HVAC systems can consume thirty percent (30%) of the total building energy needed in library, student union and classroom facilities. In laboratory and research facilities, the HVAC energy consumption can be up to sixty percent (60%). When one considers the data of traditional airside Energy Conservation Measures (ECMs), simple paybacks range from low-cost, quick paybacks to capital-intensive long paybacks. The ECMs range from simple strategies, such as night setback and/or supply air reset, to full air handler replacement or variable air volume from constant volume conversion. However, few ECMs deliver more than thirty-five percent (35%) savings for the entire university campus. Consider the ROIs on the project listed below:
ROI for Selected Lab Improvements
ROI After Utility Rebate
Leading Cancer Research enter, New York
*After utility rebates
Airside efficiency has arguably the most dramatic financial impact of any ECM when you consider on average, our airside efficiency projects have a payback of 2.5 years with an average of 38% energy reduction in buildings.
Airside Efficiency- Driving NPVs with Demand Control Ventilation
The following list of energy conservation measures is taken as the average cost and savings from five recently completed Energy Service Performance Contracts (ESPC) located in the U.S.. The spaces utilizing demand control ventilation (ECM #11 in Table 1) are primarily labs and vivarium. These types of critical spaces are high revenue producing, but also energy intensive environments consuming five to six times the energy compared to traditional office or academic space. They also provide significant opportunities for increased profitability via airside efficiency improvements.
Table 1: Average ECMs cost and savings including Demand Control Ventilation (ECM#11)
Assumes a 10-year financed term, 3.5% interest rate and a 4.5% discount rate.
When you consider the net present value (NPV) of the savings and the investment, over the term of ten years, the differences in NPV for the ECMs, with and without demand control ventilation (DCV), are shown in table 1.
Table 2: Difference in Net Present Value in Project with and without DCV
The demand control ventilation (DCV) option by far has the best savings-to-investment ratio of 5.22 and yields more than $31 million in NPV over a ten-year term.
In our experience, owners have often applied basic strategies such as HVAC, night setback and supply air reset, so there is considerable opportunity for dramatic reduction via demand control ventilation.
Consider the following energy reduction metrics for a leading cancer research center, where labs were retrofitted with demand ventilation and variable air volume systems.
Table 3: Energy Savings Metrics for Lab Retrofits at a Leading Cancer Research Institute in New York, Resulting in Approximately 50% Energy Cost Reduction
Optimized Ventilation and Data Driven Analytics
In past practice, facility managers as well as environmental, health and safety professionals typically set these spaces at fixed rates. They did not have the means to continuously monitor air contaminants such as TVOCs, particulates, and CO2 to determine the optimal airside efficiency. Laboratory ventilation rate guidelines are usually applied as constants, with the chosen ventilation rate rarely dynamically controlled or otherwise tailored, to the occupancy or conditions of the lab. This practice neither optimizes energy efficiency nor safety. Some guidelines simply recommend a range of 4 to 12 air changes per hour. The result can be excessive ventilation and data not driven by analytics.
For example, the airside efficiency program reflected in Table 3 is based on retrofitted spaces initially operating at fixed air change rates of 9.3 for labs and 20 for vivarium spaces. Through DCV, the air change rates were optimized and now operate safely at 6 air change rates for labs and 8 for vivarium spaces. This yields approximately 50% energy reduction for the building! Meanwhile facility managers and EH&S now have data on the operation and use of their buildings.
Airside efficiency is an ECM going beyond impressive energy savings- it improves the indoor environment for occupants as well. Historically commercial buildings have been ventilated with fixed amounts of fresh air, and are commonly over-ventilated during low occupancy and under-ventilated during full occupancy. The problem with fixed rates is building occupancy is diverse and occupants require the proper amount of fresh air for healthier environments and optimal productivity.
During the energy crisis in the 1970s, building owners in that era recognized the high cost of ventilation and took matters in their own hands and limited ventilation. ASHRAE recognized this, and this lead to increased fresh air requirements via ASHRAE 62.1. To go even further, USGBC recognized an increased concentration of key pollutants, including particles, nitrogen oxide, volatile organic compounds and allergens, affected occupant productivity and maintained that better IEQ led to a decrease in number of self-reported symptoms (Joseph G. Allen, 2016). Buildings today can be challenging environments to provide proper environmental control, so why would we want to statically control fresh air delivery for buildings that are increasingly diverse?
Airside efficiency solutions provide the flexibility required to effectively monitor the indoor environmental quality, and then inform building management systems about changing conditions to properly adjust HVAC settings. The result is the right amount of ventilation for almost all types of situations. This leads to healthier buildings, more productive employees and ultimately a more profitable building as well.
About the Author
Rob Boyajieff is a Strategic Account Manager for Aircuity responsible for developing strategic accounts and partners in the Healthcare, Higher Education, and Life Science markets in New York and the Southeast.
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Joseph G. Allen, 1. P. (2016). Associations of Cognitive Function Scores with Carbon Dioxide, Ventilation,. Environmental Health Perspectives, 806-812.