This diagram shows how your air circulation system should handle the dry ice test (left). As illustrated, the dry ice vapor should be lifted away from the pool water, into the air and out the ventilation system. If the vapor lies still over the water (right), you have a problem. For a closer look, click on the image.
Ever enter the natatorium and get hit with complaints about smelly air in the pool area? Many operators assume the problem is just with the water without considering the more obvious problem: air circulation.Maybe that’s because operators know how to check the water, but are a little less sure how to check their air distribution.
Here are some common-sense ways to see if you have a problem. Remember, it’s a good idea to record your results and videotape the testing if possible.
First, make sure the air system is on and operating correctly. Find out how many air exchanges your system can produce per hour. The formula for air exchange is the total cubic feet per minute divided by the volume of the indoor space multiplied by 60 minutes per hour. Air exchanges should be between four to eight per hour. (See ASRAE 62-1989 for other related rates.)
If possible, check the following using accurate measuring devices under both extreme summer and winter conditions: Relative humidity should be within 50 unoccupied to 60 percent occupied in the summer, and 50 to 55 percent unoccupied and occupied in the winter, depending on outside air conditions — that is, temperature and dew point. It’s a good idea to check this in different areas of the facility to learn if the reading is consistent. Next, check the airflow at water level using an anemometer to discern if you have airflow there. This should be anywhere from 30 to 50 feet per minute.
After that, check your indoor air temperature to see if it falls within acceptable parameters (usually about 2 to 4 degrees warmer than the highest pool-water temperature). Finally, check how far the supply air diffusers are from the pool water and where the return air is located. You may want to take some pictures of these points for future reference.
After you’ve checked all of those things, it’s time to see if your system is moving air properly. You’ll want to do this part with the building closed during nonoperating hours. Call the fire alarm/smoke alarm service, and be sure to turn alarms off. Next, take a block of dry ice and place it in a bucket, of course, using safety equipment. Now place the bucket slightly into the water’s edge. It should fog. If not, place very warm water over the dry ice. Walk the fog along the pool edge and monitor the air pattern the fog creates. If it just lies flat and does not move, you have no airflow. If it is somewhat lifted up and is moving out by the air exhaust system, you have good airflow.
Airflow off the water is important because when chlorine is introduced, it creates an invisible off-gassing byproduct. Many other halogens and sanitizers do the same. The off-gassing usually is removed with a good air system. A good air system also provides plenty of oxygen for sanitizers to burn up chloramines. Without adequate airflow, chloramine-laden air hangs low and doesn’t move. This leads to complaints about itchy skin around goggles, or body and respiratory problems from exposure.
Now that you’ve determined air movement at water level, stop the process and monitor the air higher than 2 to 6 feet above the water. How long does it take for the fog to be removed from the natatorium? It needs to match your air exchange rate (figured earlier in the formula).
The general rule for space temperature is 2 to 4 degrees above the water temp. Sometimes poor air movement is caused by stratification. The process is complex in nature, but simply put, the heat source and the airflow must reach the intended area and not form plumes or layers in the space itself. If your air is stratifying, you may need to call an HVAC professional and have the building evaluated.
Finally, when you’re through, don’t forget to call the fire alarm system back into service.