10 Considerations for Smart Solar-Heating System Design: Page 3 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.

7. Percent of Load

Calculate your heating loads. Each person in the home will typically use about 20 gallons of hot water per day. This usually covers bathing, cleaning, and laundry. But “typically” does not fit all: If you have a big bathtub, add accordingly. If you are more conservative than most, then subtract accordingly. If you’re not sure how much hot water you use on a daily basis, install a water meter on the cold water line that feeds your existing water heater. Master Meter makes quality water meters (about $60) that can be bought online.

Determining your space-heating load is more complex. First, do not use your current heater’s size—your boiler may have a 100,000 Btu per hour input, but this does not mean it consumes 100,000 Btu per hour since it cycles on and off. This could be one cycle lasting two minutes every hour in the spring and fall, to one cycle lasting 50 minutes every hour during the height of the heating season. This fluctuating load makes determining the heating load difficult.

The best way to calculate heating load is to use your monthly heating bills or have a heat loss calculation done for your building for every month of the heating season. This information will help you determine how much energy is needed to keep your building comfortable. Next, determine how much of this heating load you want to cover with solar during the winter months. Some people choose to cover all of the winter heating load, but for a more moderate and efficient system, most people aim for covering the spring and fall seasons. This is a common practice where the winter months bring cloud cover. In areas like the Southwest, however, a high solar fraction is possible even in December.

For pool heating, knowing the pool’s surface area is most important, because this is where the majority of heat loss occurs. Is it an outdoor or indoor pool? What months of the year will it be heated? Outdoor pools can gather heat from the sun but can also lose heat to cool ambient temperatures, wind, and evaporation. Indoor pools lose less heat because they are sheltered, but depending on the ventilation system of the building, a lot of heat could be pumped outside to keep the humidity levels low inside the pool room. Another big factor is using a pool cover, which can save up to 50% of the daily heating energy. It works like a comforter, keeping the pool cozy and warm, and, at the same time, slowing evaporation. Armed with this information, you can use a sizing program provided by most solar pool heating manufacturers to determine how many collectors you will need. If you have a separate electric or gas meter for your existing pool heater, you can look at your utility bills to determine the amount of energy it currently consumes.

8. Collector Type

Choose your collectors. The common types are unglazed, glazed flat plate, and evacuated tube. Each works best for a certain job in a certain climate. Unglazed collectors are generally used for year-round pool heating in a warm climate or for seasonal pool heating in cooler climates. Flat plates can be used for many jobs, such as year-round indoor pool heating and domestic water and space heating in most any climate. Evacuated tubes can be used for the same jobs as flat plates, but work best for higher-temperature applications in cloudy or very cold climates.

Once you have decided on a collector type, you will need to choose the model. Many factors should go into your decision, such as sizes available, energy output, and the quality of the components and finished product. Consider the collector’s (and manufacturer’s) reputation, its country of origin (if you like to keep it local), warranty, and, least of all, price. If you simply shop by price, more than likely you will end up disappointed with your purchase. What you are really looking for is the most Btu you can get per dollar. If your collector is cheap, but only lasts a few years, it has not paid you back. Select a collector that balances performance and cost.

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