1、4703 A Study on the Control Methods for Radiant Floor Heating and Cooling System in Residential Building Seong-Ryong Ryu Myoung-Souk Yeo, Ph.D. ABSTRACT when applying the radiant floor cooling system using Ondol-the Korean traditional radiantfloor heating system- it is important to select a precise
2、control method to maintain a stable roam temperature andfloor surface temperature and prevent surface condensation. Therefore, it is necessary to systematize various control methods and to conduct a compar- ative study of the respective control methods so as to be able to control the radiant floor h
3、eating and cooling system e ciently. As well as evaluating the level ofstabili of room tenzper- ature and floor surface temperature, we performed this study to search for a control method to minimize condensation during the cooling period without a dehumidijcation system. Based on the results of thi
4、s study, we are going to develop a radiant-floor cooling system integrated with a dehumid$ca- tion system. We aim to deal with indoor comfort in company with concern for condensation. In this study, computer simulations and model experi- ments wereperformed for this comparative analysis on control m
5、ethods usedfor the radiantfloor heatingandcooling system. And, on the basis of the results of our analysis on the control performances of respective control methods, we evaluated the applicability of control methods for the radiant floor heating and cooling system. INTRODUCTION In Korea, installatio
6、n of cooling systems in residential buildings was not taken into account due to factors such as technical problems, efficiency, and past living standard. However, today, with the growth of the industry and increase in the GNP, residents have begun to emphasize convenience Jae-Han Lim Kwang-Woo Kim,
7、Arch.D. and comforts of living. Therefore, the demand for cooling systems and installations of packaged air conditioners (PAC) has been increasing. Unfortunately, the use of PAC for cooling in residential buildings has been found to have negative effects on the environment and, apparently, causes th
8、e problem of sudden peak of electric power demand in summer. Moreover, some of the problems of a conventional cooling system with PAC include draft, local discomfort, and room temperature fluctuation. So it has become necessary to develop a cooling system that can reduce the problems caused by the u
9、se of PAC. Korean residential buildings, in general-particularly apart- ment buildings-are finished with Ondol, the Korean tradi- tional radiant floor heating system. The radiant floor heating system has been widely used as a heating method by flowing hot water into tubes embedded in the floor. And
10、so, in devel- oping a cooling system, it would be more advantageous to utilize the existing floor heating system rather than to adapt a separate system, in which case one would have to consider effective heatingkooling transformation of the floor area, conservation of resources, and the environment.
11、 Thus, the radiant floor cooling system using Ondol has been proposed as an alternative (RIESSNU 2003). In order to apply a radiant floor heating system for cooling during a hot and humid summer in Korea, there is a need to examine various factors such as surface condensation, floor surface temperat
12、ure, vertical room air temperature difference, etc. Developing accurate control is especially crucial in main- taining the stability of room temperature and floor surface temperature and preventing surface condensation. Therefore, it is important to identify the problems that may arise in the heatin
13、g and cooling panel system and to develop an appropi- ate control method that can quickly respond to such a problem and restore temperature stability. Also, it is necessary to eval- uate respective control performances through the performance Seong-Ryong Ryu and Jae-Han Lim are doctoral students, My
14、oung-Souk Ye0 is an assistant professor, and Kwang-Woo Kim is a professor in the Department of Architecture, Seoul National University, Seoul, Korea. 106 02004 ASHRAE. of a comparative analysis of control methods for the radiant floor heating and cooling system. In this study, we classified the vari
15、ous existing control methods that have been proposed or those that have been applied by control parameters until now. With water temper- ature control methods and water flow rate control methods, we performed computer simulations and experiments in the labo- ratory for the comparative analysis. In a
16、ddition, we conducted analysis of the control performances of each control method to evaluate the applicability of control methods for the radiant floor heating and cooling system. CONTROL METHODS FOR RADIANT FLOOR HEATING AND COOLING SYSTEM In the past, various control methods for the radiant floor
17、 heating system have been suggested and applied by research- ers. To control the radiant floor heating and cooling system efficiently on the basis ofthese control methods, it is necessary to systematize various control methods and to do a compara- tive study of each control method through computer s
