Thermal Environment in a Space with Capillary Mats Large-Area Cooling and Heating

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1 Thermal Environment in a Space with Capillary Mats Large-Area Cooling and Heating Vladimír Zmrhal Czech Technical University in Prague, Faculty of Mechanical Engineering Corresponding Vladimir.Zmrhal@fs.cvut.cz SUMMARY Radiant cooling and heating is relatively efficient system, which can be used to achieve optimal thermal comfort. The airflow, which is supplied into the room, can be reduced to minimal amount of the fresh air. Theoretically, the radiant heat transfer between body and surroundings is preferable than convection heat transfer in the view of thermal comfort achieving and energy consumption [3]. The paper analyses the experimental results of the thermal environment conditions measuring of large-area heating and cooling systems. The potential of using low- heating and high- cooling systems with capillary mats is presented. The capillary tube mats system is relatively new radiant system for heating and cooling, which is used especially in Western Europe, and nowadays also in Central Europe (Czech and Slovak Republic). One of the system using possibilities large area heating and cooling system is described in the paper. KEYWORDS Radiant heating and cooling, capillary tube mats, thermal environment. INTRODUCTION The capillary tube mats are composed from the net of the thin plastic tubes ( 3.5 mm) from polypropylene into the heated or cooled water is supplied. There is a very short distance (1 3 mm) between the capillary. Small water difference (2 4 K) cause practically uniform distribution of surface. Most often the capillary mats are placed on the ceiling under the plaster, but they can be installed on the walls or on the floor. Due to small diameter of capillary tubes, the thickness of the plaster is acceptable 1 15 mm, what makes it possible rapid thermal reaction of the system to boundary conditioning changes. Capillary mats system can be used practically in any building. The system is advisable for new buildings (low energy buildings, family houses, flat buildings), but also for building reconstruction. While the supply water for cooling is limited by the risk of condensation on the walls, the limited factor for heating is radiant asymmetry. Capillary mats from polypropylene make possible to use maximal operating up to 65 C. Common supply water for radiant heating systems is about 4 C to not exceed maximal surface of the floor. The supply water for cooling is mostly higher than 16 C to risk of condensation prevent. Temperature difference between supply and return water is commonly 2-4 K. Large heat transfer area allows heating with low water. In relation to small heat loss of the building (low energy buildings) the of heating water can be close to air

2 in the room. On the contrary the cooling can operate with high water (up to 24 C) [4]. 1 CEILING STRUCTURE 2 THERMAL INSULATION (3 mm) 3 PLASTER WITH CAPILLARY MATS (1-15 mm) a) b) Figure 1. Capillary mats a) detail of capillary tube mat, b) cross-section of the ceiling Radiant systems allow only sensible heat load removing. The heat transferred between surface (t s surface ) and the space (t i indoor ) for heating and cooling is indicated in Table 1. Table 1. Heat transferred between surface and the space for radiant heating and cooling by capillary mats Heating q [W/m 2 ] Cooling q [W/m 2 ] t s t i [K] Vertical walls Floor Ceiling Figure 2. Installation of the large area capillary mats system with thermal insulation on the walls and ceiling

3 MEASUREMENT The measurement was carried out in the low-energy house (Figure 3) in the village Zapy near to Prague [2]. The external wall of middle-heavy house was build out of thermo-insulated building system. Radiant heating and cooling system with capillary mats is placed on every wall including ceiling and floor (Figure 2). Moreover, the additional insulation is added between the walls and capillary mats to minimize accumulation effect (Figure 1b). The large heat transfer area and low heat loss of the house (4.7 kw) allow to heat up with mean water close to air in the space. Layout of the house is visible in figure 4. Two small air handling unit with heat recovery provides the ventilation of the house (the air flow rate in ground floor is 28 m 3 /h, in 1 st floor 8 m 3 /h). Air valves execute the air distribution in the rooms. There was no furniture in the house during the measurement and the roller curtains were on the windows. Figure 3. Experimental house in Zapy [2] The thermal environment measurements were installed in the room no. 2.1 (south) and 2.5 (north). In the middle of the each room the special multiple probes were placed for vertical distribution measurement. There were used Pt1 sensors (class A) with minimal proportions (1.6 x 3.2 x 1. mm). Each of multiple probes contains 1 sensors for air measurement. Also surface s of each active wall in the room were measured. For data collection the data logger Ahlborn ALMEMO was used. The globe, air and relative humidity were measured in the high of 1.1 m over the floor. During the measurement the surface s, supply and return water s (heating and cooling), and outdoor conditions (ambient, relative humidity and solar irradiation) were also monitored. The layout of the measurement is visible in figure 4. The measurements were carried out from February till August 26.

