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Liquid-Based Solar Heating

Air-Based Solar Heating

Selecting the Right Active Solar Heating System for You


As the threat of climate change grows more present, many people are looking for more environmentally-friendly solutions in their day-to-day lives. HVAC systems tend to use a lot of energy when they’re turned on, so finding a more efficient way of heating your house in the winter is a great idea for anyone who’d like to ease the strain on the environment while also saving some money on their monthly electricity bill.


In recent years, customers have begun to embrace a new heating technology called active solar heating. This method is extremely efficient because it uses the sun’s rays as an energy source instead of drawing electricity. Active solar heating systems capture heat from the sun throughout the day and use it to warm your house or business as needed. The first solar heater was patented in the late 1970s, and the technology has only grown and become more popular in the decades since its invention.


Today, Americans are finally starting to embrace solar heating technology. If you think it’s time for a new heating system and you’re interested in giving solar heating a try, here’s everything you’ll need to know to get started.


Liquid-Based Solar Heating

Active solar heating can come in two different forms: liquid-based solar heating, and solar air heating. Liquid solar heating is the most common method and is the most appropriate for a large central heating system that can cover your entire house or place of business. This technology has been used to make solar-powered water heaters for a few decades now and is especially popular in sunny countries like Israel, where about 85% of the water heaters are solar-powered. As liquid-based solar heating technology has advanced, its capabilities have been expanded to include central air heating. Liquid heating is far more efficient than the other types of active solar heating, which makes it perfect for larger central heating systems.


Heat Collectors

Any active solar heating system will start with a collector of some kind. The collector looks a little bit like a standard solar panel and features darkly-colored panes of glass. The glass is specially treated so sunlight can pass through it one way, but can’t escape back out the way it came in. This keeps the heat trapped inside the collector. Once the sunlight has passed into the collector, there are a few different ways that it can be distributed through your house. The difference between these methods is what separates the main types of active solar heating systems.


A liquid-based solar heating system will have a tube just underneath the glass that holds either water, antifreeze, or a refrigerant. This liquid, called the “working fluid,” absorbs the heat from the sunlight as it passes through the tube. The working fluid flows through the tube quickly to make sure that heat doesn’t escape. From there, the working fluid flows into a storage area where the heat is collected and kept until the system detects a need for it.


Heat Storage in Liquid-Based Solar Heating Systems

Liquid systems can store heat in a few different ways, but the most common is to use a large tank of water. As the heated working fluid passes through the collector tube, it transfers the heat to the water inside the storage tank before flowing back up to collect more heat from the sun. Some liquid systems use large slabs of masonry to store heat, but water tanks are the most common form of heat storage.


If you’re planning on installing a liquid-based solar heating system, you’ll have to think about where to place the storage tank. The larger the building, the larger the tank will have to be, so you’ll have to make sure you have enough space for it in your house or place of business. Because the tanks are full of water, they can get fairly heavy, so your best bet is to keep it on a lower floor just to be safe. There are plenty of factors to consider when installing a storage tank, including the material, size, and insulation, but that’s something your HVAC contractor should be able to figure out for you.


Liquid-Based Solar Heat Distribution

There are a few different methods you can use to distribute the heat from a liquid solar heating system, but the most popular are radiant floors, hot water radiators, or a standard central air system. A radiant floor will be the most expensive to install, but it’s also more efficient than the other methods. With a radiant floor system, solar-heated distribution fluid will pass through small tubes embedded in the floor tiles. As the fluid flows through the tiles, they get warmer and radiate heat up into the room. This method works well at cooler temperatures and is by far the most energy-efficient way of distributing solar heat. In fact, a well-designed radiant floor system doesn’t even require a water tank, just distributing the heat directly to the floor instead of diverting it to the storage tank first. However, carpeting will reduce the efficiency of the system, and it can also be a little slow to start, so you might have to wait a few minutes before you start feeling the heat.


You can also use a standard hot-water baseboard or radiator to distribute heat, although these systems are less efficient when heated with solar power. Radiators require water at a very specific temperature, between 160° and 180° Fahrenheit. Because solar heated distribution fluid typically stays between 90° and 120° Fahrenheit, the radiator will need to further heat the liquid before it can warm the room. However, this is still a relatively easy and inexpensive way to incorporate solar heating into an existing heat system.


Liquid-based solar heating can also be incorporated fairly easily into your standard ducted central air system. The process works pretty much the same way as a regular heat pump or air conditioner. The solar-heated distribution liquid flows from the storage tank into a large coil placed inside the central air system. A blower then passes air from outside across the coil, which heats it. The warm air is then distributed through your ducts, much like any other ducted HVAC system. While this is not quite as efficient as a radiant floor, it’s a pretty straightforward way to add solar power to your existing HVAC system.


