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Experimental investigation of a low energy consumption air conditioning system based on conventional central heating installation
Energy and Buildings 38 (2006) 45–52 www.elsevier.com/locate/enbuild
Experimental investigation of a low energy consumption air conditioning system based on conventional central heating installation G.C. Bakos *, E. Tsioliaridou, N.F. Tsagas Democritus University of Thrace, Department of Electrical and Computer Engineering, Energy Economics Laboratory, 67 100 Xanthi, Greece Received 9 December 2004; received in revised form 12 February 2005; accepted 15 February 2005
Abstract This paper deals with the development of a low cost and low energy consumption air conditioning system based on the conventional central heating installations. It is aimed to convert, with minimal cost and work intervention in the interior of the buildings, the classic central heating systems into a new type system which can cool during summer and heat during winter period. In general, the above mentioned heating– cooling system constitutes an integrated new technology in building air conditioning, with good prospects in replacing eventually the conventional air conditioning systems. The experimental installation is described in detail and the experimental results are presented and analysed. The achieved energy saving is also calculated. The advantages and disadvantages of the proposed system are discussed and useful conclusions are drawn. # 2005 Elsevier B.V. All rights reserved. Keywords: Energy efficiency technologies; Central heating installation; Air conditioning; Energy saving
1. Introduction Space air-conditioning dominates the energy consumption in residential sector. Similarly, a large amount of energy is consumed in public sector where the building use does not justify the level of energy consumption [1–3]. In 1995, the Greek Ministry of Environment, Urban Planning and Public Works prepared an Action Plan, entitled ‘‘Energy 2001’’, aiming at promoting the application of energy-efficiency technologies in the building sector. The Action Plan was prepared in order to define specific measures for the reduction of greenhouse gas emissions in buildings, in accordance with the ‘‘National Action Plan for the Abatement of CO2 and other Greenhouse Gases’’. Following the official adoption of the Action Plan by the Greek Government, ‘‘Energy 2001’’ was further reinforced by the enactment of Ministerial Decree (MD) 21475/98, which incorporated the provisions of Council Directive 93/76/EC (SAVE Directive) for the stabilisation of CO2 emissions and the efficient use of energy in buildings [4].
* Corresponding author. E-mail address: [email protected] (G.C. Bakos). 0378-7788/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.enbuild.2005.02.011
Apart from the introduction of natural gas, a major intervention in the residential and tertiary sector in order to reduce greenhouse gases emissions is energy conservation. The legislative framework in force for the promotion of energy conservation in the buildings’ sector includes the minimum energy efficiency standards set by the EU for nonindustrial boilers (Directive 92/42/EC) and Greek legislation has been harmonised in accordance with EU standards through the Presidential Decree 335/1993. However, energy efficiency (EE) technologies have encountered various difficulties into their being accepted by the Greek market. Some of them derive from a certain degree of lack of knowledge and experience on the subject. On the other hand, societal and environmental factors are deeply interlinked with wide social acceptance. Aiming at the greater penetration of EE technologies into the Greek market, this work focuses on the conversion of the classic central heating systems of residences, offices, hospitals etc. into efficient air conditioning heating–cooling systems, leading to a reduction of the annual heating oil consumption and a corresponding reduction in harmful atmosphere pollutants. Also, the reduction in heating oil consumption leads to financial savings for the building’s owner and by extension savings for the national economy.
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G.C. Bakos et al. / Energy and Buildings 38 (2006) 45–52
The proposed system functions by using the existing central heating installation, which, with appropriate technical alterations, can heat and cool the areas in an economical and healthy manner. The purpose of the work is the elimination of the need for uneconomical air-conditioning units to be installed and the reduction of all the unpleasant consequences of their use on the health of users and their global warming and pollution effects on the environment. Up to now, air conditioning systems have been developed in order to save energy and reduce pollutants. Basically, the following principles have been followed in the function of these technologies: (i) Water has been used in central heating installations as a heat transfer fluid. (ii) To cool areas, individual air-conditioning units, powered by electricity, have been used for small areas. There are various disadvantages connected with the aforementioned technology systems, in which, sooner or later, the function becomes less and less efficient, due to the following points: (a) The system cannot operate at heat transfer fluid temperatures above 90 8C or below 6 8C. (b) More heating radiators are required for a faster rise in temperature and for the maintenance of the desired temperature. This means greater consumption of energy and increasing of pollutants with harmful effects for the health and the environment. (c) The central heating installation is not used for cooling. The first objective of the present work is to provide a liquid heating–cooling air-conditioning system aiming at economising on energy which will remove all the aforementioned disadvantages of previous technologies, providing the greatest possible energy savings for heating and cooling residential buildings, offices, and civic buildings. The second objective is to provide a system which has the highest possible degree of reliability achieving simultaneously a healthy environment to improve the users’ quality of life. The third objective is to provide a low cost system that will be installed easily and quickly and will have minimal maintenance requirements. The above mentioned objectives are implemented by fitting to the existing and used heating installation the following devices: (a) an electric cooling unit for low temperature cooling, (b) a special heat transfer fluid which can also act as a coolant agent, (c) an electrical control panel, (d) evaporation and recycling units for accelerated circulation and cleaning of the air attached to each radiator unit and (e) an electric fan with an automatic electrical input/output of air.
