The world focus has shifted from the environment to 'Invironment'. This is a new terminology, being used increasingly to focus on the Indoor Air Quality (IAQ) and its effect on human health. While the outdoor environment continues to be of concern, the indoor environment is receiving increased attention as more information has become available on the presence and effect of indoor contaminants.
ASHRAE Standard 62 recommends fresh air intake of 15 to 20 cfm per person.
The origins of poor IAQ issue are well known. An emphasis on energy conservation after the oil embargo of 1970s resulted in tighter buildings with recirculated air for building ventilation and minimum amounts of fresh air being brought into commercial buildings. This minimized the amount of air to be heated or cooled and hence conserved on energy.
However, the combination of "tight" buildings with little or inadequate fresh air ventilation, produced an indoor environment with relatively high levels of chemical contaminants, bacteria, fungi and dust. It is a well recognised fact now, that indoor air in an airconditioned/mechanically ventilated space can be several times more polluted than outdoor air. The larger concentration of indoor air pollutants, combined with the fact that most people spend 85 to 90% of their time indoors, make them susceptible to illnesses related to these airborne contaminants.
02. What are the different methods of improving Indoor Air Quality?
The different methods of improving Indoor Air Quality
a) Increase the ventilation rates and air distribution. The heating, ventilation and air-conditioning systems should be designed to meet ventilation standards in the local building codes. The HVAC system should be operated and maintained properly to ensure that the desired ventilation rates are attained. If there are strong pollutants, the air may need to be directly vented to the outside. This method is especially recommended to remove pollutants that accumulate in specific areas such as rest rooms, copy rooms and printing facilities. Use of energy recovery devices help to optimize energy performance of Air Conditioning systems resulting in considerable reduction in installed tonnage, reduction in utility bills for entire life cycle, enhanced IAQ and productivity and reduced health risks.
b) Removal or modification of the pollutant source can be carried out by a routine maintenance of HVAC systems, replacing water-stained ceiling tiles and carpets, using stone, ceramic or hardwood flooring, proper water proofing, avoiding synthetic or treated upholstery fabrics, minimizing the use of electronic items and unplugging idle devices, venting contaminants to the outside, storing paints, solvents, pesticides and adhesives in close containers in well-ventilated areas and using these pollution sources in periods of low or no occupancy. Allowing time for building material in new areas to off-gas pollutants before occupancy and smoking restrictions are some measures that can be used.
c) Banning of smoking in the workplace or restricting smoking to designated well-ventilated areas away from the work stations. Installation of fresh air treatment systems in smoking zones to allow dilution of smoke.
03. Why DRI Energy Recovery Wheels?
a) Patented wheel technology that reduces energy requirements for conditioning outdoor air by 70%
b) Removal of moisture from outdoor air in the summer and addition of moisture in the winter to help keep buildings in the ideal humidity range
c) Energy recovery ventilation provides performance efficiencies unmatched by any other technology in the industry
d) All the health and productivity benefits of outdoor air ventilation without the drawbacks of excessive energy consumption and moisture problems.
04. Why do we need Energy Recovery Devices?
ASHRAE Standard 62 recommends fresh air intake of 15 to 20 cfm per person which leads to imposition of a much higher latent and sensible loads are imposed on the cooling/heating equipment. This translates in two ways :
- an improved indoor environment, and,
- significantly higher utility bills for the owners.
Introduction of even a small quantity of air into an HVAC system raises physical plant requirements dramatically, bringing to fore a new dimension of balancing energy needs with the IAQ standard. In fact the HVAC designers are faced with several parameters which need to be incorporated in response to the regulations and guidelines laid down by market needs.
As market needs for control of humidity, energy, IAQ, continue to rise, it is imperative to integrate heat/energy recovery devices to airconditioning design to keep all these requirements in mind.
Ashrae equipment handbook 1988 refers to six types of air to air heat exchange devices. There are some which are sensible only and some are total heat exchangers (sensible and latent heat or enthalpy). The twin tower loop is a total heat exchanger. The rotary exchanger or heat wheel can be either a sensible only or a total heat device. The rest are essentially sensible heat exchangers in which transfer of latent heat, if any, is incidental.
The ability to transfer both sensible and latent heat makes the enthalpy wheel far more effective in energy recovery. It is found that the total heat recovery device typically recovers nearly three times as much energy as the sensible heat recovery device.
It is seen that the enthalpy wheel has the highest effectiveness and least pressure drop at any face velocity, making it the most appropriate choice for energy recovery in comfort ventilation.
