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Here are a list of some terms you may encounter
when reading through our web site.
We have tried to make explanations as easy to understand as possible,
but if you are still un-clear please feel free to contact
us.
A-B-C-D-E-F-G-H-I-P
A
Aperture: The part of the collector through
which light enters. For evacuated tubes this refers to the cross-sectional
surface area of the outer clear glass tube measured using the internal
diameter, not the outside diameter.
(Eg. 0.0548m x 1.72m = 0.094m2).
1.72m is the exposed length of the evacuated tube.
Absorber: The part of the collector that
actively absorbs the light rays. For solar tubes this is defined
as the cross-sectional area of the inner tube (selective coated)
measured using the outside diameter. (Eg. 0.047 x 1.72m = 0.08m2)
This value is used when calculating efficiency values. For solar
tube collectors with reflective panels, the entire circumferential
surface area of the inner tube is often used when calculating absorber
area, as the reflective panel is supposed to reflect light onto
underside of the evacuated tube. The Apricus AP solar collector
does not use reflective panels, learn why by clicking here.
B
BTU - Stands for British Thermal Units.
This is an imperial unit of measurement for heat widely used in
the US and also in the UK. The conversion to the metric unit kWh
is: 1 kWh = 3412Btu, and for surface area values, 1kWh/m2/day
= 314Btu/ft2/day
C
Collector - A solar collector is not really
a solar water heater. A solar water heater is a system which may
include a tank, pump, controller and solar collector panel. A solar
collector is that part of the system which absorbs the sun's energy
and converts it into heat. The Apricus
AP model is separate from the tank as so is a solar collector.
Celsius - The metric unit for temperature
measurement. Convert as follows:
Fahrenheit = (oC x 1.8) + 32
Celsius = (oF - 32)/1.8
For Delta-T measurements the relative temperature difference is
needed.
Eg. Delta-T = 7oC turn pump on, Delta-T 2oC
turn pump off. How much is that in oF??
The conversion from Fahrenheit to Celsius is simple:
Fahrenheit = oC x 1.8
Celsius = oF / 1.8
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D
Delta-T Controller: Delta-T refers to the
difference in two temperatures. This term is often use in relation
to a solar controller. In such case the Delta-T is the difference
between the solar collector temperature and the temperature of the
water in the solar storage tank. A Delta-T controller can be configured
to turn on the pump when the Delta-T difference exceeds a certain
level (Eg.7oC / 12.7oF)
and off again when the temperature difference drops below another
setting (Eg. 2oC / 3.6oF).
The controller turns on the pump when there is heat potential in
the manifold. A Delta-T controller can also be used to provide freeze
protection by circulating warm water from the tank through the manifold
when the manifold temperature drops below 5oC.
E
Efficiency: Solar collector efficiency
is usually expressed as a percentage value, or in a performance
graph. When assessing a collector's performance make sure it is
based on the correct surface area values. Eg. If performance values
are based on gross area, then the gross area must be used when
determining total heat output. IAM
values have a significant influence on actual heat output
throughout the day, and should be considered. Looking at just
the percentage efficiency value will not give a true indication
of daily heat output.
Efficiency testing is usually completed by testing bodies such as
SPF, SRCC
and other government approved testing bodies.
Tm* is the x axis value on performance graphs for solar collectors.
Tm* is calculated as:
(water temp - ambient temp)/Insolation
Eg. (44oC - 20oC)/800Watts = 0.03
For more information on efficiency please click
here.
F
Flow Rate: The volume of water
flowing through plumbing in a given period of time. Usually measured
in volume/minute or volume/hour. 1 Litre/min = 0.264 US Gallon/min
G
Gross Area: The total surface
area of the collector including the frame, manifold and absorber.
This area is often used when comparing collectors, but a better
comparison to use is value for money.
Roof size is not usually a limiting factor for domestic solar water
heating installations, so the size of the collector is not really
that important.
H
Heat Pipe: An evacuated rod or pipe used
for heat transfer. Click here for more
information.
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I
Insolation: Don't confuse this with insulation
- the one letter change makes a big difference. Insolation refers
to the amount of sunlight falling on the earth.
Click here to learn more
Insulation: The ability to protect against
transfer of heat/cold. Apricus
solar collectors use compressed glass wool to insulate the
header from heat loss. Glass wool has excellent insulation properties,
is very light and can withstand high temperatures, making it an
ideal choice for a solar collector. It is made from a least 80%
old glass bottles and can be recycled so is very environmentally
friendly.
Irridance, Irridation: Basically the same as
Insolation - explained above.
Incidence Angle Modifier (IAM): refers
to the change in performance as the sun's angle in relation to the
collector surface changes. Perpendicular to the collector (usually
midday) is expressed as 0o, with
negative and positive angles in the morning and afternoon respectively.
Collectors with a flat absorber surface, which includes some types
of evacuated tubes, only have 100% efficiency at midday (0o),
whereas Apricus solar tubes provide peak efficiency mid morning
and mid afternoon, at around 40o
from perpendicular. This results in good stable heat output for
most of the day.
P
Pressure: Refers to the water
pressure in the system. The conversions for the most commonly used
units are: 1 bar = 1.02kg/cm2 = 14.5psi = 100kPa = 0.1Mpa
= 10m water head
If there are any words that you think we should
add to this glossary, please let us know.
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