The above appliances can be fitted to all types of central heating systems operating either in apartment blocks or in individual homes, factories, schools, offices, hospitals, hotels etc. The proposed heating–cooling air conditioning system [5,6,7] can be applied in buildings where there is central heating installation using the conventional heatemitting radiators and its existing pipe network.
2. Method of operation-theoretical background Fig. 1 provides a general view of the proposed airconditioning system consisting of: (a) a cooling unit, (b) a special liquid agent to act as a heat transfer fluid instead of water, (c) a circulation unit, (d) a stopcock (switch), (e) an electrical control panel, (f) a recycling and evaporation appliance (for accelerated air circulation), (g) heating radiators, (h) a liquid top-up tank, (i) a cold water tank, (j) filter for input of air to the heating radiators, (k) a heat pump, (l) a solar energy collector which follows the course of the sun so that the solar radiation falls vertically onto it providing auxiliary heat during the heating period, (m) a system for waste gas expulsion, (n) an automatic electric fan for input and output of air and moisture, (o) a waste gas heat exchanger and finally (p) the insulation for the whole system to avoid heat losses and accidents. According to Fig. 1, a suitable cooling unit is installed to cool the liquid agent, which will replace the water and will reside in the heating installation which employs the boiler, the burner, the piping and the radiators. The cooling unit can be connected to the already existing piping of the central heating installation before the circulation unit and immediately after the boiler and can be installed at the highest level in the building or in the boiler room or outside of it. The cooling unit itself could be one of several types. It may operate with all known cooling system agents, e.g. water, sulphur- or carbon-dioxide, freon, calcium chloride or liquid nitrogen. Three-way stopcocks, electrical or manual, are installed on the piping immediately after the boiler in order to isolate the heating or cooling system so that the system can be used continuously. In the position where the common ventilator is found, an automatic electric ventilator is installed, which has an electrical automatic system for introducing and expelling air and moisture according to the needs of the day and the season of the year.
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Fig. 1. General layout of the proposed air conditioning system.
Before the replacement of water by the liquid agent, the following procedure should take place: (i) Water should be removed from all pipes of the central heating installation and the pipes should be cleaned by a solvent liquid to remove salt deposits and iron oxides. (ii) Pressure should be applied to the interior of the pipes in order for any leaks to be found and sealed. (iii) The system is filled with the liquid agent, which contains antioxidant and anti-corrosion additive compounds.
are attached to the radiators. An appropriate air recycling unit is installed on each heating radiator, depending on the size and performance of each radiator. For the operation of the system during summer, the electrical supply is turned off at the end of the winter period and the stopcocks of the central heating are closed. Then the stopcocks of the cooling unit are opened and the cooling unit is put into operation via the electrical control panel. This procedure can take place automatically using three-way electric stopcocks and a twin-operation electronic thermostatic switch.
According to Fig. 2, an installation is made below each radiator involving an air circulation unit without drainage so as to achieve accelerated circulation and cleansing of the air of substances harmful to the health. The air circulation unit consists of: (1) a multi-speed electric ventilator for quick heat transfer due to accelerated circulation of the air, (2) small windows to extract and direct the air to an ecological perfumed air filter at the entrance to the electric fan for cleansing of the air and (3) an electric water evaporator with filter paper to regulate the humidity of the air. The air recycling appliances operate on electricity and automatically through the use of sensors and switches which
Fig. 2. Detailed schematic of the proposed radiator.
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Fig. 3. Experimental setup for studying the energy saving of the proposed air conditioning system.
