Variable Speed Pumps Explained

Why variable speed pumps?

When you consider all the pumping that occurs globally, whether in large industrial plants or in domestic heating systems, this accounts for almost 20% of the world's energy consumption. Because of this there is a huge opportunity in the pumping industry to make a significant contribution to using our energy resources efficiently. In pumping applications where the duty required is not constant, it is highly likely that installing a variable speed pump will result in significant energy savings - likely to be between 30% and 50% in many applications.

Other benefits of variable speed pumps include:

1. Improved reliability

Because variable speed pumps run at speeds below their maximum, there is a reduction in wear, particularly in mechanical seals.

2. Improved control

Variable speed pump controller can monitor small variations in pressure and make adjustments accordingly. This also means there is less liklihood of sudden changes in flow or pressure.

When should variable speed pumps be used?

Variable speed pumps should be used in any installation where the pump duty is not constant. If a pump duty is constant a fixed speed pump may be the most cost-effective option. However, even in fixed duty applications there may be an advantage to running a pump below its maximum speed. A motor running at 80% of its maximum speed uses 48% less energy.

Are there any disadvantages to using variable speed pumps?

1. Vibrations

Although running pumps below their maximum speed will tend to reduce overall system noise, altering the speed of a pump may result in structural resonances that would not occur at the pump's maximum speed. This may cause vibration which can be harmful to equipment and cause an increase in noise at certain frequencies. There are a number of products that help to alleviate these potential issues.

2. Higher initial cost

Because of the added complexity of an inverter drive, variable speed pumps and systems which include variable speed pumps will cost more initially than a fixed speed equivalent. However, this additional cost is invariably outweighed by the long-term energy cost saving.

Examples of Variable Speed Drives

Variable speed drives vary in complexity depending on the level of control required. Here are two examples of variable speed drives available from Lowara:

Hydrovar

HYDROVAR is a pump or wall-mounted variable speed microprocessor based controller. It was the world’s first of its type to manage motor speeds and match pump performance to a range of hot and cold water applications.

Due to the unique modular design, the HYDROVAR unit can be mounted or retrofitted to any existing centrifugal pump which has a standard IEC motor. This is the long-awaited solution for high-level installations requiring failsafe systems with a superior range of features, while its modularity also provides a cost-effective solution for low-level, reduced feature demands.

The HYDROVAR needs no additional master control and enables virtually any configuration of pumps and up to 8 master drives or a mix of master and slave drives to be programmed. The units are available in power ratings from 1.1 - 22 kW.

The HYDROVAR delivers much more than just changing the motor speed. It truly manages your pump performance to match a wide range of system conditions, allowing energy savings up to 70% (approved by TUEV Austria)*

* Tests carried out by TUEV Austria (Austrian testing authority) on 5 March 2005 based on comparative tables and data on intake performance at identical flow.

Teknospeed

A simplified development of the Hydrovar®, the Teknospeed integrated air-cooled frequency converter relies on a 4-20mA signal to maintain a pre-set pressure. The required pressure set-point can be adjusted by a potentiometer on the side of the unit. Contacts for a low water floatswitch and for alarm condition (NC) are standard features.

A single flashing LED on the unit identifies up to seven different types of fault. The panel provides local isolation and fuse protection. An effective combination of simplicity and sophistication.