Indoor air quality (IAQ) is currently the centre of attention for researchers, innovators, architect developers and public health officials. As every-one know, the human exposure to a variety of indoor pollutants and the high cost of energy are the motivation for these kinds of studies. Fungus and mould growth has always been a problem in subtropical climate areas due to the high temperature and high humidity. Generally, in institutional buildings, most of the internal heat load is generated by human body and thermal comfort is achieved with extensive usage of recycled air and air conditioning. The main considerations in any air conditioning system economisers are based on the usage of recycled air and air ventilation
The use of a novel desiccant assisted dehumidification and cooling system to reduce moisture from the air and to improve indoor air quality is found to be economical, environmentally friendly and readily achievable in the tropics. This technology is the future alternative to the conventional vapour compression cooling system to maintain human thermal comfort conditions and enhance indoor air quality. Solar desiccant cooling systems are also environmentally friendly and energy efficient.
What Is Indoor Air Quality?
The indoor air pollution is a serious health risk and advises residents to take steps to improve their indoor air quality. Indoor air pollution can worsen symptoms of allergies, asthma and other respiratory ailments. In otherwise healthy people, it can cause fatigue, headaches and dizziness and lead to irritation of the nose, eyes and throat. Indoor Air Quality (IAQ) is defined as the scenery or nature of air that affects the building occupant’s health and well being because exposure to pollutants and some building materials in the air may cause a high health risk; like respiratory illness. In other words, an acceptable indoor air quality is defined as air in which there are no known contaminants at harmful levels. It is also an indication of how air satisfies the thermal comfort, normal concentration of respiratory gases, such as oxygen and carbon dioxide, and acceptable limits of air pollutants. IAQ is determined by a constantly changing interaction of complex factors that affect the types, levels and importance of pollutants in the indoor environment. It is a major concern to building developers, business owners, building managers, tenants and employees because it affects the health, comfort and productivity of building occupants. The IAQ depends on both the quality of the outdoor air and on the strength of emissions from indoor air. In order to maintain an acceptable comfort level, indoor spaces must receive a sufficient quantity of clean and fresh outdoor air to create an acceptable indoor air quality.
The Importance of Indoor Air Quality
When people think of pollution, they tend to think of the outdoors. But indoor air pollution is actually more dangerous because it is more concentrated. These pollutants can cause a wide range of respiratory issues, and some studies have linked indoor pollutants to the onset of allergies and asthma. People who have respiratory conditions often experience intensified symptoms, and anyone can experience the fatigue, headaches, dry nose, itchy eyes and other issues that pollutants can cause.
Another issue with poor indoor air quality is that it fosters an environment in which bacteria and viruses can thrive. Illnesses are more easily transmitted and thus more prevalent. Other biological contaminants that can be problematic include dust, dust mites, pet dander and pollen. Poor indoor air quality can also lead to higher moisture levels, which can result in mildew and even the growth of toxic mold.
How to Improve Indoor Air Quality?
The first step in optimizing indoor air quality in your home is ensuring that you have dust under control. It is recommended that you dust your home each week and vacuum using a HEPA filter bag. It is also important to ensure that you are not inadvertently introducing contaminants, such as household cleaners and deodorants. Change HVAC air filters as needed based on visual inspection. Groom your pets as much as is necessary to control dander. Ensure that you have adequate mechanical ventilation, and when practical, open your windows for improved natural ventilation. ASHRAE also recommends seasonal maintenance of heating and cooling system and regular duct cleaning as well.
Dehumidifiers
Summer brings with it higher and often uncomfortable humidity levels. Your air conditioner does remove moisture from the air as part of cooling it but can struggle to reach an ideal relative humidity when levels are high. A dehumidifier will work in tandem with air conditioner. It not only makes indoor more comfortable but results in AC not working as hard and thus lasting longer.
Air Scrubbers
Air scrubbers are advanced technology that was originally developed as a NASA project for the International Space Station. These systems use germicidal ultraviolet light that “scrubs” the air through a catalytic process. An air scrubber can remove many of the same contaminants that an air purifier can. But it can also remove many additional contaminants, such as volatile organic compounds.
