Indoor thermal comfort by controlling heat transfer through building envelope

Transcription

1 Indoor thermal comfort by controlling heat transfer through building envelope DANIEL POPESCU 1 and CALIN CIUFUDEAN 2 1 Electrical Engineering Department Technical University of Civil Engineering Bucharest Bd. Pache Protopopescu nr.66, Bucuresti Sector 2 ROMANIA dpopescu@instal.utcb.ro 2 Computers and Control Systems Department Stefan cel Mare University of Suceava Str. Universitatii nr.9, Suceava ROMANIA calin@eed.usv.ro Abstract: The assurance of thermal comfort in buildings with heating / cooling installations distributed on the surface is the best common solution. This article proposes a new approach for analyzing the heat transfer through building envelope. Our approach consists in a distributed area of electro-thermal pumps over the building envelope capable to create antagonist thermal fluxes to those that appear naturally. In this way we can easily control the inside temperature by balancing the dynamic of heat transfer. The electro-thermal pump works by relying on the Peltier Seebeck effect. The thermal flux direction is given by the electric current direction. Building envelope equipped with electro-thermal pumps is the process who must to be controlled automatically by temperature control system dedicated. The goal of this new concept is to optimize the thermal comfort, eliminate the moisture condense on the walls and reducing the energy consumption by controlling the building s envelope temperature. Key-Words: thermal comfort, heat transfer, building envelope, HVAC (heating, ventilation, and air conditioning), automatic control of heating systems of buildings, thermoelectric systems, electro-thermal pump. 1 Thermal comfort in buildings with heating / cooling installations distributed on the surface 1.1 Temperature profiles and distributed heat sources in buildings Energy saving for heating/cooling buildings requires a fair thermal insulation of the buildings. On the other side there is a maximum optimal size of the thermal insulation. Inner thermal sources balance heat loss and keep up to the required comfort parameters. These sources are concentrated in certain areas (heating radiators, fan coil), therefore the comfort parameters may vary in different places under discontinuous functioning regimes. Therefore, distributed heat sources made in floor, ceiling or walls are increasingly used [1, 10]. 1,80 m 0,10 m Ideal Underfloor heating heating Radiator outer wall Radiator inner wall Fig.1 The temperature profile from floor to ceiling ISBN:

2 Latest Advances in Information Science, Circuits and Systems Figure 1 shows temperature profile from floor to ceiling for ideal heating system, with temperature profiles for under floor heating and wall mounted radiators [2, 3]. Note that the floor heating system ensures the best thermal comfort in building. 1.2 The thermal insulation of surface for heating / cooling Thermal insulation of floors used as surface heating/cooling must accomplish certain requirements, depending on the location in the building floor (below room temperature) [2]: a) surface heating above a heated room ( 200C); b) surface heating above a room heated in irregular intervals ( 150C); c) surface heating above a cellar (unheated basement) ( 80C); d) surface heating in direct contact with outside air or ground; Figure 4 shows how to make the thermal insulation for heating / cooling systems, the first two cases [2]: a) Surface heating above a heated room (Fig.3,a) - Insulation layer 35mm - Thermal resistivity R 0,75 (m² K) / W b) Surface heating above a room heated in irregular intervals (Fig.3.b) - Insulation layer 35 mm - Additional insulation layer 20 mm - Thermal resistivity R 1,25 (m² K) / W Figure 2 shows how to make the system of heating / cooling floor [2]. hb + 20 C he + 20 C hd Fig. 2 Under floor heating in a room Desire to improve indoor thermal comfort in buildings led in some cases to achieve the system as wall heating / cooling (Fig.3). Under floor heating elements are suitable for wall heating/cooling systems. a) hb = Floor covering hd = Insulation layer he = Screed hb he + 20 C hd + 15 C hz b) hb = Floor covering hd = Insulation layer Fig. 4 Under floor heating - thermal insulation Fig. 3 Wall heating system ISBN: he = Screed hz = Additional insulation 151

