Sustainability Journal



July 2013 Issue (files are in PDF format)



Comparison of Net Zero designs

The June 22, 2013 issue of the Ottawa Citizen has an article by Mike Holmes describing one general approach to the design of homes that produce as much energy as they use on an annual basis (Page I-14). The design approach advocated by Mr. Holmes is similar to that promoted by various Canadian federal government agencies. Exergy storage systems offer an alternative that is less expensive, much more widely applicable and that would be able to achieve the required GHG reductions within a reasonable time. What we need is a design that can be retrofitted to the millions of existing homes that will still be in use in 2050 and that is immediately cost-competitive for the construction of new homes that are still being built using fossil fuels for heating. The exergy storage concept not only meets those needs for homes but also for larger buildings that comprise a large part of Canada's building stock.

Exergy storage - temperature objectives

The design of an exergy store is primarily dependent on achieving appropriate temperatures for the heat exchange fluids in the three rings - the Outer Ring (OR) where most of the heat is injected, the Middle Ring (MR) from which most of the heat is extracted, and the Central Ring (CR) that stores heat for Domestic Hot Water (DHW). The temperatures of the OR and CR are primarily determined by their functions rather than by the design considerations for the store itself. However the temperature of MR is a compromise: its value declines as heat is withdrawn from the store so it needs to be increasingly augmented by heat withdrawn from CR, and in small systems where the solar input is limited the heat can be provided by the exergy heat pump which guarantees that there will always be enough heat available for space heating.

Scope and limitations

The first part of a review of the potential scope for applying exergy storage systems in Canada along with the corresponding limitations to their use.