This Is Part 2/2 of Building a Sustainable Future with Thermal Energy Networks by Marc Miller, Egg Geo, LLC

Modern energy demands are growing, and the need for sustainable, efficient solutions to heat and cool our homes and businesses has never been greater. Enter Thermal Energy Networks (TENs)—innovative systems that distribute and reuse energy to reduce costs, cut emissions, and optimize performance.

 

This article continues to explores the implementation of TENs, their benefits, and how one would connect their home or building to a TEN, helping you understand their potential to transform energy systems for the better.

 TENs Connected to Buildings

Regardless of whether the stakeholder is a home, a light commercial building, or an industrial building, the fundamental connection to the ATL remains the same: the decoupled secondary loop. This loop features a circulator pump sized to handle the maximum load of the system. As a result, there’s no need for a balancing valve, as the flow rate (GPM) delivered to the intermediary heat exchanger is regulated by maintaining a delta T (temperature difference) across the heat exchanger.

The pump automatically adjusts to sustain this delta T, with its rated capacity based on the maximum flow required to meet the stakeholder’s demands. For instance, in heating mode, if the ATL circulating heat transfer medium is of a low temperature, compared to normal operating conditions, the secondary pump increases speed to deliver a higher rate of flow with a lower temperature fluid. Conversely if the temperature of the fluid increases, then the flow rate can be reduced.

This is because of the following formulas:

BTU/hour = Flow Rate (GPM) × ΔT (°F) × 500

Flow Rate (GPM) = BTU/hour ÷ (ΔT (°F) × 500)

ΔT = The temperature difference between the inlet and outlet water temperature of the heat exchanger

500 = a constant that accounts for the weight of water (in pounds per gallon), the specific heat of water, and a time conversion factor.

For instance, if a stakeholder requires 120,000 BTUs to be delivered to their building while maintaining a 10°F delta T across the heat exchanger inlet and outlet water temperatures, we can determine the required GPM (gallons per minute) using the following formula:

GPM = BTU / (ΔT × 500)

Now, plug in the values:

GPM = 120,000 / (10 × 500)

GPM = 120,000 / 5,000

GPM = 24

So, the GPM required is 24 gallons per minute.

Now, if the temperature in ATL drops because of thermal diversity and temperature cascade effect, the water in the ATL will contain less thermal energy. To compensate, we would need to either increase the size of the heat exchanger to provide more surface area for thermal energy transfer or increase the volume of water that has fewer BTUs to continue to deliver 120,000. Because there are fewer BTUs the delta t will decrease to 5℉-6℉. To determine the required flow rate (GPM), we use the same formula:

GPM = BTU / (ΔT x 500)

Now, plug in the values:

GPM = 120,000 / (6 x 500)

GPM = 120,000 / 3,000

GPM = 40

So, the GPM becomes 40.

In most two-pipe systems, heat exchangers are designed to operate at a specific flow rate (gpm) and a fixed temperature differential (delta T), typically around 10°F. However, one-pipe systems are can be engineered for a varying delta T’s, which necessitates the use of a larger heat exchanger for worst case scenario.

The steady-state heat transfer equation: Q = U x A x ∆T is used applied to heat exchangers to determine its thermal energy transfer capabilities.

• Q: The total heat transfer rate (measured in BTU/hr or similar units).

• U: The overall heat transfer coefficient, which measures how effectively heat is transferred through a material or system (units: BTU/hr·ft²·°F).

• A: The surface area through which heat is being transferred (measured in square feet).

• ∆T: The temperature difference between the two sides of the material or system (measured in degrees Fahrenheit).

To calculate the heat transfer rate (Q) for a plate and frame heat exchanger made of copper/nickel using the formula Q = U x A x ∆T, we can substitute the known values directly.

Here’s the example:

Given:

• A (surface area) = 24 ft²

• ∆T (temperature difference) = 10°F Between the house water loop and the ATL

• U (overall heat transfer coefficient for copper/nickel) ≈ 500 BTU/hr·ft²·°F

Q = U x A x ∆T

120,000BTU/hr = 500 x 24 x 10°F

Result:

The heat transfer rate (Q) for this copper/nickel plate and frame heat exchanger is 120,000 BTU/hr.

This equation calculates the heat transfer rate across a surface by incorporating the area, the thermal properties of the material, and the temperature difference driving the heat flow. Widely applied in engineering disciplines such as thermodynamics and HVAC system design, it serves as a foundational tool for optimizing energy systems.

In an Ambient Temperature Loop (ATL) system, as the ATL temperature drops and the delta T narrows to just 5°F or 6°F between the inlet and outlet water temperatures to meet the required BTU transfer, the pump operates efficiently without significantly increasing its speed. This approach minimizes head pressure and reduces energy consumption for pumping. The pump’s maximum speed is calibrated to manage worst-case scenarios with a 5°F–6°F delta T, ensuring consistent and energy-efficient performance under demanding conditions.

Conversely, as the ambient loop temperature rises, the delta T proportionally increases due to the higher thermal energy present in the water. In response, the pump slows down—potentially to 50% of its capacity—to adhere to the industry-standard 50/90 design principle. This ensures both energy efficiency and system reliability across varying load conditions.

The ATL system is specifically designed to align with the 50/90 guideline, a cornerstone in HVAC system efficiency. This principle prioritizes sustainable energy use by setting pumps to operate at 50% capacity under normal conditions, reducing energy consumption while maintaining peak performance. During maximum load conditions, the system scales up to 90% capacity, leveraging pump affinity laws to ensure reliable operation without over-sizing equipment. The integration of variable speed drives further enhances this strategy, enabling precise flow control and optimizing thermal energy transfer for maximum efficiency.

Additionally, the heat exchanger acts as a hydraulic separator, ensuring no physical mixing of water between different stakeholders while facilitating efficient energy exchange. This design isolates the hydraulics of each stakeholder connected to the loop, maintaining system efficiency and providing seamless, independent energy sharing.

Why TENs Are the Future

Thermal Energy Networks represent the next evolution in energy systems—offering a path to decarbonization while improving efficiency and reducing costs. Whether adopted by urban centers, industrial complexes, or residential neighborhoods, TENs can dramatically reduce energy dependencies and support long-term climate goals.

It’s not just about scaling renewable energy; it’s about harnessing it smarter. By integrating geothermal technology, heat pumps, and innovative distribution systems, TENs set a precedent for sustainable energy solutions we can all count on.

Interested in how this technology can benefit your community or business? Start exploring implementation options today to join the growing movement toward a sustainable energy future.

Part I of this story can be found here: https://mechanical-hub.com/building-a-sustainable-future-with-thermal-energy-networks/

Marc Miller is a Mechanical Systems SME – Educator – Technical Writer – Author – Construction Management Consultant with Home – Egg Geo.  He is presently the Lead Author on two textbook projects with Egg Geo.  He may be reached at marcm@egggeo.com.