Experimental Analysis of Energy Savings in a Combined Rotary Desiccant Dehumidifier with a Purge Section

Abstract

This study focuses on improving the performance of desiccant dehumidifiers using desiccant rotors, which are widely utilized in various industries, such as manufacturing, food, and construction, to enhance product quality and production efficiency. The combined desiccant dehumidifier can reduce energy consumption compared to traditional standard or purge dehumidifiers. The system operates in normal mode during seasons with high outdoor humidity and in purge mode during seasons with low outdoor humidity. By utilizing dampers, the air passing through the dry desiccant rotor can either be directly discharged indoors or supplied to the regeneration section, allowing the system to operate in two modes within a single unit. The first part of the study involved comparing the performance of the equipment through experiments. The second part compared the results from the dehumidifier rotor performance simulation program to check for deviations and validate its effectiveness. In the first experiment, the energy consumption of the standard desiccant dehumidifier in normal mode was compared with that of the combined desiccant dehumidifier in normal mode. In the second experiment, the energy consumption of the standard desiccant dehumidifier in normal mode was compared with that of the combined desiccant dehumidifier in purge mode. The airflow, temperature, and humidity values used in each experiment were analyzed using a dehumidification performance simulation program, and the deviation was found to be within 10%. Therefore, the performance analysis via simulation was considered valid. The dehumidification performance of the combined desiccant dehumidifier was found to be 5% more efficient than the traditional standard desiccant dehumidifier and 9.5% more efficient than the purge dehumidifier. Furthermore, energy consumption simulations were conducted for representative regions in Korea. The results showed energy reductions of 65% in Seoul, 65% in Daejeon, and 67% in Busan. The findings of this study suggest that energy savings can be achieved by appropriately adjusting the operation mode between normal and purge modes based on outdoor conditions.

1. Introduction

1.1. Background and Objectives

The use of humidity control methods based on natural materials or phenomena has long been integrated into daily life, while mechanical approaches have been developed to meet industrial humidity requirements. Traditionally, cooling-based methods have been used for dehumidification; however, the introduction of the desiccant method has demonstrated superior performance and energy efficiency in numerous studies [1,2,3,4,5,6].

Initial desiccant dehumidification systems incorporated various technologies to enhance energy efficiency and ensure stable operation [2,3,5]. Nevertheless, these systems often require significant energy, particularly when oversized or operated at excessively low target humidity levels. This leads to energy waste and highlights the need for more efficient systems. To address this, a new system concept is necessary—one that improves on existing desiccant technologies. This study aims to verify the effectiveness of a combined desiccant dehumidifier and assess its suitability for industrial environmental conditions.

In Korea, rising temperatures due to climate change are accompanied by increased humidity levels [7]. When dehumidification is needed for air conditioning, both temperature and humidity variations must be considered. Figure 1 presents the average dew point temperatures for three major Korean cities from June to September over the past 30 years, showing a noticeable upward trend. Especially in the last decade, temperature increases have been significant [8,9,10]. This suggests a growing dehumidification load and underscores the importance of designing properly sized, energy-efficient dehumidification systems.

1.2. Literature Review

The objectives of dehumidification include inhibiting harmful microorganisms, improving the performance of products, and eliminating risks caused by chemical reactions resulting from moisture [11,12,13,14,15,16]. The principles and methods of dehumidification can be categorized as shown in

Table 1. Dehumidification principal and method.

Principle	Device	Areas of Use
Cooling type (condensing)	Cooling dehumidifier using refrigerant compression Cooling dehumidifier using cold water Electronic dehumidifier (Peltier effect)	HVAC (Commonly used)
	Solid adsorption type dehumidifier Liquid adsorption type dehumidifier	Used in precision equipment
Chemical type	Liquid adsorption type dehumidifier	HVAC (Industrial, dry room)
Compression type	Compression type dehumidifier	HVAC (not used often)

. In dehumidification processes, the cooling-based method involves lowering the air temperature to separate moisture by condensing the saturated water vapor. The chemical-based method utilizes desiccants to absorb moisture from the air. The compression-based method separates condensed water generated during the air compression process.

To analyze a desiccant dehumidification system, it is essential to review the components, principles, and performance indicators of the desiccant dehumidifier [17,18,19]. The performance indicators allow for a quantitative evaluation of areas requiring improvement and the extent of such improvements. They also help assess whether the system is suitable for practical application.

(1)

System Configuration

The basic configuration of a solid desiccant dehumidifier consists of a desiccant rotor, a regeneration heater, and a blower unit. The desiccant rotor is divided into two sections: the Process Part, which is responsible for dehumidification, and the Regeneration Part, which handles the drying of the desiccant. Other components, such as coolers, play a role in enhancing dehumidification capacity or adjusting the indoor temperature [17,20,21,22,23]. While the standard desiccant dehumidifier is shown below in Figure 2, purge desiccant dehumidifiers shown in Figure 3 have large energy savings during times of low outside temperature and humidity, with the added benefit of being able to produce extremely low humidity environments, like dry rooms, when used together with a pre-cooler.

(2)

Types of Rotors

As shown in Figure 4, the solid desiccant rotor is made by stacking plate sheets of approximately 0.2 mm thickness and sheets processed using a collimating method to create a honeycomb structure. The rotor is composed of a fibrous substrate impregnated with a hygroscopic material. Depending on the type of fibrous substrate, hygroscopic material, and processing method, various types of rotors can be produced, including lithium chloride-based rotors, silica gel-based rotors, synthetic zeolite-based rotors, moisture-absorbing agent-fixed rotors, and titanium oxide rotors [17].

The desiccant dehumidifier rotor is divided into two main sections: the dehumidification section (Process zone), where dehumidification performance is achieved, and the regeneration section (Regeneration zone), which ensures the continuous performance of dehumidification. It has a structure as shown in Figure 5. The boundaries of the areas in the desiccant rotor are clearly defined, and as the rotor rotates, the air passing through each section moves slightly, which impacts the overall performance of the dehumidifier [13].

