Example application for an supply air control with recirculated air addition HVAC Application Note 3 Version 14.03.2007
2 General Copyright 2007 by WAGO Kontakttechnik GmbH & Co. KG All rights reserved. WAGO Kontakttechnik GmbH & Co. KG Hansastraße 27 D-32423 Minden Phone: +49 (0) 571/8 87 0 Fax: +49 (0) 571/8 87 1 69 E-Mail: info@wago.com Web: http://www.wago.com Technical Support Tel.: +49 (0) 571/8 87 777 Fax: +49 (0) 571/8 87 8777 E-Mail: tcba@wago.com Every conceivable measure has been taken to ensure the correctness and completeness of this documentation. However, as errors can never be fully excluded, we would appreciate any information or ideas at any time. We wish to point out that the software and hardware terms as well as the trademarks of companies used and/or mentioned in the present manual are generally protected by trademark or patent.
Content 3 List of Contents 1 Important notes...4 1.1 Legal principles...4 1.1.1 Copyright... 4 1.1.2 Personnel qualification...4 1.1.3 Intended use...4 1.2 Scope of validity...5 1.3 Symbols...5 2 Description...7 3 Components...7 4 Structure...8 5 Hardware assignment...9 6 System description...10 6.1 System diagram...10 6.2 Startup behavior of the ventilation system...11 7 Program description...12 7.1 Collective malfunction...13 7.2 Starting the ventilation system...13 7.3 Antifreeze protection...14 7.3.1 Upstream antifreeze protection...14 7.3.2 Antifreeze control...15 7.3.3 Air-side antifreeze protection...15 7.4 Fan control...15 7.5 Supply air control...16 7.6 Damper control...17 7.6.1 Mixed air damper...17 7.6.2 Exhaust air damper...17 7.7 Pump control...18 7.8 Filter monitoring...18 8 Visualization interface...19
4 Important notes 1 Important notes 1.1 Legal principles 1.1.1 Copyright To ensure fast installation and start-up of the units described here, we strongly recommend that the following information and explanations be carefully read and adhered to. This document including all figures and illustrations contained therein is subject to copyright. Any use of this document which infringes the copyright provisions stipulated herein, is not permitted. Reproduction, translation and electronic and phototechnical archiving and amendments require the written consent of WAGO Kontakttechnik GmbH & Co. KG, Minden. Non-observance will entail the right of claims for damages. WAGO Kontakttechnik GmbH & Co. KG reserves the right of changes serving technical progress. All rights developing from the issue of a patent or the legal protection of utility patents are reserved to WAGO Kontakttechnik GmbH & Co. KG. Thirdparty products are always shown without any indication of patent rights. Hence, the existence of such rights must not be excluded. 1.1.2 Personnel qualification 1.1.3 Intended use The use of the product described in this manual is exclusively geared to specialists having qualifications in PLC programming, electrical specialists or persons instructed by electrical specialists who are also familiar with the appropriate applicable standards. WAGO Kontakttechnik GmbH & Co. KG declines any liability resulting from improper usage and damage to WAGO products and third party products due to disregard of the information contained in this document. For each individual application, the components are supplied by the factory with a dedicated hardware and software configuration. Changes are only admissible within the options shown in this document. All other changes to the hardware and/or software and any use of the components that is not in accordance with the intended use entail the exclusion of liability on the part of WAGO Kontakttechnik GmbH & Co. KG. Please direct any requirements pertaining to a modified and/or new hardware or software configuration directly to WAGO Kontakttechnik GmbH & Co. KG
Important notes 5 1.2 Scope of validity This application note is based upon the hardware and software of the respective manufacturers mentioned herein, and the corresponding documentation. This application note is therefore only valid for the described installation. New hardware and software versions may need to be handled differently. Please note the comprehensive description in the respective manuals. 1.3 Symbols Attention Marginal conditions that must always be observed to ensure smooth operation. Note Routines or advice for efficient use of a device and software optimization.
