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Multiprotocol wireless HVAC control system

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Nowadays there’s a big need for intelligent building (IB) environments to reach a cost effective energy management and in the same time to provide a high level of comfort and security. Heating, ventilating and air conditioning (HVAC) systems has a key importance in IBs, being responsible for providing a good quality air so their efficient operation may lead to smaller energy consumption. Performance is influenced not only by design and installation but the monitoring and control process especially when monitoring is improved using wireless sensors that can be implemented in flexible wireless sensor networks (WSN). There are many communication protocols to implement HVAC (IB) systems, their coexistence in an IB system could provide a high level of flexibility, and this can be achieved by using the Software Defined Radio (SDR) technology. The paper is focused on proposing a wireless multiprotocol monitoring and control system for HVAC (IB) systems using the SDR technology.

KEYWORDS: intelligent buildings, Software Defined Radio, HVAC system, gateway, WSN.

1. Introduction and motivation

As described in [1] the maximum amount of carbon dioxide that is allowed to be emitted by 2050 is around 1000 billion tones so not to have a temperature growth exceeding 2°C. A quarter of the carbon dioxide was already emitted between 2000 and 2006, therefore it’s necessary to reduce carbon dioxide emission by reducing each person’s carbon footprint without affecting indoor environment which has to remain fit for human habitation. These requirements can be fulfilled by IBs, implementing high technology systems to reduce energy waste. “Intelligent buildings should be sustainable, healthy, technologically aware, meet the needs of occupants and business and should be flexible and adaptable to deal with change” [2].

An Intelligent Building System (IBS) has many subsystems as presented in figure 1. In this paper we will focus only on one IB subsystem, the HVAC subsystem because one of the major expenses in operating a building is the cost of energy required for heating and air-conditioning besides illuminating the space. “A key function of IBSs is to reduce the energy costs as much as practically possible” [3].

Design and installation of HVAC systems has a very big importance in achieving a good performance but monitoring, control and management of the HVAC (IB) system has the same importance. IBS communication infrastructure can be made on “simple cable, UTP, coaxial and even fiber optical cable but the main barrier that stopped their widely usage was the high installation and maintenance costs and also that the majority of these are not suited for wide band and multimedia applications” [4] therefore wireless solutions tend to be the ideal solution beside the “PLC (Power Line Communication) that is a growing technology where data is transferred on power lines” [4] at a data rate of around 200Mbps (HomePlug). PLC technology has limitations compared to wireless technology being able to transfer big amount of data between limited number of devices due to bandwidth anyway PLC can be useful in those places where small data transfer rates are required like the lighting system control, using an adapter from wireless to PLC signals.

“The world becomes wireless” [5], therefore more and more devices are manufactured with wireless interface because it’s more practical, cheaper and more flexible than other communication interfaces but in certain conditions wireless devices can be inflexible. “The reason that wireless devices can be so inflexible is that they are generally implemented in hardware” [5], while a software solution would be better as presented in this paper.
The main purpose of this paper is to introduce into IBSs some currently unused technology that was used only in military and public safety areas for many years. The introduction of this technology will be made around a multiprotocol HVAC system that is part of the SICOMOS (Smart building Interactive COntrol and MOnitoring System) [6] IBS. This system will be designed using the SDR technology that based on its advantages over hardware implementation will provide a higher level of flexibility (new devices seamless integration into IBS) and adaptability to changes that may occur over time.

Fig. 1: Intelligent Building System with Subsystems

The rest of the paper is organized as follows: in section 2 we present in a few words the SDR technology that could bring many advantages to IBSs, in section 3 we present the Universal Gateway Device (UGD), one of the best solutions for implementing SDR technology into an Intelligent Building Management System (IBMS), in section 4 we present a test system based on the presented SDR technology (hardware and software implementation) made of two wireless nodes (WN), an UGD. The last section finishes the paper with the most important conclusions.

2. Software Defined Radio
Software Defined Radio (SDR), is a term that was coined in 1991 by Joseph Mitola III to describe devices implemented in software and running on generic hardware.

