Impact of Fume Hood Retrofits on Energy Performance of Laboratory Spaces

There seems to be a significant savings potential if the total exhausted volumes could be reduced while all safety requirements are met. Researchers have meanwhile developed and identified high-performance fume hood solutions that could facilitate a reduction of up to 75% of the consumed energy required to condition make-up air. However, most of these solutions are geared towards new construction as they require specific spatial and system design configurations. There is a lack of knowledge regarding retrofit options and their expected savings potential on energy consumption for existing laboratories. Since fume hoods interact with other systems and fulfill design requirements that are already in place, any modification will consequently impact other performance requirements within the same environment. This project set out to gain a broader understanding of direct and indirect impacts of various retrofit scenarios for individual fume hoods, their integrated function within a laboratory space, and their overall impact on energy consumption of a space.

This research project employed a long term experimental approach to measure the actual energy consumption of two different laboratory spaces, before and after retrofits. The results from measurements in the physical space were then modeled in an analytical, simulated approach to replicate the measured scenarios and consequently provide a basis for other simulation scenarios. The energy consumption of individual lab spaces was broken down by domain to disambiguate how energy is utilized in a given lab context. This approach identified the most significant contributors in terms of design requirements and their impact on actual consumption. This ultimately provided the basis for identifying the most applicable retrofit strategies.

The project showed that it is possible to reduce the energy consumption of HVAC loads for laboratory spaces up to 75% through special retrofit technologies, as demonstrated for one of the investigated laboratory spaces. However, any savings potential is highly dependent on space configuration, its actual use, and its related design context. For the second of the investigated spaces, we found several performance mandates to be conflicting with technically achievable flow rate reductions, which in turn reduced the potential energy savings to only 10%, even when considering significant additional retrofit work. The core findings of this project can be summarized as follows:

• Energy consumption for space conditioning can be reduced by 75% if no other design mandates are in conflict with the employed retrofit technologies.
• Laboratory spaces with high internal heat gains, such as from equipment loads, lighting loads, or solar gains, will achieve less reduction with constant volume systems.
• Cooling loads have been found as significant drivers of overall design volume requirements, even though the resulting annual energy consumption for these volumes is typically dominated by heating requirements.
• Lighting loads have been found to be a significant driver for the cooling demand. A reduction of lighting loads will directly save energy in form of reduced electricity consumed by the individual circuits.
• Heat gains from lighting loads typically show up as a reduction of heating requirements in the HVAC analysis. However, this reduction is not a real reduction of energy, but rather a shift of heating energy to the lighting system.
• A reduction of lighting loads can significantly lower the cooling demand and thus reduce the overall ventilation needs of a space, which results not only in a reduction of cooling consumption but even more significantly in a reduction of heating consumption.
• Controlled lighting schedules and automated lighting systems provide an opportunity to reduce overall consumption, though they do not directly contribute to a reduction of design supply volumes.
• Solar gains can offset heating loads, and reduce lighting loads. However, solar gains during the summer months will increase the cooling load and thus increase the required supply volumes. In constant volume systems, this results in an increased heating load, which cannot be compensated by solar gains.
• Variable blinds have not been assessed and simulated yet. Variable blinds may allow for harvesting more solar gains during heating periods, while still reducing the total ventilation rate due to a reduced cooling load.
• Internal gains are always problematic in laboratory spaces. Unless alternative cooling systems, such as ductless split systems are provided, or the heat sources can be moved to separated zones that allow for local recirculation instead of operating on 100% exhaust, internal loads will always require large volumes of supply air to remove gains, whether there are fume hoods in a space or not.
• In cases with high internal gains, it actually may make sense to use fume hoods as exhaust paths for the required air volumes, since this may meet other safety requirements of the laboratory space at the same time.

This project demonstrated that energy consumption savings of up to 75% for space conditioning can be achieved. However, the individual savings potential that can be achieved for a laboratory space depends on many factors, such as the actual climate where retrofits are installed, actual occupant and lighting schedules, and the actual space and equipment usage. Furthermore, the total savings potential is a function of load-related ventilation requirements versus safety-related ventilation requirements. These ratios can vary widely as our research has demonstrated, even within the same building context. Ultimately, there is no “one-size-fits-all” approach possible for fume hood retrofits, and each individual space configuration must be evaluated in its specific context. The IDEAL application developed as an outcome of this project can be a first step in this process and start the conversation with building owners and other stakeholders.