Figure 6 illustrates the difference between the ideal and actual states. The air entering the dehumidification section (①) should ideally be in the state represented by (②), but in reality, it reaches the state represented by (③). Similarly, the air entering the regeneration section (④) should ideally be in the state represented by (⑤), but in reality, it reaches the state represented by (⑥). This indicates that even when using the same material to construct the rotor, variations in rotor manufacturing methods, production techniques, and operating conditions can lead to performance differences [24,25,26,27,28,29,30,31,32].

(3)

Definition of Performance Indicators

To verify the performance and efficiency of a dehumidifier, objective criteria must be defined. The performance indicator is defined as follows [33,34,35,36,37]. The dehumidification capacity (MRC, Moisture Removal Capacity) is the mass of water vapor removed from the air per unit time (kg/h), and it is expressed by the following Equation (1)

$$\mathrm{M}\mathrm{R}\mathrm{C}={\mathrm{S}\mathrm{C}\mathrm{M}\mathrm{H}}_{\mathrm{p}\mathrm{o}}·1.2041·({\mathrm{x}}_{\mathrm{p}\mathrm{i}}-{\mathrm{x}}_{\mathrm{p}\mathrm{o}})$$

(1)

Here, SCMH_po represents the dehumidified air outlet flow rate (m³/h), x_pi is the absolute humidity at the dehumidified air inlet (kg/kg), and x_po is the absolute humidity at the dehumidified air outlet (kg/kg).

The dehumidification efficiency refers to the moisture removal capacity per unit of energy input (kg/kWh), and is expressed in two forms: the heat energy dehumidification efficiency (DE_t), which refers to the moisture removal capacity per unit of regeneration energy input, and the electric energy dehumidification efficiency (DE_e), which refers to the moisture removal capacity per unit of total electrical energy input, including energy consumption by fans and coolers. The equations are expressed as follows (2) and (3).

$$\mathrm{D}{\mathrm{E}}_{\mathrm{t}}={\displaystyle \frac{\mathrm{M}\mathrm{R}\mathrm{C}·2453}{{\mathrm{Q}}_{\mathrm{r}\mathrm{e}\mathrm{g}}·3600}}$$

(2)

$${\mathrm{D}\mathrm{E}}_{\mathrm{e}}={\displaystyle \frac{\mathrm{M}\mathrm{R}\mathrm{C}·2453}{{\mathrm{W}}_{\mathrm{e}}·3600}}$$

(3)

Here, Q_reg represents the regeneration energy (kW), W_e denotes the electrical energy input (kW), and 2453 is the latent heat of evaporation of water at 20 °C (kJ/kg). The remaining terms have been defined earlier.

(4)

Key parameters influencing dehumidification performance

Physical factors affecting desiccant dehumidification performance include indoor temperature and humidity conditions, regeneration temperature, air velocity, and rotor speed [24,25,26,27,28,29,30]. Various technological aspects have been analyzed around these physical factors, and the dehumidification performance and efficiency have been compared to explore their economic implications. Through this analysis, various applied technologies aimed at increasing dehumidification effectiveness and energy savings have been reviewed. The relationship between dehumidification capacity and the influencing factors is summarized as follows [37,38,39,40].

(1)

An increase in indoor temperature leads to an increase in the dehumidification capacity.

(2)

An increase in indoor humidity results in a higher dehumidification capacity.

(3)

As the regeneration temperature rises, the dehumidification capacity also increases.

(4)

An increase in the rotor’s rotational speed initially enhances the dehumidification capacity; however, beyond a certain threshold, it causes a significant decline.

(5)

An increase in the frontal air velocity across the rotor leads to an increase in dehumidification capacity.

2. Materials and Methodology

In this study, the rotor area ratio of the desiccant dehumidifier (Rotor type) was adjusted through experimentation, and the dehumidification efficiency and energy consumption were compared between the general operation mode and the purge operation mode to determine its practicality for real-world applications and analyze energy consumption. Furthermore, the deviation range was checked by comparing the results from simulations based on the airflow and state values in the experimental environment, and the validity of the predictions made through simulations was verified. The aim was to estimate the energy savings under various environmental conditions [41,42,43,44,45,46].

The commonly used operation modes for desiccant dehumidifiers are the general mode and the purge mode. The rotor area ratio used is typically 1:3 (regeneration: dehumidification) for general operation, and 1:1:3 (regeneration: purge: dehumidification) for purge operation. To compare the purge operation desiccant dehumidifier with the general operation mode, it is necessary to adjust the rotor area ratio. Therefore, it is essential to compare equipment with rotor area ratios of 1:3 and 1:4. Based on this, two dehumidifiers were constructed and their performance was evaluated under simultaneous operation conditions. The procedure for this study is outlined as follows and is also illustrated in Figure 7.

(1)

Literature Review: A review of previous studies was conducted on the factors influencing the performance of desiccant dehumidifiers, and the differences between these studies and the present research were analyzed.

(2)

Selection and Manufacturing of Test Equipment: In order to obtain experimental data, each piece of equipment was designed and manufactured to create the experimental environment. The experiments were prepared to operate simultaneously under the same conditions.

(3)

Performance and Energy Evaluation: Based on the experimental results, the required dehumidification performance, dehumidification efficiency, and energy consumption were analyzed.

(4)

Comparison of Performance by Operating Mode: Energy consumption for each mode was predicted using the rotor dehumidification performance simulation program.

(5)

Effectiveness analysis: The predicted values obtained using the rotor performance program were compared with the actual experimental results to determine whether the new dehumidification operating method is advantageous. Additionally, the validity of the analysis method using the program was evaluated.

(6)

Economic Analysis and Evaluation: The economic impact of implementing the new dehumidifier in different regional environments within the country was analyzed, and its applicability was evaluated.

(7)

Based on the analysis results, the prospects for technological advancements in the domestic dehumidification market and future directions for improvement were proposed.