3 Heating or cooling surfaces made in floor, ceiling or walls can contribute to heat transfer through building envelope. Temperature [ 0 C] Volume flow [m 3 /h] 2 Improving temperature control systems performance for heating under floor Under floor heating system is designed to ensure room temperature of 20 0 C if the temperature of thermal agent in the flow pipe is C. The occurrence of additional heat input into the building (eg the sun) will lead to overcoming the room temperature of 20 0 C and, therefore, the room thermostat will stop the under floor heating for a while (Fig.5). According to the classical method of control, the under floor heating circuit is closed and the flow of thermal agent is zero (Fig.6). Room temperature will drop to a value of 20 0 C and the under floor heating must start now. Total absence of heat flow (thermal agent with flow zero) has cooled too much the floor and the time response to turn on the under floor heating is too large. The overshoot may be unacceptable and floor temperature may be too high during certain periods of time; human health may be affected, increase comfort and decrease energy consumption of building heat. 30 % outside heat 30 0 C 20 0 C Under floor temperature Volume flow Heating circuit closed Fig. 6 Under floor heating with room thermostat Current requirements increase thermal comfort in buildings, along with requirements to reduce energy consumption for heating led to the use of an automatic control method for under floor heating system, where the residual flow heat in the under floor heating circuit remains constantly [2,4] when the system is stopped (Fig.7, 8). 30 % outside heat T = 21 C > T set Heat flow from the floor surface = 70 % Time T = 21 C > T set Heat flow from the floor surface = 0 % Preset table Thermostat Heating circuit closed Operation with secondary heat source - no flow rate in the heating circuit - floor surface is cooling down Fig. 5. Regulation of the under floor heating by using the room temperature control Heating circuit open Operation with secondary heat source - Thermostatic valve closed - Bypass open Fig. 7 Regulation of the under floor heating by using the preset table bypass The preset table bypass provides a constant residual flow in the circuit and therefore a minimum floor temperature. It reduces the time for heating up by 1 ½ h [2]. ISBN:

4 30 0 C 20 0 C Temperature [ 0 C] Volume flow [m 3 /h] Under floor temperature Volume flow Heating circuit partially closed 30% residual flow Time Thermoelectric HVAC enables the use of distributed cooling/heating units that cool/heat the occupants rather than the whole cabin and its components [10]. Fig. 8 Under floor heating with preset table bypass The preset table bypass prevents the floor from cooling down too much, in case of the thermostat isolating the heating circuit due to a secondary heat source [2]. 3 Electro-thermal pump distributed on the surface Thermoelectric materials may have an important role for a global sustainable energy solution. The electro-thermal pump (Fig. 9) works by relying on the Peltier Seebeck effect: on an electrified serial junction of two different metals (e.g. metals with different electron charges) we obtain different temperatures, respectively on obtain heat flow. The electro-thermal pump distributed on the surface as is composed of semiconductors plates applied on the inner surfaces of the walls has no kinetics elements and also occupies little spaces. The heat transfer through the building s envelope depends on the electric current intensity delivered by the thermal elements and is controlled by a computerized control unit. The electro-thermal pump is reversible: the thermal flux direction is given by the electric current direction. In present, a lot of projects were selected to accelerate the development of thermoelectric systems that provides the heating, ventilation, and air conditioning (HVAC) for automotive industry. The use of solid state thermoelectric devices to heat and cool a vehicle s passenger compartment can increase vehicle efficiency by reducing engine load, by reducing or eliminating the need for conventional air conditioning refrigerants, these vehicles further reduce greenhouse gas emissions. Fig. 9 Electro-thermal pump While applicable to all commercial and passenger vehicles, thermoelectric HVAC is particularly attractive for hybrids and plug-in hybrids where an electrically driven air conditioning system can maintain occupant comfort even when the engine turns off. Research direction is to develop a system thermoelectric HVAC that provides thermal comfort equivalent to current HVAC systems while using significantly less energy. The thermoelectric system components will be integrated into a demonstration vehicle for testing and evaluation. 4 Automatic control of heat transfer through building envelope Indoor thermal comfort and energy consumption of buildings depends on the heat transfer by building envelope [5]. ISBN:

