High efficiency heating, ventilation and air-conditioning (HVAC) systems are being increasingly adopted in buildings to save operational costs. HVAC systems and boilers are critical components of energy consuming equipment. HVAC systems can help buildings achieve an energy performance index (EPI) of 100-120 kWh per square metre per year. Boilers are the best choices for HVAC heating. The emerging boiler technologies are aimed at achieving energy efficiency and higher energy performance.
HVAC boilers
Heating systems can be classified as per their equipment type. The heating equipment used in commercial buildings includes boilers (oil and gas), furnaces (oil, gas and electric), heat pumps and space heaters. Boilers are the oldest heating solutions and are best suited for HVAC systems. Even the powerful HVAC systems used in hotels, warehouses and large stores utilise boilers to achieve the desired heating. Boiler-based heating systems have steam and/or water pipes to distribute heat. The heated water may be used in preheat coils in air handling units, reheat coils and local radiators. Additional uses of boilers include heating of service water and other process heating applications. In heating systems, the selection and use of appropriate boilers can help achieve energy efficiency and cost savings. The control systems in boilers manage the operations to ensure an efficient outcome and maintain equipment safety.
Broadly, boilers used in HVAC systems can be classified as steam boilers and hot water boilers. They differ in design and piping configurations. While a steam boiler system is designed to turn water into steam and uses gravity and pressure to deliver heat, a hot water boiler is designed to heat water, which is circulated using a circulator pump through a piping system to provide heat. Both these boilers can be fuelled by oil, gas and electricity. Typically, hot water boilers are more efficient than steam boilers. They entail lower heat loss in the hot water piping and the shell of the boiler as they operate at a lower temperature than steam boilers.
Boilers can be further classified based on their combustion efficiency levels – water tube boilers and fire tube boilers (including condensing boilers). Water tube boilers are used in medium to large commercial/industrial applications. Their efficiency depends on several factors such as whether it is a steam boiler or a hot water boiler, the combustion controls being used and the type of flue dampers. Fire tube boilers restrict the combustion process and gases to tubes and the water circulates around these tubes.
The condensing boilers are more efficient than conventional atmospheric boilers though they are a bit more complex and more expensive. A condensing boiler typically has two heat exchangers and absorbs more heat from flue gases. As a result, moisture in the flue gases condenses. Condensing boilers can be over 90 per cent efficient.
The output of a commercial boiler can be controlled in several ways. The simplest one is the cycling or on/off control of boilers to meet part-load conditions. Another type is the high-fire/low-fire control, which results in fewer off-cycle losses since the boiler shuts off only when loads are below the low-fire rate of fuel input. The third one is modulating control, which is used mostly in large boilers because of its ability to adjust the output to match the load whenever it is greater than the low-fire limit, which is usually not less than 15 per cent of the full load capacity. Heating controls ensure that heating systems operate safely and efficiently. A good control system not only saves energy, but also reduces plant maintenance costs and maintains a consistently comfortable environment for building occupants.
Emerging solutions
Operating an HVAC system at optimum efficiency is a challenging task. HVAC systems in buildings often operate at suboptimal levels. This is due to the complexity of the buildings. There have been significant technological advancements in HVAC systems deployed for commercial and industrial purposes, aimed at improving operational efficiency, reducing utility bills, relieving the grid and the environment, and increasing user comfort. These include movement-activated air-conditioning (sensors hung from the ceiling are activated by movement), on-demand hot water recirculator (cool water circulated back into the water heater) and ice-powered air-conditioning (water frozen in a tank during off-peak hours used in a building) systems.
Many aspects of the HVAC industry can be improved through internet of things (IoT), ranging from preventive maintenance, responsiveness and increased energy efficiency to improvement in contractors’ work processes. Intelligent HVAC systems, which can make decisions based on weather and other indicators, have the potential to cut energy consumption and costs. Connected systems have the ability to analyse the information they gather and alert managers about unusual equipment behaviour or system failure, which results in quicker response times and helps avoid faults and failures. Further, internet-based systems help reduce maintenance and repair costs.
IoT is revolutionising the commercial HVAC industry in a number of ways, including remote diagnostics and increased efficiency. Internet-connected heating and cooling systems have the ability to continuously monitor system conditions and functionality with the help of smart sensors. Smart sensors installed at the desired points measure system performance and the data thus collected can be transferred to a computer, smartphone or tablet over a Wi-Fi network. An intelligent processor can help derive meaningful interpretations from the data.
Data analytics is also being used to provide HVAC systems with sufficient accuracy, which will help facility managers take corrective action and reduce the energy demands and peak load distribution of HVAC systems. In the absence of this type of information, facility managers physically perform manual audits that are inefficient and time-consuming. Managers can also analyse the information to better understand the opportunities it presents. They can look at the normalised data for their building type, and square footage, and break it down to better understand energy consumption based on building occupancy and time. This can help them identify peak demand reduction opportunities.
The way forward
Boiler maintenance is critical for achieving HVAC savings. Regular inspections and scheduled cleaning, coupled with a water treatment programme, are critical for the safe and efficient operation of these units. Operators must also adjust combustion controls regularly. All boilers use excess air in order to ensure complete combustion of the fuel, but too much air results in increased stack losses. The frequency at which operators adjust the controls depends on the application and size of the boiler. Boiler maintenance activities also should extend to the associated distribution systems.
High performance HVAC equipment has the potential to yield energy, emission and cost savings of 10-40 per cent. Besides, with the deployment of IoT, HVAC systems have become intelligent and self-healing. While opting for HVAC systems, factors such as application, requirements of the process, space availability, load variations, operating reliability, energy conservation and the total cost should be considered. an electric heating.