Download pdf - prof. Karel Kabele - cvut.cztzb.fsv.cvut.cz/files/vyuka/125bepm/prednasky/125bepm_02...CTU 125BEMP- Handouts L2 - Introduction to building energy performance modeling and simulation

CTU 125BEMP- Handouts L2 - Introduction to building energy performance modeling and simulation - prof.Karel Kabele 08/09

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125BEPM - Building energy performance modeling

Lecture handouts

2 - Introduction to building energy performance modeling and simulation

prof. Karel Kabele


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CONTENT 1 INTRODUCTION TO BUILDING ENERGY PERFORMANCE MODELING, SIMULATION METHODS AND TOOL (SLIDES 1-13) ... 3 2 CASE STUDY 1 (SLIDES 14-21).............................................................. 3 3 INTRODUCTION TO ESP-R (SLIDES 22-24) ...................................... 3 4 CASE STUDY 2 (SLIDES 25-34).............................................................. 3 5 EXEMPLAR (SLIDES 35-55)CHYBA! ZÁLOŽKA NENÍ DEFINOVÁNA. 6 ASSIGNMENT 1 ANALYSIS OF ENERGY USE IN DIFFERENT CLIMATE CONDITIONS (SLIDES 56-58) ..... CHYBA! ZÁLOŽKA NENÍ DEFINOVÁNA. APPENDIX A ................................................................................................... 4 APPENDIX B .................................................................................................... 9


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1 Introduction to building energy performance modeling, simulation methods and tool (Slides 1-13)

ASHRAE Fundamentals Handbook 2005 - Chapter 30 - NONRESIDENTIAL COOLING AND HEATING LOAD CALCULATIONS ASHRAE Fundamentals Handbook 2005 - Chapter 32- ENERGY ESTIMATING AND MODELING METHODS http://www.eere.energy.gov/buildings/tools_directory/ http://www.ibpsa.org

2 CASE STUDY 1 (Slides 14-21) Appendix A

3 Introduction to ESP-r (Slides 22-24) http://www.esru.strath.ac.uk Basic: http://www.esru.strath.ac.uk/Documents/esp-r_cookbook.pdf Advanced http://www.esru.strath.ac.uk/Documents/ESP-r_data_doc.pdf

http://www.esru.strath.ac.uk/Documents/ESP-r_userguide.pdf Self-learning course:

http://www.esru.strath.ac.uk/Courseware/ESP-r/content.htm

4 Case study 2 (Slides 25-34) Appendix B


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Appendix A


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Low energy cooling in historical library office hall

ABSTRACT

Requirements on working environment in office buildings according to Czech law express optimal air temperature, globe temperature, humidity and air velocity. In the case of historic library office hall with skylights, located in the centre of Prague the main problem was overheating during summer period. Paper describes problem analysis using CFD tools, measurements and building energy performance modelling tool, design of energy efficient and sustainable measures and evaluation of results.

1. INTRODUCTION

Historic library office hall, built in the beginning of 20th century, is used to service library users with catalogues, administration and library front office services.(Fig 1). Due to

technology development in recent years (computers, copy machines) there was significant growth of internal heal loads simultaneously with exacting of indoor environment requirements. Next major heat load source are sky lights. The hall is designed as single zone cast concrete hall 20*40*8 m with 6 double pitched sky-lights in the flat roof. Total area of skylights is 240 m2, glazing with no reflective sheet (r = 0,9). There is warm – air ventilation system installed with no cooling, built in last century. Because the only existing way of cooling of such space is fresh outdoor air ventilation, the basic problem of the hall is overheating in summer period, when

indoor resultant temperature exceeds required 26°C. This study describes possible solution of improvement of indoor environment, respecting the historical value of the building, using simulation and engineering approach.

