HVAC test bed

Purpose of HVAC test bed

The primary purpose of the experimental HVAC unit system is to identify conditions of air flowing through the unit at any spot where the variations can be measured. The whole system is unique because it is only intended for experimental testing. HVAC unit is connected to a special testing chamber where various conditions can be set thanks to possibility to heat or cool each wall separately (more information). On the HVAC system a lot of disturbances typical for HVAC units (like clogged filter etc.) can be simulated.

 

Technical description of the test bed

Principal measured parameters are air temperature, humidity and dew point. In addition, there are measured air velocity and differential pressures. A lot of other values are subsequently calculated such as air flow rate, specific air humidity, specific enthalpy, specific density, heat recovery efficiency, thermal output of heater/cooler, effective humidification, fan air temperature increase and fan thermal output. Heat/cold consumption, water consumption and electric energy consumption are measured from energy consumption.


Used sensors:

  • Air conditions such as temperature, relative humidity and dew point are measured using intelligent sensors. Temperature range is -40 to +80°C. Accuracy of temperature measuring is ±0,2°C in 0 to 40°C range and ±0,4°C for remaining range. Relative humidity range is 0 to 100%. Accuracy of relative humidity measuring is ±1,7% RH in range 0 to 90% RH and ±2,5% RH for remaining range. There are several options for sensors connection. In our case we used serial communication using RS-485, which simplifies hardware implementation of measuring chain thanks to parallel sensor connections.


  • For the air velocity measurement we used vane wheel insertion probes with range of 0-20 m/s. Vane wheel insertion probes are characterized by uncertainty of not more than 1.5% of measured value and +0.5% of full range. Output of the sensors is linear current loop in range of 4-20mA, where 4mA corresponds to 0m/s and 20mA corresponds to 20m/s.


  • Differential pressure sensors were chosen based on assumed differential pressure. Accuracy of one type of sensor is ±3% in full-range and accuracy of second type od sensor is ±0,7% in full-range. Used ranges of differential pressure sensors are 0 - 1000Pa for fans, 0 - 300Pa for filters and 0 – 200Pa for heat exchanger. All differential pressure sensors have linear voltage output.

 

  • All the consumption energy meters are instruments designated for household use and as such they are not used for labs purposes (they are typically used for remote reading of consumed energy). In experimental HVAC system two heat/cold consumption meters are used. Sensors measure temperature of liquid at the input and output and there is also ultrasound measurement of flow. The heat/cold consumption is calculated based on measured values with measurement error less than 2%. The working range of temperature is 5 - 90°C and maximum rate of flow is 5m3/h. The consumption of heat/cold is displayed on LCD in kWh (MWh) or kJ (MJ) and at the same time the device allows to export all measured data using M-bus. For measurement of water consumption of the humidifier is used electronic water meter with metrology accuracy - B. This means that it allows to measure flow with minimum rate of 30l/h and with accuracy ±5%. The temperature of water has to be less than 30°C and nominal flow rate should be around 2,5 m3/h. The device displays measured consumption of liquid on LCD and exports measured data using M-Bus. Electric meters used for measuring of electric energy consumption are single phase energy meters. These sensors measure with maximum measurement error 1% and pulse outputs. The output of electric meter constitutes of a solid-state relay which generates pulses every time when 1 Wh is consumed. Duration of one pulse is 90ms and voltage of pulses depends on pulse adapter. Electric meters are connected to a pulse adapter, which communicates using M-Bus. Electric meters display current values of consumed energy on LCDs.

Used logger:

  • The basic unit of measuring system is IN CompactRIO 9081. It is fully-fledged industrial computer with ability to connect different measuring modules, which collects processes and stores all measured data. NI CompactRIO - 9081 runs with industrial version of operating system Windows - Windows Embedded 7 and it is programmed with NI LabVIEW graphical programming tools. In this project are used two cRIO modules - NI 9871 and NI 9207. NI 9871 consists of 4 independent RS-485 (RS-422) ports where every single port can handle up to 32 RS485-based on devices. NI 9207 allows connect up to 8 voltage-output devices and up to 8 current loop devices. Measuring ranges are ±10V and ±21,25mA with 24-bit resolution which means that quantization step is 0,6µV and 1,3nA. Sampling rate is 500 samples per second (high-speed mode) per all channels which means 30 samples per channel. For communication by M-Bus RS-232 port is used, which is directly on cRIO and RS-232/M-Bus converter. These four interfaces (RS-485, voltage-output, current loop and M-Bus) provide basic access to all of used sensors and devices. Furthermore, this layout allows easy spreading of the system in future. 

  • For data processing program in LabVIEW was created. Every single set of data measured in one cycle is displayed on diagram of HVAC system and several values are plotted in graphs. Once in a time, the last set of collected data stored as a text file on hard drive. This period can be set. These stored data can be used for further processing.

 

Gallery:

         

 

Links:

Demonstration and education laboratory of building services (cz/eng)

Data samples

 

For more information:

Research:

PhD students:


Reference:

Poster 2014 - Vladimir HORYNA, Ondrej HANUS, Air handling unit test rig for research and development of fault detection and diagnostics methods