted that the solar-radiant connection is seeing its largest amount of growth in commercial applications. 
   "There's a lot of activity in commercial applications for solar water and space heating," he said. "And it's not only in the larger facilities like hospitals, but also in smaller places like breweries, small manufacturing facilities and health care offices. The economics are good enough that with the incentives available today, and even in some cases with no incentives, solar can compete with fossil fuels." 
   Elkin of Solar U.S. said that while growth in the solar and radiant heating industries has slowed in the last couple of years, interest recently has been spiking, so the industry is still experiencing growth. 
   "The solar and radiant heating marriage is ready," he said. "People have to understand it and accept it as a new opportunity."