Our system operates under different physical principles than other systems. For example, it operates at lower temperatures (maximum of 180°F) and lower pressure (less than ambient) than typical closed loop systems and well within the tolerances for PEX. It makes for faster installation because it is flexible and can be run as one section without the need for making couplings. PEX is also the most cost effective piping material on the market today. It is important to note that although PEX is certified for domestic hot water systems, it CANNOT be used in a traditional SHW system, especially if it is a closed loop glycol system.
Normal system operation is under a vacuum. If the pressure becomes positive (i.e. higher then ambient pressure) a pressure relief valve opens and releases excess pressure by releasing fluid into an overflow reservoir that is mounted on the roof parallel to the Sunnovations pump. This reservoir acts as the temperature regulator for our system (and is why PEX can be used). If the storage tank is fully heated, the return fluid reaches a temperature of 140°F and creates positive pressure. This purges all of the fluid out of the collectors, temporarily storing it in the overflow reservoir. The system then comes to “rest” without any fluid in the collectors and will be at ambient pressure. Once the collectors cool down, all the fluid is drawn back into the system by the vacuum.
The flow rate in our system is adaptive, meaning that the rate gets higher if more solar heat is available for collection. An adaptive flow rate improves the overall energy efficiency of the system. For a two-panel system, the maximum flow rate is about 1 gallon/minute.
Stagnation is a common problem in other closed loop glycol systems because glycol can break down when it reaches high temperatures. But our system will never suffer from "stagnation", where fluid is "trapped" under high pressure and temperatures in the collectors because of our overheat protection mechanism. This makes the Sunnovations system safer and will prevent chemical breakdown of the glycol-based heat transfer fluid. Unlike the Sunnovations system, other closed loop glycol systems risk the glycol turning acidic and losing its freeze-protection properties. Also in other systems, acidic glycol corrodes the tubes and causes leaks over time, which will ruin collector panels. Yes, other systems have a backup power source that will still provide hot water, but this doesn’t make the problem go away and will eventually render their solar hot water system useless. Annual inspection and possible replacement of the glycol is mandated for other systems to prevent corrosion, but not for a Sunnovations system!
The last step after installing and filling our system is to pull a vacuum in the system with a pump. However, the system can automatically create and maintain its own vacuum after heating up by the sun. This will guarantee the system will always operate efficiently assuming proper, vacuum-tight installation.
The collectors form a part of our geyser pump system—only glazed, flat plate collectors with parallel risers can be used. These are the most common collectors for solar hot water systems in US. SRCC data shows that flat plate collectors have superior performance (except in far northern latitudes) and are the most cost-efficient choice for a majority of US climates.
No, but our system does boast some of the same advantages of a drainback system—namely stagnation avoidance (overheating) by purging fluid from the collectors when needed. The best part is our system does this without the extra cost from bigger pumps or the complexity of installation (like sloped pipes and collectors) in standard drainback systems.
Our standard system has been designed around the most cost effective solution for the greatest number of homeowners. We believe standardization will be the key for cost reductions in solar hot water systems. The basic configuration of two 4’x8’ panels plus an 80 gallon tank with internal heat exchanger should be sufficient for 80% of typical American homes. However our system can be scaled up or down, for example using one larger panel or two smaller panels. Also, two large (4’x10’) panels can be used in combination with a larger (120 gallon) tank. Adding extra collectors often increases cost without adding proportional savings. Keep in mind that unlike PV which can produce more power than is used by a homeowner, a solar hot water system should not produce more hot water than is being used.
Our “balance of systems” kit comes with everything except the tank, collectors, heat transfer fluid and piping insulation and a mixing valve, which is usually required per code to avoid scalding hot water. We will soon have available for sale entire systems with all components necessary for a solar hot water installation (a standardized “system on a skid”).
An inferior collector could be damaged, especially ones with dissimilar metals used to construct their absorber plates. Some brands may also lose the selective surface if used in a drainback application.
However, the collectors certified by Sunnovations can handle 360+F dry stagnation temperatures because of their all-copper construction absorber plates. The riser fins are molecularly bonded to the tube, meaning that everything will expand and contract at the same rate. Hence, the collectors can handle dry high temperatures and since the glycol will not turn acidic in the Sunnovations system, they are ensured a long service life.