HVAC systems have a fundamental role in modern buildings, keeping indoor conditions suitable for human occupancy. However, heating and cooling systems are characterized by high energy consumption and can account for over 50% of electricity and gas bills. Therefore, energy efficiency measures that focus on HVAC can achieve significant savings.
Since HVAC systems are available in numerous configurations, the corresponding energy efficiency measures are also varied. To achieve the best results with HVAC upgrades, a professional assessment by a mechanical engineering firm is strongly recommended.
Energy Consumption in HVAC Systems
One of the main differences among HVAC systems is the energy source. Air conditioning and ventilation normally use electricity, but heating systems use a wide variety of energy sources, including natural gas and fuel oil. For this reason, the highest electricity expenses tend to concentrate around the summer months, while fuel expenses are higher during winter.
The workload on HVAC systems is determined by several factors, and they must be taken into account during the design process: building size, occupant density, and equipment used inside the building are all considered.
Architectural design also influences the optimal HVAC configuration, and the type of construction may limit certain equipment and components. For example, air distribution with ductwork is unsuitable for the long vertical distances found in high-rise buildings.
HVAC equipment is subject to smaller heating and cooling loads when the building envelope offers airtightness and effective insulation. This reduces summer heat gain and winter heat loss, which results in heating and cooling savings.
Recommended Energy Efficiency Measures for HVAC Systems
Although each building has unique HVAC needs, it is possible to provide general recommendations that are valid for most projects. Oversized HVAC installations are common when equipment is selected with “rules of thumb”, and they are more expensive in all aspects: installed price, operating cost and maintenance.
The energy efficiency of HVAC installations be improved with two complementary approaches: upgrading key equipment and system components, and adding control devices to use the available capacity more efficiently.
With adequate planning and selection, HVAC equipment upgrades can yield an excellent return on investment. The following are some of the main system components that can be replaced with modern and more efficient units:
- Chiller Plants
- Electric motors used by hydronic pumps, air handlers, cooling towers, etc.
- Unitary equipment such as window air conditioners, packaged terminal air conditioners, and packaged rooftop units.
- Water heaters
There are energy efficiency ratings for each equipment type, similar to the gas mileage value of a car. Combustion-based boilers and furnaces use the Annual Fuel Utilization Efficiency (AFUE), chillers use the Integrated Energy Efficiency Ratio (IEER), air-source heat pumps use the Heating Seasonal Performance Factor (HSPF), and mini-split air conditioners use the Seasonal Energy Efficiency Ratio (SEER).
Electric motors have their efficiency expressed as a percentage of input power converted to shaft power. NEMA Premium Efficiency motors offer top performance in applications above 1 hp, while electronically commutated motors (ECM) are the most efficient option for fractional horsepower applications.
Enhancing HVAC Efficiency with Automatic Controls
The operating cost of HVAC systems can be lowered with high-efficiency equipment of the right capacity. However, the best possible performance can only be achieved if HVAC operation is adjusted in real time according to the needs of the building. Automatic controls provide the most effective way to accomplish this task.
HVAC systems can achieve a significant efficiency boost when the speed of motor equipment is controlled according to workload.
- A variable frequency drive (VFD) can adjust the speed of a motor when its nameplate capacity is not required, and this concept has been deployed in chiller compressors, hydronic pumps and fans.
- Under part load, motor operation at reduced speed consumes much less energy than intermittent operation at full speed, which has been the traditional control approach.
Planning HVAC Upgrades with other Building Improvements
When planning energy efficiency projects, it is important to consider how different building systems interact. For example, LED lighting reduces the air conditioning load with its low heat emission, and building envelope improvements reduce both heating and cooling loads.
hen HVAC upgrades are planned along with other energy efficiency measures, a good recommendation is checking if other projects reduce the heating or cooling load of the building. If that is the case, the new HVAC equipment can be selected not only with a higher efficiency, but also with a reduced nameplate capacity.
Author, Michael Tobias PE is a visionary in the construction industry. His passion resonates as the Founding Principal of New York Engineers, an Inc 5000 fastest growing company. New York Engineers is the most innovative construction engineering firm focusing on Mechanical, Electrical and Plumbing (MEP) engineering designs in Chicago and New York. Michael has overseen the design of over 1000 construction projects in all market sectors, including LEED certified and Passive House certified projects. He leads a global team of 50 top performers.