You may have heard about geothermal, or ground-coupled, water source heat pump systems as an alternative to oil and electric heat, but you may be wondering if it is the right type of HVAC system for your project.
This guide brings together four key areas to help you determine if a geothermal heat pump system is right for you, get started with design and construction, evaluate available system options, and know what to expect once the system is fully operational:
- Is a Geothermal System Right for Your Project?
- Getting Started With a Formation Thermal Conductivity Test
- System Options
- Recommendations for Operation and Maintenance
Are They Right for Your Project?
There are several questions that new and existing facility owners should consider before making the decision to install any HVAC system. The following factors are especially relevant when evaluating whether a geothermal system is a good fit for your facility.
Building Occupancy
What is your building occupancy? Is your building occupied year round? What is the density of occupancy? With energy-efficient systems, the higher a system’s runtime the faster the payback will be when compared against a less efficient system.
Building Location
Where will your building be located? Will it be located in a rural area or an urban area? You should evaluate the effect your building will have on the environment and surrounding neighbors from a space planning, noise and aesthetic standpoint.
Geothermal systems require a larger amount of space on the site for the bore field than other systems; however, these systems do not create the noise commonly associated with air-cooled direct expansion refrigeration equipment.
Building Configuration/Orientation
What is your building configuration/orientation? Will your facility be multi-story, a block configuration or finger configuration?
If you have a strong east-west orientation or a core-perimeter layout, there may be opportunities to share energy within the building with a water source heat pump system.
Construction Budget
What is your construction budget? The initial costs for geothermal systems have historically been higher than other, more common types of HVAC systems because they require a ground-coupled heat exchanger.
However, geothermal systems may result in significantly lower annual energy costs. Additionally, grants and other subsidies may be available to offset the higher initial investment.
Once you have determined that a geothermal heat pump system may be a good fit for your facility, the next step is to evaluate the thermal characteristics of the ground at your site.
Getting Started With a Formation Thermal Conductivity Test
Now, you should be better prepared to decide if this type of system is right for your facility. The next step is to understand how to get started with designing the system. If you determined that a geothermal heat pump system is right for your facility, the very first thing you should do is determine the thermal characteristics of the ground on your site.
These characteristics are critical for properly sizing the borehole field. Under-sizing the borehole field can result in poor system performance, while oversizing the field could cause you to exceed your budget.
The only way to accurately determine the specific ground characteristics is to perform a Formation Thermal Conductivity Test (FTCT). During a FTCT, a borehole is constructed and then tested.
The following are some tips and reminders to help you move forward with your FTCT:
- If it is not possible to perform the FTCT prior to design completion, then you should require the FTCT as part of the construction contract. If the FTCT is conducted post-design, your mechanical engineer may have to adjust the design based on the FTCT results, which could require change orders.
- A borehole FTCT can cost $8,000-$12,000; however, with proper planning, the test borehole can be incorporated into the final design and about 60-75% of this cost can be applied directly to the construction costs.
- In order to incorporate the borehole into the final heat exchanger, you must carefully plan the location of the test borehole and utilize thermally-enhanced grout similar to what will be used in the final design.
- A generator is typically used during the FTCT. Keep in mind that the generator will create noise and operate continuously for 48 hours. If you are testing in a residential area, you may want to warn nearby facility owners and residents.
- The process of creating a borehole results in the discharge of cuttings, grout, and groundwater. Make sure to clearly specify, the party who is responsible for sediment control and restoring the site upon completion of work.
Once the FTCT is complete and the ground characteristics have been established, you are ready to move forward with system design and determine which type of geothermal heat pump best fits the facility.
System Options
There are two distinct types of heat pumps that can be used in a geothermal system — a water-to-air system and a water-to-water system.
Both types use the earth as its means of rejecting and reclaiming heat; however, the processes for accepting and rejecting heat are different for each.
In a water-to-water system, the heat is accepted and rejected into a water pumping system before being transferred to an air distribution system; whereas, in a water-to-air system, the heat is accepted and rejected directly into an air distribution system.
Identifying the type of system that is right for your facility depends on the nature of your project and the conditions of your facility.
For existing facilities, replacing an existing chilled/hot water system with a geothermal, water-to-water system may be the right choice as long as the piping infrastructure is sound.
For a new facility, installing a water-to-air system may make more sense since it eliminates the need for an additional heat exchange process.
In either case, it is important to analyze the exact application to make sure that the system makes sense from a cost, energy efficiency, and performance standpoint.
Once the system type has been selected, designed and installed, proper operation and routine maintenance become key to maintaining its performance over time.
Recommendations for Operation and Maintenance
Once you have decided to install a geothermal heat pump system, there are several things to consider once the system is fully operational.
Perform Routine Maintenance
As with all HVAC systems, geothermal heat pumps require routine maintenance.
In particular, regularly cleaning the system’s strainers and replacing air filters will help prevent increased pressure drop, which in turn causes inefficiency and reduced air or water flow.
This reduced air or water flow causes the compressor to work harder, ultimately causing premature system failure.
Occasional compressor failure is common, but multiple failures across the system or repeated failures in the same unit could indicate a larger issue. Therefore, routinely monitoring compressor failures can save you time, energy, and money.
Adjust Set Backs and Set Ups
Similar to traditional systems, geothermal heat pumps allow you to make scheduled temperature adjustments—in the form of set backs or set ups—based on building occupancy.
However, geothermal systems take longer to warm up than other systems and may require adjustments to the setback or setup time to accommodate this startup lag.
Incorporate System Fill Alarm
Most commercial geothermal heat pump systems use a closed-condenser water loop, which typically has an automatic fill feature to maintain the desired level of water volume in the system.
A small amount of water is commonly lost through the process of cleaning strainers and other routine maintenance tasks, a significant or continuous flow through the automatic fill can indicate a leak in the bore field.
Installing a water meter with alarm capabilities could help to alert maintenance staff of this danger and avoid excessive water usage.
Monitor Energy Use
Once the system has been in operation for one year, it is a good idea to consult an engineer to measure and verify your building’s energy consumption to confirm your system is achieving its indented efficiency.
Comparing actual energy use to an energy model for the system could help you identify operational deficiencies that can help you maximize the system’s efficiency.
Determining whether a geothermal heat pump system is right for a facility involves more than selecting the equipment itself. Building occupancy, site conditions, budget, ground characteristics, system configuration, and long-term operation all play a role in how the system will perform and whether the investment makes sense for the project.
Starting with the right site analysis and system design, then following through with routine maintenance and ongoing energy monitoring, can help owners get the intended performance and long-term value from a geothermal system.
For more information or questions about geothermal heat pump systems, contact us to discuss how these systems may apply to your project.