What is the static pressure of a ventilation system used for?
Measuring the total external static pressure of a ventilation system is extremely important. This assesses the existing duct system and installation conditions. This simple test can help you uncover problems associated with restricted duct systems that are invisible to those who don’t measure.
Here is the easiest way to explain the static pressure of a ventilation system. This way is to compare it to blood pressure. This comparison is a great parallel like every time you go to the doctor for a checkup. One of the first things that is done by the doctor is a blood pressure test. This baseline gives the doctor a starting point as to your overall health. Static pressure is the same thing, as it is a good indication of the overall health of a ventilation system.
Fans for residential systems are designed to operate at a maximum of 0.50 inches of water column. From the field data we collect, the majority of deficient ventilation systems are operating at a total external static pressure of 0.82 inches of water column (far too high) and delivering less than 300 CFM per ton in cooling mode. cooling.
In order to better understand, total external static pressure of 0.82 is like having a blood pressure of 200 over 130 (normally healthy blood pressure should be 120 over 80.) So when you come across readings like this Here, it’s time to check it all out at the hospital for further diagnosis.
We can convert actual static pressure readings to blood pressure readings. To do this, we need to know the total external static pressure of the system (measured) and the maximum static pressure of the fan (which can be found on the nameplate data). Once you have these two numbers, you can do a little math and figure out what the vent system blood pressure is.
Let’s say you measure a total actual pressure of the external static pressure of 0.75 inches of water column and the maximum static pressure of the fan is 0.50 inches of water column. You will need to divide the actual static pressure by the rated static pressure to get a multiplier.
The calculations would look like this: .75 (actual) ÷ .50 (rated) = 1.5
So a normal blood pressure reading is 120 over 80, you apply that multiplier to each of the blood pressure numbers to determine blood pressure.
(120 x 1.5 = 180) and (80 x 1.5 = 120) the equivalent blood pressure reading for this system would be 180 over 120.
The importance of a healthy system
If the fan is rated for 0.50 inch water column (most fan motors fit this rating) compare the measured total external static pressure reading against this rating. In this example, the measured total external static pressure measurement must not exceed 0.50 inches of water column. If the total outdoor static pressure measurement exceeds the nameplate value, you have ventilation problems. Your electric furnace will not be able to move the necessary airflow when the total external static pressure is above the rating plate rating.
Although the majority of furnace motors are rated at 0.50 inches of water column, models with constant speed fans are often equipped with very weak fans. Because of this, they are barely able to move the required volume of air. The best choice when using this style of furnace is to select a model that is equipped with a variable speed blower. This will give you more fan force to compensate for the pressure drop of the coil, filter and duct system.
The evaporator coil
When measuring total external static pressure, the coil of a one-piece furnace is included in the equipment. This means that the motor pressure drop should not be included in the measurement of the total external static pressure.
If we have a modular furnace, the central heat pump coil pressure drop must be included as it is not factory installed.
The air filter
Various manufacturers will include a factory air cleaner with a one-piece air handler. Although this practice has become much less common than it used to be, you should still be aware of the impacts it can potentially have on total external static pressure readings. The majority of factory filters have very low pressure drop. For simplicity, include the filter pressure drop in the total external static pressure reading.
electrical elements
While electric heater strips are a pressure drop, they are generally not enough to influence fan airflow in a residential fan.
One-piece furnace
2-piece furnace
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