3. Description of the experimental setup The electrical energy consumption of two identical heating installations with different heat transfer fluids was calculated. The first installation (Chamber I) used water simulating the existing conventional heating installations and the second installation (Chamber II) is similar but uses different heat transfer fluid (the so called ‘‘liquid agent’’). The liquid agent consists of water, antifreeze and other anticorrosive agents. This liquid agent constitutes a new heating–cooling liquid transfer fluid which has specific weight 0.874 g/cm3, specific heat 0.581 kcal/kg 8C, a freezing point below 20 8C and a boiling point in excess of 115 8C. The twin-chamber installation is operating in the Laboratory of Energy Economics of Democritus University of Thrace in Xanthi-Nothern Greece. The experimental setup has been satisfying enough in order to have reliable indications of the effectiveness of the proposed system. The heating installation consisted of all the devices and instruments of a contemporary installation (boiler, circulator, expansion vessel, thermostat, etc.), except the mixing valve (a three- or four-way mixing valve) because of the low power and the small quantity of water of the installation. The piping network was constructed of copper tubes. Two identical chambers were constructed in the laboratory from compound polystyrene slates with dimensions 3.00 m 3.00 m 3.00 m. In both chambers, portable air cooling devices and heaters were fitted in order to control the room temperature before the start of the experiments. Also small electric ventilators were fitted to each radiator. Through the installation of the ventilator under each radiator, warm air is circulated quickly throughout the area it covers, leading to rapid warming of the room. Thus, the boiler works for less time and consequently a further electrical energy saving is achieved due to the accelerated
circulation of air. The operational diagram of the experimental setup installation and the physical representation of the twin-chamber installation are shown in Fig. 3 and Photo 1, respectively. The pipe network of each small scale central heating installation is shown in Photos 2 and 3 and the respective electrical equipment is shown in Photo 4. The radiator– ventilator system used inside the chambers is shown in Photo 5. The experimental results were collected and analysed using the LABVIEW 5.1 software package running on an Intel Pentium PC. The measured values of the temperature and the electric energy consumption together with the exact actual time are stored in a computer file. The sampling rate was 5 ms and the time interval of measurement storage can be controlled through the developed software. The data acquisition interface (Photo 6) is based on two Advantech cards. The first is an A/D input card PCI-1714 which can accept up to 32 analog inputs and the second is a D/A output card with 8 output channels. Six (6) thermometers and four (4) electrical energy meters are connected to
Plate 1. View of experimental twin-chamber installation.
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Plate 2. Small scale heating–cooling installation of Chamber II. Plate 5. View of radiator–ventilator system.
4. Experimental results 4.1. Twin-chamber heat loss calibration test
the PCI-1714. Two (2) thermometers measure room air temperature within a range of 20 8C to +50 8C and four (4) measure liquid temperature within a range of 20 8C to +120 8C. The electric energy meters produce one pulse when the electric energy consumption exceeds 100 Wh.
A heat loss calibration test was carried out for the twin chamber installation before the start of heat and cooling experiments. The temperature inside the two chambers was set to 25.5 8C using the available portable heating devices. When this temperature was reached, the chambers remained closed and the temperature variation was monitored. As it can be seen in Fig. 4, the temperature fluctuation inside the two chambers was similar following a reduction to approximately 18 8C after a time period of 65 min. After the heat loss calibration test, various experiments took place regarding the heat and cooling of the twin chamber facility. During the heating and cooling experiments, air–liquid temperatures and electrical energy consumption indications of the two chambers were recorded continuously. For all experiments, the temperature inside the laboratory (i.e. outside the two chambers) was set to 18 8C.
Plate 4. View of electric equipment.
Plate 6. View of developed data acquisition interface.
Plate 3. View of pipe network of Chamber I.
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Fig. 4. Variation of indoor temperature in twin-chamber facility during the calibration test [Chamber 1*: water as heat transfer fluid; Chamber 2*: liquid agent as heat transfer fluid].
4.2. Twin-chamber heating experiment Before the start of the heating experiment, the temperature inside the two chambers was set to 12 8C using the available cooling devices installed inside the chambers for this purpose. The maximum operating temperature of water (Chamber I) was set to 90 8C and of the liquid agent (Chamber II) to 110 8C. The starting temperature for both heat transfer fluids is similar and it is equal to 23 8C. The required temperature inside the two chambers was set to 31 8C. The temperature requirements in the interior of the two chambers simulate the actual heat
demand of residential buildings. The duration of the experiment was 96 h of continuous operation and the experimental results are presented in Photo 7. It can be noticed that the electrical energy consumption in the case of Chamber II with the liquid agent as heat transfer fluid is reduced to approximately 20% compared to Chamber I where water was used as heat transfer fluid. 4.3. Twin-chamber cooling experiment Before the start of the experiment, the temperature inside the two chambers was set to 35 8C using the available
Plate 7. Experimental results for twin-chamber heating experiment.
