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Green Energy Services - Residential - Solar Thermal

Residential Applications For Solar Energy: Solar Thermal (Hot Water)

About solar Hot Water: For thousands of years, humans have heated water with sunshine simply by leaving a bucket of water in the sun. It takes a lot of energy to heat water. Typically, up to 30% of a home’s energy consumption is used just to heat water for bathing, laundry and cleaning.  By installing a solar hot water system, homeowners can significantly reduce their monthly utility bill by using a free renewable energy source. Installing a solar hot water system is typically the first and most cost-effective step when turning to the sun for energy. Even if a photovoltaic system is your primary interest, a solar (thermal) hot water system along with a PV system will provide the best economics and space-efficiency on your roof.

Technology for solar thermal has had great innovations in the recent decade bringing better efficiency, cost-effectiveness and reliability not previously known.

  • Drain Back Systems have a fail-safe freeze protected with thermal limiting (active, indirect): Collector water is separate from potable water and the collector water drains into a special tank to prevent freezing and overheating concerns, once potable water reaches proper temperature or if no sunlight (heat) is available.

  • Glycol Systems: Indirect Heating, Differential or Photovoltaic (PV) Controlled Antifreeze Protection (active, indirect): Collector water is separate from potable water and contains non-toxic propylene glycol antifreeze. This is sometimes referred to as a “pressurized glycol” system and is freeze tolerant. The small electric circulation pump can be powered by a small PV collector.

  • Active Direct Systems: Direct Heating, Differential or PV Controlled (active, direct): Potable water is circulated from the storage tank to the collector when heat is available. No additional heat exchanger is required as the collector serves this purpose. The small electric circulation pump can be powered by a small PV collector. This system is for tropical, non-freezing climates.

  • Integrated Collector Storage “ICS” (passive, direct): Potable water is both pre-heated and stored in a roof-top unit before going into a conventional water heater. This basic system uses regular “street” or well water pressure to circulate water and does not require pumps or temperature controllers, but is subject to freeze damage.

  • Thermo-siphon (passive, direct): Potable water is naturally circulated from the collector to the storage tank positioned above the collector(s). Based on the principle that hot water rises, these self-contained systems heat water without use of pumps or controllers, but are subject to freeze damage. These are typically used in tropical and/or developing countries.

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Each of the above systems has their own benefits, limitations and aesthetic considerations. There are many factors that go into selecting a system that meets your needs. As we can have cloudy days and/or high-demand times for hot water, our systems include back-up heating (using electric or gas) to ensure you are never without hot water. Having a solarenergy.com dealer perform a professional site survey is your first step in having a properly sized and installed solar hot water system. Because there are different types of systems and each system requires proper sizing (based on total usage, peak demand and part of the country), it is a critical task to ensure its performance and durability.

The Economics of a Solar Water Heater
Solar water heating systems usually cost more to purchase and install than conventional water heating systems. However, a solar water heater can usually save you money in the long run.
How much money you save depends on the following:

  • The amount of hot water you use
  • Your system's performance
  • Available financing and incentives
  • The cost of conventional fuels (natural gas, oil, and electricity)
  • The cost of the fuel you use for your backup water heating system, if you have one.

On average, if you install a solar water heater, your water heating bills should drop 50%–80%. Also, because the sun is free, you're protected from future fuel shortages and price hikes.

If you're building a new home or refinancing, the economics are even more attractive. Including the price of a solar water heater in a new 30-year mortgage usually amounts to between $13 and $20 per month. The federal income tax deduction for mortgage interest attributable to the solar system reduces that by about $3–$5 per month. So if your fuel savings are more than $15 per month, the solar investment is profitable immediately. On a monthly basis, you're saving more than you're paying.

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Energy-Efficient Water Heating
To lower your water heating bills, try one or more of these energy-saving strategies:

Reduce Hot Water Use for Energy Savings

You can lower your water heating costs by using and wasting less hot water in your home. To conserve hot water, you can fix leaks, install low-flow fixtures, and purchase an energy-efficient dishwasher and clothes washer.

Fix Leaks

You can significantly reduce hot water use by simply repairing leaks in fixtures—faucets and showerheads—or pipes. A leak of one drip per second can cost $1 per month.
If your water heater's tank leaks, you need a new water heater.

