1. Introduction
In air conditioning design, it is essential to consider the addition of external air to closed environments such as offices, schools, hospitals, and malls, among others. The American Society for Heating, Refrigeration and Air-Conditioning Engineering (ASHRAE) established that if a building has more than 20% of people with symptoms of some disease or discomfort when exposed to this environment, it is considered a building that fits a Sick Building Syndrome (SBS) situation [
1].
The lack of indoor air renewal causes the accumulation of chemical pollutants (carbon monoxide and dioxide, sulfur dioxide and formaldehyde, and ammonia, among others) and biological contaminants (fungi, algae, protozoa, bacteria, and mites), which makes the air hazardous for human health and is a risk factor for people with respiratory diseases [
2]. Environments with high levels of these pollutants are conventionally called SBS; the World Health Organization (WHO) recognized this problem in 1982 [
3].
In the 1970s, an energy crisis spread globally due to conflicts between oil-exporting countries in the Middle East. As a result, oil suffered a reduction in production and a price increase, reaching 400% in 1973. In the same period, engineers looking for alternatives to reduce electric energy consumption [
4] reduced the external air supply to buildings [
5,
6]. Consequently, the first reports of SBS [
7] were seen.
Fungal exposures are receiving increasing attention as an occupational and public health problem due to the high prevalence of fungal contamination in buildings [
8]. Moisture and moisture-related problems are significant sources of fungal contamination in homes, buildings, and schools [
9]. Indoor fungi can be inhaled, and the presence of such particles has been linked to many illnesses and symptoms (infections, allergic reactions, or toxic responses) among occupants of moisture-damaged buildings [
10]. On the other hand, moisture damage in buildings could alter various components of building materials, which can be another source of deterioration in indoor air quality (IAQ) [
11]. Fungal growth is associated with moisture content, defined as the ratio between a material’s free water and dry weight [
12].
Some studies indicated a relation between humidity, indoor-measured visible biological contaminant growth, and its effects on human health. Sterling et al. [
13] analyzed the humidity impact on contaminants (such as viruses, bacteria, and fungi) and the possible impacts on human health. At room temperature, the authors observed that the required humidity range for minimizing risks to human health by biological contaminants was between 40 and 60%, as shown in
Figure 1.
In 1984, the WHO estimated that up to 30% of buildings could be affected by SBS. In the early 1980s, SBS was correlated with environmental problems.
Table 1 shows some of the main symptoms associated with SBS. However, the concept is evolving, including in terms of psychological aspects, economic implications, energy savings, and climate change [
14].
Brasche [
15] observed that women suffer more from SBS when compared to men, with 44.3% of women suffering from SBS while only 26.2% of men faced this problem, as shown in
Table 2. However, this percentage difference between genders was due to position within the company; in the same study, when men and women were in environments with the same IAQ, the rates of occurrence of SBS were similar.
In the mid-1990s, when the issue of indoor air quality began to gain importance in Brazil, air conditioning systems became a main subject for maintaining cleanliness and conservation. In 1998, with the death of the then-Minister of Communications Sérgio Motta, attributed mainly to the bacterium Legionella, the then-Minister of Health José Serra announced the formation of a study group to publish legislation that obliged those responsible for air conditioning systems to maintain clean systems, therefore preventing diseases in the Brazilian population [
16].
The Ministry of Health published in 1998 the ORDINANCE N°3523 [
17], which defines values and definitions to maintain IAQ as described in Art. 4, the definition of Sick Building Syndrome. Based on Art. 5, it is possible to mention the need to meet a minimum level of air renewal (27 m
3/h/person) and a minimum filtration of class G1. On the other hand, the Brazilian Ministry of Health published in 2003 the RESOLUTION No. 09 (RE-09) [
18], which presents additional information from ORDINANCE No. 3523/98. One of the definitions given in RE-09 is the concept of air conditioning, which corresponds to the air-treatment process intended to maintain the IAQ requirements of the conditioned space by controlling variables such as temperature, humidity, speed, particulate matter, biological particles, and carbon dioxide content.
RE No. 09 also presents parameters related to the maximum recommended value for microbiological contamination, which is 750 cfu/m
3 (colony-forming unit/cubic meter), and chemical contamination, which is 1000 ppm for the concentration of carbon dioxide (CO
2) and 80 μg/m
3 of aero dispersoids. In addition to these parameters, there are recommended operating ranges for temperature, humidity, air speed, air renewal rate, and the degree of air purity that must comply with the Brazilian Regulatory Standard NBR 16401-3 for indoor air quality [
19].
