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More
Info on Solar and Radiant Heating:
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Please
note that the answers given are abbreviated in order to be "short and
to the point". The answers are meant to provide a starting point
towards further understanding. Further research into these questions is
encouraged, or feel free to call CCE. Some books may be referenced
elsewhere in this webpage for further information.
How much carbon will a system prevent from entering
the
atmosphere?
This is a simplified answer, but may help for you to understand the
process. Your actual situation will vary with home parameters, system
design, etc....
To calculate your "carbon offset" (for example, with natural gas heat),
determine yearly BTU heat load of the dwelling (including both heating
load and domestic hot water usage). Take 70% of this BTU value
(approximate portion of heat provided yearly by sun in a well designed
system), divide this number by 100,000 (number of BTU's in a "Therm" of
natural gas; look on your monthly bill for present # of therms used).
Take resultant number and multiply it by 11.64 (lbs CO2 in one Therm
natural gas) to get yearly carbon offset. (OR; just call CCE, and we'll
calculate this!)
How much of my annual heat load can be satisfied by
solar
heat?
The answer depends on numerous factors. The answer can be anywhere
between 0-100%! Factors to consider when making this calculation are:
What type of climate/microclimate is the house located in? Was house
designed with passive solar heating principles in mind (see
question/answer below)? How well insulated is the house? What type of
heat delivery system is used (radiators, baseboard, air handlers,
radiant floor, etc.)? How much space is there on the roof for the
collector array? Is there adequate space inside the mechanical room for
a large storage tank? With a reasonably well designed house, a good,
affordable goal may be about 75% of annual fuel replacement cost
compared to a house with a conventional boiler.
Will I need a boiler in the house to provide
backup heat in case the sun doesn't shine?
In almost all cases, yes. Typically, a modulating/condensing boiler is
used for backup. When heat in the solar storage tank is depleted, the
radiant (typically) system will automatically switch over to the boiler
to provide the balance of floor heat necessary to satisfy the home
heating load. The modulating/condensing boiler will only come on when
the sun can't keep up with the load (mostly in December/January, and
decreasing in the "skirt" winter months). Generally, from March thru
early October, most of the heat (home heat and domestic hot water) will
be provided by the solar system. When it is called upon, the mod/con
boiler, which is designed to operate in it's "sweet spot" for
efficiency, will use much less fuel than a typical "traditional"
boiler.
What about using baseboard or radiators with solar
heat?
It can be done, but at lower efficiency than when radiant flooring is
used. This is because all of those other types of heat transfer devices
(baseboard/radiator)are designed to operate at higher temperatures than
a masonry/radiant floor system. Baseboard/radiators generally operate
at about 170-190 degrees, which is rarely available from a solar
system. Staple up type radiant floor systems are OK, but operate at a
higher temperature (perhaps 125-145 degrees) than masonry based
radiant, which can operate as low as 85 degrees (or even lower in some
cases, such as a garage floor). For example, comparing staple up (with,
say, an average heat requirement of 125 degrees) to "slab type" radiant
(with a requirement of, say, 90 degrees), consider this: the staple up
based system will switch over to boiler when the solar storage tank
temperature is drawn down to 125 degrees, whereas a "slab type" radiant
floor can draw down the storage tank temperature to 90 degrees before
the boiler takes over the heat load! (actual numbers vary, depending on
many factors, but this illustrates the general idea). Additionally,
when the storage tank is drawn down to a lower temperature (in the case
of the slab radiant system), it will "grab" more heat the next day from
the solar collectors, because the solar collectors operate most
efficiently with a large heat differential (between storage tank water
and collector absorber plate temperatures)! Bottom line: try and design
the heating system for the lowest temperature possible (within the
given equipment restraints), and this will help both on the solar AND
on the boiler side to improve efficiency.
What's the difference between evacuated tube and flat
plate
collectors?
Flat plate collectors have been in use for over 100 years. They are the
ones that look like large skylights. They are tough and reliable (when
installed properly!). Evacuated tube collectors are glass tubes about 7
ft. high, stacked vside by side to form arrays. They are more efficient
in colder and cloudier conditions (as with some higher altitudes here
in Colorado). They cost more, but are also easier to install in high
places (one person can lift the parts onto a roof by themselves).
How do you store solar heat collected during the
daytime
for later use?
The heat can be stored in a large (300-400 gallon, typically) hot water
storage tank. The hot water from this tank is then pumped into the
heating system later at night when it's most needed. Alternatively, the
heat from the panels can be pumped directly into a high mass floor.
Each system has it's advantages, and the choice of methods depends on
many factors in the building design, as well as how the homeowner wants
the heat distributed. CCE can help you decide on which type of system
would be most appropriate for a particular building design.
What type of system is best; drainback or glycol?
Neither is "best"; the topology chosen depends on the building design,
collector orientation, pipe chase locations, whether the array is
ground mounted, etc. Drainback systems are more efficient in
collection, and don't have overheating issues that are associated with
glycol in the summertime. However, they are susceptible to freezing if
not installed by an experienced professional.
Glycol based systems allow more flexibility in pipe runs, and minimize
concerns about running pipes through unconditioned (unheated) spaces.
They can also be powered with PV powered circulators, for a true "zero
energy use system", which is harder (though not impossible) to do with
a drainback system. Despite which type of system design is chosen, they
should be installed by, or in consultation with, a professional solar
installer, as there are many "gotchas" that can cause serious damage to
your home if not proactively addressed.
What is the difference between "passive" and "active"
solar
heating?
Passive solar heating refers to architectural design features in the
home that capture the sun's heat during daylight hours (and hopefully
retaining this heat through the nighttime hours). Passive design
features include: energy efficient south facing windows, thermal mass
(masonry floors/walls/etc), well designed eaves on the house that allow
sun in the winter but block it in the summer, home orientation on the
property (to capture sun, and avoid cold winter winds), tree and shrub
placement, etc. Passive solar design is the "low hanging fruit" of
solar heating, and should be the first consideration in any heating
system design.
Active solar heating systems utilize collector panels and circulating
pumps to "actively" collect and store the sun's heat, and then move it
around the home for use when/where needed. Active systems augment heat
provided by passive systems, and can boost total solar heat generation
to satisfy as much as 95% of heat load in the case of some well
designed homes!
How much does a solar heating system cost?
Cost varies, and depends on the answers to such questions as: New
construction? Retrofit in existing dwelling? System size/number of
collectors, storage tank type? House design (how easy it is to install
the plumbing/mount the collectors). Give some thought to these
questions, then call CCE for assistance. |