Solar desiccant air-conditioning is an emerging technology that offers the promise of reducing reliance on grid connected electricity for providing comfort air-conditioning. Development of a method of assessing the seasonal energy savings of these devices would enable a fair comparison with alternative devices. This could be used in policy support mechanisms to assist industry growth. Here we describe the application of the Component Testing System Simulation method to predict the energy savings of solar air-conditioners using the same approach as that applied successfully in the Australian solar hot water industry. The CTSS approach is made possible by the development of a new simplified generic model of the desiccant air-conditioner component. The performance of the generic model is evaluated for five different air-conditioner designs. The results suggest that the approach is valid for estimating the annual energy savings. The method will be documented in a provisional Australian Standard to be released in 2013.
Solar space heating and cooling is an emerging technology that offers the promise of reducing greenhouse gas emissions and reducing the reliance on grid connected electricity for the provision of comfort space conditioning. Presently, there are a number of solar air-conditioning technologies that could be readily deployed. These include; i) solar thermal systems with either adsorption, absorption or desiccant cooling, and ii) vapour compression systems with PV panels. While a number of commercial installations are in operation around the world (White, et al., 2012) (Kohlenbach & Dennis, 2010), they have made no measurable penetration into the residential air-conditioner market. This is largely due to the capital cost of the solar systems.
Unfortunately, at these early stages in the development of the industry, it is difficult to achieve cost effective volume manufacturing compared with the incumbent fossil fuel powered technology. Successful growth of the industry will require policies that help to address this capital cost disadvantage. Amongst other things, the International Energy Agency SHC Task 48 “Quality Assurance and Support Mechanisms for Solar Cooling” aims to develop rating tools that could be used by policy makers to award performance-based incentives to solar heating and cooling systems (Mugnier & Jakob, 2012). Such tools would ideally provide an evidence-based framework for awarding industry development incentives that reflect the greenhouse gas benefit of using solar technology over the fossil fuel based alternatives.
A number of separate and unconnected rating methodologies exist in the air-conditioning and solar industries. On the one hand, in the air-conditioning industry, standards exist for testing the performance of vapour compression air-conditioners at rated conditions (e.g. ISO5151 (ISO, 2010), AS/NZS 3822 (Standards Australia, 2012)). These have been further adapted to partially reflect annual performance in target climates through the development of seasonal (SEER) ratings (AHRI, 2008). Results from testing to these standards can be used to benchmark the performance of an air-conditioning product against reference performance levels in some form of star rating scheme (see for example (Standards Australia, 2011)).
On the other hand, in the solar industry standards exist for testing the performance of solar collectors (Standards Australia, 2007) at rated conditions. The performance of the collector can then be converted into an annual energy production or saving for a given climate using either the “Bin” method (similar to the seasonal performance rating method for air-conditioners), or using a “Component Testing System Simulation” (CTSS) method (Standards Australia, 2008) (ISO, 2013). An alternative is to test the performance of the complete solar cooling system as a package such as is described in the ASHRAE 174 desiccant air-conditioning test method (ASHRAE, 2009).
At this point, there is no clearly established method for comparing the performance of solar heating and cooling systems with that of a conventional fossil fuel based alternative. This is a significant barrier to the development of the solar heating and cooling industry because, without this methodology, consumers cannot easily compare the benefits of the new technology and policy makers do not have a basis for awarding performance-based industry support incentives.
This paper proposes use of the CTSS approach for rating individual solar heating and cooling products. It reviews the role of technical standards in the development of the solar hot water market in Australia and the successful application of the CTSS method for solar hot water in the existing Australian Renewable Energy Target certificate trading market. The paper then shows how the CTSS method could be extended for use in solar air-conditioning applications and discusses a new technical standard for rating solar air-conditioners. The development of a generic desiccant air-conditioner component model for the CTSS method is described and results are presented comparing the generic model with the exact performance for a number of example desiccant air-conditioner designs.
The Component Testing System Simulation method is the established method of estimating the energy savings of solar hot water systems in the Australian market. The method is codified in the form of an Australian Standard which is then coupled to a comprehensive system of Renewable Energy Credits which offer up-front discounts for installation of solar hot water systems. These two mechanisms have been largely responsible for the rapid growth of the solar hot water industry, and have contributed significantly to greenhouse gas emissions reductions.
By contrast, the solar air-conditioning industry is still in its infancy. Presently, worldwide there is no standardised method of estimating energy savings for solar air-conditioners. Part of the reason for this is the potential diversity of these systems, both in terms of their internal design as well as the overall system arrangement. This makes defining a cost effective and straightforward energy savings calculation method difficult.
Here we have describe a generic DCC model for desiccant based solar air-conditioners based on a simple regression based approach, which, when combined with the CTSS procedure, gives a method of establishing the energy savings of desiccant air-conditioners. The model is deceptively simple, and yet the analysis shows it can provide results of acceptable accuracy.
Previous experiences in the Australian solar hot water industry suggest that the development of such a standard is an essential step along the development path for new renewable energy technologies which would otherwise struggle to compete on a purely capital cost basis.