An essential point for maintaining IAQ is to keep the equipment in full operation; for this, it was necessary to create a Maintenance, Operation, and Control Plan (MOCP). Considering that in maintaining IAQ requirements in situations with a considerable latent heat load, as commonly found in HVAC applications, a significant amount of moisture removal is required, desiccant technologies have a significant advantage over the traditional vapor compression-based (also termed mechanical dehumidification) alternatives. This is because on the one hand, vapor compression systems need to cool the process airstream to temperatures below the dewpoint to obtain the dehumidification effect, which occurs due to regular condensation. Naturally, this involves an additional high-grade energy expense. On the other hand, when desiccant systems perform dehumidification, the subcooling becomes unnecessary, thus saving a considerable portion of high-grade energy.
In Brazil, the Civil House published Law No. 13,589 of 2018 [
20], which obliges public and collective buildings to keep the MOCP active, thus guaranteeing the ranges established for a good IAQ. Increasing air renewal in buildings without proper treatment does not solve all the problems associated with IAQ. According to Che et al. [
21], this methodology can increase indoor humidity, which can also substantially raise the potential for microbiological growth, as this increase in ventilation can augment the concentration of pollutants in the environment. However, the practice of increasing the rates of air renewal has established itself among designers [
22]. Outdoor air recommendations are stipulated for each type of design for designers seeking to increase the speed of outdoor air to the maximum allowed according to NBR 16401-3 and obtain systems that provide temperature, humidity, and specific filtration control for the condition of the environment in question. It could consider using total heat exchangers as enthalpy wheels, which can provide energy savings to the building.
According to Pargeter [
23], the energy consumption required by conventional air treatment practices for air conditioning in commercial buildings represents an average of 10% of all energy spent in the United States. The author also noted that a large part of the energy consumption for air conditioning in these commercial buildings is due to air renewal, which is different from the internal comfort conditions. In addition to electricity consumption, the higher air renewal rate leads to greater investments and maintenance costs for such Heating, Ventilation, and Air Conditioning (HVAC) systems.
One alternative to conventional refrigeration systems is the so-called desiccant cooling cycle [
24,
25], which employs active desiccant rotors for dehumidifying the outdoor air and running the produced dry air through evaporative coolers to provide the refrigeration effect. The main advantage of such technology is that no special refrigerant fluids are required and it is mainly driven by thermal energy, which means that solar or thermal waste energy can power these cycles. On the other hand, the COP of this cycle is quite low, which could not be a significant issue when considering that a renewable source or waste energy is being used as a source of power. These alternatives can also be used alongside other cooling systems, as previously demonstrated [
26,
27].
This research assessed alternatives for air HVAC systems to minimize Sick Building Syndrome and improve air quality while considering international programs/standards. For this purpose, an alternative technology known as desiccant wheels was studied by analyzing their principles and types when the existing selection software for these types of equipment was performed. In addition, energy-efficiency programs worldwide and in the Brazilian context were analyzed while aiming at implementing strategies in which desiccant wheels are appropriate. Finally, some examples of commercial software for desiccant wheels were compared with an aim to identify the different tools available in the air conditioning market.
4. Software for Selecting Desiccant Wheels
Selecting a suitable desiccant requires that the involved dehumidification process be simulated. This can be quite time-consuming depending on the level of detail necessary for a specific simulation and a considerable amount of operating and construction data related to the wheel, as shown in previous works [
84,
85,
86,
87]. As a result, commercial software became available to facilitate the selection process of dehumidifiers while considering human breathing. Thus, Dong et al. [
88] developed a plate dehumidifier model to analyze the shrinkage shape and the variable film thickness of the falling film. The results indicated that the moisture removal rates were augmented from 2.0 g/kg to 2.56 g/kg, the average film thickness decreased from 0.952 mm to 0.889 mm as the contact angles diminished from 85° to 5°, while the wetting area increased from 0.145 m
2 to 0.176 m
2.
Sun et al. [
89] compared pre- and post-operative nasal airway models based on a 3-year-old nasal cavity model with apparent adenoid hypertrophy. The results showed that nasopharynx obstruction can induce significantly biased flow distribution in the central nasal passage even if the obstruction site is downstream of the nasal airway. Some review papers offered several works; for example, Tian and Ahmadi [
90] studied the current state of computational modeling of micron and nano-elongated particle dynamics and their application to fiber transport and deposition in human respiratory airways; the most versatile and practical approach was the Eulerian–Lagrangian. Ma et al. [
91] analyzed the parameters that affect the thermal performance of latent heat thermal energy storage systems (LHTES), including the inlet temperature of the heat transfer fluid, heat transfer rate, properties of the phase-change materials (PCMs), phase-change temperature, geometric parameters, and water tube layout, among others. Finally, the authors discussed the climatic conditions for air-LHTES and found that the higher ambient temperature led to incomplete solidification of the PCMs during the limited nighttime in air-LHTES.