What is an SDR? “Software Defined Radio is a radio architecture where most signal processing tasks are performed by software instead of analogue electronic circuits.” [7]

An SDR system is a radio communication system that can tune to any frequency band, to receive any modulation across a large frequency spectrum by using software and to perform a significant amount of signal processing in a general purpose processor or a reconfigurable device such as a DSP or FPGA. An SDR has some advantages over hardware based solutions: - low power consumption; wide operating frequency band to support many air-interfaces; reconfigurable baseband; is more flexible and adaptable providing a significant life-cycle cost reduction; easy integration of future protocols into existing systems; standard architecture for many current wireless standards and future ones; small form factor (fewer discrete components).

To make IBSs even more flexible an SDR based technology could be used, this is the Cognitive Radio (CR), term that was coined in 1998 by Joseph Mitola III. Cognitive radio is a new emerging technology which implements some kind of intelligence to automatically sense, recognize and wisely use any available radio frequency in the RF spectrum. The enabler of the CR technology is the SDR technology used along with sensing hardware, sensing algorithms and some cognitive intelligence.

In this paper we will focus only on the first part, the SDR technology because CR is far more complex to introduce at this stage into the SICOMOS IBS (or HVAC system).

3. SDR implementation in IBMS
The implementation of SDR technology into IBMS will make IBS more flexible and adaptable. There are two possibilities to implement it:
• As a handheld (mobile) device;
• As a Gateway device.

3.1 Handheld SDR device
The first possibility is to design and develop a portable software defined radio device as presented in [8], but it has several disadvantages:  
• It has a big size to be used as a handheld device;
• Short battery life: ~2h (beside the SDR modules it needs a processing and display unit and batteries).
This is not one of the best solutions; maybe it will become practical when SDR modules will be more flexible and will consume even less power than now respectively processing power will
increase while processing devices will become smaller.

3.2 Gateway device
One of the best solution we have found that is supported by current technology is to implement SDR in a Gateway device that by definition it’s a network node that has the ability to connect the outside world (CATV, ADSL, etc.) with the inside world (different appliances working on different protocols).

Fig. 2: Universal Gateway Device using SDR. Data flow through the Gateway.

The Gateway concept is not new but it can be extended by implementing currently unused technologies and improve it in many different ways. From now on we’ll refer to it as Universal Gateway Device (UGD) that will be a static device, an access point built on the SDR technology and enhanced with other functionalities to form a complete IBMD (Intelligent Building Management Device) to make IBSs as flexible as possible.

There are many protocols and standards used to interconnect IB subsystem’s devices as well as IB subsystems, therefore an UGD can be used to convert data from one protocol to other protocols. In this way it will provide a high level of flexibility to IBSs and will be able to control as many devices as possible, working on whatever protocol (current or future) it’s needed. A schematic of the UGD is presented in figure 2 along with some representation of inside and outside data flow.

The UGD will be a device that will consists of an SDR module and a PC (SBC), where the configuration of the UGD will be made through a PC, PDA device, Smartphone or any other handheld wireless communication enabled device instead of using wall mounted touch panels that are not mobile and therefore their usage is not as flexible as needed. There will be possible to use as many handheld configuration devices as needed to query and set different IBS parameters.

4. System implementation

4.1 Hardware implementation
To verify the concept and the proposed system we designed and implemented a test system made of two WNs, a Gateway (PC + SDR) and configuration devices as presented in figure 3 (for configuration in this phase we will use only a PC not PDA).

4.1.1 Wireless nodes
The WN presented in figure 3 has a PIC18F4550 microcontroller as data processor; an Aurel RTX-MID-3V wireless transceiver working on 433.92 MHz ISM band (with ASK modulation); an 256KB I2C EEPROM memory for data logging; USB 1.1 connection; the module can be powered by USB, battery and DC plug; has ICSP interface; has a temperature sensor (DS1820) and humidity sensor (SHT10) and can be extended with other sensors running on I2C bus.

Fig. 3: Wireless node and HVAC system.

4.1.2 UGD
After researching the possibility to make an SDR device to be used in the UGD, we decided to use an already available SDR device and from the multitude of devices [9]-[14] we have chosen the one made by Ettus Research LLC [15]. The SDR device is named USRP that is a mainboard that accepts many daughterboards like the WBX (full-duplex communication) that works on frequencies between 50 MHz and 2.2 GHz. We have chosen a LOG PERIODIC broadband antenna working between 400 MHz to 1 GHz so WNs frequency (433.92 MHz) is supported. A picture of the system is presented in figure 4 (PC + SDR and two WNs).
In this system the UGD acts as an intermediary between configuration/monitoring devices and sensor network by hiding the complexity of the network while providing a very simple interface from the UGD to configuration/monitoring devices.

