Water Heating
From Antivist
Tankless Water Heaters Tankless water heaters are home appliances used to heat water for residential or commercial use. Also known as 'on demand' and 'instant' water heaters, tankless are designed to heat the water as the water flows through. Unlike conventional tank water heaters, tankless do not have any type of storage tank. Tankless water heaters come in natural gas, propane, and electric models. Tankless water heaters can be broken down into two categories; 'full on/full off' and 'graduated'. Full on/full off units do not change the power output at all. The unit is either on or off. Graduated tankless water heaters base the power output on the flow of water running through the unit. This is usually done through the use of a 'flow switch' and means that you will receive the same output temperature of water at .5 gallons per minute (gpm) as you will at 3.0 gpm.
Because energy is not required to maintain a tank of water at a high temperature, the net energy savings can be substantial on site. However, if enough people implement this practice in a city, it creates a peak electricity problem that can end up wasting more energy than is being saved.
Solar Heaters In some locales, solar powered water heaters are used. These are installed outside dwellings, typically on the roof or nearby, and consist of a tank and panel in which water circulates. Circulation is caused by natural convection or by a small electric pump. At night, or when insufficient sunlight is present, circulation through the panel can be stopped by closing a valve and/or stopping the circulating pump, to keep hot water in the storage tank from cooling.
Hands-on Heating Be it fire or stove, one can simply heat small quantities of water as needed. How practical this turns out to be is up to you.
Simple Solar Water Heater
Solar water heaters are based on a common natural phenomenon: cold water in a container exposed to the sun undergoes a rise in temperature. The solar water heater is basically a flat-plate collector and an insulated storage tank. The collector is commonly blackened metal plate with attached metal tubing and is usually provided with a glass cover and a layer of insulation beneath the plate. The collector tubing is connected by piping to a tank that stores hot water for use during non-sunny periods. When mounted on a roof or other suitable support, the collector absorbs radiation, by transfer of resulting heat to water circulating through the tubing, hot water is supplied to storage tank. In the most common designs, the storage tank is located above the top of the collector. The elevated position of the tank results in natural convection: water circulates from the collector to the tank.
When Solar water heater technology is so simple, how is it that developing countries are yet to catch up? The reasons are not far to seek. The main constraint is prohibitive cost. For e.g. In India a 100 litre solar water heater costs around Rs. 12,000/- (about US $ 300). Another Interesting point is that not many people living in towns and villages have access to overhead water storage tank to get continuous supply of cold water.
To overcome the above barriers, the author designed and tested a vertical and cylindrical Solar Water Heater.
Design Details
Two vertical and cylindrical collectors made of stainless steel (normally used in the manufacture of drinking water drum) of height 0.6 m and diameter 32 cm are made and placed one over the other with thermocole in between as well as at the bottom to prevent heat losses. The top cylindrical auxiliary tank is provided with an inlet at the top and provided with a cap and the same is provided with an opening at the bottom, which is connected to the bottom cylinder with a hose pipe (strong enough to withstand high temperature). There is a lever attached to the pipe to control water flow. The bottom cylinder is provided with outlet at the top from which water is drawn. Both the cylinders are provided with concentric rings to provide gap and covered with high-density transparent polyethylene sheet to simulate green house effect. A lotus flower shaped reflector (as shown in the picture) made of stainless steel acts as a reflector. This takes into account the diurnal motion of the sun.
The insulator is made of bamboo basket of dimensions height 1.3 m and diameter 45 cm (circular) and covered with 6mm glass wool (rock wool) and over it with transparent polyethylene cover so that the whole setup is airtight.
Operation
The collector is filled with potable water in the morning at 8 a.m. and is covered with the insulator (bamboo basket) at 4 p.m. The hot water can be used either in the evening, night or next morning. Hot water upto 700 C is obtainable depending on the sunshine. In 15 hours of storage about 70 C drop in the hot water temperature is observed. This 100 litre unit costs around Rs. 6,000/- (about US$ 150) in South India and will be highly useful as a pre-heater for cooking, for bathing, for washing cloths and utensils, for rural schools, hospitals etc.
Advantages
� The unit is mobile, modular and easy to install and dismantle for transporting. � No necessity of cold water supply through pipes. � No need for over head storage water tank. � There is no need to have separate collector as it is an integrated system. � Since the collector is made of stainless steel, the hot water will be hygienic. � Because of the omni-directional reflector, relatively higher water temperatures are obtained even in moderate sunshine. � The unit occupies less space being vertical and circular, on the ground or roof. � All the materials used in the fabrication of this simple and cost-effective solar water heater are available locally. � The unit is durable except that the polyethylene cover has to be replaced once in 4 months, which costs just Rs. 30/- (about US 70 cents). � By the usage of pre-heated water for cooking from this unit, considerable fuel such as firewood, kerosene, gas, electricity etc. can be conserved.
