Basic HVAC System Principles

Heating, Ventilation, and Air Conditioning (HVAC) systems are considered to be the heart of any building, designing the HVAC system is strongly dependent on the application, while an office space can be turned into a surgical orthopedics operations theater by modifying its HVAC System and some other minor adjustments !

Most of current HVAC systems basically depend on the well-known refrigeration cycle shown below:

Figure 1: Basic Refrigeration Cycle “Theoretical”

Those major parts can be packaged together in a Window Type AC or Roof Top Unit (RTU) , separated just like the split systems, or even having a certain type of heat exchanger with a secondary water circuit like chilled water systems!

The bottom line , understanding the physics of this cycle will help us to identify many areas of improvement for HVAC systems.

Energy Consumption in HVAC Systems

Like all thermodynamic gas / vapor power cycles, the refrigeration cycle shown in (Figure 1) contains some energy consuming components that enable its continuous operation and hence the production of useful energy utilized in our daily life (heating / cooling).

While, one of the most important ways to distinguish one refrigerant based HVAC system over another is its energy efficiency ratio (EER) that can be represented by the following formula:
EER = PoutPinput…………………………………………………………….. (1)

Where:
EER : Energy Efficiency Ratio
Pout: Power Output
Pinput : Power Input

Typical nominal values might reach up to 3.5 (unitless), which means that this refrigeration cycle can produce 3.5 units of energy when provided with 1 unit of energy !

This might seem to be violating the first law of thermodynamics concerning energy conservation, however, it is not. We can use the following analogy to clarify that concept.

Let’s assume that we have some spilled water over a desk and we need to collect that water in a bowl, one might use a spoon to collect the water, while other might use a sponge that sucks the water from the desk then releasing it to the bowl by applying a light pressure over the sponge ! both of them have accomplished the mission (removing the water from the desk and put it inside the bowl), however, which one did the least effort ?

Similarly, a refrigerant at low pressure / low temperature can play the same role of the sponge in the previous analogy , while the refrigerant will be removing heat from your space , then going to compressor which will be playing the role of the hands applying a light pressure to enable that heat loaded refrigerant to release its heat to the atmosphere by the condenser !

Understanding the basic principles of the refrigeration cycle will help us to trace energy efficiency measures that might increase any HVAC system efficiency.

So, energy consuming parts in any HVAC systems can be summarized as follows.

  • Compressors
  • Fans
  • Pumps (in case of chilled water system)
  • Controls
Figure 2: HVAC Equipment , One of ACH Engineering Projects

HVAC System Overall Efficiency

The overall efficiency of any HVAC system depends on many factors, such as.

  • Outdoor temperature profile
  • Indoor temperature profile (user / application dependent)
  • Building envelope (insulation / infiltration)
  • Lighting systems heat emission
  • Occupancy and level of activity
  • Internal equipment heat emission
  • Internal latent load sources
  • The efficiency of HVAC system components

Many of those factors can be controlled through involving professional HVAC engineers from early stages of the project.

As we are discussing HVAC systems efficiency, and based on the previously identified energy consuming parts of the system , below figure illustrates typical energy consumption contribution for those parts.

Figure 3: Energy Consumption Contribution HVAC Parts– Manufacturer’s Catalogues

It’s obvious that most of the energy consumed by a refrigerant based HVAC system is related to the compressor(s), which justifies the current competition between HVAC systems manufacturers to improve their compressors technology to comply and exceed current energy consumption regulations

Currently , seasonal energy efficiency ratio (SEER) is being used to evaluate and compare the seasonal energy efficiency of air conditioning units, which address the ratio between the total useful energy (cooling or heating) and the total energy consumption for the same season or period of time, please, refer to AHRI related standards for more information.

Such values (EER / SEER) and any other similar (ESEER , SCOP) can help us to compare the overall efficiency of the Air Conditioning Unit, while, an overall evaluation of the HVAC system efficiency taking other system components such as fans and pumps is still need to be addressed by a professional HVAC engineer.

HVAC Systems in Cleanrooms

While HVAC system design depends heavily on the required cleanroom classification according to ISO 14644-1 which leads to adopting certain Air Change Number per hour (ACH), refer to (Figure 3) , yet thermal loads need to be addressed in early stages of the project taking into consideration all internal and external heat sources, also its important to understand that thermal load calculation is not only needed for equipment selection but it is also required to understand load fluctuations, hence choosing the most feasible HVAC system from initial cost as well as operational cost point of view.

