Advertisement
undefined

click to enlarge

Annual HVAC source energy savings potential with different efficiency measures for various studies climatic, operational and functional.
 
  

Labs are far more energy intensive than typical commercial buildings, but not all labs consume energy for the same reasons. Most available design guidance for labs provides a list of energy-efficiency strategies that include reducing design air change rates, decoupling cooling and ventilation systems and employing variable-air-volume fume hoods. However, quite a few parameters need to be evaluated for each project’s unique requirements to assess the value of any particular strategy. Utilizing a simple block model and results from multiple parametric simulations, the authors made a case based on each project’s functional requirements and location; different projects respond very differently to the same strategies.

This paper presents results from multiple energy simulations and attempts to assess relationships between the functional requirements, loads, operational flexibility, climate and the effectiveness of various energy-efficiency measures. Savings with ventilation airflow reduction vary greatly with climate; sensible and ventilation system decoupling offers savings only if the internal loads are higher than a certain threshold. An all-air system can be more efficient than a decoupled system if an air-side economizer is effective for the climate. Variable-air-volume exhaust is effective only if the use allows for airflow modulation. The results discussed are from computer simulations, which show the selection of energy-efficiency strategies in a lab project require a thorough understanding of ventilation rates, sensible and latent loads, operational airflow and humidity control requirements, envelope heat transfer and the climate.

A five zone energy model, with equal exposure to all four orientations, was created using eQuest v3.64 (DOE2.2 simulation engine) to account for the load diversity caused by envelope heat gain/loss associated with any particular orientation. The analysis utilizes the batch processing feature of DOE2.2 to simulate a total of 216 parametric runs to represent all possible permutations of varying three key parameters—climate, usage pattern and air change rates—to understand the effectiveness of three key efficiency strategies—decoupling cooling and ventilation, water-side economizer and air change rate reduction with active quality sensing. The chart above presents the energy savings for each efficiency measure across the entire range of climatic, operational and functional parameters.

The results illustrate that decoupling the cooling and ventilation systems offer maximum savings for load-driven labs in hot climates, particularly for high usage (1). In mild and cold climates, however, where air-side economizer is most effective, decoupling cooling and ventilation results in an energy penalty because of reduced free cooling potential (2). In mild and cold climates, the decision on all-air vs decoupled systems should depend on the usage pattern of the labs (3). A water-side economizer should be incorporated with decoupled systems, especially for high-usage labs in mild and cold climates (4). In hot climates, however, incorporating a water-side economizer doesn’t show any energy benefit (5).

Air quality sensing doesn’t offer any savings if the labs are load driven and high usage, offering no potential for ventilation rate reduction (6). If, however, high-usage, load-driven labs are designed with decoupled systems, air quality sensing offers substantial energy savings (7). For ventilation-driven labs, substantial energy savings can be achieved by ventilation rate reduction with strategies such as air quality sensing (8). Additionally for ventilation-driven labs, incorporating air quality sensing with decoupled systems increases the savings potential, especially for hot climates (9). The energy saving potential for air quality sensing in addition to decoupling varies with climate types. The increase is limited for mild climates, but higher for cold and hot climates (10).

To summarize the results of the study, it’s important to analyze the actual climatic, functional and operational characteristics of a lab before making decisions regarding energy-efficiency strategies. Since most of this information depends on the end users, and may vary once the lab is in operation, it’s important to utilize data from past experiences or have discussions with the end users about anticipated usage. The analysis illustrates that if strategies aren’t carefully assessed for their application in the particular project, the additional investment might offer little or no energy savings, or even result in an energy penalty.

With over a decade of experience in the field of high-performance building design, Shreshth Nagpal is an expert in the application of building performance simulation and analysis for architectural design and systems optimization. A key member of the Atelier Ten Energy Analysis practice, he brings his experience in building energy analysis including renewable energy systems and optimization of high-performance building envelope, mechanical and electrical systems. As a member of Atelier Ten’s Environmental Design and Energy Analysis practice, Jagan Pillai has expertise in building systems optimization, HVAC controls and systems selection. His wide range of project experience includes universities and corporate campuses, healthcare and commercial high-rise buildings. He also has experience with lab building energy audits and retro-commissioning.

Advertisement
Advertisement