6 Description
Description 7 2 Description This application note describes an supply air temperature control with recirculated air addition. In addition, this application note describes how the current status of the system can be displayed using the visualization of the WAGO I/O PRO CAA. The following functions shall be realized: Fans, single-stage Air-side antifreeze protection Preventative antifreeze protection with preflush Pump activation on demand Motor protection Pumps with jam protection Control of mixed air and exhaust air dampers Fan V-belt monitoring with differential pressure switch Filter monitoring Supply air control with recirculated air addition Cooling/Recirculating/Heating in sequence 3 Components Supplier Quantity Description Article No. WAGO 1 Programmable fieldbus controller 750-8xx WAGO 6 4-channel digital input module DC 24 V 750-402 WAGO 3 4-channel digital output module 24 V DC 750-504 WAGO 1 4-channel analog input module PT 100 750-460 WAGO 1 2-channel analog input module PT 100 750-461 WAGO 1 4-channel analog output module 0-10 V 750-559 WAGO 1 Bus end module 750-600 WAGO 1 WAGO-I/O-PRO CAA 759-333 Optional: WAGO Communication cable 750-920 Note The node structure described is only an example for the possible control of the ventilation system. The I/O modules may be exchanged as required by the respective application.
8 Structure 4 Structure Ethernet cross-over cable Communication cable 750-920 Fig. 1: Connection diagram WAGO-IO-SYSTEM / WAGO I/O PRO CAA Note For the visualization of the WAGO-I/O-PRO CAA, a connection between the PC and the WAGO fieldbus controller must be established. Depending on the fieldbus controller used, two options are available. The first option is available in all fieldbus controllers. For this, connection is made to the service interface of the fieldbus controller using the communication cable 750-920. Ethernet fieldbus controllers also offer the option to establish the connection via the Ethernet interface.
Hardware assignment 9 5 Hardware assignment Art.-No. Channel Description Signal Address DI 1 Mains failure %IX6.0 750-402 DI 2 Emergency-Off switch 24 V DC %IX6.1 DI 3 Fire detector %IX6.2 DI 4 Differential pressure switch supply air filter %IX6.3 DI 5 Acknowledgement %IX6.4 750-402 DI 6 Switch on %IX6.5 24 V DC DI 7 Automatic mode %IX6.6 DI 8 Manual mode %IX6.7 DI 9 Position switch exhaust air %IX6.8 750-402 DI 10 Auxiliary contact supply air fan contactor %IX6.9 24 V DC DI 11 Repair switch supply air fan %IX6.10 DI 12 Motor circuit breaker supply air fan %IX6.11 DI 13 Differential pressure switch supply air fan %IX6.12 750-402 DI 14 Auxiliary contact exhaust air fan contactor %IX6.13 24 V DC DI 15 Repair switch exhaust air fan %IX6.14 DI 16 Motor circuit breaker exhaust air fan %IX6.15 DI 17 Differential pressure switch exhaust air fan %IX7.0 750-402 DI 18 Repair switch pump heating elements %IX7.1 24 V DC DI 19 Motor circuit breaker pump heating elements %IX7.2 DI 20 Repair switch pump cooling elements %IX7.3 DI 21 Motor circuit breaker pump cooling elements %IX7.4 750-402 DI 22 Antifreeze detector %IX7.5 24 V DC DI 23 Reserve %IX7.6 DI 24 Reserve %IX7.7 DO 1 Horn %QX4.0 750-504 DO 2 Fault indicator light %QX4.1 24 V DC DO 3 Damper %QX4.2 DO 4 Supply air fan %QX4.3 DO 5 Exhaust air fan %QX4.4 750-504 DO 6 Pump heating elements %QX4.5 24 V DC DO 7 Pump cooling elements %QX4.6 DO 8 Fault pump cooling elements %QX4.7 DO 9 Alarm filter clogged %QX4.8 750-504 DO 10 Indicating light system OK %QX4.9 24 V DC DO 11 Reserve %QX4.10 DO 12 Reserve %QX4.11 AO 1 Control valve heating elements %QW0 750-559 AO 2 Control valve cooling elements %QW1 0 10 V AO 3 Setpoint value mixed air damper (fresh air portion) %QW2 AO 4 Reserve %QW3 AI 1 External temperature sensor %IW0 750-460 AI 2 Water temperature sensor %IW1 Pt 100 AI 3 Supply air temperature sensor %IW2 AI 4 Recirculated air temperature sensor %IW3 750-461 AI 5 Antifreeze sensor %IW4 Pt 100 AI 6 Reserve %IW5
10 System description 6 System description 6.1 System diagram A PI controller (RE 1) controls the ventilation system. The setpoint value of the controller is organized in three sequences (cooling/recirculation/heating). A damper with limit switch is used in the exhaust air duct. The air supply is controlled using dampers and single-stage fans. In order to utilize the cooling of the recirculated air at high outside temperatures (T exterior > T recirculated ) and thus save cooling energy, the recirculated air dampers are switched to minimum fresh air, independent to the controller output. If an antifreeze sensor is applied in addition to the heating element, a second PI controller (RE 2) provides for the heating elements to maintain a minimum temperature. In addition to the antifreeze sensor, antifreeze protection is intended for the air and the water side. The air-side antifreeze protection is realized with the antifreeze sensor. A return line sensor is intended for the upstream antifreeze protection, providing the so-called preflush of the heater, depending on the outside temperature. This return line sensor also controls the water temperature in the return of the heater for a minimum reference value and generates a fault message when the risk of freezing is detected. Fig. 2: Wiring diagram of the ventilation system
