The principal objective of controls is to automate the efficient operation of equipment. Most people consider that if the building is neither too hot nor too cold the equipment is working properly. This thought should be expanded to consider if the system is providing the desired comfort with minimum energy use.
Many controls are coordinated into a Building Automation System (BAS). Such a system should provide superior comfort, identify HVAC system problems, and reduce energy consumption. Some of the control strategies that achieve energy savings include:
- Schedule HVAC start/stop
- Turn off at night where not needed
- Optimize start/stop time
- Turn HVAC on just in time in the morning
- Economizer control
- Optimize the outside air intake needed for free cooling
- Control hot-deck/cold-deck temperature
- Minimize simultaneous heating and cooling of the same air stream
- Variable Air Volume (VAV)
- Control supply air cfm to minimize fan and coil energy use
- Chiller Operation
- Sequence running of the most efficient chillers to achieve the lowest energy use
- Demand Limiting
- Limits chiller demand and/or shuts off equipment during periods of peak demand to minimize demand charges
- Schedule lighting
- Turn off unneeded lights at night
The main problems with control systems often fall into one of these categories:
- Individual controls and/or the BAS is improperly installed and/or not properly commissioned
- Operator(s) are inadequately trained and do not understand the intended operation of the BAS and its energy conservation features.
- Operator(s) disable control components for any one of a number of reasons, including concerns over job security
- The BAS is not periodically tuned, including
- Verifying the operational status
- Correct any operational programming errors of each strategy
- Trending the logged data to see if strategies are properly controlling the equipment
- Temporarily monitoring the data to verify the correctness
- Examine all components for proper settings and operation, including time-clocks, sensors, actuators, valves and dampers
- Correcting all problems found, including recalibration, software modification or updating, plus air and water flow rebalancing
- Failed components are not replaced
Operation & Maintenance
The maintenance of the HVAC system in small stores should be contracted to a reliable and capable service company on an annual basis. This contract should include regular filter cleaning or replacement, seasonal start-up and shut-down, as well as scheduled inspection and repair or replacement of system components.
Operating costs can be reduced by use of outdoor air economizers; cooling the space with all-outdoor air when it is cool outside. These are typically available as a factory option on roof-top units. Night setback should be evaluated and it can often be integrated with economizer controls.
Many local codes specify minimum insulation and fenestration requirements to reduce the energy used for heating and cooling.