Comprehensive Guide: How to Measure Thermal Energy in Geothermal Systems

Measuring the thermal energy in geothermal systems is crucial for understanding the efficiency and performance of these renewable energy sources. This comprehensive guide will provide you with the necessary tools, formulas, and techniques to accurately measure the thermal energy in geothermal systems.

Measuring the Capacity of a Geothermal Heat Pump (GHP) System

The capacity of a GHP system is measured in tons, with 1 ton equaling 12,000 British thermal units per hour (Btu/h). This capacity is determined by the facility’s heating or cooling demand profile, which is influenced by factors such as the size of the building, the number of occupants, and the climate conditions.

To measure the capacity of a GHP system, you can use the following formula:

Capacity (tons) = Heating or Cooling Demand (Btu/h) / 12,000 Btu/h per ton

For example, if a building has a heating or cooling demand of 60,000 Btu/h, the capacity of the GHP system would be:

Capacity (tons) = 60,000 Btu/h / 12,000 Btu/h per ton = 5 tons

Measuring the Length and Depth of the Loop Field

The loop field, which consists of pipes buried in the ground that exchange heat with the earth, is a crucial component of a geothermal system. The length and depth of the loop field are influenced by various factors, including the equipment size, type of soil, mean temperature, and climate conditions.

To measure the length and depth of the loop field, you can use the following guidelines:

• Measure the total length of the buried pipes in the loop field.
• Measure the depth of the buried pipes, which can range from 4 to 6 feet for horizontal loops or 100 to 400 feet for vertical loops.
• Consider the type of soil, as different soil types have varying thermal conductivity and heat transfer properties.
• Take into account the mean temperature of the soil, as this can affect the heat exchange efficiency.
• Factor in the local climate conditions, as they can influence the heat transfer between the ground and the loop field.

Measuring the Coefficient of Performance (COP), Energy Efficiency Ratio (EER), and Seasonal Energy Efficiency Ratio (SEER)

The COP, EER, and SEER are metrics that measure the performance and efficiency of a geothermal system.

Coefficient of Performance (COP)

The COP is the ratio of usable thermal energy to the thermal equivalent of the electricity consumed to power the system. It is calculated using the following formula:

COP = Usable Thermal Energy / Thermal Equivalent of Electricity Consumed

A higher COP value indicates greater heat pump efficiency. For example, a GHP system with a COP of 3.5 produces 3.5 units of usable thermal energy for every unit of electricity consumed.

Energy Efficiency Ratio (EER)

The EER is the ratio of cooling output (in Btu/h) to energy (electricity) input (in Watts). It is calculated using the following formula:

EER = Cooling Output (Btu/h) / Energy (Electricity) Input (Watt)

A higher EER value indicates greater heat pump efficiency. For example, a GHP system with an EER of 14 produces 14 units of cooling output for every unit of electricity input.

Seasonal Energy Efficiency Ratio (SEER)

The SEER measures the central air conditioning efficiency throughout a season. It is calculated using the following formula:

SEER = Cooling Output (Btu) / Energy (Electricity) Input (Watt-hour)

A higher SEER value indicates greater heat pump efficiency. For example, a GHP system with a SEER of 18 has a seasonal energy efficiency ratio of 18.

Modeling the Geothermal System as a Hybrid System

In some cases, the ground source heat exchanger system can be modeled as a hybrid system in conjunction with an existing heating system that depends on another type of energy, such as liquid propane. To accurately calculate the reduction in energy usage after the installation of a ground source heat exchanger, you need to gather detailed information about the hybrid system, including:

• The type and efficiency of the existing heating system
• The heating and cooling loads of the building
• The performance characteristics of the ground source heat exchanger

By modeling the system as a hybrid, you can assess the adequacy of the GHP system’s performance in addressing the building’s heating and cooling needs and determine the potential energy savings.

Measuring the Actual Performance of the Ground Heat Exchanger System

Once the geothermal system is installed, you can measure, track, and report the actual performance of the ground heat exchanger system. This involves:

1. Sub-metering the Electricity Consumption: Determine the electricity consumption of the GHP system through sub-metering to understand its energy usage.

2. Measuring Heat Exchange Performance Data: Collect data on the heat exchange performance, such as the measured entering/exiting water temperatures and circulation rates for the heat pump over time. This data can provide insights into the system’s efficiency and heat transfer capabilities.

By combining the capacity measurements, efficiency metrics, and actual performance data, you can gain a comprehensive understanding of the thermal energy in the geothermal system and optimize its performance for maximum efficiency and energy savings.

Theorem/Physics Formula:

• COP = Usable Thermal Energy / Thermal Equivalent of Electricity Consumed
• EER = Cooling Output (Btu/h) / Energy (Electricity) Input (Watt)
• SEER = Cooling Output (Btu) / Energy (Electricity) Input (Watt-hour)

Physics Examples:

• A GHP system with a COP of 3.5 produces 3.5 units of usable thermal energy for every unit of electricity consumed.
• A GHP system with an EER of 14 produces 14 units of cooling output for every unit of electricity input.
• A GHP system with a SEER of 18 has a seasonal energy efficiency ratio of 18.

Physics Numerical Problems:

1. A GHP system has a COP of 4.0 and consumes 5,000 watts of electricity. How much usable thermal energy does it produce?

2. Answer: 20,000 watts (4.0 COP × 5,000 watts = 20,000 watts)

3. A GHP system has an EER of 12 and produces 36,000 Btu/h of cooling output. How much electricity does it consume?

4. Answer: 3,000 watts (36,000 Btu/h / 12 EER = 3,000 watts)

5. A GHP system has a SEER of 16 and operates for 1,000 hours in a season. How much energy does it consume in the season?

6. Answer: 16,000 watt-hours (16 SEER × 1,000 hours = 16,000 watt-hours)

Figures, Data Points, Values, Measurements:

• Capacity of a GHP system measured in tons, with 1 ton equaling 12,000 Btu/h
• Length and depth of the loop field influenced by equipment size, type of soil, mean temperature, and climate conditions
• COP, EER, and SEER values indicating greater heat pump efficiency with higher values
• Electricity consumption of a GHP system determined through sub-metering
• Heat exchange performance data, including measured entering/exiting water temperatures and circulation rates for the heat pump over time

References:

1. Thermtest. (2022). Thermal Conductivity for Geothermal Exploration. Retrieved from https://thermtest.com/the-importance-of-thermal-conductivity-for-geothermal-exploration-and-the-development-of-successful-geothermal-heating-systems
2. EFB Public. (2022). How Do You Measure Geothermal Energy? Retrieved from https://www.efbpublic.org/how-do-you-measure-geothermal-energy/
3. SpringerOpen. (2019). Monitoring the impact of intensive shallow geothermal energy use on groundwater temperatures in a residential neighborhood. Retrieved from https://geothermal-energy-journal.springeropen.com/articles/10.1186/s40517-019-0123-x
4. iCAP Portal, University of Illinois. (2020). Measuring geothermal energy. Retrieved from https://icap.sustainability.illinois.edu/project-update/measuring-geothermal-energy
5. National Park Service. (2018). Monitoring Geothermal Systems and Hydrothermal Features. Retrieved from https://www.nps.gov/articles/geothermal-systems-and-monitoring-hydrothermal-features.htm