22 April 2019
How Future HVAC Systems Must Adapt to Climate Change
The winter of 2017 saw Ras Al Khaimah, an emirate in the desert country of the United Arab Emirates, experience unprecedented snowfall and Dubai, normally home to blistering heat, endure hailstorms and arctic winds. Unusually hot weather in Europe in 2018 produced drought, wildfires, crop failures and a heat wave of record-breaking temperatures. Researchers estimate that the likelihood of a heat wave was doubled by global warming. Polar temperatures are rising faster than those at mid latitudes, a development known as polar amplification.
Climate change has far-reaching effects – and it’s not just extreme and unusual precipitation, winds and heat, but the domino effect of extreme weather changes can result in electricity grid crashes, even across continents. Scientists predict a 3-foot rise in sea levels, an average temperature increase of 5 degrees and polar temperature increases of up to 10 degrees at the end of the century, as a result of global climate change-inducing human activities.
With a medley of predicted changes in our future living environment, it becomes imperative to change the way we live now. As climate change is forecast to significantly affect global temperatures, the way we live indoors, particularly our HVAC energy consumption and requirements, must adapt to the situation with intelligent and ecologically feasible MEP engineering design.
Coastal buildings will be required to install utilities, HVAC systems and ducts above the DFE, or Designated Flood Elevation. Floodwaters, depending on their volume and intensity, present issues of inundation, velocity flow and debris impact on outdoor HVAC systems and equipment. Power circuits, controls and HVAC mechanical parts are all vulnerable to floodwaters. Possible outcomes include the shorting of power units and the failure of HVAC equipment operation as well as the possibility that the equipment be torn from its location and carried away. Waters with high salt content can result in corrosion and deterioration of metal HVAC components. Pipes and ducts can be separated. Currently, prevention of these outcomes involves the elevation of all outdoor HVAC equipment and ductwork above the DFE and confining them securely to try and prevent their movement.
Load calculations for air conditioners will have to be reviewed. Also, an increase of envelope insulations and efficiency standards can counteract and prevent rises in cooling loads due to increasing outside temperatures.
Climate impacts HVAC system design in several ways. These are a few determining factors:
- The infiltration rate in heating/cooling load calculations are impacted by the intensity and temperature of prevailing winds.
- The air leakage rates (heating/cooling energy) are affected.
- Distribution of temperature and the transport of moisture within walls will be altered.
- The heating, cooling and dehumidification capacity of HVAC systems require changes, depending on the precipitation in the area.
- The building envelope must be designed to manage precipitation and the condensation of water vapour.
- The envelope should be created also according to the optimum positions of thermal insulation, vapour retarder, air barrier and drainage planes.
In the United States, the American Institute of Architects wants zero net energy consumption for all new buildings by 2025 or 2030. How this happens depends on the swift and strict adoption of aggressive building energy efficiency measures. They include changing indoor pollutant sources, heat loads, ventilation rates, HVAC equipment types and building operating practices. These changes must noticeably affect indoor environmental quality (IEQ). The goal will be to develop and use HVAC technologies and practices so that
building energy consumption is significantly reduced while improving IEQ.
Potential changes in HVAC system design and use that can help achieve these goals include:
- Increased use of mechanical outdoor air ventilation systems in houses with airtight envelopes and commercial outdoor air ventilation systems that ensure minimum ventilation rates
- HVAC systems with smaller capacities, larger ratios of latent to sensible capacity specifically for buildings with greater thermal efficiency in envelopes and lower internal heat loads
- Increased use of low energy cooling systems, eg. systems with evaporative cooling
- Evaporative cooling systems that reduce microbial risks
- Increased use of demand-controlled ventilation, heat recovery and gas phase air cleaning to decrease the energy need for outdoor air (OA) ventilation
- Increased use of air supply and removal technologies that increase ventilation
- Reduced HVAC air flows, pressure drops and fan energy consumption
- Increased use of low pressure drop filtration systems and auxiliary filtration systems independent of the HVAC supply air streams
- Using a separate HVAC for OA ventilation
- Increased radiant heating and cooling, reduced air recirculation and lower pressure drop filtration systems so that fan energy needs are reduced
- Hybrid HVAC systems, cooling systems with greater spatial and temporal control and greater mechanical ventilation without air conditioning
- Hybrid HVAC systems that cool only during peak weather
- Night cooling systems integrated with thermal storage
- Use of radiant cooling and heating technologies
- Ultraviolet germicidal irradiation of cooling coils
- Increased use of flexible air exhaust systems
- Increased monitoring of HVAC maintenance and control system problem correction
- Mechanical ventilation without air conditioning
- Chair-based or workstation cooling systems
In the future, HVAC needs will also include improved integration of all HVAC components and improved integration of HVAC systems with other building systems. Additional measures involve the development of construction materials and components with low toxic pollutant emissions.
Standards for building energy systems in the future must be based on measured energy consumption, prescribing minimum IEQ maintenance. Systems to measure IEQ will be integrated with HVAC controls.
Refrigerants less likely to contribute to global warming should be used in global warming potential (GWP) compressors. The HFCs used in refrigerants can be up to a thousand times more powerful per pound than carbon dioxide. Replacing these HFCs has the potential to reduce global warming and the effects of climate change by 0.5˚C, representing a 10% reduction in the regular increase of global temperatures.
Much needs to be done and much can be done to improve HVAC systems in the future to combat the far-reaching effects of climate change, and the direction to follow must be set by design specialists. To improve and optimise HVAC systems design, HVAC mechanical engineering consultants must be employed with clear guidelines on what to use and how to use available components and perhaps even design new components for the specific purpose of combating climate change. The increasing demand for such consultants in Western countries has meant that offshore engineering consultants and offshore MEP design services are increasingly used for full or partial design support. The expertise and technical knowhow of these HVAC mechanical engineering consultants will assist in creating a new vision for battling the effects of climate change in the construction industry.