Fig. 4: Universal Gateway Device and two wireless nodes.

4.2 Software implementation

4.2.1 Wireless nodes
There are many protocols and standards that can be implemented into HVAC (IB) systems like LonTalk (LonWorks), BACnet and many others but for this test system we have chosen two simple protocols to implement. The first one has implemented a Modbus protocol (Modbus is a serial communication protocol used for connecting industrial electronic devices) and the second one the X10 protocol (is an international and open industry standard for communication among electronic devices used for home automation).
According to each module’s communication protocol the UGD will query data from the two WNs when needed and will receive any data sent by these nodes as well as possible alarm signals. WNs measured data (temperature and humidity) will be saved into the EEPROM memory; there is no need to send each data to the UGD. Each WN will have a few parameters (min and max temperature, reading interval, etc.) set by UGD that will form its behavior.

4.2.2    UGD
The UGD is a management system therefore it will have to store informations regarding the number of connected devices, device transfer rates, device location in building, device protocol and others. These data will be saved into a database located on the SBC or PC. The database management system we have chosen is the Firebird RDBMS because it’s a very robust and exceptionally reliable relational database therefore its usage will bring many advantages to UGD.

The RF signal processing is based on the GNU Radio [16] framework that is a modular, block-based architecture with hybrid Python and C++ programming model, where C++ implementation is used for CPU-intensive processing and Python implementation is used to define complex interactions.
System configuration process for a newly attached device is presented in figure 5. Data will be received by the SDR and passed to SBC or PC through USB 2.0 interface that will be processed by the Intelligent Building Management Device Interface (IBMDI) hosted on the UGD. The IBMDI is a plugin based interface that will introduce an easy way to extend an IBS by setting devices parameters through a script (frequency, modulation, timings, implemented protocol and many other parameters) executed by IBMDI. Data will be provided in a Graphical User Interface (GUI) through configuration/monitoring devices to users and saved into database if needed. As a future capability, newly connected devices will send their script file to the UGD for automatic configuration. If a plugin is not available then a small script can be written specifying protocol, modulation, etc.
The test system had been tested with two simple scripts for MODBUS and X10 protocols, the UGD was able to set and query data to and from WNs. We can conclude that the test system is working therefore validating the proposed system functionality.

Fig. 5: System configuration process for newly attached device.

5. Conclusions
As described in [2] an intelligent building should be “flexible and adaptable to deal with change”, this is what we have proposed in this paper with the UGD, to make a very flexible and adaptable IBS that can be extended very easily in old and new buildings due to its wireless interface.

The proposed system was also tested with two simple WNs and the UGD. We made basic data transfer between WNs and UGD using different protocols therefore we can conclude that the proposed system functionality was validated as well the concept of introducing SDR into IBS.

UGD will not need any new hardware equipment to be able to establish communication with other newly attached wireless devices through various air-interfaces, it only requires a small script describing device’s parameters. Thus the installation of a new device into an IBS will be very easy therefore heaving low installation costs. IBS easy configuration and expansion with new devices is the most noticeable advantage that an SDR based UGD can provide compared to a hardware based Gateway or any other solution that is supported by current technology.
“Nowadays there are few technologies, with wide recognition, wide range of products but having nothing in common with each other so the adoption of a global communication protocol is impossible” [4] anyway the usage of the SDR technology will enable the UGD to work with various devices on different protocols like X10, Profibus, Insteon, BACnet, LonTalk (LonWorks), EIB and many others by simply describing through a script the protocol, modulation, air-interface, etc. it has implemented.  

The UGD can also be used to implement a cognitive radio system that can utilize unused licensed frequencies to obtain more bandwidth and to enable WNs to communicate between them. By using the CR technology there will be possible to make a real Plug and Play system to provide a higher level of flexibility to IBS where newly started devices will configure themselves, will connect autonomously to the UGD and will start to work without any help.

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