1、4748 A Study for Evaluating Performance of Radiant Floor Cooling Integrated with Con t ro I I ed Vent i I at i o n S.B. Leigh, ArchD Associate Member ASHRAE D.S. Song, DrEng S.H. Hwang S.Y. Lee ABSTRACT This study aims at developing a radiant floor cooling system using the existing Ondol (radiantflo
2、or heating system). It was found that theproposedsystem couldprovide cooling for thermal comfort with higher energy eficiency. However, prob- lems still exist due to the condensation on the floor surface while the radiantfloor cooling system is in operation. To solve this problem, radiant jloor cool
3、ing integrated with controlled ventilation was proposed as an alternative approach. The ventilator brings fresh outside air to meet the minimum requirement for indoor air quality and a dew-point sensor activates dehumidijication by means of cooling coils in the ventilator: To evaluate the performanc
4、e of the proposed system, both a physical experiment in a laboratory setting and computer simulation have been conducted. The results show that radiant jloor cooling integrated with a ventilation system properly maintains the indoor setpoint temperatures as well asprevent- ing condensation on theflo
5、or surface. Also, radiantfloor cool- ing integrated with ventilation provides cooling with only one- third of the energy required by the conventionalpackaged air- conditioning system based on TRNSYS simulation. INTRODUCTION In many countries hydronic radiant floor heating systems are widely used, bu
6、t very few systems are used for cooling. Due to the high radiant heat output and the fact that the occu- pants are close to the heat source, the same floor system obvi- ously could also be used for cooling (Olesen 1997). Cooling of a building equipped with an air system signif- icantly contributes t
7、o the increase of electrical energy consumption and to electrical peak demand. HVAC systems are designed to maintain indoor air quality and provide ther- mal space conditioning. As an alternative approach to provide cooling through a combination of radiation and convection inside the building, a hyd
8、ronic radiant cooling system allows the separation of the tasks of ventilation and cooling. While primary air distribution is used to fulfill the ventilation requirements for indoor air quality, the secondary water distri- bution system provides thermal conditioning to the building. The separation o
9、f tasks not only improves comfort conditions but increases indoor air quality as well. The logical choice is the coupling of a displacement ventilation system with hydronic radiant cooling, a strategy that allows the separation of the tasks of ventilation and cooling in the building (Feustel and Ste
10、tiu 1995). Hydronic radiant floor heating systems are popular in Korean housing where the tubes are embedded inside the concrete floor slabs and heat is supplied by running warm water through the tubing. In recent years, the need for cooling in residential buildings has been sharply increased. Accor
11、d- ingly, there has been a higher demand for room air condition- ing, resulting in a higher electrical peak demand during the cooling season (KEPCO 1997). As one of the alternative approaches, the concept of radi- ant floor cooling has been proposed by running chilled water through the existing tube
12、s installed for heating, together with a separate ventilator that is operated only for air renewal and humidity control. A minimum amount of outside air must be introduced for indoor air quality, and most of the cooling load is removed by radiant means. Thus, the proposed system can provide cooling
13、with a minimum energy requirement as well as control humidity to prevent condensation. Seung-Bok Leigh is aprofessor in the Department ofArchitecture, Yonsei University, Seoul, South Korea. Doosam Song is an assistant profes- sor in the Department of Architectural Engineering, Sungkyunkwan Universit
14、y, South Korea. Suckho Hwang is a doctoral student at the Insti- tute of Industrial Science, University of Tokyo, Japan. Sang-Youp Lee is an engineer at HIMEC, Seoul, South Korea. 02005 ASHRAE. 71 Heat gain from solar radiation Heat gain through roof (A) Room air-conditioner + ventilation (B) Radian
15、t floor cooling + ventilation (wlo dehumidification) Figure 1 Concept of radiant floor cooling integrated with controlled Ventilation. Heat gain from Heat gain throuah roof Heat gai InrOJgh Coollng by radiant floo window throrign wail Moisture tieat ga ci, Unfortunately, literature has not been foun
16、d that describes the dynamic thermal behavior of hydronic radiant cooling. Dynamics might be an important issue in further studies for validating the proposed system in terms of thermal comfort and energy performance. Therefore, this study tried to (1) establish a concept of hydronic radiant floor c
17、ooling integrated with controlled ventilation, (2) evaluate its applicability through physical experiment in a laboratory setting, and finally (3) analyze the indoor environmental conditions for comfort and energy performance of the radiant floor cooling system compared to a conventional solution of