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Plate 8. Experimental results for twin-chamber cooling experiment.
portable heating devices. The minimum operating temperature of the water (Chamber I) was set to 7 8C and of the liquid agent to 10 8C. The starting temperature of both fluids is similar and it is equal to 19 8C. The required temperature inside the two chambers was set to 20 8C. The indoor temperature requirements for both chambers correspond to the actual cooling demand of residential buildings. The duration of the experiment was 120 h of continuous operation and the experimental results are presented in Photo 8. In this case, it can also be noticed that the electrical energy consumption for Chamber II is approximately 10% lower compared to Chamber I where water is used as heat transfer fluid.
5. Discussion–conclusions Various measurements have been made to verify the energy advantages of the special liquid agent in comparison to water for the air conditioning of two identical rooms (chambers). The results show that for the same calorific energy consumption the temperature of the liquid agent and of the space heated is higher than the temperature of water and space heated thereby. The space heated by the liquid agent experiences a more rapid temperature increase than the same space heated by water. The conclusion is that smaller quantities of energy are required to maintain at a suitable temperature the chamber heated by the liquid agent. Similar system behaviour is noticed in case of cooling
operation of the system. As a result, the energy savings achieved when the liquid agent is used as heat transfer fluid for combined heating–cooling operation is approximately 30% compared to water. Furthermore, the operation of the proposed air conditioning system is very simple. The administrator (or the concierge) of a building, with the heating switched-off can open the cooling system and switch on the cooling unit. For efficient climatization, doors and windows in the building should be closed and insulated, so that a temperature about the required level is maintained, regulated by a thermostat on the central board. It is understood that the cooling system employs existing installations, but is used independently, as the heating boiler is cut off. The proposed air conditioning system is effective with ordinary radiators, serpentine radiators, as well as with any other type, irrespective of material or construction. It is efficient with all kinds of central-heating systems in apartment blocks, in hotels, factories, hospitals. The advantages of the proposed system are summarised below: (a) It is noticed a total reduction of approximately 30% in the energy consumption, resulting to a corresponding reduction in harmful pollutants in the atmosphere generated in the form of waste gases which cause the greenhouse effect. (b) Simple operation of the system during the summer months assures central air cooling which is an
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economical and healthy solution to air-conditioning in all interior areas and apartments in buildings. (c) The required number of heating–cooling radiator units is reduced significantly, due to the properties of the liquid agent, which can function at temperature levels at which water cannot. However, there are some points which need further consideration and are presented below: 1. During the combined space heating–cooling procedure, the use of special pipes may be necessary during the long operation of the system to withstand the temperature differences of the liquid agent. 2. It is suggested that the next step will be the use of different liquid agents and the application of the system to a real building so that a real heating–cooling cycle could be applied in combination with the energy management method described in [1] for maximum energy efficiency. 3. The proposed liquid air heating–cooling system could integrate renewable energy sources in order to reduce the energy consumption for domestic heating applications. For example, the simultaneous use of solar collectors as an auxiliary source of fluid heating is recommended in countries with very high yearly insolation such as Greece. In this case, a simple temperature control system is also required in order to ensure the highest possible efficiency of the liquid heating–cooling system.
Acknowledgements The authors would like to thank the Greek General Secretariat for Research & Technology (GSRT) for the financial support of this project under the Operational Programme for Competitiveness (OPC). Also, the authors would like to express their gratitude to Mrs. M. Batziou, Mr. E. Georgantzis, Mr. K. Moutzouridis and Mr. I. Kyriakou for their valuable contribution throughout this project. References [1] G.C. Bakos, A. Spirou, N.F. Tsagas, Energy management method for fuel saving in central heating installations, Energy and Buildings 29 (1999) 135–139. [2] European Commission, Directorate XVII, Retrofitting of Metering and Control Technology for Heating Systems in Residential Buildings, Programme THERMIE, 1998. [3] G.C. Bakos, Insulation protection studies for energy saving in residential and tertiary section, Energy and Buildings 31 (2000) 251–259. [4] G.C. Bakos, Technical Report WP1, Review of current policy strategies and promotion schemes for RUE & RES in various countries and regions, ALTENER-2002-094, May–December 2003. [5] K. Mountzouridis, N.F. Tsagas, Liquid Heating–Cooling Air Conditioning System, Greek Patent No. 1004485 (2004) (in Greek). [6] G.J. Plagakos, N.F. Tsagas, K. Mountzouridis, D.A. Karadimos, I. Afisov, Liquid heating–cooling air conditioning system, in: Proceedings of the International Conference on Ecological Protection of the Planet Earth I, Xanthi, Greece, 5–8 June 2001. [7] K. Mountzouridis, N.F. Tsagas, G.C. Bakos, A.Th. Hatzigaidas, A.I. Papastergiou, Liquid heating–cooling air conditioning system, in: Proceedings of the 2nd International Conference on Ecological Protection of the Planet Earth, Sofia, Bulgaria, 2003.