System description 11 6.2 Startup behavior of the ventilation system The overall function of the system is organized in individual function modules. A specific activation sequence must be adhered to in the startup. Two conditions usually require realization for the startup of a module: 1.) The central system enable signal must be present. 2.) The preceding module signals that it executes or has executed its function. This results in the following startup sequence schematically: 1st step Collective malfunction Switch on No fault 2nd step System start / stop Enable System 3rd step Pump heating elements Pump cooling elements Fan control Antifreeze protection water (preflush) Enable control 4th step Supply air control Set value Mixed air damper 5th step Mixed air damper Enable Damper 6th step Exhaust air damper
12 Program description 7 Program description Fig. 3 shows how the temperature measured by the resistor terminal (Pt 100) is converted to a REAL value. In addition, the application note demonstrates how the contactor monitoring can be bridged if the fan protector does not have an auxiliary contact. The selection modules (SEL) ensure that, in the simulation, the undefined measurement values of the analog and digital I/O modules are not used. Fig. 3: Contactor simulation + conversion Fig. 4 shows the program for the supply air control with recirculated air addition.the sub-program "SupplyAirControlWithRecirculationAir" provides the PLC variables to be gated directly with the inputs and outputs of the WAGO I/O system. Fig. 4: Supply air control with recirculated air addition program
Program description 13 7.1 Collective malfunction The collective malfunction module evaluates all faults resulting in an enforced deactivation of the ventilation system. The faults are indicated visually and acoustically. In this application sample, the input "xenablesystem" is set to TRUE constantly. Therefore, the collective malfunctions are evaluated even when the system is turned off. Fig. 5: Evaluation of fault alarms Note All external fault alarms acquired via the digital inputs are "NC" and must be negated at the input of the function module. 7.2 Starting the ventilation system The start / stop module turns the ventilation system on or off. If the collective malfunction module indicates a severe system fault, the whole system is turned off, via the start / stop module. The selection between automatic and manual mode is usually realized via a rotary switch at the control cabinet. This rotary switch has the positions: Auto - Off Man. Fig. 6: Enabling the ventilation system Note In automatic mode, the ventilation system may be controlled using, e.g., a time switch program from "Scheduler.lib".
14 Program description 7.3 Antifreeze protection At low outside temperatures, the air-sided antifreeze protection may respond when the system is turned on. To avoid this, the heater is heated up via the upstream antifreeze protection, prior to opening the dampers and activating the fans. The following antifreeze functions are implemented in the sample project: Frost alarm when falling below a critical water temperature Minimum reference value control of the heater return temperature (also at system standstill) Time monitoring of the flushing process from the heater (if warm water is not available) Minimum valve opening at low outside temperatures (also at system standstill ) Enforced activation of the pumps at low outside temperatures Supply air temperature monitoring using an antifreeze sensor Minimum referemce value control of the supply air temperature (also at system standstill) 7.3.1 Upstream antifreeze protection The upstream antifreeze protection serves as preventative antifreeze protection via the so-called preflush of the heater. If the outside temperature falls below a definable limit value, the heater is pre-flushed until the water temperature in the return exceeds 30 C. Upon conclusion of the preflush, the dampers are released. As an additional antifreeze protective function, the heater return temperature is limited to a minimum setpoint value of 15 C, independently from the system status. If the heater return temperature still falls below a definable limit value, a frost alarm will be output. Fig. 7: Upstream antifreeze protection with integrated start operation. Note If no return sensor is used, the preflush is time-controlled. Upon conclusion of the preflush, the set value is reduced by the heater valve within 10 minutes from 50 % to 0 %.
