Designing the optimal water boosting system
To ensure constant pressure, tall commercial buildings face two major challenges. First, pre-pressure in water mains is rarely high enough to cover the whole building. Second, water demand changes constantly. Break tanks are typically installed to keep water on stock. However, this makes the need for pumps even more urgent as water needs to be boosted to reach different users. This means a booster system must not only be reliable but also have the intelligence to maintain the right pressure regardless of consumption. Single booster systems, however, can result in unacceptably high pressure within the lower floors. When this happens the system needs expensive pressure relief valves that waste energy to remove excessive pressure.
Choosing the right pressure system depends on the height of the building and the load profile. But in most cases a zone divided system, where a number of boosters serve their own pressure zone, offers the most efficient solution. Zone divided boosters ensure no more pressure is added to the system than what is needed. This means your building has equal water pressure to all floors without wasting energy – even under fluctuating consumption. A zone divided approach also offers the reliability of multiple pumps and ensures the system can adapt to fluctuating consumption.
Single booster vs. zone divided: A calculation
Exactly how significant is the benefit from choosing an intelligent system? We calculated the energy consumption of two different designs for a booster system for a 20-story hospital to find out.
We used Grundfos Product Center to size booster applications for a hospital with 800 beds and a water consumption of 300 m3/year per bed. The allowable tap pressure is 2.5 to 4.0 bar and the building and floor height is 80m and 4m respectively. With 60% of the water consumption occurring on the first storeys, a single booster system consumes 106,530 kWh/year. The zone divided solution uses only 72,937 kWh/year – 31.5% less.
How to calculate in Grundfos Product Center
The intelligent solution: A zone divided system
Single booster system
The simplest way to achieve equal tap water pressure on all floors is by producing excessive pressure – and then removing it again.
Having just one booster set delivering water to the whole building leads to significant pressure differences in the system. The boosting station in the basement has the pump power to overcome the pressure head loss of a system that reaches all the way to the top floor. But this also means that the tap water pressure at the lower floors far exceeds an acceptable level. This requires pressure relief valves to be installed in order to remove excessive pressure. In other words, not only do you need to invest in additional components, you’re also removing the pressure you just spent energy on producing.
Zone divided system
The intelligent way to boost water is to produce the pressure needed at each floor – no more, no less.
By dividing a tall building into booster zones, you can define the flow and pressure needed at each zone. Sizing each booster to meet your exact demands is then an easy calculation in Grundfos Product Center. With each booster now pumping at the exact speed required, the effect on energy consumption is clear: there is no more energy waste from reducing overpressure, and the pumps perform for the load profile of each zone. Our booster sets intelligently adapt to demand, eliminating the need for pressure relief valves – all while ensuring reliable and efficient operation at all times.