AIR QUALITY
The quickest route to energy saving
There are many reasons why deploying variable speed drives is the easiest way to lower your energy bill, as ABB’s Carl Turbitt explains.
V
ariable speed drives (VSDs) are some 40 years old – ample time, you’d think, to spread the merits of their energy saving potential. Yet evidence suggests that many businesses think changing energy supplier is a better way to lower bills than installing energy efficient equipment like VSDs. However, with many energy suppliers offering comparable rates, and with energy prices generally only going one way, this option merely moves the problem from one place to another, rather than curing it. A far more effective alternative is to deploy a VSD to regulate the speed of the millions of electric motors powering everything from air handling units, industrial process cooling pumps, chilled water pumps and hot water circulation pumps. In fact, electric motors account for some 67% of all industrial electricity consumed. Applying a VSD, particularly to variable torque applications like centrifugal pumps and fans, often saves between 40-60% of the energy bill and can frequently give a payback within a matter of months. So, the impact far outstrips any other energy saving opportunities and should be top of the priority list for all companies using motor- driven applications.
Freeze refrigeration costs
Refrigeration is one of the major costs of many industries. Since refrigeration systems typically
20 June 2019
run 24 hours, most fan and pump applications are potential candidates for VSDs. Essentially, any refrigeration system with a wide variation in operating hours or with a heat load that is less than the peak load can benefit from a VSD. Many refrigeration systems which use pumps, fans and compressors are still using inefficient on/off or two speed controls for the condenser fans. Significant savings can be made by using a VSD to directly control the speed of the electric motor. Where drive belts are used on the fan systems, the VSD reduces belt stress and maintenance costs.
An example is Ginsters bakery, which asked ABB to carry out an energy appraisal at its plant. The appraisal focused on the refrigeration system, in which chilled water pumps ran constantly with a full unrestricted flow. These pumps provide chilled water to the cold storage and production areas of the plant.
The power consumption of the pumps was measured over 24 hours and analysis showed that using a VSD to achieve a speed reduction of only 6% would reduce energy consumption and therefore operational costs by some 17%. A trial installation of an ABB drive showed improved stability of the system and again reduced power consumption. Following this, permanent ABB drives were installed on all pumps.
Retrofitting the VSDs in an existing HVAC system could give it a whole new lease of life, without the need for drastic replacement of ductwork, motors and fans. In common with many other industrial installations and facilities, HVAC systems need regular reviews to ensure that they are both meeting the current needs of the building they serve and are operating to the maximum efficiency possible with modern equipment. A retrofit will endeavour to salvage as much of the existing VSD system infrastructure as possible, while introducing a far more compact, robust and efficient drive. It also brings the possibility to have some new features such as an improved user interface or new functionality such as fault loggers.
In a retrofit project, existing cabling, motors and cabinets often remain in use, while the VSD is replaced either completely or partly. Retrofitting is typically carried out during planned shutdowns, without causing extra downtime.
There are a number of reasons why a building operator may want to retrofit the drives in a HVAC system, with technical, operational and legislative developments all being possible triggers.
Life cycle issues One major technical reason to retrofit may
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