Greater savings
September 1st 2006 New variable speed screw compressors from Gardner Denver meet customer demands for more energy efficient solutions in compressed air generation.
Companies wanting to reduce their operating expenses should not overlook the cost of providing compressed air, which is a major item in the energy balance of most companies. Variable Speed (VS) screw compressors help reduce these costs significantly. One reason is that VS compressors generate compressed air with minimum idle time, whereas a traditional screw compressor still consumes about 30% of its full load energy cost even if no air is being produced. The second reason is that a preset pressure can be held constant within 0.2 bar without costintensive over-pressure, whereas traditional pressure switch control can have 0.5 1 bar differential (1 bar pressure reduction saves some 6 - 7% of energy costs). Gardner Denver, a subsidiary of the US Gardner Denver Group, was quick to take advantage of the significant advantages of speedcontrolled screw compressors.
Specific output is 13% higher The core of Gardner Denver's VS compressor is the integrated TEMPEST compressor unit with the ENDURO compressor block having ground rotors with ENDURO-Plus profile. The energy/flow characteristic of the compressor air end is almost constant throughout the speed range.
Therefore, the mean air production costs vary only marginally. This contrasts with traditional air end designs that emphasize full speed efficiency at the expense of part load efficiency. The compressors run at low mean speed, which has the benefit of extending the bearing service life. The shaft oil seal is also protected by an additional dust seal.
The oil separator vessel, oil filter and integrated fine separation cartridge with lifeextending upstream baffle separator are mounted on the compressor stage as a common unit with no external connections to eliminate leaks. A simple, flow optimized intake controller without spring load improves the efficiency of the machine between 1 to 2 % by reducing pressure losses. All in all, with these changes, the specific output of the new direct-coupled VS series from Gardner Denver is up to 13 % higher than similar units.
The main drive motor (insulation class F, IP 55) and inverter package has high efficiency across the full speed range. A flexible drive coupling eliminates energy losses. "Depending on the rating and age of a machine, a vee-belt drive can account for a loss of between 1.5 and 2.5 %. VS speedcontrolled machines, whether as base unit or peak-load machine, are normally always running. So, throughout the life of the directcoupled machine, these savings accumulate dramatically. Lifetime energy costs far outweigh initial purchase costs, and users are now starting to realize the importance of this in their decision-making.
This system which Gardner Denver preferred for their new VS screw compressors also reduces the maintenance costs in comparison with vee-belt drive machines. Gardner Denver warrants a life of at least 20 000 operating hours for all coupling parts and access for maintenance could not be easier. By comparison, life data of vee-belt systems specified by the industry is around 6000- 8000 hours, which, Gardner Denver says, cannot always be reached in practice because environmental factors play a major part. Besides, if the pressure demand is changed, the customer has no extra costs, for belt pulley ratios to be changed. In the new direct-coupled machines from Gardner Denver, this change is controlled by the frequency converter, whose operating range has been extended substantially for the new machines.
AirSmart control The user merely enters the required pressure value between 3 and 13 bars in the 16-language clear-text display of the control panel of the new AirSmart controller.
The machine makes a soft start with the benefit of low starting current. In a station with two VS machines, both compressors run in what we call energy-optimized mode: Compressor 1 is the first to start. When that compressor cannot supply the air needs alone, compressor 2 cuts in. Upon reaching the set pressure, each compressor reduces its output until 40 % capacity is reached, when compressor 2 cuts out after a brief idle phase. Compressor 1 then increases output to supply all the air required.
The standard version of the integrated control provides all relevant information (temperatures, pressures, etc.) in a 4-line display and has a diagnostic memory.
Scheduled maintenance of components are indicated for quick and ready reference. RS 485 interface and Ethernet networking technology support communication between the compressors and transfer data to a central control room or a defined service station. An optional higher-level control module is available to optimize the energy consumption of up to eight compressors.
Extended oil life Low oil temperatures extend the oil life reducing maintenance costs and expenditure for disposal of waste oil. To achieve this, an intelligent control system in the new, direct-coupled VS machines keeps the oil temperature as low as possible. With this solution the intervals for changing the oil in the new VS machines are defined as a function of the thermal stress of the oil and are calculated by the AirSmart control system. The system works at a constant temperature ( 2 C) even in harshest environments to ensure energy efficiency.
Having a variable flow system to stabilize the oil temperature, the VS machines are exposed to very little stress extending the life of components such as the flexible hoses.
With the AirSmart control the optimal compressor oil temperature is calculated as a function of the intake temperature. This results in the best thermal efficiency in the air end without the possibility of condensation.
Efficient Cooling For optimal efficiency of the cooling air, these new VS compressors have separate flow paths for the air intake, cooling fan and inverter. The cooling fan has specially designed blades to run at low speed and generates low noise levels, only 64 dB (A) at 50% load. The generously dimensioned cooler ensures a low temperature difference between the intake air and the compressed air and favorable entry temperatures for the downstream air treatment equipment. The optimal temperature environment improves the operating safety and reliability of all parts of the control system for smooth operation of the compressor.
Optional extras These compressors were developed by Gardner Denver for the world market and can be used within a wide voltage range.
All machines are available with integrated refrigeration dryer (pressure dew point of +3 C). The dryers are charged with environmentally compatible R 404 A refrigerant. They operate at ambient temperatures of up to +45 C with a very low pressure loss. If requested by the customer, VS compressors with watercooling are also available. All can also be supplied with heat recovery equipment to further reduce energy consumption.
Special long life, energy efficient synthetic AEON compressor oils can also be used. More articles from Gardner Denver Limited: | 