The purpose of an air scrubber is to remove pollutants and contaminants from an indoor air supply. In many cases, a scrubber is the only way to remove these impurities at these levels or even at all. Poor indoor air quality exacerbates asthma and allergy symptoms, irritates your respiratory system, makes airborne illnesses more prevalent, and may even have serious long-term health ramifications. This technology is a great way to improve quality of life and help ensure the health of occupants.
Air Filters
Regularly changing air filters is essential to keeping dust and other contaminants out of HVAC system. The general advice is to change them out every three months, but it is best to inspect them visually each month and change them whenever dust accumulation is visible. You may also want to consider a whole-house air cleaner, such as the Air Ranger system. It integrates into existing HVAC air filtration system and is able to trap dust, pollen, pathogens and much more.
Air Purification
The bottom line is that the air inside will not be cleaner than the air outside it unless you have some form of mechanical air cleaning. ASHRAE recommends a whole-home air purifier. These units are integrated into your existing heating and cooling system and will clean the air before it enters the living spaces. These units can remove dust, dander, pollen, mold spores and much more.
Desiccant Assisted Dehumidification and Cooling Systems
In general, desiccant materials have a low moisture content which attracts vapour and moisture out of processed air and this is as a result of moisture pressure difference between the processed air and the desiccant materials surface. Continuous air dehumidification makes desiccant materials saturated, and cannot function again unless it is regenerated. For this purpose and in order to use the desiccant material again a thermal energy is required for the regeneration process. Generally, this thermal energy can be supplied by gas or solar. The process of attracting moisture from the air can be done using adsorption or absorption: the adsorption process is a physical process where the property of the desiccant material remains unchanged; while with absorption process, the physical characteristic of the material changes while attracting moisture. Desiccant materials are available as solid or liquid. An example of solid desiccant are silica gel, titanium silicates, calcium chloride, activated aluminas, zeolite (natural and synthetic), molecular sieve, lithium chloride, organic-based desiccants, polymers, compound and composite desiccants. Available desiccant systems are based on five technologies: liquid spray towers, solid packed tower, rotating horizontal bed, multiple vertical bed and rotating desiccant wheel.
Desiccant cooling process relies on desiccant materials reducing the air moisture content for air cooling and dehumidification. In desiccant cooling systems, desiccant material dries the supplied air. As a result, the treated air becomes unavoidably warm as in Fig. 1. In order to reduce air sensible temperature, there are cheap air-cooling techniques, like evaporative cooling or heat exchanger which are deployed to cool the dehumidified air to near ambient temperature. In short the produced dry air is further cooled down to a near ambient temperature or to near comfort level and then the cooled air would be passed to the conditioned space.
Conclusion
Achieving a comfortable and healthy indoor air environment is essential. Recently Indoor Thermal Comfort and Indoor Air Quality (IAQ) have improved due to the availability of improved air-cooling techniques. Still health problems that relate to indoor air quality are a major concern due to contaminant and polluted air. Thus, control of relative humidity is an essential aspect of maintaining indoor air quality in an air-conditioned space. Desiccant assisted dehumidification and cooling systems can help to provide indoor thermal comfort level, maintain indoor air quality and save energy and gas emissions. In many literatures, it is found that desiccant cooling technologies are able to offer alternatives to the conventional air conditioning systems by using renewable energy resources and using environmentally friendly materials. Besides, desiccant cooling technology is a simple technology that can be utilised with other cooling system to improve their performance and to improve indoor air quality. The energy performance of the desiccant cooling systems could be further improved through a lower regeneration temperature approach, more efficient solar thermal collectors, market availability and a lower setup cost.
Dr. (Prof.) D. B. Jani; an Associate Professor at GEC, Dahod under Gujarat Technological University (GTU), Ahmedabad; received his Ph.D. in Thermal Science (Mechanical Engineering) from Indian Institute of Technology (IIT) Roorkee. Currently, he is a recognized Ph.D. Supervisor at GTU. He published more than 150 Research Articles in reputed International Conferences and Journals along with five popular books. His areas of research include Desiccant cooling, ANN, TRNSYS and Exergy.
