A common mistake of hvac metope sensor installation
Here is a series of related sensor installation hvac common errors of the blog article first paper (a total of three papers), this paper focus on the physical measurement error caused by incorrect installation.It will focus on introducing the humidity, temperature and CO2The installation of sensors on the wall.
The importance of representative position
Sensor installation metope bear in mind that the sensor is used to measure people's indoor conditions.You should choose a representative position: the free flow of air, near the heat source.Common mistake is to install the sensor in air flow is restricted places (such as ambry after), or install where can lead to temperature sensor, such as direct sunlight or near heat sources (e.g., radiators) other places.Notice also that the metope of ordinary sensors are usually not suitable for installation on the ceiling, if you want to install on the ceiling sensor, need to buy a special design for this special sensor.
Figure 1: the metope of hvac sensors typical installation location
In a recent case, a conference center of CO2 sensors were installed in the room rafter, that can be used well to the new risk control system, but the check ground CO2Level, detect the reading is about 2000 PPM.Contractor explained that the sensor is installed in the room rafter, because would be easier to put them here.Although the sensor near CO2Perfectly acceptable level, but on the floor (room rafter five or six meters below, where all people), CO2A high level.Sensor can be installed in the room rafter save trouble, but it really is not a good solution.
Install the metope of sensor
Install metope sensor when some special mistake.According to the design, metope sensors need to be installed in a particular direction, for example, if the specifications "this side up", it must be done according to the request.This is because the metope of any electronic equipment plant will generate heat.If you are in the right direction sensor installation metope, excess heat to take away through the air, not interfere with the measurement.Sensors, unfortunately, sometimes inclined to one side to install, because it would look better.This practice is not desirable: this will cause the temperature measurements on the high side, low humidity readings.
Figure 2. Thermal imaging shows metope sensor will produce a lot of calories, especially CO2Sensors and some other gas sensor.
As shown in figure 2, the heat is easy to be detected by the thermal imager.This picture shows the lower sensor perfectly normal -- it installed in the correct direction.But the problem is that it's the second sensor was installed above, lower temperature at the bottom of the sensor to the upper sensor shell.For example, if you have a carbon dioxide sensor installed at the top of temperature or humidity sensor is a very bad idea, please don't do it.Otherwise, you will get a high temperature and low humidity reading.
Differential pressure
Another source of error may be differential pressure.If your room pressure is too low, could lead to the cold air or CO2Low concentration of air flow sensors directly, so that the distortion.Cable connectors are often to blame for this problem, so you may need to be at the back of the sensor, and especially the cable connection mouth behind the use of a seal - probably some putty filler or similar sealing material.
Pressure also affect CO2Readings.Carbon dioxide sensorUsually compensated by atmospheric pressure, because they are based on CO2Molecular count to work.In order to accurately measure the concentration (PPM), pressure sensor needs to know the right environment.In fact, the sensor with effective pressure sensor or pressure setting.If use both outdoor and indoor CO2Sensors, please make sure they have effective pressure measurement, or, if you have pressure setting, please in the metope of the sensor and outdoor sensors on the same pressure setting.Otherwise, will increase or decrease of the airflow offset into the system.
New pouring concrete
Another source of error may be a new pouring concrete, because the concrete absorbs CO2.In has exposed on the surface of the concrete interior, CO2Level will be low.If the sensor is installed directly on the exposed surface of the concrete, you will get very low in the sensor shell CO2Concentration, this did not represent the outside air.In some cases, you can at the back of the sensor placed a piece of plate, which is used to prevent the CO2Flow, thus improving measurement conditions.If you are using with automatic background logic control (ABC) sensor, it's on the CO2Concentration decreased to about 200 parts per million (PPM), no one place to work around performance will reach the ideal state.Sometimes people assume levels to drop to around 400 parts per million (this is the external background concentration), the sensor readings to zero, but this is not a very good method, can't get the reliable results.
Special environment
Please note that the conventional metope sensor designed to work well in a general office environment.If you have special circumstances or similarClean room(here usually has forced down the airflow) environment, these sensors can work performance is poor, because the heat generated by the electronic devices will be passed on to the sensor, which makes reading distortion.With down flow applications, you need to ensure that the sensor is designed for such occasions.
Wall materials
Metope sensor readings also will be affected by heat conduction of wall materials (such as steel or concrete).If you connect the sensor by bolts directly to the wall, may not be able to correct instructions indoor temperature, it shows the approximate temperature of the wall itself.Common wall materials in the office will not bring any problems, however, if the wall contains metal or concrete materials, between the sensor and the wall materials should use some kind of insulating material.
Please continue to pay attention to our blog posts in December, it will introduce physical measurement error influence on hvac duct sensor installation.