Water source heat pumps are currently one of the fastest-growing air conditioning systems, widely used in office buildings, shopping malls, residential areas, and other applications due to their flexibility and energy efficiency. These units can be combined with cooling towers and low-temperature heat sources to form large-scale water source heat pump systems. They come in two types: water-to-air and water-to-water, where the heat is extracted from or released into the water. To ensure the unit’s cooling and heating performance, the water flow through each heat pump must match the design flow. This is not only essential for performance but also critical for the stable and safe operation of the system. If the flow rate is insufficient, it may cause high condensing pressure, frequent cycling, and even equipment failure. The following sections discuss methods to ensure proper water flow for water source heat pumps.
Method One: Flow Balance Valve + Flow Switch
The flow balance valve is installed at the outlet of the water source heat pump, and it is adjusted using a flow meter to match the required flow rate for the unit. However, this method has several drawbacks. The flow balance valve is costly, and the adjustment and commissioning process can account for about 30% of the total cost, making it an expensive solution. In addition, a flow switch must be installed to provide feedback to the heat pump controller. Without a flow balance valve, it becomes difficult to guarantee the necessary water flow, which could result in high-pressure protection trips or compressor damage. If no flow switch is used, operators might not detect a lack of water flow, leading to compressor startup without water, which can cause serious damage. Moreover, the flow balance valve introduces some resistance to the water system due to its differential pressure-based operation.
Method Two: Pressure-Type Flow Switch + Ball Valve
This method uses the pressure drop across the heat exchanger or plate heat exchanger to determine the flow rate. A differential pressure switch is set to trigger when the flow drops below a certain level and reset when it returns to the required value. The reset flow refers to the minimum flow needed after the pump starts to ensure the system operates properly, while the action flow is the point at which the switch turns off. Setting the reset flow correctly ensures that the water flow through the heat exchanger meets the design requirements. Typically, the reset value of the pressure switch on the water side of the heat pump should be greater than 80% of the rated flow to guarantee sufficient water circulation. The pressure switch can be factory-installed or field-installed, but before installation, it must be tested for pressure and flow to determine the appropriate settings. By adjusting the ball valve, the differential pressure switch can be triggered, ensuring that the flow through the heat exchanger exceeds 80% of the rated flow. This method offers accurate flow control, minimal system resistance, no need for specific pipe diameters, and no disturbance to the water flow. It can replace any type of target flow switch in HVAC systems. This approach is simple to commission, cost-effective, and provides a reliable solution for controlling water flow in water source heat pumps.