2.1. Review of Dehumidification Method

In Korea, it is common practice to design standard-type desiccant dehumidifiers with a rotor area ratio of regeneration to dehumidification set at 1:3, while purge-type dehumidifiers are typically manufactured with a rotor area ratio of regeneration/purge/dehumidification as 1:1:3 [39]. A comparison of the desiccant dehumidifiers studied is provided in

Table 2. Comparison of desiccant dehumidification systems.

Description	System Diagram	Features	Rotor
Standard desiccant dehumidifier		- The typical operating method of a desiccant dehumidifier - The most common method when not operating in an ultra-low humidity dry room	Rotor area ratio [regen./purge/process] 1:0:3
Purge desiccant dehumidifier		- A method used under conditions that require lower humidity than the range for standard operation - A method to enhance dehumidification capacity by using the air with reduced humidity, which has passed through the dehumidification section of the rotor, for regeneration - By using a portion of the rotor for purge, the area ratio of the dehumidification section of the rotor is reduced	Rotor area ratio [regen./purge/process] 1:1:3
Combined desiccant dehumidifier		- A method that allows the selection between standard operation and purge operation depending on dehumidification conditions and external air conditions - A rotor capable of purge operation is used, and the operating mode can be changed based on indoor requirements and external conditions (temperature and humidity)	Rotor area ratio [regen./purge/process] 1:0:4 (standard) 1:0:4 (purge mode) 1:1:3

. As shown in Figure 8, the combined desiccant dehumidifier is a newly developed concept that allows switching between general mode and purge mode. Therefore, the rotor configuration had to be specified during the initial design stage. The rotor was divided into a 1:1:3 ratio, and the system was designed to operate in a 1:4 configuration in general mode and in a 1:1:3 configuration in purge mode. The mode conversion is facilitated by motorized dampers installed at both ends of the rotor, which open and close to create a passage, allowing the airflow to switch between the supply and regeneration sections.

2.2. Desiccant Dehumidifier Experiment and Simulation

2.2.1. Desiccant Dehumidifier Specification

The specifications of the standard dehumidifier and the combined dehumidifier, which were fabricated for the experiment, are presented in

Table 3. Specification of combined desiccant dehumidifier.

Image	Combined Desiccant Dehumidifier
	Contents	Q’ty	Value
	Frame	-	1.2~5.0 mm
	Casing	-	1.2~5.0 mm
	Process fan	1	600 m3/h
	Regeneration fan	1	200 m3/h
	Desiccant rotor	1	D350, 200 mm [1:3, regeneration/process]
	Heater	1	8.0 kW
	Geared motor	1	220 V, 25 W
	Controller	1	PLC
	Damper	4	D100

and

Table 4. Specification of standard desiccant dehumidifier.

Image	Standard Desiccant Dehumidifier
	Contents	Q’ty	Value
	Frame	-	1.2~5.0 mm
	Casing	-	1.2~5.0 mm
	Process fan	1	600 m3/h
	Regeneration fan	1	D350, 200 mm
	Desiccant rotor	1	D350, 200 mm [1:4 ] or [1:1:3]
	Heater	1	8.0 kW
	Geared motor	1	220 V, 25 W
	Controller	1	PLC
	Motor damper	4	D100

. Since the desiccant rotor has a diameter of 350 mm and a thickness of 200 mm, the total airflow passing through the dehumidification, purge, and regeneration sections is 800 CMH for both devices. Depending on the operating conditions, the rotor is partitioned into regeneration, purge, and dehumidification zones. In the combined desiccant dehumidifier, the operating mode is changed by four motor dampers installed at the front and rear ends of the rotor.

2.2.2. System Diagram and Data Measurement Location

Figure 9 shows the experimental setup and the locations of the data measurement devices. The two dehumidifiers are configured to operate simultaneously, with the necessary measurement instruments installed.

Table 5. Measurement location and item.

Location	Item	Location	Item
A1	T, H, ῡ, V	B1	T, H, ῡ, V
A2	T, H, ῡ, V	B2	T, H, ῡ, V
A3	T, H, ῡ, V	B3	T, H, ῡ, V
A4	T, H, ῡ, V	B4	T, H, ῡ, V
E1	E	E2	E

Where, T is the dry-bulb temperature (°C), H is the relative humidity (%), ῡ is the average wind speed (m/s), V is the passing air volume (m³/h), and E is the power (kW). The air volume was calculated by measuring the average air velocity passing through the air outlet.

presents the data obtained from the measurement locations. In the actual environment, the dehumidifiers are operated, and the measurement devices are categorized into temperature and humidity measurement instruments for assessing dehumidification performance, and devices for measuring input energy. Since only electricity is used for input energy in this experiment, a power meter was installed. As both dehumidifiers operate in the same zone simultaneously, the outdoor air and indoor recirculated air have the same temperature and humidity values.

2.2.3. Measuring Equipment Specification

The measurement devices used for the experiment include a temperature and humidity meter, a current meter, and a temperature and humidity data recorder. The detailed specifications of the measurement devices are shown in

Table 6. Measuring equipment.

Item	Temperature and Humidity Sensor		Item	Power Meter
	Value	Image		Value	Image
Model	Testo 435		Model	Hioki 3280-10F
Manufacturer	Testo (Germany)		Manufacturer	Hioki (Japan)
Temperature	−20~+70 °C (±0.2 °C)		AC	42/420/1000 A (±1.5%)
Humidity	+2~+98%RH (±2%RH)		AC voltage	4.2/42/420/600 V (±1.0%)
Velocity	+0.6~+40 m/s (±0.03 m/s)		Resistence	420/4.2 k/420 k/4.2 M/42 MΩ (±2.0%)
Dimension	74 W × 220 H × 46 D (428 g)		Dimension	57 W × 175 H × 160 D, 100 g
Item	Temperature and Humidity Recorder		Item	Temperature and Humidity Recorder
	Value	Image		Value	Image
Model	ST-50A		Model	SDR100 (input ± 0.1%)
Manufacturer	SEKONIK (Japan)		Manufacturer	Samwon Technology (Republic of Korea)
Temp. range	−20~80 °C (±0.5 °C)		Display	5.7” TFT LCD
Humid. range	0~100%RH (±3%RH)			640 W × 480 H
Usage environment	−20~50 °C, 20~90%RH		Sampling time	500 ms
Dimension	300 W × 245 H × 105 D, 2.9 kg		Dimension	144 W × 144 H 188 D, 1.1 kg

.

