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Sun Volt Solar Blog

earth, the final frontier

Clean Energy, Clean Environment

We are at a cross roads in human history, we can choose to continue on as we have been, or we can make a change to improve our future and quite possibly the future for several generations to come. We are here to promote energy independence, a better environment with a higher return on investment for your hard earned money. It is what I believe in, it is why I am in the solar business.

Solar Thermal Systems

21 Feb 08 | General

When you say solar, most people assume that you are talking about photovoltaics. Solar thermal systems have been around for longer than photovoltaics and have a proven track record of working well and paying back there costs many times over.

I install both types, and lately I have been receiving quit a few calls regarding solar thermal (i.e. solar hot water, or radiant floor heating) systems. I think this will continue as the price of energy goes up.

A solar thermal system move fluid through solar collectors, which collect heat.  The fluid is then stored or used in the building. In reality, a solar thermal system is about plumbing.  A Solar Domestic Hot Water (SDHW) system has three unique parts that other hot water systems or heating systems don’t have. The first is the solar collectors, the second is some type of heat exchanger and the third is some type of controller. As regarding the solar collectors, I believe that SDHW systems work best with flat plate collectors.

The flat plat collector design has been around for many years. Newer solar selective coatings have been created that increase the system efficiency. In addition to that, better insulation and better high transmisity glass have all improved on the flat plate collector design. Evacuated tubes run at higher temperatures and have problems with the seals between the glass tube and the copper pipe on the inputs and outputs of each tube.

The next unique thing in a solar system is the heat exchanger. The heat exchanger takes the hot fluid from the solar collector and cools it with the fluid from the solar hot water tank. This can be implemented in a number of ways. Some heat exchangers are part of the solar storage tank, some are a part of a drainback tank, and some are external.  All heat exchangers are made of metal (stainless steel or copper) and use counter-flow properties to move the heat from one fluid reservoir to another.

Finally, the system controller, which measures the temperature of the collector outputs and the solar storage tank. If there is enough energy in the collectors to transfer to the storage tank, the controller turns the system on, which begins collecting energy.

Beyond that, a solar system is copper piping, valves, drains, hot water tanks, pumps, and other miscellaneous hardware which is all available at the local plumbing supply house.

Solar thermal systems that are designed for space heating are very similar to SDHW, only they are usually quit a bit larger with more storage.

In most cases, all solar thermal systems should have some way of operating in backup mode in case there is a long period of inclement weather. These back up systems entail some type of conventional heating system installed in parallel with the solar system. For example a SDHW system may have an electric tank or electric element in the solar tank designed to turn on if the water temperature gets too cool. A radiant floor heating system may have a small oil or gas fired backup furnace in standby duty.

A well designed solar system should be designed to produce about 80 to 85 percent of the energy needs. More than that and the system design will be too large, causing it to over produce and over heat under normal operating conditions. Less than that and you are leaving a good deal of money on the table, to be taken by the gas/oil companies.

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21 Feb 08 | General | Comments (0)

Radiant floor heating

12 Nov 07 | Conservation, Environment, Geothermal, Solar Hot Water

Buildings use a lot of energy. Heating, cooling, hot water supply, lighting, and appliances can use lots of electricity, oil, gas, etc. Each BTU that is used requires that something be converted from fuel to energy and by products. The by products in question depend on the type of fuel, but they can be anything from CO2 to NOx, SOx, and mercury to name but a few. As you can see, the more energy efficient our homes become, the less it will cost to energize them and the better off it will be for the environment.

I spoke with somebody on the phone this morning about solar space heating. This is a topic of conversation I had with my brother in law last year at some point. Basically, in this climate, effective solar space heating consists of passive solar design and or radiant floor heating.

Conventional hydronic heating equipment e.g., radiators and base board convectors, requires water temperatures above 140 degrees Fahrenheit (60 C). During the coldest months of the year, December and January, a flat plate collector would not be able to collect enough energy to heat the water to that temperature. Evacuated tube collector may be able to, but the volume of water would not be enough. Most HVAC professionals agree that solar coupled with a radiant floor heating system, where water temperatures only need to be about 85 degrees, works the best.

Radiant floor heating is a really cool idea. These systems work great when a house is built on a concrete slab. Several inches of rigid foam installation is used to insulate the concrete slab from the earth. The heating loops are embedded in the concrete slab and the entire system can be broken up into one room zones. The heating loops use low cost PEX (Cross-linked polyethylene) pipe, which is easy to work with. With a solar system, a small conventionally fired (oil or gas) furnace is required in case there are several days of cloudy weather that prevent the solar collectors from working.

Obviously this type of installation requires a great deal of pre-planing in order to work right. House siting, orientation, solar panel positioning, tilt angles, and heat storage tank options all need to be worked out before the house is built. A new house needs to be designed from the bottom up to accommodate solar radiant floor heating, passive solar design can also be incorporated to enhance the thermal design.

In addition to solar, radiant floor heating works will with ground source geothermal heat pumps. These systems can supply a good deal of heat to larger structures that may be too large to heat with solar collectors alone.

Retro-fitting older houses with radiant floor heating is also possible. Older homes with wood floors require a number of compromises to get the system to work efficiently. In addition to that, before a radiant heating system is installed in an older home, the structure should have a complete energy audit done. This will ensure that the building envelope is where it should be regarding insulation, weather stripping, windows, etc. It makes no real sense to install an energy efficient system if all that energy is going to go out the window anyway.

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12 Nov 07 | Conservation, Environment, Geothermal, Solar Hot Water | Comments (0)