Category Archives: Sonar-Collecttors

Performance Analysis of R123 and R134-a. Cooling Cycles Powered by a Flat Solar Collector

Mohammedi K.; Mabizari S.; Badkouf D.; Chegroun N., LMMC/GTT
University M. Bougara, Boumerdes 35000, Algeria.

• introduction:

The most widespread cooling systems are based on the mechanical compression of refrigerant vapours. The installation of such equipments in lonely areas, in particular in developing countries, often runs up against the non­availability of classical sources of energy. While in Developed countries, relying heavily on fossil energy, need to use more effectively renewable energy sources which are less harmful for the earth’s environment is growing and more according to Kyoto protocol. The conversion of solar energy to cooling energy by the thermodynamic way can be obtained by a three-heat-reservoir refrigerating system evolving between two sources and a heat sink. Here, the coincidence of the maximum cooling loads with the maximum availability of the solar radiation is of great interest in solar refrigeration [4],[6].

This paper is dealing with the development of a computational simulation of a cooling cycle powered with a flat solar collector working with a two-phase thermosiphon [1].

DESCRIPTION OF THE REALISED SYSTEM

The solar DEC plant serves two meeting rooms of the chamber of commerce in Freiburg. The rooms are almost fully glazed with outside shading devices. Figure 2 shows the smaller one of the two meeting rooms ("Cafeteria”) and the collector field situated on the roof of the building. It is divided in four parallel fields of each 25 m2. Two fields are facing west, the other two facing east. The inclination of the collectors are 15° in either case. The reason to mount the collectors with this roof given inclination was to reduce the costs for the support construction. In this way the system cost for the solar collector field including the installation was reduced down to 210 € per m2 /12/. The Cafeteria has a maximum capacity of 20 persons, the meeting room (“Sitzungssaal”) a capacity of 100 persons. The nominal volume flow rate is 10.200 m3/h. The meeting rooms can be air-conditioned

Figure 2: the small meeting room and the collector field

separately. The maximum volume flow of the Cafeteria is 2700 m3/h, for the meeting room 7800 m3/h.

Daylight in underground (exposition) spaces

Truus de Bruin-Hordijk, Siuhang Chan and Marinus van der Voorden Building Physics Group, Faculty of Architecture, Delft University of Technology P. O. Box 5043, 2600 GA Delft, The Netherlands E-mail: G. J.de Bruin-Hordijk@bk. tudelft. nl

The world population is still growing and people will always need more space for living. Problems arise especially in the urban environment. One of the possibilities to solve the problems is to make constructions and buildings below the earth’ s surface. However, underground spaces give many people negative associations with cold, dampness and most of all darkness. It feels gloomy and unsafe. People need light, natural light where possible, and they like to be connected with their surroundings.

Daylight is dynamic and gives information about the weather and the time. The possibilities for the use of daylight in underground spaces has been investigated.

1. THE SCOPE OF THIS PAPER

In order to investigate the possibilities for the use of daylight in underground spaces we have limited our study to one underground space with only one light entrance, a tube in the ceiling, to measure the level of illuminance for different dimensions of the space and the tube. One light entrance for one space was a precondition made beforehand, because it is the most simple model and one light entrance above earth surface can be easily integrated into the surroundings or can be hidden by landscaping.

First, preliminary experiments in the daylight chamber of our faculty were done.

After that, a simulation model of an underground exposition space is made with the computer program (desktop) Radiance [1]. Computer simulations with a diffuse sky and a clear sky are done. After the first conclusions, different variants for the light entrance are simulated in Radiance in order to avoid the negative effects of the direct sunlight. At the end of this paper a design concept for the light entrance is shown.

Model Measurements in the Artificial Sky

Figure 4: Artificial Sky at the T. U.B.

