Chiller Sets New Benchmarks For Energy Efficiency, Tight Control
Plastics Technology, April 24, 2017
Here are more details on what is heralded as “the most efficient industrial process chiller on the market,” first discussed briefly in last month’s Keeping Up section. Jochen Naujokat, president of Delta T Systems, Richfield, Wis., and Rick Holzhauer, the firm’s chief mechanical engineer, previewed this development exclusively for Plastics Technology. These units are loaded with features that are either “firsts” in the field of process chilling, or are still quite rare for smaller chillers, or are standard capabilities that are usually expensive options.
To be launched in July, the new line will start with small portable chillers of 1 to 15 tons, with larger portable models up to 30 tons and central models to follow thereafter. Initial models will be air cooled, though water-cooled units will not be far behind.
The new Delta T system monitors the process temperature and signals the drive to speed up or slow down the compressor. It eliminates the wear and tear of on/off cycling of the compressor or energy- wasting hot-gas bypass valves. Compared with conventional fixed- speed compressors with hot-gas bypass, the new technology uses up to 50% less energy, according to Delta T Systems, or 30-50% of the initial investment, and thereby pays for itself in two to three years. Naujokat says these estimated savings are conservative because “Most chillers are selected based on the peak-usage time of the year, which means the chiller is oversized for the average use.”
The savings are analogous to the savings from variable-speed hydraulic pump drives vs. standard fixed-speed pumps in molding machines. Like a conventional fixed-speed hydraulic pump, a fixed-speed compressor runs at 100% of the rated load regardless of the process needs. A more advanced option is the hot-gas bypass valve, which vents the hot, compressed refrigerant gas to the evaporator if no cooling load is needed. This is wasteful in the same sense that a conventional fixed-speed hydraulic system dumps excess oil over a relief valve when not required by the process.
According to Naujokat, variable-speed compressors have historically been designed for HVAC use, and only recently have models tailored for industrial chilling become available. A key requirement for industrial versions is a wider operating envelope, Holzhauer explains. Another element critical to the development of the new chillers was that Delta T Systems Inc. worked with controls manufacturers to create a system specifically for use with these compressors.
The controller continuously monitors the suction and discharge pressures to ensure the compressor stays within its operating envelope. However, that operating envelope is now between 10% and 100% of rated capacity, which means that a 10-ton chiller can operate efficiently at loads of 1 to 10 tons. That compares with a 30% to 100% operating range for conventional chillers, says Naujokat.
Another new energy-saving feature is an electronic expansion valve, which works with the variable-speed compressor to tune the valve to the system needs based on data from temperature and pressure sensors. The valve is driven by a DC stepper motor, which moves a pin up or down to allow more or less refrigerant to flow through the valve. Up to now, this technology has been available mainly on larger chillers of 20 tons or more capacity. (It is also used on Thermal Care’s NQV series small portable chillers.)
The new chillers also use variable-speed condenser fans, which use onboard sensors to monitor the refrigeration system to keep the fan operating at the most efficient point. What’s more, monitoring the refrigerant discharge pressure also protects the compressor by helping to keep it within its operating envelope. The variable-speed condenser uses a permanent-magnet, electronic computated motor (ECM), described by Delta T Systems as “the latest development for condenser-fan motors and the quietest, most efficient, and most reliable motor technology in the industry.” It eliminates the small copper refrigerant capillary tubes from a mechanical expansion valve or mechanical pressure controls that can fail over time due to vibration, Holzhauer explains. ECM is another feature adopted from the HVAC industry, and variable-speed fans have until now been relatively rare in process chilling, where they have been offered as expensive options—but are standard on the new units from Delta T Systems.
Also contributing to efficiency are oversized, stainless-steel, brazed-plate evaporators with a larger heat-transfer surface than competitive units, which reduces compressor demand and energy consumption. And microchannel aluminum condenser coils eliminate the galvanic corrosion between dissimilar metals seen in copper-tube coils with aluminum fins. Microchannel aluminum coils are “the latest technology in the industry,” according to Naujokat, and have appeared so far on only a few industrial chillers.
In addition, cleanable condenser air-inlet filters to protect the condensers from dust and debris are standard features on the new chillers but not on all competitive models. Delta T Systems also added a cleanable evaporator strainer to protect the evaporator channels from clogging; unlike similar features on other chillers, it employs a new method of straining and a quick-disconnect on the water side that eliminates threads and hose clamps.