Schematic overview
NOT FOR SALE YET - Temperature control | AC fans | plate recuperator
Solution description
Advanced temperature-based control system for dual air handling unit.
The unit is equipped with a plate recuperator, complete with a damper-controlled bypass. Additionally, it includes water heater with a pump and a 3-way valve for temperature control. This unit includes a water cooler with a 3-way valve and chiller.
This solution features two fans with AC 3-phase 400 V motors and a maximum current of 9,5 A per motor. Comprehensive protection system safeguards against both air and water frost, ensuring uninterrupted operation even in extreme conditions. Complete command over the supply and exhaust dampers.
Additional specifications and description
This solution is designed to monitor and control air handling unit that is shown on schematic below:
Air handling unit consists of nine parts, which are: supply (1) and exhaust (9) air dampers, supply (2) and exhaust (7) air filters, plate recuperator (3), supply (4) and exhaust (8) fans, air heater (5) and air cooler (6).
Control logic description
The AHU has two operating modes – “Cold period” and “Warm period”. Operating mode is selected automatically, using outdoor temperature and humidity sensor ODTHM. For these operating modes different working scenarios will be used, but first we will state some constant logics.
Supply and exhaust air dampers open 30 seconds before supply and exhaust fans start. It is essential for high air flow AHU and will prevent air dampers from possible damage.
Air filters condition is measured via dual differential pressure transmitter HPD-G-1K0. The measurements are transferred to HVAC controller DRPUM (master device). In case the pressure drop on the filters becomes higher than the setpoint, user will be notified to perform their maintenance. However, the AHU continues its operation no matter how clogged the filters are.
Supply and exhaust fan speed can be controlled manually or automatically via frequency inverters FI-E44095E2. We also use differential pressure transmitters HPS-M-1K0-2 to control fan operation. In case of mechanical fan failure (jamming, bearing breakdown), there will be no pressure drop and the master device will produce the following steps: switch off frequency inverters, close air dampers and inform the user about the error. In automatic mode HPS-M-1K0-2 can be used to maintain certain pressure difference.
Cold period
Switching on the AHU in cold period will be executed in following steps:
Air handling unit consists of nine parts, which are: supply (1) and exhaust (9) air dampers, supply (2) and exhaust (7) air filters, plate recuperator (3), supply (4) and exhaust (8) fans, air heater (5) and air cooler (6).
Control logic description
The AHU has two operating modes – “Cold period” and “Warm period”. Operating mode is selected automatically, using outdoor temperature and humidity sensor ODTHM. For these operating modes different working scenarios will be used, but first we will state some constant logics.
Supply and exhaust air dampers open 30 seconds before supply and exhaust fans start. It is essential for high air flow AHU and will prevent air dampers from possible damage.
Air filters condition is measured via dual differential pressure transmitter HPD-G-1K0. The measurements are transferred to HVAC controller DRPUM (master device). In case the pressure drop on the filters becomes higher than the setpoint, user will be notified to perform their maintenance. However, the AHU continues its operation no matter how clogged the filters are.
Supply and exhaust fan speed can be controlled manually or automatically via frequency inverters FI-E44095E2. We also use differential pressure transmitters HPS-M-1K0-2 to control fan operation. In case of mechanical fan failure (jamming, bearing breakdown), there will be no pressure drop and the master device will produce the following steps: switch off frequency inverters, close air dampers and inform the user about the error. In automatic mode HPS-M-1K0-2 can be used to maintain certain pressure difference.
Cold period
Switching on the AHU in cold period will be executed in following steps:
- Pump starts and 3-way valve fully opens to pre-heat the air heater, this operating mode maintains for 2 minutes;
- Supply and exhaust air dampers open and 30 seconds after supply and exhaust fans start.
Plate recuperator is used to transfer heat from exhaust to supply air, thus reducing the required heater capacity. Exhaust air contains moisture that will condensate when its temperature decreases. Exposed to even lower temperatures, these water drops will freeze, forming the ice crust on the surface of recuperator. This leads to pressure drop raise, which can increase the fan load dramatically. Moreover, ice crust significantly affect heat transfer efficiency. To avoid these conditions, plate recuperator has a bypass with actuator controlled damper, which is used to direct outdoor air (partially or completely) without passing through recuperator. The quantity of bypassing outdoor air depends on the exhaust air temperature after recuperator. It is measured with duct temperature and humidity sensor DSTHM-2. If the value drops to 0°C, bypass damper will start to open gradually. After the exhaust air temperature rises, damper will close. This algorithm protects plate recuperator from freezing.