Figure 5: Cross-Section of the Artificial Sky

The most convenient, reliable and precise solution to describe and follow the illuminance distribution and efficiency of the skylight is to perform scaled model measurements in the artificial sky. The main advantage of these physical model measurement it is possible to follow and analyse all the necessary and investigated material and geometry properties and characteristics — even without knowing the exact mathematical and physical background of the events. In case of the artificial sky the Input can be precisely determined — since any standard CIE sky condition can be set-up. With the help of the scaled, physical model of the daylighting system — the Output can also be measured enabling to analyse, compare and evaluate all the investigated illumination characteristics of actual skylight. The accuracy of this method meets all practical requirements. The sky itself is a 6 m diameter hemisphere, illuminated around its parameter under its horizontal plane. All required standard sky conditions — i. e. CIE Overcast Sky — can be achieved and maintained throughout the measurements. The daylighting model can be placed in the middle of the sky, and inside the model all the illumination values can be measured and the efficiency of the system can be precisely analyzed.

Existing calculation method

to determine light distribution and illuminance efficiency

1.

2.

3.

4.

5.

6.

Transmis­sion of trans­parent structures

Clear or diffused transpa­rent

structures

Obstruction of trans­parent structures

Reflection of trans­parent structures

Shiny or matte light — guiding surfaces

Geometry of skylight

I. Grunn Method

Yes

No

No

No

No

Partly

II. Daniluk Method

Yes

No

Yes

Yes

No

Partly

III. C. I.E.16. Pub­lication, "Skylights”

Yes

No

No

No

No

Partly

IV. C. I.E.16. Publ., "Monitor skylights”

Yes

No

No

No

No

Partly

V. C. I.E.16. Publ., "Shed skylights”

Yes

No

No

No

No

Partly

VI. Lumen Micro 7.0 computer software

Yes

Yes

No

No

No

Partly

VII. TTI TS-A5 Dim. "Dome skylights”

Yes

No

No

Yes

No

Partly

VIII. TTI TS-A5 Effi­ciency of skylights

Yes

No

Yes

No

No

Partly

IX. S. Birch, I. Frame, Daylight

Yes

No

No

No

No

Partly

X. B. R. S. Method

Yes

No

No

No

No

Partly

XI. Lightscape computer software

Yes

Yes

No

No

No

Partly

XII. Skylight Dimen­sioning Method

Yes

Yes

Yes

No

No

Partly

Table 1: Existing Daylighting Calculation and Dimensioning Methods

Existing Daylighting Calculation Methods

The table above (Table 1.) indicates some of the existing investigating methods, and it also lists the properties, taken into consideration to determine the illuminance distribution in the space bellow. None of the listed existing methods or computer software consider all the properties of the skylights, which are playing an important and basic role in the light distribution and efficiency.

These methods are not able to differentiate between shiny or matte surfaces and they are not able to handle all the geometrical properties of a certain light modulating structure. At the calculation of diffused surfaces the transmission values are taken into consideration on a very base level, because these formulae are not including inclination angles of surfaces, which can play very important and determining role in some case.

These facts are proving that the existing calculation methods are all neglecting some important features, this is leading to the necessity to handle the problem using a new and different system of investigation. The model measurements in the artificial sky are able to provide a more exact and global answer to this question.

POWER LAW MODEL

The derivation requires two generalisations: a pressure potential versus flow relationship, and a system pressure drop versus flow relationship. A very simple but useful assumption for the relationship between pressure potential and volume flow is:

pp = KPVm (1)

Figure 1: Pressure potential vs. volume flow

where Kp = ppref/Vrefm is determined at a reference point (Vref, pref) near the optimum, and m is a negative exponent. Fig. 1 shows pressure potential lines for a few values of m. Note that if m = 0, then pp = Kp, denoting a constant pressure potential.

A useful assumption for the system pressure drop in incompressible flow is: Pl = K|_Vn

(2)

where n will typically be 2 when system pressure drop is dominated by minor losses, and closer to 1.75 when the pressure drop is dominated by Reynolds number dependent wall friction losses (White, 2003). The solid line in Fig. 2 represents the system loss curve.

Note that the effect of the variation of density with temperature rise through the system is disregarded, but may be included in the choice of K and n in the vicinity of each operating point. The turbine pressure drop is then: pt = pp — pL = pp — KL V (3)

Figure 2: Pressure potential and pressure loss vs. volume

flow, and fluid power (shaded area)

Since the change in density across a solar chimney turbine is typically small (Apt < 2 %) we can regard the air flowing through the turbine as incompressible, i. e. the fluid power is equal to the product of the volume flow and total pressure drop across the turbine:

P = pt V = (pp — Kl Vn) V (4)

The shaded area in Fig. 2 represents the fluid power. The power generation rate of the turbine depends not only on the characteristics of the flow system it is part of, but also on those of the turbine itself. In the present paper, however, we assume that the turbine efficiency does not vary appreciably with changes in flow rate, or, if it does, the variation in turbine losses may be accounted for in the system pressure losses.

