Ground Loop & Heat Pump Configuration Flashcards

During a thermal response test (TRT), what two key ground parameters are determined?

Answer: Ground thermal conductivity and borehole thermal resistance

A TRT injects or extracts heat at a known rate and measures temperature response over time to calculate ground thermal conductivity and borehole thermal resistance.

A header manifold in a parallel ground loop field is sized primarily to:

Answer: Ensure equal flow distribution to all parallel bore circuits

Proper manifold sizing and reverse-return or balanced-tee design ensures equal flow through each bore, preventing short-circuiting of cooler or warmer fluid.

What is 'undisturbed ground temperature' (UGT) and why is it critical in loop design?

Answer: The native soil temperature before system installation, representing the baseline for heat exchange calculations

UGT is the soil temperature before any system influence; it sets the source/sink baseline that determines heat pump COP and required bore length.

Which of the following best describes the 'EWT' that appears on a heat pump performance data table?

Answer: Entering water temperature to the heat pump from the ground loop

EWT (Entering Water Temperature) is the ground loop fluid temperature entering the heat pump's water-to-refrigerant heat exchanger, directly affecting rated capacity and efficiency.

What happens to heat pump heating COP as entering water temperature (EWT) decreases during cold winters?

Answer: COP decreases because the temperature lift the compressor must overcome increases

Lower EWT means the refrigerant must evaporate at a lower pressure, increasing compressor compression ratio and work input, thereby reducing COP.

In a hybrid geothermal system, a supplemental cooling tower is added primarily to:

Answer: Reject excess heat during cooling-dominated operation to reduce ground temperature rise

A cooling tower dissipates excess heat rejection in cooling-dominated climates, preventing long-term ground warming that would degrade heat pump COP over years.

Which design tool calculation method does ASHRAE recommend for sizing vertical bore fields in commercial and residential applications?

Answer: The g-function method using dimensionless borehole response functions

ASHRAE and IGSHPA recommend the g-function (Eskilson) method, which uses borehole response functions to account for thermal interference and long-term ground temperature changes.