DESIGO - Answers for infrastructure. Energy-efficient applications: h,x-controlled Economizer tx2. Application data sheet

Transcription

1 DESIGO - Energy-efficient applications: h,x-controlled Economizer tx2 Application data sheet Answers for infrastructure. s

2 2

3 Table of contents 1 Introduction to Economizer tx Basics Economizer tx Overview Principles of the tx2 Economizer strategy The principle functions Comfort area tx2 control ERC strategy Weighted processes Energy comparison with other strategies Additional functions Energy savings Advantages and customer benefits Advantages Customer benefits Field of use Display and operation System hardware Field devices Versioning Appendix Plant components h,x-diagram ERC control behavior About this document

4 4

5 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. Economizer tx2 optimizes the room state within a setpoint field resulting in optimum setpoint settings for ventilation while at the same time optimizing energy recovery resulting in the best possible air aftertreatment. Optimization can be based on energy, costs, or CO 2. As a result, Economizer tx2 helps lower energy costs and offers an excellent basis for highly efficient operation. In fact, up to 40% energy can be saved compared to conventional air conditioning. At the same time, comfort control ensures that limit values are maintained for temperature and humidity. The innovative application is modular in design and includes a number of plant variants to control air handling units. Definition of terms ERC: Energy recovery Economizer tx2 2-dimensional optimization Absolute humidity Temperature Figure 1-1 Basic diagram for an air conditioning plant with Economizer tx2 5

6 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. However, strategies for controlling air conditioning plants have hardly changed over the past few years. For example, energy recovery is typically controlled according to enthalpy, i.e. separate temperature and humidity control loops with their own energy-neutral zones but without inter-harmonization. This method does not always guarantee optimal behavior and generally is deficient with regard to dynamics. This is where our Economizer tx2 comes in: Systematic exploitation of comfort limits inter-harmonization of setpoints, process control, and energy recovery mode. 3 Economizer tx2 3.1 Overview An air conditioning plant ready for operation with energy recovery serves as our starting point. This air conditioning plant is tasked with providing adequate comfort conditions (use-adjusted room conditions) at the lowest possible operating costs. Minimizing operating costs, however, may not be at the expense of comfort. The following aggregates can be used as air handling units: Hot water heating coil Chilled water cooling coil Steam humidifier, washer, spray humidifier Plate heat exchanger, rotating ERC, or mixed air dampers 6

7 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. The tx2-strategy controls the heat recovery system so that the air handling process is cost-optimized considering predominant air states and specific costs of air handling aggregates. The principle functions are explained in greater detail below. 7

8 3.3 The principle functions 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. A temperature setpoint of 22 C and a setpoint for relative humidity of 45% with a deviation of e.g. ±2 C and ±15%r.h. are typical for office work. Additionally, it is meaningful to limit absolute humidity at high temperatures; or else, the air become too muggy. This limit value typically is ca. 11g/kg. Energy savings: The greater the comfort area area, the greater the energy savings potential. Figure 3-2 Comfort area in the h,x diagram 8

9 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. The temperature and humidity controller are used as room air supply sequence cascade controllers. The reference controller calculates the reference variable for supply air from the room-side control deviation. The supply air controllers calculate the positioning signals for heating, cooling, humidification and dehumidification from supply air-side control deviations. Defining the room setpoint Economizer tx2 (Figure 3-3) identifies the best room setpoint at the border or within the comfort area and applies optimized ERC (Figure 3-4). Demand for heating, cooling, humidification, and dehumidification or a combination thereof is based on the preconditioned air state and supply air setpoint. For "heating and humidification", "cooling and dehumidification" and humidification and possible reheating", the related setpoint is identical to the most energy-efficient corner point within the comfort area. For "cooling only", the setpoint is achieved by projecting the actual value to the upper limit of the comfort area. For "heating only", projection is to the lower limit. The range with relative humidity forming the limit represents a special case. Here, the temperature setpoint is shifted along the relative humidity line. This results in greater heating 9

10 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. Figure 3-4 Possible state changes in the h,x diagram for the comfort area. See Section 11-2 for additional information on the h,x diagram. Cascade controller Advantages: Better dynamic behavior The dynamic controller (Figure 3-3) comprises a cascade controller for temperature and humidity control. Temperature and relative humidity represent measured variables, temperature and absolute humidity, however, represent reference variables. The absolute humidity is calculated from temperature and relative humidity. This conversion decouples the two reference variables, resulting in improved dynamic behavior. The cascade contains two important components: Room controller Supply air controller 10

