Heating from Active Solar

The heated fluid—either liquid or air—is transmitted by active solar heating systems either directly to the interior space or to a storage system for later use. In the event that the solar system is unable to provide enough space heating, an additional or backup system provides the additional heat. Liquid systems are more usually used when storage is present and are perfect for absorption heat pumps, coolers, and boilers with hot water radiators. Forced air systems can incorporate liquid or air-based technologies.

Active Solar Liquid Heating

The best solar liquid collectors for central heating. They are the same ones used in residential solar water heating systems. Flat-plate collectors are the most common type of collector, though concentrating and evacuated tube collectors are also available. A heat transfer or “working” fluid, such as water, antifreeze (typically non-toxic propylene glycol), or another type of liquid, absorbs the solar heat in the collector. A controller activates a circulating pump when it’s time to let fluid flow through the collector.

The liquid’s temperature barely climbs by 10° to 20°F (5.6° to 11°C) during this time due to how swiftly it moves through the collector. When a smaller volume of liquid is heated to a higher temperature, the system’s efficiency decreases and the amount of heat lost from the collector increases. The liquid is transferred to a storage tank or a heat exchanger for immediate use. Additional system components include piping, pumps, valves, an expansion tank, a heat exchanger, a storage tank, and controls.

The heat transfer fluid affects the flow rate.For further details on the various varieties of liquid solar collectors, their sizes, maintenance requirements, and other issues, see solar water heating.

Heat Storage in Liquid Systems

Liquid systems store solar heat in water tanks or the brick mass of a radiant slab system. In tank-type storage systems, heat from the working fluid is transferred to a distribution fluid using a heat exchanger either outside or within the tank.

Tanks may or may not be pressurized, depending on the architecture of the entire system. Consider a storage tank’s price, size, durability, placement (outdoor or in the basement), and installation requirements before choosing one. If a tank of the required size cannot go through the doorways that are currently in place, you might need to build a tank on the spot. Additionally, tanks must abide by regional building, plumbing, and mechanical requirements as well as temperature and pressure restrictions. Keep in mind the sort of protective coating or sealing needed to prevent leaks or corrosion, as well as the quantity of insulation needed to prevent excessive heat loss.

Specialty or specialist tanks could be needed in systems with unusually high storage requirements. They are frequently composed of stainless steel, fiberglass, or high-temperature plastic. There are other concrete and wooden tanks (for hot tubs). Due to its size and weight, each tank form has advantages and disadvantages and all call for careful installation. It might be more practical to use several smaller tanks rather than one large one. The simplest storage option is to use standard domestic water heaters. They meet the requirements set forth by building rules for pressure vessels, are easy to install, and are lined to prevent corrosion.

Heat Transfer in Liquid Systems

You can use a radiant floor, hot water baseboards or radiators, or a central forced-air system to distribute the solar heat. A radiant floor system circulates warm liquid throughout the room by pumping it through pipes embedded in a thin concrete slab floor. Due to its efficiency at low temperatures, radiant floor heating is very advantageous for liquid solar systems. A properly designed system might not need a separate heat storage tank, even though most systems include them for temperature control. A standard boiler or even a home water heater can be used to produce backup heat. The slab is usually finished with tiling. Radiant slab systems require longer than other types of heat distribution systems to “warm up” the house after a chilly start. However, once they get going, they produce a constant stream of heat. The system’s effectiveness will be reduced by rugs and carpeting.For more details, see radiant heating.

Hot-water baseboards and radiators require water that is between 160° and 180°F (71° and 82°C) in temperature to function properly. Flat-plate liquid collectors are commonly used to heat the transfer and distribution fluids to temperatures between 90° and 120°F (32° and 49°C). It is necessary to increase the baseboards’ or radiators’ surface area, employ a backup system to boost the temperature of the solar-heated liquid, or swap to a medium-temperature solar collector in favor of a flat-plate collector in order to use baseboards or radiators with a solar heating system.

There are various ways to incorporate a liquid system into a forced-air heating system. The fundamental design demands for the installation of a liquid-to-air heat exchanger, also known as a heating coil, before the primary room-air return duct reaches the furnace. Air returning from the living room is warm as it travels through the liquid in the heat exchanger that has been heated by solar energy. The furnace supplies additional heat as needed. At the lowest operating temperature of the collector, the coil must be large enough to transfer enough heat to the air.

