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Case Studies

Pressure Up vs Pressure Down – Water Supply for High Rise

September 20 2017

When considering water supply for high rise buildings, structural engineers will want to take into account the pros and cons of pressure up and pressure down water supply systems.

With a pressure up system, the system is typically divided into zones and a number of booster pumps provide the pressure which is necessary for optimum user comfort. A pressure down system involves a roof tank, a solution that was created as taller buildings were built, resulting in a requirement for more water for both domestic use and fire-fighting.

Design Considerations for a Pressure Down Situation

With a roof tank on a high rise building, water pressure and water supply for domestic use and fire-fighting is readily available, even when there is no electrical power. However, there are greater structural requirements for installing a water tank on a roof. The demand for space, the restrictions it will impose in terms of extending the height of a building, and its impact on the value of real estate must also be taken into account.

Practical Solutions From Allied Pumps

With many new buildings, there is a push to use a single basement tank and basement pumps pressuring to the top of the high rise or apartment block. With Motive Apartments in Perth, we designed a system to keep the rooftop tank full by installing a small pump in the basement. The pump effectively transfers water from the basement to the rooftop. The top floors of the block are served by smaller, variable speed pumps, and the lower levels are fed by gravity.

Since the system uses smaller pumps that run less often, the client has benefited from huge savings in terms of electricity costs, and the system can still supply water to residents in the event of a power outage.

Typical Installations of Pressurised Water Systems

System configurations for pressure up systems include: a single booster system; a zone divided system where a zone supplies 12 floors; a series-connected system with intermediate break tanks so that every zone is served by its own booster set; and a series-connected system.

ADVANTAGES AND DISADVANTAGES OF PRESSURE UP VS PRESSURE DOWN SYSTEMS

Advantages of Pressurised Systems Include:

  •        Less of a demand for space than with a roof tank
  •        Lower life cycle costs
  •        Lower maintenance costs

Disadvantages of Pressurised Systems Include:

  •        Electricity required

Advantages of Roof Top Water Tanks 

  •        Continuance of water supply
  •        Smaller power supplies required
  •        Lower capital cost of pump equipment (in many cases): Small flow feed pump; Small variable speed pressure system for top floss; Less probability of water hammer; Smoother system supply

Disadvantages of Roof Top Water Tanks 

  •        Greater structural requirements
  •        Higher initial costs for piping, valves and tank
  •        High operating costs
  •        Lack of pressure control
  •        Maintenance costs and difficulty: tanks must be emptied and cleansed every year as they are a breeding ground for bacteria such as legionella

The Correct Installation Process

When selecting the right system for your application, take the following into account:

  •        Reliability
  •        Efficiency
  •        Noise associated with operation
  •        Requirement for consistency of temperature and pressure

Choose a supplier that can offer a turnkey package and who is willing to partner with you to achieve the exact configuration you need. This has to include technical support during and after installation, troubleshooting, and system sustainability.

To discuss your next pressurised water system project please contact Allied Pumps today

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