BSEE
BES, discusses innovative approaches to designing energy efficiency into clean rooms despite the challenges of these highly serviced technical environments
compliance need not be mutually exclusive; far from it.
F
In fact, a holistic approach to designing energy efficiency into the requirements of a clean room 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 clean room inefficiency ‘
As the cleanroom requires more cooling energy than heating, a clear emphasis should be placed on maximising the efficiency of the cooling system
’
Depending on the specific class or application of the clean room, up to 60 per cent 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 of HVAC systems can reduce HVAC energy demand by as much as 50 per cent, simply by avoiding common assumptions and over-specification. Although clean rooms are a specialist workplace, generic commercial thinking often results in a tendency to include future-proofing in the spatial planning, ‘just in case’ additional processes, equipment or staff numbers are required at a later date. This can have a significant and unnecessary impact on the facility’s energy consumption, far beyond the negligible additional energy loads involved in future-proofing a centrally air conditioned office of a similar size, where air flows are likely to be around five times less. Consequently, part of the clean room specialist’s remit is to fully interrogate the brief and understand the immediate needs of the organisation, which may result in a an agreed reduction of the proposed space or 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. While air change requirements are dictated by the clean room grade or classification, the guidance does not stipulate how these requirements should be achieved. Moreover, much of today’s common specification practice does not take sufficient note of advances in calculation methodology and filtration technology that could enable reduced flow rates, while still achieving the required clean room standard.
Energy consumption is also increased by the assumed need to ensure an operational environment within the clean room at all times, despite the disparity in the number of particles
or most end users, the key success factor in clean room design is functionality rather than energy efficiency or operational cost. But the aims of environmental efficiency and technical
ENERGY EFFICIENCY Can clean rooms be energy efficient?
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 clean room’s classification status. If a wider temperature and relative humidity band is set for non-operational hours during initial clean room validation, and pressure regimes are maintained during these periods, much less cooling (for humidity control) and reheat energy (for temperature balancing) is required. This approach calls upon the knowledge of the clean room specialist to calculate advise the operational and non-operational temperature and relative humidity bands required to balance optimum energy efficiency within the required clean room environment, including the use of computational fluid dynamics (CFD) modelling data to analyse air flow, when required. The clean room design team can then suggest possible layout or workflow modifications.
Designing energy efficiency into the spec
Although it’s up to building control officers to decide whether individual clean rooms need to comply with Part L, any clean room can comply. Indeed, it’s often possible for them to exceed regulatory standards for energy efficiency and meet the requirements for a BREEAM or RICS’ SKA rating for sustainable fit out.
To achieve this, the clean room specialist must be flexible enough to 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 to maintaining the clean room’s controlled environment.
As the clean room requires more cooling energy than heating, a clear emphasis should be placed on maximising the efficiency of the cooling system and selecting the correct HVAC arrangement for the installation. Where possible latent (moisture) and sensible (heat) cooling systems should be separated to enable the use of high efficiency chillers and free cooling.
For clean rooms with lower cleanliness requirements, a traditional air conditioning system may be sufficient, with heat recovery contributing to the re-heat requirements of humidity control. For those with more demanding 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, where air from outside is used to control latent cooling and relative humidity, is the most appropriate option for larger or multi-clean room high performance 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, thereby optimising cooling efficiency.
In clean rooms requiring very low space relative humidity, desiccant dehumidification may be specified for use in combination with the most appropriate HVAC approach above. It’s important to note that, while selection of the most suitable HVAC approach is pivotal to an energy efficient specification, it is the detail of the HVAC design that will provide the substantial and sustainable energy reduction gains possible in a technically-advanced facility. 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.
Achievable challenge
uAs the clean room requires more cooling energy than heating, a clear emphasis should be placed on maximising the efficiency of the cooling system
28 BUILDING SERVICES & ENVIRONMENTAL ENGINEER MARCH 2019
Ultimately, the principles of energy efficient building services still apply to clean rooms; they simply need to be applied to a more specialist approach to specifying low energy plant and equipment, such as efficient boilers, chillers, fans and lighting, alongside bespoke HVAC design.
www.besltd.org Read the latest at:
www.bsee.co.uk
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48
