Available online at www.sciencedirect.com ScienceDirect Energy Procedia 78 (2015 ) 1093 1098 6th International Building Physics Conference, IBPC 2015 Verifying a need of artificial cooling - a simplified method dedicated to single-family houses in Poland Hanna Jędrzejuk a *, Joanna Rucińska b a Warsaw University of Technology, Institute of Heat Engineering, Nowowiejska 21/25, Warsaw 00-665, Poland b Warsaw University of Technology, Faculty of Environmental Engineering, Nowowiejska 20, Warsaw 00-653, Poland Abstract This paper presents a simplified comparative method supporting decision-making process if a particular construction of a singlefamily house involves applying artificial cooling. A variety of building constructions are applied in the case of single-family houses, some of which actually require cooling so that the internal thermal comfort can be provided, as a result of specific dynamic properties of a building. A normalised relative standard deviation of the operative temperature and normalised internal heat capacity were selected as important parameters. To solve the problem the simplified 5R1C model was applied and various methods of overheat protection were tested. 2015 The Authors. Published by by Elsevier Elsevier Ltd. Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the CENTRO CONGRESSI INTERNAZIONALE SRL. Peer-review under responsibility of the CENTRO CONGRESSI INTERNAZIONALE SRL Keywords: optimisation; simulation; internal thermal comfort; Nomenclature A f surface area of a thermally conditioned space, m 2 A m internal heat transfer surface area, m 2 C m internal heat capacity, J/(K m 2 ) I tot mean hourly solar radiation per unit area, Wh/m 2 * Corresponding author. Tel.:+48-22-234-7257 ; fax: +48-22-825-0565. E-mail address: Hanna.Jedrzejuk@itc.pw.edu.pl 1876-6102 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the CENTRO CONGRESSI INTERNAZIONALE SRL doi:10.1016/j.egypro.2015.11.061
1094 Hanna Jędrzejuk and Joanna Rucińska / Energy Procedia 78 (2015 ) 1093 1098 n number of hours during the summer period, h y selected physical quantity y max maximum value of the physical quantity y n normalised physical quantity Q c annual useful energy demand for cooling, kwh/year θ op operative temperature, C θ limit,c limit operative temperature in the summer period, C θ op,c mean operative temperature in the summer period, C op,c - set-point (expected value) of the operative temperature in the summer period, C 1. Introduction Following political and economic changes, new technologies have been introduced in housebuilding industry in Poland for the last twenty-five years; these technologies have reduced building time and costs, and provided for better thermal performance of the building envelope. At the same time, architectural concepts have significantly evolved, e.g. the glazing-to-wall ratio has increased. Occupancy conditions of an attic, being a thermal buffer zone in traditional designs, have also changed. At present, attics in most single-family houses are habitable, and windows are frequently mounted in pitched roofs. As a consequence, building dynamic properties have changed, and solar heat gains have considerably increased. This is why single-family buildings are increasingly equipped with cooling systems. This type of additional equipment significantly influences the building s energy performance assessment which, under legal regulations, should be provided in the form of a certificate. In this connection, the paper presents a simplified method of analysing, as early as during the design phase, how various building constructions affect the need to equip single-family buildings with cooling systems. Operative temperature and internal heat capacity were proposed as verification criteria; the number of hours when the operative temperature exceeds the limit was defined for various building constructions, and the relative standard deviation was calculated. The proposed assessment method is closely related to the adopted mathematical model of a building, so the model will be described in the first place. 2. Simplified mathematical model of a building A quasi-static method of monthly balances is used to assess energy performance of buildings in Poland [11]. However, since dynamic processes had to be considered, a simplified model with concentrated heat capacity, 5R1C, was adopted [8]. It should be emphasized that both the method of monthly balances and the hourly method without heat coupling between zones require a similar number of building parameters. The hourly method has a considerable advantage in that calculations can be performed in any spreadsheet, and their results provide better dynamic description of heat transfer processes [7]. The dynamic method which was adopted for the purpose of the analysis allows us to determine the energy demand for heating or cooling and the internal, mean radiant and operative temperatures on an hour-by-hour basis. 3. Verifying the necessity for cooling Indoor conditions determine whether or not cooling systems are required. To assess the indoor conditions, widely known models are commonly used: Fanger [3], Pierce (modified) [4], and KSU [1]; owing to their level of detail and complex process description, the quality of indoor climate can be representatively assessed. The 5R1C [8] model provides an operative temperature θ op as a weighted average of the air and mean radiant temperatures; this quantity was assumed to be a criterion of the necessity for cooling.