11 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. The tx2-algorithm then calculates the positioning signal for heat recovery from the weighted demand signals so that the mixed air or air state after ERC continues to be conditioned by the follow-on air handling aggregates at minimum energy expense and costs. Energy recovery is controlled so that the sum of all weighted demand signals for heating, cooling, humidification, and dehumidification is minimized. The ERC strategy is based on the t,x diagram. Each process is assigned a vector at the t,x level (Figure 3-5) and weighting (Section 3.3.6). The vectors reflect the theoretical impact of each process. During operation, only two vectors can be active at any given time in addition to the ERC vector. The supply air setpoint is at the center of the diagram. In addition, the model shows the actual values for room and outside air. The ERC vector results from this, depending on the degree of recovery for temperature and humidity, based on the actual value for outside air. The aim is to identify the point on the ERC vector that minimizes the sum of the theoretical impact of both active processes. Example: The outside air is cooler than the room air. ERC also should condition cooler air, thereby increasing the amount of outside air, if cooling demand is high. This action reduces the required cooling energy. If humidification is required at the same time, an additional dimension is added (Section 3.3.5). Figure 3-5: t,x diagram 11

12 3.3.4 Weighted processes Advantages: Minimize energy costs Reduce energy consumption Reduce CO 2 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 CO 2 emissions Example: Energy costs Energy recovery optimizes energy costs by preconditioning outside air. To do this, the supply air controller's (Figure 3-3) demand signals are weighted by the specific costs of the corresponding processes (Table 3-6) and energy recovery is controlled. Process Specific costs Relative weighting Heating Cooling Humidification Dehumidification Table 3-6 Example for specific costs and relative weighting. Specific costs are in relative to a 1K temperature difference and a one-hour operating period. 12

13 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. Table 3-7 Energy comparison table with conventional ERC control and Economizer tx2 in DESIGO INSIGHT A B C D Present power in [kw] Provided energy (cumulated power) in [kw] Present cost Total cost (cumulated cost) The energy comparison table (Table 3-7) displays conventional ERC strategies: Strategy Max ERC recovery ERC is fully controlled Strategy Temp. ERC is integrated in the temperature sequence Strategy Hum. ERC is integrated in the humidity sequence Strategy Enthalpy. ERC is controlled to the supply air setpoint enthalpy The last column contains the Economizer tx2 strategy. The table visualizes the following variables: Output and energy consumption for thermal air handling, provided by the processes heating, cooling, humidification and dehumidification. Water costs as a function of the humidity increase. Momentary and added costs as a function using cost factors for weighted output and energy consumption. Fan energy and temperature increase caused by the fan. Electrical output and energy is calculated based on volume flow and overall pressure difference via the ventilator. 13

14 Additional information is available in the appendix (Section 11.3) Additional functions Modular designed standard library applications including graphics for plant operation using DESIGO INSIGHT to operate air conditioning plants Control of air handling unit for multiple plant variants Summer/winter compensation for greater comfort Summer compensation for additional energy savings Fault shutdown for maximum safety Data logging and monitoring 14

15 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. Building: Museum Primary plant: Heating: Gas burner, centralized ventilation plant with heating coils Cooling and dehumidification: Refrigeration machine, centralized ventilation plant with cooling coils for humidification and dehumidification Humidification: Central ventilation plant with steam humidifier ERC control: ERC is integrated in the temperature sequence with comfort band Result: Simulation results show that the Economizer tx2 application results in typical energy savings of 5 to 10% annually. Savings of up to 40% are possible depending on room use and outside air conditions. 15

16 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 5.2 Customer benefits Suitable for existing plants, since optimization is achieved using purely controltechnical measures without costly modifications to plant hardware Reduced air conditioning costs Optimized costs by considering energy tariffs Concrete means of sustainably reducing CO 2 thanks to energy savings Time and costs savings during engineering, commissioning and occupancy phases as well as lower service costs thanks to tested applications and detailed documentation Meets the highest energy class in EN and increases the value of the plant as well as the potential resale value of the building Figure Field of use The following list outlines applications where it makes sense to use Economizer tx2: Museums Printing shops Food industry Production or assembly halls with special requirements for ambient conditions Computer centers Pharmaceutical industry Labs Operating rooms The application can be used on both new and existing plants. 16