Modeling and Simulation of Solar-Assisted Absorption Cooling System

Teclemariam G. Nemariam, Royal Institute of Technology, Dept. of Energy Technology, Div. of Applied Thermodynamics and refrigeration, Brinellvagen 60, SE-100 44 Stockholm Prof. Per Lundqvist, Royal Institute of Technology, Dept. of Energy Technology, Div. of Applied Thermodynamics and refrigeration, Brinellvagen 60, SE-100 44 Stockholm

Abstract

In this paper an analytical study is performed on solar energy utilization in space cooling of a building using a solar driven single-effect absorption refrigeration system. It is modeled with a transient modeling tool TRNSYS, Transient Simulation Program. The main components of the system are, solar collector, hot water storage tank, auxiliary heater, absorption chiller, and different components of building. Two types of solar collectors: double-glazed and evacuated tube collectors are used in this study. Two different locations: Assab, Eritrea and Nicosia, Cyprus are chosen to see how system performance and efficient vary.

The effect of collector area and hot water storage tank volume on the solar energy extraction is studied and discussed. The effect of hot water and cooling water temperatures on the performance of the absorption machine is studied.

The effect of sizes of insulation thickness, shading devices, overhang and wing wall on cooling load of the building is calculated and discussed.

The highest system efficiency is obtained when evacuated tube solar collector is used in both locations, but is higher for Assab for a given collector area. The generator inlet water temperatures for Assab are 86°C and 85°C when evacuated and double-glazed collectors are used respectively, while for Nicosia they are 86°C and 83°C. The yearly cooling load for Assab is 265 MJ and for Nicosia it is 78.6 MJ. The highest cooling load for both locations is obtained during July and for the non-insulated building it is 30.5 MJ for Assab and 16.02 MJ for Nicosia. The lowest cooling load is obtained when 0.2 m insulation thickness and 1.5 m overhang and wing wall is added. The cooling load reduces 34% for Assab and 25% for Nicosia in the first addition of 0.05 m insulation thickness.

Introduction

Electricity and some natural gas are the common energy sources for air conditioning systems. Alternative energy sources are needed for near future since the demand of air conditioning and the cost of energy is increasing. Solar energy is one of the possible alternative energy sources for cooling systems and one of the advantages of using solar energy, as energy source is that the maximum energy is obtained when the cooling load is at its peak.

Absorption refrigeration system is one of the available technologies, which use solar energy as heat source. Most solar-powered absorption cooling projects to date have used single-effect lithium bromide absorption systems. Single-effect absorption system gives best results in the temperature range of 80 to 100oC and limited in COP to about 0.6 to 0.8 [1]. If one considers an absorption refrigeration application system to include the solar collectors, storage tank auxiliary heater, building pumps, piping systems etc, it is not only the absorption chiller, solar collectors and other components which must minimize energy usage, but the cooling load of the building must also reduce as much as possible.

Constructing a hardware model of a building cooling system and performing a test in order to obtain all parameters that are needed for a complete design of a system consumes more time and money compared to that of computer modeling and
simulation. Many researchers have studied and modeled different solar assisted air conditioning systems. Comparison has been made between conventional and solar cooling systems [2], between solar assisted single-effect, double-effect and triple­effect cooling systems [3], between flat plate solar collector, evacuated tube collector and compound parabolic collector [4], and between cooling systems of various combinations of solar collectors and absorption cycles [1]. Most of them were interested in energy supply and cooling systems and the application of each model is limited to a particular condition. The cooling load minimization has not been taken into consideration.

