A COMFORTABLE CHOICE In HVAC
A COMFORTABLE CHOICE In HVAC
TOPICS
Building Contaminants: VOCs, Bacteria, Viruses, Fungi
ASHRAE standards: ASHRAE 62.1, ASHRAE 90.1
Building codes: Mechanical Codes, Green Building Standards, LEED V4
Environment impact on mechanical ventilation: Wind Effects, Stack Pressure
System impact on mechanical ventilation: Fan speed, Damper
ABSTRACT – IAQ affects occupant well-being, owner/engineer risk, and facility operations. Steps to achieve acceptable IAQ requires an understanding of the contaminants of concern and potential methods to maintain contaminants below threshold levels. Applicable industry standards, codes and rating systems are discussed. Contaminant level maintenance and acceptable IAQ using outdoor air for contaminant dilution and filtration for contaminant removal is presented as the primary means to achieve acceptable IAQ. Factors that affect outdoor air delivery are reviewed that strongly suggest that outdoor air intake flow rates must controlled to achieve acceptable IAQ.
TOPICS
Indirect Airflow Measurement: Temperature Ratio Method, Return Fan Tracking
Uncertainty of Outdoor Air: Field Measurement Errors
Damper Minimum Position: Fixed and Modulating Dampers
Mixing Box Pressure: Mixed Air Plenum Pressure
Differential Pressure: Fixed Orifice
Outdoor Air Monitoring: IgCC, 189.1, LEED
ABSTRACT – Part 1 makes a strong case for controlling the outdoor air intake flow rate is a prerequisite to acceptable IAQ; however, it does not make the case that direct outdoor airflow measurement is the best method to provide proper dilution ventilation to the ventilation zone. Part 2 considers calculated, indirect, and direct measurement techniques and makes a compelling case that direct outdoor airflow measurement, using thermal dispersion technology, is the only reliable method for determining and controlling outdoor airflow rates.
TOPICS
Ventilation Impacts: Health, Productivity, Sick Buildings, Energy Consumption
CO2 Levels: Ventilation CFM per person, Steady State
CO2 Generation: Age, Gender, Diet, Body Mass, Activity Level
CO2 Measurement: Uncertainty, Lag
Demand Control Ventilation: CO2 DCV Strategies, CO2 Setpoints
ABSTRACT – CO2 levels are often used as a proxy for acceptable IAQ. Many believe CO2 is a contaminant and a direct measure of IAQ. Part 3 discusses CO2 ventilation control and its rise in popularity as a method to save energy while exposing the ventilation uncertainties and associated IAQ risk when CO2 levels alone are used to establish IAQ acceptability. The relationship between CO2 levels and ventilation are discussed as well as the uncertainties and misconceptions associated with the use of CO2 as a sole indicator of IAQ.
ABSTRACT – DCV is desirable on high population density, variable occupancy spaces. Part 4 discusses when DCV is required and demonstrates compliance requirements of today’s ventilation standards and codes. Population-based DCV and two improved methods of traditional CO2-based DCV are presented. The ventilation provided when contaminant removal systems are used with CO2-based DCV is also discussed.
TOPICS
ASHRAE Standards: DCV Requirements
DCV Control Strategies: CO2, Population Estimate, People Counters, Airflow Limits
ASHRAE 62.1: Using CO2 with Ventilation Rate and IAQ Procedures
TOPICS
Negative Pressure Impacts: Infiltration of Moisture, Unfiltered Air, Unconditioned Air
Pressurization: Introducing the Pressurization Flow
ABSTRACT – Building pressurization is paramount to acceptable IAQ. Negative building pressure transports moisture, hot and cold outdoor air, and unfiltered outdoor air across the building envelope and into occupied spaces. Part 5 discusses this transport mechanism during all modes of HVAC operation and provides specific analysis on moisture transport in the United States that can lead to mold and fungal growth within the building envelope. Negative building pressure results when the pressurization airflow rate from the mechanical system is negative (i.e., more air is mechanically exhausted or relieved than brought in as outdoor air). The concept of building pressure control through direct control of the pressurization airflow rate is discussed.
ABSTRACT – Part 6 integrates outdoor air ventilation control with building pressure control and discusses the key airflow path that must be controlled. An overview of measurement requirements in supply and return air recirculating fan systems and several variants of dedicated outdoor air (DOAS) systems are discussed.
TOPICS
Pressurization Flow: Measurement and Tracking
Pressurization Control Strategies: Supply and Return Air Fan Systems, DOAS, Economizers
TOPICS
Dilution Ventilation: How it works
ASHRAE’s Position: Increased Ventilation Needs
Ventilation Standards: Comparison of ASHRAE 62.1 and ASHRAE 170.1
Airflow Measurement and Control: Healthcare and Non-Healthcare Facilities
ABSTRACT – ASHRAE’s position document of infectious aerosols is discussed to demonstrate the importance of HVAC design and operation to mitigate the transmission of infectious aerosols such as COVID-19. Of particular importance are the desiccated aerosols that remain airborne and infectious for extended periods of time that are transported by the HVAC air distribution system. Dilution ventilation and filtration are discussed as part of a strategy to remove and dilute the infectious aerosols and the concept of “normal” and “pandemic” mode operation is discussed.
ABSTRACT – Accurate airflow measurement is key to a successful IAQ program and COVID-19 mitigation. Part 8 explains EBTRON’s thermal dispersion technology and what has made EBTRON the leader in airflow measurement for more than 35 years. A short presentation on EBTRON products is also provided.
TOPICS
Thermal Dispersion: Technology Overview
Thermistors: Bead-in-Glass Benefits
Ebtron Advantage: Benefits of Calibration, Materials, Electronics, Construction
Product Range: Duct Mounted, Outdoor Air Intake, Fan Inlet, Fan Arrays, Dampers, HVAC Equipment
EB-Link Bluetooth® Phone App: Service, Commissioning, Balancing, Flow Verification