Air-Based Solar Heating

Solar air heating works pretty similarly to liquid-based systems. The sunlight passes through the glass of the collector, but instead of using working fluid and distribution fluid to transfer the heat throughout the system, this method uses air. From the collector, the system can then blow the hot air directly into the room or pass it through the hot air coil of a central air system. Some solar air systems use a bed of stones as heat storage, but we don’t recommend this method because condensation in the stone bed can cause mold to grow, potentially affecting the air quality inside your home.


Solar air heating does have a few advantages over liquid-based heating. Because air can transfer heat faster than water, a solar air system will be able to generate heat earlier in the morning and later at night than a liquid system. That means that over the course of each year, a solar air system will generate more total heat than a liquid system of the same size. Solar air systems are also a little less delicate. They won’t freeze in the winter like liquid systems sometimes do, and a leak in the collector or distribution ducts won’t cause the whole system to fail. Finally, solar air systems can be integrated into the existing structure of your home more easily, and don’t require a storage tank.


That being said, solar air systems are much less efficient than liquid systems. Air is a less effective and efficient medium for heat transfer than water is, so you’ll be losing more heat along the way. All told, a liquid-based solar heating system will pretty much always be more powerful and efficient than an air-based one of the same size, despite requiring a little more maintenance. This is especially true if you’re trying to distribute heat to an entire house instead of a small area.


Single-Room and Passive Solar Air Heaters

Because solar air systems are simpler than their liquid-based counterparts, they’re ideal for smaller, room-sized heaters. A single small collector placed on the roof or an exterior wall can easily provide enough heat for a bedroom or other room. In fact, while a factory-built small solar air collector can be purchased for only a few hundred dollars, lots of people are experimenting with their own DIY solar collectors that can be made cheaply and effectively with a little hard work.


These small solar collectors work essentially the same way the larger ones do. Inside an airtight metal frame, a small collector attracts the sun’s rays, which pass through it. The sunlight then heats the air trapped inside the collector itself. Most pre-built solar collectors will use a small electric fan or blower to force the warmed air back into the room, although some do-it-yourselfers are eschewing the fan and instead using two openings to the room, one above the other. Cold air enters the collector through the lower opening and heats up in the sunlight. Because hot air rises, the newly-warmed air rises and escapes back into the room through the higher opening. These are called passive solar heaters.


While DIY passive heaters provide much less warmth than an active one would, they can still be a fun project and an inexpensive way to warm your bedroom during the fall or winter. We’ve seen passive solar air heaters made of sheet metal, PVC pipes, and even empty soda cans. Just keep in mind that you’ll only be receiving a small amount of heat from these homemade heaters, and they don’t have any way to store heat for when it’s cloudy. If you’re interested in making your own DIY solar heater, we recommend checking out YouTube or just browsing around on the internet. There are a lot of engineering geniuses out there!


Transpired Air Collectors

For larger buildings that require a lot more ventilation, like factories and other industrial buildings, air can be solar heated extremely efficiently with a transpired air collector. Transpired collectors take up a lot of space, but they’re fairly simple and highly efficient. They don’t require as many moving parts as a standard active solar heater and are relatively inexpensive to purchase and install. Commonly referred to as “solar walls,” transpired collectors are becoming increasingly popular for use in industrial settings for their efficiency, simplicity, and the fact that they require very little maintenance.


Unlike most active solar collectors, transpired air collectors use large, dark metal sheets instead of the more expensive glazed glass. These sheets are perforated with small holes and attached to an outside, south-facing wall. Ideally, you should try to cover the entire wall, since the larger the collector, the more heat you’ll be able to distribute. The perforated metal sheets are fixed close to the wall but with a few inches of separation, creating an air space between the wall and the collector. Finally, a ventilation fan is embedded near the top of the wall.


When the ventilation fan is turned on, it draws air in from the outside through the small holes in the metal. The solar heat absorbed by the metal sheets then warms the air, and the hot air is drawn into the building through the ventilation fan. In this way, it works fairly similarly to the passive solar heaters you can make on your own, but with the addition of the fan and the holes to create more airflow.


While transpired collectors aren’t ideal for today’s tightly-sealed houses, they’re perfect for large industrial buildings that need a ton of ventilation. More and more industrial businesses are adopting solar walls to keep their buildings warm, so if you own a factory and you’re tired of paying for heating, you might consider building one.


