In a busy BPO facility in Delhi, floor operations had just began in the morning, with the employees logging into their systems and getting ready for the shift. The floor air conditioning suddenly stopped and the facility manager took it to be a routine stoppage for a change over but when the Air Handling Unit (AHU) did not start after the normal 3 to 5 minutes, he got worried and enquired with the building manager. The news was not good – the electrical power to the building’s central chiller as well as the risers to the floor was down due to a rupture of the bus duct of that section of the building.
The temperature on the floor kept on increasing and the temperature in the server rooms shot up rapidly, leading to the IT team having to shut down the servers. By the time the supply was restored, over two hours had passed, and considerable damage was done to not only business but also the reputation of the company’s image with their clients! So, a problem in the building’s electrical system brought down the HVAC system and in turn impacted the business operations.
This kind of scenario is played out in buildings and offices all over the country on a very regular basis, and the impact on business operations is usually quite severe as the modern business operations are heavily dependent on IT services – which in turn are dependent on continuous, uninterrupted and quality power.
Electrical system interconnect to the HVAC system – as the chillers are the largest load in the building, and therefore a very important and critical part of a building. The HVAC electrical system thus require the highest level of upkeep and maintenance, and also effective operations. While this is understood by most building operators and owners, it is quite often a neglected aspect of building maintenance. There are many instances where the electrical systems have not been taken off grid to carry out servicing for over two years – this usually results in a major incident occurring in the third year and of course, someone paying for the loss in business either by getting a reprimand or even getting fired!
Key components of the building HVAC electrical system
All building services and facilities depend on electrical power for their operations, and hence, the electrical system connects to all parts and components of the building. Thus, the system has linkages to all areas of a building such as the HVAC systems, security systems, plumbing systems (for the pumps), vertical transport systems and so on.
While building electrical systems link to all other systems, when the HVAC electrical system is discussed, it typically covers the following:
- High Tension (HT) side distribution switchgear (HT breakers, panels)
- Transformers
- Low Tension (LT) side distribution switchgear for the chillers, primary and secondary pumps, etc (LT breakers, panels, control systems)
- Standby power generation systems (DG sets, synchronizing panels, control systems)
- Electrical cabling/bus ducts to plant rooms and floor tap off points, AHUs etc.
What can go wrong and where?
Each component in a building system is critical to ensure power reaches the users when it is needed. Since the systems are linear in that one component feeds to the next, a breakdown in one of these can lead to a disruption in the system downstream.
Redundancies are built in the system where cost permits or critically mandates, but even then, when a section of the system goes down, the parallel system is again vulnerable till the breakdown is rectified.
Since all components are equally critical, the operators and maintainers need to pay equal attention to the entire system. The most common defects that occur in the various components of the electrical system are:
Breakers: The HT and LT breakers channel the power to the required areas. Vacuum circuit breakers are usually found in the HT section _ whereas Air Circuit Breakers (ACBs) are used in the LT side. A typical ACB, which is the most common breaker found in buildings is shown in figure 1. The most common problem encountered with such breakers is their inability to ‘engage’ or ‘disengage’ when required.
This results in either supply not reaching the downstream user or power not getting cut off when it is needed to. Modern ACBs have control systems that switch on or off the breaker and problems in the control circuit can often result in the ACB not functioning properly. Flashing of the breaker contacts is also a problem faced that can lead to power disruption. Mechanical interlocks can at times also not function as designed, resulting in the breaker not engaging.
Transformers: The transformer is a capital cost head for a building and usually does not fail, as the design is robust. However, the operating conditions of the transformer affects the life and functioning of the transformer. If the frequency of grid supply failure is very high, the transformer will be cycle between load and no load more frequently, resulting in degradation of the system health. One common defect that occurs in oil type transformer (shown in figure 2) is the contamination of oil due to water ingress. Failure of windings is not very common, but does occur occasionally due to mostly design or mechanical failure.
Power distribution circuits: The weakest link in the electrical systems is the distribution system within the building. The power is distributed through either bus bars or through bust ducts, with the late being seen in most modern constructions. The failures occur mostly at the points where joints are made _ such as the lugs at the panel terminations or where the bust duct changes direction.
Failure can occur due to accidental cutting of cabling or degradation of the insulation between the conductors in the bus duct due to moisture. A common problem seen in many buildings is the positioning of the bus ducts or riser cables under plumbing lines leading to water ingress in case of any water leakages from the lines.
Maintaining the electrical system
Like all building systems, a robust and documented Planned Preventive Maintenance (PPM) plan is essential to keep the system functioning as intended.
The staff needs to be trained on the functioning of the electrical system and the limitations of the system _ so that it is used correctly. Many breakdowns occur due to incorrect operations or overloading. Some of the best practices that the maintenance team can adopt to increase the life of the electrical system as well as maintain it at high level of efficiency are list below.
Annual shutdowns: As maintenance cannot be undertaken on most components of the electrical system when the system is live, a ‘shutdown’ is needed where the building operations are stopped and the system is de energized and maintenance work carried out.
This is easier said than done as there is usually pressure from the building business operations team to delay the shut down as it means transferring critical IT data to another location, which is time consuming and costly. A shutdown once a year is an absolute necessity as it gives the operators time to check the system health. Key aspects that are covered in shut down are shown in figure 3.
Thermography: An efficient way to identify defects in a live system is to use thermography, where a thermal imaging camera is used to map the heat signatures of the various components of the electrical system. Areas that are defective come up as hotter than the surrounding, and can be rectified before a breakdown occurs. For large buildings, an in house thermal camera is recommended so that more frequent (six monthly) test runs can be done. For smaller buildings, third party agencies can be called to undertake the thermography once a year just prior to the shutdown so that rectification can be done when the system is deenergised. Figure 4 shows a typical thermography image of a hot spot in a panel.
Power quality audits: The quality of power reaching the end users can degrade due to various reasons such as generations of harmonics due to inductive loads, low power factor, improper grounding etc. Poor power quality can lead to various problems like voltage spikes, burnouts, tripping of MCCB etc. A power quality audit will identify the cause of the poor quality and also suggest rectification measures.
An annual power quality audit is recommended for mid to large sized office buildings. Poor power quality can result in failure of motors and frequent tripping of breakers, which in turn put higher cyclical load on the chillers, leading to reduction in their operating life.
Earth resistance checks: One of the easiest ways to keep an electrical system healthy is to ensure that the earth or grounding of the system is good. Typically, the earth resistance should be in the range of 0 to 2 ohms, with a maximum of 5 ohms. Quarterly checking of the earth resistance and maintenance of the earth pits will go a long way in ensuring good power quality and lower defects in the system.
Safety aspects in maintenance of HVAC electrical systems
Anyone who has had a mild electrical shock will vouch that it’s not a pleasant experience. 220 V is enough voltage to cause fatal injuries to personnel, and hence there is need for the highest level of safety to be adhered to _ when undertaking maintenance of electrical systems. The key aspects of safety when maintaining power systems are shown in demo bands above.
Conclusion
HVAC systems depend heavily on the electrical systems in the building to function effectively, right from the HT breakers to the low voltage control circuits.
The consequences of a poorly maintained electrical system directly impact the air conditioning systems _ and eventually lead to loss of business and cost, and can also lead to serious injuries to personnel.
The cost of maintaining the system is however low as compared to other building systems, and hence a focused approach to electrical system maintenance can pay very rich dividends.
With advances in predictive maintenance, technologies such as thermography, it is easier to anticipate failures and assess system health. The maintenance plan should thus include these tools to ensure a healthy system. The last but very critical aspect of electrical system maintenance is the need for adhering to the highest standards of safety.