2.2.4. Test Condition and Method

The experiment was conducted in a stepwise manner as follows. The indoor temperature was lowered using a cooling device, and to vary the outdoor air intake temperature, a fan heater was used, setting up the experimental conditions as shown in

Table 7. Temperature and humidity conditions.

Item		Outdoor Air	Indoor Air	Note
Case A	Temperature (°C)	16.9~17.7	19.3~23.2	Air-conditioner and heater
	Relative humidity (%)	75.3~79.9	50.5~59.6
Case B	Temperature (°C)	18.5~21	20.4~28.2
	Relative humidity (%)	62.4~69.4	32.7~57.1

.

(1)

The equipment was pre-heated for more than 30 min and measured for more than 30 min.

(2)

The operating modes of the equipment were divided into Case A and Case B, and the tests were conducted sequentially.

(3)

The simulator applied a load to the indoor space using a fan heater and air conditioner.

(4)

The airflow and power consumption of the dehumidifier were measured and recorded using an anemometer and power meter.

(5)

The temperature and humidity of the supply air (SA) and return air (RA) were measured and recorded every minute using an automatic data recorder.

2.3. Simulation

The air conditions for both outdoor air (OA) and return air (RA) were set to match the experimental environment, and the air state values were predicted using the rotor selection program [47,48,49]. The rotor selection program used in this study was the ECODRY program by DRI. The air conditions to be simulated can be input as shown in Figure 10, allowing the prediction of the regeneration air state and energy consumption corresponding to the required humidity. The temperature and humidity states of the dehumidified air are determined by the moisture and energy balance of the air before and after the rotor.

2.4. Prediction of Dehumidification Energy Consumption by Region and Temperature–Humidity Conditions

Korea experiences distinct seasonal climate changes, with significant temperature and humidity fluctuations across different times of the day and regions. Therefore, it is essential to analyze the annual energy consumption to evaluate the energy-saving effects of the combined desiccant dehumidifier. First, to verify the validity of the simulation analysis, dehumidification efficiency, energy usage, and energy savings must be compared with the experimental results under conditions similar to the experimental setup. Afterward, simulations were conducted based on the standard, purge, and combined desiccant dehumidifiers, establishing indoor temperature and humidity criteria and simulating energy consumption according to the regional outdoor environment.

The standard dehumidifier was applied with a rotor area ratio of 1:3, while the combined dehumidifier could operate in either the 1:4 general mode or the 1:1:3 purge mode. The combined dehumidifier can operate between the general mode and the purge mode depending on the conditions of the outdoor air and the air at the rotor inlet. During winter, when outdoor temperature and humidity are low, the purge mode is advantageous for energy savings. In other seasons, however, operating in the general mode is preferable to prevent disruption of indoor humidity levels caused by mode switching [50,51,52,53,54,55].

2.4.1. Setting of Equipment and Indoor Conditions

The indoor conditions for the simulation were defined as shown in

Table 8. Simulation condition (room layout and dehumidification load).

Image	Parameter
	Room Cooling Load	No cooling load
	Person	18.6 m2/person 80(m2)/18.6(m2/person) = 4.3 person → 4 person
	Dehumidification Load	Latent heat load 0.6 kW/(person, h) × 4 person = 2.4 kW 0.3 kW/0.695 kWh/kg = about 0.5 kg/
	Positive air	100 m3/h
	Exhaust air	0 m3/h
	Pre cooler	No pre cooling
	After cooler	EER 3.6~7.6
	Regenerating heater	90 °C (min.)~180 °C (max.)

. The performance evaluation metrics were based on the dehumidification coefficient and annual energy consumption. As shown in

Table 9. Simulation condition (room temperature and relative humidity).

Description	Case 1	Case 2	Case 3	Case 4
Dry-bulb temperature (°C, DB)	23 °C	23 °C	23 °C	23 °C
Wet-bulb temperature (°C, WB)	9.33	11.22	12.99	14.66
Relative humidity (%, RH)	10%	20%	30%	40%
Absolute humidity (g/kg, x)	1.73	3.47	5.22	6.98
Dew-point temperature (°C, DP)	−9.11	−1.01	4.51	8.69
Enthalpy (kJ/kg, h)	27.52	31.94	36.39	40.86

, the indoor temperature was fixed at 23 °C, and the relative humidity was varied at 10%, 20%, 30%, and 40%. The dehumidification coefficient and power consumption were calculated to analyze energy efficiency.

The indoor area for the industrial facility was defined as 80 m², and the latent heat load generated by occupants was calculated based on the number of workers required for production. Although the sensible cooling load within the space was assumed to be zero, the temperature of the dehumidified air increases due to the influence of regeneration heat. Therefore, the cooling capacity of an after-cooler was assumed to reduce the air temperature to indoor levels. The cooling efficiency of the after cooler was represented by an Energy Efficiency Ratio (EER), ranging from 3.6 to 7.6, depending on the outdoor air temperature, with higher EER values at lower temperatures.

The latent heat generated by occupants was considered as the indoor dehumidification load, and a dehumidification performance simulation program was used accordingly. In addition, constant airflow rates were assumed for the supply fans used in both dehumidification and regeneration processes, and their corresponding power consumption was applied. Air leakage from ducts and equipment was not considered.

2.4.2. Outdoor Condition Setup

The performance difference between the standard dehumidifier and the combined dehumidifier needs to be evaluated [56,57,58,59,60]. The outdoor conditions for the simulation were based on three major cities in South Korea: Seoul, Daejeon, and Busan. Monthly average temperatures for each region were calculated based on 30 years of data from the Korea Meteorological Administration, and the results were displayed in

Table 10. Monthly average temperature and humidity (Seoul).