2. METHODOLOGY

First idea to solve the summer overheating was to install traditional air cooling system, but due to high heat gains (over 140 kW) and limited possibilities of existing duct size increase this solution was cancelled. After

deeper problem analysis (Novoselac, Srebric 2002) together with architect, client and historical authority representative the integrated solution has been accepted. First step has been aimed to decrease exterior heat load from skylights. To achieve that, existing glazing has been covered by additional reflex film layer with shading coefficient s = 0,4. This step decreased heat load in critical summer period from 140 to 70 kW. In spite of reduced heat gains, existing ventilation system

Figure 2 Working places layout

Figure 1 Library hall


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with no cooling was not able to ensure thermal comfort in working zone. Next step was to

improve microenvironment at the working places of permanent employees, which are located generally at hall perimeter (Fig.3 marked with boxed numbers). There was accepted technical solution based of installation of radiative cooling ceilings below the lowered gallery, which runs along three sides of hall. Radiative cooled ceiling, designed for temperature gradient 17/20°C on the area 70 m2 has design cooling output 6 kW, which covers only less than 10% of total heat gains (ASHRAE 2001). This solution of course does not create thermal comfort in entire space of the hall, but according to engineering practice should improve thermal comfort locally, at the fixed working spaces. To evaluate this engineering prediction, CFD model of the hall has been created to simulate expected thermal behaviour and thermal comfort. 3. MODELLING AND SIMULATION To model solved hall, we used CFD package Flovent (Flomerics 2001; Kabele, Kabrhel 2003).

3.1 Model

Based on optimisation of detail level, computing time and computing stability we described problem with a grid of 122 240 cells covering the simulated space with variable density. Simulation runs under turbulent air flow model k-ε and static boundary condition, describing critical situation, when ambient temperature is +32°C.

There were three alternatives simulated (Fig 3.)

• Alternative 1 - reference, describes existing situation with no cooling ceiling installed.

• Alternative 2 describes situation, when cooled ceiling is installed along 2 sides of the hall

Figure 3. Simulated alternatives of cooled ceilings

1

2

3


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• Alternative 3 cooled ceiling installed along all three sides of the hall).

Cooling ceiling is installed in the height 2,45 m above floor level, width of the active zone is 0,6 m at the longer sides and 1,6 m at the shorter side of the hall. Surface temperature was set to constant +19°C to avoid air moisture condensation.

3.2. Results

CFD simulation method results into set of data, describing air velocity vectors and temperature scalars in each of grid cells. To select conclusive data from this huge data set (more than 40 MB of values for each simulated alternative) we used air temperature data presented by comparative graphs for monitored working places (Fig 4) and spectral air temperature and vector velocity analysis in cross-over sections of the hall. (Fig 5) Above described mathematical model was compiled to find out the influence of synergic action of thermal radiation and convection on the final state of internal environment in an office hall from the view of operative temperature and air temperature in local workplaces. Modell compared the current situation and the designed one, where two positions of cooling ceilings were designed (Kabele, Dvořáková 2004). Applied method of CFD (computational fluid dynamics) provides an idea of three – dimensional layout of temperatures and speed vectors of air flux in studied interior. In our case a static model was applied using external conditions

currently used to desing air-conditioning in summer period covering external air temperature influence and solar radiation with values for the noon of 21st July, next the influence of the floor being on the ground and the northern wall bordering the complex of massive buildings of the library. Concerning iternal sources thermal gains from office equipment (computers and copiers) were involved in computation installed according to the investor´s assignment. The main task was to reach the idea of the cooling ceilings´ impact on microclimate in a critical situation

Fig. 5 Operative temperature and air flow patterns –alternatives 1,2,3

1

2

3

Figure 4 Comparison of air temperatures in monitored working places


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therefore no working air-conditioning (assigned just for ventilation not for cooling) is improving thermal balance of the examinant space. Examined alternatives – positions of the cooling ceiling on two or three sides of the hall below the lowered galleries – clearly show the ifluence on the reduction of the operative temperature in the working places of the library during summer period. Alternative 2 – position of the cooling ceiling on three sides - proves better temperature distribution and heat load reduction in monitoring places. Negative radiation of cooling ceilings in these places causes the decrease of operative temperature as well as the decrease of air temperature by the influence of convective flows so that according to the conditions mentioned above the maximum of air temperature in monitoring points reaches 26,9 °C. It is necessary to warn that this solution doesn’t provide any elimination of heat loads or any temperature reduction in the whole space of the hall, but it only provides improvement of conditions on a local level in working places so that the working environment reaches the requirement of NV 178/2001, where the operative temperature in closed workplaces during the summer period is set to be 20-28 °C at the air flow speed of 0,1-0,2 m/s. Advantage of this solution is in low energy demand on the cooling source - capacity runs into 6 kW in maximum, which is approximately 11 % of heat loads of the entire place of the hall, reduced after the shading of glazing to 75 kW.

