IMD

Karel Deist of the SABS.

Homeowners interested in investing in a solar water heating system face the challenge of selecting the correct type of system. In the second part of Plumbing Africa’s series, Karel Deist of the SABS focuses on collectors and storage combinations…

The collector 
The collector or solar panel is an integral part of the solar system and transfers the solar radiation into heat, which is then directly or indirectly transferred to the water.

The collector comprises of two types: the flat plate collector and the evacuated tube collector.

All flat plate collectors have a collector box, usually made from steel or aluminium sheets. The insulation is placed at the bottom of the collector to prevent the loss of heat at the bottom of the box. The absorber plate which is attached to the tube risers is placed above the insulator.

The absorber plate helps to heat up the risers which can contain water or a heating fluid for the indirect system. The final part is the transparent collector cover which traps the solar radiation, which in turn heats up the collector.

Evacuated tubes are double walled cylindrical glass tubes where the inner part of the tube had air removed to form a vacuum. All tubes are coated with a radiation absorbing material which helps in the heating of the fluids.

The evacuated tubes have an indirect and direct way of transferring heat to the water. The direct way is when water flows in the tube. The indirect way has sealed copper tubes filled with refrigerant liquid.

The copper tube is attached to absorber fins which help to transfer the heat. The evacuated tubes are connected as a system integrally, or connected to a manifold as in the picture below:

Collector/storage combinations:

The integral system is a system in which the hot water storage tank is incorporated integrally with the collector and water is stored in the body of the collector and storage tank unit.

A cistern type combination unit storage water heater has a container supplied by water under gravity from a cistern, which is incorporated in or directly fixed onto the appliance within a height of 500mm above the upper surface of the water container. The expanded water can return to the cistern and the flow of water is controlled by one or more valves in the outlet system.

These types of systems are popular in areas operating on gravity feed for water pressure. Such a system can’t be installed in a balanced water pressure installation.

SANS 10252-1 requires that where a mixing valve (tempering) is used, the difference in water pressure between the hot and cold water sides should be less than 50kPa. This is impossible to achieve in the typical installation in an area using pressurised municipal water supply.

There are also high pressure integral systems that don’t have a cistern tank. They are supplied directly with high pressure municipal water.

Close-coupled system

This is a system in which hot water is stored in a separate, but close-coupled water storage tank, where the mechanical coupling between the collector and the tank are pre-manufactured and controls the position of the collector in relation to the tank.

Separate storage systems

There are two types of split systems: a split thermo siphon and a split pump system.

Split thermo-siphon systems are geysers which are placed no more than 350mm above the top of the collector. This system is designed for places where the storage tank is placed in the roof of the house and the collector outside.

An advantage of a split thermo-siphon system is that it doesn’t require any mechanical components to circulate water between the panels and the storage tank. These systems are notoriously difficult to install though. The pipe runs must be smooth and even. It is important that the pipe work not only looks good, but also prevents the natural thermo-siphon of the water.

A split pump system is a hot water storage container which is remote from the collector. A pump (12V DC or 230V AC) is used as a circulation method from the collector to the storage tank. The 12V DC systems usually have a PV panel and a control box that has circuit controllers and batteries. The function of a PV panel is to recharge the batteries that are used to run the 12V pump. The circuit controller is to measure the temperature in the system and give instructions via the controller to circulate the fluid via the pump through the system.

The advantage of such a system is the controlled manner of water circulation, ensuring optimal heat transfer under all conditions. It is however using mechanical components that need to run continuously and would therefore require maintenance and repair costs over the years.

Heat transfer method using either direct or indirect heating.

A direct heating system is when the potable water to be heated is circulated through the absorber, and the solar heat gathered by the collector is transferred directly to the potable water itself.

An indirect heating system absorber transfers heat via a heat exchanger to the potable water to be heated.

Circulation method:

Thermo-siphon circulation
This is a system in which water is circulated between the collector and storage tank by means of density changes of the heat transfer fluid.

Pumped circulation

Pumped circulation systems are systems in which water is circulated between the collector and storage tank by means of a mechanical circulation device.

As all plumbers know, having the right tool for the job is important. In the same way, selecting the correct system for the applications is important to ensure that the user gets what he or she expects. Spending the extra time with a homeowner to help him or her decide on the best system for an application will result in a happy client.

It is also advisable that installers are registered PRIB members and have completed their solar installation courses. Check their references.

By: Matt Chapuran – IAPMO correspondent

On his website Gene Trumbull of Custom Built Spas notes that a pool or spa outfitted with a salt water sanitation system can reduce or even eliminate the red eyes, green hair, dry irritated skin or smell associated with traditionally chlorinated pools.

Proponents of salt water pools and spas – otherwise known as saline (salt) systems – don’t guarantee an end to the need for chlorine. Rather, they argue that by releasing the chlorine already existent in salt, the user will be able to better manage sanitation levels for a healthier pool or spa, often with a lower cost.

But there isn’t universal consensus in the pool and spa industry that saline systems can deliver on their promises.

Better living through chemistry
A 25-year veteran of the water treatment/pool industry, Bob Trepp, president of Tempe-based Saline Generating Systems, attributes the smell, taste and aggressive redolence of chemicals associated with chlorine pools to both routine chlorine shocking and the inevitable buildup of chloramines. “It’s generally accepted that chlorine is a carcinogen and only the extreme (to which chlorine is carcinogenic) is arguable,” Trepp says.

Saline systems or salt-water pools use an electrolytic cell to break down salt (sodium chloride) into its component parts, one of which is chlorine. A control box monitors the chlorine level in the pool or spa and either continues the electrolysis that breaks down the sodium chloride or permits the two individual elements to reconstitute back into salt.

In ideal circumstances, saline systems shouldn’t lose any salt unless water splashes out and evaporates on the decking or the pool is diluted by rainfall. Not only is the salt naturally recycled and reused by the saline system, no additional stabilisers or extenders are required. Fewer chemicals are introduced into the water environment and the need for shocking the system is greatly diminished, if not entirely eliminated.

Trumbull says his customers appreciate eliminating the storage of dangerous chemicals – which by necessity expose the pool owner to the risk of spillage or a pet or child infiltrating the standing supply. These dangers are significantly less of a concern with benign salt. However, Trumbull admits that it wasn’t love at first sight for his company and saline systems.

“The first years I didn’t have a lot of faith in them,” he says.

The first units Trumbull sold were imported and suffered sporadic operational failure, due to mechanical issues rather than any shortcoming of the underlying technology. But over time, he found manufacturers that delivered a highly reliable unit that led to a renewed confidence offering saline sanitation systems. These units are now more warmly accepted by his customer base.

“Once you adjust to the required intervals of the monitoring needed for maintaining your specific water chemistry parameters, it becomes easy to stay on top of the sanitation requirements of a pool or spa,” Trumbull says. His customers frequently comment that the water feels softer. He also points out an obvious savings. “A forty pound bag of salt – typically enough to treat a 700 gallon spa twice a year – costs around $25 (R220). The amount of package or liquid chlorine products required would be significantly higher treating the same amount of water.”

And while a retrofit installation may require some added upfront costs over a traditionally chlorinated pool or spa, the reliability and reduced traditional chemical costs can often offset this expense. To date, Trumbull says only one of his customers has experienced a salt cell failure, which was attributed to user error.

Trepp says that an active electrolytic cell in a saline pool will show wear and tear over time, but points to his product’s five-year warranty and says “if they’re maintained and sized properly, the life of cells in the field can be substantial. Five to seven years on a cell is a realistic number”, assuming routine and appropriate maintenance.

How salty is it?
Though referred to as ‘salt water’ pools or spas, saline systems don’t replicate the effect of swimming in the ocean or other natural bodies of salt water. “The noticeability of salt is minimal,” Trepp says. Where salt occurs in the ocean in the magnitude of 20 000-35 000 parts per million (ppm), Trepp says that the salt in a saline system is closer to 3 500-4 000 ppm. Trepp compares that salt content to half of what is found in a human tear drop and says the user shouldn’t notice any salty residue.

Trumbull agrees. “Water with a salt content of under 6 000 ppm is still considered to be fresh,” he says. “Your eye contains about 9 000 ppm of salt. At 3 500 ppm, you generally won’t be able to detect the taste the salt.”

One of the most obvious criticisms of a saline system is the corrosive property of salt.

