...(PAQ). Thermal comfort can be divided into two categories: general thermal comfort and local thermal comfort. General thermal comfort refers to the overall comfort level, while local thermal comfort refers to the comfort of a specific part of a person. Generally, thermal comfort is dominated by the temperature of the air within the space. Other factors that can influence the comfort of occupants include metabolic rate of the occupants, amount of clothing worn by the occupants, and the radiation, air speed, and relative humidity (RH) levels in the space.

IAQ is a measure of the concentration of contaminants in the air. Numerous gaseous contaminants such as volatile organic compounds, odors, and carbon monoxide can pollute the air. To maintain good IAQ, these contaminants must be kept below certain harmful levels. Poor IAQ can result in a loss of productivity, as shown in studies by Kosonen and Tan (2004a, 2004b). A commonly practiced method of maintaining adequate IAQ in commercial and residential buildings is the use of outdoor ventilation.

PAQ is a measure of how the occupants in a space perceive the quality of the indoor air conditions. Even if the actual IAQ is good, that is, the air is free of contaminants, the air can seem to be of poor quality if the temperature and humidity are too high. If the PAQ is poor, then the percent dissatisfied (PD) with the space will be high. Studies by Fang et al. (1998a, 1998b) have shown that temperature and humidity have a strong impact on the PAQ of a space. They developed equations to calculate the PD based on the acceptability of the air that are used in this study to determine the PD with PAQ ([PD.sub.PAQ]). The correlation used in this paper is

[PD.sub.PAQ] = exp(-0.18-5.28Acc)/1 + exp(-0.18-5.28Acc) 100, (1)

where Acc is the acceptability of the air. The air in the office building is assumed to be clean air; therefore, the acceptability is calculated using (Fang et al. 1998a)

Acc = - 0.033H + 1.662, (2)

where H is the enthalpy of the air (kJ/kg).

The focus of this paper will be on the effect of moderating RH levels to improve thermal comfort and PAQ. Low indoor RH levels can cause the space to feel too dry and people may experience physical discomfort such as dry, itchy eyes and skin. On the other hand, high RH levels can reduce evaporative cooling rates from the body as well as cause respiratory discomfort, making the air seem too warm and stuffy. According to ISO Standard 7730 (ISO 1994), the RH in a space should be between 30% RH and 70% RH to decrease the risk of wet or dry skin, eye irritation, respiratory diseases, and microbial growth. The PD with general thermal comfort ([PD.sub.tc]) is calculated by the TRNSYS program (SEL 2005) based on ISO Standard 7730.

As noted above, indoor RH control is important because RH affects comfort and PAQ. Current methods for controlling RH levels in a space include using mechanical cooling equipment in humid climates and humidifiers and outdoor ventilation in dry climates to humidify or dehumidify the space. Some disadvantages of these methods include the initial costs of purchasing and installing the equipment, as well as the large operational costs associated with the equipment. In addition, if the outdoor air is too dry or too humid, it can actually make the indoor RH levels worse. Recent research has proposed a new alternative to these methods. Simonson et al. (2002, 2004) have shown that using hygroscopic materials in a space can help to moderate RH levels and improve comfort and PAQ. The purpose of this paper is to determine if similar results can be achieved by using hygroscopic materials in the HVAC system in the form of a desiccant-coated energy wheel. Energy wheels are currently employed in many buildings to reduce the amount of energy that the building uses, as a large portion of the total energy consumed by the building is used for conditioning the air in the building. This study will determine if a rotary air-to-air energy wheel that transfers both sensible and latent heat can help moderate the indoor RH levels and improve comfort conditions as well as reduce energy consumption and cost.

The performance of an energy wheel is described by its effectiveness to transfer sensible and latent energy. It is often assumed that the effectiveness of an energy wheel is constant regardless of fluctuations in the inlet fluid temperature. While this is the case for a sensible heat exchanger with no phase change, Simonson and Besant (1999a, 1999b) have shown that the effectiveness of an energy wheel changes as the inlet humidity and temperature change. This means that the effectiveness of the energy wheel will change throughout the year, which is often neglected in the design and analysis of HVAC systems with energy wheels (Mercer and Braun 2005). Therefore, an additional purpose of this paper is to investigate whether the assumption of a constant effectiveness value for energy wheels has a noticeable effect on the calculated energy use and humidity levels in a building.

THE OFFICE BUILDING

The floor plan of the office building is shown in Figure 1. This building is modeled after one used by Dhital (1994) and Dhital et al. (1995), who tested the effects of a run-around heat exchanger on energy use and life-cycle costs. The office building consists of 15 floors, 14 of which are occupied and need to be conditioned. The building has dimensions of 40.5 X 40.5 X 54.5 m (133 X 133 X 179 ft). There is a 1 m (3.3 ft) high plenum located above the occupied space of each of the floors, 1 through 14. The first floor consists mainly of a lobby and office spaces, while the remaining 13 floors are all office spaces, as seen in Figure 1. Permanent walls exist around the stairwell, elevators, washrooms, and duct chase only. The offices are all divided using movable partitions. The office space, lobby, washrooms, elevator, and stairwells are all supplied with outdoor air. Each of these spaces is considered a thermal zone, so that all of the offices in the building are in one thermal zone, all of the washrooms are in the washroom thermal zone, and so on.

[FIGURE 1 OMITTED]

The construction of the exterior walls and the roof of the office building are shown in Tables 1 and 2, respectively. The U-factor of the exterior walls is 0.211 W/([m.sup.2]*K) (thermal resistance, R = 26.9 h [ft.sup.2]*[degrees]F/Btu) and the roof has a U-factor of 0.496 W/([m.sup.2]*K) (R = 11.5 h*[ft.sup.2] [degrees]F/Btu). The windows are double glazed and have a U-factor of 2.7 W/ ([m.sup.2]*K) (R = 2.1 h*[ft.sup.2]*[degrees]F/Btu). They cover 40% of the exterior wall area. The interior walls are...

NOTE: All illustrations and photos have been removed from this article.



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