Figure 4: ACH Estimate for Different ISO classes – For Accurate Estimate, Consult a Professional Controlled Environment Service Provider

Evaluating Cleanroom HVAC System Energy Efficiency

To evaluate a Cleanroom HVAC system from energy efficiency perspective, we need to understand its thermal load fluctuation that depends on many factors such as.

  • At rest schedule Vs. Operational schedule
  • Thermal behavior of internal loads, i.e. equipment , processes
  • Surrounding environment thermal behavior
  • Ambient thermal behavior

A thermal load behavior for collective components might be as shown below (Figure 4).

Figure 5: Thermal Load Fluctuation for a Typical Cleanroom Application

One of the challenges that face a controlled environment and cleanroom service provider is to choose the appropriate HVAC system that responds to such load fluctuation, while choosing inappropriate HVAC system (either oversized or undersized) will incur initial cost as well as running cost implications that might affect business bottom line.

the following tips can be considered to optimize energy consumption of cleanroom HVAC system:

  • Consider the controlled environment room height before equipment selection , and check for height reduction possibilities (every foot counts !)
  • The use of variable air volume systems through considering variable frequency drive (VFD) fans and Variable Air Volume controls (VAV’s)
  • The use of efficient air conditioning units that complies with ASHRAE 90.1, corresponding AHRI standards and current ENERGY STAR regulations through utilizing VFD drive compressors and fans
  • Considering Computational Fluid Dynamics simulation for further design optimization (Figure 5).
Figure 6: Computational Fluid Dynamics Simulation Example

The engagement of a professional controlled environment / cleanroom service provider from early design stages helps making effective decisions that lead to optimized design and selection.

We at ACH Engineering are proud to provide comprehensive evaluation of your controlled environment / cleanroom application, including HVAC system evaluation through:

  • Thermal load calculation and evaluation
  • HVAC system design
  • HVAC system selection
  • Energy cost evaluation

ACH Engineering is a controlled environment and cleanroom solutions provider that attends your project from early design stages and up to certification by providing the following holistic products and services:

  • Engineering & Design

We provide comprehensive engineering and design service for your controlled environment and cleanroom application from Architectural, Structural and MEP perspectives and according to local applicable codes and regulatory requirements.

  • Manufacture & Supply

Our cGMP modular room panels, ceilings, doors, and vision panels are manufactured to satisfy the corresponding requirements of the most stringent standards (FDA , cGMP, and Health Canada).

  • Manage & Execute

Our teams are ready to turn design documents and drawings into materialized operational fact through utilizing their construction project management expertise

  • Validate

Validating our projects to be certified is the organic result of the providing seamless and professional service throughout the complete value chain.

FAQs – Controlled Environment / Cleanroom HVAC Systems

1- Do I need an HVAC System for my Cleanroom ?

HVAC System is the heart of any clean room, while changing the indoor air at certain exchange rate (ACH) is necessary to achieve the required particle contamination level according to ISO 14644-1, maintaining proper temperature and humidity is also necessary for process integrity and people health and safety.

2- Who can do the HVAC design and installation for a cleanroom ?

Developing a proper HVAC design for cleanroom applications requires special knowledge and expertise, design shall be developed by a professional engineer who is licensed by a regulatory body (i.e. Professional Engineers of Ontario), while installation can be done through experienced mechanical contractors preferably under professional supervision from controlled environment / cleanroom solutions provider.

3- What is the importance of having a professional HVAC system design / installation for my controlled environment / cleanroom application ?

HVAC system design & installation is critical for controlled environment / cleanroom applications due to its vital impact on internal process integrity, processes taking place in controlled environments and cleanrooms are related to human health , research and development , delicate manufacturing processes and more !

4- What is the difference between a controlled environment and a cleanroom ?

According to ISO 14644-1: A cleanroom is a room within which the number concentration of airborne particles is controlled and classified, and which is DESIGNED, CONSTRUCTED and CERTIFIED in a manner to control the introduction, generation, and retention of particles inside the room, while other elements might need to be controlled such as temperature, pressure, electrostatic discharge, vibration, lighting and humidity.
While, A controlled environment, or a critical environment, refers to a space with controlled temperature, pressure, and humidity without referring to particle contamination.
Basically, a cleanroom is a more stringent version of a controlled environment.

5- What are the ideal conditions of a cleanroom?

Cleanrooms can be classified according to the required indoor particle number per unit volume as per (ISO 14644-1), while the following tests shall be done to maintain the classification:

  • Particles per cu.mt volume
  • HEPA / ULPA filter leak test
  • Room pressurization test
  • Room air change per hour (ACH)
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