Digging Deep: a Geothermal Solution to Sustainable Cooling
Of all the buzz words floating around the architecture space in the present climate, sustainability is perhaps the most oft-used and under-explained. Commonly associated with solar panels in the public consciousness, and associated with high capital costs in the commercial sphere, the term 'sustainable design' has the taint of the unattainable - beautiful eco boxes spread across magazine pages. However, designing for sustainability encompasses so much more than solar panels and aspirational hero projects, and can in fact be the most efficient and cost effective option for the pragmatic long-term property owner.
From the ground up.
At the ground level, sustainable design requires a team of people on the same page. Clients with long term vision; architects who understand the various energy sources available on the specific site and how to harness them; and contractors with an understanding of how all the working parts fit together to form one harmonious system.
We are lucky to have worked with many such teams in our portfolio of projects, seeing the implementation of a long list of sustainability measures that have made for more comfortable living and working environments with low running costs over the long term. The constantly evolving field of sustainable design requires that we are always researching and learning to determine the best combination of systems that will get the best results for each specific site and project.
The right solution for the site.
One current project for the Metropolitan Cemeteries Board (MCB) will implement a climate control system that remains relatively underused in Australia - Geothermal HVAC (heating, ventilating, and air conditioning). While Geothermal pumps are common in cooler climates, such as parts of the U.S.A., the benefits of such a system in more temperate climates tend to be less pronounced. However, when combined with systems such as indirect evaporative air conditioning, the geothermal solution can be hugely cost effective, while at the same time substantially reducing the carbon footprint of the development.
In particular, the chapel at the new MCB Mausoleum site poses the problem of a large space that will be used sporadically, but must be kept at an ambient temperature over long hours. On any given day, the chapel may host several services or none at all, yet it will remain open to families and mourners all day. In a venue with such fluctuating usage, keeping conventional ducted air conditioning running is projected to produce five times more carbon than a geothermal combination system, due to the amount of fossil-based energy used. Additionally, such a system would prove to be expensive to run over the long term, and is therefore not a viable option.
In problem solving for this site, we worked with Healey Engineering to compare four temperature control systems on projected carbon usage and overall cost (upfront capital cost + long term running cost) over a twenty year period. Represented by the yellow line, the combination of Geothermal AC and Climate Wizard is clearly the best option from a carbon usage perspective, and came in at second best in overall cost, assuming traditional energy supply costs remain static. However, we anticipate that the Geothermal AC and Climate Wizard combination will prove to be the most cost effective as the table is adjusted to reflect increasing energy prices in the future.
Harnessing the stability of subterranean temperatures throughout the year, the geothermal pump on the MCB site will combine a chilled water system with floor heating coils to provide heating in the winter and cooling in the summer. The pump for the reticulation system requires some energy to run, and this is more than adequately covered by four solar arrays.
The true cost of cooling
One of the most common objections to sustainable design is that it can involve considerable up-front costs. In this case the objective is to harness natural energy over the long term to reduce - or even eliminate - dependence on fossil fuel energy supply. Assuming energy costs remain static, the worst-case pay off period for this project will be less than 12 years - relatively short in terms of the design life of the complex which will exceed 100 years. What makes the sustainable solution more compelling, however, is that the probability of energy costs remaining constant over the coming decade is close to nil. As the cost of energy increases (and by all accounts, this is inevitable), the pay off period for the site will reduce accordingly, making this up front investment all the more valuable.
The bottom line is that it has been possible in this case and for a relatively small investment over the base cost of the project, to reduce the ongoing outgoings for the development towards negligible carbon emissions and introduced energy consumption
At Slavin Architects, we favour sustainable design for a number of reasons, including the hope of leaving the planet intact and thriving for future generations. Nevertheless, even a purely pragmatic assessment shows that sustainable solutions such as the system being constructed at the MCB site are the way of the future. We commend the MCB for their foresight and commitment to building structures that will pay off over the long term.