Technical article in TGA FACHPLANER
New cooling system for the crown center
In summer 2019, the building and civil engineering department of the city of Bietigheim-Bissingen had the refrigeration technology in the city’s largest event hall replaced. Skadec won the public tender with its R290 (propane) concept, having previously advised the client on the use of natural refrigerants.
With the Kronenzentrum, Bietigheim-Bissingen offers the city’s largest event hall for all occasions: conferences, concerts, dance events, theater performances, trade fairs, exhibitions and family celebrations find the right ambience here in a central location in Bietigheim’s old town. Due to the high number of events, replacing the refrigeration technology proved to be a challenge. The previous chiller, which used R22 refrigerant, had been out of operation for some time. The first step was to replace it with an R410A refrigeration brine unit. To this end, two variants with R410A refrigerant were considered at the start of the planning phase.
With an R410A system in a split design, a GWP (global warming potential; CO2 equivalent) of 417,600 (!) would have been achieved with a refrigerant charge of approx. 200 kg. The second variant, a compact machine with a filling quantity of approx. 30 kg, also had a GWP of 62,640. However, both variants were rejected after consultation with Skadec. The R290 cold brine set with a filling quantity of 5 kg per refrigeration circuit that was finally implemented achieved a total GWP of 45 – the refrigerant filling quantity therefore has a significantly lower global warming potential than the R410A variants.
FUNDING FROM THE BAFA (only available for projects located in Germany)
Public clients can also receive funding for projects with particularly energy-efficient system technology and natural refrigerants via the “Refrigeration and air conditioning systems” funding program administered by the Federal Office of Economics and Export Control (BAFA) (see note). In total, the city of Bietigheim received 43,000 euros in funding thanks to the sustainable system concept. This made the future-proof investment significantly cheaper than using chillers with an HFC or HFO refrigerant. The program provides funding for stationary refrigeration and air conditioning systems that are operated with non-halogenated refrigerants or where the refrigeration unit is newly constructed but the refrigerant system (water, brine, air distribution system) remains the same. The Skadec concept is based on a 290 kW propane refrigeration brine unit with three redundant circuits. As a natural refrigerant, propane will not be affected by the restrictions and bans of the F-Gas Regulation in the future either. By dividing the refrigeration capacity into three redundant circuits, only 5 kg of refrigerant is required in each circuit. For comparison: The GWP of the refrigerant filling quantity of 45 thus only corresponds to the CO2 equivalent determined for around one full-load operating hour of the refrigeration machine with electricity from the German power plant fleet (electricity mix 2018, 474 gCO2/kWhel).
Note: Companies, non-profit organizations, municipalities, local authorities, special-purpose associations and municipal enterprises, universities and schools, hospitals and church institutions are eligible to apply for stationary systems under the “Refrigeration and air conditioning systems” funding programme, regardless of their intention to make a profit. Federal states and their institutions as well as state-owned companies are not eligible to apply, with the exception of the institutions expressly mentioned above. The applicant is either the owner, leaseholder or tenant of the land on which the facility is located or an energy service company (contractor) commissioned by the owner, leaseholder or tenant of the land.
PROPANE REFRIGERATION BRINE SET
The chiller has three frequency-controlled reciprocating compressors from Bitzer to regulate the cooling capacity as required. The fine load adjustment prevents the compressors from cycling. This increases the energy efficiency of the system and significantly extends its service life. To optimize system efficiency, each circuit was equipped with an internal heat exchanger. The microchannel condensers in combination with EC fans from ebm-papst also increase the coefficient of performance of the cold brine set. A total cooling capacity of 290 kW is available. The dimensioning of the individual refrigeration circuits is calculated in such a way that the crown center can still be sufficiently air-conditioned even if one refrigeration circuit fails on summer days with temperatures above 30° C. The integrated industry-standard PLC machine control guarantees operational reliability and high system availability. Operation is intuitive via a touch panel – specialist personnel can quickly change settings and find the correct operating parameters even without an operating manual. A secondary network filled with a glycol mixture with two 1500 l buffer tanks is connected upstream of the consumer network. The associated hydraulic module is integrated into the cold brine unit and equipped with a frequency-controlled high-efficiency pump from Wilo. Due to the flammability of propane (safety class A3), the new chiller was installed on the roof. In order to do justice to the inner city location, the machine has also been optimized with regard to the sound pressure level, especially during night-time operation. The buffer storage tanks, pumps and heat exchangers for system separation are also located in the plant room. The hydraulic piping is made of TIG-welded steel pipe. Extensive road closures in the old town of Bietigheim were necessary to bring in the large components and place the chiller on the roof. The new structure is now much easier to service, as the system components are now easily accessible. The project also included the dismantling of the old chiller and hydraulics in the plant room. To do this, all components had to be dismantled for removal by crane via the roof.
CONTROL AND REGULATION
In addition to the PLC-supported machine control, the Skadec software solution was also used to control the secondary circuit. The additional module for buffer management was placed in a separate, internally installed control cabinet. It monitors and controls two cold buffer storage tanks, as well as all associated valves and charge pumps. Direct communication with the cold brine set makes it possible to permanently adjust various process setpoints, such as the flow temperature of the cold brine set, to the requirements in order to further optimize the energy efficiency of the entire system. In addition, the two systems monitor each other with regard to function and process reliability. The 15″ touch panel installed in the control cabinet allows the operator to conveniently access the visualization of both systems and operate them on site. The investment will also have a positive impact in the long term thanks to the use of the latest control technology and perfect coordination of the systems. The aim is to increase operational reliability and reduce operating costs. The system’s operating options and the space gained by relocating the chiller to the outside area also make maintenance work easier.
RISK MANAGEMENT
The Skadec safety concept was very easy to implement for this project. The risks were considered for an outdoor installation with a very low refrigerant charge. Access to the roof is restricted and only possible for trained personnel. Furthermore, a propane gas sensor is installed inside the machine, which de-energizes the system via two switching stages. The EX-protected system components are supplied with a separate supply line. An integrated EX fan ventilates the housing and guarantees that no explosive mixture can form.