05. How Energy Recovery Wheels Work?
DRI energy recovery wheels rotate between the incoming outdoor airstream and the building exhaust airstream.
As the wheel rotates, it transfers a percentage of the heat and moisture differential from one airstream to the other Consequently, the outdoor air is 'pre-conditioned' significantly reducing the capacity and energy needed from the mechanical HVAC system
06. What We Know About Building Ventilation?
- Indoor air can be 2-5 times more polluted than outdoor air.
- Outdoor air reduces indoor air pollution improving IAQ
- Low outdoor air ventilation rates result in health risks to building occupants
- Higher outdoor air rates not only improve occupant health, but also increase productivity - more is better!
- Conditioning outdoor air can represent 40% of an HVAC system's capacity
- Everyone wants to keep energy costs low
- A primary cause of indoor moisture problems is moisture laden outdoor air entering the building
07. What is DESICCANT TECHNOLOGY?
There are three basic types of gas cooling technologies: absorption system, gas engine chiller systems and desiccant cooling cycle and the regenerative cycle.
In the dehumidification/cooling cycle the moist (humid) return air from the storage area and some makeup air from outside is filtered and then passed through the very slowly rotating fluted desiccant media [rotor/wheel] which adsorbs moisture.
This air comes out of the wheel/rotor as warm dry air which is then passed through the air handling unit to be cooled and distributed back to the storage area. The regenerative cycle is basically regenerating the moisture laden section of the desiccant wheel so that as it rotates back into the supply air stream it is ready to extract moisture from the process air. Air is taken from outside and heated by gas to be hot enough to remove the moisture from the wheel, resulting in warm moist air that is returned back outside.
Using psychrometrics the properties of the air can be followed through the system. In the conventional system it is seen that the air is cooled to the Apparatus Dew Point (ADP) temperature so that the moisture can be removed, then the air is reheated to the desired temperature - resulting in wasted energy where as the Desiccant based systems removes the latent load from the HVAC system thus saving energy.
One must understand that both the latent load an important role in designing of an air-conditioning system. The advantage of the desiccant system is that it removes the latent load by the use of a lower cost energy alternative, i.e. Gas.
As the process air is already been dry only sensible cooling is required, so the evaporator coils can be operated at higher temperatures. Thus, hybrid systems with a combination of the desiccant wheel and the existing air conditioning system operates on less energy input than the conventional system.
08. What are the Pollutants contributing to poor IAQ?
Sulphur, nitrogen dioxide, carbon monoxide produced by combustion and emission, high pollen counts, pesticides, chemical compounds, all contribute to outdoor pollution. Indoor air will contain all of the pollutants of the outdoor air as well as those generated indoors by the occupants and their activities.
The indoor air contaminants which can be hazardous to health include Environmental Tobacco Smoke (ETS), formaldehyde, radon, asbestos, VOCs emanating from solvents, paints, varnishes, carpets causing long term and short term illnesses. Biologicals like bacteria, viruses, fungus due to presence of high humidity, directly affect the health of the occupants. Odours and dust can cause significant discomfort, feelings of unpleasantness.
09. What is the SICK BUILDING SYNDROME (SBS)?
"Sick Building Syndrome" is a term that describes the presence of acute non-specific symptoms in the majority of the people, caused by working in buildings with an adverse indoor environment. It is a cluster of complex irritative symptoms that include irritation of the eyes, blocked nose and throat, headaches, dizziness, lethargy, fatigue, irritation, wheezing, sinus congestion, dry skin, skin rash, sensory discomfort from odours, and nausea.
Symptoms are usually work related, that is, they begin a short time after a person enters a building and disappear within a few hours after he leaves it.
However, a more serious long term, damaging effect on health may arise due to a long exposure to a building related illness, typically the legionnaires' disease. The economic consequences of the sick building syndrome and building related illnesses relate to decreased productivity, absenteeism and the cost of providing the correct environment.
While there is no proof that maximum comfort leads to maximum productivity, there is ample evidence that an improved environment decreases worker complaints and absenteeism, thus indirectly enhancing productivity.
SBS in buildings may be due to a variety of causes like: a) Inadequate maintenance of the HVAC system, which becomes a source of contamination. b) Increased load (occupancy and activities) than designed. c) Inadequate fresh air/ventilation. d) Poor circulation or badly placed vents to prevent outside air reaching the occupants. e) Improperly located outdoor vents bringing in contaminanted air from automobile exhausts or restrooms.
