Through the Energy & Climate Projects Series, we will be introducing key projects from Sheridan’s campus-wide energy saving initiatives as implemented by the Integrated Energy and Climate Master Plan (IECMP). Last week, we delved into how modernizing the HVAC air handling unit brought about improved building control, energy efficiency, and occupant comfort.
Problem Diagnosis
Have you ever felt that your office space or classroom was overly warm or cold despite the thermostat being set to room temperature? Surely, you’ve been in that one meeting room for too long and started to feel the room getting stuffy.
As previously mentioned in our introduction to a basic HVAC system, the goal of any HVAC system is to maintain temperature, fresh air supply, filtration, and humidity. Even with the upgrades to the air handling unit, maintaining these parameters is complex when multiple zones are involved.
In many Sheridan HVAC systems, the air handling unit (AHU) directs a constant volume of air down a system of ductwork of sequentially decreasing size. The amount of air delivered to an individual zone is ultimately dependent on the sizes of upstream ductwork and the various air terminals in the room.
The original design engineer will have selected these components to meet room airflow requirements based on the expected maximum occupancy, equipment, type of activity, lighting and heat loss through the building walls, windows and ceiling.
In Sheridan’s context, this design approach creates four potential problems:
- The original system may have been designed to codes and standards from the date of construction that are inconsistent with today’s practice.
- When room function changes such that occupancy, activity level or equipment differ, the airflow requirement is no longer matched to the space.
- When occupancy or activity levels are less than maximum in various spaces throughout the building, the system cannot scale back to conserve energy.
- As equipment degrades over time, the airflow delivered to spaces may be less than required or desired.
Therefore, uncomfortable “stuffiness”, humidity or temperature levels are common symptoms of the constant air volume (CAV) design and gradual deterioration of the systems.
The other difficulty encountered with the CAV system is that addition of heat for winter heating or humidity control is handled in the larger ductwork upstream of several zones. This sets up a competition for heating among the various zones, which typically leads to some zones being too hot, while others are too cold.
An Integrative and Technological Solution
As part of the BAS Replacement and Mechanical Upgrades project, the IECMP team has taken steps to improve control in individual zones by installing or repairing variable air volume (VAV) boxes throughout our HVAC systems. The installation of VAV boxes is one of the team’s key tools for providing better control of humidity and temperature in individual spaces while improving energy savings.
The diagram below shows a basic VAV box with a reheat coil similar to the ones installed around Sheridan. A local thermostat compares actual room temperature to the desired temperature set point, and signals the controller when additional heating or cooling is required. In response, the controller opens or closes a valve to modulate the amount of hot water passing through the hot water reheat coil to add heat to the air stream, or adjusts the airflow damper to control the amount of air flowing into the room.
Throughout the year, air leaves the air handling unit at a slightly colder temperature than is delivered to our rooms. In winter heating mode, the hot water circulating in the reheat coil bumps the temperature of the air before it enters the room.
During summer cooling, the cold dehumidified air from the air handler receives a bit of additional heat from the coil to eliminate cold drafts. Although it may seem that energy is being wasted to reheat air that was deliberately cooled in the AHU, the reheat feature is crucial to maintaining proper conditions, and if used properly, is not required very often. Hot water for summer reheat can be generated from heat dissipated by cooling equipment that is normally rejected to the atmosphere.
By precisely regulating the amount of conditioned air as per space requirements, we are able to prevent the following problems:
- Drafty air distribution
- Excessive cold air
- Stuffiness
- Overheating or cooling of air
- Wasted energy
Because room occupancy varies throughout the day, CO2 sensors interact with the VAV to adjust the amount of air delivered to the room. We will discuss the role of CO2 sensors in optimizing energy efficiency and occupant comfort in a future article.
The Results
VAV installations and repairs have been completed in Trafalgar’s G-Wing, E-Wing, C-Wing, portions of SCAET, and in recent room renovations at Davis Campus. If you find yourself in any of these spaces, you may notice the VAV boxes installed overhead like the one shown in the picture below. The exposed copper pipes are the hot water coils.
Since everyone has their own idea of comfort, zone control has been an important priority in Sheridan’s HVAC upgrades. Our goal is to ensure that every employee and student feels the same level of comfort as Jim who is depicted below. If you were in any of the buildings prior to these renovations, you will likely have felt like Mark or Steve at one point or another.
In terms of energy savings, the VAV installation offers the following advantages and benefits:
- Flexibility for varying air flow and heat delivery depending on zone loads
- Ability to balance and optimize energy consumption by the HVAC system
- Tighter control of environmental conditions
- Ability to recycle otherwise wasted heat
Energy Manager of the Office for Sustainability, Herbert Sinnock, notes that the IECMP team welcomes feedback from the Sheridan Community with regard to the new HVAC system and other ongoing projects. As always, if you’re in any of the upgraded buildings and feeling overly hot or cold like Mark and Steve, please let us know. By providing your feedback on comfort levels, we can direct our efforts to improve system operations. Please send us your feedback at constructionfeedback@sheridancollege.ca.