The Development of Solar Hot Water Systems


HVAC design engineers have used pressurized glycol programs for many years to switch warmth from boilers to the load. This technique is the usual for hydronic heating programs and lots of industrial warmth switch duties. Naturally, they utilized this design to photo voltaic programs, treating the collectors because the boiler and the tank because the receiver. If you happen to stroll into {most professional} engineering corporations and ask them to design you a hydronic heating system OR a photo voltaic system, they are going to seize their manuals that present tips on how to assemble a pressurized glycol loop.

Since it’s too costly to fill the photo voltaic storage tank with a glycol answer, the warmth is transferred from the collector loop into the tank via a warmth exchanger. The collector fluid goes via one aspect of the exchanger and the tank water goes via the opposite aspect. There are two pumps, one on both sides of the exchanger, and controls to show the pumps on. Glycol loops are “charged” on a regular basis. That is good. They continue to be able to run each time the pump kicks in. When such a system is put in, coin vents (can flip the screw with a dime) are put in in any respect the excessive factors the place air can accumulate and vapor lock the system. The startup process is to fill and pressurize the traces (possibly 15 psi) and go round to all of the coin vents and burp the air out. Through the years, folks have invented intelligent coin vents that when dry will leak air and when moist will seal. That manner you do not have to go to every one to burp it, it would accomplish that by itself. It’s just like the rope caulking utilized in boat hulls for hundreds of years. So long as the boat stays within the water, all is okay. If you happen to take it out and let the caulking dry out, it would leak till the caulking will get soaked once more. There are lots of different kinds of automated air vents, some primarily based on the float system seen in bathrooms. Security additionally requires a pop-off valve close to the boiler (i.e. collectors) to alleviate stress in case the boiler controls go haywire. A glycol-water combine is a good solvent for shingles and plastics, together with tile flooring. So the pop-off valves should have a pipe operating to a drain to include the liquid within the occasion of a failure.

Since stress goes up and down with temperature, a intelligent system was devised to take care of a nominal stress within the loop. A tank, referred to as an enlargement tank, is put in in a tee within the line. The enlargement tank has a rubber membrane operating throughout the center. The system fluid fills up one aspect and air fills the opposite aspect. The fluid within the system can broaden and contract with temperature into the enlargement tank, and the air bladder will hold the stress inside a specified vary. The air stress is about with an air hose and tire inflator, similar to a automotive tire. A chart is used to find out the right stress based on the temperature of the system on the time. Nonetheless, enlargement tanks have a lifetime. The rubber (or neoprene, or no matter) bladder will sometime crack from flexing because it ages and the enlargement and stress regulation advantages of the tank are misplaced. The system will often vapor lock someplace and the entire startup process must be repeated.

Sadly, photo voltaic sizzling water programs do not wish to play by the principles. They don’t seem to be well-behaved. Typical HVAC glycol programs don’t undergo the acute temperatures that photo voltaic collectors do. A boiler heating loop could have a most temperature of 140-160ºF. It by no means will get colder than room temperature inside a constructing, so the utmost temperature swing from summer time to winter could also be 90ºF (70-160ºF).

A photo voltaic sizzling water system, however, has the “boiler” sitting outdoors within the climate. It’s at all times off at evening the place there is no such thing as a solar. Within the winter, the temperature could go right down to -40ºF (Willmar, MN). Even within the mountains of NC, winter night temperatures can go effectively under zero. A photo voltaic sizzling water system can have a most temperature swing as excessive as 260ºF (-40-220), or virtually 3 times what a typical boiler system sees. In the summertime time, the photo voltaic sizzling water system will see its most temperature, which varies based on the applying. Probably the most excessive case happens when there’s a extremely popular day with excessive photo voltaic radiation, and there may be no use for the new water. This may happen randomly on weekends, or summer time holidays, and particularly on area heating programs that sit idle all summer time. When this situation occurs, the warmth from the collectors will not be wanted and the temperature builds up till the boiling level is reached.

This identical downside can happen if there’s a energy failure and the pump stops. At this level, a glycol system is in huge hassle. If it will get to the boiling level, it would blow the pop-off valve. This drops the stress within the system. The subsequent evening, there will probably be vacuum within the traces and the air vents will leak air in, vapor locking the system. The subsequent day the new glycol answer has air in it. A chemical response happens with the oxygen that breaks the glycol into fatty acids, which may clog and eat the pipes if the state of affairs will not be corrected promptly. This situation will not be self-correcting. The system stops working, compounding the issue, and must be attended to. This can be a progressive failure mode. The pump ought to by no means cease operating through the day on a glycol system in heat climate. To keep away from the over temperature downside, massive glycol programs have extra tools put in to dump extra warmth. It often consists of an enormous fan coil unit within the collector loop that kicks in when the temperature will get too excessive and dumps the warmth to the surface world. The parts embrace temperature controls, bypass valves, followers, and pumps. The added complexity simply provides extra failure modes. Warmth dump programs can’t overcome energy failures, except you add a again up generator, which may have its personal failure modes. At evening within the winter when the collectors are chilly, the chilly glycol answer will attempt to flow into naturally down the provision line, making a thermal convection loop. Some programs have even frozen the warmth exchanger on this method, inflicting rupture of the chilly break water point. A test valve should be put in within the collector provide line to forestall fluid from flowing backwards underneath chilly circumstances.


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