Schematic overview
NOT FOR SALE YET - Temperature control | AC fans | rotary recuperator
Solution description
Sophisticated temperature-based control system for supply and exhaust air handling unit.
This solution includes two AC motors with 3-phase 400 V power supply and maximum current of 9,5 A per motor. Paired with advanced frequency inverters, these motors deliver control precision and efficiency. The 3-phase 400 V power supply motor of rotary recuperator is also controlled by frequency inverter with a maximum current of 2,2 A.
Controlled AHU is equipped with water heater, featuring a pump and a modulating 3-way valve. This combination enables precise temperature regulation and unparalleled comfort. Notably, our comprehensive frost protection system provides dual-level safeguards, ensuring uninterrupted operation even in the harshest conditions. Our solution integrates a freon cooler and an AC outdoor unit. This solution provides the user with effortless management of the supply and exhaust dampers.
Additional specifications and description
This solution is designed to monitor and control air handling displayed in the 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, rotary recuperator (3), supply (4) and exhaust (8) fans, air heater (5) and air cooler (6).
Control logic description
The AHU operates in two modes – “Cold period” and “Warm period”. The specific mode is automatically selected using ODTHM. Different operational scenarios are employed for these modes, but first constant logics are outlined.
Supply and exhaust air dampers open 30 seconds before supply and exhaust fans start. This is crucial for AHUs with high air flow to prevent potential damage to the air dampers.
The condition of air filters is monitored by dual differential pressure transmitter HPD-G-1K0. The measurements are sent to the HVAC controller DRPUM (master device). If the pressure drop across the filters exceeds the setpoint, user is alerted for maintenance. However, the AHU continues its operation regardless of how clogged the filters are.
The speed of supply and exhaust fans can be manually or automatically controlled using frequency inverters FI-E-44095E2. Fan operation is also monitored using differential pressure transmitters HPS-M-1K0-2. In case of mechanical fan failure (such as jamming or bearing breakdown), resulting in no pressure drop, the DRPUM will take the following steps: turn off frequency inverters, close down air dampers and inform the user of the error. In automatic mode HPS-M-1K0-2 are used to maintain specific differential pressure.
Cold period
The AHU is switched on following these steps:
Air handling unit consists of nine parts, which are: supply (1) and exhaust (9) air dampers, supply (2) and exhaust (7) air filters, rotary recuperator (3), supply (4) and exhaust (8) fans, air heater (5) and air cooler (6).
Control logic description
The AHU operates in two modes – “Cold period” and “Warm period”. The specific mode is automatically selected using ODTHM. Different operational scenarios are employed for these modes, but first constant logics are outlined.
Supply and exhaust air dampers open 30 seconds before supply and exhaust fans start. This is crucial for AHUs with high air flow to prevent potential damage to the air dampers.
The condition of air filters is monitored by dual differential pressure transmitter HPD-G-1K0. The measurements are sent to the HVAC controller DRPUM (master device). If the pressure drop across the filters exceeds the setpoint, user is alerted for maintenance. However, the AHU continues its operation regardless of how clogged the filters are.
The speed of supply and exhaust fans can be manually or automatically controlled using frequency inverters FI-E-44095E2. Fan operation is also monitored using differential pressure transmitters HPS-M-1K0-2. In case of mechanical fan failure (such as jamming or bearing breakdown), resulting in no pressure drop, the DRPUM will take the following steps: turn off frequency inverters, close down air dampers and inform the user of the error. In automatic mode HPS-M-1K0-2 are used to maintain specific differential pressure.
Cold period
The AHU is switched on following these steps:
- The pump starts, and the 3-way valve fully opens to pre-heat the air heater. This mode lasts for 2 minutes;
- Supply and exhaust air dampers open, supply and exhaust fans start 30 seconds after that.
Rotary recuperator transfers heat from exhaust to supply air, reducing the required heater capacity. Exhaust air contains moisture that will condensate when its temperature drops. Exposed to even lower temperatures, these water drops will freeze, forming the ice crust on the surface of recuperator. This leads to significant pressure drop raise, which can increase the fan load dramatically. Moreover, ice crust has negative impact on heat transfer efficiency. To prevent these issues, a frequency inverter FI-E44022E2 controls the speed of the rotary wheel.
Under normal conditions, the rotary speed is set at 10 rpm. Although higher speeds don't notably enhance heat exchange efficiency, they significantly elevate pressure loss. Readings from outdoor sensor ODTHM and DSTHM-2, positioned after the recuperator on the exhaust side, are used to calculate the conditions, when condensate freezing will most likely occur. In such instances, the speed of the wheel is reduced to 0.5 rpm, safeguarding the rotary recuperator from freezing.
