Simulation-aided commissioning of the Katsan building

Transcription

1 Simulation-aided commissioning of the Katsan building Pär Carling, ÅF-Installation, Stockholm Per Isakson, Building Sciences, KTH, Stockholm Per Blomberg, ÅF-Installation, Stockholm Jörgen Eriksson, ÅF-Installation, Göteborg SWEDEN Type of documents: Glossary Cx process Project Tool Model Type of building: Type of commissioning: Initial-cx re-cx retro-cx Continuous-cx Glossary check: yes no MQC task: Program Design Elaboration Realisation Operation Summary This paper describes an approach to initial building commissioning based on detailed simulation, measurements using the BEMS and evaluation and comparison of the simulated and measured result through powerful visualization. We demonstrate the approach on an office building in Stockholm, Katsan, which is currently under construction. The paper briefly describes the Katsan building including the HVAC-systems the detailed whole building simulation model built in IDA Climate and Energy some results from evaluation of the simulation model using the visualization tool Pia how the approach may support the commissioning process major obstacles to simulation-aided initial commissioning on the building level future work Introduction Not all HVAC-systems perform as well as they should. There is a vast potential to supply a satisfactory indoor climate and simultaneously save energy by better system solutions, better manufacturing, better commissioning and operation. Our basic assumptions in this research project is that A consistent focus on the performance in the design and construction process would lead to better and energy-saving HVAC-systems. The responsibility for the performance must be distinct. Simulation may play an important role in the performance-based construction process. Simulation is necessary during design and for verification of the performance of technical solutions in all stages. Design documents need to be scrutinized by an external party and comparison with a simulation model is an appropriate way of verifying performance in early stages. Appropriate interactive tools for analysis of measurements and simulation results would contribute to better HVAC-systems. Faults and malfunctions would be detected earlier and

2 to a lower cost. An experienced eye quickly detects many types of faults if data is presented in a proper way. The tools existing today are inadequate. In this paper we describe how we use a whole building simulation model of the Katsan building to perform initial commissioning of the system selection and design. The target is to decide whether the design is made in a proper way. The next step will include evaluation of the real building by use of measurements.

3 The Katsan building The Katsan building is located in Stockholm, Sweden and is currently under construction. The tenant that will move in late spring 200 is the architectural company (White Arkitekter) that designed the building. Figure 1 (left) presents the exterior. The entire façade is covered by glass. White Arkitekter organized a competition, containing distinct performance requirements, for the design of the HVAC-system. The winning contribution uses a slab-cooling system (figure 1, right) to cool the building mainly from cold ceilings. Figure 2 indicates a schematic over the HVAC-system. The primary energy source of cooling is seawater, also used for cooling of supply air. A combined coil either cools or preheats the outside air. Preheating use recovered energy from the return air. District heating is used for the convector system in the zones as well as post heating of air. The control system tries to maintain the heavy concrete slab at a certain temperature depending on outside temperature and time of the day. Cooling beams supply, if necessary, additional cooling in certain zones. Furthermore a temperature controlled VAV-system is used. The building is equipped with a modern BEMS. We will use the BEMS to collect data for evaluation of building performance. Semi-automatic data transfer via Internet is planned. Figure 1. The exterior of the Katsan building (photomontage) and the slab cooling system before the concrete have been poured on the floor structure. Sun Wind Tout Sea water Return fan Outside air Heat recovery coil Combined cooling and preheating coil Heating coil Supply fan The Katsan building Return air Supply air Slab cooling Cooling beams Figure 2. Schematic of the HVAC-system. The main systems are the slab cooling system, the convector system and the ventilation system. Primary thermal energy sources are sea water and district heating. Temperature sensor District heating Floor heating Pressure sensor Control valve Convectors Floor heating Pump Energy meter Heat exchanger Hot water

4 The system solution chosen is rather unconventional. A lot of effort was spent by the HVACdesigner on simulations to verify performance. The main concern was whether the slab-cooling and seawater systems were sufficient to meet the requirements. Simulation result supplied the HVAC-designer with basis to select appropriate windows, sunshade, temperature levels and flow rates. During the construction stage some major changes have been realized. The area reserved for the cooling coils in the floor structure turned out to be smaller than expected depending on a different design of the floor beams than documented on the drawings. This had of course effects on the possibilities of absorbing heat in the floor structure. Another change in a late stage was that the tenant on the first floor turned out to be a restaurant. This lead to changes in the ventilation system due to different operation schedules. A detailed simulation model of Katsan We have built a detailed simulation model of Katsan using the equation based simulation tool IDA ( Figure gives examples of the user interface. The model consists of twelve zones each of which includes walls, windows, convectors, cooling beams, slab-cooling system, supply air terminal device, exhaust air terminal device and detailed control of the systems. Furthermore a fairly detailed air-handling unit and the device for heat transfer from the primary side is modeled. The model consists of about 000 variables and simulation of a year takes about three hours on a modern pc (P4, 1.2 GHz). Figure. The detailed simulation model of Katsan. We use the equation based simulation tool IDA. The figure consists of a few screencopies of IDA s GUI. Each box contains either a component model (including equations, variables, parameters and links) or an aggregation (macro) of models.

