Guest Column

Role of tech-enabled HVAC systems in achieving greater energy efficiency

efficiency

Improving the energy efficiency of buildings has become a pressing global priority due to their significant role in consuming 40 percent of the world’s primary energy and contributing to 33 percent of greenhouse gas emissions (Source: 2021 World Economic Forum). This urgency is particularly pronounced in countries like India, where reliance on fossil fuels remains high for generating a substantial part of electrical energy.

The government has introduced numerous regulations and recommendations to encourage the implementation of energy conservation measures within buildings. These recommendations include strengthening the regulatory energy standards for new buildings, controlling the quality and maintenance of existing buildings, encouraging energy-saving behaviour by homeowners, and stimulating the diffusion and innovation of energy-efficient technologies.

Regulations like Energy Star Labelling for residential and commercial equipment, including electric fans, air conditioners, refrigerators, and more, incentivise manufacturers to create more energy-efficient products. This labelling system empowers consumers by offering them a choice primarily based on efficiency when selecting these appliances. Energy Conservation Building Code (ECBC) is another excellent regulatory framework that encourages building owners to use more efficient equipment & systems to reduce energy consumption in Buildings.

HVAC and the role of technology

Technological innovation could play a significant role in reducing the overall energy consumption of buildings. The energy efficiency of insulation materials, cooling and heating systems, and other appliances has improved over the past decades. However, there is further scope for improving the efficiency of overall systems, particularly concerning the Heating, Ventilation, and Air Conditioning systems.

HVAC systems have a key role in making buildings more efficient since they use 35-40 per cent of building energy, and approximately 65 per cent of that is used by chillers. Hence, the chiller plant room design is significant in building energy conservation measures. Adopting innovative technologies & design concepts for HVAC systems will be pivotal in significantly reducing the building energy consumption.

Here are a few considerations for designers when planning HVAC system plant rooms.

Variable speed chillers

In recent decades, significant gains have been achieved in chiller efficiency at full & part load through advances in Heat Exchanger design, compressor, motor, driveline, and economisers. However, the biggest single efficiency gain has been at reduced ‘lift’ condition when adopting the variable speed drive. Variable speed chillers easily save 20-30 per cent of energy over a constant speed system and provide many other benefits such as low inrush current, High displacement power factor, the convenience of starting all chillers together etc.

Primary variable flow systems

Primary Variable Flow (PVF) pumping systems are one of the most useful methods to reduce the pumping power consumption in HVAC. It helps to save approximately 30 percent more energy than primary-secondary systems, as it also helps to reduce plant room space & better controllability.

Cooling Tower Efficiency

The cooling tower is a highly efficient heat transfer device within the HVAC system. Optimal design involves choosing a tower with the smallest feasible approach temperature, presenting significant potential for energy conservation with chillers when weather conditions permit using the lowest achievable cooling water temperature for the chillers. There is no need to keep the cooling tower water constant since modern chillers can accept the lowest cooling water temperatures. 

Re-evaluate design temperature

The design operating temperature of the chiller holds an extremely high significance with energy efficiency. An approximate temperature decrease of 0.55C (1F) of condenser water inlet results in a 1.5 percent to 2 percent gain in chiller efficiency. It is applicable for the chiller outlet temperature as well. Designers may evaluate all options and choose an optimised temperature profile for applications like data centres, radiant cooling applications and some ‘Process Applications’ where elevated chilled water temperatures can be used.

Series Counterflow systems

Series counterflow systems enhance efficiency in medium to large plant rooms and district cooling plants. Series counterflow chillers help reduce the lift since the ∆T is split between the chillers. Designers could compare parallel flow vs. series counterflow systems to ensure energy savings.

Wide Delta T chilled water design

A higher Delta T design is an excellent way to reduce HVAC pumping energy. Instead of a traditional ten-degree F delta T design, a 12-degree delta T design gives 20 percent savings on installed BHP, whereas a 14-degree delta T design gives 29 percent saving on pumping. It also helps to reduce the pipe & valve sizing, reduction in thermal insulation area & size of electrical accessories.

Use of De-coupled systems

De-coupled systems offer a fantastic method for improving efficiency, employing one HVAC system dedicated to de-humidification and another solely for sensible cooling purposes. This approach enables the utilisation of higher outlet chilled water temperatures for sensible cooling, resulting in energy savings for the chiller operation.

Heat Pumps

Heat Pumps offer a valuable means to enhance a building or facility’s heating and cooling system efficiency by repurposing waste heat or heat that would otherwise be discharged into the atmosphere. Traditionally, buildings utilise chillers for cooling (expelling heat through cooling towers) and boilers for heating. Introducing Heat Pumps increases overall system efficiency, reducing operational costs by potentially replacing or supplementing existing heating systems. They also function in reverse to provide cooling in summer. Furthermore, in scenarios where cooling and heating occur concurrently, Heat Pumps offer an ideal solution. Their usual performance yields a notably high Coefficient of Performance (COP).

Chiller plant optimisation

Implementing an optimised control system has the potential to yield energy savings of around 30 percent compared to prevailing manual operation methods. Achieving greater energy efficiency requires the central plant equipment and its components to be designed, installed, and operated as a single, integrated system rather than disparate elements with independent controls. The larger the building and cooling load, the more critical it is to holistically design, operate, and maintain the central chilled water plant.

To conclude, buildings are crucial in maintaining health, operating effectively, and contributing to national decarbonisation objectives. HVAC accounts for over fifty percent of energy consumption in commercial buildings, making it the primary focus for those committed to cutting energy expenses, enhancing ventilation and indoor air quality, and reducing emissions. Exceptionally high-efficiency HVAC systems deliver these advantages comprehensively.

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