Is Solar Heating For You? Narrative Discussion
In Vermont, November is a quite cloudy month, but it is generally mild.
"IS SOLAR HEATING FOR YOU?, PART 1" |
"PART 2" | "ANALYSIS METHOD"
THE SOLAR RESOURCE - One factor that really helps with solar heating
performance is the fact that the sunshine often comes when you really need
it. In Vermont, November is a quite cloudy month, but it is generally
mild. The cloudiness tends to result from warmer air coming up from the
South. The brutally cold weather that we get in winter, along with much
of the Northern parts of the US, is the result of very clear, cold and
dry air coming down from the North. The result is the most brilliant sunshine
that we get all year, just when it is coldest. This "happy confluence of
solar circumstances" is just what we need to get the most from our solar
heating systems.
SOLAR STORAGE - We all know that the sun doesn't always shine during the day,
and that it never shines at night. This means that we need a certain
amount of storage potential for our solar energy in order for solar to
meet a high percentage of our needs (a high solar heating fraction).
A solar heating system for use in a Vermont home needs about 2 times as many
solar collectors and twice as much thermal storage as a home in Colorado
would. This is not as much of a burden as it may seem. The cost of the
controls and mechanicals will be the same, and if the cost of thermal storage
is reasonable, things can work out fairly well. An alternative would be
to construct a building that conserves energy better in the cloudier climate.
SOLAR HEATING FRACTION - The solar heating fraction is the
percent of your energy need that solar energy will meet. It is a function of the same four
items that are considered for a solar performance calculation, i.e.:
- The Solar Resource.
- The energy requirement to be met.
- The ability to store solar energy for use in cloudy periods.
- The efficiency of the system.
It is theoretically possible to achieve a 100% solar heating fraction in cold
climates, and some purists will do what it takes to do accomplish this
goal. In general however, the over design that is needed to meet peaking
needs under low sun conditions results is a wasted investment for much
of the year. It is neither necessary nor even desirable to reach the 100%
in many cases. Extremes in architecture can be costly. It is never a good
idea to spoil the architecture of a building with too many solar collectors.
But, to each his own.
If a person needed $100 and found a $50 bill on the floor, most people would
be wise enough to pick it up. If a solar energy system "only" provides
50% of the heating requirement, that could still be very nice. Such a system
could provide all of the heat for much of the year and luxurious quantities
of free domestic hot water and ventilation in sunny periods. It should
provide a very nice tax-free return on the investment.
If you factor the four important criteria for solar performance these will
be the results for various areas of the continental United States. We will
assume the example of a 2,000 square ft building, and we will assume the
use of solar collectors measuring 4'x8'. We also assume that the solar
collectors will face within 20 degrees of True South and that the angle
of the collectors will equal the latitude plus 15 degrees.
CLIMATES WITH VERY COLD WINTERS AND SOME PROLONGED CLOUDY SPELLS
(The Northern Tier of the United States)
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| SOLAR FRACTION |
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| 100% |
Architectural flexibility will be very restrictive. You must basically construct an underground
home, or one that is very aggressively bermed with earth. This design will
give very high efficiency and the very high heat storage within the ground
that will be needed. (Solar Option One)
http://www.radiantsolar.com/optionI.php.
You will need 8-10 solar collectors. Cost effectiveness will be good.
|
| 80-90% |
Architectural flexibility will be moderate. Slab on grade construction
will be needed in significant areas of the house. Solar energy can be stored within the
slab and the compacted earth beneath. (Solar
Option One) http://www.radiantsolar.com/optionI.php.
You will need 8-10 solar collectors. Cost effectiveness will be good.
|
| Up to 50% |
Excellent architectural flexibility. No particular measures to store heat within
the structure of the house or the materials that the house is made from.
Use a radiant heating system using the domestic hot water heater as the
heat source. Then use solar energy to make domestic hot water.
(Solar Option 2) http://www.radiantsolar.com/optionII.php. Add
one or two extra domestic hot water heaters for added heat storage.
You can use 5-6 solar collectors. Additional solar collectors will have limited
value because of limited heat storage ability. Cost effectiveness is good
up to about 40-50%, but declines rapidly thereafter.