Install Low-Flow Fixtures

Federal regulations mandate that new showerhead flow rates can't exceed more than 2.5 gallons per minute (gpm) at a water pressure of 80 pounds per square inch (psi). New faucet flow rates can't exceed 2.5 gpm at 80 psi or 2.2 gpm at 60 psi. You can purchase some quality, low-flow fixtures for around $10 to $20 a piece and achieve water savings of 25%–60%.

Showerheads

For maximum water efficiency, select a shower head with a flow rate of less than 2.5 gpm. There are two basic types of low-flow showerheads: aerating and laminar-flow. Aerating showerheads mix air with water, forming a misty spray. Laminar-flow showerheads form individual streams of water. If you live in a humid climate, you might want to use a laminar-flow showerhead because it won't create as much steam and moisture as an aerating one.
Before 1992, some showerheads had flow rates of 5.5 gpm. Therefore, if you have fixtures that pre-date 1992, you might want to replace them if you're not sure of their flow rates. Here's a quick test to determine whether you should replace a showerhead:

  • Place a bucket—marked in gallon increments—under your shower head.
  • Turn on the shower at the normal water pressure you use.
  • Time how many seconds it takes to fill the bucket to the 1-gallon (3.8 liter) mark.

If it takes less than 20 seconds to reach the 1-gallon mark, you could benefit from a low-flow shower head.

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Faucets

The aerator—the screw-on tip of the faucet—ultimately determines the maximum flow rate of a faucet. Typically, new kitchen faucets come equipped with aerators that restrict flow rates to 2.2 gpm, while new bathroom faucets have ones that restrict flow rates from 1.5 to 0.5 gpm.
Aerators are inexpensive to replace and they can be one of the most cost-effective water conservation measures. For maximum water efficiency, purchase aerators that have flow rates of no more than 1.0 gpm. Some aerators even come with shut-off valves that allow you to stop the flow of water without affecting the temperature. When replacing an aerator, bring the one you're replacing to the store with you to ensure a proper fit.

Purchase Energy-Efficient Dishwashers and Clothes Washers

The biggest cost of washing dishes and clothes comes from the energy required to heat the water. You'll significantly reduce your energy costs if you purchase and use an energy-efficient dishwasher and clothes washer.

Dishwashers

It's commonly assumed that washing dishes by hand saves hot water. However, washing dishes by hand several times a day can be more expensive than operating an energy-efficient dishwasher. You can consume less energy with an energy-efficient dishwasher when properly used and when only operating it with full loads.

When purchasing a new dishwasher, check the Energy Guide label to see how much energy it uses.

Dishwashers fall into one of two categories: compact capacity and standard capacity. Although compact-capacity dishwashers may appear to be more energy efficient on the Energy Guide Label, they hold fewer dishes, which may force you to use it more frequently. In this case, your energy costs could be higher than with a standard-capacity dishwasher.

One feature that makes a dishwasher more energy efficient is a booster heater. A booster heater increases the temperature of the water entering the dishwasher to the 140ºF recommended for cleaning. Some dishwashers have built-in boosters, while others require manual selection before the wash cycle begins. Some also only activate the booster during the heavy-duty cycle. Dishwashers with booster heaters typically cost more, but they pay for themselves with energy savings in about 1 year if you also lower the water temperature on your water heater.

Another dishwasher feature that reduces hot water use is the availability of cycle selections. Shorter cycles require less water, thereby reducing energy cost.

If you want to ensure that your new dishwasher is energy efficient, purchase one with an ENERGY STAR® label.

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Clothes Washers

Unlike dishwashers, clothes washers don't require a minimum temperature for optimum cleaning. Therefore, to reduce energy costs, you can use either cold or warm water for most laundry loads. Cold water is always sufficient for rinsing.
Inefficient clothes washers can cost three times as much to operate than energy-efficient ones. Select a new machine that allows you to adjust the water temperature and levels for different loads. Efficient clothes washers spin-dry your clothes more effectively too, saving energy when drying as well. Also, front-loading machines use less water and, consequently, less energy than top loaders.
Small-capacity clothes washers often have better Energy Guide label ratings. However, a reduced capacity might increase the number of loads you need to run, which could increase your energy costs.
If you want to ensure that your new clothes washer is energy efficient, purchase one with an ENERGY STAR label.

 

Illustration of a water thermostat with the dial set at 120 degrees Fahrenheit.Lower Water Heating Temperature for Energy Savings


You can reduce your water heating costs by simply lowering the thermostat setting on your water heater. For each 10ºF reduction in water temperature, you can save between 3%–5% in energy costs.