18、 packaged air conditioner through TRNSYS simulation. RADIANT FLOOR COOLING INTEGRATED WITH VENTILATION The radiant floor cooling system removes heat, which is obtained mostly by radiant heat transfer into a relatively cool surface, and maintains the heat balance and thus the indoor setpoint temperat
19、ure of the space. So the basic principles of radiant floor cooling would be very similar to those of radiant floor heating. Figure 1A shows the concept of space cooling by a conventional air conditioner in which the room air is cooled and dehumidified while the air changes are based on natural venti
20、lation through openings. Figure 1B shows the concept of radiant floor cooling in which the thermal comfort conditions are provided by the combined effect of room air and mean radiant temperatures. However, the radiant floor cooling may cause condensation on a floor surface due to the moisture brough
21、t in through natural ventilation. Figure 1C illustrates the concept in which fully controlled ventilation is proposed during operation of the radiant cooling system. Thus, the tasks of ventilation and cooling are separated by distributing fresh air to fulfill the ventilation requirements for indoor
22、air quality and by distributing chilled water to provide space cooling and dehumidification. Based on the assumption that moisture comes from the humid outside air through ventilation, the indoor humidity and, accordingly, the dew-point temperature can be controlled by circulating chilled water to t
23、he cooling coils in the ventilator. In addition, condensation can be effec- (C) Radiant floor cooling + ventilation (wl dehumidification) tively prevented by coupling the humidity sensor with a control algorithm that allows a safety margin of 2“C(3.6“F) between floor surface temperature and dew-poin
24、t tempera- ture. PHYSICAL EXPERIMENT FOR EVALUATING APPLICABILITY A laboratory experiment has been conducted to evaluate the applicability and effectiveness of dehumidification for a radiant floor cooling system integrated with controlled venti- lation. Experimental Setup Construction of Test Cells.
25、 For the experiment, four identical test cells were constructed and outfitted with differ- ent cooling and control systems for comparative analysis. The cells were designed and built specifically for investigating dynamic thermal behavior of a space having dimensions of 2.4 m (7.9 ft) (W) x 2.4 m (D
26、) x 2.4 m (H). The cells are oriented to the south, having windows on the southern faade measuring 1.8 m (5.9 ft) (W) x 1.2 m (3.9 ft) (H) with entrance doors 0.8 m (2.6 ft) (W) x 1.6 m (5.3 ft) (H) on the opposite side. The construction of test cells and radiant floor is shown in Figure 2. Installa
27、tion of Radiant Floor Cooling System. For this purpose, two identical test cells were selected in which radiant floor cooling systems are installed. Test cell A is equipped with a ventilation system that has cooling coils that respond to remove moisture from the incoming outside air and to perform c
28、onvective cooling during the peak load conditions. In contrast, test cell B is equipped with the same ventilator with- out dehumidification. The fan speed has been set at 13.824 CMH (8.12 cfm) to provide 1 ACH for both test cells. Since the limiting factor in designing a radiant cooling system is th
29、e floor surface temperature, the floor surface temperature should not be lower than 19“C(66F) for comfort reasons and should also be higher than the dew-point temper- ature in the space to prevent condensation. Thus, the temperature of chilled water produced by a cool- ing plant has been set at 15C(
30、59“F) for experimental 72 ASHRAE Transactions: Research Unit : mm 2760 I_ 1200 9 3 Ret urn -Ilc Supply I Floorconstruction I O Tube spacing average 140 mm U Tube outside diameter 15 mm O Tube wall thickness 2 mm O Tube wall conductivity 1 23 kJI hmPK _I - - _ -_-i Linoleum Mortar (50mm) Insulation (
31、160mm) I Floorsection 1 Section of test cell Plan and tubing layout of test cell Figure 2 Construction of test cells and radiantfloor Figure 3 Conjguration of radiant floor cooling systems installed for laboratory experiment: A is for ventilation integrated with dehumidijkation and B is for ventilat
32、ion only, purposes. It is sent directly to the cooling coils in the ventilator when the dew-point control is needed, and the supply water temperature is regulated for the radiant floor via a three-way mixing valve and heat exchanger so that the floor surface temperature will not be lower than 19C (6
33、6F). For both cases, the outdoor reset with indoor temperature feedback control is applied, which primarily modulates the supply water temperature as a function of outdoor temperature variations. Secondarily it is adjusted based on offset from the setpoint. The configuration of radiant floor cooling