Experimental investigation of a low energy consumption air conditioning system based on conventional central heating installation G.C. Bakos *, E. Tsioliaridou, N.F. Tsagas Democritus University of Thrace, Department of Electrical and Computer Engineering, Energy Economics Laboratory, 67 100 Xanthi, Greece Received 9 December 2004; received in revised form 12 February 2005; accepted 15 February 2005
Abstract This paper deals with the development of a low cost and low energy consumption air conditioning system based on the conventional central heating installations. It is aimed to convert, with minimal cost and work intervention in the interior of the buildings, the classic central heating systems into a new type system which can cool during summer and heat during winter period. In general, the above mentioned heating– cooling system constitutes an integrated new technology in building air conditioning, with good prospects in replacing eventually the conventional air conditioning systems. The experimental installation is described in detail and the experimental results are presented and analysed. The achieved energy saving is also calculated. The advantages and disadvantages of the proposed system are discussed and useful conclusions are drawn. # 2005 Elsevier B.V. All rights reserved. Keywords: Energy efficiency technologies; Central heating installation; Air conditioning; Energy saving
1. Introduction Space air-conditioning dominates the energy consumption in residential sector. Similarly, a large amount of energy is consumed in public sector where the building use does not justify the level of energy consumption [1–3]. In 1995, the Greek Ministry of Environment, Urban Planning and Public Works prepared an Action Plan, entitled ‘‘Energy 2001’’, aiming at promoting the application of energy-efficiency technologies in the building sector. The Action Plan was prepared in order to define specific measures for the reduction of greenhouse gas emissions in buildings, in accordance with the ‘‘National Action Plan for the Abatement of CO2 and other Greenhouse Gases’’. Following the official adoption of the Action Plan by the Greek Government, ‘‘Energy 2001’’ was further reinforced by the enactment of Ministerial Decree (MD) 21475/98, which incorporated the provisions of Council Directive 93/76/EC (SAVE Directive) for the stabilisation of CO2 emissions and the efficient use of energy in buildings [4].
* Corresponding author. E-mail address: [email protected] (G.C. Bakos). 0378-7788/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.enbuild.2005.02.011
Apart from the introduction of natural gas, a major intervention in the residential and tertiary sector in order to reduce greenhouse gases emissions is energy conservation. The legislative framework in force for the promotion of energy conservation in the buildings’ sector includes the minimum energy efficiency standards set by the EU for nonindustrial boilers (Directive 92/42/EC) and Greek legislation has been harmonised in accordance with EU standards through the Presidential Decree 335/1993. However, energy efficiency (EE) technologies have encountered various difficulties into their being accepted by the Greek market. Some of them derive from a certain degree of lack of knowledge and experience on the subject. On the other hand, societal and environmental factors are deeply interlinked with wide social acceptance. Aiming at the greater penetration of EE technologies into the Greek market, this work focuses on the conversion of the classic central heating systems of residences, offices, hospitals etc. into efficient air conditioning heating–cooling systems, leading to a reduction of the annual heating oil consumption and a corresponding reduction in harmful atmosphere pollutants. Also, the reduction in heating oil consumption leads to financial savings for the building’s owner and by extension savings for the national economy.
46
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The proposed system functions by using the existing central heating installation, which, with appropriate technical alterations, can heat and cool the areas in an economical and healthy manner. The purpose of the work is the elimination of the need for uneconomical air-conditioning units to be installed and the reduction of all the unpleasant consequences of their use on the health of users and their global warming and pollution effects on the environment. Up to now, air conditioning systems have been developed in order to save energy and reduce pollutants. Basically, the following principles have been followed in the function of these technologies: (i) Water has been used in central heating installations as a heat transfer fluid. (ii) To cool areas, individual air-conditioning units, powered by electricity, have been used for small areas. There are various disadvantages connected with the aforementioned technology systems, in which, sooner or later, the function becomes less and less efficient, due to the following points: (a) The system cannot operate at heat transfer fluid temperatures above 90 8C or below 6 8C. (b) More heating radiators are required for a faster rise in temperature and for the maintenance of the desired temperature. This means greater consumption of energy and increasing of pollutants with harmful effects for the health and the environment. (c) The central heating installation is not used for cooling. The first objective of the present work is to provide a liquid heating–cooling air-conditioning system aiming at economising on energy which will remove all the aforementioned disadvantages of previous technologies, providing the greatest possible energy savings for heating and cooling residential buildings, offices, and civic buildings. The second objective is to provide a system which has the highest possible degree of reliability achieving simultaneously a healthy environment to improve the users’ quality of life. The third objective is to provide a low cost system that will be installed easily and quickly and will have minimal maintenance requirements. The above mentioned objectives are implemented by fitting to the existing and used heating installation the following devices: (a) an electric cooling unit for low temperature cooling, (b) a special heat transfer fluid which can also act as a coolant agent, (c) an electrical control panel, (d) evaporation and recycling units for accelerated circulation and cleaning of the air attached to each radiator unit and (e) an electric fan with an automatic electrical input/output of air.
The above appliances can be fitted to all types of central heating systems operating either in apartment blocks or in individual homes, factories, schools, offices, hospitals, hotels etc. The proposed heating–cooling air conditioning system [5,6,7] can be applied in buildings where there is central heating installation using the conventional heatemitting radiators and its existing pipe network.
2. Method of operation-theoretical background Fig. 1 provides a general view of the proposed airconditioning system consisting of: (a) a cooling unit, (b) a special liquid agent to act as a heat transfer fluid instead of water, (c) a circulation unit, (d) a stopcock (switch), (e) an electrical control panel, (f) a recycling and evaporation appliance (for accelerated air circulation), (g) heating radiators, (h) a liquid top-up tank, (i) a cold water tank, (j) filter for input of air to the heating radiators, (k) a heat pump, (l) a solar energy collector which follows the course of the sun so that the solar radiation falls vertically onto it providing auxiliary heat during the heating period, (m) a system for waste gas expulsion, (n) an automatic electric fan for input and output of air and moisture, (o) a waste gas heat exchanger and finally (p) the insulation for the whole system to avoid heat losses and accidents. According to Fig. 1, a suitable cooling unit is installed to cool the liquid agent, which will replace the water and will reside in the heating installation which employs the boiler, the burner, the piping and the radiators. The cooling unit can be connected to the already existing piping of the central heating installation before the circulation unit and immediately after the boiler and can be installed at the highest level in the building or in the boiler room or outside of it. The cooling unit itself could be one of several types. It may operate with all known cooling system agents, e.g. water, sulphur- or carbon-dioxide, freon, calcium chloride or liquid nitrogen. Three-way stopcocks, electrical or manual, are installed on the piping immediately after the boiler in order to isolate the heating or cooling system so that the system can be used continuously. In the position where the common ventilator is found, an automatic electric ventilator is installed, which has an electrical automatic system for introducing and expelling air and moisture according to the needs of the day and the season of the year.
G.C. Bakos et al. / Energy and Buildings 38 (2006) 45–52
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Fig. 1. General layout of the proposed air conditioning system.
Before the replacement of water by the liquid agent, the following procedure should take place: (i) Water should be removed from all pipes of the central heating installation and the pipes should be cleaned by a solvent liquid to remove salt deposits and iron oxides. (ii) Pressure should be applied to the interior of the pipes in order for any leaks to be found and sealed. (iii) The system is filled with the liquid agent, which contains antioxidant and anti-corrosion additive compounds.
are attached to the radiators. An appropriate air recycling unit is installed on each heating radiator, depending on the size and performance of each radiator. For the operation of the system during summer, the electrical supply is turned off at the end of the winter period and the stopcocks of the central heating are closed. Then the stopcocks of the cooling unit are opened and the cooling unit is put into operation via the electrical control panel. This procedure can take place automatically using three-way electric stopcocks and a twin-operation electronic thermostatic switch.
According to Fig. 2, an installation is made below each radiator involving an air circulation unit without drainage so as to achieve accelerated circulation and cleansing of the air of substances harmful to the health. The air circulation unit consists of: (1) a multi-speed electric ventilator for quick heat transfer due to accelerated circulation of the air, (2) small windows to extract and direct the air to an ecological perfumed air filter at the entrance to the electric fan for cleansing of the air and (3) an electric water evaporator with filter paper to regulate the humidity of the air. The air recycling appliances operate on electricity and automatically through the use of sensors and switches which
Fig. 2. Detailed schematic of the proposed radiator.
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Fig. 3. Experimental setup for studying the energy saving of the proposed air conditioning system.
