WATER SOURCE HEAT PUMP

A water-source heat pump (WSHP), also known as a water-source heat exchanger, is a type of heat pump that utilizes a natural or engineered body of water as the external heat reservoir or sink. A WSHP system extracts thermal energy from the water source and transfers that thermal energy to a building’s heating or cooling circuit via a closed-loop refrigeration cycle that operates using electricity.

In contrast to a combustion-based heating system, a WSHP system does not produce heat; instead, it extracts low-grade thermal energy from water, raises the thermal energy level via compression and provides usable heat to the building. When the system is operating in a cooling mode, the system reverses the direction of heat transfer and rejects heat generated indoors into the water source.

The defining feature of a WSHP when compared to other heat pump systems is the use of water as the environmental heat reservoir versus ambient air or ground soil.

Learn the basics of heat pump technology.

What is a Water-Source Heat Pump?

A water-source heat pump is a thermal energy transfer system utilizing water with stable temperature characteristics as the heat exchange medium.

Common water sources for WSHP systems are:

  • Lakes and ponds
  • Rivers and canals
  • Groundwater wells
  • Artificial water reservoirs

The WSHP system is able to extract thermal energy from water at very low temperatures. Through mechanical compression, the low-grade thermal energy extracted from the water is elevated to a temperature suitable for either building heating or hot water supply.

Additionally, the refrigeration circuit can be operated in a reversible manner, allowing the WSHP system to function as a cooling device, extracting heat from the building and transferring it into the water source.

Water-source heat pump system extracting thermal energy from lakes, rivers, groundwater wells and reservoirs for building heating and hot water supply.

Characteristics Defining Water-Source Heat Pumps

Use of Water as the Environmental Heat Reservoir

The primary energy source utilized by a WSHP system is water as opposed to air or soil. As a result, the water body typically maintains more consistent seasonal temperatures than do air or soil, thereby providing consistent thermal exchange conditions during each season.

Water-to-Refrigerant Heat Transfer Interface

As opposed to using an outdoor air coil with fan-assisted airflow to absorb heat, WSHP systems utilize liquid-based heat exchangers to facilitate thermal energy exchange between the circulating water and refrigerant through plate or coaxial heat exchangers.

As a direct result of the utilization of liquid-based heat exchangers, WSHP systems do not require the use of external airflow-based heat absorption.

Separation of Heat Generation and Delivery

The WSHP system operates solely as the heat generation component. Delivery of thermal energy to occupied spaces is managed by separate building systems including:

  • Hydronic circuits
  • Air handling units
  • Buffer storage tanks
  • Control and regulation systems

Through the modular separation of heat generation and distribution, the WSHP technology can be integrated into various architectural configurations of buildings without modifying the fundamental operating principle of the WSHP technology.

Stable Thermal Operating Conditions

Due to the fact that the temperature of water is relatively constant compared to the temperature of outdoor air, WSHP systems operate over a more narrow temperature range of thermal input. As a direct consequence of the reduced range of thermal input, the performance of thermal exchange is improved across the entire spectrum of seasonal operation.

Defining characteristics of a water-source heat pump showing water-based heat exchange, separation of heat generation and distribution, and stable operating temperatures.

Operating Principle of a Water-Source Heat Pump

WSHP systems operate using the same thermodynamic refrigeration cycle as all vapor-compression heat pump systems.

Heat Absorption (Evaporation)

Refrigerant in the low-pressure state absorbs thermal energy from the water source via a heat exchanger. At the same time, the water source loses thermal energy and the refrigerant vaporizes into the gaseous state.

Compression

The gaseous refrigerant is subjected to compression by an electrical-driven compressor. Due to the increased pressure and temperature associated with the compression process, the energy level of the absorbed thermal energy is elevated.

Heat Release (Condensation)

The high-temperature refrigerant releases thermal energy to the building’s heating circuit. As a direct result of the release of thermal energy, the refrigerant condenses back into the liquid state.

Expansion

The liquid refrigerant then passes through an expansion device. Due to the reduction in pressure and temperature, the refrigerant is prepared for the next heat absorption cycle.