10. Who Can Be Sued for SBS?
Architects, contractors, HVAC contractors, building owners and managers, manufacturers, distributors of products, leasing agents, and real estate agents.
Education and communication are important parts of any air quality management programme. When everyone associated with the building, designers, architects, contractors, owners, managers and occupants fully understand the issues and communicate with each other they can work more effectively together to prevent and solve problems.
Architects when designing and building new homes and building can incorporate ideas as well the choice of materials that ensure that IAQ issues of ventilation, humidity control and source control of pollutants are kept in mind. Some of them can be
a) Use radon resistant construction techniques b) Choose building materials and furnishings that will keep indoor air pollutant to a minimum c) Provide proper drainage and seal foundations in new construction d) Install mechanical ventilation systems e) Ensure that combustion appliances are properly vented.
It is also important that architects provide adequate space, while designing a building, for ventilation and ventilation equipment so that airconditioning consultants can incorporate the same.
Most buildings are not designed to accommodate equipment which can improve ventilation. Thus, engineers, and designers, today, constantly face the challenge to conceptualise, design and specify cost-effective solution for conditioning large volumes of fresh air. An ideal 'airconditioning' equipment should sanitise, cool, heat, humidify/dehumidify, evenly distribution air through the area and all; cost effectively. That is the challenge, the designer faces today.
Innovative designs of the building and efficient design of the HVAC system with incorporation of energy recovery systems can reduce energy bills and reduce first costs as well.
11. What role does CO2 play in measurement of IAQ?
In order to evaluate excessive indoor air pollution and its health effects, it is important to identify which pollutants are present in a room or building and to determine how the levels of each vary with the time. Monitors are available for particulates and a few gases such as radon, formaldehyde, nitrogen dioxide, sulphur dioxide and carbon monoxide; however analysis of each can be complex, costly and time consuming. In some situations the source of contamination may be unknown and testing for a broad spectrum of possible pollutants may be required.
Although it is extremely expensive and difficult to detect or measure the indoor air contaminants, CO2 (carbon dioxide) has been recognised by ASHRAE (American Soceity for Heating, Refrigeration and Airconditioning Engineers) as the surrogate ventilation index or the only measurable variable.
Carbondioxide levels in an airconditioned room is a good indicator of occupancy and ventilation rate within a space. CO2 by itself is not considered an indoor air contaminant. Humans are the major source of CO2. As people exhale CO2, they also exhale and give off a wide range of 'bioeffluents'. These bioeffluents include gases, odours, particulate, bacteria, viruses. When these bioeffluents are allowed to build up in space, due to poor ventilation, occupants complain of fatigue, headache and general discomfort. The assumption is that if there is sufficient ventilation to remove the human generated contaminants, there will be no discomfort. Outside levels of CO2 are relatively constant and range between (350 to 600 ppm); inside levels will never be below the outside level. The amount of CO2 in the space can give us an indication of the number of persons within the space. Therefore, the concentration of CO2 in a space can provide an indication of the actual ventilation rate per person within the space. If the CO2 levels are higher than 1000 ppm (parts per million), then it is an indication that not enough outdoor air is coming in to dilute the CO2 level. Therefore the indoor air is being recirculated and the levels of the other pollutants in the enclosed space must be high.
CO2 itself does not create these symptoms but elevated CO2 concentrations will often occur at the same time other pollutant levels build up.
The real value of CO2 in Indoor Air Quality control is a very good indicator of ventilation rates within a space. The time it takes for a room to reach equilibrium is dependent on the number of people in a room or building zone, the volume of the space and the ventilation rate within the space. If the room is poorly ventilated and has very low occupant densities, it may take a number of hours before the equilibrium level is reached. However, once concentrations inside exceeds a certain inside outside differential, (such as 700 ppm differential equal to 15 cfm per person) one can conclude that the ventilation rate is probably below acceptable levels.
12. Why are Enthalpy Wheels the best option for IAQ enhancement?
The enthalpy wheel is a cylinder, usually 4 to 10 inches deep, packed with a heat transfer medium that has numerous small air passages, or flutes, parallel to the direction of airflow. The flutes are triangular or semicircular in cross-section. The structure, commonly referred to as the honeycomb matrix, is produced by interleaving flat and corrugated layers of a high conductivity material, usually aluminium, surfaced with a desiccant. Stainless steel, ceramic, and synthetic materials may be used, instead of aluminium, in specific applications. The flutes in most wheels measure between 1.5 mm to 2.0 mm in height. The surface area exposed to airflow in a wheel lies between 300 to 3300 m2/m3, depending upon the configuration.