5 4.1 Infrared thermograph method of building envelope Between the period at the Technical University of Civil Engineering Bucharest was developed a research grant concerning the automatic control of heating systems of buildings by measuring the heat transfer through outside bulding surfaces. As a result of the research work for this grant there have been designed and implemented an automat control system that measures the heat transfer through the building walls [6, 7. 8]; so that one may thermo graphically measure the temperature of the exterior walls and by converting from analog to numeric the measured values one may control the thermal confort through a computerized system which control the debit of thermal agent inside the bulding. Automatic control basically consists on regulating the flow of the thermal agent as a function of heat loss through the exterior walls of the building. In order to have an accurate control one may have to supervise the temperature fluctuation at the surface of the exterior walls. This process involves experimentally charting the temperature of the exterior walls and memorizing it into the computerized control systems, such that any changes in temperature distribution through the walls surface is sesized by the control system which will act on the thermal agent debit accordingly [8]. 4.2 Automatic control of heat transfer through building envelope with electrothermal pump distributed on the surface This article proposes a different approach for thermal transfer through buildings envelopes [9], namely by surface distributed electro-thermal pumps which control heat transfer through envelope. The above-mentioned approach is possible by heating thermal flows opposite to natural flows which will determine a controlled temperature balance of the building s inner walls. This new approach will ensure the thermal comfort as an alternative to the conventional heating methods of buildings. The solution is based on achieving an electro pumps distributed on the surface, which controls the heat transfer through the building s envelope. This new approach will ensure the thermal comfort as an alternative to the conventional heating methods of buildings eliminate condensation in walls and reducing energy consumption in buildings through building envelope temperature control. It acts directly on the building envelope that is the part of the building which loses heat to the outside. The thermoelectric elements are placed on different types of materials constituting the walls of buildings in order to obtain a homogeneous temperature distribution. For walls equipped with thermoelectric elements heat transfer is evaluated by thermograph method. Among those models who we studied, we choose those that could withstand the winter and summer weather, i.e. heating and cooling regimes and determine the extreme limits of operation. The building envelope equipped with electrothermal pumps is the process to be controlled automatically with a dedicated temperature control system. 5 Conclusions The new concept proposed allows obtaining the same temperature inside the building envelope, regardless of the orientation of the walls, so basically dynamics of heat transfer through the inner walls of the building depends only on evolution of internal sources of heat. Thermal insulation of building envelope can be greatly reduced. By adjusting the building envelope temperature is obtained a good indoor thermal comfort, is eliminated the condensation in walls and energy consumption in building is reducing. Control of heat transfer through building envelope by using electro-thermal pumps distributed on the surface can replace total or partial traditional heating / cooling systems, remain to be used only fresh air-conditioning systems that ensures indoor air quality. References: [1] Atmaca, I., Kaynakli, O., Yigit, A., Effects of radiant temperature on thermal comfort, Building and Environment, Volume 42, Issue 9, September 2007, pp [2] Surface heating and cooling [3] Mira, N., Enciclopedia tehnică de instalaţii Volume E, ARTECNO Bucureşti Publishing House, 2010, ISBN [4] Peters, R; Zerwas, M; Krempen, T; Krause, HJ, Optimisation of thermal comfort in existing ISBN:

6 buildings, BAUPHYSIK, ISSN , 10/2010, Volume 32, Issue 5, pp [5] Wang, SW and Ma, ZJ, Supervisory and optimal control of building HVAC systems, HVAC&R RESEARCH, ISSN , 01/2008, Volume 14, Issue 1, pp [6] Popescu, D., A New Solution for Automatic Control of Heating Systems in Buildings Based on Measuring Heat Transfer Through Outer Surfaces, Proceedings of the 10th WSEAS International Conference on Automatic Control, Modeling and Simulation (ACMOS'08), pp , Istanbul, Turkey, May 27-30, [7] Popescu, D., Ciufudean, C., Automatic Control System for Heating Systems in Buildings Based on Measuring the Heat Exchange through Outer Surfaces, Proceedings of the 8th WSEAS International Conference on Simulation, Modelling and Optimization (SMO'08), pp , Santander, Cantabria, Spain, September 23-25, 2008 [8] Popescu, D., Ciufudean, C., Ionescu, D., Experimental Analysis of the Automated System for Heating Control based on Heat Losses through Building s Envelope. 9th WSEAS International Conference on Simulation, Modelling and Optimization (SMO'09), pp , Budapest Tech University, Budapest, Hungary, September 3-5, [9] Spiro N Pollalis, Energy and the Building Envelope, Buildings, ISSN , 12/2005, Volume 99, Issue 12, p. 14. [10] Nilsson, Hakan O., Local evaluation of thermal comfort, International Journal of Vehicle Design, Volume 42, Issue 1-2, 2006, pp ISBN: