DESIGO Energy-efficient applications: h,x-controlled Economizer tx2 Application data sheet Answers for infrastructure.
Table of contents 1 Introduction to Economizer tx2 .............................................................5 2 Basics.......................................................................................................6 3 Economizer tx2........................................................................................6 3.1 Overview ...................................................................................................6 3.2 Principles of the tx2 Economizer strategy...........
1 Introduction to Economizer tx2 The Economizer tx2 application offers energy-optimized air conditioning plant control by conditioning the air supplied to the rooms using the most favorable type of energy. Our patented procedure continuously calculates air conditioning costs, allowing for targeted selection of the most favorable method.
2 Basics Air conditioning plants do not always enjoy the best of reputations. The reasons mainly concern plant hygiene, partly incorrect plant design, often high energy consumption as well, especially with older plants or certain designs. Nevertheless, air conditioning plants perform important tasks and have an established place in modern building control. A great deal of progress has been made in recent times, especially with regard to plant hygiene, energy management, and plant equipment.
3.2 Principles of the tx2 Economizer strategy Figure 3-1 Economizer tx2 principle. – Comfort area control (tx2 control) and energy recovery control (tx2 ERC strategy) together contribute to optimizing air conditioning plant operating costs through interharmonization and coupling. The Economizer tx2 corresponds to h,x-controlled temperature and humidity control.
3.3 The principle functions 3.3.1 Comfort area Advantages: – Better comfort sensation – Greater potential energy savings Economizer tx2 uses the so-called comfort area as a setpoint (see Figure 3-2). There are two reasons why a field is used as a setpoint. Comfort sensation: Optimal working environment conditions exist not just at a specific setpoint for room temperature and room humidity, but within a particular range.
3.3.2 tx2 control Figure 3-3 tx2 control – Determination of the room setpoint and cascade control for temperature and absolute humidity. Both room temperature and humidity are controlled as follows using the Economizer tx2: The comfort area determines the room air setpoint for temparature and humidity based on the present room air state and the defined comfort area. The comfort area is not actively controlled. When elements are activated, control is exercised to the field's limit.
demand. But, no cooling and reheating is required to achieve the relative room humidity in this range. This lowers costs thanks to lower cooling energy requirements. – For "humidification only", the relative humidity actual value is projected to the relative humidity line. This results in greater humidification demand. But, no cooling is required in this range. This in turn lowers costs, as humidification normally costs less than cooling.
3.3.3 ERC strategy Advantages: – Optimal use of ERC The position signals are converted into demand signals for the ERC strategy (Figure 3-1) and weighted using specific costs for heating, cooling, humidification and dehumidification. Weighting can be set for each plant to allow for costoptimized operation of the plant.
3.3.4 Weighted processes Advantages: – Minimize energy costs – Reduce energy consumption – Reduce CO2 emissions Relative weightings are used to optimize ERC. They result from the energy provisioning processes for heating, cooling, humidification, and dehumidification. The weighting factors can be used to optimize: – Energy costs – Energy consumption – CO2 emissions Example: Energy costs Energy recovery optimizes energy costs by preconditioning outside air.
3.3.5 Energy comparison with other strategies The DESIGO INSIGHT management station allows for displaying savings by means of an energy comparison table. The most important characteristic values are calculated and displayed online based on known plant variables.
Additional information is available in the appendix (Section 11.3). 3.3.
4 Energy savings Comprehensive building simulations have been examined for energy consumption, comfort, and control accuracy. The Economizer tx2 algorithm generates the corner values to compare energy consumption to a conventional air conditioning plant control with ERC control included in the temperature sequence.
5 Advantages and customer benefits 5.1 Advantages – – – – Comfort control to maintain temperature and humidity limits Cost-optimized use of available energies Monetary display of plant efficiency Modular designed standard library applications including graphics for plant operation using DESIGO INSIGHT to simplify engineering and commissioning 5.
7 Display and operation DESIGO INSIGHT offers predefined plant pictures for air handling units. A table shows a comparison of the most common energy consumption means (Table 3-7). Figure 7-1 Overview picture with operating elements for air handling unit 8 System hardware The Economizer tx2 application is approved for installation on the primary automation station PXC. 9 Field devices No special requirements are placed on field devices with regard to measuring precision, quality, etc.
11 Appendix 11.1 Plant components The Economizer tx2 application offers a modular design allowing for adaptation to different types of air conditioning plants. It contains various variants and options. Resulting in broad coverage of typical plants.
11.2 h,x-diagram Simplifying calculation of air state changes graphically was attempted a long time ago. Diagrams for psychrometric calculations (e.g. enthalpy, dewpoint etc.) exist in various forms. The Mollier diagram normally is used in Europe, and Carrier in the U.S. Both diagrams use the same principal approach, only the orientation of the axes varies. The temperature axis in the Mollier diagram is vertical, and horizontal in Carrier. Water content in Mollier is horizontal, and vertical in Carrier.
11.3 ERC control behavior The best known, conventional control procedures for ERC are list below. – Stg 1: Strategy Max ERC recovery ERC is fully controlled – Stg 2: Strategy Temp. ERC is integrated in the temperature sequence – Stg 3: Strategy Hum. ERC is integrated in the humidity sequence – Stg 4: Strategy Enthalpy. ERC is controlled to the supply air setpoint enthalpy. The air state after ERC depends on the selected strategy. Figure 11-2 h,x diagram with schematic of the 4 strategies.
Figure 11-3: Diagram for an air conditioning plant with entered, principal air states 1 (Sta1) and 2 (Sta2) for energy calculation: - Air state 1 corresponds to the state of the air after ERC - Air state 2 corresponds to the state of the air after air handling Ex Oa Sta1 Exhaust air Outside air Air state 1; depends on ERC strategy Sta2 Su Air state 2 Supply air 21
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