In a typical installation, the wheel is positioned in a duct system such that it is divided into two half moon sections. Stale air from the conditioned space is exhausted through one half while outdoor air is drawn through the other half in a counter flow pattern. At the same time, the wheel is rotated slowly (2 to 20 RPM). Sensible heat is transferred as the metallic substrate picks up and stores heat from the hot air stream and gives it up to the cold one. Latent heat is transferred as the medium condenses moisture from the air stream that has the higher humidity ratio through adsorption by the desiccant (with a simultaneous release of heat) and releases the moisture through evaporation (and heat pick up) into the air stream that has the lower humidity ratio.
The new generation of enthalpy wheels have several features which have distinct advantages over others, which need to be carefully studied before selecting the correct wheel for the application.
a) Selective adsorption which eliminates cross contamination of bacteria and air borne contaminates. b) In-built purge sector eliminates cross contamination. c) Models of heat wheels using non contact seals have a distinct advantage of larger life and effective sealing due to the use of four pass labyrinth seal. d) The choice of desiccant is the key element in the enthalpy wheel technology. Silica gel, activated alumina and molecular sieves are the desiccants currently being offered on enthalpy wheels.
13. Why is IAQ of utmost importance in Hospitals / Nursing Homes?
Nowhere, is the importance of IAQ as critical as in Hospitals and health care facilities. Continual advances in medicine and technology necessitate the air-conditioning of hospitals and medical facilities.
It is the need of the day, for health professionals as well as building designers to understand the health effects arising from poor indoor air quality and to understand how and what factors affect the indoor air quality in offices, auditoria, hospitals and nursing homes and what could be done to improve the air quality!
Hospital airconditioning assumes a more important role than just the promotion of comfort. In many cases, proper airconditioning is a factor in patient therapy in some instances, it is the major treatment. However the relatively high cost of air conditioning, some times lead to an inadequate and improperly designed systems with not enough care to factor in specific requirements for ventilation, filtration and cross contamination. If outdoor air intakes are properly located and areas adjacent to outdoor air intakes are properly maintained, outdoor air, in comparison to room air is virtually free of bacteria and viruses. Infection control problems frequently involve a bacteria or viral source within a hospital.
Ventilation air dilutes the viral and bacterial contamination within a hospital. If ventilation systems are properly designed, constructed and maintained to preserve the correct pressure relations between functional areas, they remove airborne infectious agents from the hospital environment. Areas of the hospital which require more careful control of the aseptic condition of the environment are the surgical suites, postoperative recovery rooms, ICUs, burn wards, isolation units. Ventilation with 100% fresh air is the only means to keeping the airborne organisms contamination low. Other areas which require high rates of ventilation are Radiology department, laboratories, infectious disease and virus laboratories, autopsy rooms and animal quarters.
Increased fresh air ventilation is the answer "THE SOLUTION TO POLLUTION IS DILUTION"!
14. How does the Energy/Enthalpy Wheel help to increase Ventilation as well as Save Energy?
The energy wheel preconditions fresh outside air before it is introduced to a building. The system can easily be tapped into an existing ventilation system. A portion of the air that would normally be recirculated through the system is exhausted through the wheel and fresh air is introduced into the building in its place. Operating in virtually any climate zone, a single desiccant wheel operated with just a small motor to rotate the wheel can deliver fresh air on a year round basis that is generally within 3-7 degrees and 10% RH of inside conditions, regardless of what outside conditions are (without any type of mechanical cooling or heating). The cost to provide high levels of fresh air ventilation becomes minimal compared to the normal heating cooling requirements of the building. The potential benefits are numerous.
a) Current standards for outside air ventilation can be met or exceeded with minimal energy cost impact on the building. b) Incoming outside air is dehumidified by the desiccant wheel, allowing the rest of the ventilation c) system to run dry. As a result, indoor humidities are maintainable well below the conditions that would favour the growth of mould, mildew and other microbial contamination.
The need for cooling capacity that normally would be required to dehumidify and cool outside air is eliminated. This is typically 30 to 50% of total system capacity. In most cases, the cost of the energy wheels is almost less than the cooling capacity it is replacing. The first cost of a building's cooling system can actually be reduced with a wheel system.