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SOLAR GLOSSARY
BELOW IS A LIST OF COMMON TERMS;
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.
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 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
DELTA-T CONTROLLER
Delta-T refers to the difference in two temperatures. This term is often used in relation to a solar controller. In such cases 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.
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
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.
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.
HEAT PIPE
An evacuated rod or pipe used for heat transfer.
INSOLATION
Insolation refers to the amount of sunlight falling on the earth.
INSULATION
The ability to protect against transfer of heat/cold.
IRRIDANCE, IRRIDATION
Basically the same as Insolation
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 our 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.
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.
Please find the full glossary for download here;
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