Modeling of Energy Consumption in Civil Building of IST and Definition of Rationalization Measures of Energy Consumption

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1 Modeling of Energy Consumption in Civil Building of IST and Definition of Rationalization Measures of Energy Consumption João Miguel de Almeida Nunes Patrício Abstract The main objective of the following paper was the disaggregation of the energy consumption in Civil Building of Instituto Superior Técnico in Alameda Campus. The results were obtained through measurements of the energy consumed in the switchboards in the building, using power analyzers appropriated for the task. The Natural Gas consumption was determined based on the existing meter readings. The analysis of these results allowed the disaggregation of the building s energy consumption in its many plots and the setting of some saving measures based only in the elimination of unnecessary consumption, mainly in night regime. Some changes in the installed systems were also proposed, mainly in HVAC, based in a preliminary study that tried to determine the annual energy saving and an estimate for the investments required. Keywords: Energy Consumption, Energy Audit, Disaggregation, Savings Potential 1. Introduction The energy consumption of civil engineering building in IST is the largest of all the campus buildings, according to the meter readings promoted by the Maintenance Department of IST. There are some areas in which some energy savings could be achieved, namely in the HVAC system, building envelope and illumination equipment installed. An energy audit was performed to the building, in order to disaggregate the energy consumption in all its forms and determine measures that would allow its reduction, improving the building s energetic efficiency Graph 1 - Buildings energy consumption through years, in tep (ton of oil equivalent) 1

2 2012 Civil Enginnering 45% 17% 11% 6% 14% 7% Central Building North Tower South Tower Interdisciplinary Complex Remaining Buildings Graph 2 - Comparative of energy consumption between Civil Engineering building and other buildings in the campus in Methodology The main objective of an energy audit is to list and characterize all the building s systems and equipment that consume energy in all its forms. All the actions performed are synthetized in the following list: All the relevant technical departments were contacted, in order to gather all the available information about the building. Records of the meter readings, plants and documents about the spaces division, HVAC system technical information and previous studies on the buildings energetic efficiency were obtained A spaces survey was performed in order to identify and characterize all the spaces in the building An energetic survey was performed including many actions such as: list and characterization of all the energy consuming equipment; Central systems schedules and utilization; Inquiries to most of the permanent occupants (services employees, teachers, among others) in the building, in order to determine their schedules and utilization of energy consuming equipment; Energy consumption measurements of standard office equipment using a plug analyzer. An initial estimate of energy consumption disaggregation was obtained with the results of the energy survey. The buildings electrical distribution diagram was produced, since there was none available. Energy measurements in all the relevant switchboards across the building were performed. All the measurements performed were analyzed in order to determine the daily electric energy consumption of all the equipments associated to every switchboard. 2

3 The daily energy consumption of all plots was extrapolated to an annual energy consumption model, through the definition of different regimes along the year, according to the spaces occupation and systems utilization during the year Energy Rationalization Measures were determined with the results of the model, with special attention to the energy consumption during night and weekend regimes. 3. Building Description The building is a teaching and research facility localized in Avenida Rovisco Pais, in Lisbon, Portugal. It possesses classrooms, study rooms, offices, research and educational laboratories, a museum and a library, a bar and a restaurant, technical installations for the HVAC system and an underground parking. The building is open throughout all year, from 7h to 21h during the week and from 7h to 17h at Saturday. The study rooms at ground level are open 24h per day, all year round. Lighting systems in most of the building s rooms uses fluorescent TL-D T8 58W lamps with magnetic ballasts. HVAC system is composed by a central thermal production plant, consisting in 2 vapor compression chillers that work alternatively and a cooling tower, all installed at roof level. In the bottom floor the HVAC distribution system is installed, consisting in various centrifugal electrical pumps, storage tanks for cold and hot water and heat exchangers. Across the building terminal units are installed consisting mainly in reversible heat pumps. Associated to the existing large amphitheaters air handling units (AHU) are installed. There are also 6 lifts, a wind tunnel and a high energy consumption electric oven in the laboratories and a compressed air system. The total area of interior pavement determined was m Energy Audit Results Common lighting (Corridors) Common equipment* 2% 2% 2% 34% 3% 7% 1% 14% 17% 11% 3% 4% Local Lighting Computers Other Office Equipment Laboratory Equipment Bar and Restaurant Natural Gas Central Compressed Air Lifts Portable Heaters HVAC System Graph 3 - Annual Energy Consumption Disaggregation 3

