10 Considerations for Smart Solar-Heating System Design: Page 2 of 4

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Solar heating systems can be an efficient, economical method of space heating.
Solar heating systems can be an efficient, economical method of space heating. With attention to careful design and sizing for your household’s needs, they can provide decades of productive service.
Solar heating systems can be an efficient, economical method of domestic water heating.
Solar heating systems can be an efficient, economical method of domestic water heating. With attention to careful design and sizing for your household’s needs, they can provide decades of productive service.
Solar heating systems can be an efficient, economical method of pool heating.
Solar heating systems can be an efficient, economical method of pool heating. With attention to careful design and sizing for your household’s needs, they can provide decades of productive service.
A natural gas or propane-fired furnace and water heater take care of DHW and space heating in the absence of sun.
A natural gas or propane-fired furnace and water heater take care of DHW and space heating in the absence of sun.
Heat pumps can heat water for both DHW or space heating, as well as provide stand-alone space heating.
Heat pumps can heat water for both DHW or space heating, as well as provide stand-alone space heating.
Gas or electric on-demand water heaters can act as backup for DHW and space-heating applications.
Gas or electric on-demand water heaters can act as backup for DHW and space-heating applications.
Closed-loop systems using an antifreeze heat-transfer fluid are best for cold climes.
Closed-loop systems using an antifreeze heat-transfer fluid are best for cold climes, but require more maintenance than other system types.
PV-powered DC pumps are a perfect match for SHW circulation, since they run when the sun shines.
PV-powered DC pumps are a perfect match for SHW circulation, since they run when the sun shines.
An open-loop system sends potable water through the collectors.
An open-loop system sends potable water through the collectors. Simple and inexpensive, these systems are best in nonfreezing climates.
Drainback systems allow the collectors to drain to prevent freezing or overheating.
Drainback systems allow the collectors to drain to prevent freezing or overheating.
Roof mounting is common for solar heating systems.
Roof mounting is common for solar heating systems. Collectors can be angled for optimum exposure or set flush for streamlined aesthetics with only a minor decrease in efficiency.
Wall-mounted collectors can be vertical for winter-specific exposure or awning-mounted for year-round exposure and shading beneath.
Wall-mounted collectors can be vertical for winter-specific exposure or awning-mounted for year-round exposure and shading beneath.
A ground mount can get your collectors in the sun when orientation, space restrictions, or shading prevents roof-mounting.
A ground mount can get your collectors in the sun when orientation, space restrictions, or shading prevents roof-mounting.
Shading isn’t always a bad thing: Here, winter sun cuts through deciduous branches, while summer foliage will help prevent overheating.
Shading isn’t always a bad thing: Here, winter sun cuts through deciduous branches, while summer foliage will help prevent overheating.
A simple one-tank system may meet your family’s needs at a reasonable price.
A simple one-tank system may meet your family’s needs at a reasonable price. In most climates, solar hot water systems have a quick payback.
Storage tank volume choice is a factor of climate and collector area.
Storage tank volume choice is a factor of climate and collector area: too much storage and water will never come up to temperature; too little storage and overheating becomes a problem.
SHW can help offset a little or a lot of your DHW and space-heating needs.
SHW can help offset a little or a lot of your DHW and space-heating needs. But beware that oversizing systems can result in wasted money and summertime overheating.
Because swimming pools require lower temperatures, less expensive, unglazed pool-specific collectors can be used.
Because swimming pools require lower temperatures, less expensive, unglazed pool-specific collectors can be used.
Flat-plate collectors are the most common type.
Flat-plate collectors are the most common type, and are available in styles for open- and closed-loop systems, and in horizontal and vertical orientations.
Evacuated tubes are more expensive, but can perform better in situations that require higher temperatures.
Evacuated tubes are more expensive, but can perform better in situations that require higher temperatures.
Good system design is critical to optimize performance.
Whether a system is installed to provide winter space heating or summer water heating affects collector area and tilt angle, and storage tank size. Good system design is critical to optimize performance and meet needs without undue cost or excess heat production.
System components can take up a lot of space, especially in large combisystems.
System components can take up a lot of space, especially in large combisystems.
Solar heating systems can be an efficient, economical method of space heating.
Solar heating systems can be an efficient, economical method of domestic water heating.
Solar heating systems can be an efficient, economical method of pool heating.
A natural gas or propane-fired furnace and water heater take care of DHW and space heating in the absence of sun.
Heat pumps can heat water for both DHW or space heating, as well as provide stand-alone space heating.
Gas or electric on-demand water heaters can act as backup for DHW and space-heating applications.
Closed-loop systems using an antifreeze heat-transfer fluid are best for cold climes.
PV-powered DC pumps are a perfect match for SHW circulation, since they run when the sun shines.
An open-loop system sends potable water through the collectors.
Drainback systems allow the collectors to drain to prevent freezing or overheating.
Roof mounting is common for solar heating systems.
Wall-mounted collectors can be vertical for winter-specific exposure or awning-mounted for year-round exposure and shading beneath.
A ground mount can get your collectors in the sun when orientation, space restrictions, or shading prevents roof-mounting.
Shading isn’t always a bad thing: Here, winter sun cuts through deciduous branches, while summer foliage will help prevent overheating.
A simple one-tank system may meet your family’s needs at a reasonable price.
Storage tank volume choice is a factor of climate and collector area.
SHW can help offset a little or a lot of your DHW and space-heating needs.
Because swimming pools require lower temperatures, less expensive, unglazed pool-specific collectors can be used.
Flat-plate collectors are the most common type.
Evacuated tubes are more expensive, but can perform better in situations that require higher temperatures.
Good system design is critical to optimize performance.
System components can take up a lot of space, especially in large combisystems.