The purpose of this work is to model and simulate a solar assisted air conditioning system for two locations; Assab, Eritrea and Nicosia, Cyprus and comparison has made in terms of optimum collector slope, solar fraction, system efficiency, hot water inlet temperature and cooling water temperature. In addition, the cooling load of the building is calculated with and without insulation, overhang and wing walls. The system is modeled for one year using a TRNSYS program together with meteorological weather data of both locations. System performance of two different collector models: evacuated solar collector and double-glazed selective surface flat plate collector has been done. The optimum system efficiency and solar fraction of each system is calculated and compared based on the appropriate area and slope of collector, size of storage tank, insulation thickness, overhang and wing walls.

IEA-SHC Task25 Design tool

In the framework of IEA Solar Heating and Cooling Task 25 activities, a new software is currently developed /6/. The aim was to produce a user-friendly tool, which would allow the user to design a system without extensive software training.

The simulation program calculates the hourly energy demand of the solar-assisted air­conditioning sub-systems. The calculations are performed on an hourly basis and are summed up to calculate the annual energy demand.

The outputs of the software include the following: electrical energy demand for fans, pumps and compressors; energy demand of the (thermal) back-up system; water consumption. The annual total costs of the system are calculated based on the annual energy demand of the components and their investment, maintenance and capital costs.

The building loads can be calculated or imported if evaluated through building simulation programs like e. g. TRNSYS, EnergyPlus, ESP-r.

Several solar assisted air-conditioning technological solutions can be simulated using this tool. Numerous types of solar collectors are available in a selection diagram that already includes all the necessary coefficient/performance settings and a minimum storage capacity calculation routine. The user can define the collector area and orientation. In general, the routines dealing with the solar energy supply allows a detailed calculation of the performance capability of the plant.

The refrigeration module enables calculation of the following types of cold water production: Vapour compression machine, absorption system, adsorption system, free cooling by means of cooling tower, use of well water. Calculations can be made for air-based systems as well as for combined water-air systems. Depending on the selected systems (with/without air handling unit, with/without chiller), the conditioned space can be supplied with mechanical ventilation or infiltration only, and chilled ceiling or fan-coil systems are possible for sensible cooling.

The design tool will be available for free for the first year after publication in summer 2004.

BRDF results and validation

As detailed in Andersen (2002), three types of graphical representations were developed to provide various visualization possibilities of the transmitted or reflected light distribution features, in addition to a recombined view of the six calibrated images, gathering the latter into a unique orthogonal projection:

• the projection of the BT(R)DF values on a virtual hemisphere, allowing a precise anal­ysis of the angular distribution;

• a photometric solid, representing the BT(R)DF data in spherical coordinates with grow­ing radii and lighter colors for higher values, illustrated in Figure 6;

• several section views of this solid, providing an accurate display of the numerical values distribution.

BRDF visualization*: photometric solid (hemispherical light reflectance* = 0,5)

BRDF visualization*: photometric solid (hemispherical light reflectance* = 0.01)

.

Figure 6: BRDF representation as a photometric solid.

285

270 I 10.05 255

‘ I.

(a) Opalescentplexiglas, (вг, фг) = (40P, CP) (b) Holographic film (HOE), (вг, фг) = (OP, OP)

An in-depth validation of both BTDF and BRDF was conducted, based on different ap­proaches (Andersen, 2004): [13]

• bidirectional measurements of systems presenting a known symmetry and verification against standard luminance-meter data or analytical calculations;

• empirical validation based on bidirectional measurements comparisons between dif­ferent devices; in case of disagreement, however, no conclusion can be established;

• assessment of hemispherical optical properties by integrating BT(R)DF data over the whole hemisphere and comparison to Ulbricht sphere measurements (Commission Internationale de l’Eclairage, 1998);

• comparison of monitored data with ray-tracing simulations to achieve a higher level of details in the BT(R)DF behaviour assessment.

These studies led to a relative error on BT(R)DF data of only 10%, allowing to confirm the high accuracy and reliability of this novel device.

Conclusions

This paper presents the conception and construction of an innovative, time-efficient bidi­rectional goniophotometer based on digital imaging techniques and combining BTDF and BRDF assessments. To allow reflection measurements, a controlled passage of the incident beam into the measurement space was created, minimizing parasitic reflections around the sample. Openings in the detection screen for the situations where it obstructs the incom­ing light flux were also required, made as small as possible to restrict the produced blind zones; to remove these elliptic covers, a motorized extraction and repositioning system was developed and tested successfully

This design proved efficient and reliable, for both the light beam penetration into the mea­surement space and the passage through the obstructing screen. The high accuracy achieved for BTDF assessments was checked to be kept for BRDF measurements as well, placing re­liance on the assumptions made in the construction of the instrument.

