Assessing the feasibility of a geoexchange system requires an understanding of the heating, cooling and hot water requirements of the building(s) as well as the geological, hydrological and hydrogeological conditions of the site. The building and the local environment play equally important roles in the performance of the final system and as such both require to be equally addressed in any feasibility. The typical cycle of a geoexchange project is as follows:
1. Client expresses interest in geoexchange system.
- Initial conversation with Client to advise on the suitability of geoexchange to their project.
2. Initial Review:
- The Building: Heating, cooling and hot water requirements;
- The Mechanical Services: air / hydronics and centralised / distributed plant;
- The Ground Loop: Land area, soil/rock type, water bodies
3. Desktop Review:
- The Building: Preliminary loads using w/sqm or similar and often only peak values;
- The Ground Loop: Generic capacity based on theoretical values for expected geology;
4. Detailed Data Collection:
- The Building: Thermal / energy model with hourly data;
- The Ground Loop:
In-situ test to provide site specific data for geological conditions, thermal conductivity, thermal diffusivity and mean earth temperature.
5. Final Geoexchange Design:
- Combines results from the Detailed Data Collection using recognised independently developed industry software.
The above enables the Client to step through the feasibility and design process in a way that provides them with increasing levels of detail on the technology. In most instances, Steps 1 and 2 can be undertaken very simply either over the phone or in a meeting. Master Plan level documentation is commonly all that is required at this stage.
Desktop Feasibility Assessments
Step 3 is the start of the more detailed feasibility process and requires a Desktop Feasibility Assessment. A typical Scope of Works for this Assessment is as follows:
- Assessment of preliminary building heat load calculations using the W/sqm method or adoption of data from third party;
- Equipment sizes and selections based on preliminary loads and zoning;
- Geoexchange options - ground loop and ground source heat pumps;
- Preliminary ground loop design using anticipated ground conditions;
- Indicative capital costs on preferred Geoexchange design and comparison with conventional system;
- Indicative operational costs on preferred Geoexchange design and comparison with conventional system;
- Indicative CO2e and Electrical Maximum Demand (EMD) savings on preferred Geoexchange design and comparison with conventional system;
-
Preliminary drawings showing anticipated location(s) of Ground Source Heat Pumps;
-
Preliminary drawings showing anticipated location of ground loop;
-
Consultation with project team members; and
- Preparation of Report.
These reviews have been undertaken on projects ranging from single buildings and warehouses to CBD areas and residential subdivisions. They provide valuable information to the key decision makers of the project and provide them with the confidence that proper assessment has been made on the merits of geoexchange for their project. Our Clientele on such projects has included both consulting engineers, where we provide the specialty geoexchange design services, as well as end Clients in both the private and public sectors.
Detailed Data Collection
The two components of this Step are the Building and the Ground Loop. With respect to the Building, we have strong experience in the development of building thermal and energy modelling and can undertake these works. It is also common for us to be provided this detail by a third party such as mechanical or sustainability engineering consultant.
The detailed data collection for the ground loop is our specialty area and we are the only team in the country with appropriate equipment and experience to undertake this service. This step involves the conduct of an
in-situ Thermal Conductivity Test (TCT) or Thermal Response Test (TRT) and requires the drilling of a test borehole to the anticipated design depth as assessed in the Desktop Feasibility Assessment.
A ground loop is constructed in the test borehole as if it were part of the final system and is many instances the test borehole becomes part of the final ground loop. The TC test is undertaken in accordance with ASHRAE procedures over an approximately 48 hour period and the data collected analysed to provide the key geoexchange parameters of Thermal Conductivity (TC), Thermal Diffusivity (TD) and Mean Earth Temperature (MET). Valuable information is also provided during this test on the geology present at the site, the time taken to drill the borehole, hydrogeological conditions
etc that are valuable in the development and planning of the final drilling programme.
A White Paper discussing the Value of TC testing is available
here
Final Geoexchange Design
The last component is the development of the final geoexchange design and its documentation. There is not a one size fits all approach to ground loop design with ground loop capacity on a unit basis a function of the dynamic balance between the heating and cooling demands of the building and the ground conditions. For example, a data centre with its constant heat rejection requirement will require a very different ground loop design to a similar capacity office building that has a balanced heating and cooling load.
Quantit
y, depth and spacing of the boreholes as well as the length of the modelled operational life, all contribute to the final geoexchange design.
GeoExchange Australia has the experience and expertise to assist Clients either directly, or in conjunction with their project team, through the above process. Contact the office now to find out more.