Healthy Buildings 2017 Europe July 2-5, 2017, Lublin, Poland

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1 Healthy Buildings 2017 Europe July 2-5, 2017, Lublin, Poland Paper ID 0320 ISBN: The Analysis of the Air Velocity Distribution above the Trench Heater with Natural Convection Mariusz A. Skwarczynski 1,2,*, Marzenna R. Dudzińska 1, Paweł Mroczkowski 2, Wojciech Karolinski 2 1 Faculty of Environmental Engineering, Lublin University of Technology, Nadbystrzycka 40B, Lublin, Poland 2 VERANO Ryszard Miazga, R&D Department, Vetterow 7A, Lublin, Poland, * Corresponding m.skwarczynski@pollub.pl SUMMARY The paper describes an experimental setup used for capacity evaluation of trench heater with natural convection and visualization of velocity vector filed of convective air stream formed above the heater using PIV method. Investigation were performed for trench convector at inlet and outlet temperature 75/70 o C, 75/65 o C and 75/60 o C. Velocity distribution at one sections above the trench heater were observed and the most efficient position of the heat exchanger in the heater with natural convection in the centre or at the side opposite to adjacent wall of the room was noticed. KEYWORDS PIV, capacity of heaters, air velocity distribution, EN , 1. INTRODUCTION The trench heaters are devices used for heating in places where the conventional radiators cannot be installed. The main objective of the research of the radiators is focused on the increase of their thermal efficiency (Yashar H. Cho, 2007; Peukert and Müller, 2012; Kerrigan et al., 2013). According to the new standard EN :2015 for the measurement of the output power of the floor convectors, their heating power can be measured by two methods. The first method is based on the measurement of the mass flow rate through the radiators. The second method is based on the measurement of the electric power used for the heating of the fluid. In both cases a given temperature difference must be achieved on the trench convectors via flow rate regulation. This paper is focused on the improvement of heat transfer rates in the trench convectors, the position of the heat exchanger inside the trench convectors and also the investigation of the air flow above the radiator.

2 2. MATERIAL AND METHOD A thermal performance test facility was constructed to evaluate the overall performance of the trench heater. The tests were performed in a 4 m 4 m 3 m climate controlled room, compliant with the standard EN : In order not to disturb the natural air convection airflow, air temperature inside the climate chamber was regulated by special water panels mounted on walls and ceiling. It allows for precise control of the internal air temperature. This allows to control the internal air temperature precisely. The main features of the test rig are illustrated in Figure 1. The special thermostat Presto A45 (14) was installed to keep the proper inlet temperature. The volume of water flow was controlled by an automatically balanced combination valve ABQM-15 LF (13) and measured with an inline turbine flow meter DTK-1230 (12). Flexible hoses are then fixed to the inlet, and outlet fitting of the trench heater is being tested. The Pt1000 calibrated to ±0.1 C are mounted inside the pipe at the inlet and outlet of the heat exchanger. In order to measure the room temperature, Pt1000 sensors were used at the centre of the room at vertical heights of 0.05 m, 0.75 m, and 1.50 m from the bottom, and 0.05 m from the ceiling. Pt1000 temperature sensors and the flow meter are connected to the computer and monitored in real time with software. Fig. 1.: Scheme of climate chamber: 1 trench convector, 2 laser Nd:YAG, 3 camera, 4 aerosol generator, 5 pipe of aerosol generator, 6 laser unit with cooling, 7 synchronizer, 8 control panel of laser unit, 9 desktop computer, 10 wall chamber with constant temperature of 16 o C, 11 PT1000 temperature sensor, 12 volume flow meter, 13 automatically balanced combination valve, 14 ultratermostat In order to perform the visualization of the air flow above the convector a droplets generator (4) were used. The investigated area is illuminated by continuous-wave laser (2) with wavelength 532 nm. The circular laser beam is transformed via cylindrical lens to a sheet of light. A CCD camera with a 60 mm Nikkor lens covered with a green filter (532 nm wavelength)

