A: An HVAC chilled water pump is any type of centrifugal pump that is circulating water within an HVAC/air conditioning or heating unit. It helps keep the water cool, the air temperature moderated, and keeps the entire system running correctly.
While there are a variety of pumps used for fluid transfer, centrifugal pumps are the most common type used in commercial HVAC systems. These pumps can work in one of two ways— volute flow or axial flow. Volute flow pumps get water from the impeller and pushes it out perpendicular to the pump shaft. However, an axial flow pump pushes the water at a parallel to the pump shaft.
HVAC Chilled Water Pump Configurations
Centrifugal pumps are available in many different configurations including single and multi-stage end suction, vertical inline, single and multi-stage split case, and circulating pumps. Each configuration is designed with specific applications in mind. It is especially important that the HVAC chilled water pump you choose can handle more than your project requires.
It’s a risky move to try and get by with the bare minimum configuration since there are many variables. It’s better to choose something that can sufficiently handle your system’s minimum requirements and then some. You should make yourself familiar with the intent and limitations of each pump configuration.
Circulating
Circulating pumps are typically used for systems that are low pressure and low capacity. Typically, systems using this configuration are rated for under 150 GPM with a max operating pressure of 125 PSIG. Usually, the pump is mounted directly into the piping system which also supports it and the motor can be oriented vertically or horizontally.
End-Suction
End-suction pumps are single-suction only and they can be configured to be either flexible-coupled or close- coupled. The difference between the two comes down to the positioning and mounting of the impeller. In a close-coupled configuration, the impeller is mounted right on the motor shaft directly. The benefit of this configuration is that the alignment of the impeller to the motor shaft is static and cannot move. A flexible-coupled configuration has a flexible coupling that separates the motor shaft and the impeller. Since the alignment of the impeller to the shaft is not fixed, a flexible-coupled pump can have some drawbacks. For example, the pump can slip out of alignment during routine pump maintenance and cause serious issues if not corrected properly. You should always use professionally trained technicians to reassemble a pump that has gotten out of alignment.
The advantage of using a close-coupled pump comes down to space. Close-coupled pumps don’t need as much space as flexible alternatives but there is a downside—the motor. On flexible-coupled pumps, the motors used are universal and standard in design. However, on close-coupled, the motor is matched to the shaft type and the seals. This can cause issues when repairs are needed in terms of part sourcing and compatibility.
End-suction pumps are designed to draw the incoming water into the pump horizontally and discharged vertically or perpendicular to the suction. End-suction pumps, no matter the configuration, need a sturdy foundation since they are used for large systems. Typically, the installation would be bolted to a solid base plate affixed to the floor and reinforced. The reinforcement and stability are crucial as HVAC systems that use these pumps have capacities of up to 4000 GPM.
Split-Case
Split-case pumps are similar to end-suction pumps but only the flexible-coupled version as the motor and pump are also flexible-coupled. The entire assembly is also required to be mounted to a rigid base plate. The suction and discharge arrangement is also the same but the pumps are available in single or double-suction.
In a single-suction pump, water enters solely from one side versus double-action where water enters from both sides. The advantage of double-suction is that it reduces the chance of a hydraulic imbalance. It is for this reason that double-suction split-case pumps are preferred by a large margin over single-suction models.
Now, split-case pumps also can have more than one impeller to use in a multi-stage operation mode. The use of multiple impellers provides a boost in the available head all within a single pump.
Pump orientation also varies as split-case pumps can be horizontally or vertically oriented. In the horizontal configuration, the impeller casing is split horizontally and in vertical it’s split vertically. Either configuration offers a huge advantage regarding maintenance. The split casing allows for easy impeller access when repairs or upkeep is needed.
The most often used application for split-case pumps is in fire protection systems for commercial buildings. However, they are also used for large HVAC systems with capacities up to 6,500 GPM and 600 ft of head. Increased operating pressures of up to 400 PSIG are also an advantageous feature for large commercial HVAC systems.
Vertical Inline
When there is less space available for installation, vertical inline pumps are a perfect solution in most cases. The pump design includes a reduced footprint since they are close-coupled and don’t need an inertia base. However, for larger capacity vertical inline pumps, one may be installed to reduce vibration within the pump. Vertical in-line pumps are available in a single or double-suction configuration and can handle capacities up to 25,000 GPM and 300 ft of head.
Selecting An HVAC Chilled Water Pump
When you’re choosing a pump you need to consider several determining factors. First, you need to determine the building’s HVAC loads—that allows you to get the flow rate needed. From there, you can calculate the pressure losses.
Once you know the pressure loss and flow rate of the system needed for your project you can confidently shop for pumps. First, you need to decide what the best type of pump is for your system. You do that by reviewing the technical datasheets for each type of pump to learn each one’s operational range.
Most manufacturers’ websites have calculators available that can help you with choosing a proper pump for your application. The pump you choose needs to be able to meet both the minimum flow rate as well as the maximum flow rate. If you cannot hit those numbers with a single pump, then you will need to pipe in a second pump in a parallel configuration.
There are other factors besides efficiency and hitting minimum and maximum flow rates. You also need to factor in the lifetime operating cost of the system. This is crucial in energy usage and can vary greatly between different pump configurations. Two different pump configurations can perform for the same number of hours yet one could cost you significantly more to run.
Flow rate, best efficiency point compared to duty point, pressure losses, and operating costs all come together to give you the big picture. You should simply start with the flow rate needed so you can determine the right kind of pump you need. Then, use a pump curve and operating cost analysis to get your final selection. However, getting all those numbers together and then figuring out which pump is best can be time-consuming and tedious.
Let Us Find The Right HVAC Chilled Water Pump For Your Project!
When it comes to selecting the right HVAC chilled water pump for your application, we help with the leg work. We have seasoned technicians with a background in MEP and HVAC design that can help you take the guesswork out of the purchase process. You tell us your system requirements and our consultants can help get the right pump that will get the job done efficiently.
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