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安装HVAC室外传感器时的常见陷阱

Lars Stormbom

高级产品经理

Published: 2020年1月13日

Buildings and Indoor Air Quality

Industrial Measurements

This is the third in a series of three blog posts looking at common pitfalls when installing HVAC sensors, focusing on physical measurement errors that are caused by incorrect installation. This post focuses on outdoor humidity and CO₂传感器。室外传感器受到天气和太阳辐射的影响，并以较低的数量安装，这意味着其安装中的许多错误可能取决于较低的熟悉程度。

Solar radiation

It’s important to have a sensor with a proper radiation shield – if you use a low-quality solar radiation shield, sensors will heat up significantly, causing inaccurate measurements. It is also important to check that the surfaces under the plates in the radiation shield are black. See Figure 1 below.

辐射罩中的黑色底面。 — *Figure 1: Black undersides in a radiation shield.*

如果这些板的底面是白色的，则辐射屏蔽将无法正常工作，这将增加太阳辐射的加热效果。由于辐射屏蔽也可能变得肮脏，尤其是在城市环境中，这可能会增加供暖，因此最好是一个好主意radiation shield和传感器时不时地保持测量精度。

Location

To reduce any heating effects, outdoor HVAC measurement sensors should be mounted in a location where air flow and wind is unhindered, ideally on a pole completely away from any buildings, or on the roof. For wall-mounted sensors a north-facing wall is better, but walls do heat up with solar radiation, warming the surrounding air which then flows up into the sensor, causing measurement inaccuracies. Avoid dark surfaces, and do not mount sensors under the eaves although it’s sometimes recommended by manufacturers who haven’t used proper radiation shields in their products. They do this to reduce the effects of solar radiation by ensuring their sensors are not exposed to direct sunlight. What actually happens is sunlight heats up the wall and hot air then accumulates under the eaves, causing inaccurate and unreliable measurement results.

Exhaust air ducts

一个频繁的安装错误是将室外传感器安装到离排气管道太近的地方。这使排气空气可以进入您的室外传感器，然后测量排气空气而不是环境条件。

If you aremeasuring carbon dioxide outdoorsto balance your air flows, you should avoid mounting your sensor in a dead space: good air flow is vital. This is a mistake that is often made in car parks. Cars are a major source of carbon dioxide, and if you have dead space you can have elevated CO₂concentrations that are not at all representative of the outdoor air. If you’re measuring outdoor CO₂, mounting in an open location and close to the air inlet is recommended.

co₂测量以达到房间中正确的气流速率。室外和室内公司之间的区别₂浓度被用作占用的代理 - 您要控制的空间中有多少人。例如，如果您有室外公司₂sensor, heavy traffic will increase the CO₂level. This level is compared with the reading from an indoor CO₂测量传感器，可以安装在返回气管中（图2）。

*Figure 2: High CO2 conditions are being measured by an outdoor sensor, with lower levels being recorded by an indoor sensor installed in the return air duct.*

这两个传感器之间的实际差异通常是您试图控制为600 ppm的，用于确定您需要多少新鲜的室外空气以及可以重新调节其中的湿度和温度。通过避免使用过多的新鲜空气，您可以在某些情况下节省大量能源，尤其是如果您需要显着除去空气，然后才能使用它。

It’s a good idea to chooseone high-quality CO₂设计用于户外使用的传感器并使用其信号来平衡建筑物内部的所有不同区域，每个区域都有自己的室内传感器。这有助于您确保正确维护室外传感器，并意味着您可以安装不会随着时间的流逝而漂移的高质量。由于实际上是一个很小的测量范围，您需要在户外进行测量，因此，要正确执行此操作，您的传感器也需要充分补偿温度变化。它还需要比用于室内测量的传感器具有更高的准确性和稳定性。如果户外公司₂sensor drifts, it will change the air flows to the building.

Weather

The weather isn’t always sunny; there’s also rain, snow, and various other kinds of bad weather to take into account. When it rains, for example, water will get on the sensor, which may cause drift or humidity readings that are too high. Good air flow will cause water to evaporate and ensure reliable measurements. But if you need to have 100 percent-accurate readings for mission-critical applications, you can also consider a setup with probe heating. This will keep the sensor dry at all times, but will also require an extra temperature measurement because the heated sensor will not measure the ambient temperature correctly, just the humidity. In addition to rain, there can also be high winds, so the sensor should be able to withstand icing and high wind speeds. Figure 3 shows an outdoor sensor with a heavy buildup of ice after a freezing rain test – I can happily say that Vaisala sensors are easily able to cope with this kind of treatment.