Pump energy type is another factor in solar loop choice. The most common circulating pumps are 120 or 240 VAC. DC pumps are also available that can be energized by PV modules or batteries. AC pumps come in hundreds of sizes and are easy to find at most supply houses or home centers. More expensive DC pumps are available in fewer sizes, but can provide a grid-free solar heating system.

4. Space Available

Calculate how much space is available for the solar thermal collectors. For optimum performance, you will need a shade-free south-facing area for your collectors. It is best to have no shading from 9:30 a.m. to 3:30 p.m. throughout the entire year. If you have any doubts, this can be verified by using a shade analysis tool such as a Solar Pathfinder. Also consider future shading from tree growth or new construction.

Facing the collectors south is important but not critical. If your collectors are 30° east or west of true south, there will only be a 5% to 10% performance penalty—though some areas have late or early fog to consider. Keep in mind that the roof is not the only option—collectors can be mounted on the ground, the side of the building (like awnings), or even pole-mounted.

5. Budget

What’s your budget? This is often the biggest limiting factor. Decide what makes financial sense for you, while still meeting your goals, such as specific building standards like Passivhaus or LEED; carbon dioxide offsets; or total energy offset. Utility grants, state rebates, tax incentives, the anticipation of reduced utility bills; and private or government financing options can help you more accurately arrive at a final up-front cost.

Installation costs vary widely from region to region because of differences in labor cost, permit fees, code requirements, climate-specific equipment, and other region-specific factors. Get estimates from reputable solar contractors to gauge what the cost will be. You can dramatically reduce your system costs by taking advantage of local and state government incentives or utility programs. Also, if you have a federal tax liability, you can take a 30% tax credit on the entire installation cost. Check dsireusa.org for available utility, local, state, and federal incentive programs.

6. Storage Size

Calculate how much solar storage you need—a place to park extra heat until it’s needed. If the sun is shining and there is no immediate load, there is no need to let it go to waste. Water is the most common heat storage medium because of its ease of use and ability to transfer heat easily to a load.

Hot water use is usually sporadic. Solar tanks are usually sized to store a full day’s worth of hot water. A good rule is 1.25 gallons of storage for every square foot of collector in the Northeast and Northwest; 2 gallons per square foot in the Southwest; and 1.5 gallons most everywhere else. Even in locations with excellent winter insolation (like the Southwest), most designers use a 1:2 ratio. Having too much storage can result in the collectors not raising the tank temperature enough each day.

For space heating, it’s a little more complicated. If your building needs a lot of heating even when the sun is out, little storage is needed. But if you also have passive solar heating in your building, you might not need all of the harvested solar hot water until the evening. Storage sizing for space heating systems can be from 1 to 3 gallons per square foot of collector area—it depends on when you will need the heat and when it is available. Thermal mass—such as extra sand under the slab or the concrete slab itself—can also be used for storage by hydronic floor space heating systems.

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