When a building has been properly air balanced, the primary evidence to the occupants is that the rooms are all the same temperature. If you’re in the field without your air balancing hood, one way to test a building is to check temperature balance.
The test procedure is quite simple. Test the temperatures in each of the rooms. If they’re all within two degrees of each other, the building is balanced. That’s it in the proverbial nutshell.
Of course, you must expect that The Doc is going to tell you there’s more to it than that. I will not disappoint you! So let’s take a closer look at a temperature balance and see how it really has to be done in the field.
To prepare for the testing, start the system by setting the thermostat for normal conditions required by the current outside temperature. Let the equipment run until it has either cycled once or has run for at least 15 minutes.
Start by recording the time of day and then measure the outdoor ambient air temperature (be sure to test in the shade on hot sunny days). Also, record the outside humidity.
Typically, because of speed and ease, it’s best to use an infrared thermometer to measure the room temperatures. There are some rules to remember when measuring room temperature with an infrared. It doesn’t measure air temperatures, so you have to choose a standard location in each room so your readings will accurately represent the average room temperature.
When using an infrared thermometer it’s important to understand how your particular instrument reads. The key is to comprehend the test area read by the tool. The more expensive the instrument, the smaller the area the beam reads. All infrared thermometers are rated by the ratio the width of the test beam increases as the distance from the instrument increases.
Cheap infrareds costing $100 or less may have a 1:4 ratio. This means that it averages the temperature of a 10 sq.ft. area at a wall 10 ft. away. Under the same conditions, a good quality infrared thermometer costing $300 to $500, will have a ratio of 1:50 and will measure the temperature of an area less than one square foot. The key is to understand how the instrument you are sing is reading temperature.
The best test location to test in a room to get the best room temperature is chest high, on an inside wall, away from the airflow of a supply register. The test location should also be away from any direct sunlight or other heat source (click here for an example). Measure the temperature in each room.
Next, find the average temperature in the building by averaging the temperatures that you’ve just taken in the building. It’s best to throw out the highest temperature reading and the lowest temperature reading. Then, average the rest of the readings to get a fair average of the temperatures.
Finally, subtract the difference between the average building temperature and each room temperature to find the degree difference from average for each room. Write a recommendation for each room that has a temperature difference of greater than 2F.
This test also can also be used after installation when the system has been balanced to measure the accuracy of ACCA Manual J load calculations. Some assumptions of wall or ceiling R-Values and other building components are made when collecting the data for a Manual J calculation. Verify the accuracy of your calculations during extreme weather by measuring room temperatures.
One last note: temperature testing is only valid during extreme weather with a temperature difference of 15F or more between inside and outside. If the house is 70F and it’s 70F, it’s not the right time to effectively temperature balance.
To most of our customers, temperature is our product. Try temperature balancing to evaluate the performance of one of your systems. It’s a fairly fast, simple process that provides evidence of a job well done.
Rob “Doc” Falke serves the industry as president of National Comfort Institute a training company specializing in measuring, rating, improving and verifying HVAC system performance. If you're an HVAC contractor or technician interested in a free temperature balancing test procedure, contact Doc at firstname.lastname@example.org or call him at 800/633-7058. Go to NCI’s website at www.nationalcomfortinstitute.com for free information, technical articles and downloads.