18、imula- tions and experiments in the laboratory. First, we classified existing control methods that have been suggested or applied until now by control parameters. Control Parameters Control parameters for the radiant floor heating and cool- ing system can be classified into input variables, controll
19、ed variables, and manipulated variables, as shown in Table 1. It may be much simpler and systematic to classi Algren 1953). In order to control the flow rate of supply water, there are two types of control methods that can be used-the continuous flow rate control and the intermittent flow rate contr
20、ol. Vari- able flow control has a continuous flow rate, and onoff bang- bang control and odoff pulse-width modulation (PWM) control have a intermittent flow rate (Tekmar 1996). The on/ off bang-bang control (called the onoff control) is installed in almost every apartment building in Korea. The appl
21、ication of variable flow control is rare because it is difficult to control the flow rate precisely in the range of low flow rate due to nonlin- ear correlation between flow rate and heat output (Bourne 1989). Classification of Control Parameters Table 1. ASHRAE Transactions: Research 107 Table 2. C
22、ontrol Methods for the Radiant Floor Heating and Cooling System I I l Control Parameters Continuous flow Constant flow Flow rate L Heat Flux Constant Temperature Variable Temperature - Outdoor reset control Flux modulation I Supply Water Temperature intermittent flow - Variable flow Variable flow co
23、ntrol - Outdoor reset + - Bang-bang control Ordoff bang-bang control bang-bang control Pulse-width modula- Ordoff PWM control Outdoor reset + - tion(PWM) onioffPWM control Outdoor reset with indoor temperature feedback control The water temperature plus flow rate control methods are control methods
24、for multiple zones, where the supply water temperature is controlled by sensing the outdoor temperature, according to which the water flow rate is intermittently controlled using an odoff valve. The water temperature plus flow control method can be classified into outdoor reset plus odoff bang-bang
25、control, which is installed in apartment buildings via district heating in Korea, and outdoor reset plus onoff PWM control (Gibbs 1994). In flux modulation, the on-time ratio of the boiler can be controlled using pulse-width modulation such as odoff pulse- width control (MacCluer 1989). The boiler u
26、sed in flux modu- lation should be characteristic of a constant output and a lower thermal storage effect. SIMULATION TOOLS AND EXPERIMENTAL FACILITY Normally, in the control methods for the radiant floor heating system in Korea, the odoff bang-bang control is installed in every apartment building v
27、ia central boiler heating or individual heating, whereas the outdoor reset plus odoff bang-bang control is partly applied to apartment buildings via district heating. In order to decide on a suitable control method, one could assume that it is preferable to perform computer simulations and experimen
28、ts using control methods that are actually being applied in apartment buildings. Therefore, we performed computer simulations and experiments in the laboratory on the water temperature control methods and water flow rate control methods in order to conduct a comparative analysis on control methods f
29、or the radiant floor heating and cooling system. These computer simulations and model experiments for both heating and cool- ing were performed under the same conditions. The simulation tools and experimental facility were set up in consideration of the possibility that computer simulations and expe
30、riments for the comparative analysis on other control methods, as shown in Table 2, may have to be performed addi- tionally. 108 Conditions and Tools for Computer Simulation Room for Simulation. We chose the Spical Ondol room on the mid-floor of an apartment building as our sample. The room had one
31、wall facing the outside, and the ceiling, the floor, and the three other walls were in contact with identical Ondol rooms. Structure of Ondol Floor. The commonly used Ondol floor structure of the construction companies of Korea consists of a 135 mm concrete slab, 55 mm ALC (autoclaved lightweight co
32、ncrete), 20 mm cement mortar embedded with a 230 mm-spaced XI, pipe, and 25 mm cement mortar as a finishing layer from bottom to top. Outdoor Temperature. The simulations were performed in the winter and summer seasons according to the standard meteorological data of Seoul (SAREK 1998). Simulation P
33、rogram. The simulations were perfomed with the aid of a dynamic simulation program (Kim 1999). This simulation program can analyze the thermal behavior of multiple rooms with unsteady-state calculation. The program was validated in previous research (MOCIE 1996; Lee 1999). Test Cells and Equipment T
