EMCS - Energy Management Control Services

Energy Management Control Services 41 Cannifton Rd. P.O. Box 713 Belleville, Ontario K8N 5B3 T.877.811.3627 F.613.634.8061
ENERGY conservation depends greatly on how well building heating, ventilation and airconditioning (HVAC) systems are controlled to match occupant needs. In recent years, Direct Digital Control (DDC) systems, which can easily and accurately control building HVAC systems, have become so cost-effective that they are replacing manual and electromechanical controls in retrofits, and are also being installed in almost all new buildings. This fact sheet looks at implementing methods of controlling air systems to minimize the amount of energy used to operate fans and preheat or cool ventilation air. It addresses three key strategies: Demand ventilation using carbon dioxide (CO₂) and occupancy sensors. Reducing reheat energy by automatically resetting supply air temperature (Enthalpy control). Employing optimal start-up routines to bring space to temperature after a setback period. To employ these methods, systems should be equipped with an air quality (CO₂) sensor, space temperature and humidity sensors installed in various locations, outdoor air temperature and humidity sensor and occupancy sensors that can feed signals back to the central control system. Demand Controlled Ventilation (DCV) – DCV can be achieved by various means, the most effective of which is by determining air quality by the amount of CO₂. The American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (ASHRAE) has determined that the acceptable CO₂ level of air in commercial and institutional buildings is 1000 parts per million (ppm), with outdoor air concentrations at about 400 ppm. A typical control setpoint would be 800 to 900 ppm. CO₂ concentrations are measured in the return air duct for areas with similar occupancy and use, or in the controlled space. If only one sensor is used for a large area, it should be placed in the zone that is likely to have the highest occupancy. Occupancy sensors can be used as override switches to turn on the fan for a short time during a normally unoccupied period, or as indicators of occupancy during occupied periods. In an unoccupied auditorium or a gymnasium, the air system might simply maintain a minimum temperature with no ventilation. When the space is occupied, the CO₂ measurement will be used to control ventilation air quantities by modulating the outside air damper from fully closed to fully open to maintain the desired CO₂ level. Supply Air Temperature Reset (SATR) for Constant Volume Air Systems – Air systems with heating and cooling usually have an economizer (or enthalpy) control to modulate outdoor air (OA) and return air (RA) dampers to bring in cooler outdoor air and avoid mechanical cooling. However, when some zones require cooling and some heating, the mixed supply air is usually controlled to a fixed temperature of, for example, 13°C (55°F). By looking at feedback from sensors in various zones, the supply air temperature can be reset to a higher value, up to 25°C (77°F). This will minimize the amount of simultaneous heating and cooling. This system requires DCV sensors in the discharge air and four to five space sensors per system to provide space temperature feedback. The control computer will look for the warmest (or coolest) zone and adjust the supply-air temperature. Optimal Start/Stop of HVAC Systems – Under night setback or setup conditions in both heating and cooling seasons, the building setpoint can be varied during unoccupied periods. However, when the systems are turned back to occupied mode, the building air must be returned to operating temperature as quickly as possible. Because all buildings, and zones within a building, have different thermal inertia, an optimum start algorithm must be used to anticipate the latest time to turn the system back on. These algorithms look at the lowest zone temperature, the outdoor air temperature, and the time lag to heat (or cool) to the setpoint in order to improve the estimate of the start time. They then retrieve and analyse historical temperature and thermal time lag information. These same algorithms can also be used to turn off HVAC systems at the end of the day while the building is still occupied, a technique that is especially effective for buildings with high thermal inertia. The schematic in this figure shows a typical air handling unit control system that is instrumented for DCV operation. Comparison It is difficult to calculate energy savings from system optimization, but they can be compared to non-optimized control systems. DCV can save up to 50 percent of fan energy and 10 percent of heating energy for a system during occupied hours. Ventilation air heating accounts for up to 30 percent of total heating energy for a commercial building. Reducing the OA with DCV could yield to huge savings compared to non-optimized systems. Supply air reset could increase the setpoint by up to 2°C or 25 percent of the average temperature rise (Vancouver). Night setback of heating can save from 6 to 12 percent for heavily constructed buildings, and from 16 to 32 percent for lighter constructions. Optimum start/stop can increase the setback/setup time by one to two hours per day. For a 10-hour unoccupied period, the savings can be as high as 3 to 6 percent for light constructions. EMCS helps commercial businesses and public institutions improve energy efficiency and reduce greenhouse gas emissions that contribute climate change. For more information, or to discuss how we can help you make your property more energy efficient, please contact us. References CO2 Monitoring [PDF] AirTest CO2 Articles & Papers for Reference [PDF] CO₂-Based DCV Using 62.1-2004 - ASHRAE [PDF] Indoor Air Quality in Office Buildings: A Technical Guide - Health Canada [PDF] Application Of CO2 Based Demand Controlled Ventilation [PDF] Ventilation Design (COPE) - National Research Counci Canada [www]

Energy Management Control Services
41 Cannifton Rd. P.O. Box 713
Belleville, Ontario K8N 5B3
T.877.811.3627
F.613.634.8061

ENERGY

conservation depends greatly on how well building heating, ventilation and airconditioning (HVAC) systems are controlled to match occupant needs. In recent years, Direct Digital Control (DDC) systems, which can easily and accurately control building HVAC systems, have become so cost-effective that they are replacing manual and electromechanical controls in retrofits, and are also being installed in almost all new buildings.