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CLIMATES WITH SOMEWHAT MILDER WINTERS AND MORE ABUNDANT AND MORE CONSISTANT SUNSHINE
(Southern New England to Virginia, the Midwest, Northern California)
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| 100% |
Architectural flexibility will be very restrictive. You must basically construct an underground
home, or one that is very aggressively bermed with earth. This design will
give very high efficiency and the very high heat storage within the ground
that will be needed. (Solar
Option One) http://www.radiantsolar.com/optionI.php.
You will need 7-9 solar collectors. Cost effectiveness will be good.
|
| 80-90% |
Architectural flexibility will be moderate. Slab on grade construction will be needed
in significant areas of the house. Solar energy can be stored within the
slab and the compacted earth beneath. (Solar
Option One) http://www.radiantsolar.com/optionI.php.
You will need 6-8 solar collectors and cost effectiveness will be good.
|
| Up to 50% |
Excellent architectural flexibility. No particular measures to store heat within
the structure of the house or the materials that the house is made from.
Use a radiant heating system using the domestic hot water heater as the
heat source. Then use solar energy to make domestic hot water.
(Solar Option 2). http://www.radiantsolar.com/optionII.php Add
one or two extra domestic hot water heaters for added heat storage.
You can use 4-5 solar collectors. Additional solar collectors will have limited
value because of limited heat storage ability. Cost effectiveness is good
up to about 40-50%, but declines rapidly thereafter.
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THE SOUTHWEST (COLD WINTERS, GOOD CONSISTANT SUNSHINE)
(Colorado, Arizona and other States with similar climates)
|
| 100% |
Architectural flexibility will be somewhat restrictive. You must construct a home with
considerable thermal mass and good to excellent energy conservation, or
one that is very aggressively bermed with earth. Adobe or masonry is typical.
This design will give very high-energy efficiency and the very high heat
storage within the building and the ground beneath that will be needed.
(Solar
Option One) http://www.radiantsolar.com/optionI.php.
You will need 6-8 solar collectors. Cost effectiveness will be excellent.
|
| 80-90% |
Architectural flexibility will be moderate. Slab on grade construction will be needed
in some areas of the house. Solar energy can be stored within the slab
and the compacted earth beneath. (Solar Option One).
You will need 5-7 solar collectors and cost effectiveness will be excellent.
|
| Up to 80% |
Excellent architectural flexibility. No particular measures to store heat within
the structure of the house or the materials that the house is made from.
Use a radiant heating system using the domestic hot water heater as the
heat source. Then use solar energy to make domestic hot water.
(Solar Option 2) http://www.radiantsolar.com/optionII.php. Add
one or two extra domestic hot water heaters for added heat storage.
You can use 5-6 solar collectors. Additional solar collectors will have limited
value because of limited heat storage ability. Cost effectiveness is good
up to about 60-70%, but declines thereafter.
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CLIMATES WITH MILDER WINTERS AND GOOD SUNSHINE
(Florida, Louisiana, Texas, Southern California)
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| 100% |
Architectural flexibility will be good. You should construct a home of masonry materials
that can store heat (or cool temperatures) and use slab on grade construction
for added thermal mass. Use a radiant heating system using the domestic
hot water heater as the heat source. Then use solar energy to make domestic
hot water. (Solar
Option 2) http://www.radiantsolar.com/optionII.php. Add one extra
domestic hot water heaters for added heat storage. Take advantage of the
cooling benefit when you use water.
You will need 5-6 solar collectors. Cost effectiveness will be excellent.
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| 80-90% |
Architectural flexibility will be very good. Slab on grade construction will be helpful
on the first floor. Solar energy can be stored within the slab, and thermal
mass will help with cooling as well. Use a radiant heating system using
the domestic hot water heater as the heat source. Then use solar energy
to make domestic hot water. (Solar
Option 2) http://www.radiantsolar.com/optionII.php. Add one or
two extra domestic hot water heaters for added heat storage.
You will need 4-5 solar collectors and cost effectiveness will be excellent.
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