3 was used for image capturing. The radiator and the wall with the radiator mounted were painted with a black low reflection paint. The heat output is calculated from temperature data collected under steady state climate chamber conditions, using inlet and outlet temperature values (Eq.1-Eq.5). After the steady state conditions were obtained, approximately after 2 hours, measurements were started, and all tests lasted for one hour. where: ts = (tz + tp)/2 [ o C] m=ρ(ts)v [kg/s] cw = ts ts [J/(kg K)] Φ = m cw (tz-tp) [W] ΔT = ts - θp [K] tz inlet water temperature, [ o C], tp outlet water temperature, [ o C], ts mean water temperature, [ o C], V volume water flow, [m 3 /s], m mass water flow, [kg/s], ρ(ts) water density at the mean water temperature, [kg/m 3 ], cw heat capacity [J/(kgK)], Φ heating power, [W], ΔT temperature differences, [K], θp air temperature, [ o C]. (Eq.1) (Eq.2) (Eq.3) (Eq.4) (Eq.5) Based on variable parameters, a total of 9 measurement series were obtained (tab.1). Table 1: Measurements series Number of series Name of series ΔT [K] Location of heating coil 1 5_C 5 from the side of the chamber 2 5_M 5 in the midst of trench casing 3 5_W 5 from the wall of the chamber 4 10_C 10 from the side of the chamber 5 10_M 10 in the midst of trench casing 6 10_W 10 from the wall of the chamber 7 15_C 15 from the side of the chamber 8 15_M 15 in the midst of trench casing 9 15_W 15 from the wall of the chamber The different position of aluminium-copper coil inside the trench convector is presented in Figure 2.

4 Fig. 2.: Position of aluminium-copper coil inside the trench convector (1 aluminium-copper heat exchanger, 2 wall chamber with constant temperature of 16 o C, 3 trench casing) a) view from the side of the chamber, b) view in the midst of trench casing, c) view from the wall of the chamber 3. RESULTS AND DISCUSSION The results obtained from the PIV measurements and heat power are described in this part of the study. The presented results were obtained for three cases of inlet and outlet water temperature i.e. 75/70 C, 75/65 C, 75/60 C and three positions of the heat exchanger while maintaining the temperature of the internal air at 20 C. The measurements of air velocity were performed above the trench convector to observe the velocity and flow field of heated air above the radiator. Figures 3 5 show the velocity distribution at different heat exchanger positions and water outlet temperature. As it can be observed, the velocity distribution changes with different position of the heat exchanger. This is due to the different temperature distributions of the heat exchanger which directly effects the velocity distribution and values. Another important observation is that the velocity distribution is not symmetrical considering the mid between the two panels of the radiator as symmetry line.

5 Fig /70/20 a) coil from the side of the chamber, b) coil in the midst of trench casing, c) coil from the wall of the chamber Fig /65/20 a) coil from the side of the chamber, b) coil in the midst of trench casing, c) coil from the wall of the chamber Fig /60/20 a) coil from the side of the chamber, b) coil in the midst of trench casing, c) coil from the wall of the chamber When the heat exchanger was installed on the side of the chamber, it can have a negative effect on the outlet flow suction in the inlet flow, which decrease the thermal efficiency of the convector. Results of the other two conditions can be seen as similar, however increasing the T allows to further increase the efficiency of the model with coil mounted on the side of the wall of the chamber compared to the other models. Figure 6 shows plots of the correlation between heat capacity compared with temperature differences T. Fig. 6.: Correlation between heat capacity ϕ compared with temperature differences ΔT

6 4. CONCLUSION The laboratory measurements of heating performance of the trench heaters were performed. First result of measurements was already obtained and was already included into the current R&D processes. 5. ACKNOWLEDGMENT The present study is supported financially by the Lublin University of Technology under Grant number 130/WIS/2016 and also VERANO Ryszard Miazga. We are gratefully acknowledged. REFERENCES Kerrigan K., Jouhara H., O Donnell G. E., Robinson A.J., 2013, A naturally aspirated convector for domestic heating application with low water temperature sources, Energy & Buildings, vol. 67, No 4, str Yashar H. Cho, Air-Side Velocity Distribution in Finned-Tube Heat Exchangers, U.S. department of commerce National Institute of Standards and Technology, Maryland, 2007 Peukert P., Müller M., 2012, Measurement of floor convectors at special laboratory and first results, EPJ Web of Conferences, vol. 25, No 9, str EN : , Fan assisted radiators, convectors and trench convectors - Part 2: Test method and rating for thermal output