34、 systems installed for the laboratory experiment is shown in Figure 3. Data Collection and Control Algorithm. For monitor- ing and collecting the data, as well as operating cooling systems, a data acquisition system and a desktop computer were employed. K-type thermocouples were used for measur- ing
35、 temperatures inside/outside the test cells as well as the temperatures for supply and return water of radiant cooling systems and cooling coils in the ventilator.Also, the relative humidity was measured in each test cell via a humidity sensor. The measured data were transmitted to a computer via I/
36、O boards of the data acquisition system and the chillers and vari- ous types of valves, pumps, and fans were controlled via control algorithms, illustrated in Figure 4, using LabVIEW 6.0 programming. The control algorithm consists of two major components: one is for outdoor reset control with indoor
37、 temperature feed- back for the modulation of supply water temperature to the radiant floor and the other is for control of cooling coils in the ventilator to prevent condensation as well as to provide subsid- iary cooling during peak load conditions. For the outdoor reset control, the reset ratio v
38、aries depending upon the thermal characteristics of the building construction. Thus, the reset ratio for this experiment has been ASHRAE Transactions: Research 73 ( START ) Chiller A on set-point 150 Chilled water pump on Tex lm Fan on.Tset 260 Tout. Outdoor temperature Tset Indoor set-point Tsuf Su
39、rface temperature Figure 4 Control algorithm applied for radiant floor cooling wil,. dehumidipcation. derived from empirical data through pilot tests previously conducted in a laboratory as T, = -0.9 x To, + (49.4 +O. 1 x i), where T, is the supply water temperature to the radiant floor and To, is t
40、he outdoor temperature. Also, the reset ratio will be shifted to adjust the supply water temperature if the indoor temperature offset from the setpoint is greater than 0.2“C(0.36“F). For control of cooling coils in the ventilator, the indoor temperature is once more compared with the setpoint. If th
41、e offset from the setpoint is greater than 0.5“C(0.9“F), then the valve is opened to circulate the chilled water to the coils for subsidiary cooling of the space. Also, ifthe temperature differ- ence between floor surface and room dew point is less than 2.OoC(3.6“F), then the cooling coils will oper
42、ate for dehumid- ification. Experimental Results Figure 5 shows the test results of radiant floor cooling in both test cells: A, ventilation with dehumidification, and B, ventilation only. For both cases, the ventilation rate of 1 ach is maintained during the test, and the thermal dynamics of indoor
43、 environmental conditions, such as indoor, floor surface, and room dew-point temperature variations and the dynamic response of radiant floor cooling and ventilation systems, are presented. During the test periods, the outdoor temperature varied from 20C (68.0“F) to 34C (93.2“F) and the average indo
44、or temperature oftest cell A was 25.36“C (77.6“F) and that ofcell B was 26.16“C (79.1“F). In case of cell B, the maximum indoor temperature reached 28“C, 2 degrees above the setpoint, on the second day, which represents the limitation of cooling capacity of the radiant floor to meet the peak load 74
45、 ASH RAE Transactions: Research 40 1 Radiant floh cooling + Ventilation dith dehumidlfication I Outdoor air l I I (68.02“F) , Roam dell-point Floorsurface r- - I Temperature difference beiwein room and setpoint (7436F) (68.65“F) I (75.67“F) E- ? 40 Radiant flobr cooling +Ventilation dio;dehumidifica
46、tion . outdobrair 30 25 20 E $2 ; -2 ao io , Floorsurface .- I 1 suppiy water to noor 30 i- I _ 30 i * Supply wster to venfiletioh system 25 20 15 00000 ? 9 ? 0 ? 1 w 1% 8 aw D A a I$! f R 99n rnM Time(hr) (A) Ventilation with dehumidification o o o o o o o o o o o0 D 8 B 8 Z f M 8 6 Y SR Time(hr) (
47、B) Ventilation only Figure 5 Test results ofradiantfloor cooling: A is for ventilation integrated with dehumidijkation and B is for ventilation only. conditions with the requirement of a minimum floor surface temperature of 20C (68F) (Table 1). Thus, it could be said that convective cooling through
48、the ventilator separated from the radiant cooling would be helpful, not only for dehumidi- fication, but also for sharing the cooling load at the peak load conditions. In addition, the combined effect of radiant and convective cooling in the case of cell A showed a faster response to reach the setpo
49、int after the system started. Both systems started at the indoor temperatures of 30C (86“F), and it took less than 5 hours to reach the setpoint for system A and it took 7.5 hours to reach the setpoint for system B. This is because the control algorithm in system A is designed to operate the cooling coils in the ventilator when the indoor temperature offset from the setpoint is greater than 021C (0.9“F), which definitely helps the system to respond faster at full-load conditions. In the case of system B, condensation occurred on the floor
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