4.CONCLUSION

The presented case study shows possible uses of the method to decrease energy consumption in the office hall using local cooling. The development of application of the methods of computer simulation opens up a large space for future research in the field of optimization of the building energy performance.

6. REFERENCES: ASHRAE (2001). Handbook 2001 Fundamentals.

Atlanta:ASHRAE Flomerics (2001), FLOVENT – Introduction to Version

3.2 – Tutorial,. Flomerics: http://www.flovent.com/ Novoselac, A., Srebric, J.(2002) A critical review on the

performance and design of combined cooled ceiling and displacement ventilation systems. Energy and Buildings, Volume 34, Issue 5, June 2002, Pages 497-509

Kabele,K.,Kabrhel,M.(2003) Low-energy building heating system modelling. Proceedings of Eight international IBPSA Conference Building Simulation 2003, Vol.2,pp.599-604,11.-14.8.2003 Eindhoven, Netherlands, ISBN90-386-1566-3

Kabele,K.,Dvořáková,P.(2004).Optimization of work environment in library office hall with sky-lights. Proceedings of Indoor climate of buildings 2004, str.331-336, 21.-24.11.2004, Vysoké Tatry, SSTP, ISBN 80-969030-8-x


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Appendix B


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Indoor air quality in sustainable architecture

K.Kabele and P.Dvořáková

Summary: New tasks in indoor air quality are brought by sustainable building philosophy focusing on minimizing energy consumption like increasing the danger of moulds and CO2 concentration by lowering ventilation rates. Paper describes basic principles for sustainable buildings in Central Europe climate conditions taking into consideration common energy system solutions – integrated heating, cooling and ventilation system. Various alternatives are discussed in typical, low-energy and passive houses building envelope solution standards. Evaluation of indoor environment and energy performance is based on computer simulation results, using ESP-r based models, to quantify thermal comfort and energy consumption.

Keywords: sustainable building, modeling, ESP-r, IAQ, thermal comfort, energy consumption Category: Case Study

1 Introduction Low-energy building heating and cooling design concept in climate conditions of Central Europe is based on minimizing energy consumption as one of the critical criterions in building design aiming to decrease total energy consumption and environmental pollution at the same time with preserving or improving indoor air quality. The main question in low energy architecture is not only a well insulated building envelope, but also the design and the control of heating and cooling system,

which being energy distributors in the building are the main producers of the operational pollution. Heating/cooling system must cover transmission and ventilation heat losses/gains. Comparing with traditional buildings, where the main part of heat loss is transmission, the low-energy buildings are typical with reverse ratio of transmission and ventilation heat losses. There are several building elements, which are used to minimize energy consumption. Besides a well- insulated building envelope, there are elements like heat recovery, controlled air exchange rate, earth pre-heater, accumulation, solar energy utilization (PV and

water systems), wind energy utilization and systems like warm-air heating, radiant heating and cooling. In the Czech Republic computer modeling and energy performance simulation as well as indoor environment simulation are not usually used at the first stage of architectural design process for common buildings. Usually an expert for energy use and environmental control is invited to participate the design process at the stage when the building shape and structure is practically fixed. All recommendations given by this expert, coming out from an energy and environmental performance analysis, have to be carried out in such a designed building. This implementation is mostly very inefficient and expensive due to the difficulties in making major changes in the building philosophy. In our case, which is the subject of this paper, there was a very good co-operation between an architect and a specialist in building energy performance simulation. This could be a good example for a new approach to architectural design process. We hope that this case will help to answer the architect his usual question - "In which design stage it is the time to carry out an

energy and environmental simulation and what can I expect from it?" The co-operation between the

Fig. 2. Architectural concept of a typical office building

Fig. 1. Air heating/cooling concept for low-energy houses in Central Europe.

