A Simple Step by Step Guide to Geothermal Heating

1. Geothermal Heat load estimate

Geothermal Heating Load Estimate

A heat load estimate or heat load calculation is important because it is used to make the selections for all the geothermal heating system. It is a calculation of how much heat moves into or out of the building given a nominated temperature differential. These movements of energy in or out of the building can be modelled to high complexity based on historical weather data sourced from the BOM or by using recommended outdoor temperatures for both winter and summer based on building usage and geographic location. The latter method sometimes known as average peak loads will provide a close estimate of the capacities required for the building. It is important to decide on whether the whole building will be used simultaneously because the system may be able to be zoned reducing the investment. In this case it may be necessary to carry out heat load estimates for each zone.

Geothermal Heating Calculator

Fortunately there have been some excellent online calculators you can use to help size your geothermal heating system external to this site that you can use free of charge here at the home page The Calculating Cool Page or at the start page here The Calculating Cool Start Page and is affiliated with Sustainability Victoria. Although it may require a small investment of your time, we recommend that you engage in this process because you can make changes to your building to improve the efficiency of the building thus reducing the geothermal heating size. This has a fourfold benefit both reducing the geothermal heat pump size, the ground loop size, power supply requirements and also the operating costs. This method involves calculating the square metres of all the different types of materials used to construct the home so you can perform the heat load calculation.

Otherwise if you would like to put your building information into our online form we can carry out a more comprehensive average peak load calculation Geomaster Geothermal Heating Calculator.  After you have submitted your form we will carry out a heat load in our geothermal heating calculator. Your architect The Australian Institute of Architects will likely have a professional in this field. If not there is a possibility to engage your own professional for this advice Engineers Australia.

Geothermal Heat Load Importance

This heat load is critical to not only the size of the geothermal heating but also the running costs and investment amount. From the heat load estimate interpolations or models can be created to determine what the annual energy usage will be based on historical weather data. Interpolating using a heat load estimate will require a much lower investment than producing accurate models. There is recent commentary suggesting that rather than only looking at the COP or Coefficient Of Performance of given heat pumps that all the components of for example the geothermal heating or HVAC system are taken into account to produce ratio of efficiency for the building rather than just the heap pump or primary plant and equipment. This means taking into consideration the ancillary components such as fans, pumps, actuators, etc. This can all be done based on the heat load estimate [1].

3. Geothermal Drilling

The next step is to take soil samples as an indicator to predict as much as practically possible what the properties are of the material below the surface. These core samples are an investment in the project because they tell us what equipment is required to install the loop fields in the ground. The amount of core samples, how many and where they are taken will depend on what options exist as explained in step two.

Very different core samples are taken depending on whether the geothermal heating system uses a loop field which is vertical or horizontal. Some further information on core samples The Wikipedia Core Sample Page. There are many methods of taking core samples including gravity coring, vibracoring, drilling, percussion sidewall coring and rotary sidewall coring. There are modern methods that require much simpler, less invasive drilling rigs that require much less labour. [2] Video showing a drilling rig demonstration.

The physical examination by our geologists and engineers of the samples provides an insight into what will be required for either the drilling or excavation and also what the thermal properties are. There will likely be a combination of soil (The Wikipedia Soil Classification Page) and rock classification (The Wikipedia Rock Classification Page) depending on the depth and location of the core samples.  While this insight is required it isn’t enough information to rely on for the full design of the loop field. At the end of this process it will be known within certain parameters what the likely properties are below the surface on your site.

5. Finalise Design

The geothermal heating system designer now has enough information to design not only the loop field but also the geothermal heat pump, fan coils, air handling units, floor coils, tanks, pumps and other ancillary items depending on the building stakeholder requirements.

With the past dependence on fossil fuels and their increasing costs alternative energy sources including solar are incorporated into new and existing buildings. [4] Holistic designs integrating geothermal heating, solar thermal, solar panels (photovoltaics) [5], battery storage, desuperheaters and solar hot water will be essential as more and more building owners move toward zero energy [6] see The Wikipedia Zero Energy Building Page and off-the-grid [7] infrastructure see The Wikipedia Off The Grid Page.

Solar Thermal Integration

Depending on the design requirements solar heat collection may be incorporated into the system. The limitation of standalone solar hydronic or solar thermal heating is that on days of low solar irradiation the system may not be able to collect enough heat to satisfy the building loads. Adding more solar collection area is an option but then in summer months over collection needs to be managed. For more information The Clean Energy Council Website.

Whilst it can be a good idea to incorporate solar thermal into the system design it must be remembered that on overcast days it is likely supplementary geothermal heating will need to be relied on.

Desuperheater Integration

Another option is to use a desuperheater to heat hot water for the fixtures throughout the building. [8] This can make the system more efficient in summer because it increases the heat rejection ability of the geothermal heat pump. In winter it takes heating capacity that otherwise would have gone to the heating system and uses it to heat hot water to go to fixtures. For information on where the desuperheater is installed in the heat pump there is a diagram which may help

Geothermal heating diagram showing multiple options with desuperheater

Control systems are another important consideration for the designer and will usually decide during consultation with the stakeholders when deciding on the building performance requirements. Control of the geothermal heating system can take the form of standalone servers, standalone controllers, work modules, integrated control systems, building management systems and home automation systems. For further reading here is information on more basic thermostats The Wikipedia Thermostat Page and more advanced controls systems The Wikipedia HVAC Controls Page.

It is important for all of these aspects to be balanced for which a professional design company is best placed with engineering expertise and also experience from past projects. Often the manufacturer will provide design services which provides a smooth transition to the installation. For Geomaster geothermal heating and cooling systems please contact us.

7. Commissioning

It’s very important once the system is installed that the geothermal heating system is commissioned to meet the design criteria within a tolerance. Depending on the system configuration this can involve balancing geothermal loop field flows, hydronic flows, air flow balancing, electrical monitoring, refrigeration capacity analysis, water side capacity analysis and electrical current reporting. For further reading on commissioning The City of Melbourne has some good resources.

To put it into perspective buildings consume around 40% of our energy. [10] It has been found that using correct commissioning procedures can result in significant energy savings. [11] A properly correctly commissioned system ensures that the building remains sustainable over the longer term in line with the original design. [12] So it is critically important that geothermal heating and cooling systems are correctly commissioned.

9. Maintenance

The feedback loop from ongoing monitoring needs to go back to the personnel responsible for the maintenance. The data that is recorded from building management system and manual in person inspections that shows areas of the plant that need attention should be entered into a schedule showing the items which need to be attended to in order of priority.

Fortunately, geothermal heat pump systems are one of most reliable HVAC systems. Geothermal heating systems not only cost less to operate but also less to maintain. [14] Another major advantage is that the geothermal heat pump is easily serviced due to its self-contained design. Due to the favourable pressures compared to air source heat pump systems the components tend to have a longer service life. The water treatment in the closed ground loop circuit needs checked during an annual service. The Australian Government Department of the Environment and Energy have a good resource page for further reading.