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SunWater Pics 080Heating domestic hot water is an important topic as people focus on reducing both energy usage and greenhouse gasses.  People across the country are beginning to recognize that there are better alternatives to typical hot water tanks and boilers that are for the most part inefficient and major contributors of green house gas emissions.

In fact, nearly 30% of a typical homes energy budget goes to water heating.  Tankless water heaters have become one of the most popular ways to heat water in an eco-friendly way but there are other alternatives such as solar hot water systems and ultra high-efficiency water heaters that should be explored as well.  Let’s take a look at some of the options available to make your hot water heating system as efficient and green as possible.

In a typical natural gas fired hot water heater, water is stored in a cylindrical tank and is kept hot by a burner that uses natural gas as its fuel.   The average family of four using this type of water heater can expect it to emit almost a ton of carbon each year into the environment.  These types of tanks remain popular because of their lower price point and are widely installed by plumbers.  There are also tank-based electric hot water heaters that use an electric element to heat the water but it takes much more energy to heat water with electricity compared to gas.

One way to reduce the carbon output is to use a more efficient hot water heater and tankless hot water heaters accomplish this by heating water only as it is being used.  Instead of keeping a cylinder of water hot at all times, when there is a demand for hot water the tankless unit heats the water as it flows through thus eliminating the need to store water.  These systems can be fueled by either gas or electricity and are typically 20% (or more) efficient than your traditional hot water heater.

There are other advantages of these tankless systems as well.  There is less space needed for the unit as it does not store water.  They also provide endless hot water within the flow rate limits of the system.   But this can also be a disadvantage of the system- without a limit to the amount of hot water available some people actually find that their hot water usage goes up which offsets the efficiency advantage.

There are other disadvantages as well- the systems are more expensive than your traditional systems and it costs more to install.  Often the supply line- whether it be natural gas or electricity- must be upgraded to give the system the higher amounts of energy needed to instantly heat the water and this adds to the labor costs to install the system.  The tankless systems also tend to take a little longer to deliver hot water and the unit must be sized correctly or there will be difficulties in its ability to heat water.

Recently, there have been some product innovations that have dramatically increased the efficiency of the traditional tank- style gas water heaters as well as tankless water heaters.  The new ultra-efficient systems are called this because they achieve efficiency rates in the 90-99% range by sending the hot exhaust gasses generated by the burner through a heat exchanger through the water thus giving it a second method of being heated.  Many of these systems are also modulating meaning they can heat the water in the tank at different rates depending on the rate of hot water use.

One important thing to remember about either of these systems is that the source of fuel to heat the water is most likely coming from a non-renewable source.   This is where solar water heating can be a great alternative.

Solar water heating uses the sun’s renewable energy to heat a tank of hot water that can be used for domestic hot water.  Solar collectors heat fluids traveling through them and that heat is then transferred to a solar storage tank where water temperatures can often exceed 150 degrees (the typical temperature of water used in a house is around 110 degrees or less).   Because the solar storage tanks are very well insulated, they can store the heat for a longer period of time.  These systems do require conventional systems to serve as back up when solar energy isn’t available to heat the water.

The most common way the system is set up is to have the solar generated hot water  that is stored in the solar tank feed hot water into the water heaters that were already discussed .  But rather than having cold water coming into these systems from the water main the water is already heated by the sun which saves on the energy costs of heating cold water up to the desired temperature.

Typical solar hot water systems sized appropriately for the domestic hot water load can offset up to 70% or more of that hot water load.  So rather than just making the system more efficient, the system uses the sun as a free and renewable source of energy that does not emit carbon and other pollutants.

So what are the disadvantages?  The initial price of the system is often cited as the primary reason more people aren’t investing in the systems.  There is more labor required to install the systems and the systems also cost more compared to traditional hot water systems.  But there are a variety of tax incentives and rebates available for solar hot water systems today and many municipalities are beginning to offer low-interest finance programs that allow people to invest in solar hot water without the initial upfront cost.   Also, people don’t usually think of the cost of using a traditional system over the life of the system but these traditional systems will always be using fuel that must be purchased in order to heat the water.  How much natural gas or electricity will be used over the lifetime of a traditional tank?

If a solar hot water system is within the budget and it can be backed up by a high-efficiency water heating system than this combination presents the best way to save money over the long term and to cut down on greenhouse gas emissions.   Any of the systems discussed here can go a long way to reducing greenhouse gasses and saving money as well.

Category: Water Heaters
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Posted On : Monday, October 12, 2009

Making hot water from the sun...

SunWater Solar is a design/build company based in the San Francisco Bay Area, specializing in solar water heating systems. The company provides these systems for many types of commercial projects. More»


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