The operation of the air heater is regulated by the duct temperature and humidity sensor DSTHM-2. If the measured temperature exceeds the desired level, the 3-way valve starts to close, reducing the supply of hot water to the air heater. Conversely, if the measured temperature falls below the desired value, 3-way valve will open gradually. Throughout, the pump maintains a constant speed to uphold the hydraulic system.
The air heater has two types of frost protection: air and water. Air frost protection is provided with special relay - frost protection thermostat, located directly after the heater. If the measured temperature drops below 10°C, the following sequence occurs: both supply and exhaust fans stop, air dampers close, and the 3-way valve fully opens. Normal operation resumes when the air temperature after the heater exceeds 10°C.
Water frost protection is ensured by using temperature sensor DTP-M, installed on the return water pipe at the exit from the air heater. If the measured water temperature falls below 25°C, the following scenario will happen: both supply and exhaust fans stop, air dampers close, and the 3-way valve fully opens. Operations return to normal when the air temperature after the heater exceeds 25°C.
The air cooler remains inactive during the 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.
Rotary recuperator operates under most conditions, except when the exhaust air temperature surpasses the outdoor temperature. In this case, the rotary recuperator motor is halted to prevent heat exchange between the supply and exhaust air streams.
The operation of the air cooler is determined by readings from the room temperature and humidity sensor RSTHM-2. If the current temperature exceeds the desired level, the AC outdoor unit begins supplying the air cooler with freon. The AC outdoor unit operates independently under its own control system. Duct temperature sensors are not utilized to regulate the air cooler due to the potential warming of air as it passes through fans and ducts, which could lead to a less comfortable room environment.
The air heater remains inactive during the warm period.
System configuration
The solution incorporates DIG-M-2 network gateway, providing users access to the online HVAC platform SenteraWeb. Connectivity options include Ethernet cable or Wi-Fi network, allowing remote monitoring of data and adjustment of settings for connected HVAC devices over the internet. Data logging capabilities are also supported.
Under normal conditions, the rotary speed is set at 10 rpm. Although higher speeds don't notably enhance heat exchange efficiency, they significantly elevate pressure loss. Readings from outdoor sensor ODTHM and DSTHM-2, positioned after the recuperator on the exhaust side, are used to calculate the conditions, when condensate freezing will most likely occur. In such instances, the speed of the wheel is reduced to 0.5 rpm, safeguarding the rotary recuperator from freezing.
The operation of the air heater is regulated by the duct temperature and humidity sensor DSTHM-2. If the measured temperature exceeds the desired level, the 3-way valve starts to close, reducing the supply of hot water to the air heater. Conversely, if the measured temperature falls below the desired value, 3-way valve will open gradually. Throughout, the pump maintains a constant speed to uphold the hydraulic system.
The air heater has two types of frost protection: air and water. Air frost protection is provided with special relay - frost protection thermostat, located directly after the heater. If the measured temperature drops below 10°C, the following sequence occurs: both supply and exhaust fans stop, air dampers close, and the 3-way valve fully opens. Normal operation resumes when the air temperature after the heater exceeds 10°C.
Water frost protection is ensured by using temperature sensor DTP-M, installed on the return water pipe at the exit from the air heater. If the measured water temperature falls below 25°C, the following scenario will happen: both supply and exhaust fans stop, air dampers close, and the 3-way valve fully opens. Operations return to normal when the air temperature after the heater exceeds 25°C.
The air cooler remains inactive during the 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.
Rotary recuperator operates under most conditions, except when the exhaust air temperature surpasses the outdoor temperature. In this case, the rotary recuperator motor is halted to prevent heat exchange between the supply and exhaust air streams.
The operation of the air cooler is determined by readings from the room temperature and humidity sensor RSTHM-2. If the current temperature exceeds the desired level, the AC outdoor unit begins supplying the air cooler with freon. The AC outdoor unit operates independently under its own control system. Duct temperature sensors are not utilized to regulate the air cooler due to the potential warming of air as it passes through fans and ducts, which could lead to a less comfortable room environment.
The air heater remains inactive during the warm period.
System configuration
The solution incorporates DIG-M-2 network gateway, providing users access to the online HVAC platform SenteraWeb. Connectivity options include Ethernet cable or Wi-Fi network, allowing remote monitoring of data and adjustment of settings for connected HVAC devices over the internet. Data logging capabilities are also supported.
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