17 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 PC. 9 Field devices No special requirements are placed on field devices with regard to measuring precision, quality, etc. Siemens field devices should be used whenever possible. 10 Versioning Economizer tx2 can be used from DESIGO V

18 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. Components supported by Economizer tx2: Components Economizer tx2 Comment ERC types Mixing air Rotary heat exchanger Plate heat exchanger Heating coil Preheater Reheating coil Humidifier types Steam humidifier Washer Spray humidifier Cold water steam humidifier Cooling coil Cooling Fan Single-speed Two-speed Modulating Table 11-1 Supported 18

19 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. Figure 11-1 h,x diagram by Mollier Name Unit Description A Temperature T [ C] Designates the heating condition of air. Indicated in degrees C or absolute in Kelvin K. B Absolute humidity x [g/kg] Absolute humidity x is the amount of water per kg in dry air, expressed in g. C Relative humidity % [r.h.] Dry air can only absorb a specific maximum amount of steam at a particular temperature. The higher the temperature, the greater the possible amount of water in the air. D E Heat unit or enthalpy Steam pressure h [kj/kg] Pw [mbar] One of the most important calculations in terms of ventilation is determining the amount of heat needed to achieve an air state predefined by temperature and humidity. In this case, air, whose state is unknown, must either be mixed, heated, cooled, humidified, or dehumidified to achieve the required air state. The heat contents h (in kj/kg) plays a significant role. Overheated steam mixed in air has a particular steam pressure Pw. This steam pressure is part of the entire air pressure and, for this reason, is also referred to as partial pressure for steam. This partial pressure depends on the mixing ratio of steam to dry air. The higher the steam content of air, the greater the partial pressure of steam Pw. As a result, steam partial pressure Pw can be displayed in the mbar parallel, horizontal to water content x, thus allowing for determining the partial pressure Pw corresponding to a particular water content x [g/kg]. 19

20 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. On the ERC lines, i.e. in the case of recirculated air on the line between the outside air and extract air, all possible states for the mixed air are entered after mixed air damper control. 4 points on the line are special; they are the starting points for energy calculations. Ex Extract air SpSu Supply air setpoint x Steam content absolute T Temperature Oa Outside air Energy consumption is calculated based on air states 1 and 2 as per Figure 11-3 and the weighting factors to evaluate the energy of the strategies per strategy: State 2 is given by the supply air temperature and supply air humidity. State 1 can be determined for temperature and humidity based on the ERC strategy and the effectiveness of the ERC. Calculation of energy costs considers the related air handling aggregates and their specific costs. Involved aggregates result from the required change of state and aggregate-specific, possible changes of state. The strategies Stg 1 to Stg 4 (Figure 11-2) are displayed in DESIGO INSIGHT. For inactive strategies, the setpoint for Sta 2 is used for calculation, see Table

21 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 Exhaust air Sta2 Air state 2 Oa Outside air Su Supply air Sta1 Air state 1; depends on ERC strategy 21

22 12 About this document Before using our products, it is important that you read the documents supplied with or ordered at the same time as the products (equipment, applications, tools etc.) carefully and in full. We assume that persons using our products and documents are authorized and properly trained and have the requisite technical knowledge to use our products as intended. Additional information on products and applications is available: At your next Siemens branch office or at your system suppliers. From the support team in the headquarters if no local POC is available. Siemens assumes no liability to the extent allowed under the law for any losses resulting from a failure to comply with the aforementioned points or for the improper compliance of the same. 22

23 23

24 Siemens Switzerland Ltd Industry Sector Building Technologies Division International Headquarters Gubelstrasse Zug Switzerland Tel Siemens Ltd Industry Sector Building Technologies Division 22/F, Two Landmark East 100 How Ming Street, Kwun Tong Kowloon, Hong Kong Tel Siemens Building Technologies Industry Sector Brunel House Sir William Siemens Square, Frimley Camberley Surrey, GU16 8QD United Kingdom Tel The information contained in this document represents a general description of the technical capabilities only and may not apply to all cases. The desired features should therefore be set forth upon entering into an agreement. Siemens Switzerland Ltd, 2011 Order no. CM110745en-T2 24