3. Description of the experimental setup The electrical energy consumption of two identical heating installations with different heat transfer fluids was calculated. The first installation (Chamber I) used water simulating the existing conventional heating installations and the second installation (Chamber II) is similar but uses different heat transfer fluid (the so called ‘‘liquid agent’’). The liquid agent consists of water, antifreeze and other anticorrosive agents. This liquid agent constitutes a new heating–cooling liquid transfer fluid which has specific weight 0.874 g/cm3, specific heat 0.581 kcal/kg 8C, a freezing point below 20 8C and a boiling point in excess of 115 8C. The twin-chamber installation is operating in the Laboratory of Energy Economics of Democritus University of Thrace in Xanthi-Nothern Greece. The experimental setup has been satisfying enough in order to have reliable indications of the effectiveness of the proposed system. The heating installation consisted of all the devices and instruments of a contemporary installation (boiler, circulator, expansion vessel, thermostat, etc.), except the mixing valve (a three- or four-way mixing valve) because of the low power and the small quantity of water of the installation. The piping network was constructed of copper tubes. Two identical chambers were constructed in the laboratory from compound polystyrene slates with dimensions 3.00 m 3.00 m 3.00 m. In both chambers, portable air cooling devices and heaters were fitted in order to control the room temperature before the start of the experiments. Also small electric ventilators were fitted to each radiator. Through the installation of the ventilator under each radiator, warm air is circulated quickly throughout the area it covers, leading to rapid warming of the room. Thus, the boiler works for less time and consequently a further electrical energy saving is achieved due to the accelerated
circulation of air. The operational diagram of the experimental setup installation and the physical representation of the twin-chamber installation are shown in Fig. 3 and Photo 1, respectively. The pipe network of each small scale central heating installation is shown in Photos 2 and 3 and the respective electrical equipment is shown in Photo 4. The radiator– ventilator system used inside the chambers is shown in Photo 5. The experimental results were collected and analysed using the LABVIEW 5.1 software package running on an Intel Pentium PC. The measured values of the temperature and the electric energy consumption together with the exact actual time are stored in a computer file. The sampling rate was 5 ms and the time interval of measurement storage can be controlled through the developed software. The data acquisition interface (Photo 6) is based on two Advantech cards. The first is an A/D input card PCI-1714 which can accept up to 32 analog inputs and the second is a D/A output card with 8 output channels. Six (6) thermometers and four (4) electrical energy meters are connected to
Plate 1. View of experimental twin-chamber installation.
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Plate 2. Small scale heating–cooling installation of Chamber II. Plate 5. View of radiator–ventilator system.
4. Experimental results 4.1. Twin-chamber heat loss calibration test
the PCI-1714. Two (2) thermometers measure room air temperature within a range of 20 8C to +50 8C and four (4) measure liquid temperature within a range of 20 8C to +120 8C. The electric energy meters produce one pulse when the electric energy consumption exceeds 100 Wh.
A heat loss calibration test was carried out for the twin chamber installation before the start of heat and cooling experiments. The temperature inside the two chambers was set to 25.5 8C using the available portable heating devices. When this temperature was reached, the chambers remained closed and the temperature variation was monitored. As it can be seen in Fig. 4, the temperature fluctuation inside the two chambers was similar following a reduction to approximately 18 8C after a time period of 65 min. After the heat loss calibration test, various experiments took place regarding the heat and cooling of the twin chamber facility. During the heating and cooling experiments, air–liquid temperatures and electrical energy consumption indications of the two chambers were recorded continuously. For all experiments, the temperature inside the laboratory (i.e. outside the two chambers) was set to 18 8C.
Plate 4. View of electric equipment.
Plate 6. View of developed data acquisition interface.
Plate 3. View of pipe network of Chamber I.
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Fig. 4. Variation of indoor temperature in twin-chamber facility during the calibration test [Chamber 1*: water as heat transfer fluid; Chamber 2*: liquid agent as heat transfer fluid].
4.2. Twin-chamber heating experiment Before the start of the heating experiment, the temperature inside the two chambers was set to 12 8C using the available cooling devices installed inside the chambers for this purpose. The maximum operating temperature of water (Chamber I) was set to 90 8C and of the liquid agent (Chamber II) to 110 8C. The starting temperature for both heat transfer fluids is similar and it is equal to 23 8C. The required temperature inside the two chambers was set to 31 8C. The temperature requirements in the interior of the two chambers simulate the actual heat
demand of residential buildings. The duration of the experiment was 96 h of continuous operation and the experimental results are presented in Photo 7. It can be noticed that the electrical energy consumption in the case of Chamber II with the liquid agent as heat transfer fluid is reduced to approximately 20% compared to Chamber I where water was used as heat transfer fluid. 4.3. Twin-chamber cooling experiment Before the start of the experiment, the temperature inside the two chambers was set to 35 8C using the available
Plate 7. Experimental results for twin-chamber heating experiment.
