Integration: electrical and HVAC systems
System integration of electrical and HVAC systems provides a smart building solution, where the systems are coordinated to allow opportunities to lower costs and achieve greater energy efficiencies.
- Assess the options for integrating HVAC and electrical systems in nonresidential buildings.
- Evaluate the codes, standards, and guidelines that assist engineers in smart building design related to HVAC and electrical systems.
- Identify ways to achieve greater energy efficiency in facilities.
The integration of electrical and HVAC systems is an important step in providing a smart building solution to improve the overall energy performance of the building and increase efficiencies of the systems within the building. Further emphasizing this concept, several codes, standards, and guidelines are in place that require integrated system design to reduce building energy usage.
Mechanical and electrical consulting engineers can work together during the design development stage to design and select systems where performance and efficiencies are improved during the building's lifecycle and operation. Many mechanical and electrical systems are interconnected, whereby higher efficiencies and coordination in one system will result in increased efficiencies and lower energy consumption in the other. Integration of these systems is essential to minimize capital costs during construction, reduce the lifecycle costs of energy consumption and maintenance, and help assist with maintaining comfort of occupants within the building.
A few solutions where electrical and mechanical engineers can coordinate with each other and design systems that are integrated include the building automation system (BAS), variable frequency drive (VFD) considerations, renewable energy systems, cogeneration, and specification of energy-efficient lighting and controls.
BAS and controls
A smart building's foundation is its BAS. The BAS is a crucial integrator of building system functions and controls. Sophisticated systems can coordinate and control a growing number of individual building systems to increase building operational efficiency. This also can enable many different building demand-response programs, notably for owner-occupied buildings where one system can access these. However, it should be noted that multitenant buildings may complicate a system integration program, so this should be considered during the design process. The following are a few examples where the BAS can be used to integrate building mechanical and electrical systems for this purpose.
Smart BAS generally interlock HVAC operation with automatic lighting controls, depending upon the space type and size, that may be required by standards such as ASHRAE Standard 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings Section 9.4.1, California Title 24 Part 6-2013 Section 130.1, and the International Energy Conservation Code (IECC) Section 405.2.2.2.
For example, indoor shut-off lighting controls are required by Section 130.1(c) of Title 24 and may be controlled by occupancy sensors, automatic time-switch controls, or signals from other building systems. Where occupancy or vacancy sensors are used for automatic lighting control, HVAC operation interlock includes space-conditioning system setpoint setback as well as outdoor airflow rate reduction. Section 120.2(e) of Title 24 requires that space-conditioning systems shut off or reset to a setback heating or cooling thermostat setpoint during periods of nonuse by means of an occupancy sensor. Section 120.1(c)5 of Title 24 lists requirements for occupant sensors as ventilation control devices to reduce outdoor airflow rates below code minimums where occupants are not present. This ability can serve to greatly reduce building cooling or heating demand. See Figure 2 for an example of a smart meeting room with the aforementioned design elements identified.
Emerging subsystem software used by the building occupants also may be linked into this complementary system interlock with increasing frequency. Meeting- or conference-room scheduling software that allocates meeting rooms to occupants may be integrated into the BAS and serve to help funnel meetings to the fewest amount of meeting rooms a day, potentially maximizing the amount of time that these rooms are allowed thermostat setback, reduced outdoor airflow rate, and lighting usage.
For example, if an office contained four identical meeting rooms equipped with individual zone dampers and its occupants requested eight 1-hour meetings with no particular time-of-day requirement, the scheduling software might suggest meeting-room allocation for the day to a single meeting room to accommodate all of the meetings, one after the other. Assuming the occupants adhere to their room and time allocations, the other three meeting rooms are then kept unoccupied for the full day.
A worst-case scenario for comparison purposes would be an allocation scheme involving all of the meeting rooms at intervals greater than 30 minutes apart. On the other hand, when considering the Title 24 requirement that outside airflow-rate reduction may only occur after 30 minutes of room vacancy and assuming a lighting timeout delay of 5 minutes, this best-case scenario has the potential to reduce outdoor airflow intake time and lighting time by 240 minutes and 40 minutes, respectively. This is further emphasized if the system includes an embedded delay in the switchover from unoccupied to occupied status to correct for brief or transient entries into the space. The space-conditioning-system demand also would be reduced because setback setpoints would remain undisturbed in the three vacant meeting rooms for the duration of the working day.
As mobile computing becomes more mainstream, we may see additional methods for optimizing building system usage based on room occupancy develop with advances in mobile-computing technologies.
A smart BAS creates opportunities to synchronize mechanical system operation setpoints with central plant loading status and/or current or predicted weather data. This ability allows for rapid-reaction load-shedding measures during peak energy-demand periods as well as early cool-down programs in certain types of chilled-water systems to reduce energy consumption during predicted high-demand periods.
One example of a load-shedding program, which was explored during a recent hospitality project, involves setback of space-temperature setpoints in normally unoccupied electrical equipment rooms equipped with a building ventilation or cooling system tied into the BAS. Many electrical equipment rooms are programmed for space-temperature setpoints in the 75° to 80° F range to be only slightly warmer than normal occupied spaces and to limit heat transfer to adjacent spaces through uninsulated interior walls.A BAS also may take advantage of (or create them for this purpose) existing power distribution hierarchies, such as emergency, legally required standby, optional standby, and/or business critical to prioritize power-load de-energization during peak-demand periods. The less critical loads will be off-loaded during these periods of peak demand to reduce energy consumption. Automatic demand shed controls for noncritical zones are a requirement of Title 24 120.2(h) and can allow or prepare a building to realize savings from smart grid electricity contracts.
The electrical equipment contained within these rooms, however, may be rated for operation at higher temperatures (typically 104° F). See Figure 3 for an example of an interior transformer located in an electrical room. Via the BAS, a facility operator may allow for temporary temperature setpoint setback in these rooms during high- or peak-demand periods if the electrical equipment carries higher temperature ratings and the rooms are expected to be unoccupied during this time.