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The following is a guideline on recommended pipe diameters for larger installations.
Pump sizing should be an additional consideration when installing larger systems.
Pump sizing
All Firebird solar pump stations include a circulating pump suitable for most domestic solar applications.
When installing a solar system, the following information should be checked to ensure sufficient pump pressure
is present:
1. Total volume (litres) of fluid in collector. Guideline of 1 litre per m
2
collector.
2. Total volume (litres) in pipe work system.
The volumes (litres) should be, less than that of the pump flow rate
i.e.
2 Flat Panels, 3l volume pipework =
total volume (1.4 x 2) + 3 = 5.8l/min. requirements.
Standard pump 13l/min., therefore system pump okay.
Should you have any queries or require additional calculations to be undertaken please contact our technical
department.
Expansion vessel sizing
The purpose of an expansion vessel is to absorb the volume increase of the water/anti freeze mixture in the
pressurised circuit as the temperature increases. At all times, the expansion vessel is installed on the return line
of the solar circuit and the pipe should be un-insulated. A guideline calculation for solar expansion vessel is as
follows:
Basic Rule of Thumb:
Expansion vessel = m
2
collector x 1 litre solar fluid x 4
(FETAC Guidelines)
Advanced Calculation Method:
Expansion vessel = Total system volume x 25%
Intermediate vessel
The Eurpoean VDI 6002 directive recommends that an intermediate “cooling” vessel is installed when the
contents of the pipes between the collector’s field and the expansion vessel is lower that 50% of the reception
capacity of the expansion vessel”. It is also recommended that when an expansion vessel is fed from the
bottom, an intermediate vessel should be installed.
Air vent / Isolating valve
An automatic air vent is fitted at the highest point in the system. In most systems this is on the roof at the point
where the flow pipe leaves the panels. In systems with more than one bank of collectors, an air vent should be
fitted to each bank. An isolating valve should be fitted before the air vent. This valve should be closed once the
system has been commissioned.
Anti-scald mixing valve
An anti-scald (mixing) valve must be fitted close to the hot water outlet of the solar tank so that delivery to the
taps does not exceed 65°C.
Collector area
Pipe diameter
10 - 20 m
2
22 mm
20 - 30 m
2
28 mm
30 - 50 m
2
35 mm
50 - 70 m
2
42 mm
SOLAR SYSTEM DESIGN