5 In order to get a correct simulation model we implemented some additional models related to the control system in Neutral Model Format (NMF) and inserted the new models in the application IDA Climate and Energy. The model described is certainly a more elaborated model than what is usual in Swedish design projects. Compared to the more straightforward model used by the HVAC-designer the current one for example includes: The whole building instead of only critical zones The dynamic slab-cooling system including control instead of a constant temperature in the one of the slab layers The variable air volume system instead of using several models with different constant flow to check different operational modes Different zone temperature set-points during day and night instead of constant set-points Simulation-aided commissioning of the design Figure 4 illustrates an example of result (six variables) from a whole year simulation of the described model. We recently started to use carpet plots in the visualization tool Pia (see A40-D-M-SWE-ÅF/KTH-1) to analyze the result. We find carpet plots as a very clear way of communicating the result to the designer and client. The variables in figure 4 are (from the top); the outdoor temperature, the direct sun radiation perpendicular to the sun beams, the diffuse radiation to a horizontal surface, the total cooling power from the slab-cooling system, the operative temperature on floor 5, and the air supply flow to floor 5. The three first variables are taken from a measured climate file (Bromma 177). The notch in spring and fall is due to daylight-saving time. The first diagram indicates that the outside temperature in the climate file varies between 20ºC and +0ºC. A five-day period in the middle of the year (10 to 14 of June) reaches temperatures between +27ºC and +2ºC. The second and third diagrams illustrate the typical solar radiation profile in a northern country like Sweden. The fourth diagram indicates The slab-cooling system supplies cooling power in the afternoons in the middle of the winter. The order of magnitude is 50 kw. The maximum heat absorption occurs during the highest outside temperature (10 to 14 of June) and the maximum power is 0 kw. The control system was suggested to absorb heat only between and Other periods the slab system should redistribute energy in the floor structure. The diagram reveals that no heat is absorbed during and The fifth diagram shows that the operative temperature on floor 5 is usually between +ºC and +2ºC during daytime. However, during the hot period (10 to 14 of June) the temperature reaches +28ºC, which is higher than the performance requirements stated by the client. Thus, the results from the simulation model helped us to suggest a better control strategy than first suggested by the HVAC-designer, namely: run the slab-cooling system also between and during hot periods. The sixth diagram illustrates the airflow rate in the VAV-system. The highest flow rate is often utilized.

6 PiaPrint: :44 1, 01-Jan :00:00, 01-Jan :00:00 5, 01-Jan :00:00 1, tute 2, qsol_direk, qsol_diffu 4, qpbj_lklag 5, tz5opera_1, mz5tilluft Figure 4. An example of simulation result from the described Katsan model using a carpet plot in the visualization tool Pia. The variables are (from the top); the outdoor temperature, the direct sun radiation perpendicular to the beams, the diffuse radiation to a horizontal surface, the total cooling power from the slab system, the operative temperature on floor 5, and the air supply flow on floor 5. The three first variables are taken from a measured climate file. The notch in spring and fall is due to daylight-saving time , 01-Jan :00:00 4, 01-Jan :00:00, 01-Jan :00: The use of the visualization tool Pia has been absolutely necessary when evaluating such large data sets as those generated when performing whole year simulation with the comprehensive simulation model described.

7 Obstacles to simulation-aided commissioning The time that currently has to be spent for setting up a detailed whole building model is a major obstacle to simulation-aided commissioning. To build the described model we have used several weeks. In IDA there is a macro-function where it s possible to combine many component models to conglomerate of models. The use of this function may be a fruitful way to decrease the amount of time spent for modeling. Equation-based simulation is rather new. We expect that the equation solvers in the future will be able to handle more difficult cases. Today it seems like the user must be aware of several tricks in order not to get numerical problems. Another obstacle is that there is a lack of component models. In this project we were forced to develop a few additional models in order to correctly model the building. Developing models takes resources and preferably more models should be attached to the simulation software. If few models are available you tend to use the available ones for purposes not intended. This may lead to such coarse simplifications that the result becomes incorrect. A third barrier is that it is very easy to make a mistake when feeding input. A decimal point in the wrong place may ruin the result. Automatic data transfer from CAD like suggested by the IFC-concept is eagerly awaited. Some simulation software provides tools to support comparison of input (see for example It is crucial that the simulation model is made in a well structured manner. The filenames should be structured, and changes should be documented in a proper way. When building detailed whole building models and expecting the completed building to perform like described in the model we have realized that there are several steps in the construction process where the performance described in the model may get lost: The control contractor sometimes implements the control in a different way than suggested by the HVAC-designer. The control contractor prefers standard solutions to decrease the time spent for programming the control system whereas the HVAC-designer often tries to customize the system. Building contractors often changes the products specified in the terms of contract and consequently also the characteristics of the building. The operational staff running the building and HVAC-plant may change the operation due to complaints from the tenants and thus run the plant in a different way than suggested by the HVAC-designer. This will for example influence the energy performance. Future work We will continuously use the developed model to support the commissioning process of the Katsan building. We will examine how the model may be used to support performance tests. As soon as possible we will start to collect data via the BEMS. Measured data will be used to calibrate the model which will be tested with design boundary conditions to see whether the building perform as intended during design conditions. We will also look at how the model may support fault detection during the operational phase.