Calibration of Building Simulation Model by Using Building Automation System a Case Study

Transcription

1 Calibration of Building Simulation Model by Using Building Automation System a Case Study Hannu Keränen, Tuomas Suur-Uski, Mika Vuolle HVAC-Laboratory, Helsinki University of Technology, P.O. Box 4400, Hut 02015, Finland Corresponding hannu.keranen@tkk.fi SUMMARY A thermal simulation program called IDA-ICE was used in the evaluation of the energy efficiency and indoor climate of a pilot-building in Jyväskylä, Finland. The simulation model was calibrated concerning the heating and cooling energy, because the performance of the building was evaluated using results of the calibrated simulation model as reference to the measured performance. The calibrated simulation model was built for continues commissioning. This paper explains the calibration process and its results. The measured and calculated energy use of the building corresponded to each other as the result of the calibration. INTRODUCTION The purpose of the study was to evaluate, how calibrated simulation model can be used in assessment of the building energy performance. The heat use and electricity use of the HVACsystem were evaluated as well as the indoor temperatures. In the year 2003 the first version of the simulation model was established and the pilotbuilding was constructed. The measured and simulated results differed from each other about 30 % concerning the heat use and 15 % concerning the electricity use in the first year. The results are presented more exactly in sources [1] and [2]. The simulation model was calibrated utilizing building automation system (BAS) and building energy management system (BEMS). The building automation system was used in determining the ventilation air flow rates, the set point temperatures of the room devices and of the supply air. The air flow rates, which were underestimated in the original model, were corrected to the calibrated model. The measured air flow rates and temperature of the supply air and the electricity use of the lighting and the office devices were used as time dependent input parameters in the simulation model. The building energy management system was utilized in determination of the electricity use and the heat use of the building. The input files needed in the simulations were generated from BAS and BEMS. The indoor temperatures were evaluated using duration curves concerning utilization time of the building. The duration curves were also compared to the simulated temperatures. Basic Information of the Building The case building is situated in Jyväskylä, 350 km from the Finnish capital, Helsinki. The building gives accommodation for the Department of Information Technology of Jyväskylä

2 Polytechnic. The construction works was finished by May 2003 and the building was taken into actual use in August The five-storey building consists mainly of classrooms. The building has also an assembly hall, a library, an auditorium, a lunchroom, a kitchen and a bomb shelter, which are situated in the ground floor. The working rooms of teachers are situated in the fifth floor. The floor area of the Pilot building is approximately m 2 and its exterior volume is m 3. Over students are studying and more than 40 teachers and other personnel are working in the building. The Principle of the HVAC System The classrooms and the working rooms of the case building have heating and cooling panels detached from the ceiling. Floor heating is used all over the ground floor. The conventional radiators are not used for heating. The building is heated by district heating and it is cooled by electricity using two refrigeration compressors and one storage tank and in addition free cooling by outdoor air is used. The ventilation system has combined heating-cooling-free cooling coils and a rotating heat recovery unit. HVAC-system has also a mechanism, which recovers the indoor overheat from the cooling panel s liquids to the supply air. The innovative patented system is advance low temperature heating system. The principle of the HVAC-system is explained in reference [3]. The building is conditioned using an integrated heating, ventilation and cooling system. The heating and cooling liquids are transferred through a 3-pipe system with common return liquid. The HVAC-system is presented in figure 1. The building has variable air volume (VAV) ventilation system [4], which is controlled with the both indoor air temperature and carbon dioxide level [5]. EMS and BEMS The case building has separate energy building management system (EMS) and building automation system (BAS). BES measures hourly heat, electricity and cold water uses. Measured values are reported monthly, daily and hourly using tables and figures. Heat use, which is weather corrected by degree day method, is also available. Besides the control of the HVAC-system, building automation system measures temperatures in 20 of the total 50 rooms, temperatures of liquids, position of valves, rotation speeds of the motors of fans and pumps as well as chamber pressures in air-handling-units. Also timetables of the AHUs and set points and set point curves can be viewed on the BAS. BAS can be used over internet, using a password protected user interface. A part of the measured data is saved to the BAS server of the case building, and it can be transferred trough the Internet using three file formats, HTML, CSV and XML. CSV-protocol was used in the evaluation of the performance of the building.

3 Air-handling unit Incoming air Water to air heat exchanger Water to air heat exchanger Supply air Rotating heat recovery system Exhaust air Return air Cooling tank Water to water heat exchanger Water to water heat exchanger ROOM Cooling of rooms Heating of supply air Cooling panels Heating panels District heating Heating and cooling liquids are merged Figure 1 The HVAC-system of case building METHODS Simulation Program IDA-Indoor Climate and Energy is a program designed for studying the indoor climate of zones of a building and for simulating energy consumption of a building [6]. IDA-ICE is an extension to an IDA simulation environment and an advanced user can simulate any system with the aid of the general functionality of the IDA simulation environment.