Month	Dry-Bulb Temperature (°C, DB)	Relative Humidity (%, RH)	Absolute Humidity (g/kg, x)	Dew-Point Temperature (°C, DP)	Enthalpy (kJ/kg, h)	Density (kg/m3, γ)
1	−2.0	55.7	1.78	−8.82	2.42	1.30
2	0.8	54.1	2.16	−6.59	6.21	1.28
3	6.4	54.3	3.22	−1.90	14.53	1.25
4	12.8	54.5	4.99	3.87	25.45	1.22
5	18.4	59.6	7.84	10.41	38.37	1.19
6	22.9	65.8	11.49	16.17	52.24	1.18
7	25.7	75.8	15.76	21.11	66.00	1.15
8	26.3	73.6	15.86	21.20	67.22	1.15
9	21.8	66.6	10.87	15.31	49.53	1.18
10	15.2	62.2	6.67	8.03	32.14	1.20
11	7.6	60.4	3.89	0.43	17.43	1.25
12	0.0	57.6	2.17	−6.53	5.42	1.28

,

Table 11. Monthly average temperature and humidity (Daejeon).

Month	Dry-Bulb Temperature (°C, DB)	Relative Humidity (%, RH)	Absolute Humidity (g/kg, x)	Dew-Point Temperature (°C, DP)	Enthalpy (kJ/kg, h)	Density (kg/m3, γ)
1	−1.1	64.9	2.23	−6.20	4.47	1.30
2	1.5	59.6	2.50	−4.88	7.77	1.28
3	6.9	57.2	3.51	−0.86	15.77	1.25
4	13.2	56.4	5.30	4.73	26.65	1.22
5	18.6	61.9	8.25	11.16	39.62	1.19
6	22.9	69.1	12.08	16.94	53.74	1.18
7	25.7	79.0	16.45	21.78	67.74	1.15
8	26.2	78.2	16.78	22.10	69.10	1.15
9	21.4	75.3	12.01	16.85	52.02	1.18
10	14.8	71.9	7.52	9.79	33.89	1.20
11	7.9	69.0	4.55	2.58	19.38	1.25
12	0.9	67.7	2.72	−3.89	7.72	1.28

and

Table 12. Monthly average temperature and humidity (Busan).

Month	Dry-Bulb Temperature (°C, DB)	Relative Humidity (%, RH)	Absolute Humidity (g/kg, x)	Dew-Point Temperature (°C, DP)	Enthalpy (kJ/kg, h)	Density (kg/m3, γ)
1	3.5	46.1	2.23	−6.21	9.11	1.27
2	5.5	49.3	2.75	−3.79	12.42	1.27
3	9.4	56.1	4.09	1.10	19.74	1.23
4	13.9	61.1	6.01	6.54	29.17	1.22
5	18.0	67.8	8.71	11.97	40.17	1.19
6	21.2	76.3	12.02	16.86	51.85	1.18
7	24.7	82.9	16.26	21.59	66.22	1.15
8	26.4	78.0	16.94	22.25	69.72	1.15
9	22.7	72.7	12.56	17.55	54.76	1.16
10	18.0	62.6	8.03	10.77	38.45	1.19
11	12.1	55.7	4.87	3.52	24.44	1.23
12	5.6	47.5	2.66	−4.14	12.32	1.27

for the simulation [7,33,34,35,36].

3. Results

3.1. Analysis of Experimental Results

The experimental measurement results are summarized in

Table 13. Test results.

Description		Case A		Case B
Dehumidifier Type		Standard	Combined	Standard	Combined
Operation mode		General operation	General operation	General operation	Purge
Rotor area ratio [regeneration/process] or [regeneration/purge/process]		1:3 Rotor	1:4 Rotor	1:3 Rotor	1:1:3 Rotor
Supply air	Temperature (°C, DB)	44.9	51.2	48.2	46.4
	Relative humidity (%, RH)	7.4	5.3	6.0	5.8
	Absolute humidity (g/kg)	4.35	4.30	4.21	3.72
	Enthalpy (kJ/kg)	56.36	62.62	59.34	56.25
	Density (kg/m3)	1.10	1.08	1.09	1.10
Exhaust air	Temperature (°C, DB)	41.2	40.7	43.7	46.1
	Relative humidity (%, RH)	52.5	59.1	42.1	34.3
	Absolute humidity (g/kg)	26.46	29.12	24.07	22.15
	Enthalpy (kJ/kg)	109.59	115.92	106.06	103.61
	Density (kg/m3)	1.08	1.08	1.08	1.06
Return air	Temperature (°C, DB)	21.1	21.1	26.0	26.0
	Relative humidity (%, RH)	54.9	54.9	39.4	39.4
	Absolute humidity (g/kg)	8.55	8.55	8.25	8.25
	Enthalpy (kJ/kg)	42.92	42.92	47.16	47.16
	Density (kg/m3)	1.18	1.18	1.16	1.16
Process air	Temperature (°C, DB)	21.1	21.1	26.0	24.3
	Relative humidity (%, RH)	54.9	54.9	39.4	45.0
	Absolute humidity (g/kg)	8.55	8.55	8.25	8.56
	Enthalpy (kJ/kg)	42.92	42.92	47.16	46.09
	Density (kg/m3)	1.18	1.18	1.16	1.05
Outside air	Temperature (°C, DB)	17.4	17.4	19.5	19.5
	Relative humidity (%, RH)	77.5	77.5	66.8	66.8
	Absolute humidity (g/kg)	9.60	9.60	9.44	9.44
	Enthalpy (kJ/kg)	41.80	41.80	43.55	43.55
	Density (kg/m3)	1.19	1.19	1.19	1.19
Air volume	Supply air (m3/h)	598	695	598	547
	Exhaust air (m3/h)	191	133	191	190
Power consumption (kWh)		5.20	5.80	4.92	4.44
Dehumidification capacity (kg/h)		2.96	3.49	2.80	2.78
Dehumidification coefficient (kg/kWh)		0.57	0.60	0.57	0.63

below. In Case A, since two units operate simultaneously in the same space, the temperature and humidity of the return air (RA) entering each unit are identical, and the temperature and humidity of the outdoor air (OA) are also the same. This condition is likewise applicable in Case B.

