10 Considerations for Smart Solar-Heating System Design

By: 
Kurt Koegel
Last Updated: 
08/02/12
Beginner

Inside this Article

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.
  • Beginner

Off-the-shelf solar heating systems don’t always fill the bill. This is where good design and smart planning come in.

1. System Type

Determine the type of heating your system will be supplementing.

Solar thermal can be used for many applications, from water heating to air conditioning to biodiesel processing, but the most common are domestic water heating, pool heating, and space heating. “Combisystems” cover more than one of these applications.Off-the-shelf solar heating systems don’t always fill the bill. This is where good design and smart planning come in.

2. Backup Source

Figure out what type of backup source will be used.

When your solar heating system can’t take care of the whole load, there are many backup heating choices. The energy source your backup water heater uses will determine the choices you have. For natural gas or propane, traditional tank-type and tankless are the most common. For electricity, you can choose from tank-type, tankless, or heat pump/hybrid water heaters. Gas or electric boilers can also be used to heat water, which is then pumped to an indirect water heater (aka coil tank) or even a plate heater.

For space-heating backup, natural gas, propane, or electric boilers can be used as well as air, ground, or water-sourced heat pumps. The key to selecting is in the heat delivery—the lower the required temperature, the more solar can contribute. Solar thermal is most efficient when the desired water temperature is in the 70°F to 140°F range. Radiant heating works at temperatures from 90°F to 120°F, so this makes it a great match with solar thermal. Next is forced air that works at temperatures from 100°F to 140°F. Last is hot water baseboard heating that works at temperatures between 120°F and 190°F.

In most cases, the solar system ties into the existing space heating system and assists it by preheating the HTF before it gets to the boiler, but after it has left its heat in the floor loop. In this way, solar can contribute the most because the HTF will be at its coldest. If the solar system can produce hotter HTF than comes out of the load, then solar is contributing. If it cannot, then the boiler operates normally with no solar contribution.

3. Solar Loop Type

Specify the solar loop type that will work best for your application and climate. The main choices are direct, glycol, or drainback systems.

A direct system routes potable water directly through the solar collectors. These systems are only used in year-round warm climates (like Hawaii) where the ambient air temperature never drops below freezing.

In a glycol or pressurized closed-loop system, the solar loop and collectors are filled with a glycol antifreeze solution. The collectors can be mounted in any orientation and be located above or below the solar storage because they require pumps. Some drawbacks are antifreeze maintenance and potential summertime overheating.

A drainback system circulates antifreeze or, more typically, plain water through the collectors only when they are warmer than the load or solar tank. The rest of the time, the collectors and outside pipes are “drained back” and empty—the fluid drains to a holding tank. Advantages are less or no fluid maintenance, higher efficiency, and no possibility of overheating. Drawbacks are that larger circulating pumps are needed, and the orientation of the collectors and pipes must allow unfettered draining back to the holding tank.

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