Although some manufacturers set water heater thermostats at 140ºF, most households usually only require them set at 120ºF. Water heated at 140ºF also poses a safety hazard—scalding. However, if you have a dishwasher without a booster heater, it may require a water temperature within a range of 130ºF to 140ºF for optimum cleaning.

Reducing your water temperature to 120ºF also slows mineral buildup and corrosion in your water heater and pipes. This helps your water heater last longer and operate at its maximum efficiency.

Consult your water heater owner's manual for instructions on how to operate the thermostat. You can find a thermostat dial for a gas storage water heater near the bottom of the tank on the gas valve. Electric water heaters, on the other hand, may have thermostats positioned behind screw-on plates or panels. As a safety precaution, shut off the electricity to the water heater before removing/opening the panels. Keep in mind that an electric water heater may have two thermostats—one each for the upper and lower heating elements.

Mark the beginning temperature and the adjusted temperature on the thermostat dial for future reference. After turning it down, check the water temperature with a thermometer at the tap farthest from the water heater. Thermostat dials are often inaccurate. Several adjustments may be necessary before you get the right temperature.

If you plan to be away from home for at least 3 days, turn the thermostat down to the lowest setting or completely turn off the water heater. To turn off an electric water heater, switch off the circuit breaker to it. For a gas water heater, make sure you know how to safely relight the pilot light before turning it off.

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Insulate Your Water Heater Tank for Energy Savings

Unless your water heater's storage tank already has a high R-value of insulation (at least R-24), adding insulation to it can reduce standby heat losses by 25%–45%. This will save you around 4%–9% in water heating costs.
If you don't know your water heater tank's R-value, touch it. A tank that's warm to the touch needs additional insulation.
Insulating your storage water heater tank is fairly simple and inexpensive, and it will pay for itself in about a year. You can find pre-cut jackets or blankets available from around $10–$20. Choose one with an insulating value of at least R-8. Some utilities sell them at low prices, offer rebates, and even install them at a low or no cost.

Insulating an Electric Water Heater Tank

You can probably install an insulating pre-cut jacket or blanket on your electric water heater tank yourself. Read and follow the directions carefully. Leave the thermostat access panel(s) uncovered. Don't set the thermostat above 130ºF on electric water heater with an insulating jacket or blanket—the wiring may overheat.

You also might consider placing a piece of rigid insulation—a bottom board— under the tank of your electric water heater. This will help prevent heat loss into the floor, saving another 4%–9% of water heating energy. It's best done when installing a new water heater.

Illustration showing insulation jackets for electric and gas water heater. The electric water heater has cut-outs in the insulation for the heating coil elements, and the gas heater has cut-outs for combustion air. The insulation placed on top of the heaters has cut-outs for the heat trap pipes.

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Insulating a Gas Water Heater Tank

The installation of insulating blankets or jackets on gas and oil-fired water heater tanks is more difficult than those for electric water heater tanks. It's best to have a qualified plumbing and heating contractor add the insulation. If you want to install it yourself, read and follow the directions very carefully. Keep the jacket or blanket away from the drain at the bottom and the flue at the top. Make sure the airflow to the burner isn't obstructed. Leave the thermostat uncovered, and don't insulate the top of a gas water heater tank—the insulation is combustible and can interfere with the draft diverter.

Insulate Hot Water Pipes for Energy Savings
Insulating your hot water pipes reduces heat loss and can raise water temperature 2ºF–4ºF hotter than uninsulated pipes can deliver, allowing for a lower water temperature setting. You also won't have to wait as long for hot water when you turn on a faucet or showerhead, which helps conserve water.

Insulate all accessible hot water pipes, especially within 3 feet of the water heater. It's also a good idea to insulate the cold water inlet pipes for the first 3 feet.

Use quality pipe insulation wrap, or neatly tape strips of fiberglass insulation around the pipes. Pipe sleeves made with polyethylene or neoprene foam are the most commonly used insulation. Match the pipe sleeve's inside diameter to the pipes outside diameter for a snug fit. Place the pipe sleeve so the seam will be face down on the pipe. Tape, wire, or clamp (with a cable tie) it every foot or two to secure it to the pipe. If you use tape, some recommend using acrylic tape instead of duct tape.

On gas water heaters, keep insulation at least 6 inches from the flue. If pipes are within 8 inches of the flue, your safest choice is to use fiberglass pipe-wrap (at least 1-inch thick) without a facing. You can use either wire or aluminum foil tape to secure it to the pipe.

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