Benefits of an Active Solar Heating System

The main benefits of an active solar heating system are twofold. First, installing a solar-powered heater can drastically cut down on your heating bills every winter. Active solar heating does use some electricity to move the working liquid or air around inside the system, as well as to distribute the heat throughout your house. However, because the actual heat and energy generation is coming from the sun, you should still be able to drastically reduce your heating bills with a solar heating system. This is especially true if you live in an area with colder temperatures but plenty of clear, sunny weather. Even if you live somewhere warmer, a solar heating system can still save you plenty of money year-round by replacing your electric water heater.


Additionally, some of the costs of purchasing and installing an active solar heating system can be recovered through federal tax credits, which are worth 26% of the value of the system and can be claimed on your federal income tax returns. Some states, like New York, Rhode Island, and Iowa, offer additional tax credits for solar power users, as well as sales tax exemptions that save you a little extra.


Solar heating systems are also significantly better for the environment than traditional HVAC systems. Central heating uses a tremendous amount of electricity every year, and much of that power is still generated by power plants that use coal and other finite natural resources while releasing CO2. According to current emissions reports, coal-based electricity generation accounts for about 30% of global CO2 emissions. The sun, on the other hand, is endlessly generating energy that can be harnessed by solar heating systems without causing damage to the environment.


Selecting the Right Active Solar Heating System for You

Every building is unique and has unique heating requirements. Local ordinances and building codes can also place restrictions on the solar heating options available to you, so your best bet is to work with an HVAC contractor with experience in active solar heating to figure out which system is best for you.


As a general rule, it’s most efficient to design an active solar heating system that provides between 40% and 80% of your home’s heating needs. Installing a system that provides less than 40% of your heating needs is no longer cost-effective, and reaching 100% is impractical and difficult to achieve. Many building codes and mortgage lenders require a backup heating system in case of persistent cloudy weather that drains the entirety of your solar-powered heat storage. However, a well-built and designed house can generate close to 100% of its heating requirements through active solar heating and some auxiliary passive solar collectors. If you’re concerned about installing an inefficient backup heating system, you can make do with something as simple as a wood stove without raising your power bill during periods of cloudy weather.


Active Solar Heating System Maintenance

Like any HVAC system, an active solar heater requires regular maintenance to make sure it’s running properly. Though some maintenance can be performed on your own, we recommend bringing in an HVAC professional at least once a year to make sure things are going smoothly. Here’s a quick checklist of items you should look over when performing maintenance on your active solar heating system:

  • Collector Shading – Shade on your solar collectors can drastically reduce the efficiency of the system, so it’s worth checking at least once a year to make sure that vegetation growth hasn’t created shade over the collectors.
  • Collector Cleaning – Rain should usually be enough to keep the collectors clean, but you should still check every once in a while to make sure they’re not getting dirty.
  • Collector Glazing and Seals – Check once a year for cracks in the glazing and seals. If air can escape, the efficiency of the system is reduced.
  • Roof Connections and Support – Check around the areas where the collectors attach to the roof and make sure nothing is leaking. Make sure the nuts and bolts of the support structures are secure.
  • Storage Systems – Make sure there are no cracks in the storage tank if you have a liquid-based system. You should also keep an eye out for any rust or corrosion if the tank is metal.
  • Valves and Dampers – If you have a liquid system, make sure the pressure relief valve is functional and not stuck. If you have an air system, make sure the dampers open and close properly and aren’t getting stuck.
  • Plumbing and Ductwork – If your system is liquid-based, make sure all the pipes holding the distribution liquid are secure and aren’t leaking anything. For air-based systems, you should do the same with the ducts. Additionally, it’s worth checking the insulation around the pipes and ducts to make sure it hasn’t degraded or come apart.
  • Pumps and Blowers – Periodically, listen to make sure the pumps (for liquid systems) or blowers (for air systems) are switching on and running properly when the sun is up. Typically, the system should be running by mid-morning, so if it gets to about noon and it hasn’t turned on yet, you might have a problem. This is usually a failure of the starting capacitor, which can be easily replaced without having to buy a new pump or blower.


Through regular yearly maintenance, you can keep your active solar heating system running for quite some time. Typically, these systems come with a warranty for 10 years, but they can be kept functional for decades after that as long as you keep them in good working order.


Call Today for More Information

If you live in Sonoma, Napa, or Marin counties and you’re interested in installing an active solar heating system, feel free to get in touch with Valley Comfort Heating & Air either online or by phone at (707) 539-4533. We’re also happy to answer any additional questions you might have about solar heating.