4 Based on the results obtained in the electric energy measurements and energy surveys performed, the building s annual energy consumption was disaggregated in all its plots, according to the existing type of equipment. The results obtained in the model were compared with the annual energy consumption indicated by the meter readings. The overall difference found was around 9% which was considered acceptable. The Natural Gas consumption was compared with the electrical consumption. The HVAC system energy consumption was disaggregated in its plots between the heating and cooling season based in the measurements performed. The results obtained are shown in the following table. kwh/year tep/year /year CO2 equivalent emissions (tonco2e) Common lighting (Corridors) Common equipment* Local Lighting Computers Other Office Equipment Laboratory Equipment Bar and Restaurant Natural Gas Central Compressed Air Lifts Portable Heaters HVAC System Total Specific Electric Energy Consumption (kwh/m 2.year) Current 76 Good Practice 79 [1] *Server units, Door Access Systems, Bathroom Hand Dryers, Vending Machines among others Table 1 - Disaggregation of Civil Engineering building annual energy consumption Cooling (kwh/regime) Heating (kwh/regime) Between Seasons (kwh/regime) Annual (kwh/year) Chillers and Cooling Tower Air Handlling Units Fresh Air Handlling Units Terminal Units Electric Pumps Extraction and Insufflation Fans Computer Laboratory HVAC System Total Table 2 - HVAC consumption disaggregation 4

5 5. Savings Potential 5.1 Control Strategies for Energy Consumption Rationalization According to the measurements performed, unexpected energy consumption during night and weekend regimes was observed, mainly in central HVAC systems and in the offices. Regarding HVAC system, there are 2 clocks responsible for the automatic shutdown of all the equipment at a defined schedule. The analysis and reconfiguration of these clocks is suggested, in order to determine if all HVAC related equipment is in fact associated to this control. Alternatively, while this measure takes place, it is recommended the manual shutdown of the equipment in the existing controls located on the HVAC switchboards. The start of an awareness program for energy savings directed to the energy users in the offices is also proposed. The installation of free software for the automatic shutdown of individual computers, available nowadays, could be recommended since it appears that the majority of office equipments stay on during the night, according to the measurements performed. Lighting levels in some corridors and study rooms were also determined through measurements with a luximeter. Some equipment installed in common areas, normally turned on during daytime, could be turned off since there are good natural lighting levels, according to the European standards consulted [2]. Energy consumption associated to these regimes and savings potential is shown in the following table. Plot Action Suggested Annual Savings Potential (kwh) Annual Savings Potential (Euros) HVAC System Manual Control Office Equipment Awareness Program Lighting Shutdown Selected Circuits Total Savings Regarding Global Building Energy Consumption (%) 9.65% Table 3 - Potential Savings with control strategies for energy consumption 5.2 Lighting A significant energy consumption reduction could be achieved by substituting the current TL-D T8 lamps in the corridors by Retrofit T5 32W lamps with electronic ballasts. These lamps are equipped in T8 tubes so the current luminaires could be maintained. The annual energy saving determined with this measure is kwh equivalent to 5949 per year. According to the brochure of these lamps [3], the payback time rounds 1 year. 5

6 5.3 HVAC System related Measures Currently the fluids distribution system consists in three separate circuits, hot water, cold water and a third circuit called condensation circuit, which provides or removes heat from all the terminal units in both cooling and heating season and removes heat from most of the AHU in cooling season. The heat exchange between this circuit and the primary plant circuits is achieved through plate heat exchangers. The suppression of the condensation circuit in order to avoid energy losses in the heat exchangers is proposed. With this action the heat pumps units across the building could be substituted by fan coils, and the current direct expansion (DX) AHU units substituted by AHU units with cooling batteries, resulting in considerable annual energy savings. The current AHU units installed use R22 refrigerant fluid which, according to European Parliament s Regulation nº 1005/2009 [4], will be forbidden from January 1 st Actions towards these units are rather urgent. The level of efficiency of the electric pumps was also determined, based on the European Union s Directive nº 640/2009 [5]. The substitution of the current pumps for equipment with higher level of efficiency is also recommended. An alternative for the primary plant, incorporating renewable energy sources was considered. The system proposed consists in adsorption chiller assisted by solar thermal panels, maintaining one of the existing vapor compression chillers as a backup system. Figures 1, 2 - General scheme for solar assisted HVAC plant; Operating Principle of Adsorption Chillers Fonts: Solar-Assisted Air-Conditioning in Buildings A Handbook for Planners [6]; [7] The enterprise ECO-MAX Adsorption Chillers [8] from United States was contacted in order to collect technical and cost information about adsorption chillers. The solar thermal panels system was dimensioned using climate and economical data obtained from the program SOLTERM 5 [9]. Average values of efficiency for these panels throughout the year were determined, based on this equipment s characteristic curve [10]. With this information, the thermal power available in the panels was estimated and compared with the thermal loads in the building, obtained from a previous energy efficiency study [11], in order to determine the solar fraction throughout the year regarding HVAC needs. The maximum thermal load was used to determine the adsorption chiller thermal power requirement. Energy savings were estimated comparing the solar fraction with the annual 6