4 2.7 STAIRS 5,75m2 ROOM 2.1 2,m2 2.3 HALL 4,8m2 WINTER GARDEN 1. 6,45m2 BEDROOM ,4m2 2.4 BATHROOM 8,24m2 2.5 FITNESS/ HOBBY 17,7m2 Figure 4. Layout of the 1 st floor including the location of measurement instruments RESULTS AND ANALYSIS Figure 5 show the course of external climatic conditions (ambient t e and solar irradiation G), operative and mean water during specific week interval in winter (Figure 5a) and summer (Figure 5b). As it is visible in figure 5b, the room no. 2.5 is heated up to higher (21 C) than room no. 2.1 (2 C). While the operative in the north room (2.5) is practically stable, in the south room (2.1) the fluctuation is visible during a day caused by direct solar irradiation. The similar situation is visible during the summer (Figure 5b), but in this case the operative is higher. Generally the operative s during extreme climatic conditions (ambient t e and solar irradiation G in Czech Republic) not exceed 27 C. Since the long-term monitoring of the thermal environment in the room, the results were analysed statistically. The results of the measurement during the winter and summer interval are summarised in tables 3 and 4. The tables 3 and 4 present the percentage of hours in a specific interval. The operative was evaluated for air velocity w <.2 m/s, because there was no source of mechanical ventilation during the measurement. Mean surface presents the measured surface of active walls with capillary mats on average. The effect of the transparent surfaces (windows) implicate mean radiant t r, which is determined from globe t g. Supply water t w1 and return water t w2 were monitored close to heat exchanger, which is placed between the heat source and heating system.

5 Ambient t e [ C] 5-5 te [ C] G [W/m2] Solar irradiation G [W/m 2 ] Ambient t e [ C] te [ C] G [W/m2] Solar irradiation G [W/m 2 ] Operative [ C] to (room 2.1) to (room 2.5) RH [%] Relative humidity [%] Operative [ C] to (room 2.1) to (room 2.5) RH [ C] Relative humidity [%] Supply Temperature - tw1 Supply - tw1 Water Temperature t w [ C] Return Temperature - tw2 NO MEASUREMENT NO MEASUREMENT Water Temperature t w [ C] Return Temperature - tw a) b) Figure 5. The course of outdoor climatic conditions (t e, G), operative (t o ), and water (t w1, t w2 ), for selected week a) winter, b) summer As table 3 presents, for the operative achieving in the room with large area heating the of supply water is very close to the room air, maximally 26 C. Mentioned fact is visible especially for the room no. 2.5 (north), where the return water corresponds to indoor air. The heat loads from external environment in south room (2.1) are greater than in the north facing room (2.5), therefore the operative can exceed 24 C in this room. During the summer (Table 4) the effect of heat load from outdoor environment is present. The operative sometimes exceeds 26 C, but the cooling water is close to air in the room.

