What type of pump is typically used for high-head, low-flow applications in HVAC systems?

A positive displacement pump is typically used for high-head, low-flow applications in HVAC systems. Positive displacement pumps, such as gear pumps, piston pumps, and vane pumps, deliver a fixed volume of fluid with each revolution or stroke, regardless of the discharge pressure. This characteristic makes them well-suited for applications where a high pressure (head) is required, but the flow rate is relatively low. In contrast, centrifugal pumps, which are commonly used in HVAC systems for general water circulation, are less efficient at high heads and low flows. For example, in a closed-loop hydronic system with a high static head due to the building's height, a positive displacement pump might be used to ensure adequate flow to the upper floors, even though the total flow rate for the system is relatively low. Another application could be chemical dosing, where a small, precise flow rate of chemical additives is required at a high pressure to inject it into the system. The ability of positive displacement pumps to maintain a consistent flow rate against high pressure makes them ideal for these types of applications.