Air heater operation is controlled using duct temperature and humidity sensor DSTHM-2. If the measured temperature is higher, than the desired one, 3-way valve starts to close, reducing the amount of hot water supplied to the air heater. Otherwise, if the measured temperature becomes lower than desired value, 3-way valve will open gradually. The pump keeps working at the same speed at all time to maintain hydraulic regime. The pump and the valve can be installed in the technical room to ensure simple maintenance and protect against external factors.
Air heater has two types of frost protection: air and water. Air frost protection is provided with special relay - frost protection thermostat. It is placed directly after the heater and used to measure temperature. If the measured value drops below 10°C (this setpoint can be changed), the following scenario will happen:
Air heater operation is controlled using duct temperature and humidity sensor DSTHM-2. If the measured temperature is higher, than the desired one, 3-way valve starts to close, reducing the amount of hot water supplied to the air heater. Otherwise, if the measured temperature becomes lower than desired value, 3-way valve will open gradually. The pump keeps working at the same speed at all time to maintain hydraulic regime. The pump and the valve can be installed in the technical room to ensure simple maintenance and protect against external factors.
Air heater has two types of frost protection: air and water. Air frost protection is provided with special relay - frost protection thermostat. It is placed directly after the heater and used to measure temperature. If the measured value drops below 10°C (this setpoint can be changed), the following scenario will happen:
- Both supply and exhaust fans stop, air dampers close;
- 3-way valve fully opens;
- When the air temperature after heater becomes higher than 10°C, dampers and fans will resume their normal operation.
Water frost protection is ensured by using temperature sensor for fluid pipes DTP-M. It should be installed on return water pipe at the exit from air heater. If the measured water temperature drops below 25°C (this setpoint can be changed), the following scenario will happen:
- Both supply and exhaust fans stop, air dampers close;
- 3-way valve fully opens;
- When the air temperature after heater becomes higher than 25°C, dampers and fans will resume their normal operation.
Air cooler is not used during cold period.
Warm period
Switching on the AHU in warm period will be executed in following sequence – supply and exhaust air dampers open and 30 seconds after supply and exhaust fans start.
Plate recuperator operates in most conditions. The only exception is when the exhaust air temperature is higher than outdoor temperature. Therefore, all outdoor air will pass directly to cooler, skipping the plate recuperator.
Air cooler operation depends on measurements given by room temperature and humidity sensor RSTHM-2. We do not use duct temperature sensors to control air cooler due to the fact that air can warm up passing through fan and ducts. The three-way valve, which can be placed in technical room, supplies air cooler with cold water. Valve position depends on temperature differential – the hotter the room, the wider opens the valve. Chiller is located outside and used to produce cold water.
Air heater is not used during warm period.
System configuration
This solution includes network gateway DIG-M-2. It provides the user with the access to the online HVAC platform – SenteraWeb. The connection can be provided via an Ethernet cable or via a Wi-Fi network. It allows to remotely monitor data and adjust settings of the connected HVAC devices via internet. Data logging is also possible.
Warm period
Switching on the AHU in warm period will be executed in following sequence – supply and exhaust air dampers open and 30 seconds after supply and exhaust fans start.
Plate recuperator operates in most conditions. The only exception is when the exhaust air temperature is higher than outdoor temperature. Therefore, all outdoor air will pass directly to cooler, skipping the plate recuperator.
Air cooler operation depends on measurements given by room temperature and humidity sensor RSTHM-2. We do not use duct temperature sensors to control air cooler due to the fact that air can warm up passing through fan and ducts. The three-way valve, which can be placed in technical room, supplies air cooler with cold water. Valve position depends on temperature differential – the hotter the room, the wider opens the valve. Chiller is located outside and used to produce cold water.
Air heater is not used during warm period.
System configuration
This solution includes network gateway DIG-M-2. It provides the user with the access to the online HVAC platform – SenteraWeb. The connection can be provided via an Ethernet cable or via a Wi-Fi network. It allows to remotely monitor data and adjust settings of the connected HVAC devices via internet. Data logging is also possible.
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