Solar water heater design and plans

Batch Solar Water Heater Design

Batch solar water heaters are time tested, in fact this design has been used in the United States and throughout the world for hundreds of years. This design uses an integrated collector storage or an ICS solar collector.

The collector and storage tank form a single component, and the storage tank contains domestic water. The storage tank is insulated and covered by a glazed box. This box is often referred to as the collector box.

The collector box is mounted outdoors and above the back up storage tank or back up power source. When the water is heated by the sun, the heated water from the top of the tank naturally circulates to the indoor back up source. 

The cold domestic water is plumbed into the bottom of the tank in the collector box, and this simple but yet reliable process is repeated.

The biggest advantage with a batch solar water heater design is the overall simplicity. With these systems, DIY installations can be performed. With batch designs, over night heat loss is the biggest setback. In fact these systems are primarily designed for peak hour hot water use.

Batch solar water heater designs and plans also provide no protection against freeze, making most applications ideal only in tropical and warm climate regions.

Where best applied

climate regions where freezing is infrequent or non existent. households or buildings with only 1 to 3 adults that use only 20 to 40 gallons of hot water daily and primarily during peak hours.

Thermosyhon Solar Water Heater Design

Thermosyphon solar water heater designs and plans are also time tested, there the mostly common used systems throughout much of the United States and most of the world. From Florida, to Israel and to Japan, thermosyphon solar hot water heaters have been used for many decades.

These designs and plans are essentially more modern versions of collector or batch solar water heating systems. The very basic principle that hot fluid will rise is the magic behind a thermosyphon design. Domestic water is heated in a solar water panel, either a flat plate collector or an evacuated tube collector.

The heated water then natural rises into a well insulated storage tank which is installed directly above the panel, or collector. The hot water stored outdoors in the tank is then circulated to the indoor back up tank or heating source.

Much like with batch designs, thermosyphon solar hot water heaters require no mechanical assistance to circulate the heated fluid. Although manufactures have recently introduced thermosyphon designs with pumps to assist in applications where fluid flow rate is a major concern.

In general these solar water heater designs offer a limited amount of freeze protection, although newer designs and plans that have circulating pumps can be installed in relatively moderate climate regions.

The biggest advantage to using a thermosyphon solar water heater design is the considerably less heat loss experienced when compared to batch systems, these designs and plans generally offer more storage capacity as well.

Where best applied

climate regions where freezing is infrequent or non existent. households or buildings with a few adults that use only 30 to 80 gallons of hot water daily.

Direct Pump Solar Water Heater Design

Direct pump systems are by far the simplest active designs and plans currently available. In fact, in many ways they're similar to passive systems. The major exception is that a low head solar hot water pump is required to circulate water through the loop. The water pump is both activated and deactivated by either a differential thermostat control or a PV module.

There's added flexibility as well, since the tank and collector aren't integrated and the storage isn't installed above the panel or collector, the solar storage tank should be installed indoors and preferably next to the back up tank. This provides greater insulation and reduces off peak heat loss.

The heated domestic water from the panel, or collector, is routed to the storage tank. Then, much like with any other solar water heating system, the hot water is plumbed to the back up source for on demand use.

Direct pump solar hot water heater designs provide minimal freeze protection, making application ideal in warmer climate regions. The major advantages to installing a direct pump design over a passive one is the larger storage capacity that these systems generally provide, and the added flexibility in application.

Where best applied

climate regions where freezing is relatively infrequent or non existent. households or buildings with a few adults that use anywhere from 40 to 80 gallons of hot water daily.

Drainback Solar Water Heater Design

Drainback solar hot water heaters are the simplest of the two closed loop or indirect circulation designs and plans. The water pump circulates a heat transfer fluid (usually distilled water) into the panel, or collector, and then through the heat exchanger. The heat exchanger transfers heat from the distilled water to the stored or circulating domestic water.

When a drainback solar water heating system is idle and the temperature of the hot water panel has sizable decreased, the water pump is deactivated by either a differential thermostat control or a PV module.

The heat transfer fluid in drainback solar water heater plans is designed to drain from the plumbing loop and into the drainback tank. The drainback tank further protects the system from freeze, because it guarantees that there's never idle fluid within the plumbing loop when the pump is deactivated.

Most drainback solar water heater designs and plans can also use antifreeze as a heat transfer fluid for even additional freeze protection. 

The biggest advantage to installing a drainback solar water heater design is the lack of periodic maintenance these systems generally require, especially when distilled water is used as the heat transfer fluid. The distilled water in these systems seldom had to be replaced.

When an antifreeze solution is used, the fluid generally has to be changed more frequently, but replacing the heat transfer fluid in drainback designs is usually as simply as draining the drainback tank when the system is idle.

The only glaring disadvantage to installing a drainback solar hot water heater is the initial cost of the high head solar hot water pump. Usually a more powerful water pump is required to collect the heat transfer fluid from the drainback tank and circulate the fluid and water through the plumbing loop.

Where best applied

climate regions where annual freezing is relatively frequent. households or buildings with several adults that require anywhere from 40 to 100 gallons of hot water daily.

Antifreeze Solar Water Heater Design

Antifreeze solar water heating systems are generally a little more complex than drainback designs, but they provide the most protection against winter time freeze. These systems use water pumps to circulate an antifreeze solution, usually propylene glycol, to the hot water panels and to the heat exchanger.

The heat exchanger performs the same function it does in drainback closed loop designs, it transfers heat from the antifreeze solution to the stored or circulating domestic water.

While most of the major components are required, an antifreeze solar water heater design (more times than not) will require more plumbing fixtures than most other designs and plans.

The most important additional plumbing requirement is the expansion tank. An expansion tank is required in these designs and plans because the antifreeze solution will significantly expand when it's introduced to heat.

A fill valve and flush valve are also required in the solar loop. These valves serve as service points when the antifreeze system requires draining or charging. A charging pump will be required to both drain and circulate the new antifreeze solution, as well as to remove any unwanted air pockets within the loop.

The biggest advantage to installing an antifreeze solar hot water heater is the unmatched freeze protection. These designs can be installed in the coldest of climate regions, as long as the site has an adequate solar resource.

One disadvantage is the extra periodic maintenance that is generally required. In order for an antifreeze solar water heating system to perform efficiently and effectively, the antifreeze heat transfer fluid will require periodic replacement.

Where best applied

climate regions where annual freezing is frequent or very common. households or buildings with several adults that require anywhere from 40 to 100 gallons of hot water daily.

Single Tank Solar Water Heater Design

As of late, manufacturers have introduced single tank solar hot water heaters. This all in one design is quickly gaining popularity throughout the United States. 

In this design direct back up solar hot water tanks are used as both the storage and the back up water heating source. The storage in single tank designs often have immersed solar heat exchangers, and the tank always come equipped with a built in secondary heating element to provide hot water during off peak times.

With single tank systems, there is a lot of flexibility in the design and application. They can be designed as either open loop circulation, or closed loop circulation systems, or as drainback or antifreeze solar hot water heating systems.

One of the biggest advantages with using a single tank design is the immediate reduction of standby heat loss, because there's is no back up storage required. 

If the systems' hot water panels and the storage tank volume (or capacity) are sized properly, the integrated back up heating element should only be utilized during the cold season, and when the sun's thermal energy is unaccessible.

Where best applied

Single tank designs are ideal for those applications that don't have an adequate water heating system to potentially serve as a back up. These solar water heater designs and plans are also ideal for new constructions. households that have only a few adults and that have a fairly routine daily hot water use.

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