The Flat plate collector system is assumed to consist of a solar panel using propylene glycol as the heat transfer medium, linked to a heat exchanger that transfers the collected solar heat to a storage cylinder. The mains cold water supply is preheated in this cylinder before being fed into the DHW storage tank.
Solar panel:
Area
Aperture area of the solar panel (m2).
Azimuth
Panel azimuth angle in degrees clockwise from north.
Tilt
Panel tilt angle in degrees from horizontal.
Shading factor
If the solar panel is shaded by buildings or other objects the average shading effect can be modelled by reducing the shading factor from the default value of 1.
Degradation factor
This factor accounts for the effects of soiling and aging of the panel.
Conversion efficiency at ambient temperature (η0 ), First order heat loss coefficient (a1 ), Second order heat loss coefficient (a2 )
Data on solar panels expresses the performance of the device in terms of a conversion efficiency at ambient temperature, η 0 , and two heat loss coefficients, a 1 and a 2 . The heat output of the device is written in terms of these coefficients by the equation
W = η0 I – a1 (T-Ta ) – a2 (T-Ta )2
where
W is the heat output per unit panel area
I is the incident solar irradiance (after allowing for shading and degradation)
T is the panel temperature, and
Ta is the outside air temperature.
Values for η 0 , a 1 and a 2 are available from solar panel manufacturers.
Flow rate
The fluid flow rate through the solar panel, expressed per unit panel area. A figure of 50 l/(h.m2) is typical.
Pump power
The rated power of the pump within the solar water heating system.
Heat exchanger effectiveness
The model assumes the storage tank is heated from the collector loop by a heat exchanger of some kind, either an internal coil or an external exchanger. The heat exchanger effectiveness is the ratio of the temperature drop across the heat exchanger on the collector loop side to the maximum theoretical temperature drop (which would bring the collector loop fluid down to the tank temperature).
Storage tank
Volume
Volume of the storage tank. This is used to calculate tank losses.
Storage loss at maximum temperature
The DHW storage tank loss factor (kWh/l/day). This is used, with the preceding parameter, to calculate tank losses.
Tables 2 and 2a from SAP (2005), quoted above in relation to DHW storage, may be helpful in setting this parameter.
