solar industries

SWH system performance depends on a number of aspects in which collector performance is just one characteristic. More importantly is where and how the system is installed, how the hot water is being used on a daily basis, and how the supplementary heating controller is configured.

Most systems gives similar performance in NZ - the aspects above are more important than any differences between the systems.

Potential purchasers of systems should check if the information provided by SWH suppliers relates to total system performance or is just relating to the efficiency of the collector. Much information provided to the public by some suppliers is misleading as it only relates to the collector. Collector performance has little relevance as it is the performance of the whole system that affects the efficient use of solar energy to heat water. System performance can be significantly affected by pump flow rate, location of inlet and outlet ports on tanks, location of supplementary heating in a tank, and supplementary heating controller settings.

A standard AS/NZS 4234 is available so that systems can be tested under standard reference conditions. This will provide a good guide on system performance in individual situations. It should be noted however that system performance calculations are based on packaged systems. Packaged systems are fully designed systems where all the components have been tested to ensure that they each meet the standard. The design of a packaged system is based on optimal integration of the components. Some suppliers are importing components and making what are called "custom built" systems. A retrofit installation where the existing hot water cylinder is used is a custom built system. The energy performance of a custom built system can not be calculated until after it is built and it is likely that energy performance will be lower than for a similar packaged system which has been designed as an integrated whole for optimal energy performance.

The standard AS/NZS 4234 sets out a methodology for calculating the energy performance of an SWH system under reference conditions in specific climate zones . In Australia there are four zones and in New Zealand two zones for which the energy performance is calculated.

If thermal performance of a system is to be claimed the method of calculation should be AS/NZS 4234. While the calculation is under specific reference conditions these have been chosen so as to closely resemble actual performance. However because every solar water heating application is different it is necessary to standardise variables such as hot water demand, irradiation, inclination and orientation.

The methodology is based on measurement of the performance of each system component eg collector, tank, supplementary heating controller and pump. The performance characteristics of each element are then combined in a computer simulation to calculate the likely energy performance of that particular arrangement of the system components and under the reference conditions.

Only packaged systems where identifiable system components are combined in specified arrangements and with specified pump flow rate, supplementary heating control settings, and differential temperature settings can have their energy performance calculated. The advantage of using computer simulation to calculate energy performance is that different arrangements or settings can be easily specified and the recalculation done.

When reference is made to a system performance it is important that all characteristics of the system including flow rate and controller settings are specified otherwise the performance data provided is meaningless as it is not identifiable to a specific nominated packaged system.

If a supplier can not provide you with certified energy performance results defined from AS/NZS 4234 then a comparison of systems may be obtained from the Australian Office of the Renewable Energy Regulator website. This site only refers to systems they have listed for the four Australian zones, but Zone 4 is similar to the New Zealand Zone 5 which covers the North Island and warmer parts of the South Island..

The list of systems is in Schedule 7 of the regulations Renewable Energy (Electricity) Regulations 2001 (incorporating Amendment Regulations 2005 (No. 2) ).