Sep 1, 2015 - Building
The Cold That Came out of the Heat
ConclusionCHPs have received public attention recently due to the increasing number of systems for renewable energy generation. The gas drives the motor in a soundproof housing, which in turn runs a generator to produce electricity. One question regarding their ecological sustainability, if land is turned from agricultural use to energy production, is as worthy of discussion as questions about their operation, if the CHP is used only for electrical generation without the logical use of the heat energy as well. In this case, only the power is used from the cogeneration system, and the generated heat is discharged, unused, to the outside.
“We have thought about using cogeneration systems at WAGO for a long time. The senior director was always bringing this up,” recalls Achim Zerbst. But the problem always remained, which everyone had always had with regard to cogeneration systems: what do you do with the heat? “We ran comprehensive analyses about how the company could use the heat.” During the cooler seasons, the whole thing could be easily configured. Today, the CHP is connected via a stratified storage to the local heat network that supplies most of the buildings at the location. And in summer?
According to the information from the building services engineer, who has headed up Energy Management at WAGO for years, it was clear from the beginning that this project would only be implemented if an ecological use could be joined to the economical one. “Running a CHP in summer and discharging the heat out the roof was never considered here, nor were we interested in selling the electricity.” It was also not an option to shut the system down in the summer. In searching for a complete system that made consistent sense, the missing component was discovered to be an absorption cooling system, which uses the heat produced in the summer to generate cold air. And the demand for cooling for the plastic injection molding machines is quite large, particularly during production in the summer.
“Generate cold from heat”, is the simple explanation of the operating principle of an absorption cooling system. The conversion from heat into cold is carried out in a vacuum using a specialized cooling circuit. This consists of the so-called working pair of lithium bromide and water. The water functions as the coolant and the lithium bromide as the absorption medium. The water arrives in the evaporator via a sprinkler system. The evaporator functions at close to vacuum, which allows the water to boil far below the known 100 degrees Celsius. This evaporation draws heat from the environment and thus generates the desired cooling. The coolant vapor is subsequently absorbed by the lithium bromide solution (absorption) and, by applying heat — generated by the CHP — driven out again.
This versatility of the combination of CHP and absorption cooling system made it abundantly clear why a significant project goal consisted in designing a system that runs around the clock in the optimal operating state.
WAGO based the dimensions of the absorption cooling system and CHP on the consumption and output numbers for electricity, heating, and cooling. “The technology was designed based on the demands for heating and cooling — compared with electrical base load requirements. It was never intended to be independent from the electrical grid, but instead to cover a portion of the base load of electricity that is needed throughout the year,” explains Zerbst. The foundation for this design was laid by the available energy measurement data, recorded using in-house products, and additional information from the building control system. This provided resilient information about which forms of energy had to be available at which points and times.
Today, the Otto engine provides 239 kW of gas powered electrical energy, which can supply the production systems as well as the infrastructure at the plant. The heat output from the system is once again above 200 kW and is supplied to WAGO's internal heating network. Pivot and fulcrum for the hot water distribution is the socalled Zortström distributor. This is a buffer storage with stratified temperature layers. Heat producers feed efficiently into this, for example, the heat recovered from the cooling and compressed air supply, which WAGO has operated for years; while consumers draw off the thermal energy they need from the heat exchanger.
This detail should make it clear, that various systems have to operate in sync in order for the whole to run at high efficiency levels. Boiler, CHP, absorption cooling, compression cooling, free cooling, heat recovery from compressed air: “We work with several individual systems, whose controllers have to be data linked to the network so that we can tailor them to each other,” explains Zerbst. At this point, the project team, composed of specialists in design and services, could exploit the capacity of their own products. The WAGO-I/O-SYSTEM 750 can really prove its strengths in exactly this type of conglomerate made of different controllers, signal types, and communication languages. “Thus, we were able to link the production and building technology systems with each other. Because there is no longer a division, we can now optimize past the system limits.” Behind this statement lies the challenge of breaking the limits of individual systems on behalf of the whole. This ultimately forms the basis for a controllable, efficient operation.
The new supply technology has been a very interesting testing ground for WAGO, allowing them to examine complex relationships in their own house — the increased experience will ultimately lead to direct advantages on the customer side. With regard to devices, WAGO relies on two PFC200 Controllers in the supply system – the heating and cooling sides each have one respective controller. The mapping of the project specific relationships into two controllers could only be realized so easily, according to Zerbst, because the current controller series has a correspondingly high processing performance. “This close functional networking would not have been as problem-free with the older device generation.” For Zerbst himself, the work is far from complete. “Even if we have achieved a good, efficient result from the very beginning, we are gaining experience during operation, and are constantly discovering additional optimization potentials.”
- System design for effective base load supply
- WAGO-I/O-SYSTEM 750 as the interface to the existing systems
- Linking production and building technology for the purpose of increased energy efficiency
Text: Thorsten Sienk, freelance journalist