First, as shown in Figure 11, the power measured for Case A with rotor area ratios of 1:3 and 1:4 were 5.20 kW and 5.80 kW, respectively, with the 1:4 configuration measuring 11.5% higher. This indicates that the dehumidifier’s performance is influenced by the regeneration capability of the rotor, which is known to be affected by factors, such as the regeneration area, regeneration temperature (heat), and the airflow velocity passing through the regeneration section. Therefore, since the regeneration area decreased and the airflow velocity increased, it can be inferred that more electrical power was required to regenerate at a higher temperature in order to enhance the regeneration capability. As a result of the increased electrical energy, the temperatures of the exhaust air (EA) and supply air (SA) were higher compared to the 1:3 configuration. The dehumidification rate was 2.96 kg/h and 3.49 kg/h for the 1:3 and 1:4 configurations, respectively, showing an improvement of 0.53 kg/h (17.9% improvement) for the 1:4 configuration. Since input energy and dehumidification capacity are interrelated, the dehumidification coefficient, as defined earlier, should be compared for an objective performance evaluation. The dehumidification coefficients were calculated to be 0.57 for 1:3 and 0.60 for 1:4. A 0.03 increase in the dehumidification coefficient and a 5.3% improvement were observed for the 1:4 configuration. This suggests that under the experimental conditions, even when adjusting the rotor area ratio from 1:3 to 1:4 in the general operating mode, the indoor humidity conditions can still be met [61,62,63].

As shown in Figure 12, the power measured for Case B with rotor area ratios of 1:3 and 1:1:3 were 4.92 kW and 4.44 kW, respectively, with the 1:1:3 configuration showing a 9.8% lower power. The dehumidification rate for the 1:3 and 1:1:3 configurations were 2.8 kg/h and 2.78 kg/h, respectively, indicating a decrease of 0.02 kg/h (0.7%) for the 1:1:3 configuration. The dehumidification coefficients were calculated to be 0.57 for the 1:3 configuration and 0.63 for the 1:1:3 configuration. A 0.06 increase in the dehumidification coefficient and a 10.5% improvement were observed for the 1:1:3 configuration. This suggests that under the experimental conditions, switching from the general operation mode with a 1:3 rotor area ratio to the purge mode with a 1:1:3 rotor area ratio can still meet the indoor humidity conditions. Additionally, when operating in purge mode, the cooling effect on the supply and exhaust air in the rotor leads to a reduction in the supply air (SA) temperature. This, in turn, lowers the cooling load (after cooler) required to maintain the indoor temperature, resulting in energy savings.

3.2. Experimental Results and Accuracy Analysis of the Simulation

The dehumidification and regeneration air flow rates based on the rotor area ratio were adjusted according to the design criteria for analysis. The results from the program are shown in Figure 13, and the air state values at each location are summarized in

Table 14. Simulation results.

Description		Case A		Case B
Dehumidifier Type		Standard	Combined	Standard	Combined
Operation mode		General operation	General operation	General operation	Purge
Rotor area ratio [regeneration/process] or [regeneration/purge/process]		1:3 Rotor	1:4 Rotor	1:3 Rotor	1:1:3 Rotor
Supply air	Temperature (°C, DB)	37.0	38.3	41.6	38.5
	Relative humidity (%, RH)	11.2	10.3	8.5	8.8
	Absolute humidity (g/kg)	4.35	4.30	4.21	3.72
	Enthalpy (kJ/kg)	48.4	49.55	52.66	48.26
	Specific weight (kg/m3)	1.14	1.12	1.11	1.12
Exhaust air	Temperature (°C, DB)	37.9	41.3	43.6	49.9
	Relative humidity (%, RH)	53.9	57.1	38.5	26.0
	Absolute humidity (g/kg)	22.60	29.04	21.82	20.74
	Enthalpy (kJ/kg)	96.19	116.35	100.15	103.93
	Specific weight (kg/m3)	1.10	1.08	1.08	1.05
Return air	Temperature (°C, DB)	21.1	21.1	26.0	26.0
	Relative humidity (%, RH)	54.9	54.9	39.4	39.4
	Absolute humidity (g/kg)	8.55	8.55	8.25	8.25
	Enthalpy (kJ/kg)	42.92	42.92	47.16	47.16
	Specific weight (kg/m3)	1.18	1.18	1.16	1.16
Process air	Temperature (°C, DB)	21.1	21.1	26.0	24.3
	Relative humidity (%, RH)	54.9	54.9	39.4	45.0
	Absolute humidity (g/kg)	8.55	8.55	8.25	8.56
	Enthalpy (kJ/kg)	42.92	42.92	47.16	46.09
	Specific weight (kg/m3)	1.18	1.18	1.16	1.05
Outside air	Temperature (°C, DB)	17.4	17.4	19.5	19.5
	Relative humidity (%, RH)	77.5	77.5	66.8	66.8
	Absolute humidity (g/kg)	9.60	9.60	9.44	9.44
	Enthalpy (kJ/kg)	41.80	41.80	43.55	43.55
	Specific weight (kg/m3)	1.19	1.19	1.19	1.19
Air volume	Supply air (m3/h)	598	695	598	547
	Exhaust air (m3/h)	191	133	191	190
Power Consumption (kWh)		5.19	5.58	5.30	4.88
Dehumidification Capacity (kg/h)		2.96	3.49	2.80	2.78
Dehumidification Coefficient (kg/kWh)		0.57	0.63	0.53	0.57

.

