Geothermal System Controls, Electrical & Auxiliary Components Flashcards

Which type of thermostat is most recommended for geothermal heat pump systems to prevent unnecessary auxiliary heat activation?

Answer: Two-stage thermostat with intelligent recovery

Two-stage thermostats with intelligent recovery gradually bring the space to setpoint using only the heat pump, avoiding premature activation of auxiliary resistance heat.

What is the primary function of a desuperheater in a residential geothermal heat pump system?

Answer: Pre-heat domestic hot water using waste heat from the refrigerant cycle

A desuperheater captures high-temperature waste heat from the refrigerant before it reaches the condenser and uses it to pre-heat domestic hot water at no additional energy cost.

In a geothermal heat pump system, what does an auxiliary heat 'lockout' control primarily accomplish?

Answer: Prevents backup resistance heat from activating when the heat pump can adequately handle the load

An auxiliary heat lockout control inhibits backup resistance elements from energizing whenever the heat pump is capable of maintaining comfort, preserving system efficiency.

What is the purpose of a flow center in a geothermal ground loop system?

Answer: To house the circulating pumps and provide a service/purging point for the ground loop

A flow center contains the ground loop circulating pumps, isolation valves, and purge ports, providing a single service location for the hydronic ground loop.

Which control strategy improves geothermal heat pump efficiency by varying compressor output to match the actual heating or cooling load?

Answer: Variable capacity or variable speed compressor control

Variable capacity compressors modulate their output to closely match the building load, reducing cycling losses and improving overall system COP.

What voltage supply is most commonly used for residential geothermal heat pump compressors in the United States?

Answer: 208/230V single-phase

Residential geothermal heat pumps in the US are designed for 208/230V single-phase power, which is the standard service voltage available in most homes.

What is the primary benefit of adding a buffer tank (or hydraulic separator) to a hydronic geothermal heat pump system?

Answer: It adds thermal mass to prevent short cycling of the heat pump compressor

A buffer tank provides thermal mass between the heat pump and the distribution system, ensuring the compressor runs for adequate minimum on-times and preventing short cycling.

Which NEC-required electrical protection device is mandatory for geothermal heat pump equipment installed in wet or damp locations?

Answer: Ground fault circuit interrupter (GFCI)

The NEC requires GFCI protection for electrical equipment installed in wet or damp locations to protect against ground fault shock hazards.

What type of wiring installation is required for geothermal ground loop electrical connections that transition from underground to inside the building?

Answer: Direct burial-rated cable or appropriate conductors in listed conduit

Underground electrical connections to flow center pumps must use UF-B (underground feeder) direct burial cable or THWN/THWN-2 conductors in listed conduit rated for wet locations.

What electrical component is most effective at protecting geothermal heat pump electronics from utility power surges and voltage transients?

Answer: Type 2 surge protective device (SPD) at the panel

A Type 2 surge protective device (SPD) installed at the electrical panel clamps voltage transients before they can damage sensitive heat pump electronics and variable speed drives.

What is the primary purpose of a hard start kit (potential relay and start capacitor) used with geothermal heat pump compressors?

Answer: To reduce locked rotor amperage and provide extra torque during compressor start-up

A hard start kit reduces inrush (locked rotor) current and provides additional starting torque, which is especially useful on circuits with marginal voltage or when starting against system pressure.

What is the standard control voltage used in residential geothermal heat pump low-voltage wiring between the thermostat and air handler?

Answer: 24V AC

Residential HVAC systems, including geothermal heat pumps, use 24V AC low-voltage control wiring to carry command signals between the thermostat and system components.

During geothermal system commissioning, which electrical measurement is most critical for verifying proper compressor operation?

Answer: Running amperage of the compressor compared to nameplate full-load amps

Measuring compressor running amperage and comparing it to nameplate FLA confirms that the compressor is operating within design parameters and not drawing excessive current due to a fault.

In a residential geothermal installation, why is it important to verify that the circuit breaker size matches the unit's Maximum Overcurrent Protection (MOP) rating on the nameplate?

Answer: Correct breaker sizing ensures adequate short circuit and overload protection without nuisance tripping

Installing a breaker at or below the nameplate MOP rating ensures proper overcurrent protection that safely interrupts faults while allowing normal starting current without nuisance trips.

What control function does a 'desuperheater priority' mode provide in an advanced geothermal heat pump controller?

Answer: It allows the heat pump to run specifically to satisfy domestic hot water demand when the storage tank temperature drops

Desuperheater priority mode commands the heat pump to operate specifically to recover domestic hot water when tank temperature falls below setpoint, maximizing the use of free waste heat.

When two or more geothermal heat pumps serve a single residence, which control strategy best equalizes wear and extends equipment life?

Answer: Lead-lag sequencing with automatic runtime hour balancing between units

Lead-lag control with runtime equalization automatically rotates which unit leads, ensuring both accumulate similar operating hours and neither experiences disproportionate wear.

Why should large nighttime temperature setbacks be used cautiously with geothermal heat pump systems?

Answer: A large setback recovery may activate auxiliary resistance heat, eliminating the efficiency advantage of the heat pump

If the recovery from a large setback exceeds the heat pump's capacity, the thermostat will call for auxiliary heat, which consumes far more energy than the savings from the setback period.

What control feature monitors entering water temperature (EWT) to the heat pump and protects the unit when loop temperatures fall outside safe operating limits?

Answer: Loop temperature protection or low-EWT lockout control

A low-EWT (entering water temperature) lockout control shuts the heat pump down if loop temperatures drop below the minimum operating limit, preventing compressor damage.

In a geothermal system with multiple conditioned zones, what device mechanically controls conditioned airflow to each individual zone?

Answer: Motorized zone dampers controlled by a zone control board

Motorized zone dampers open and close on command from a zone control board, directing conditioned airflow only to zones calling for heating or cooling.

What advantage does an electronic expansion valve (EEV) provide over a fixed orifice or thermostatic expansion valve (TXV) in a geothermal heat pump?

Answer: It precisely modulates refrigerant flow in real time based on system conditions, improving efficiency across a wider operating range

An EEV uses a stepper motor and controller to modulate refrigerant metering with precision across varying load and loop temperature conditions, achieving higher efficiency than fixed-orifice devices.