This fact sheet looks at implementing methods of controlling air systems to minimize the amount of energy used to operate fans and preheat or cool ventilation air. It addresses three key strategies:

Demand ventilation using carbon dioxide (CO₂) and occupancy sensors.
Reducing reheat energy by automatically resetting supply air temperature (Enthalpy control).
Employing optimal start-up routines to bring space to temperature after a setback period.

To employ these methods, systems should be equipped with an air quality (CO₂) sensor, space temperature and humidity sensors installed in various locations, outdoor air temperature and humidity sensor and occupancy sensors that can feed signals back to the central control system.

Demand Controlled Ventilation (DCV) – DCV can be achieved by various means, the most effective of which is by determining air quality by the amount of CO₂. The American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (ASHRAE) has determined that the acceptable CO₂ level of air in commercial and institutional buildings is 1000 parts per million (ppm), with outdoor air concentrations at about 400 ppm. A typical control setpoint would be 800 to 900 ppm. CO₂ concentrations are measured in the return air duct for areas with similar occupancy and use, or in the controlled space. If only one sensor is used for a large area, it should be placed in the zone that is likely to have the highest occupancy. Occupancy sensors can be used as override switches to turn on the fan for a short time during a normally unoccupied period, or as indicators of occupancy during occupied periods. In an unoccupied auditorium or a gymnasium, the air system might simply maintain a minimum temperature with no ventilation. When the space is occupied, the CO₂ measurement will be used to control ventilation air quantities by modulating the outside air damper from fully closed to fully open to maintain the desired CO₂ level.

Supply Air Temperature Reset (SATR) for Constant Volume Air Systems – Air systems with heating and cooling usually have an economizer (or enthalpy) control to modulate outdoor air (OA) and return air (RA) dampers to bring in cooler outdoor air and avoid mechanical cooling. However, when some zones require cooling and some heating, the mixed supply air is usually controlled to a fixed temperature of, for example, 13°C (55°F). By looking at feedback from sensors in various zones, the supply air temperature can be reset to a higher value, up to 25°C (77°F). This will minimize the amount of simultaneous heating and cooling. This system requires DCV sensors in the discharge air and four to five space sensors per system to provide space temperature feedback. The control computer will look for the warmest (or coolest) zone and adjust the supply-air temperature.

Optimal Start/Stop of HVAC Systems – Under night setback or setup conditions in both heating and cooling seasons, the building setpoint can be varied during unoccupied periods. However, when the systems are turned back to occupied mode, the building air must be returned to operating temperature as quickly as possible. Because all buildings, and zones within a building, have different thermal inertia, an optimum start algorithm must be used to anticipate the latest time to turn the system back on. These algorithms look at the lowest zone temperature, the outdoor air temperature, and the time lag to heat (or cool) to the setpoint in order to improve the estimate of the start time. They then retrieve and analyse historical temperature and thermal time lag information. These same algorithms can also be used to turn off HVAC systems at the end of the day while the building is still occupied, a technique that is especially effective for buildings with high thermal inertia.

The schematic in this figure shows a typical air handling unit control system that is instrumented for DCV operation.

Comparison

It is difficult to calculate energy savings from system optimization, but they can be compared to non-optimized control systems. DCV can save up to 50 percent of fan energy and 10 percent of heating energy for a system during occupied hours. Ventilation air heating accounts for up to 30 percent of total heating energy for a commercial building. Reducing the OA with DCV could yield to huge savings compared to non-optimized systems. Supply air reset could increase the setpoint by up to 2°C or 25 percent of the average temperature rise (Vancouver). Night setback of heating can save from 6 to 12 percent for heavily constructed buildings, and from 16 to 32 percent for lighter constructions. Optimum start/stop can increase the setback/setup time by one to two hours per day. For a 10-hour unoccupied period, the savings can be as high as 3 to 6 percent for light constructions.

EMCS

helps commercial businesses and public institutions improve energy efficiency and reduce greenhouse gas emissions that contribute climate change. For more information, or to discuss how we can help you make your property more energy efficient, please contact us.

References

CO2 Monitoring [PDF]
AirTest CO2 Articles & Papers for Reference [PDF]
CO₂-Based DCV Using 62.1-2004 - ASHRAE [PDF]
Indoor Air Quality in Office Buildings: A Technical Guide - Health Canada [PDF]
Application Of CO2 Based Demand Controlled Ventilation [PDF]
Ventilation Design (COPE) - National Research Counci Canada [www]

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