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.
Aperture: The outside 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. 0.058m x 1.80m = 0.1044m2). 1.80m 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 coated with a special substance (AI-N/AI) which is used to absorb solar radiation and trap it within the Evacuated Tube, increasing the efficiency of the system and measured using the outside diameter. (Eg. 0.047 x 1.8m = 0.085m2) 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.
BTU: Equal to British Thermal Units. This is 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
Collector: A solar collector is a typical part of the solar water heater.But a system always include a solar pannel(such as solar collector) ,a pump,a water tank,a control and a working station. A solar collector is the mainly part of the system which transfer the light into heater.
The WesTech SP model is separate from the tank, so that it is a solar collector.
Celsius: The metric unit for temperature measurement. Here are convert equation:
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: Delta-T refers to the difference in two temperatures. This term is often use in relation to a solar controller.The Delta-T is the difference between the circulation liquid temperature and the temperature of the water in the solar storage tank.If the Delta-T difference exceeds a certain level (Eg.7oC / 12.7oF),the pump turns on. When the temperature difference drops below another setting (Eg. 2oC / 3.6oF), a Delta-T controller can turn on the pump. The controller turns on the pump if only there is heat potential. 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, ENEA 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.
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. Click here for more information.
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.
Westech solar collectors use rock wool to insulate the header from heat loss. The choice of rock wool insulation is important for a number of reasons: Rock wool can handle high temperatures, in fact it is non-flammable Provides excellent insulation performance (often used in cavity insulation) Is environmentally friendly as it is a natural, recyclable material Focus collectors are as much as possible, a "Green" product.
As you can see from the above picture, the rock wool is compressed into blocks. Each block is 106cm long, so 4 are used for a 20 tube collector, 6 in a 30 tube collector. The mold shape fits tightly around the header pipe and tube port shape to ensure maximum insulation
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 ,whereas WesTech 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.