34、he test cell (total of four units) had four walls, a window at the south, a door at the north, a ceiling, and the radiant floor for heating and cooling, which were modeled by one of the rooms of the apartment building?s south facing orientation. To ensure the same amount of heat loss or heat gain pe
35、r floor area, test cells were built with the same K-value and the same floor structure as in an existing apartment building (see Figure 1). For controlling these devices, the heating and cooling source, pump and distribution systems, temperature and humidity sensors in space, water temperature senso
36、rs and water flow meter in supply water, weather station, analog input and output devices, and computer with algorithm need to be programmed. In order to supply hot water of constant temperature for radiant floor heating, electric heating is used as the heating source, and in supplying cold water of
37、 constant temperature for radiant floor cooling, an ice storage tank is used as a cooling source. ASHRAE Transactions: Research (a) Section of test model (b) Plan of test model % In case of variable flow rate control. 2-way valve is used instead of 3-way valve % Ice storage system for cooling source
38、 and Electric heating for heating source 8% Solenoid valve & 3-way valve sensor L+ Strainer 57 Pressure gage Electric heater (C) Piping for model experiment Figure 1 Test model andpiping system. For the ordoff bang-bang control and the variable flow control, the water was heated by an electric heate
39、r or cooled by ice storage, and controlled by a heat exchanger to meet the set temperature and supplied to the cell. For the outdoor reset with indoor temperature feedback control, the water was readjusted to the required water temperature and supplied to the cell using a three-way valve. Room air t
40、emperature and humidity, floor surface temper- ature, surface temperatures of walls and windows, supply and return water temperatures, globe temperature, outdoor temperature, and humidity were measured. In order to remove the effect by radiation, room air temperature was measured by a double concent
41、ric tube with a T-type thermocouple. In measuring surface temperature, a T-type thermocouple was attached to the walls and floor with aluminium tape. A sensor pocket with a T-type thermocouple was installed inside pipes to measure supply and return water temperature. Measured data were stored in com
42、puters using an analog input device and a datalogging system. For weather data, direct and diffuse irradiation were measured using extra sensors installed on the j: rooftop. Measurement of wind direction and speed were also obtained from the weather station. To test the various heating and cooling c
43、ontrol modes in radiant floor heating and cool- ing, an input and output board for sensor and valve interface was integrated with the computer containing the algorithms for controlling these devices (see Figure 2). SIMULATIONS AND EXPERIMENTS FOR RADIANT FLOOR HEATING Outdoor reset with indoor tempe
44、rature feedback control as a water temperature control and odoff bang-bang control, ordoff PWM control, and variable flow control as a water flow control were compared through computer simulations and experiments for radiant floor heating. To evaluate the level of stability of room temperature and f
45、loor surface temperature, respective control methods were evaluated through a compar- ative analysis. Also, in the experiment for heating, the control performance of the water temperature plus flow rate control for multi-zone control, which is applied to district heating apartment buildings in Korea
46、, was tested as well. ASHRAE Transactions: Research 1 o9 measured analogue input signal digital input signal -3 temperature sensor anfuogue input board control program T-type therrnocoupie Test cell e- actuator 4 _- anaiogue output board t actuating d8Vh pump, solenoid vaive 4SSR (solid state relay)
47、 control output power analogue output signal Figure 2 Scheme of control system. 30 Ouidoor reset with indoor temperature feedback control (floor surface temDeraturel Onioff bana-bang control (floor surface temperature) artable flow control 28 h P L v 26 3 c $ 24 Q E : 22 20 12AM 12AM 12AM 12AM 12AM
48、12AM Time(hr) Figure 3 Comparison of control methods in terms of room andfloor surface temperature. Results and Discussion for Simulation Figure 3 shows the profiles of room air temperature and floor surface temperature for the week where outdoor temper- atures were lowest. In the case of ordoff ban
49、g-bang control and variable flow control, the fluctuation of room air temperature and floor surface temperature was greater than that with outdoor reset with indoor temperature feedback control. As shown in the profile of room air temperature, the room air temperature was well maintained around the set temperature in the following order: outdoor reset with indoor temperature feedback control, variable flow control, and onloff bang-bang control. This suggests that outdoor reset with indoor temper- ature feedback control has better performance than the others in terms of the stabi
