How does proper HVAC System sizing reduce operational cost
In many construction and industrial projects, HVAC systems are still treated as a necessary expense rather than a strategic investment. However, from our experience at Alfa Therm, HVAC design, especially system sizing, is one of the most powerful tools for controlling long-term operational costs.
Improper sizing, whether through conservative oversizing or simplified assumptions, almost always leads to higher energy consumption, unstable operation, and unnecessary lifecycle costs. On the other hand, a properly sized system does not only meet technical requirements; it actively reduces energy demand, optimizes equipment operation, and improves overall system efficiency.
Sizing based on real demands, not assumptions
At Alfa Therm, HVAC sizing is not based on fixed or conservative values,
but on real operating conditions.
This approach is aligned with principles such as those defined in SIA 382-1,
Where airflow is based on the actual needs of the space and its usage over time, rather than constantmaximum values.
In practice, this means that we define system capacity and airflow based on:
- actual occupancy and process loads
- daily and weekly operating schedules
- realistic usage scenarios instead of peak-only conditions
By doing so, we avoid designing systems that operate inefficiently for most of their lifecycle. Instead, the system is adapted to real demand, which is the
first and most important step in reducing operational costs.
Airflow as the main driver of energy consumption
InHVAC systems, especially in cleanrooms, airflow is the dominant factor influencingenergy consumption.
Cleanroom HVAC systems can account for up to 50–75% of total facility energy use, primarily due to continuous air handling and high air change rates. Because of this, reducing airflow has a direct and highly intensified impact on energy consumption.
Due to fan energy relationships (cube law), even moderate reductions in airflow can result in significant energy savings. In practical applications, a reduction of around 10–20% in airflow can typically result in approximately 20–50% reduction in fan energy consumption, depending on the system and control strategy. This makes airflow optimization one of the most effective and realistic cost-reduction measures in HVAC design.
Optimizing Air Change Rates (ACH)
Traditionally, cleanrooms were designed using conservative air change rates, often significantly higher than actually required.
Today, best practice is to define ACH through a combination of technical analysis and cost evaluation. At Alfa Therm, we approach this as a joint process with the investor, where we balance:
- process requirements and compliance
- particle generation (especially personnel-driven)
- energy and operational cost impact
It is important to emphasize that this approach does not mean deviating from standards. On the contrary, we fully comply with all applicable regulations and guidelines regarding air change rates and cleanroom performance.
However, within those frameworks, there is often room for optimization. Instead of applying conservative or fixed values, we focus on identifying the actual airflow required to meet compliance criteria and process needs.This includes evaluating where reductions are possible without compromising cleanliness, pressure regimes, or recovery performance.
In practice, this means that we do not design for maximum values by default but rather determine where airflow and especially fresh air intake can be reduced based on real operating conditions.
In many cases, this approach allows us to maintain full compliance while achieving energy savings of up to 30%, simply by eliminating unnecessary air handling.
Airflow reduction during operation
One of the most effective extensions of proper system sizing is the implementation of airflow reduction during non-operational periods.
Instead of running at full capacity 24/7, systems can operate in different modes:
- full airflow during production
- reduced airflow during downtime
This concept, often referred to as Airflow Reduction Mode, can lead to up to 40% savings in ventilation energy, depending on the operating profile of the facility.
This clearly demonstrates that proper sizing is not only about design conditions, but also about how the system behaves during real operation.
Recirculation vs. Fresh Air – A key design decision
Another major factor directly linked to system sizing is the proportion of fresh air versus recirculated air.
Conditioning fresh air is one of the most energy-intensive processes in HVAC systems. Every unit of outside air must be heated, cooled, and treated to meet internal requirements.
For this reason, modern cleanroom design relies heavily on recirculation.
Real project example – pharma industry
In one of our pharmaceutical projects at Alfa Therm, we implemented recirculation AHUs instead of a conventional full fresh air system.
Through detailed analysis and coordination with the investor, we significantly reduced the required volume of conditioned fresh air, while maintaining all process and compliance requirements.
The result was:
- lower heating and cooling demand
- reduced air treatment loads
- significant reduction in overall HVAC energy consumption
In similar applications, airflow reductions of around 30% are achievable, resulting in substantial operational cost savings.
This example clearly illustrates that proper HVAC sizing is not only about equipment capacity, but about minimizing the amount of air that needs to be treated.
CAPEX and OPEX Impact
From an investor’s perspective, proper HVAC sizing delivers value on two levels.
On the operational side (OPEX), reducing airflow, optimizing air change rates, and implementing recirculation can lead to 20–40% energy savings in HVAC systems, which often represent the largest share of building energy consumption.
On the capital side (CAPEX), lower airflow requirements directly reduce system size. This leads to:
- smaller air handling units
- reduced duct dimensions
- smaller heating and cooling equipment
- optimized electrical infrastructure
In large projects, systems with extensive recirculation are often more complex and may require a higher initial investment. However, the reduction in energy consumption during operation typically outweighs this increase, making the solution more cost-effective over the lifecycle of the facility.
Proper HVAC system sizing is one of the most effective way to reduce operational costs across the entire lifecycle of a building.
According to our experience at Alfa Therm, the key lies in designing systems based on real demand, not assumptions. This includes optimizing air change rates, reducing airflow during non-operational periods, and implementing recirculation wherever possible.
Ultimately, the goal is to ensure that the system delivers exactly the required performance while maintaining full compliance and achieving maximum energy efficiency.
A properly sized HVAC system does not only meet technical requirements but also ensures long-term efficiency, reduces energy consumption, and protects the investor’s investment over time.