Energysource


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architect and the building energy specialist in our case started at the very beginning of the design process in finding conceptual solution of the building. In this phase, an energy and environmental analysis of various building concepts was carried out. The aim of this paper is to investigate how the energy demand and indoor climate are affected by changing boundary conditions, it is trying to express the difference between traditional and low-energy architecture. It takes into consideration both the quality of the building envelope and the heating system. ESP-r, an energy simulation program, was used for this purpose. Predicted mean vote (PMV), Percentage Dissatisfied PPD and cooling/heating loads are used as parameter indices for thermal comfort and energy consumption evaluation.

2 Problem description The idea was to design a low-energy office building with comfort indoor environment. The building itself is a three tracts office building. The office rooms for 1-3 persons are oriented south-north (Fig.2). The first requirement was to create comfortable working environment, the second to save energy together with finding low-cost solution. During a long discussion about using different low energy technologies (natural ventilation, solar chimney, heat storage) several basic questions raised like which U-value of the building envelope structures should be used, what kind of heating /cooling system should be designed and what level of indoor environment will be achieved using this system. Thinking of previous experience we accepted that in climate condition of Central Europe it is difficult to fulfill comfort requirements in an office building during summer period without an active cooling system. Therefore a concept of mixed radiant and convective heating/cooling system was accepted.

Table 1. Maximum values of overall coefficient of heat transmission according to Czech building regulations

Alternative U wall [W/m2K]

U window [W/m2K]

Demanded (DEM) 0,38 1,7 Recommended (REC) 0,25 1,2 Low-energy (LE) 0,15 0,8

In terms of energy three main categories of buildings are taken into account according to Czech building regulations [1], where the maximum values of overall coefficient of heat transmission are set. Parameters of the constructions in mentioned categories are in Table. 1. 3 Modeling and simulation To evaluate annual energy consumption and indoor environment quality during the entire year we selected ESP-r [2] modeling, simulating and analyzing tool, which enables with adequate accuracy and sensitivity

to obtain data to answer all of the questions from above. 3.1 Model A typical part of the building was chosen for simulation purposes containing two office rooms (each facing different cardinal point) connected with central corridor. Each of the rooms as well as the corridor represents one zone. (Fig.3)

Office rooms have the same following dimensions 4m x 6m x 3m, corridor 2m x 6m x 3m. Room 1 has one exterior wall with a window (dimensions 4,2m x 1,6m ) facing south and one door leading to corridor, Room 2 has a window of the same dimension as Room 1 facing north and also a door leading to corridor. No heat flux through side internal walls, ceilings and floors is assumed. Building envelope properties are the subject of simulation alternatives and are selected as three options according to Table 1. Heating and cooling system was defined by heating capacity controlled in range 0-500W, cooling capacity 0-2500W in each of the office rooms. Control of the system is running as pre-heat and pre-cool controller according to sensors, located in both of the rooms sensing mix of zone dry bulb temperature and MRT (mean radiant temperature). Actuator representing heating/cooling system transmits energy as mix of 75 % convection and 25% radiation, Set point for heating is 20°C; for cooling 26°C. There is no humidity control considered. Ventilation system was modeled supposing air change rate during working hours using value of 1 ac/hr for offices besides the value of 0,2 ac/hr representing infiltration during non-working hours. To get the knowledge about casual gains inside the building it is necessary to see the occupancy, equipment and lighting situation. Hours between 8 and 17 are considered to be working time. During this time in each office there are two people with two computers. Lighting during all seasons provides 500lx. According to [3] these sources produce 140W/person, 200W/computer and lighting 35W/m2. 3.2 Simulation

Fig. 3. ESP-r model of the building


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In the simulation we created three alternatives of the model. The insulation thickness was changed in the simulation to reach different U-values entering the computation (see Table 1). The whole year period was studied using Prague (Czech Republic) climate files. Integrated building simulation was used, with time step 1 hour and initial period 3 days. During simulation, no major problems were detected by the program. The discussion about the results was focused on heating/cooling energy consumption. PMV and PPD parameters were used to evaluate thermal comfort.