Program description 15 7.3.2 Antifreeze control The antifreeze controller provides for the supply air temperature to be limited to a minimum reference value, even at a deactivated system. For this, an antifreeze sensor is mounted after the heater in the system. Fig. 8: Antifreeze controller 7.3.3 Air-side antifreeze protection In standard operation, the air-side antifreeze protection determines the set value of the heater valve using a MAX-selection. When the supply air is below the set temperature of the antifreeze sensor, a frost alarm is triggered and the heater valve is opened completely. Fig. 9: Air-side antifreeze protection 7.4 Fan control The fan control monitors the fault free function of the fans using motor circuit breakers, repair switches, contactor monitoring and differential pressure switches. When the ventilation system is turned on, the fans can be turned on timedelayed using a start time delay. This delay time may be required for a possible start at reduced load. Note Whether the supply air or the exhaust air fan starts first depends on whether a momentary over-pressure or low-air pressure is tolerated during the system start.
16 Program description Fig. 10: Supply and exhaust air fan control 7.5 Supply air control The supply air controller is only activated when the preflush of the heater is concluded. The supply air temperature is controlled using a controller with PI behavior and is split at the output to three sequences (cooling/recirculated air/heating). A neutral zone of 5 % is designed between cooling, recirculation and heating demand. The setting range of the mixed air damper is limited by the minimum fresh air portion. Fig. 11: Supply air control with three sequences for cooling/recirculation/heating
Program description 17 7.6 Damper control 7.6.1 Mixed air damper The mixed air damper control controls the mixed air damper in dependence to the set value of the supply air controller. In addition, the mixed air damper control provides the release of the exhaust air damper. 7.6.2 Exhaust air damper Fig. 12: Activation of the mixed air damper The damper control monitors the exhaust air damper function over the operating time. The limit switches will return a corresponding signal when the damper is wholly opened. Fig. 13: Control of the exhaust air damper
18 Program description 7.7 Pump control The pump control provides for a demand-driven activation of the pump. In the case of extended standstill times of the pump, the implemented block protection provides for the actuation of the pump for a short time. The fault-free operation of the pump is monitored by the motor circuit breaker and the repair switch. When a frost alarm is reported or when the external temperature falls below a defined limit value, the pump for the heater will be turned on automatically. 7.8 Filter monitoring Fig. 14: Control pump heating and cooling elements A differential pressure sensor monitors the filters for clogging. The module reacts time-delayed to the differential pressure sensor, to avoid for any pressure fluctuation within the air duct to trigger a maintenance request of the filter. Fig. 15: Filter monitoring
Visualization interface 19 8 Visualization interface Note The font "Arial, Standard, 9" was used in the CoDeSys editor for the Supply air control with recirculation air addition" subprogram. Fig. 16: Visualization interface of the ventilation system The above described visualization interface displays the state of the ventilation system. In addition, there is the possibility to simulate the system in the PC. For this, the checkmark for "Simulation" must be set in the WAGO I/O PRO CAA under "Online". Subsequently, the measuring values and switch conditions can be modified in the online mode. The "Simulation" button permits to assign valid start values to the system. Note The visualization elements are stored in the "Building_HVAC_01" library and opened via the "Visualization" button. The visualization elements are linked to the corresponding function modules via wildcards.
WAGO Kontakttechnik GmbH & Co. KG P.O. Box 2880 D-32385 Minden Hansastraße 27 D-32423 Minden Phone: 05 71/8 87 0 Fax: 05 71/8 87 1 69 E-Mail: info@wago.com Internet: http://www.wago.com