John Rush subject matter expert — HVAC, from specialist cleanroom design and construction provider BES, discusses strategies for designing more energy efficient cleanrooms.
Efficiency
The environmental footprint and operational cost of a cleanroom facility is usually secondary to considerations of functionality and performance. However, the aims of environmental efficiency and technical compliance are not mutually exclusive. In fact, a holistic approach to designing energy efficiency into the requirements of a cleanroom can result in a working environment that meets good manufacturing practice (GMP) requirements, while complementing the wider energy management strategy of the site or organisation.
Causes of cleanroom inefficiency
Depending on the specific class or application of the cleanroom, up to 60% of the facility’s energy consumption is usually accounted for by its HVAC system. Ostensibly, this is unavoidable because of the need to maintain a controlled environment through heating, cooling, humidity control, air changes and pressure regimes. However, innovative design approaches and bespoke specification can reduce energy demand of HVAC systems by as much as 50% by avoiding common assumptions and over-specification.
Generic commercial thinking often pervades specification of the HVAC system with a tendency to over-specify on a ‘just in case’ basis. This can have a significant and unnecessary impact on the facility’s energy consumption, far beyond the negligible additional energy loads involved in futureproofing a centrally air-conditioned office of a similar size, where air flows are likely to be around five times less. Consequently, part of the cleanroom specialist’s remit is to fully interrogate the brief and understand the immediate needs of the organisation, which may result in a reduction of the proposed space or a modification of the layout aligned to the equipment, processes and designated staff numbers, when preparing the user requirement brief (URB).
The impulse to over-specify is often underpinned by the lack of clarity offered by current guidance, which does not stipulate how air change requirements should be achieved. Moreover, common specification practice does not take sufficient note of advances in calculation methodology and filtration technology that could enable reduced flow rates — and enhanced energy efficiency — while achieving the required cleanroom standard.
Energy consumption is also increased by the assumed need to ensure an operational environment within the cleanroom at all times, despite the disparity in particles entering the space when it is unoccupied. By altering the temperature, humidity and air change parameters for non-operational hours, energy consumption can be reduced by up to two thirds, without de-validating the cleanroom’s classification status. If a wider temperature and relative humidity band is set for non-operational hours during initial validation, and pressure regimes are maintained during these periods, much less cooling (for humidity control) and re-heat energy (for temperature balancing) is required.
Designing energy efficiency into the spec
It is commonly assumed that cleanrooms do not need to comply with Part L building regulations, but all cleanrooms can comply with Part L and it is often possible for them to meet the requirements for a RICS’ SKA rating for sustainable fit out too.
To achieve this, the cleanroom specialist must evolve the specification in line with the developing brief from the end user, while using best practice data and modelling from previous installations to demonstrate how high standards can be achieved using less energy. The design team must also consider ancillary accommodation — such as change areas, stores and access routes — to ensure the pressure regime strategy supports an energy efficient approach.
As the cleanroom requires more cooling energy than heating, cooling system efficiency should be prioritised. Where possible latent (moisture) and sensible (heat) cooling systems should be separated to enable the use of high efficiency chillers and free cooling.
For higher ISO classes (with lower cleanliness standards), where the clean air requirement is similar to the cooling demand, a traditional air conditioning system may be sufficient, with heat recovery contributing to the re-heat requirements of humidity control. For facilities with a lower ISO classification (higher cleanliness standards), where air change rates exceed those required for cooling, partial conditioning with separate latent and sensible cooling units will reduce the fan, cooling and re-heat energy load.
Outdoor air conditioning is the most appropriate option for larger or multi-cleanroom high standard facilities, where air change rates exceed those required for cooling. Here, sensible cooling is provided by a separate, primary air handling unit (AHU), removing the need for re-heat and enabling the use of high temperature chilled water from very efficient chillers, combined with free cooling, to serve the primary AHU.
In cleanrooms requiring very low space relative humidity, desiccant dehumidification may be specified for use in combination with the most appropriate HVAC.
Selection of the most suitable HVAC approach is pivotal to an energy efficient specification, but it is the detail of the HVAC design that will provide the most substantial and sustainable energy reduction gains. Innovative design methodologies for reducing air moisture content before the air reaches the cooling system can significantly cut the cooling energy load, for example, and a more complex, multi-layered HVAC system will use substantially less energy over all.
Holistic thinking
An expertly-designed HVAC should be specified in combination with a thermally-efficient building envelope. The use of renewable energy sources can also enhance sustainability and drive down operational costs. For example, ground source heat pumps are ideal for the lower temperature outputs required by heating coils in air handling units and CHP is an energy efficient solution for larger sites.
Low energy plant and equipment, such as efficient boilers, chillers and fans can all contribute to more energy efficient cleanrooms, along with LED lighting and presence-detection controls, which can enhance the lighting scheme while reducing energy waste.
Achievable challenge
The core principles of energy efficient building services still apply to cleanroom facilities; they simply require a more sector-specific, innovation-led design approach. As the pharmaceutical industry continues to be held to account on matters of environmental impact and sustainability, while addressing the challenges of operational cost management, designing energy efficiency into cleanrooms is an achievable challenge that should and can be met.