How to Pick a HVAC Centrifugal Pump Part 3: Mechanical Room Space and Type of Pump Selected

By Chad Edmondson and Norman Hall

In our last blog we discussed the differences between inline and base mounted pumps. When the engineer or contractor is selecting the type of pump to use, available space is always one of the criteria. This week we look at the space required by base mounted inline pumps and base mounted end suction pumps.

It’s easy to become fixated on floor space when designing a hydronic system. After all, space often equates to money in construction, a fact that can leave mechanical engineers starved for mechanical space. This is what makes the idea of pipe-supported inline pumps so attractive and even popular. Sometimes the choice is fine, other times it is not. For long term satisfaction and serviceability, there are a few things an engineer must consider before deciding to get that pump off the floor and in the air and (theoretically) out of the way.

How large is the pump?

Small inline or booster pumps do take up less space than base mounted pumps of similar capacities.  They are traditionally pipe supported and can be installed without taking up any actual floor space as shown here:  

This works fine, assuming the pump and motor aren’t too large and the pump isn’t installed so high and/or in a space where servicing becomes difficult or even dangerous. Remember that the piping supports must be designed for the extra weight of not only the pump but the pump accessories (e.g. the triple duty check and balance valve).

Seismic concerns, if there are any, complicate matters even further. For these reasons, we recommend installing inline pumps that are 15 HP or larger on the floor. Notice the increase in motor weight in the chart below when the horsepower changes from 10 to 15.

What kind of service area is needed around the pump?

Clearly, it’s important that there be no obstructions to servicing the pump whether it is in the air or on the floor. If the inline pump is installed on the floor, keep in mind it will have be installed with a suction diffuser or long radius elbow and 5 pipe diameters of straight pipe and discharge elbow, all of which will increase the amount of floor space required on both the suction and discharge side of the pump.  (See Below)

May require vibration base If mounted on an upper floor

In a case like this, we would most likely recommend considering an end-suction or vertical double suction base mounted pump in lieu of the vertical floor mounted inline. An end-suction base mounted pump eliminates the need for the discharge elbow; a vertical split case double suction pump eliminates both the discharge elbow and suction diffuser.   Plus, either base-mounted pump can be serviced without necessarily having to remove the motor.

As the below graphic shows, the base-mounted pumps can actually take up less space, especially if maintenance is taken into consideration.

Floor-mounted-pump-spacing.jpg

Will multiple pumps be piped in parallel with N+1 standby?

If more than two pumps are to be piped and installed in parallel we would again recommend base mounted pumps for motor serviceability. As you can see by the below image of the skid mounted vertical inline pumps, there is very little room to service the inside pumps. However, a base mounted arrangement, as shown on the right, provides access to all the pump internals from the back end of the skid.