As shown in Figure 14, the power consumption for Case A, calculated for the 1:3 and 1:4 rotor area ratios, was 5.19 kWh and 5.58 kWh, respectively, with the 1:4 case showing a 7.6% higher value. This result is an arithmetic calculation based on the air flow passing through the rotor and the set regeneration temperature, where the regeneration air flow decreased from 191 CMH to 133 CMH. Since the air conditioning conditions before and after the dehumidifier were set to be the same as the experimental conditions, the dehumidification rates were calculated to be 2.96 kg/h and 3.49 kg/h for the 1:3 and 1:4 cases, respectively, which were consistent with the experimental results. Since input energy and dehumidification capacity are interrelated, the dehumidification coefficients, previously defined, were compared for objective performance evaluation. The dehumidification coefficients were calculated to be 0.57 for the 1:3 case and 0.60 for the 1:4 case. The dehumidification coefficient increased by 0.03, showing a 5.3% improvement. This indicates that, under the simulation conditions, even when the rotor area ratio is adjusted from 1:3 to 1:4 in the normal operation mode, the indoor humidity conditions can still be met.

As shown in Figure 15, the power consumption for Case B, calculated for the 1:3 and 1:1:3 rotor area ratios, was 5.3 kWh and 4.88 kWh, respectively, with the 1:1:3 case showing a 7.9% lower value. The dehumidification rates for the 1:3 and 1:1:3 cases were 2.8 kg/h and 2.78 kg/h, respectively, indicating a decrease of 0.02 kg/h for the 1:1:3 case, which represents a 0.7% reduction. The dehumidification coefficients for the 1:3 and 1:1:3 cases were calculated to be 0.53 and 0.57, respectively. The dehumidification coefficient increased by 0.04 in the 1:1:3 case, showing a 7.5% improvement. This indicates that, under the simulation conditions, even when the rotor area ratio is changed from 1:3 in normal mode to 1:1:3 in purge mode, the indoor humidity conditions can still be met. Furthermore, when operating in purge mode, the cooling effect of the air supply and exhaust in the rotor results in a decrease in the supply air (SA) temperature, which in turn, reduces the cooling (after cooler) heat required to maintain the indoor temperature, leading to energy savings.

The simulation results were compared with the experimental data, and the conditions for Case A are summarized in

Table 15. Comparison of experimental and simulation results (Case A).

Description	Power Consumption (kWh)			D/H Capacity (kg/h)			D/H Coefficient (kg/kWh)
	1:3	1:4	Ratio (%)	1:3	1:4	Ratio (%)	1:3	1:4	Ratio (%)
Test	5.20	5.80	112%	2.96	3.49	118%	0.57	0.60	105%
Simulation	5.19	5.58	108%	2.96	3.49	118%	0.57	0.63	111%
Test/Simulation	99.8%	96.3%		100%	100%		100%	105%
Deviation	−0.2%	−3.7%					0%	+5.0%

, while those for Case B are summarized in

Table 16. Comparison of experimental and simulation results (Case B).

Description	Power Consumption (kWh)			D/H Capacity (kg/h)			D/H Coefficient (kg/kWh)
	1:3	1:4	Ratio (%)	1:3	1:4	Ratio (%)	1:3	1:4	Ratio (%)
Test	4.92%	4.44	90%	2.80	2.78	99%	0.57	0.63	111%
Simulation	5.30%	4.88	92%	2.80	2.78	99%	0.53	0.57	108%
Test/Simulation	107.7%	109.9%		100%	100%		93.0%	90.5%
Deviation	+7.7%	+9.9%					−7.0%	−9.5%

. Since the simulations were conducted based on the same dehumidification amount, meaningful conclusions can be drawn by comparing the power consumption and dehumidification coefficients. The power consumption deviations were −0.2% and −3.7% for Case A, and +7.7% and +9.9% for Case B. The dehumidification coefficients showed deviations of 0% and +5% for Case A, and −7.0% and −9.5% for Case B. Given that the deviations in power consumption and dehumidification coefficients were within ±10%, it was determined that the simulation results could also be validated.

3.3. The Prediction Results of Energy Consumption by Region

The performance simulation results of the standard desiccant dehumidifier and the combined desiccant dehumidifier, based on the differences in the outdoor environmental conditions of three major cities in South Korea, are shown in

Table 17. Comparison of dehumidifier performance by region (dehumidification coefficient, kg/kWh).

Description	Case 1		Case 2		Case 3		Case 4
	23 °C DB, 10% RH		23 °C DB, 20% RH		23 °C DB, 30% RH		23 °C DB, 40% RH
	Standard	Combined	Standard	Combined	Standard	Combined	Standard	Combined
Seoul	0.20	0.32	0.24	0.35	0.26	0.32	0.25	0.28
Daejun	0.20	0.27	0.32	0.41	0.41	0.52	0.48	0.60
Busan	0.21	0.27	0.33	0.41	0.42	0.52	0.50	0.59
Average	0.20	0.29	0.30	0.39	0.36	0.45	0.41	0.49
Ratio (%)	100%	145.0%	100%	130.0%	100%	125.0%	100%	119.5%
Gap.		+45.0%		+30.0%		+25.0%		+19.5%

. In regions where the variation in outdoor temperature and humidity is not significant, no major performance differences were observed. However, the average dehumidification coefficient under the indoor humidity setting conditions showed significant improvements of 60%, 40%, 26%, and 20%. Particularly, as the required indoor humidity decreased, the performance of the combined desiccant dehumidifier showed a significant improvement.

For the combined dehumidifier, during the warm season, when the outdoor temperature and humidity are high, the dehumidification performance in purge mode was either ineffective or not superior to the general mode. However, during the winter months, when the outdoor temperature and humidity are lower, the performance of the purge mode was significantly better, and the combined dehumidifier can be considered superior in terms of overall performance. In this simulation, the operational mode switching of the hybrid desiccant dehumidifier was configured to optimize dehumidification stability. Specifically, a monthly operational mode switching strategy was employed to ensure that when purge mode could not provide sufficient performance, the system would operate solely in general mode during those times.

The performance of the simulation conducted for three cities and four indoor temperature and humidity conditions, along with the annual average energy consumption, is presented in

Table 18. Comparison of dehumidifier performance by region (annual energy consumption, kWh).

