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.

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_________________________________________

In order to examine the feasibility of integrating external solar heat into the water steam cycle of a power plant, a model based on an existing reference plant was de­fined. This reference plant is a typical fossil fueled conventional steam power plant with an output of 393 MW and 7 feed-water preheating stages. Using APROS a com­prehensive model of this power plant was built-up, adapted and parameterized. Es­pecially the parameterizing is a very time-consuming step due the great amount of lay-out data like geometries, isometries, geodetic elevations, thermodynamic data, valve characteristics and automation concepts that have to be integrated into the model.

The power plant has been subdivided into more than 500 single components. For each component the one dimensional unsteady differential equations for the conser­vation of mass, momentum and energy are solved. Heat transfer, heat capacity of solid walls and two phase flow phenomena are taken into account. On the basis of this model several different kinds of plant configurations with or without an external heat source have been simulated. Careful calibration of the model has been carried out to meet the steady-state design and guarantee values.

To model the parabolic trough collector in APROS, design values calculated by steady state simulations combined with data taken from the literature were used [1,9]. The generation of steam with a heat capacity of 60 MW at noon in July was set as boundary condition for the collector design. The simulation is done with parabolic collectors of the type LS-3 (see figure 2) with a length of 100 m. Ten of them are added up to a 1000 m collector line. According to this, 15 lines in parallel are neces­sary to provide a peak load of 60 MW required for the simulation.

The collector efficiency is assumed to be constant at 67 %. This simplification is of sufficient accurancy for the simulations carried out in this paper, but will be corrected in future work. The collector feedwater pump control guarantees that the water pumped through the absorber tubes gets vaporized and superheated to a constant temperature of 380°C.

• System configuration:

Figure 2 shows the configuration of the three heat reservoir cooling system. The main section of the solar cooling system can be divided into three flow loops: The solar collector flow loop, the ejector and cooling flow loop. The three flow loops are crossed by the same working fluid (R134a, R123). The choice of the refrigerants was subordinate to the saturation curve shape and to a certain extent to the knowledge of their thermodynamic and thermophysical properties.

The superheated vapour produced in the solar collector is sent to the ejector flow loop where the driving effect is produced. In our case, the intensity of the solar radiation has a direct influence on the vapour mass throughput of fluid at the collector exit and implies an intermittent flow (e. g. the solar collector in Tamanrasset (far south) will record a value of mass flow rate higher than in Algiers (north)). At the condenser exit the fluid flow separates into the driving massflowrate and the secondary massflowrate related each other by the entrainment ratio ra.

In Figure 3, the double Rankine cycle is illustrated in a logP-h thermodynamic diagram. It’s a combination of two basic Rankine cycles. The R123 and the R134a refrigerants have a positive — slope saturated vapor line. So we do not need important superheating compared to negative slope saturated line fluids where the isentropic expansion 1-2’ can induce vapor condensation that could affect the ejector performances.

Fig.1 the solar cooling ejector system

The DEC — plant is continuously monitored by registration of about 70 measuring points. All the important process information like temperature, humidity, volume-flow, operation signals of the humidifiers, ventilators, desiccant and heat recovery wheel, volume-flow controller and the position of the air duct flaps are registered in a 10 s — time step. For the evaluation one minute average values are used.

The monitoring campaign gives the chance to have a detailed look on non-ideal plant behaviour and offers thereby the basis for optimisation. Furthermore the monitoring suits to the purpose of evaluating the customer satisfaction and of evaluating the energy performance. The important value for the customer satisfaction are the room conditions. The energy performance is characterised by electricity and fuel consumption, solar gains and the efficiency of the heating and cooling performance.

Figure 3 shows a sketch of the flow sheet of the desiccant cooling plant including the ducts to the room.

1.0 Accuracy of measurements

Evaluating the monitored data some systematic errors came up:

• volume-flow measurement of small volume-flows: The volume-flow-meter has to work reliably in a range of 500 to 10200 mF/h. This is almost impossible for one single volume-flow-meter. Therefore the small volume-flows values have a large error margin.