6 Table 3. Percentage of hours in a specific interval during winter (from 8 th February till 5 th April 26) 2.1 bedroom 2.5 fitness, hobby from [ C] till [ C] Operative temp. 35,3 52,9 7,5 4,2,2 99,4,5 Air 46,1 45, 7,9,92,5 99,5 Mean surface temp. 34,5 59,7 5,6,2,7,4 98,9 Supply water temp. 22, 38,9 39, 22, 38,9 39, Return water temp.,1 98,3 1,6,1 98,3 1,6 Table 4. Percentage of hours in a specific interval during summer (from 12 th June till 3 th August 26) 2.1 bedroom 2.5 fitness, hobby from [ C] till [ C] Operative temp. 12,7 5,5 34,4 2,4 1,5 56, 32,3 1,2 Air 13,8 54,4 29,8 1,9 1,7 58,7 29,7,9 Mean surface temp. 14,8 59,1 24,9 1,2 12, 63,9 23,8,3 Supply water temp. 27,5 62, 9,2 1,4 27,5 62, 9,2 1,4 Return water temp.,1 4,3 51,9 41,6 2,2,1 4,3 51,9 41,6 2,2 Vertical distribution Figure 6 present the vertical distribution in investigated rooms with capillary mats. Due to different room high H (2.7 m in the room 2.1 and 2.4 m in the room 2.5), the y-axis in figure 6 is dimensionless. Dimension h is high of the measurement point over the floor. Vertical distribution is represented by mean air during the steady state. Together with profile the globe is presented in Figure 6. Table 5 presents the measurement conditions for vertical profiles (Figure 6). Mean air represents outdoors air on average from 7. am till 7. pm. The mean surface include the of all active surface with embedded capillary mats in measurement rooms during the steady state. Mean water s were evaluated during 24 hours. Table 5. Measurement condition for selected days Date Mean air Mean supply water Mean return water Mean surface (room 2.1) Mean surface (room 2.5) t a [ C] t w1 [ C] t w2 [ C] t p1 [ C] t p2 [ C] Winter 21 st Feb.,8 23,8 21,5 2,2 21,3 Spring 18 th May 16,4 21,2 21,3 2,9 2,9 Summer 3 rd July 22, 21,7 22,7 23,4 22,7 Temperature profiles in Figure 6 show the straight vertical distribution for every season. As mentioned above, the room no. 2.5 is heated up to higher air than room no Mentioned fact is also visible in table 5. Mean surface in the room no. 2.1 is lower than in the room 2.5, but the difference is only 1.1 K. In winter the slight slope of the profiles is visible, what is caused by water distribution in the

7 surrounding walls (down from top). Figure 6 also present the globe t g in the space. The globe is higher than air and corresponds to mean surface (Table 5). The effect of the cold window is practically insignificant in measurement positions. Vertical profiles during the spring (Figure 6b) are well balanced and practically the same. Mean surface s for both rooms are identical and also the difference between supply and return water is very small (Table 5). In this time the rooms are not heated, but occasionally cooled. The globe in the room no. 2.1 is slightly higher than air, what is caused by higher surface of surrounding walls. Typical vertical profile in summer is presents in figure 6c. Also in this case the straight vertical profiles are visible. Direct solar irradiation causes the higher air and global in the room 2.1. As it is shown in table 5 also the surface in the room 2.5 is slightly higher. In the room 2.5 with north orientation, which is not affected by direct solar irradiation during a day, the surface corresponds to return water (Table 5) and the difference between surface and air is very small (Figure 6c). The global in the room 2.5 practically corresponds to the air (+,1 K). 1,9 21/2/26 1,9 18/5/26 1,9 3/7/26,8,8,8 High over the floor h / H [-],7,6,5,4,3,2 tg 2.5,1 tg 2.1 h=,1 m 19, 2, 21, 22, 23, Air t a [ C] a) tg 2.1 High over the floor h / H [-],7,6,5,4,3, tg 2.5,1 tg 2.1 h=,1 m 2, 21, 22, 23, 24, Air t a [ C] b) tg 2.1 High over the floor h / H [-],7,6,5,4 2.1,3 2.5,2 tg 2.1 tg 2.5,1 tg 2.1 h=,1 m 22, 23, 24, 25, 26, Air t a [ C] c) Figure 6. Typical vertical distribution in the room with embedded large-area cooling and heating system a) winter day, b) spring day, c) summer day CONCLUSION The presented vertical profiles in a space with capillary mats heating and cooling looks like optimal distribution in a room, what is caused by large heat transferred area of the presented system. Large heat transfer area allows also heating with low water and cooling with high water. In relation to small heat loss and heat

8 gains of the building (low energy buildings) the mean of heating or cooling water can be close to air in the room. Mentioned fact allows applying of low energy or alternative heat sources as heat pump (air water, water water and ground water) with high coefficient of performance COP and efficiency of energy recovery EER. The using of capillary tube systems in relation to low energy heat sources can provide optimal indoor thermal environment without great demands on energy consumption. ACKNOWLEDGEMENT This paper is integrated in the framework of CTU Research Aim MSM REFERENCES [1] ASHRAE Handbook 1996 Systems and Equipment. 1996, Atlanta: ASHRAE. ISBN [2] Instaplast Praha a.s., Home page Instaplast - NERD, updated Available in: < [3] ZMRHAL V. Thermal Comfort and Energy Balance of the Cooled Ceiling System. 25, Doctoral Thesis, Czech Technical University in Prague. [4] ZMRHAL V. Tepelné prostředí v prostoru s kapilárními rohožemi (in Czech). In: Vytápění, větrání, Instalace Společnost pro techniku prostředí, 27, pp