Description	Case 1		Case 2		Case 3		Case 4
	23 °C DB, 10% RH		23 °C DB, 20% RH		23 °C DB, 30% RH		23 °C DB, 40% RH
	Standard	Combined	Standard	Combined	Standard	Combined	Standard	Combined
Seoul	77,473	57,950	76,439	50,211	76,957	46,504	77,336	45,024
Daejun	77,716	58,676	76,224	50,241	76,743	46,512	77,078	44,485
Busan	75,982	58,026	74,345	50,457	74,536	46,412	72,700	45,274
Average	77,057	58,217	75,669	50,303	76,079	46,476	75,705	44,928
Ratio (%)	100%	75.6%	100%	66.5%	100%	61.1%	100%	59.3%
Gap.		−24.4%		−33.5%		−38.9%		−40.7%

. The results show average energy savings of 23%, 20%, 14%, and 10% depending on the indoor conditions. The discrepancy between the dehumidification coefficient and energy savings is due to the power consumption of the fan motors for dehumidified air and regeneration air, as well as the cooling load in the desiccant dehumidifier. In this study’s simulation, the supply air volume (for dehumidification) and regeneration air volume were assumed to be fixed air volumes, and the cooling load for indoor air supply was also considered. Even during the winter season, when the outdoor temperature is low, a minimum amount of regeneration power is required, which leads to the need for dehumidification energy.

4. Discussion

This study was conducted to verify the dehumidification performance and energy consumption of a combined desiccant dehumidifier, which can switch between standard operation and purge operation depending on outdoor and indoor temperature and humidity conditions. Although desiccant dehumidifiers are used in various operation modes and manufacturing methods, the combined dehumidifier used in this study had not been developed before, and no verification data existed [64,65,66,67,68]. Therefore, it was necessary to compare the product performance through experiments and verify the energy consumption through rotor performance simulations. As a result, during the winter season with low outdoor temperature and humidity, the combined desiccant dehumidifier demonstrated good dehumidification efficiency and significant energy savings, making it useful. However, in conditions with high outdoor temperatures and humidity, purge mode cannot be used without a pre-cooler, and additional equipment may be required. Furthermore, solutions to overcome limitations, such as maintaining a minimum airflow for performance stability and keeping the minimum regeneration temperature, need to be developed. Additionally, more research into new dehumidification operation technologies is required. Similar to previous studies, it was confirmed that the dehumidification capacity follows the same pattern according to the indoor set temperature, indoor set humidity, outdoor temperature, outdoor humidity, regeneration temperature, and regeneration airflow rate. Additionally, the results also indicate that dehumidification capacity and dehumidification efficiency are not directly proportional.

This study used monthly average temperature and humidity to calculate annual energy consumption, which means it could not reflect real-time outdoor temperature and humidity conditions, and it has limitations in determining appropriate operational standards for mode switching according to outdoor temperature, humidity, and indoor load conditions. Therefore, future studies should focus on collecting energy consumption data through annual operation and fan power adjustments, while also ensuring stable indoor conditions and determining operational standards for mode changes. Furthermore, establishing specific criteria for temperature and humidity thresholds in conjunction with operational mode switching strategies may contribute to energy savings. In particular, future expansion to daily, hourly, or real-time mode switching could lead to substantial improvements in energy efficiency. However, rapid changes in airflow rate and regeneration temperature may result in insufficient dehumidification capacity, causing fluctuations in indoor humidity levels. Therefore, further research is required to explore and validate various control strategies [60,69,70,71].

5. Conclusions

This study was conducted to verify whether a newly configured desiccant dehumidifier, based on modifications to conventional standard or purge-type systems, could achieve comparable dehumidification performance and efficiency under identical indoor and outdoor conditions. The system is capable of operating in both general and purge modes using a single unit. Given the fixed rotor configuration and dimensions, it is essential to redistribute the supply and regeneration airflow appropriately. Therefore, the system must allow for adjusted airflow allocation compared to conventional configurations. The results obtained from the experiments and simulations can be summarized as follows.

(1)

According to the experimental results, the power consumption of the combined desiccant dehumidifier in general mode was 11.5% higher than that of the standard desiccant dehumidifier in general mode. However, the dehumidification capacity in-creased by 17.9%, resulting in a 5.2% improvement in dehumidification efficiency. Additionally, compared to the standard dehumidifier in general mode, the purge mode of the combined dehumidifier showed a slight reduction in dehumidification capacity by 0.7%, but the power consumption decreased by 9.8%, leading to a 10.5% improvement in dehumidification efficiency

(2)

The simulation results under the same conditions as the experiment showed that the dehumidification coefficient deviated by 0% at a 1:3 ratio and +5% at a 1:4 ratio in Case A, and by −7% at a 1:3 ratio and −9.5% at a 1:1:3 ratio in Case B. These deviations are within a ±10% error margin.

(3)

Based on the monthly average temperature and humidity conditions of three representative cities in Korea, energy consumption was simulated. The combined desiccant dehumidifier showed superior performance, with energy consumption reduced by 35% in Seoul, 35% in Daejeon, and 33% in Busan.

(4)

In the energy consumption simulations conducted under varying indoor humidity conditions, the combined desiccant dehumidifier demonstrated energy savings of 24.4% for Case 1 (10% RH), 33.5% for Case 2 (20% RH), 38.8% for Case 3 (30% RH), and 40.7% for Case 4 (40% RH). The results indicate that the combined desiccant dehumidifier achieves greater energy savings under conditions with higher indoor humidity requirements.

This study validated the accuracy of the simulation program in predicting the dehumidification performance, dehumidification efficiency, and energy consumption of the combined desiccant dehumidifier. The results confirmed that the program can be reliably used as an analytical tool. The application of the combined desiccant dehumidifier in industrial settings can improve dehumidification performance and reduce energy consumption. However, various factors, such as real-time fluctuations in outdoor temperature and humidity, indoor cooling and dehumidification loads, air leakage in ducts and equipment, and accumulated thermal loads in structural elements, must also be considered.

Accordingly, future research will focus on determining the optimal timing and method for switching operating modes and establishing appropriate operational guidelines.