HVAC systems are designed to provide a comfortable, safe and productive environment for occupants in the form of adequate ventilation and comfortable temperature and humidity levels. In this section the scope of HVAC will be limited to the control and delivery subsystems. The heating, cooling and humidification equipment, which provides the energy source for HVAC, is covered elsewhere in this guide.
Before implementing EMOs on HVAC systems, it is important to have some knowledge of the factors that affect environmental comfort. These include air temperature, mean radiant temperature, humidity, air quality, air velocity, activity level and clothing thermal resistance. HVAC changes can affect these factors and cause adverse reactions in the occupants. It follows that knowledge of the effects can prevent problems occurring. HVAC systems can be quite complex, with a wide range of operating modes depending on the outdoor ambient conditions, occupancy schedules, and seasonal and other factors. Therefore it is essential to have a good understanding of how a system is designed to operate as well as how it is actually operating. You can often achieve substantial savings simply by restoring a system to its design condition. Historical operational information from logbooks or interviews with operators can be quite useful in evaluating a system over a full range of operating conditions.
Typically, the greatest savings in HVAC systems can be attained by matching the conditioning of the space to occupancy (schedules and levels). This is generally accomplished by system scheduling and control, preferably by means of closed-loop (feedback from the space and outside air) control strategies. Recording power and temperature meters are useful tools in gauging the efficiency of HVAC systems. Many modern control systems have the capability to log monitored points (temperature, airflow, humidity, run-time, etc.).
The various losses shown in the Sankey diagram in Figure 2.6 are itemized and defined in Table 2.11.
Identifying energy savings opportunities in HVAC systems involves critically assessing the existing energy use. Table 2.12 provides examples of EMOs for HVAC systems according to the three-step method detailed in Section B-8, “Identify Energy Management Opportunities.”
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technic al supp lement | det ails of Energy- Consuming systems 160 Figure 2��6 sankey diagram of hvaC Energy Flowstable 2��11 Energy Flows in an hvaC system
Energy Flow description key Factors for Evaluation of Flow Portable instrumentation used for Evaluation
HVAC System Mixing Losses
Mixing of hot and cold fluid streams
Temperature and flow of streams; design requirements for mixing
Temperature and flow measurement devices
Space-Conditioning Losses
Maintaining conditions above required levels
Use of space, inadequate or uneven distribution system
Recording thermometer/ psychrometer
Ventilation System Loads
Losses due to necessary fresh air requirements
Outside air inflow, mixed air settings
Space Loads Occupant requirements,
internal heat gains
Occupied density, lights and equipment
Temperature and humidity measurement
Auxiliary Equipment Gains/Losses
Heat introduced by fans/
pumps into system Motor size Recording power meter
Excess Energy from Other Systems
Crossover heating or cooling from another system
Free Cooling
Outside air when temperature/humidity is within range to be used as cooling
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technic al supp lement | det ails of Energy- Consuming systems 161 table 2��12 Energy Management opportunities in hvaC systemsstep actions d et er m in e th e n ee
d q Document the load on the system – meter cooling or heating input.
q Evaluate the space requirements – schedules, occupancy, temperatures, and humidity, exhaust and ventilation.
q Consider carefully any effect an EMO might have on the environmental quality of the conditioned space.
q The load on the system will change as a result of other energy management actions at the end-use – this step may need to be revised periodically.
M at ch th e n ee d
q Ensure that supply temperature and humidity are not significantly greater than required. Operate at the minimum possible temperature, humidity, fresh air % and/or airflow. Consider ventilation on demand.
q Monitor overall HVAC performance (energy input to conditioned space).
q Minimize load swings and stagger demand and startups (ideally at point of end-use) where possible. q Make use of free cooling where possible.
q Schedule systems and/or temperatures to match occupancy and O/A conditions. q Ensure that controls are operating properly and calibrated regularly.
q Consider control upgrades to direct digital offering more flexible control of systems to loads, provided that underlying systems are capable of the appropriate modulation.
q Use variable speed drives where operating hours, conditions and economics dictate.
q Install local air treatment units (e.g. electronic air cleaners, activated charcoal odour-absorbing filter, high-efficiency filters) to reduce the need for general exhaust.
M ax im iz e Effi ci en
cy q Regularly check mechanical maintenance items (fans, bearings, alignment, etc.).
q Ensure that air filters and ducts are clean.
q Use EE motors where operating hours, conditions and economics dictate. q Insulate distribution system – pipes, ductwork.
q Maintain seals, air ducts, breeching and access doors to ensure airtightness. q Ensure that duct and pipe insulation is up to standard.
o pt im iz e su pp
ly q Reclaim exhausted heat and cooling.q Utilize thermal storage in cooling systems to optimize purchase of electricity.
q Consider a solar wall – a metal collector designed to provide preheated ventilation (make-up air) for buildings with large south-facing walls.
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Technic al Supp lement | Det ails of Energy- Consuming Systems 162 HVAC ReferencesModern Industrial Assessments: A Training Manual, Version 2.0, Rutgers, The State University of New Jersey, September 2001
Web site: www.iac.rutgers.edu/indassess.php
Energy-Efficient Motor Systems Assessment Guide, Natural Resources Canada, 2004
oee.rncan.gc.ca/cipec/ieep/newscentre/motor_system/index.cfm
CanMOST: The Canadian Motor Selection Tool, Natural Resources Canada, 2004
oee.nrcan.gc.ca/industrial/equipment/software/intro.cfm?attr=24
Team Up for Energy Savings – Heating and Cooling (HVAC) (fact sheet), Natural Resources Canada, 2005
oee.nrcan.gc.ca/publications/industrial/cipec/heating-cooling.cfm
Industrial Energy Efficient Equipment, Natural Resources Canada