Hanna Jędrzejuk and Joanna Rucińska / Energy Procedia 78 (2015 ) 1093 1098 1095 4. Methodology The proposed method assumes that the only parameters to consider are those required for calculations and those for which the hourly values are determined using the simplified 5R1C [8] method. The internal heat capacity and operative temperature were chosen as basic parameters. The internal heat capacity C m affects the rate of heat transfer processes, and it characterises the dynamic properties of the building construction. Furthermore, the operative temperature θ op reflects, in a very simplified way, thermal comfort conditions, and is influenced by time-dependent factors: external climate, internal gains, effects of the shadowing elements, and the air flow caused by the ventilation system. That is why it could be treated as a complex parameter. A human body can adapt to perceived temperature; it has been found that changes in this temperature exceeding only 1 K can result in discomfort [2]. Hence, a conclusion was drawn that a representative assessment can be performed on the basis of the relative standard deviation (RSD) of the perceived temperature in the summer period. To provide the simulation according to the 5R1C [8] methodology, the external climate conditions in the location of the building must be given. They must be defined at least at the national level to guarantee that the results are representative and comparable. Additionally, the hourly values of the internal gains are necessary so that the specific building operation can be reflected. This specific data include: metabolic heat from occupants; heat dissipated from appliances; heat dissipated from lighting devices; heat dissipated from or absorbed by hot and mains water and sewage systems; heat dissipated from or absorbed by heating, cooling and ventilation systems; and heat supplied by or released to processes and goods. Based on the operative temperatures obtained from the simulation, the relative standard deviation (RDS) in the summer period can be calculated: RDS n op,i op,c 2 n 1 op,c if op,i lim it,c (1) Depending on the amount of building data available, a summary of internal heat capacities of the buildings concerned and the resulting values of RSD in the summer period can be easily provided. Verifying a design consists in determining selected building performance parameters, i.e. internal heat capacity C m, and RSD of the operative temperature in the summer period, and comparing them to the performance of other buildings of which internal climate parameters are known. Comparing different quantities requires normalisation: y n y y max (2) 5. Example A two-storey single-family building was analysed with a conditioned space area of 200 m 2, located near Warsaw in central Poland. The building is inhabited by four residents. Required hourly data for determining the outdoor conditions were adopted from typical statistical climate data for the Polish area for building energy performance purposes [12], which ensures compliance with the methodology of building energy performance assessment [11]. The required indoor temperature during the heating season was assumed to be 20 C [10]; during the summer period it cannot exceed 26 C [9]. All values concerning thermal performance of envelope elements and the required glass area were established according to current requirements ([10], [11]).
1096 Hanna Jędrzejuk and Joanna Rucińska / Energy Procedia 78 (2015 ) 1093 1098 The quantities and schedules for indoor heat gains were adopted as in a typical reference single-family house designed on the basis of statistics by National Energy Conservation Agency in Poland [7] and verified according to national regulations [11]. The following values were assumed: heat gains from lighting 5.0 W/m 2, from electrical equipment 3.14 W/m 2, and from occupants 50 W per occupant. The artificial lighting is switched on when the light is needed for the activity of the occupants and when the total (direct normal and diffuse) solar irradiance on a horizontal surface is below 70 W/m 2. A possibility to decrease solar gains was provided by applying shading devices, operated periodically, when the mean hourly solar radiation exceeds 200 Wh/m 2. The shading effectiveness was assumed as 50%. In the 5R1C model the dynamic properties of a building are described by the internal heat transfer surface area (A m) and the internal heat capacity (C m). Data used in calculations are listed in Tab. 1. Both the properties indicated in PN-EN ISO-13790 [8] and those traditionally describing buildings in Poland (ultra heavy class) are included. Table 1. Internal heat capacity [8]. Type Building class Internal heat transfer surface area A m, (m 2 ) Internal heat capacity C m, (J/K) A Very light 2.5 A f 80 000 A f B Light 2.5 A f 110 000 A f C Medium 2.5 A f 165 000 A f D Heavy 3.0 A f 260 000 A f E Very heavy 3.5 A f 370 000 A f F Ultra heavy (PL) 3.5 A f 500 000 A f The classification listed in Tab. 1 is simplified. It describes the internal heat capacity and the internal heat transfer surface area as functions of the heated or cooled area [8]. In the case of existing buildings the classes could comprise the following constructions: class A timber-framed building, walls filled with thermal insulation; class B wooden construction; class C closely ribbed ceilings and lightweight concrete walls; class D heavy slabs; class E concrete construction, clay block walls; class F concrete construction, sand-lime brick walls. For each building class, calculations were performed twice: without and with periodical operation of shading devices. A sample operative temperature trend in various types of buildings is shown in Fig. 1. 32,0 31,0 Operative temperture ( C) 30,0 29,0 28,0 27,0 26,0 25,0 24,0 5424 5448 5472 5496 Time (hour of the year), (h) A [ C ] B [ C ] C [ C ] D [ C ] E [ C ] F [ C ]
