APPP 506 – Master of Engineering Leadership Capstone Project, University of British Columbia
Sonali Das MEL Candidate | December 12, 2020
Abstract
ASHRAE’s position on COVID-19 complies with position of WHO and CDC, that engineering control in building operations including heating, ventilation, and air conditioning (HVAC) system can reduce airborne exposures or particles and droplets that might contain the virus. There are strong circumstantial evidence of aerosol transmission of COVID-19 as seen in SARS outbreak, however, there is a lack of data to support the same. ASHRAE does not recommends avoiding the challenge by disabling of HAVC systems as a measure to control the virus. The measures suggested by ASHRAE may increase energy consumption, are expensive to implement and potentially compromises the energy efficiency of the building systems. The energy modeling of the building HVAC system provides an estimate of the increase in energy consumption of the building. With the overall increase in energy consumption, new energy saving methods are required to lower the energy cost with the new regulations in place.
Introduction
ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) has developed guidelines on reopening and operation of buildings during Covid-19 pandemic for maximum safety, these are defined in ASHRAE 62.1. The outbreak of Covid-19 has created new challenges in building operations and maintaining energy efficiency. There is sufficient evidence of transmission of Covid-19 by air which justifies improving ventilation and air circulation in buildings [1], still more research is necessary to establish the extent of role played by HVAC systems. The duration of the pandemic is unknown which makes it even more important to prepare commercial building for a second wave as we try to bring back the buildings to “normal’ operation mode. The infection control pyramid adapted from US CDC (2015) rates the infection control methods from most effective to least effective.
Background
The energy consumption data and Building Automation System (BAS) information for a commercial building in Metro Vancouver was taken for this study. ASHRAE Covid-19 guidelines were applied to the building HVAC system and the subsequent energy consumption data was calculated.
A few approaches suggested by ASHRAE are as follows:
- Ventilation
- Filtration
- Sterilization
- Temperature and Humidity
- No recirculation
Building Details
The building is a 35-storey building located in Metro Vancouver in climate zone 4, with a total area of 596,389 m2. The heating of the building is done by district steam supply, the electricity is provided by BC Hydro.
HVAC system: The HVAC system operated from 8AM to 6 PM on weekdays. There are two separate Air Handling Units (AHU). The interior AHU and Perimeter AHU. The interior AHU provides air at a constant volume and pre set temperature. The perimeter AHU is a DDC Controlled VAV system and reheat. The office space is heated to 22 deg C in winters and to 24 deg C in summers. The general ventilation rate is 0.13 cfm per square foot of the occupied area.
Research Methods
Due to lack of research on the subject matter, similar studies on SARS (2003 pandemic) were referenced for research purposes.
For the purpose of this analysis, based on the data available, the following guidelines were applied on the building for energy consumption calculations for re-occupancy.
- Air Flushing – ASHRAE recommends 3 air changes of outside air or 2 hours of air flushing before and after occupancy hours of the building [2].
- Increasing outdoor air intake – ASHRAE recommends 100% outdoor air, this not only increases the overall energy consumption of the building, but there is also a need to evaluate the capacity of the equipment to operate at the desired condition. There is also a change in the building space pressurization.
- Filtration – ASHRAE recommends at least Minimum Efficiency Reporting Value (MERV)-13 filters for capturing airborne virus. Many HVAC systems are designed to handle MERV 6 to MERV 8 filters, MERV 13 filters can induce additional pressure drop on the air handling system. It is important to verify that the capacity of the HVAC system is sufficient to handle MERV-13 filters.
- Disabling Demand Control Ventilation (DCV) – DCV sequences occupancy-based ventilation based on the CO2 concentration within the building
- Disabling Recirculation – Virus particles can re-enter the building in case of a leakage in recirculation units. Recirculation dampers are considered to be in closed position. Fan coil units are also turned off since they also use local recirculation.
Energy Modeling Approach
Modeling of Electricity and Gas consumption based on the correlation with degree days was performed to estimate the new energy consumption after application of the ASHRAE guidelines. Working on the available data, each of the applicable ASHRAE guidelines were applied and the increase in building energy for heating and electricity was calculated
The pre- and post-energy consumption and cost were compared to assess the energy and financial impact of the guidelines on the building operation. RET screen is used for HVAC energy calculations.
Results
The results of the energy modeling demonstrate considerable increase in both electricity and Heating energy consumption and also an increase in the associated costs. The Thermal Energy Demand Intensity (TEDI), Thermal Energy Use Intensity (TEUI) and Green House Gas Intensity (GHGI) of the building increases 6 times as compared to pre COVID-19 values.
Thermal Energy Demand Intensity (TEDI) provides a measure of the amount of energy a building requires to maintain an indoor temperature that is be thermally comfortable for occupants, per meter of conditioned floor area per year. [3]
Total Energy Use Intensity (TEUI) provides a measure of a building’s total energy use, including both “process” and “regulated” loads, per meter of building area per year. [3]
Discussion and Conclusions
Along with the cost of implementation of implementing the guidelines and the associated operating charges, there are other implications on which need to be taken into consideration.
- Performance gap between design and required operation- Most of the HVAC systems are not designed for features like intake of 100% out door air.
- High energy consumption due to application of guidelines will lead to energy efficiency issues and possible loss of energy rating of the building.
- Changes in building space pressure may lead to issues in opening or closing of doors.
- Most HVAC systems are designed for MERV 6 to MERV 8 filters.
- Design constraints of the ventilation system to provide 3 air changes in hours.
Following energy conservation measures (ECMs) can be applied along with ASHRAE guidelines to reduce energy consumption:
- Optimization of Building Automation System (BAS) control – Enable remote access for better monitoring and control.
- Training of Operations and Maintenance Staff- Inform and train the maintenance staff regarding the pandemic guidelines to minimize human error.
- Building operation schedule optimization – Monitoring the occupancy rate and zones of the building and subsequent adjustment to the weekly schedule.
- Embed weather forecasting – With the increase of outdoor air in ventilation, the energy use will heavily depend on the outdoor air conditions, incorporating weather forecasting with the BAS system reduce the energy consumption.
Pandemic Mode
When the best operating conditions of the building have been achieved in terms of occupant comfort, pandemic guidelines and energy efficiency, it is recommended to program a “Pandemic Mode” in the BAS for any future requirements. This mode should be able to apply required HVAC operation parameters with just one click.
Contact
Sonali Das
Email: sonali07@student.ubc.ca | sonalidas83@gmail.com | Ph: (778)-321-6981| Linkedin:https://www.linkedin.com/in/sonali-das83/
References
[1] Filling the Knowledge Gaps HVAC and COVID-19 BY ED LIGHT, CIH, MEMBER ASHRAE; JAMES BAILEY, P.E., MEMBER ASHRAE; REID LUCAS, ASSOCIATE MEMBER ASHRAE; LAURENCE LEE, CIH
[2] ASHRAE building readiness https://www.ashrae.org/about/news/2020/ashrae-offers-covid-19-building-readiness-reopening-guidance
[3] BC Energy Step Code, September 2017 https://www.bchousing.org/publications/BC-Energy-Step-Code-2017-Metrics-Summary.pdf