4 In normal circumstances, the building to be simulated consists of one or more zones and a primary (heat producing) system and one or more air handling units. The weather data is supplied by weather data files or it can be synthetically generated. The shading of the surrounding buildings is also evaluated. Predefined building components and other parameter objects can be loaded from a database. This can also be used to store personally defined building components. The mathematical models of IDA-ICE are described in terms of equations using a formal language named NMF, which can be used to make new modules or to replace existing program modules. The actual function of the components and relationship between the components models are modeled using NMF-files. Calibration of the Simulation Model The calibration of the simulation model of the case building included the following steps: 1. Developing a model which determines the volume flows of VAV-system using the rotation speed and pressure rice over the fans in calculation 2. The internal heat gains from the electric devices were determined using hourly electricity measurements from the BEMS 3. The leaking of the building was evaluated using information from the literature 4. The set temperatures of the supply air as well as the room temperatures were determined using the BAS 5. The set temperatures of the entering heating and the cooling liquids were also determined using the measurements of the BAS 6. The simulated output values, for instance for the indoor air temperature, the temperature of return liquids, and the energy consumptions, were compared to measured ones to evaluate the validity of the input parameters The first version of the simulation model of case building was made by a Finnish HVAC engineer company Olof A. Granlund. They modeled the building with a simulation program RIUSKA [7], which is based on DOE 2.1 E. Case building was modeled again by the researchers IDA-ICE and the model was calibrated using the measurements of building automation system. The principle of the calibration process is presented more precisely in the reference [8] concerning the commissioning and in the reference [9] concerning simulation model itself. The volume flows to each of the rooms were calculated based on the calculated indoor temperature and the calculated carbon dioxide emission from the people. However, the calculated total volume flows differed much from the measured ones, because the exact patent protected control strategy and the real occupancy level were not known. Due to that the measured and calculated heat uses differed quite much from each other. At the next phase the volume flows of each of the VAV-flow AHUs were taken directly from BAS-measurements based calculation model to the simulation program. The volume flows were divided in the rooms in the proportion of the floor areas, because the exact volume flows of the rooms were not saved to database of the BAS. At the same time the electricity use of the rooms were determined from the hourly electricity measurements and divided in the rooms with the same principles as the division of the volume flows. The electricity use of the HVAC was reduced from the total electricity use.

5 RESULTS Use of Energy for Heating Figure 2 presents the measured and calculated heat use of the case building in the first and second year of the building in use. The measured heat use was 30 % more than the simulated one during the first year. The difference was mainly due to the difficulty to determine the actual volume flows of VAV-system. The heat use of the second year was calculated after several corrections to the model. The calibration process included procedure explained in the previous chapter. The most important measure was to determine the variable air volume flows using a model. It was found out comparing the first estimation of the volume flows afterwards, that volume flows were underestimated with 30 % in the first year. 180 The heat use of IT-Dynamo in 1. and 2. year Heat use / floor area [kwh/m 2 /a] MEASURED IDA-ICE RIUSKA EN Heat use 1. year Heat use 2. year Figure 2 The heat use of the case building during the first and second year in use The heat use of the second year was calculated using three different calculation programs, two simulation program IDA-ICE and RIUSKA and a standard calculation method (EN 13790) [10]. The results of RIUSKA were not calibrated, and that is why the results of calibrated model of IDA-ICE correspond best to the measured heat use in the second year. The result of standard calculation overestimated the heat use with several percents. The Electricity use of HVAC-system Evaluation of the electricity use HCAC-system including fans, pumps, cooling devices etc. was difficult due to the same problems as in the determination of the heat use. The electricity use of the fans was dominant concerning the electricity use of HVAC. That is why the determination of the volume flows [4] was important also to find out the exact electricity use of fans and therefore the whole HVAC-system.

