July • 2013
Commissioning HVAC Systems
It’s a common complaint that the performance of HVAC systems in buildings deteriorates with time. This can occur due to many reasons, such as problems in the features meant for energy conservation and control, non-functioning sensors, or improper installation of the components of the system. To tackle these issues, facility managers can adopt different strategies. The steps taken within the strategy are intended to rectify the operational deficiencies of the system and to enhance performance. Optimizing the HVAC systems includes energy auditing and commissioning.
According to the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE), a quick Level 1 energy audit involves a brief meeting with facility managers to become acquainted with the building operations and a walk-through of the building to identify all blatant areas of energy waste and inefficiency. The audit is primarily used to determine whether the building should be permitted to continue on to the next step. The energy auditing process is done in accordance with the requirements of LEED and EBOM management practices.
Usually, only significant problem areas will be included during this sort of audit. Corrective procedures can be explained, with quick estimates of implementation costs, along with possible operating cost savings. Additionally, list of energy conservation measures (ECMs, or energy conservation opportunities, ECOs) is also made available.
Retro-commissioning is done based on the results obtained from Level 1 energy auditing by ASHRAE. This is a low-cost way to save energy and optimize the performance of a facility, thus allowing it to operate by making the best out of its equipment and systems. Retro-commissioning, which should be performed every three to five years, consists of a review of data obtained from the buildings, the testing of HVAC systems, and the sequence in which their operation takes place. The testing will ensure that the systems are working in the exact sequence in which they are programmed to do so, and the review of data will help to optimize the performance of systems.
By carrying out retro-commissioning, you will be able to figure out the changes in space use, which in turn necessitate the operational changes in the system. It will also help to identify the systems that are faulty, and also the systems which may be working perfectly fine but can be optimized further to give better results. The higher the energy usage of a building or a facility, the more it will benefit from the procedure of retro-commissioning.
Ongoing commissioning, otherwise known as monitor based commissioning, can be used to identify the faulty systems and the systems that work perfectly fine, on an ongoing basis. Here, continuous monitoring of the system is done by a group of engineers, and a weekly download of this information will alert the operators in charge of the system to identify when there is an opportunity to make an adjustment. The alerts may include an alarm going off when the temperature gets too warm or too cold and when the efficiency of an air conditioner drops down to a very low level. This type of commissioning helps to foresee long-term operations and also re-evaluate the building’s operations on a continuous basis.
Based on the auditing and commissioning of HVAC systems, a set of standard measures can be adopted to optimize their performance. These include optimizing air-side dry-bulb and enthalpy economizer controls, reducing ventilation, reducing the set point of the static pressure, and resetting the chilled water and condenser water temperatures. The start and stop sequence of the air handler should be matched to reduce space usage, and the set point of the pump differential pressure should be adjusted. You should also schedule automatic controls on lighting to reduce cooling loads and usage of electricity.