C.D.S. Newsletter December 2011
In this issue ...
- CO2-Based Demand-Controlled Ventilation in TRACE 700
- Single-Zone VAV System Coming Soon to TRACE 700
- TRACE 700 Design Reports: A Quick Reference Guide
- Courses Available for LEED Credential Maintenance
- Frequently Asked Support Question
CO2-Based Demand-Controlled Ventilation (DCV) calculates the hourly CO2 level in each space and then determines the required outdoor air quantity. The hourly CO2 value is a function of the space volume, the number of people, the ventilation airflow into the space, and the CO2 level of the previous hour. The amount of CO2 generated by breathing varies with the people activity level, which is a direct function of the People Sensible+Latent values entered. TRACE calculates the CO2 generated per person and uses the weather location to determine ambient CO2 levels. The default ambient CO2 level for all weather locations is set at 400 ppm and can be changed through the weather overrides button options under the "Select Weather Information" section of the program. The hourly space CO2 level calculation ignores any effect due to infiltration.
How to Model CO2 Sensors in TRACE 700
CO2 sensors can be modeled in TRACE by following these steps:
Step 1: On the Rooms tab of Create Rooms (or on the thermostat template), select a CO2 Sensor location (either Room or None) for the rooms that will have demand-control ventilation control.
Step 2: On the Airflows tab of Create Rooms, select Yes in the Apply ASHRAE Std 62.1-2004/2007 field and enter the appropriate information to properly describe space level ventilation requirements.
Step 3: On the Selection tab of Create Systems, click the Advanced button. Select the option ASHRAE Std 62.1-2004/2007 w/ Vent Reset in the System Ventilation Flag field.
Note: System-level ventilation reset is required for the system to be able to handle zone-level demand-control ventilation.
Step 4: At the bottom of the screen, select the desired C02-based DCV option (None, Proportional Control, or Single Setpoint).
When Proportional Control is selected, the outdoor air controller will adjust the outdoor air intake flow proportionally between the minimum ventilation flow and the design ventilation flow.
When Single Setpoint is selected, the intake airflow is adjusted to maintain the indoor CO2 concentration at the minimum CO2 concentration in the space for any population. If the OA damper reaches the minimum outdoor air intake flow and the population in the zone continues to drop, the OA damper remains at the minimum outdoor air intake flow as specified in the DCV Minimum OA Intake field on the Create Rooms – Airflows screen.
The CO2 DCV controls have no effect on the Design calculations. During the System Simulation, the CO2 DCV controls are disabled during economizer operation.
For additional information on DCV, refer to the following resources:
- For a detailed explanation of what DCV is, and/or how to model it in TRACE 700, click here.
- Engineers Newsletter, volume 34-5, "CO2-Based Demand-Controlled Ventilation with ASHRAE Standard 62.1-2004"
- Engineers Newsletter Live, "CO2-Based Demand-Controlled Ventilation"
In the continued effort to provide our customers with the latest HVAC design functionality, the next update for TRACE™ 700 will feature a single-zone VAV system type. Single-zone VAV is a prescriptive requirement of ASHRAE 90.1-2010 220.127.116.11, and 90.1-2010 will be a prerequisite to achieve LEED 2012 certification. Effective January 1, 2012, both ASHRAE Standard 90.1 and California Code Title 24-2008 extend the requirement for the inclusion of VAV to single-zone DX units ≥ 110,000 Btu/h. The TRACE update will be available in the first quarter of 2012.
To receive e-mail notifications about TRACE updates, subscribe on the C.D.S. News page. Updates are made available from the Download Center.
For more information about the requirements, refer to the following:
- ASHRAE 90.1 addenda [PDF] (refer to addendum n on p. 50)
- California Code Title 24 [PDF] (refer to Section 144-L on p. 108)
TRACE has several design reports that provide detailed information about the cooling/heating loads, airflow capacities, ASHRAE Standard 62.1 calculations and much more. To help you determine which report contains the information you need, we've created a quick reference guide that describes each design report.
Quick Reference Guide: TRACE 700 Design Reports [PDF]
On-demand courses are available on the Trane.com Continuing Education offering, including courses that qualify for 1.5 LEED-specific continuing education (CE) hours from the U.S. Green Building Council (USGBC). As part of USGBC’s credential maintenance program, LEED APs are required to earn 30 CE hours biennially, 6 of which must be LEED-specific. View the course offerings at www.trane.com/continuingeducation.
Course Spotlight: High-Performance VAV Systems
This course will discuss design and control strategies that can significantly reduce energy use and ensure proper ventilation in VAV systems. Topics include ventilation system design and control, optimized VAV system controls, cold air distribution, and other energy‐saving strategies. [Runtime 75 minutes]
What is the difference between block load vs. sum of the peaks?
Block sizing methodology is commonly used for VAV systems. It considers the design load profiles for individual spaces that make up the zone or system and finds the collective maximum load that will occur at any time. TRACE will then determine fan and/or coil sizes based on this maximum simultaneous load.
Sum-of-Peaks sizing methodology determines the fan and/or coil sizes based on the sum of the individual spaces’ maximum loads that make up the zone or system. This methodology is most commonly used for constant-volume systems.