Ventilation can be tested using a number of different types of equipment. They each have pros and cons, and each is useful in different environments. Here’s a list of the main ones:
With no moving parts, these can be very robust. They work by heating a wire to a known temperature using electricity, and then measure the rate of cooling. The rate of cooling is proportional to airspeed.
- sensitive to very low airflows
- fast response times
- good to measure turbulence in flows
- some models allow you to specify the current air temperature
- not so good for dusty or humid environments
- cheaper models are calibrated for a fixed temperature and are less-accurate when air is warmer or colder than this
- don’t work well with fluctuating temperatures
This is essentially a freely-rotating propellor. The speed of rotation depends on the airspeed, and is measured electronically or – in older models – via an analogue dial.
- quite robust for use on site
- simple to use
- measured flow rate is independent of temperature and humidity
- does not require any compensation calculations for air density or atmospheric pressure
- rotating propellor reduces airflow and this must be compensated for manually during airflow calculations
- requires access to vent outlet or inlet
- less sensitive to low flow rates
- requires careful alignment with airflow direction for accurate results
Powered Flow Hood
This measures and compensates for airflow loss caused by measuring equipment. A hood seals over the inlet terminal and a powered fan controlled by a sensor within in ensures that pressure remains constant across the tested outlet.
- accurate measurement of airflows
- does not require compensation calculations for air density caused by humidity, temperature or atmostpheric pressure changes
- less portable than other options
- expensive to buy!
That has given you an overview of some of the different equipment used to test ventilation and hopefully helped you understand the benefits and drawbacks of these kinds of ventilation test equipment.