6 In the first year the measured electricity use of HVAC was 47 kwh/floor-m 2 /a as while the calculated one was 35 kwh/floor-m 2 /a. The measured and calculated electricity use of HVAC -system was according to both the measurement and the simulation 40 kwh/floor-m 2 /a in the second year. The difference between the measured and calculated values disappeared because of the calibration. Besides the determination of the volume flows, the electricity of the cooling devices was able to be determined more exactly in the second year than in the first year. That was done developing a mathematical model based on measurements. The electricity use of the cooling system was according to electricity measurements 12 kwh/floor-m 2 /a. The energy production of the free cooling system was according to the measurement based model 36 kwh/floor-m 2 and according to simulations 33 kwh/floor-m 2 /a. The whole panel cooling energy use of was according to the measurements and the simulations 48 kwh/floor-m 2 /a at the same time, and therefore 75 % of the cooling power was produced using the free cooling. The measured and the calculated total cooling energy need are presented in figure 3. The total and free energy needs were underestimated a little in the simulations compared to the measurements in spring Cooling energy per conditioned area Energy, kwh/floor-m /04 10/04 11/04 12/04 1/05 2/05 3/05 4/05 Tot al measured Free measured Total calculated Free calculated Figure 3 The measured and calculated energy use for cooling in the case building between Approximately 23 kwh/m 2 /a of the total electricity use of the HVAC-system 40 kwh/m 2 /a was consumed by the fans in the ventilation system. The electricity use for the cooling was 12 kwh/m 2 /a. The rest of the electricity 5 kwh/m 2 /a was consumed by the pumps and the control devices. The electricity use of the lighting, PC:s and other office devices was 83 kwh/m 2 /a in the second year, which was two times higher compared to the consumption of a similar buildings in Finland.

7 Free Energy Savings An estimation of the energy production of the free cooling system was measured to be 286 MWh and simulated to be 259 MWh between 09/ /2005. The total COP of the cooling system is estimated to be 1.2, which is typical COP-value of the whole cooling system. The total COP includes all the power losses in the production of the cooling energy. It is not the same as COP of a refrigerator, which is normally between 2 and 3. The savings of heat use were 162 or 107 MWh according to measurements and calculations respectively. In the calculations the lowering in efficiency of the heat recovery unit was taken into account. The total energy savings was about 14 % in heat use, 25 % in electricity use and 20 % in the average according to the measurements. The same values were a little lower according to the simulation results, but the differences are because the deficiencies in the model. Savings are calculated also in euros in a year and current value of the savings in ten years calculated with an interest rate of 5 %. The investment costs of the system are not remarkable more than in a regular system according to manufacturer of the system. The results are presented in Table 1. Table 1 Comparison of calculated and measured savings in the case building Measured Simulated Electricity Heat Total Electricity Heat Total Total energy use in MWh Energy saving in MWh Saving in % Saving in euro Current value in euros / 10 years Figure 4 Duration curves of the indoor temperatures in the case building

8 Evaluation of the Indoor Climate The indoor temperatures of the class rooms and the working rooms were estimated using duration curves. The duration curves presented in figure 4 were calculated concerning the time, when the building has been in actual use. The temperature has remained between 21 C and 26 C in the class rooms and between 20 C and 23 C in the working room. The calculated and measured temperatures correspond quite well to each other in a little working room 530, but differed about 1 C from each other in large classrooms 207 and 426 between and DISCUSSION The energy performance and the indoor climate of an educational building were evaluated using measurements results and simulation model. The calibration of the simulation model was done based on measurements of the building automation system and energy management system. The calibration process took two years, but after that the measurement and simulation results to correspond to each other. The main reason for differences between measurement and calculation results were the difficulties in determining the exact volume flows, the control strategy and the actual the utilization factor of the building. The lack of the information of the exact control strategy was found out to be the main reason for difficulties to calculate the exact volume flows, the indoor temperatures and the energy use for cooling. When the volume flows and indoor set temperature was taken from measurement results of BAS, the calculated heat use and electricity use of HVAC-system correspond to each other quite well. The simulation model should be kept as simple as possible when assessing a real system. The complicated models are difficult to calibrate, when the calculation parameters are more difficult to find out. The duration of the calibration process should also be much shorter, one month or two at the most, to make the calibration cost-effective. LITERATURE 1. Evaluation of the energy efficiency of a complex educational building, IBRI 2005, Hannu Keränen, Timo Kalema, Tampere University of Technology, Finland, 2005, 9 p. 2. Experiences of using models and information of building automation system in commissioning, Hannu Keränen, ICEBO 2004, Timo Kalema, Anssi Pesonen, Tampere University of Technology, Suomi, 2004, 17 p Modelling the ductwork of VAV-system, Annex 40, Hannu Keränen, Timo Kalema, Tampere University of Technology, unpublished, Finland 2004, 15 p aspx, IDA Indoor Climate and Energy, EQUA Simulation AB, Sweden, 2002, 243 p. 7. RIUSKA- Energy Simulation Tool - for the entire Building Life Cycle, Olof Granlund Oy, 2 p. 8. Using whole-building simulation models in commissioning, ANNEX 40, David E, Claridge, TAMU, USA, 2002, 14 p. 9. ASHRAE GUIDELINE 14, Measurement of Energy and Demand Savings, ASHRAE, USA, 2002, 165 p. 10. Thermal performance of buildings calculation of energy use for space heating, EN ISO 13790, CEN, 2003, 60 p.