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Plate 8. Experimental results for twin-chamber cooling experiment.
portable heating devices. The minimum operating temperature of the water (Chamber I) was set to 7 8C and of the liquid agent to 10 8C. The starting temperature of both fluids is similar and it is equal to 19 8C. The required temperature inside the two chambers was set to 20 8C. The indoor temperature requirements for both chambers correspond to the actual cooling demand of residential buildings. The duration of the experiment was 120 h of continuous operation and the experimental results are presented in Photo 8. In this case, it can also be noticed that the electrical energy consumption for Chamber II is approximately 10% lower compared to Chamber I where water is used as heat transfer fluid.
5. Discussion–conclusions Various measurements have been made to verify the energy advantages of the special liquid agent in comparison to water for the air conditioning of two identical rooms (chambers). The results show that for the same calorific energy consumption the temperature of the liquid agent and of the space heated is higher than the temperature of water and space heated thereby. The space heated by the liquid agent experiences a more rapid temperature increase than the same space heated by water. The conclusion is that smaller quantities of energy are required to maintain at a suitable temperature the chamber heated by the liquid agent. Similar system behaviour is noticed in case of cooling
operation of the system. As a result, the energy savings achieved when the liquid agent is used as heat transfer fluid for combined heating–cooling operation is approximately 30% compared to water. Furthermore, the operation of the proposed air conditioning system is very simple. The administrator (or the concierge) of a building, with the heating switched-off can open the cooling system and switch on the cooling unit. For efficient climatization, doors and windows in the building should be closed and insulated, so that a temperature about the required level is maintained, regulated by a thermostat on the central board. It is understood that the cooling system employs existing installations, but is used independently, as the heating boiler is cut off. The proposed air conditioning system is effective with ordinary radiators, serpentine radiators, as well as with any other type, irrespective of material or construction. It is efficient with all kinds of central-heating systems in apartment blocks, in hotels, factories, hospitals. The advantages of the proposed system are summarised below: (a) It is noticed a total reduction of approximately 30% in the energy consumption, resulting to a corresponding reduction in harmful pollutants in the atmosphere generated in the form of waste gases which cause the greenhouse effect. (b) Simple operation of the system during the summer months assures central air cooling which is an
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economical and healthy solution to air-conditioning in all interior areas and apartments in buildings. (c) The required number of heating–cooling radiator units is reduced significantly, due to the properties of the liquid agent, which can function at temperature levels at which water cannot. However, there are some points which need further consideration and are presented below: 1. During the combined space heating–cooling procedure, the use of special pipes may be necessary during the long operation of the system to withstand the temperature differences of the liquid agent. 2. It is suggested that the next step will be the use of different liquid agents and the application of the system to a real building so that a real heating–cooling cycle could be applied in combination with the energy management method described in [1] for maximum energy efficiency. 3. The proposed liquid air heating–cooling system could integrate renewable energy sources in order to reduce the energy consumption for domestic heating applications. For example, the simultaneous use of solar collectors as an auxiliary source of fluid heating is recommended in countries with very high yearly insolation such as Greece. In this case, a simple temperature control system is also required in order to ensure the highest possible efficiency of the liquid heating–cooling system.
Acknowledgements The authors would like to thank the Greek General Secretariat for Research & Technology (GSRT) for the financial support of this project under the Operational Programme for Competitiveness (OPC). Also, the authors would like to express their gratitude to Mrs. M. Batziou, Mr. E. Georgantzis, Mr. K. Moutzouridis and Mr. I. Kyriakou for their valuable contribution throughout this project. References [1] G.C. Bakos, A. Spirou, N.F. Tsagas, Energy management method for fuel saving in central heating installations, Energy and Buildings 29 (1999) 135–139. [2] European Commission, Directorate XVII, Retrofitting of Metering and Control Technology for Heating Systems in Residential Buildings, Programme THERMIE, 1998. [3] G.C. Bakos, Insulation protection studies for energy saving in residential and tertiary section, Energy and Buildings 31 (2000) 251–259. [4] G.C. Bakos, Technical Report WP1, Review of current policy strategies and promotion schemes for RUE & RES in various countries and regions, ALTENER-2002-094, May–December 2003. [5] K. Mountzouridis, N.F. Tsagas, Liquid Heating–Cooling Air Conditioning System, Greek Patent No. 1004485 (2004) (in Greek). [6] G.J. Plagakos, N.F. Tsagas, K. Mountzouridis, D.A. Karadimos, I. Afisov, Liquid heating–cooling air conditioning system, in: Proceedings of the International Conference on Ecological Protection of the Planet Earth I, Xanthi, Greece, 5–8 June 2001. [7] K. Mountzouridis, N.F. Tsagas, G.C. Bakos, A.Th. Hatzigaidas, A.I. Papastergiou, Liquid heating–cooling air conditioning system, in: Proceedings of the 2nd International Conference on Ecological Protection of the Planet Earth, Sofia, Bulgaria, 2003.