Hanna Jędrzejuk and Joanna Rucińska / Energy Procedia 78 (2015 ) 1093 1098 1097 Fig. 1. Operative temperature trend in buildings A, B, C, D, E and F period: 14 August (11p.m.) 17 August (11 p.m.). The effect of applying periodical shading on cooling power in the building with the lowest internal heat capacity is illustrated in Fig. 2. -3500-3000 Cooling power, ( W) -2500-2000 -1500-1000 -500 0 5424 5448 5472 5496 Time (hour of the year), (h) A F A1 F1 Fig. 2. The effect of periodically operated shading devices on cooling power in buildings A, A1, F, and F1. The results are listed and compiled in Tab. 2 and Fig. 3. The data in the table were supplemented with values obtained via simulation [5]. Next, the heat capacity and RSD of operative temperature in the summer period were normalised according to the equation (2). Type of building Table 2. Performance of the buildings. Internal heat capacity, C m, Normalised internal heat capacity, C m,n Relative standard Normalised relative standard Energy demand for cooling the (J/K) (J/(Km 2 )) deviation in deviation in the building, Q c, the summer summer period, (kwh/year) period, RDS RDS n A *) 16 000 000 0.160 2.278 1.000 2714.1 B *) 22 000 000 0.220 1.890 0.830 2650.1 C *) 33 000 000 0.330 1.622 0.712 2588.0 D *) 52 000 000 0.520 1.497 0.657 2503.8 E *) 74 000 000 0.740 1.486 0.652 2431.9 F *) 100 000 000 1.000 1.454 0.638 2364.2 A1 **) 16 000 000 0.160 1.423 0.625 1235.2 B1 **) 22 000 000 0.220 1.238 0.543 1162.1 C1 **) 33 000 000 0.330 1.039 0.456 1075.0 D1 **) 52 000 000 0.520 0.908 0.399 981.8 E1 **) 74 000 000 0.740 0.854 0.375 909.7 F1 **) 100 000 000 1.000 0.772 0.339 848.2 Building X1 *) 24 636 037 0.246 1.720 0.755 - Building X2 *) 46 482 514 0.465 0.990 0.435 - Building X3 *) 62 979 024 0.630 0.770 0.338 -
1098 Hanna Jędrzejuk and Joanna Rucińska / Energy Procedia 78 (2015 ) 1093 1098 Building X4 *) 69 273 745 0.693 0.690 0.303 - Max = 100 000 000 Max = 2.278 *) - shading not provided; **) - shading provided if I tot > 200 Wh/m 2. Normalised relative standard deviation in the summer period 1,000 A 0,900 0,800 B 0,700 C 0,600 A1 X1 D E F B1 0,500 C1 0,400 D1 E1 X2 F1 0,300 0,200 0,100 0,000 0,000 0,100 0,200 0,300 0,400 0,500 X3 0,600 X4 0,700 0,800 0,900 1,000 Normalised internal heat capacity Fig. 3. Verification of the solutions. 6. Conclusions The paper proposes a simple comparative method for assessing the need to apply cooling systems. The example shown relates to Polish conditions but the method can also be applied in other locations and under different conditions. Tests of typical buildings (in Poland) provide grounds for an assumption that designs featuring normalised RSD of temperature in the summer period below 0.660 (absolute value 1.5), and the normalised internal heat capacity of 0.45 will require no cooling systems provided that basic measures protecting from overheating are in place. This method, however, needs to be further verified. References [1] Azer N.Z., Hsu S. The prediction of Thermal Sensation from Simple model of Human Physiological Regulatory Response, ASHRAE Trans., Vol.83, Pt 1, 1977. [2] Chojnacka A. Determination of thermal comfort conditions in rooms using PMV and PPD indicators (in Polish), Bezpieczenstwo Pracy, 5/2007, pp. 19-23. [3] Fanger P.O., Thermal Comfort-Analysis and Applications in Environmental Engineering, Danish Technical Press, Copenhagen, 1970. [4] Fountain M.E., Huizenga C. A Thermal Sensation Prediction Tool for Use by the Profession, ASHRAE Trans., Vol.103, Pt 2, 1997. [5] Jedrzejuk H, Dybinski O The influence of a heating system control program and thermal mass of external walls on the internal comfort in the Polish climate (not published). [6] Kwiatkowski J., Mijakowski M., Sowa J. Reference single family house by NAPE (NECA) (in Polish) (http://www.nape.pl/). [7] Mijakowski M., Narowski P., Sowa J.: Integrated calculations of thermal behaviour of buildings and processes in AHU - the tool for assessment of energy performance of complex buildings, Eleventh International IBPSA Conference Glasgow, Building Simulation 2009, Scotland July 27-30, 2009. [8] PN-EN ISO 13790:2008 Energy performance of buildings. Calculation of energy use for heating and cooling (in Polish). [9] PN-B-03421:1978 Ventilation and air conditioning - Calculation parameters of indoor air in rooms intended for permanent human habitation (in Polish). [10] Ordinance of Minister of Infrastructure on the technical requirements for buildings and their location from 12 th April 2002 [11] Decree of the Minister of Infrastructure and Development on the methodology for calculating the energy performance of buildings and dwelling or building which is part of the whole technical self-utility, and the preparation and presentation of certificates of energy performance from 2 nd July 2014. [12] Typical statistical climate data for the Polish area for building energy performance purposes, Ministry of Infrastructure and Development (in Polish), (http://www.mir.gov.pl/budownictwo/rynek_budowlany_i_technika/efektywnosc_energetyczna_budynkow/typowe_lata_meteorolo giczne/strony/start.aspx ).