How Phoenix Controls Venturi Valves win over CAV and traditional VAV systems

Cleanroom applications such as battery manufacturing facilities, pharmaceutical production, and semiconductor fabrication all have one thing in common: they use excessive amounts of energy. According to various sources, cleanrooms can use anywhere from 2-50 times more energy than non-classified rooms [1], [2], [3]. Unsurprisingly, most of this energy use can be attributed to the HVAC system [1].

Given the high value of the outputs of these facilities, there is often more emphasis placed on reducing risk over saving energy, and this is a valid concern for facilities owners. However, what if we told you there is a way to achieve both high quality product, and improved energy management?

The Constant Volume Approach

ISO 14644-1 is the main standard for the classification of air cleanliness in cleanrooms and controlled environments. The standard identifies 10 ISO Classes, with ISO Class 1 being the most stringent (i.e., allowing the fewest particles and creating the cleanest environment) and ISO Class 10 being the least stringent. These classes are defined solely by the maximum concentration of particles in the air – there is nothing explicitly stated about air change rates (ACRs) or circulation.

That said, during the design phase, there is no way to tell exactly what the particulate count of a room will be during operation, so designers are left to estimate the appropriate ACR to achieve the required ISO Class cleanliness level without information on the defining factor of ISO class. This, in itself, raises issues.

As mentioned before, the products coming out of these facilities are of high economic value, so the top priority is to mitigate any risk of contamination or low-quality yields. In many cases, this leads designers to decide on applying a constant volume approach to airflow control. The idea here is to supply a constant flow of air that allows for more air changes- and higher air changes per hour (ACH) generally means a cleaner room in terms of airborne particulates. Additionally, because these are constant volume, the same ACR is supplied nearly 24/7, and while this practice does keep the space sterile at all times, it does no favors to the facilities bottom line as they are using incredible amounts of energy to maintain the air changes [1].

Demand Based Ventilation & Demand Controlled Filtration (DBV and DCF)

Implementing demand-based airflow strategies can reduce energy consumption up to 60-80%!

Sterility of a cleanroom space is the main priority, and it should be. However, it does not have to come with increased operating costs and energy usage.

It is important to note that the main source of pollution and contamination in cleanrooms comes from processes, not from the air itself. In fact, people are the predominant source of particle generation [4], and in “at rest” situations when no one is occupying the space, particle concentrations can be 10-100 times lower than design values [1].

This tells us that a constant volume approach of supplying air at a constant rate, is not the most efficient manner of keeping cleanrooms sterile – because, when occupants are not present, particle concentrations are inherently lower and high air change rates are not needed. This is where Demand Based (Controlled) Ventilation (DBV/DCV) and Demand Controlled Filtration (DCF) come into play.

These concepts are very similar – both involve basing the ACR on the actual particle generation in a cleanroom space. The difference is that DBV/DCV focuses on adjusting ventilation to either remove contaminants and replenish indoor air with clean air when air quality deteriorates, or decreasing ventilation when air quality is acceptable, or occupancy is low. On the other hand, DCF focuses on activating air filtration.

In this article, we focus on ventilation – DBV/DCV. You can employ DBV/DCV strategies by using air quality sensors to sense the particulate count in the room, or by using occupancy sensors to determine if people are present as people, equipment, and processes are often the main source of particle generation. Then, you must also specify a variable air volume control strategy during the design process for the ability to adjust the airflow to a space based on the sensor readings. This can be a blade damper solution or a venturi valve.

The goal of DBV is still to remove and dilute contamination (moisture, particles, organic material, etc.), but it does so while using the minimum required air volume and adjusts based on actual environmental conditions.  Multiple studies have shown that implementing demand-based airflow strategies can reduce energy consumption up to 60-80% [1], [4] by reducing airflow during unoccupied times (weekends/nights) or when particle count is sufficiently low enough to comply with ISO class standards - without compromising cleanliness of the space.

Another benefit of DBV is its predictive quality. By capturing data using sensors, and understanding what key particle generating activities are, you can predict when the system will need to increase air changes. This allows you to be proactive rather than reactive with adjusting airflow to maintain cleanliness and reduces the risk of contamination during peak times.

Why Phoenix Controls Venturi Valves are the Better VAV Solution When Applying a DBV/DCV Approach.

We’ve already covered why constant volume is not the right airflow method for cleanroom facilities when it comes to operating expenses and energy consumption – variable air volume is the way to go. However, typical blade damper solutions, like a VAV terminal box, still fall short.

Pressurization Control

One major parameter that affects the sterility and cleanliness of the air in a space is pressure. This is where challenges with VAV boxes arise. Firstly, in a typical HVAC system, there are multiple VAV boxes – each controlling specific spaces and requiring communication with the building automation system (BAS) telling it to adjust to meet temperature and pressure demands. Every time one VAV box changes the position of its blade damper, it affects the static pressure throughout the duct system, which in turn requires other units to change their position to meet their spaces’ demands, and the cycle continues. The result here is inefficient, unbalanced, and unstable airflow.

Unstable airflow creates an unstable environment. A loss of directional airflow and positive pressure can result in particulate entering a cleanroom space, costing millions of dollars in lost product due to contamination.

Phoenix Controls venturi valves can maintain precise, consistent pressure control because they are mechanically pressure independent. This mechanical pressure independence comes from the cone and spring assembly housed inside the valve. Using an NVLAP accredited characterization process, we precisely map the cone and spring position on the valve shaft to an airflow volume. Once the actuator positions the shaft and cone assembly to the desired airflow based on the flow curve, the cone and spring can still freely move along the shaft in response to pressure changes in the duct. When the pressure increases, the spring will compress, and the cone moves into the throat reducing the area for air to flow. When the pressure decreases, the spring expands, and the cone slides out of the throat increasing the area for air to pass.

In a cleanroom environment, this allows us to accurately maintain tight pressure differentials between spaces using a volumetric offset approach. Depending on the needs of the cleanroom facility, this control sequence can be automatically programmed into a room controller or Programmable Logic Controller (PLC).  If customizations are needed, Phoenix Controls offers a freely programmable BACnet controller that enables you to design a sequence specific to the needs of the room.

It is also important to note that VAV terminal boxes have an inherent signal latency given their requirement to communicate with the BAS to change position. Phoenix Controls venturi valves have virtually no latency with our high-speed actuation allowing for a less than 1-second speed of response time to pressure fluctuations [KU1][CR2]. This mitigates the risk of incorrect room pressure.