Tag Archives: Types

Types of Solar Water Heaters

Types of Solar Water Heaters

Solar water heaters can be either active or passive. An active system uses an electric pump to circulate the heat-transfer fluid; a passive system has no pump. The amount of hot water a solar water heater produces depends on the type and size of the system, the amount of sun available at the site, proper installation, and the tilt angle and orientation of the collectors.

Solar water heaters are also characterized as open loop (also called “direct”) or closed loop (also called “indirect”). An open-loop system circulates household (potable) water through the collector. A closed-loop system uses a heat-transfer fluid (water or diluted antifreeze, for example) to collect heat and a heat exchanger to transfer the heat to household water.

Active Systems

Active systems use electric pumps, valves, and controllers to circulate water or other heat-transfer fluids through the collectors. They are usually more expensive than passive systems but are also more efficient. Active systems are usually easier to retrofit than passive systems because their storage

tanks do not need to be installed above or close to the collectors. But because they use electricity, they will not function in a power outage. Active systems range in price from about ,000 to ,000 installed.

Open-Loop Active Systems

Open-loop active systems use pumps to circulate household water through the collectors. This design is efficient and lowers operating costs but is not appropriate if your water is hard or acidic because scale  and corrosion quickly disable the system.

These open-loop systems are popular in nonfreezing climates such as Hawaii. They should never be installed in climates that experience freezing temperatures for sustained periods. You can install them in mild but occasionally freezing climates, but you must consider freeze protection.

Recirculation systems are a specific type of open-loop system that provide freeze protection. They use the system pump to circulate warm water from storage tanks through collectors and exposed piping when temperatures approach freezing. Consider recirculation systems only where mild freezes occur once or twice a year at most. Activating the freeze protection more frequently wastes electricity and stored heat.

Of course, when the power is out, the pump will not work and the system will freeze. To guard against this, a freeze valve can be installed to provide additional protection in the event the pump doesn’t operate. In freezing weather, the valve dribbles warmer water through the collector to prevent freezing.

Closed-Loop Active Systems

These systems pump heat-transfer fluids (usually a glycol-water antifreeze mixture) through collectors. Heat exchangers transfer the heat from the fluid to the household water stored in the tanks. Double-walled heat exchangers prevent contamination of household water. Some codes require double walls when the heattransfer fluid is anything other than household water. Closed-loop glycol systems are popular in areas subject to extended freezing temperatures because they offer good freeze

protection.

However, glycol antifreeze systems are a bit more expensive to buy and install, and the glycol must be checked each year and changed every 3 to 10 years, depending on glycol quality and system temperatures. Drainback systems use water as the heattransfer fluid in the collector loop. A pump circulates the water through the collectors.

The water drains by gravity to the storage tank and heat exchanger; there are no valves to fail. When the pumps are off, the collectors are empty, which assures freeze protection and also allows the system to turn off if the water in the storage tank becomes too hot.

Pumps in Active Systems

The pumps in solar water heaters have low power requirements, and some companies now include direct current (DC) pumps powered by small solar-electric (photovoltaic, or PV) panels. PV panels convert sunlight into DC electricity. Such systems cost nothing to operate and continue to function during power outages.

Passive Systems

Passive systems move household water or a heat-transfer fluid through the system without pumps. Passive systems have no electric components to break. This makes them generally more reliable, easier to maintain, and possibly longer lasting than active systems.

Passive systems can be less expensive than active systems, but they can also be less efficient. Installed costs for passive systems range from about ,000 to ,000, depending on whether it is a simple batch heater or a sophisticated thermosiphon system.

Batch Heaters

Batch heaters (also known as “bread box”  or integral collector storage systems) are simple passive systems consisting of one or more storage tanks placed in an insulated box that has a glazed side facing the sun. Batch heaters are inexpensive and have few components—in other words, less maintenance and fewer failures. A batch heater is mounted on the ground or on the roof (make sure your roof structure is strong enough to support it). Some batch heaters use “selective” surfaces on the tank(s).

These surfaces absorb sun well but inhibit radiative loss. In climates where freezing occurs, batch heaters must either be protected from freezing or drained for the winter. In welldesigned systems, the most vulnerable components for freezing are the pipes, if located in uninsulated areas, that lead to the solar water heater.

If these pipes are well insulated, the warmth from the tank will prevent freezing. Certified systems clearly state the temperature level that can cause damage. In addition, you can install heat tape (electrical plug-in tape to wrap around the pipes to keep them from freezing), insulate exposed pipes, or both.

Remember, heat tape requires electricity, so the combination of freezing weather and a power outage can lead to burst pipes. If you live in an area where freezing is infrequent, you can use plastic pipe that does not crack or burst when it freezes. Keep in mind, though, that some of these pipes can’t withstand unlimited freeze/thaw cycles before they crack.

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Written by YoniL

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Types and Prevention of Bacteria

What is bacteria?

Bacteria are among the oldest living organisms on Earth, and are very small. Because the bacteria structure is so minute, it can only be seen through a microscope. Bacteria is commonly found in the ground, water and in other living organisms. While some types of bacteria can cause diseases and become harmful to the environment, animals and humans, others offer benefits that we likely could not live without.

Different Types Of Bacteria

Aerobic and anaerobic bacteria:
Bacteria are also classified based on the requirement of oxygen for their survival. Bacteria those need oxygen for their survival are called Aerobic bacteria and bacteria those do not require oxygen for survival.

Staphylococcus Aureus

Staphylococcus aureus bacteria are present in the nasal passages, throats, hair and skin of 50 percent of healthy people, according to the U.S. Food and Drug Administration (FDA).

Autotrophic and heterotrophic bacteria:
This is one of the most important classification types as it takes into account the most important aspect of bacteria growth and reproduction. Autotrophic bacteria (also known as autotrophs) obtain the carbon it requires from carbon-dioxide.

Listeria monocytogenes

Eating food contaminated with listeria bacteria can cause an infection called listeriosis, along with meningitis, encephalitis and intrauterine infections.

Food Safety Of Bacteria
Food Safety can no longer be ignored. Regularly the public learns of food borne illness outbreaks. Some are small in scale and others are large, nevertheless all jolt public confidence in our industry. Moreover, very few operations survive the aftershock of a food poisoning incident.

Always wash cutting boards, knives and other utensils with hot soapy water after they come in contact with raw meat, poultry and seafood. Then sanitize with 1 teaspoon liquid chlorine bleach per quart of water.

Make sure there are no cold spots in food (where bacteria can survive) when cooking in a microwave oven. For best results, cover food, stir and rotate for even cooking. If there is no turntable, rotate the dish by hand once or twice during cooking.

Bacteria Live on Human Skin

When you hear the word “bacteria,” most people people either get a disgusted look on their face or proceed to find the nearest anti bacteria cleaner. What most people don’t know is that one of the places with the most bacteria is their own skin.

Types of bacteria found on the body

Bacteria are often known as the causes of human and animal disease. However, not all bacteria are pathogens.

Bacteria put the tang in yogurt and the sour in sourdough bread; bacteria help to break down dead organic matter; bacteria make up the base of the food web in many environments.

We also benefit from the helpful bacteria that live inside of us. It is estimated that between 5,000 and 10,000 different types of bacteria inhabit the human body. In the large intestine a complex microflora community synthesizes vitamins such as vitamin K, folic acid and biotin. Within days after birth, newborns are colonized by Lactobacilli, a group of helpful bacteria that convert milk protein to lactic acid. The bacteria remain present throughout life. These microbes are widely used in the production of sour milks, yogurt and cheese.

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