cover of Journal of Building Engineering

Modeling Impacts of Ventilation and Filtration Methods on Energy Use and Airborne Disease Transmission in Classrooms

Lowering the potential of airborne disease transmission in school buildings is especially important in the wake of the COVID-19 pandemic. The benefits of increased ventilation and filtration for reducing disease transmission compared to drawbacks of reduced thermal comfort and increased energy consumption and electricity demand are not well described.

A comprehensive simulation of outdoor air ventilation rates and filtration methods was performed with a modified Wells-Riley equation and EnergyPlus building simulation to understand the trade-offs between infection probability and energy consumption for a simulated classroom in 13 cities across the US. A packaged heating, ventilation, and air conditioning unit was configured, sized, and simulated for each city to understand the impact of five ventilation flow rates and three filtration systems. Higher ventilation rates increased energy consumption and resulted in a high number of unmet heating and cooling hours in most cities (excluding Los Angeles and San Francisco).

On average, across the 13 cities simulated, annual energy consumed by an improved filtration system was 31% lower than the energy consumed by 100% outdoor air ventilation. In addition, the infection probability was 29% lower with improved filtration.

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Residential Solar Water Heating: California Adopters and their Experiences

Solar water heating provides domestic hot water with lower greenhouse gas emissions compared to more typical natural-gas water heating. Solar water heating has a long history, particularly in places where the climate is favorable, such as California where state-backed incentive programs have been successful in creating small bursts of adoption. However, widespread adoption of solar water heating has not occurred in California despite these conditions. This research surveyed 227 single-family households with solar water heating across the state of California to understand their motivations and experiences, and draw implications regarding barriers to adoption. The survey explored households’ experiences across five stages of adoption, as outlined in Rogers’ Diffusion of Innovation theory: Knowledge, Persuasion, Decision, Implementation, and Confirmation. Findings revealed challenges at each stage. Most notably, prevalent disappointment in lower-than-expected energy and bill savings (31%) and high rates of technical problems (41%) appear to be the most significant issues.

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Considerations for Use and Selection of Portable Air Cleaners for Classrooms

Central HVAC Systems generally provide heating, cooling, and ventilation (outdoor air) to a classroom. Central HVAC systems are generally equipped with filters that have a minimum efficiency rating value (MERV). Higher MERV ratings remove a greater percentage of small particles. A standard pleated HVAC filter will have a MERV8 rating. The American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE) recommends installing MERV13 filters to capture airborne viruses. A typical classroom of 960 ft2 will have an HVAC system supply air filtration rate of about 1,000 cubic feet per minute (CFM), meaning that the all the air in the classroom will be filtered six times per hour. Note that the HVAC fan must be running to provide filtration.

Portable Air Cleaners with High Efficiency Particulate Air (HEPA) filtration are widely available. They are measured in terms of their “Clean Air Delivery Rate” (CADR) which is a measure of the cleaning speed of the system in removing particles in a controlled environment. Portable air cleaners have CADR’s ranging from about 25-400 CFM (depending on size), and more than one could be used in a classroom to increase the amount of filtration provided.

An interactive tool published by the California Department of Public Health (CADPH) to estimate the change in relative risk of long-range airborne virus transmission under a range of filtration methods was used to predict the impact of portable air cleaners.

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Low-Cost, Large-Diameter Shallow Ground Loops for Ground-Coupled Heat Pumps

This project developed and validated modeling tools for simulating a ground heat exchanger technology that provides a less expensive method for implementing ground-source heat pumps and significantly reduces energy use in many California climate zones, furthering attainment of California’s energy goals. It is well documented that properly sized and installed ground-source heat pumps enjoy higher system efficiencies than conventional air-source systems by exchanging heat with the ground rather than with ambient air. Ambient air temperatures are hottest when cooling is most required and coldest when heating is most required. Exchanging heat with the ground reduces the temperature extremes and improves heat pump performance.

Market adoption of ground-source heat pump technology has been slow largely due to the significant cost of installing the ground heat exchangers. This technology generally requires drilling deep to place the heat exchanger. Typical California valley soil conditions require 200-foot-deep bores for each ton of heat pump capacity, so a three-ton system would require three 200-foot bores, costing at least $9,000. The large-diameter shallow bore technology studied in this project, however, costs roughly one-third the cost of the deep bore technology.

To evaluate the benefits to California ratepayers, this project performed an analysis using EnergyPlus, and considered the effect of using the large-diameter shallow bore ground-source heat pump on heating and cooling energy end uses for a prototypical single-family home located in each of California’s 16 climate zones. Simulations show a significant reduction in energy use for many California climate zones, with an average heating and cooling energy savings of 20 percent and 23 percent, respectively. Based on a general cost of $0.20 per kilowatt-hour, the annual savings for California ratepayers would be more than $100 for eight of the 16 climate zones and more than $300 for climate zone 16.

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Testing, Adjusting and Balancing HVAC Systems: An Overview of Certification Agencies

Testing, adjusting, and balancing (TAB) is a process where air and hydronic flows in a building
are measured, adjusted, and documented to meet design specifications and local building codes
to ensure thermal comfort, indoor air quality, and system energy efficiency are optimized. In
order to improve the quality of the TAB process, tests should follow a standardized
methodology and be completed by a certified technician. TAB certified specialists use their
knowledge and experience to verify, test, and adjust heating, ventilation, and air conditioning
(HVAC) systems after installation or retrofit, during a building’s commissioning process, or
anytime evaluation of existing buildings is needed.

In this article, we will examine the benefits of using a certified contractor for TAB and describe
the three main certifying agencies and differences between them. The three main certifying
agencies are:

• Associated Air Balance Council (AABC)
• National Environmental Balancing Bureau (NEBB)
• Testing, Adjusting and Balancing Bureau (TABB)

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