“Anybody who lives in the north knows salt is corrosive,” says David Leech, owner of Caribbean Clear, a company that offers a copper/silver ionisation alternative to salt and chlorine. “Anybody who’s seen salt on the roads knows what it does to metal and concrete.”

Significant splashing can leave salty water outside the pool or spa environment and once evaporation has occurred, the salt remains, if not routinely cleaned away. Among the potential casualties are metallic pool equipment like ladders, the bolts fastening diving boards in place, or even local landscaping or the decking itself. Some manufacturer warranties can be voided if the root source of the damage is salt contamination.

Trumbull admits that some stainless steel filters can suffer from corrosion when working with a salt water system. But Tripp dismisses these concerns. “Salt in solution doesn’t become corrosive until 8 000 ppm,” he says. He concedes that there could be some effect on the metal equipment within the pool when salt levels exceed 8 000 ppm.

On its website, Ecosmarte USA of Richfield, suggests that introducing solid blocks of chlorine in order to eliminate the health risks associated with cyanide-related stabilisers may carry its own set of health risks.

“Sodium absorption through the skin has long been known to present health risks at levels far below the 3 000-5 000 ppm levels salt chlorine generators require,” the company writes on its website. “For nearly 20 years, people with high blood pressure, stroke history or other circulatory system issues have been asked to stop using their water softeners (at 200-400 ppm sodium in the water for just ten minutes in the shower) to avoid the heart mortality risks.”

In 2005 the Santa Clarita Valley Sanitation District of Los Angeles County prohibited the installation of salt-water swimming pools that discharge into the municipal systems. The restrictions carry strict penalties, including potential jail time and a $1 000 fine. Dave Snyder, the Industrial Waste Section Head for the Los Angeles County Sanitation Districts, clarifies that the action of his department was “river specific to that area with low salt tolerance”, with the build-up increase causing difficulty for local strawberries and other crops growing downstream.

The salt moving from the occasional draining of pools with saline systems in the sewer system can cause more severe difficulties for an environment with light rainfall and occasional drought conditions than it would in other circumstances. “We’ve been monitoring for these salts for years and years,” Snyder says. Even still, it suggests that the homeowner should consider investigating local restrictions – or potential restrictions – before initiating an installation.

Endless alternatives
On its website Snyder’s department offers a plethora of pool cleansing technologies as alternatives to traditional chlorine or saline, including ‘activated carbon units, reverse osmosis systems, portable exchange tank softeners, salt-free water conditioning devices, or water filtration systems’.

One such alternative is copper and silver. Leech’s Batesburg-based company has marketed a system of ionisation using a copper and silver alloy since 1982, leveraging the biocidal properties inherent in the metals. Leech says his company’s third-party certified system will keep pool water clean – without the need for typical levels of chlorine (1-3 ppm) and the side-effects such as itchy skin, bleached bathing suits and eye irritation typically associated with traditionally chlorinated pools – and provide a payback in two to three years. However, even Leech’s system requires a trace of 0,4 ppm chlorine.

In contrast, Larry Couture at Ecosmarte USA says that his system, which combines copper and oxygen to clean pool water, requires no additional chemicals. “Because salt generates gas, it is usually a softer, milder chlorine and consumers don’t know of our products, even after 17 years,” Couture says. “It is easy for me to see why half or more of all new pools built currently get a salt-to-chlorine generator. I believe it reached a high of 2/3 on the new construction in 2008 and the trend is now back in our favour.”

Any pool or spa requires some diligence on the part of the owner. “There needs to be some attention to detail regardless of the system,” Leech says. “Improper chemistry can damage pools.”

Different technologies will have differing demands and results.

"Some states require that chemical feeders be able to generate three pounds of chlorine per 10 000 gallons of pool water daily,” Leech says. “Or three pounds of chlorine per 1 000 gallons of spa water per day. This is a conservative and protective sizing requirement. Residential products can be more of a risk since they are more likely to be uncertified for performance and safety and residential product users tend to be less experienced. Combined, this creates a recipe for problems.

“So don’t get in over your head or experience level. Use certified products, follow instructions, and find a good local pool service company to help you start-up or for regular service.”

There is always some level of user maintenance and responsibility. No matter how good the chemical feeding/generation product is, “if you don’t fastidiously maintain water chemistry your chemical feeding efforts will be undermined and bad things can happen, so stay on top of it”.