7 consumption of the current electric chillers, according to the measurements performed. The adsorption chiller electric consumption is very low: the maximum power peak rounds 2 kw while the maximum peak in the current chillers observed was around 120 kw. Annual Savings Potential (kwh) Annual Savings Potential ( ) Investment ( ) Adsorption Chiller (Excluding installation costs) Solar Thermal Panels (Excluding installation costs) AHU with cooling batteries in substitution DX AHU Fan Coils Units in substitution of reversible heat pumps (Excluding installation costs) Electric Pumps with higher level of efficiency (Excluding installation costs) Total Table 4 - Annual savings and total investment for solar HVAC 6. Recommendations Other actions are also recommended in order to promote energetic efficiency in the building Recommendations Studies on lighting levels in classrooms, study rooms and offices in order to propose the substitution of T8 lamps with magnetic ballast by T5 lamps with electronic ballasts in these spaces Consider the lighting circuits sectorisation in the internal corridors, in order to reduce the number of lamps working during daytime Studies related to water flows and temperatures in the heat exchangers, in order to assess overall efficiency of HVAC system Detailed studies on water flows and thermal loads associated to every distribution system, in order to evaluate the possibility of reducing installed power in electric pumps. Assess the possibility of equipping existing electric pumps with variable speed electronic devices, to adapt the speed in electric motors according to the thermal loads Assess the efficiency of extraction and insufflation fans across the building, to determine if it's possible to install equipment with higher level of efficiency Studies on the building's envelope, in order to quantify the savings potential with the substitution of all the single glazing by double glazing, installation of solar protection in horizontal glazing in the last floor and repair of all broken shutters Table 5 - Recommendations for energetic efficiency in the building 7

8 7. Energy Management Introducing energy management strategies is essential to assess the buildings energy consumption. An ongoing initiative is currently assessing the energy consumption in all the existing buildings in IST campus, in order to increase energy use efficiency. Awareness programs directed to all energy users, frequent energy consumption measurements, the definition of goals regarding this consumption and the optimization of equipment maintenance plans are all required actions regarding the efficient use of energy. 8. Conclusions The electric energy consumption measurements in the building s switchboards using energy analyzers had not been performed to date. The building s real energy consumption was determined in an annual base and disaggregated according to all existing equipment. All the documents produced in order to allow the energy measurements were made available to the ongoing energy initiative. The savings potential is considerable with the implementation of control strategies in order to reduce night and weekend regimes energy consumption. The proposed substitution of HVAC system is not economically profitable, but presents many other advantages. The adsorption chillers are considered green systems since they don t use any refrigerant fluids harmful for the environment. This equipment is suitable to be connected to a solar thermal panels system, which means that the driving force of adsorption chillers can come from an entirely renewable energy source. The inexistence of rotating components in this equipment means also that the maintenance costs are much lower comparing with other chiller technologies. The establishment of protocols for external investment might be possible, given that this project would bring recognition to the building regarding energetic efficiency and use of renewable energies. 9. References [1] CIBSE (2004), Guide F Energy efficiency in buildings, 2 nd Edition, The Chartered Institution of Building Services Engineers London [2] European Standard EN , Light and lighting Lighting of work places [3] ecotreecity, Eficiência Energética, Lda, Lâmpada Retrofit T5 (Retrofit Lamp T5) [4] European Parliament s Regulation nº 1005/2009 of 16 September 2009 on substances that deplete the ozone layer [5] European Union s Directive nº 640/2009 of 22 July 2009 with regard to ecodesign requirements for electric motors 8

9 [6] Hans-Martin Henning (2004), Solar-Assisted Air-Conditioning in Buildings A Handbook for Planners, SpringerWienNewYork [7] [8] [9] INETI, SOLTERM 5, Programa para Análise de Desempenho de Sistemas Solares Térmicos e Fotovoltaicos (Program for Performance Analysis of Photovoltaic and Solar Thermal Systems) [10] [11] Onésimo Silva (2009), Eficiência Energética do Pavilhão de Civil do Instituto Superior Técnico (Energetic Efficiency of Civil Engineering Building from Instituto Superior Técnico) 9