1. What sensor is and how it changes our comfort?
2. Most commonly used sensors in BAS.

1. What is a sensor and how it changes our comfort?

Typical Monday, you finally get to your office after a few dozens of minutes of forcing your way through the morning traffic jam. At your full speed, with thoughts about tasks of the week, you are entering the entrance hall. You did not even slow down before the main door, because your brain learned that the door opens automatically. Ah, that’s just a motion sensor, not a big deal, you might think. Well, it is a big deal if you think about it in a technological sense. There is a device, mounted above the door, which constantly monitors the amount of thermal energy within its range. When you enter the ‘sensored’ area it detects the increase in infrared energy, which releases your body through heat. The sensor, therefore, changed the output to give the door controller signal that the motion was detected, and the door auto-magically opened. Such events most probably happen around you multiple times during the day, without you even noticing. And all of that because sensors of different types quietly do their job. Some of them may even save your life one day.

So what is a ‘sensor’? It is a device whose purpose is to detect changes in its environment and send the information to other electronic devices. In the case of Building Automation sensors typically used to monitor environmental conditions, ensure safety and save energy. ‘What you can measure you can control’ is often repeated truth among the BMS Engineers. When you get to your office, you expect a pleasant and safe environment. Sensors allow for controlling algorithms to compare current conditions to the predefined commonly known standards of comfort or defined specifically by the end-user. For example, if the temperature in a room is below 18 deg. C, the heating should be turned on, regardless, of the area is occupied or not. Also if the occupant prefers a  higher temperature than the standard one and changes the setpoint, we need to know how to maintain the desired temperature most efficiently. For that, we have temperature sensors on the output of the Air Handle Unit, on the wall in the controlled room and the return of the air duct.  Sensors give us information for precise and efficient control. Generally, the more sensors there are available, the more prices control we potentially can have and thus fewer energy losses.

Pic. 1. iSMA-B-LP (example of multi-sensor)

2. Most commonly used sensors in BAS.

There are several ‘superstars’ among sensors, which are essential and thus very commonly used in building automation.

• Number one is a Temperature sensor. With its simplicity and relatively low cost, this sensor provides a very good return on investment. The precision of temperature control greatly influences the energy efficiency of a building and tenants comfort. Such a sensor is made up of two metals, which generate electrical voltage or resistance once it detects the temperature change.
• Humidity sensor. Another important characteristic of air is its humidity. RH (Relative Humidity) can change how the temperature is perceived by humans. Also, humidity is an important factor in controlling infections and bacteria.
• CO2 sensor. When we take a breath, we pull air into our lungs that contain mostly nitrogen and oxygen. When we exhale, we breathe out mostly carbon dioxide. SO the level of CO2 can be a good indicator of the amount of fresh air needed in a specific area. For example, a conference room, with a larger number of people may require more than a normal amount of fresh air to ensure breathing comfort.
• Water detection sensor. These sensors are often installed in data centres/server rooms under or above equipment to ensure that there are no leaks that may damage expensive computer equipment.
• Pressure sensor. These sensors are typically used to measure air pressure in ventilation systems and water pressure in water distribution systems. They operate as a transducer that generates signals (typically 0-10V / 0-20mA) depending on the pressure imposed. 
• Light level sensor. Light sensors can measure the amount of light they are exposed to and generate a signal or change their resistance depending on the type of the sensor. Lighting is very important in terms of the comfort, health and safety of tenants. Besides that lighting typically uses from 20% to 40% of energy in a building, so precise lighting control can come with significant savings.
• Motion sensor. This sensor detects whether there is a movement in a certain area. Information from this kind of sensor may be used for lighting, occupancy control, ventilation, and temperature control.
• Gas sensor. These sensors are often used in areas where leakages or concentrations of various gases may occur. For example, in parking areas, the level of CO and NO2 is monitored to ensure safety, and in situations when the levels approaching dangerous, additional ventilation may be activated.

Lately, a large number of sensors are created according to IoT standards, have their IP address and are ready for integration to BMS wirelessly. But yet most of them are hard-wired to controllers or I/O modules that can read their values depending on the type of the sensor. For that purpose, I/O modules are equipped with Digital Inputs (signals true/false) and Analog Inputs (for measuring voltage, current or resistance values). There is also a common practice among BMS equipment manufacturers to implement Universal Inputs (they can act both as Digital or Analog) as it’s done in iSMA-B-MIX-38.

Pic 2.  iSMA-B-MIX38 (example of I/O Module)