In Houston, there was a construction boom in the 1970’s and 80’s with hundreds of high-rise buildings adding to the skyline. Many of these buildings are still using the original mechanical systems for HVAC and pumping applications. Potential mechanical failure and energy savings are forcing building operators to choose between modifying existing equipment or replacing them all together.
Commercial buildings have seen a lot of changes in the last 50 years. The push for energy efficiency and a reduced carbon footprint affect everything in the building, from the exterior designs to the mechanical systems in the basement. Low flow water fixtures, water recovery systems, and improving HVAC systems reduce water flow load profile today compared to years past.
Pressure Boosting System Design has also seen drastic changes in the same time period. 50 years ago, large constant speed, single stage, centrifugal pump systems were the design standard. These workhorses run 24/7, 365 days a year, regardless of the system demand in the building. This results in wasted energy and unnecessary wear on the pumps and piping. With smaller flow demands today, older pumps still in service are grossly over-sized making them much less energy efficient.
Grundfos introduced the inline Vertical Multi-Stage Pump in 1971. It has multiple impellers, each one boosting the pressure higher making them ideal for domestic pressure boosting applications. However, these applications were not widely adopted in the US until years later. Because they can create higher pressures, Multi-Stage Pumps typically require pressure control either through a Pressure Reducing Valve (PRV) or Variable Frequency Drive (VFD).
A PRV is a mechanical device used to reduce the pump pressure to the pressure required for the building. This is the equivalent of driving a car by flooring the gas pedal and using the brake to control the vehicle’s speed. No one would even think to drive their car this way, but until Variable Frequency Drives (VFD) and improved controls, the PRV was the best method of pressure control for booster systems.
The application of VFD’s and Control Systems to booster pumps have transformed them from dumb work horses to finely tuned Controls Packages. A VFD and Controller combined with Vertical Multi-Stage Pumps will only operate pumps at the speed required to maintain a constant pressure in the building. Operating a pump at a reduced speed for partial load demands creates massive energy savings. Due to affinity laws, power is proportional to the cube of pump speed. This means a 20% reduction in speed is not a 20% reduction in power consumption, it is a 48% reduction in power!
So, can you add VFD’s to an old pump system and achieve similar energy savings and performance? Can you teach that old dog new tricks? In this case the answer is almost always NO! The addition of new controls can’t overcome the underlying issues of the older single stage pumps – they are over-sized and not ideal for pressure boosting. The pumps were not designed to operate at reduced speeds, so adding VFD’s to older systems usually yields very little energy savings as the pumps still operate at close to or at full speed most of the time.
Replacing older pump systems with new, properly sized systems with VFD’s and controls will always generate more energy savings and a faster payback. For more information or for a free building assessment, contact us here.