3.3 Results Temperature. In all three alternatives the temperature in both office rooms was within the acceptable range. During working time, when the system was on, temperature did not exceed required boundaries. The results in a one year period obtained from the simulation are summarized in tables 2 and 3. Resultant temperature ranges verify correct sizing of the heating/cooling system capacity.

Table 2. Max annual temperatures in zones. Alternative Room 1 Corridor Room 2 LE 27,52 30,84 29,08 DEM 27,54 30,78 29,08 REC 27,76 30,79 29,05

Table 3. Min annual temperatures in zones. Alternative Room 1 Corridor Room 2 LE 19,07 18,92 19,11 DEM 19,07 18,66 19,19 REC 19,01 18,81 19,12

Energy. Figures 4, 5 and 6 show annual energy consumption for heating and cooling and summary heating and cooling energy consumption. The improving of the building envelope thermal properties in this case decreases obviously heating energy demand and so logically increases cooling energy demand. We can say taking into account significant internal heat gains that the total value of heating and cooling energy consumption is the lowest in the building with “demanded” envelope parameters contrary to all expectation rising of course from the “low-energy” building envelope solution.

Energy consumption - heating

22,41

69,45

32,12

85,72

32,24

79,89

0102030405060708090

100

Room1 Room2

kWh/

a LEDEMREC

Fig.4 Annual heating energy consumption

Energy consumption - cooling

-8261

-5479

-7078

-4457

-7733

-5005

-9000-8000-7000-6000-5000-4000-3000-2000-1000

0Room1 Room2

kWh/

a LEDEMREC

Fig.5 Annual cooling energy consumption

Heating and cooling energy consumption

020004000

60008000

1000012000

1400016000

LE DEM REC

kWh/

a

Fig.6 Annual total cooling and heating energy consumption Thermal comfort evaluation is based on PMV and PPD classification of heated/cooled spaces. PMV is defined by six thermal variables from indoor-air and human condition that is air temperature, air humidity, air velocity, mean radiant temperature, clothing insulation and human activity. The value of PMV index has range from −3 to +3, which corresponds to human sensation from cold to hot, respectively where the null value of PMV index means neutral to maintain the PMV at level 0 with a tolerance of ±0.5 to ensure a comfortable indoor climate [3]. The PPD index is a description of estimated thermal comfort and a function of four physical parameters: dry bulb temperature, mean radiant temperature, relative humidity and air velocity, and parameters connected to the occupant such as clothing level, metabolic rate and external work. Tables 4, 5 and 6 and figure 7 summarize comfort evaluation during working time within a year. Comfort evaluation is based on activity level 70 W/m 2 with clothing level equal to 0,75 clo .


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Table 4. Comfort evaluation for LE alternative

LE Comfort PMV (-) Description Maximum Minimum Mean Standard value value value deviation room2 1.53 -1.43 0.5 0.42corridor 1.91 -1.43 0.98 0.43room1 2.13 -1.42 0.75 0.41All 2.13 -1.43 0.74 LE Comfort PPD (%) Description Maximum Minimum Mean Standard value value value deviation room2 52.31 5 14 7.05corridor 72.58 5 28.74 14.53room1 82.31 5 20.15 10.98All 82.31 5 20.96 Table 5. Comfort evaluation for DEM alternative

4 Conclusion Presented case study has shown a possible utilization of integrated simulation supporting the early conceptual design phase. The recommendation based on this approach is to continue in designing alternative DEM- demanded U-values, which will give the best results in terms of energy consumption together with the best results in comfort evaluation. The reason, why the results of the thermal comfort evaluation are so unsatisfactory (more than 40% of working time is PMV>1) is due to the relatively high summer temperature set point (+26°C) in connection with settled clothing value and activity of the occupants. 5 Acknowledgments This paper was supported by Research Plan CEZ MSM 6840770003.

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Comfort 9,7% 16,9% 15,6%Acceptable 44,3% 40,5% 41,3%Discomfort 46% 43% 43%

LE DEM REC

FFig.7 Annual distribution of PMV during working time. Comfort -0,5