By Rob Boyajieff
From the April 2017 Issue
When one considers the data of traditional airside energy conservation measures (ECMs), simple paybacks range from low cost, quick payback to capital intensive, long payback. And 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. Taking a university campus as an example, consider that HVAC systems can consume 30% of the total building energy needed in library, student union, and classroom facilities; and in laboratory and research facilities, the HVAC energy consumption can be up to 60%. Few ECMs deliver more than 35% savings for an entire university campus. But demand control ventilation (DCV) has arguably the most dramatic financial impact of any ECM. On average, DCV (sometime referred to as airside efficiency) projects conducted by my firm have a payback of 2.5 years with an average of 38% energy reduction in buildings.
The following list of ECMs is taken as the average cost and savings from five recently completed Energy Service Performance Contracts (ESPC) located in the United States. The spaces utilizing DCV (ECM #11 in Table 1) are primarily labs and vivarium. These type of critical spaces are high revenue producing but also energy intensive environments that consume five to six times the energy compared to traditional office or academic space, and provide significant opportunities for increased profitability via DCV improvements.
As seen in Table 1, the DCV option has the best savings to investment ratio of 5.22 and yields more than $31M in NPV over a 10-year term. Meanwhile, when considering the NPV of the savings and the investment over the term of 10 years, the differences in NPV for the ECMs with and without DCV are seen in Table 2 below. Assumptions for Table 2 are a 10 year financed term, 3.5% interest rate, 4.5% discount rate.
In my firm’s experience, facility owners have often applied basic strategies such as HVAC, night setback and supply air reset, so there is considerable opportunity for dramatic reduction via DCV.
Optimized Ventilation, Data Driven Analytics
In past practice, facility managers and environmental, health and safety professionals typically set these spaces at fixed rates because they did not have the means to monitor air contaminants such as total volatile organic compounds (VOCs), particulates, and CO2 continuously to determine the optimal DCV. 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 four to 12 air changes per hour. The result can be excessive ventilation, and on top of that, there is no data driven analytics available.
Another project involving DCV was for retrofitted spaces, which were initially operating at fixed air change rates of 9.3 for labs and 20 for vivarium spaces. Through the use of DCV, the air change rates were optimized and now operate safely at six air change rates for labs and eight for vivarium spaces. This yielded approximately 50% energy reduction for the building, and this also provides operators data on operations.
DCV (or airside efficiency) is an ECM that goes 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 increased concentration of key pollutants including particles, nitrogen oxide, volatile organic compounds, and allergens affected occupant productivity and maintained that better indoor environmental quality led to a decrease number of self-reported symptoms.¹
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? DCV solutions provide the flexibility required to monitor the indoor environmental quality effectively and then to inform building management systems about changing conditions to adjust HVAC settings properly. The result is the right amount of ventilation for almost all types of situations. This leads to healthier buildings, more productive occupants, and ultimately a more efficient facility.
¹ Joseph G. Allen, 1. P. (2016). Associations of Cognitive Function Scores with Carbon Dioxide, Ventilation, Environmental Health Perspectives, 806-812.
Boyajieff is strategic account manager with Aircuity, a Newton, MA-based airside efficiency company providing building owners with sustained energy savings by optimizing ventilation rates through intelligent measurement solutions. After spending 18 years as a merchant marine and then power industry, Boyajieff transitioned into the field of performance contracting.
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