HUMIDITY CALIBRATION.

May we wish all of our readers and customers a healthy and prosperous 2010.

As the temperature for us in the northern hemisphere continues to drop, it is important to note that the current cost of energy is not yet conducive enough to encourage facility engineers into validating their Air Handling Unit (AHU) settings. However it is widely anticipated that as the economy starts to grow again, so will the cost of energy. Then it will be absolutely imperative to ensure that AHU settings are optimised for minimum energy consumption.

The energy used by an AHU varies with the design and capacity of the AHU. However there is an optimum balance that all AHU’s should attain where there is just sufficient preheating; to allow, just sufficient chilling; to condense out the excess humidity without overcooling the air and then requiring a large energy input to reheat the air to the required room; air entry temperature.

The single most troublesome sensor here is the humidity sensor. A three percent adverse error can cause a fifteen percent increase in energy consumption. A ten percent adverse error can cause a hundred percent increase in energy consumption. We recently dealt with a system where the humidity sensor had ceased to operate and gave a continuous output of fifty percent relative humidity. An adverse error that would vary (depending on ambient humidity) between zero and one hundred percent and cause (in the worst instance) a five hundred percent increase in energy requirements.

In the southern hemisphere where the requirement is often to reduce temperature and humidity, faulty humidity sensing often results in air that is over-dried; having to be re-humidified prior to room entry. This results in energy consumption that is far higher than necessary.

Calibration of Humidity & Hygrometer Sensors.

Humidity sensors require frequent calibration and continual monitoring, they are, along with pH sensors, the most prone to error sensors in general facility use. They should be calibrated against a range of Chemical mixtures that establish a specified humidity calibration level in small atmospheric containers. These chemical mixtures are issued with UKAS traceable humidity calibration certification. They are supplied in a kit that includes three certified standards covering the low mid and high sectors of the relative humidity calibration percentage range.

The kit includes three ready to use enclosures (with certification of their values), a range of adaptors to suit your sensors, a sample FDA compliant calibration certificate and a complete detailed method statement on exactly what to do. All these items are contained in a robust neat and easy to handle carrying case.

With HEPA filters, the manufacturers recommended dirty filter change pressure differential (PD), is only correct if the filter is used at exactly the the same air flow as the makers specify. If there is any digression (there is often as much as 50% digression) then the makers PD must be corrected. If this is not carried out you can compromise the integrity of your room / machine pressure regimes. As you are no doubt aware this would be a very serious state to be in. There are also health and safety problems that can arise, if personnel are not getting the air flow protection that is sometimes designed into the system. This test script is not in the standard OQ, and is only available here as a download. Regulators ask to review your writen justification for these filter change PD's; make certain you have them.