This section presented software for selecting desiccant wheels provided by manufacturers, and some characteristics were analyzed. It is worth noting that there are other programs available for desiccant wheel simulations (TRNSYS, ESP, and Modelica, among others); however, this paper focused on desiccant manufacturer software; therefore, the analysis of other software was left for future studies.
4.1. Novel Aire
Novel Aire Technologies, based in the United States, is a company that has been operating in the dehumidification market for approximately 20 years with energy conservation products and desiccant wheels that has more than 500 customers in 25 countries around the world. The characteristics of Novel Aire software are presented in
Table 3.
4.2. Munters
Munters was founded by Carl Munters in 1955 and is based in Sweden. It functions in the dehumidification and air conditioning market and serves thousands of customers with about 3500 employees, 17 factories worldwide, and an installed base of 320,000 air-treatment systems. The characteristics of Munters software are presented in
Table 4.
4.3. Rotor Source
Rotor Source was founded in 1999 and is headquartered in the United States. It currently operates the dehumidification market and focuses on selling desiccant wheels to manufacturers of dehumidification equipment. The characteristics of Rotor Source software are presented in
Table 5.
4.4. Puresci
Puresci is a China-based company with over 10 years of experience in the desiccant rotor field. It has projects with more than 1000 clients around the world. The characteristics of the rotor source Puresci are presented in
Table 6.
4.5. Comparison between Software
Several companies that develop heat-recovery technologies using desiccant wheels are recognized by international organizations such as Eurovent and AHR Exhibition and by Brazilian agencies such as ABRAVA and the South Brazilian Association of Refrigeration, Air Conditioning, Heating and Ventilation (ASBRAV) were studied.
The research on commercial software for the technologies studied (
Table 7) does not present a careful analysis of the operating results over a year; in most cases, the software only shows the efficiency and output data. In addition, it is necessary that for all software, the user must have external knowledge of thermal engineering to be able to analyze a project.
Therefore, the software should incorporate an updated database, such as the ASHRAE weather data viewer, into its source code to cover as many locations as possible with updated data. It is also necessary for the software to be able to perform a dynamic analysis of the total hours of the year and not just a one-off analysis.
5. Conclusions
This work presented options for reducing electrical energy consumption in air conditioning and refrigeration systems using desiccant dehumidification technologies. Initially, the importance of air renewal in buildings was analyzed, and it was observed that the circulation lack of renewed air could contribute to the environment being a favorable place for spreading respiratory diseases, which is a risk factor for a worker in any organization. Thus, a building with a high level of pollutants falls under the Sick Building Syndrome.
Subsequently, it was observed that the consumption of conventional air conditioning systems in countries such as the United States and Brazil may require up to 10% of the electricity demand of these countries. Therefore, programs aimed at energy efficiency were created or strengthened to obtain better results when referring to air conditioning systems, increases in renewal air, and electric energy consumption. For example, European Union countries adopted an energy policy known as Horizon 20-20 to reduce greenhouse gas emissions and implemented various laws and projects to achieve the Horizon 20-20 objectives.
The Brazilian Labeling Program has been implemented in Brazil since 1984 to indicate an item’s energy efficiency through informative labels. This program was strengthened by adding two policies: the National Energy Conservation Program and the National Program Rationalization of the Use of Petroleum Derivatives and Natural Gas. Other guidelines, such as Law No. 9478 of 1997, Law No. 9991 of 2000, and Law No. 10,295 of 2001, were implemented to promote efficiency and energy conservation in Brazil. All these programs were created to meet the current and future markets that demand high energy consumption. However, it is necessary to explore new technologies such as desiccant dehumidification, which have shown promising results in terms of energy efficiency.
It is worth noting that a desiccant dehumidification system has a coating applied for airflow dehumidification. As the wheel turns, the desiccant alternately passes through the incoming air (where humidity is adsorbed) and through a regeneration zone (where the desiccant is dried and humidity is expelled). The wheel continues to rotate, and the adsorption process is repeated. Several variables can affect desiccant performance; these include the inlet dry bulb temperature, absolute inlet humidity, and speed of the desiccant face, among others. Hence, selecting desiccant wheels is fundamental depending on the project to be developed. Thus, several examples of desiccant wheel selection software were investigated to list and present the main characteristics of each one. It was observed that the multiple programs studied did not offer a detailed analysis of the annual operation and usually only showed the output data. Therefore, the selection software could be improved by incorporating a database update and considering ASHRAE weather data viewer to cover more locations, especially in Brazil.
For future studies, it is suggested to develop software focused on measuring energy and economic benefits when using the technology of desiccant/enthalpic wheels in the recovery of energy from the renewal air and that contemplates improvements concerning the software researched in this work. In addition, other examples of commercial software for desiccant wheel modeling can be assessed.