Moving Forward with Efficient HVAC Systems

Comfortable living is primarily dependent on the efficiency and continued long-term performance of MEP systems in living spaces, whether they are residences, offices or commercial areas. Efficiency levels are influenced by a building’s energy consumption, which will then impact global consumption and ultimately affect the environment. Optimising HVAC system performance can significantly benefit energy consumption and living standards. Enabling this level of performance requires intelligent MEP engineering design. In this article, we look at what efficient HVAC systems duct design require and how we can move forward with them.

Heating, ventilating and air conditioning services are known as HVAC services. Energy efficiency in HVAC systems generally works on the principle of using less and making the most of what is available to save expenditure. HVAC energy costs are a major chunk of overall energy expense. To better comprehend the efficiency of HVAC systems, it helps to understand how the different services of HVAC work.

Different HVAC Systems

• Heating results by increasing the temperature of air within a confined space or heating occupants directly (e.g. use of radiators or floor, ceiling or wall radiation)
• Ventilation involves maintaining the required mixture of gases in the air, controlling odours and removing toxins or contaminants from spaces through natural ventilation or fan-powered mechanical distribution systems.
• Air-conditioning involves the control of air temperature and air humidity. Air cooling is controlled by transferring between spaces, for example with a water loop heat pump, or by sending warm air outside through air-cooled or water-cooled equipment. Condensing the moisture in air on a cold surface results in dehumidification. Air can be cooled by evaporation as well.

How can HVAC be designed for higher efficiency? Typically, energy efficiency is measured with the Seer-Seasonal Energy Efficiency Ratio in BTU (British thermal units) for cooling systems, which is the ratio of cooling output (in BTU) divided by electricity usage in kilowatt hours. The higher this number is, it has a greater level of HVAC energy efficiency. Some of the most important features for general HVAC efficiency are:

• Sustainability Principle - Sustainable design promotes reduce, recycle and reuse. It is desirable to use every resource of HVAC design the maximum number of times before it becomes necessary to discard or replace that resource.
• Using Site Potential - Natural advantages of a site can be used for more efficient building performance. Natural sunlight and wind currents can be harnessed in a building, considering its orientation. This will enable efficient heating, cooling and ventilation. Solar energy for the occupants’ HVAC requirements can be generated through the installation of solar panels.
• Material Use - Use of material with optimum heat-transfer coefficients can reduce the burden on HVAC systems, depending on the building’s orientation.
• Indoor Air Quality Improvement - Air curtains and fresh air handling units with heat recovery options can reduce thermal exchange through a building.

HVAC Energy Performance Deciders

Several factors can affect HVAC energy performance goals. A reduction of almost 30 percent in annual energy costs can result from using high-performance HVAC units. Higher savings can be achieved through natural ventilation in summer and the use of highly insulated warmer wall and window surfaces during winter.

When design goals are decided early on, the design teams know what to work towards well ahead of the construction documents phase. Design team communication can also be prioritised.

HVAC systems account for 32 percent of energy use in a building, according to the U.S. Department of Energy. How can intelligent design help plan an energy-efficient HVAC system, one that reduces costs and environmental degradation?

• Overall design can reduce the amount of cooling and heating a building will require.
• Natural ventilation and natural heat sources can minimise energy use.
• Use of renewable energy sources, such as solar and wind power, can help reduce energy costs and environmental impact.
• Power and special systems incorporating new technologies can be helpful in reducing energy use.

Energy-efficient HVAC designs ultimately require greater effort and collaboration from the design teams. Design goals need to be decided early. For example, energy code requirements and HVAC systems that use 40 percent less energy than the local code will have different designs. There could be differences in component sizes and system types.

Size does matter. HVAC systems must be of the right size to enable energy efficiency. Oversized equipment tends to operate with less efficiency and at a greater cost than those of the correct size. An example would be oversized cooling systems that do not dehumidify the air properly, with the result that spaces are cool but ‘moist’.

HVAC systems must be designed with an eye on expansion but not necessarily a change in the building. Adding new technologies may lead to a demand for more cooling. However, it could be wasteful to provide excess capacity before decisions on expansion are taken. The equipment could be out of date by the time those decisions occur. Still, to save construction and operating costs, extra physical space should be provided for additional boilers, chillers, pumps and cooling towers, and distribution systems could be designed to accept additional equipment and expand for future requirements. Mechanical rooms can also consider using modular equipment.

Ideally, building design should include all features that reduce HVAC loads. Some examples are:

• Sun control, shading devices and thermal mass (passive heating or cooling) can be employed in skin-load dominated structures.
• Glazing with a high cooling index can be included in internal load-dominated buildings.
• Air retarder systems can be featured on exterior walls.
• Walls with the highest r-value and cost-effective roof construction can be included.
• Efficient lighting systems, with daylight dimming controls, could be included.

Other methods of reducing HVAC loads involve using systems that work efficiently at part-load, such as:

• Fan motors that have variable volume fan systems and variable speed drive controls 
• Boiler plants that operate at variable capacity (e.g., step-fired (hi/lo) boilers, modular plants, modulating flame boilers)
• Efficient condensing boilers (operating at 95%–96%) 
• Cooling plants that operate at variable capacity (e.g., modular chiller plants, multiple compressor equipment and variable speed chillers)
• Cooling tower of variable capacity (e.g., multiple cell towers with variable speed or two-speed fans, reset controls)
• Supplied air with temperature reset controls

Since carbon dioxide emissions result from fossil fuel combustion to provide heating and cooling in a building, smart and efficient designs coupled with regular maintenance can reduce the volume of carbon dioxide produced.

BIM (Building Information Modelling) is being increasingly favoured by MEP engineers to help design energy-efficient HVAC systems. For greater success, it becomes crucial to employ BIM-trained personnel early in the HVAC design process to ensure the accuracy and reliability of the final design. Since 3D graphics are connected to data-rich intelligent objects that host component specification, modifications made on one component are automatically updated wherever that component appears. Therefore, HVAC design changes are easier and more efficient for HVAC designers adept at working with BIM technology.

The use of BIM technology for HVAC systems is particularly helpful when HVAC designers download data to run HVAC load and performance calculations. Components can be moved, edited or modified to improve performance while the said changes are automatically updated on all drawings and other design services, including MEP shop drawing services. Using multiple views, ducting system design can be routed for efficient air flow and avoiding clashes with structural or electrical or plumbing elements. Clearances can be maintained adequately for all these elements and the placement of hangers and supports can follow industry codes and regulations with the use of parametric rules of geometry to warn the designer when a code is violated.

Seamless coordination and teamwork is essential between architects, HVAC designers, MEP consultants and contractors to efficiently design and build energy-efficient HVAC systems with minimal environmental impact. This collaborative effort, employing BIM technologies, is the way to move forward with efficient HVAC systems.