Preheating ventilation

In solar air heating systems, air acts as the working fluid, absorbing and transferring solar energy. Solar air collectors can either directly heat certain rooms or pre-heat the air entering a heat recovery ventilator or passing through the air coil of an air-source heat pump.

Since air collectors produce heat earlier and later in the day than liquid systems do, they may provide more useable energy throughout the course of a heating season. Unlike liquid systems, air systems do not freeze, and small gaps in the collection or distribution Ducts will impair performance but won’t significantly affect how the system works. Solar air collectors, however, function at lower efficiency than solar liquid collectors because air is a less effective heat transfer medium than liquid.

Although some early systems did this to store energy, it is not recommended due to the inefficiencies involved, the danger of condensation and mold growth in the rock layer, and the detrimental impact that moisture and mold have on interior air quality.

Solar air collectors are typically installed behind walls or roofs to hide their appearance. For instance, air flow pathways could be incorporated into a tile roof to utilize the heat that is absorbed by the tiles.

Heaters for Rooms

The heating of one or more rooms can be accomplished by installing air collectors on a roof or an exterior (south-facing) wall. DIYers have the option of building and installing their own air collector even though factory-built collectors for on-site installation are available. For a few hundred dollars, a basic window air heater collector can be built.

The heat-absorbing black metal plate for the collector has glazing in front of it and is enclosed in an airtight, insulated metal frame. The air in the collector is warmed by the plate after it has been heated by solar radiation. Air is drawn out of the space by an electric fan or blower, collected, and then blown back into the space. Ducts are needed to transport air between the room and the collector when using roof-mounted collectors. Directly on a south-facing wall, wall-mounted collectors are installed, and holes are made into the wall for the collection air input and outlets.

In an existing window aperture, straightforward “window box collectors” fit. Both active and passive methods are available. When using a passive kind, air enters the collector at the bottom, heats up as it rises, and then enters the room. When the sun is not shining, a baffle or damper prevents reverse thermosiphoning, which is the movement of room air back into the panel. Because the collector area is so small, these devices only produce a little quantity of heat.

Collectors for Transpiring Air

Using a straightforward mechanism, transpired air collectors warm buildings by soaking up the sun’s heat. The collectors are mounted over the south-facing walls of buildings and are made of black, perforated metal panels. Between the old wall and the new facade, a space is created with air. Even on sunny days when the outside air is frigid, the black exterior facade quickly warms up by absorbing solar radiation.

Through tiny openings in the collectors and the air space between them and the south wall, a fan or blower forces ventilation air up through these openings and into the building. Up to 40°F of airflow across the collectors is heated by the solar energy they have absorbed. Transpired air collectors do not require pricey glazing, in contrast to other space heating solutions.

Transpired air collectors are typically not ideal for the tightly sealed dwellings of today. Instead, they are best suited for large structures with heavy ventilation loads. Small transpired air collectors, on the other hand, could be used to warm the air coil on an air source heat pump or to pre-warm the air entering a heat recovery ventilator, increasing the efficiency and comfort level of the latter on chilly days. On the cost-effectiveness of doing this with a transpired air collector, however, there is currently no information.

Aspects of Active Solar Heating Systems That Are Economical

Active solar heating systems are most cost-effective when they replace more expensive heating fuels like electricity, propane, and oil in cold climates with abundant sunlight. Several states offer sales tax exemptions, income tax credits or deductions, and property tax exemptions or deductions for solar energy systems. Could insert the following here: At DSIRE, you can find a list of incentives for renewable energy sources, including active solar thermal.

The cost of an operable solar heating system will vary. Commercially available collectors have at least a ten-year warranty and ought to last for many more years. By using a collector that would otherwise be idle to heat water in the summer, an active space heating system can operate more economically.

Using an active solar energy system to heat your home can drastically lower your winter heating costs. A solar heating system will help lessen the quantity of greenhouse gases and air pollution that are produced when you heat your home or generate energy using fossil fuels.

Selecting and Sizing a Solar Heating System

When selecting the ideal solar energy system, it’s crucial to take your home’s location, architecture, and heating needs into account. Local covenants may restrict your options; for instance, homeowner organizations may prohibit the installation of solar collectors on particular dwelling components (although many homeowners have been successful in doing this in the past).

