Static Pressure Reset

Static pressure reset is a building control strategy that aims to reduce energy consumption without compromising comfort level. For this strategy to be effective, the building air supply system will need to be variable volume with multiple zones. The main goal of this reset strategy is to continually optimize the supply duct static pressure setpoint. This will enable the supply fans to use the minimum necessary energy to maintain comfortable indoor temperature and humidity levels.

So how is this accomplished? Most buildings will have a fixed static pressure setpoint. For example, let us imagine a facility that has a static pressure setpoint of 2” WC (inches water column). This will dictate how much airflow is needed within the duct to satisfy the setpoint, thus how much fan energy is necessary. With a high static pressure, that ensures that there is plenty of conditioned air to satisfy the temperature and humidity requirements of each zone within a building.

When a zone needs to increase or decrease temperature/humidity, it will open or close its damper position to control the inflow of conditioned air. Too large of an opening and the zone will over heat/cool. Too small of an opening and the zone will not be able to meet its setpoint requirements. High static pressure equals more airflow which equals a smaller damper position. And vice versa, lower static pressure equals less airflow which equals a larger damper position to intake the same volume of air.

Let’s look at a simple example below:

We have 4 zones that all have different heating requirements. With a static pressure value of 2” WC, the zone damper positions have settled to the following positions: 25%, 50%, 0%, and 33%. No damper position is fully open at 100%. This means that we are wasting energy.  

Static pressure reset is usually implemented by using a PID (proportional, integral, derivative) loop. That would deserve its own article. But in essence, the static pressure value will gradually be reduced until at least one damper position is fully open to 100%.  

So for example, we could have the following scenario after a successful reset:

Using this simple example, we were able to reduce the static pressure setpoint from 2” WC to 1” WC.  

Now, how does this save energy? Let’s look at the fan affinity laws to determine how much energy savings we can expect from this example. 

By rearranging these equations, we arrive at the following:

 And plugging in the values from our example, we can expect a reduction in energy consumption of: