An adaptive ventilation control system can be designed on different levels. A low cost system can be designed with a small single-board computer like Rasberry Pi2 or Arduino3, equipped with an IO-module connected to a relay for control of the fan. Sensors to such system are preferably a system on chip solution i.e. pre-calibrated integrated relative humidity and temperature sensors on one chip. These sensor types have instrumentation amplifiers and A/D conversion embedded in the chip and the data is transmitted via I2C4 bus interface to the single board computer. This type of sensors have become more and more used in this type of applications as they don’t require instrumentation amplifiers nor expensive calibration after manufacturing and assembly. For the outdoor sensor it is important to use a filter cap to prevent the senor from salt and other airborne pollutions. In addition to the hardware also housing for the single-board computer and sensors is required, together with power modules to the hardware and finally some cabling between computer and sensors. The hardware of the whole system can be purchased for approximately 100-150 Euros, but it requires some skills
2 www.raspberrypi.org
3 www.arduino.cc
4 www.i2c-bus.org
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in electronics and software development before it will run. Manufacturing such system in large series would of course result in decreased prices.
A perhaps more professional alternative is to integrate the adaptive ventilation system in a commercial of-the-shelf building automation system. The sensors must then be adapted for industrial interface which means that the sensors have embedded instrument amplifiers with industry standard 0-10 V or 4-20 mA analogue interfaces to connect to the automation system.
There are combined sensor units with temperature and relative humidity as well as pure temperature and relative humidity units. The building automation system choice is of course more reliable and sensors and installation material can be purchased classified for outdoor use. Further, a building automation system has often possibilities to store data and is also more user friendly to program. The cost is on the other hand much higher. Up to 10 times higher compared with the first solution, but then the number of hours of engineering work becomes lesser. Still it is a low cost measure compared to the other common climate control measures.
In order to better understand how the adaptive ventilation is working practically and how it should be designed within a control system, the latter high end type was developed. The AV controller was developed in LabVIEW on a PC with an NI Compact DAQ I/O chassis with modules for 0-10 V analogue automation signals, PT100 sensors, digital input with edge detection and relay output. The Compact DAQ was connected via USB to the PC. The Compact DAQ was mounted in a cabinet together with two power supplies, one for measurements and one for control in order to minimize the effect of disturbances. The outdoor sensor was a Vaisala Humicap for temperature and relative humidity connected to a HMT100 Transmitter. Between the transmitter and the LabVIEW CDAQ unit, two 0-10V analogue signal wires were connected. Indoors temperature and relative unit was measured with a Testo 6621 A01C01 with display. Also this unit was connected to the LabVIEW CDAQ unit with two 0-10V analogue signal wires. Four PT100 temperature sensors adapted for surface mounting were also connected to the LabWIEW CDAQ unit, only for the surface temperature measurements. The LabVIEW software saved data on the laptop hard drive with 10 minute sampling.
For control of the fan a relay was connected to the NI Compact NAQ relay output modules.
See Figure 5.3.
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Figure 5.2 The cabinet with control equipment.
Figure 5.3 Scheme of the electrical peripheral components required to the control system.
The controller software was developed in the graphical environment from LabVIEV. See figure 5.4. The software compared indoor AH with outdoor AH which was calculated from the respective temperature and relative humidity sensors. A hysteresis of 0.1 g/m3 was also implemented within the relay based controller. Additionally to the adaptive ventilation, optional controller functions were implemented that started a heater if the indoor temperature was below 5C and switched on a dehumidifier, if the indoor relative humidity increased to values over 75% RH. After development and programming, the control system was tested in situ in a small building to validate that the control system worked. To validate the adaptive ventilation controller, humidity tests were carried out by buckets of water were poured on the
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floor in the building at the same time as the system was running and comparative measurements were carried out. The result showed that the adaptive ventilation control was running according to the requirements. Other things that had to be tested were how the system worked at power break-down and also test of the remote control i.e. the ability to operate the PC on remote. The remote control possibilities were solved by using the software LogMeIn.
Internet was established by a radio router connected to the PC. The conclusion for the design was that the control system worked as required and was ready to be tested in real case studies.
Figure 5.4 The LabVIEV software scheme for the control system