The local environment, the type and effectiveness of the collector(s), and the collection area all affect how much heat a solar heating system may generate. The most economical choice is normally to design an active system to meet 40% to 80% of the home’s heating needs. Systems that offer less than 40% of a home’s heat are rarely economically feasible, with the exception of when using solar air heater collectors that heat one or two rooms and require no heat storage. It may not even require much more heat from sources other than the sun in a well-built, well-insulated home that uses passive solar heating techniques. Instead, it will require a smaller, less expensive heating system of any sort.

The majority of building codes and mortgage lenders need a backup heating system, in addition to the fact that it is often difficult and expensive to design an active system to produce enough heat 100% of the time. Supplemental or backup systems supply heat if the solar system is unable to meet the needed heating load. Both a wood fire and a conventional central heating system are suitable fallback options.

Solar heating systems: Building Codes, Covenants, and Regulations

Before constructing a solar energy system, you should investigate the area’s construction codes, zoning regulations, subdivision covenants, and any other special requirements. You most certainly require a building permit in order to install a solar energy system on an existing building.

While the majority of towns and communities support home renewable energy installations, there are a few where such installations are more of a novelty and as such may not have been covered by their laws. You must adhere to the most recent construction and legal requirements while installing your system.

Solar panel installation compliance with zoning and building codes is typically a municipal problem. Even if there is a state-wide building code, your city, county, or parish is likely to enforce it. The following are typical problems homeowners have encountered with building codes:

• overly heavy for the roof,
• Insufficient heat exchangers,
• incorrect wiring,
• unauthorized tampering with sources of drinkable water.

Possible zoning problems include the following:

• interfering with side yards,
• putting up unauthorized protrusions on roofs,
• placing the system too close to property lines, such as streets.

Additional local rules, such as covenants imposed by the homeowner’s association, subdivision, or neighborhood, must also be followed. It is simple to overlook these covenants, historic district restrictions, and floodplain rules. For information on what is necessary for local compliance, get in touch with your local government’s zoning and building enforcement divisions as well as any pertinent homeowner, subdivision, neighborhood, and/or community associations (s).

Solar heating system controls

Controls for solar heating systems are often more complex than those for conventional heating systems since they have to consider more signals and manage more components (including the conventional back-up heating system). Solar controls are utilized to regulate the system using sensors, switches, and/or motors. The system’s other controls prevent the collectors from freezing or heating up excessively.

The brain of the control system, a differential thermostat, measures the temperature differential between the storage unit and the collectors. When the collectors are 10° to 20°F (5.6° to 11°C) warmer than the storage unit, the thermostat activates a pump or fan to circulate water or air through the collector to heat the storage medium or the residence.

These controls operate, perform, and cost differently. Certain control systems monitor the temperatures of various system components to evaluate the system’s performance. Microprocessors are used in the most sophisticated systems to control and optimize the heat flow to storage spaces and other regions of the house.

Low voltage, direct current (DC) pumps or blowers (for air collectors) can be powered by solar panels (for liquid collectors). The solar collector absorbs as much heat from the sun as the solar panels are capable of generating. In order to maximize the amount of solar gain to the working fluid, the blower or pump speed is precisely sized. In low-sun conditions, the blower or pump operates slowly; in high-sun conditions, it operates swiftly.

It might not be essential to use separate controllers when used with a room air collection. Furthermore, this ensures that the system will work in the event of a utility power outage. Although it is costly for large installations, a solar power system with battery storage can also supply power to run a central heating system.

Installing and Maintaining Your Solar Heating System

Effective siting, system design, installation, and component quality and durability all affect how well an active solar energy system functions. Although today’s collectors and controllers are of the highest standard, finding a trained contractor who can correctly design and install the system may be challenging.

After installation, a system needs to be carefully maintained in order to maximize performance and avoid breakdowns. You should create a calendar outlining the maintenance chores that the component makers and installer prescribe for your installation because different systems require various kinds of maintenance.

Most solar water heaters are currently covered by your homeowner’s insurance policy. However, freezing-related damage is typically not. Contact your insurance provider to find out more about its policy. It is best to notify your provider in writing that you have a new system even if they will cover it.