Cooling Mode of Operation

When the WSHP system is operating in the cooling mode, the direction of refrigerant flow is reversed. Therefore, the system is able to absorb heat from the indoor spaces and transfer that heat to the water source, thereby providing cooling to the indoor spaces. The same hardware is utilized to perform both heating and cooling operations.

Configuration Categories of Water-Source Heat Pumps

WSHP systems are categorized according to two dimensional characteristics of structure:

Source-Side Configuration

Open-Loop Systems

The water is directly drawn from the source and passed through the heat exchanger before being returned to the environment. Direct heat exchange occurs between the source water and the WSHP system.

Closed-Loop Systems

A sealed fluid loop is established between the water body and the WSHP system. Indirect heat exchange occurs between the circulating fluid and the water body as the fluid is submerged in the water body contained within a pipe.

Load-Side Configuration

Water-to-Air Systems

The thermal energy supplied by the WSHP system is delivered to the indoor air distribution systems. The WSHP system supplies heated or cooled air directly to the occupied spaces.

Water-to-Water Systems

The thermal energy supplied by the WSHP system is delivered to the hydronic circuits. The WSHP system supplies heated or chilled water to the radiators, underfloor heating systems, fan coils, or storage tanks.

Water-source heat pump distribution configurations showing water-to-air systems for indoor air heating and water-to-water systems for hydronic heating circuits.

Role of WSHP in Building Energy Systems

At the system level, the WSHP is the thermal energy conversion unit.

Function of Heat Generation

The WSHP upgrades the environmental thermal energy and delivers usable thermal energy to downstream systems.

Interface for Thermal Energy Distribution

Downstream systems deliver thermal energy to the occupied spaces. These systems include:

  • Thermal energy distribution piping networks
  • Air handling units
  • Terminal heat emitters

Integration with Thermal Storage Systems

Thermal energy storage tanks may be connected to the WSHP to buffer the heating output and enhance stability of the WSHP operation.

Integration with Control and Regulation Systems

Control systems regulate the temperature setpoint, the operating mode, the flow rate, and the priority of loads. The WSHP responds to the control signals but does not manage the logic for distribution of thermal energy internally.

Role of a water-source heat pump in a building energy system converting environmental thermal energy into usable heating through storage tanks, piping networks and air handling units.

Comparison to Other Types of Heat Pumps

All types of heat pump systems operate using the same thermodynamic refrigeration cycle.

The difference among types of heat pump systems lies in the type of external source utilized for the heat transfer process.

Types of heat pump system are classified based on external source of heat

  • Air-source
  • Ground-source
  • Water-source Natural

Therefore, the difference among types of heat pump systems is due to the differences in thermal boundary conditions between the water source and the heat transfer process, and not the differences in physical technology.

Frequently Asked Questions (FAQs)

A water source heat pump is a heating and cooling system that transfers thermal energy from a natural or engineered water source into a building. It uses electricity to move existing heat from water to indoor spaces for heating, and reverses the process for cooling.

A water source heat pump works by extracting low-temperature heat from water using a refrigerant cycle. The system compresses the refrigerant to raise its temperature and then transfers the heat into the building’s heating system.

Water source heat pumps work by circulating refrigerant through a closed thermodynamic cycle. Heat is absorbed from water at the evaporator, compressed to increase temperature, and released indoors through a heat exchanger.

A water source heat pump provides space heating, space cooling, and optionally domestic hot water by upgrading environmental heat from water sources and delivering it to building heating and distribution systems.

A water source heat pump system consists of a heat pump unit, a water-side heat exchange loop, and a building-side distribution network. Together, these components transfer thermal energy from water into usable heating or cooling output.

Yes, water source heat pumps use refrigerant to transfer heat. The refrigerant absorbs thermal energy from water, is compressed to increase temperature, and releases heat into the building through heat exchangers.

Yes, a water source heat pump contains a compressor. The compressor increases refrigerant pressure and temperature, enabling low-temperature environmental heat to be upgraded into usable heating energy.

Yes, water source heat pumps can provide domestic hot water by transferring upgraded thermal energy into a dedicated hot water storage system or hydronic circuit, depending on system configuration.

Water source heat pumps are considered high-efficiency systems because water temperatures remain more stable than air. This allows the heat pump to operate under favorable thermal conditions and achieve higher seasonal performance.