Save time designing a liquid chiller with the BITZER SOFTWARE

An air conditioning system has to be planned for an office building. The specifications: the water cooled liquid chiller has to run on a propane compact screw compressor and have a refrigerating capacity of 300 kW. But what components are best suited to working together and delivering exceptional energy efficiency? The BITZER SOFTWARE can answer these questions in minutes.

Quick overview of operating parameters

In the example at hand, we intuitively enter the BITZER SOFTWARE through the ‘Compact screw compressor’ module to design the compressor in stage one. It takes just a couple of clicks to set the chosen refrigerant (R290), the required refrigerating capacity (300 kW) and other project specifications:
 

• Evaporation temperature +4°C (water flow temperature +7°C)
• Condensing temperature +38°C
• Liquid subcooling 3 K
• Usable suction gas superheat Δtoh 5 K

The software then suggests two compatible compressor designs for the planned air conditioning system: the CSHP8553 with the required capacity and the CSHP8563 with somewhat greater capacity. It can pay off to select a slightly smaller compressor with economiser mode, especially if the maximum refrigerating capacity is only needed rarely or for short durations. In no time at all, the calculation provides the user with an overview of the key system parameters under the given operating conditions, such as cooling capacity or power input, coefficient of performance COP and discharge gas temperature (image 1).

In this case, the user chooses the CSHP8563-125P-40P compact screw compressor with a refrigerating capacity of 312 kW. The software updates the schematic of the refrigerant circuit and makes all data available for download, including the polynomial needed to calculate power consumption, refrigerating capacity, current consumption and refrigerant mass flow. Further self-explanatory tabs in the BITZER SOFTWARE guide the user to more in-depth technical data, such as the application limits and dimensional drawings, as well as available accessories for the compressor.

From oil separator and oil cooler through compressor protection device and frequency inverter to motor and coupling for open drive compressors – once a compressor has been selected, the BITZER SOFTWARE automatically suggests options to optimise the energy efficiency of the system with coordinated components. In the case of the CSHP compressor in the example, K series condensers are available. With water as a coolant and a water inlet temperature of +30°C, the type K3803P (two pass) with a condensing capacity of 380 kW is suggested. Just like with the compressor design, additional useful information about the chosen accessory is available under ‘Technical data’, ‘Dimensions’ and ‘Documentation’ in the menu.

Evaporator design made easy

The BITZER SOFTWARE is just as intuitive and helpful when it comes to designing an evaporator. With SQD shell and tube evaporators, an important new product group has been added to the software. These direct expansion evaporators are individually adaptable, deliver high levels of efficiency with their quadratic cross sections and meet current efficiency requirements. That is why the user in the example chose an SQD evaporator with a capacity of 303 kW. It only takes a few clicks to complete the design. The chosen inlet temperature of +12°C and outlet temperature of +7°C are entered under ‘Heat transfer fluid parameters’ and the following parameters are entered under ‘Refrigerant parameters:
 

• Condensing temperature (dew) +38°C
• Subcooling 3 K
• Evaporating temperature (dew) +4°C
• Superheating 5 K (usable)
• Pressure drop target for optimal refrigerant distribution with propane under the given operating conditions: 200 kPa

A maximum or target pressure drop can be entered for both sets of operating conditions. Click on the ‘i’ symbol for more information. The software can compare a wide range of potential combinations to find the optimal solution for every application. For example, other specifications, such as shell size or tube length, can be selected in the design settings. The calculation then displays multiple compatible evaporators for the office building’s planned single-circuit air conditioning system (image 2). The following aspects must be taken into consideration when selecting a specific model:
 

• What is the desired margin (difference between the required and calculated evaporation temperature)?
• How long can the evaporator be (tube length)?
• What volume/mass flows are suitable?
• What is the desired pressure drop?

For the air conditioning system in the example, the optimal evaporator proves to be the SQD2513114-11-6035 with a 3943 mm tube length and approx. 1% margin. Once all the necessary system components have been selected, all calculations can be exported in PDF format or saved in the software directly for use at a later date after the user has logged in via myBITZER.