Acknowledgements

This work was supported by the Swiss Federal Institute of Technology (EPFL) and the Com­mission for Technology and Innovation (CTI). The authors wish to thank Pierre Loesch and Serge Bringolf for their contribution in the photogoniometer’s mechanical development.

Monthly and daily performance

3000

2500

2000 :

500

0

Figure 6 shows the daily delivery water temperature (OTL), ambient tem­perature, and tank bounding walls tem­peratures. It is ob­served that there is a fall of water tem­perature having co­incidence with the occurence of water consumption (curve ). This fall

is in the order of 2 Figure 6: Daily performance of the facade for domestic hot water pro­to 6 depending duction. Day March 11th. Barcelona climate. Consumption profile 1

on the water flow

required (at 19 hours, the larger consumption produces the larger drop of temperature). Numerical monthly results obtained for both climatic conditions, are shown in Table 6. represents the mean monthly outlet water temperature from tank (delivery temperature).

Barcelona:

Month QLOADMJ/ni~}

OTL°C

Sol,

ih

Geneve:

QLOADMJ/in-}

OTL°C]

Sol,

ih

1

158.01

26.07

0.38

0.46

72.53

20.14

0.17

0.37

2

145.73

26.15

0.38

0.46

76.38

20.83

0.2

0.38

3

166.73

26.49

0.4

0.47

134.33

24.21

0.32

0.43

4

158.7

26.29

0.39

0.49

129.71

24.16

0.32

0.46

5

161.22

25.93

0.38

0.5

140.07

24.43

0.33

0.49

6

162.73

26.53

0.4

0.53

160.31

26.24

0.39

0.52

7

175.19

26.94

0.41

0.55

183.16

27.57

0.44

0.53

8

189.16

28.25

0.45

0.55

181.99

27.43

0.43

0.52

9

191.02

28.82

0.47

0.53

172.76

27.36

0.43

0.5

10

196.6

28.65

0.47

0.5

141.12

24.79

0.34

0.47

11

175.33

27.63

0.43

0.48

72.2

20.23

0.18

0.39

12

156.18

26.51

0.38

0.45

61.23

19.55

0.15

0.34

Total

2036.59

27.02

0.41

0.5

1525.79

23.91

0.31

0.45

Table 6: Monthly perfomance for both climatic conditions. Consumption profile 1, stratifica­tion considered represented by 5 nodes_________________________________________

How those issues were addressed —

The architectural approach was an holistic one, from environmentally responsible design, to a healthy building for its users, with positive commitments at all levels. The building not only addresses ecological and energy issues, but health, economy and community.

From a global perspective, the intent was to whatever possible, within the given constraints of an existing building and limited budget, to contribute to the reduction of greenhouse gases. This has been achieved by an array of ESD measures, including solar passive design where possible, supplemented with energy efficient and energy reducing means for active systems where able.

From a national perspective, there was a conscious effort to utilise Australian products in preference to imported products where available, to be a leader in local government, and to contribute to society in a socially responsible way.

From a local perspective, local and regional tradespersons, suppliers and manufacturers were given preference where possible, including the local Builder who won the tender over several larger metropolitan based firms.

The most significant of these is the Geothermal HVAC system, utilising the stability of the below-ground temperature. In a climate with winter frosts and sub-zero temperatures, over 40 degree heat in summer, and a diurnal range in spring and autumn of 20 degrees plus, the geothermal, despite its initial capital cost, incurred a payback of just over four years.

Timescale

The project was engaged in November, 1998, and the first sketch plans presented to Council prior to Christmas that year. Construction documentation was completed for the Tendering process by April, 1999, with construction commencing in May, 1999.

Work was completed in February, 2000 with an official opening by the Premier of NSW soon after. Awards include Banksia 2001 Environmental Awards nomination, the Inaugural 2001 Green Building Awards Bronze Medal, and 2001 RAIA Country Division Awards.