• Humidity and temperature measurement in air ducts with rotating elements and little turbulence gives only the temperature information of the measuring position. For the introduced SDEC plant the dehumidification of the desiccant wheel can be analysed only in tendencies. The absolute values of adsorbed water vapour are not representative because of the strong influence of the rotation on local temperature and humidity distribution /6/.

• As inlet temperature the ambient temperature, measured at the north side of the building, is used. Meanwhile additional temperature measurements showed that the inlet temperature at the entrance of the plant is higher than the north side temperature. The reason for this temperature difference are natural convection effects at the east facade of the building, where the inlet duct for the desiccant plant is located.

1.1 Plant operation

The yearly plant operation hours depend on the using times of the rooms. Both rooms are used as meeting rooms and therefore they are discontinuously occupied. In 2002 the total amount of operation hours amounts up to 1335 hours, in 2003 up to 1289 hours.

Table 1 shows the operation hours and real using hours of both rooms. Operation hours means the hours the plant is running and air conditioning the room. Using hours or hours of occupancy means the hours where the rooms are really used by people for meetings. In 2002 for example the "Cafeteria” was air conditioned for 681 hours, but used "only” 506 hours. This difference is caused by the start — up period of the plant, where the rooms have to reach the comfort conditions.

operation hours Cafeteria on Cafeteria occupied Sitzungssaal on Sitzungssaal occupied 01 — 12/2002 1335 681 506 901 623 01 — 12/2003 1289 517 336 962 731 table 1: comparison of operation hours and hours of occupancy, 2002/ 2003

For evaluating the difference the facility manager of the IHK SO is keeping note of the hours of occupancy.

1.2 Room conditions and user satisfaction

The room conditions can be compared against the requirements of the German standard DIN 1946 part II /13/. This standard defines temperature and humidity thresholds for indoor comfort. These requirements, given by the red frame, can be visualised in a temperature — humidity — diagram, as shown exemplary in figure 3.

figure 3: comfort area (cp. DIN 1946 part II) of the “Sitzungssaal”, 1 — 12/ 2003

The points represent 1-minute average values of return air temperature and humidity in the rooms. The return air values represent the whole room situation. Therefore they are controlled and evaluated. The different seasons of the year are illustrated by different symbols. Most of the measured return air values are inside the comfort area. For the summer and spring quarter some data points are lying outside. These data points are mainly exceeding the limit of 11,5 g/ kg absolute humidity but keeping the limit of 65 % relative humidity. This situation is caused by the control design, which was controlling only a threshold of relative humidity. This control design was changed in July 2003. Now there is included an absolute threshold limit.

Characterising the comfort conditions the hours of threshold exceedance were evaluated. Table 2 shows the using hours and exceeding hours of both rooms for 2002 and 2003 separately. The calculated ratio shows clearly the more difficult situation of the "Cafeteria”. Their glazed facade is orientated to east, south and west and therefore extremely influenced by external loads caused by irradiation.

	Cafeteria Occupied th]	limits exceeded th]	ratio	Sitzungssaal occupied th]	limits exceeded th]	ratio
01 — 12/2002	506	150	0.30	623	56	0.09
01 — 12/2003	336	87	0.26	731	95	0.13

table 2: absolute and relative hours of limit exceedance, 01/2002 — 12/ 2003

The main part of the exceeding hours are caused by humidity limit exceedance. As mentioned above there where some reasons within the control design. Analysing the plant performance, some other reasons could be found out. For example, the assumed efficiency of the heat recovery wheel was not reached. Looking for reasons, it was realised that the two rotating wheels, i. e. dehumidifer wheel and heat recovery wheel, have to rotate in opposite direction in the cooling case /6/ and in same direction in the winter case. Caused by the german climate the wheels were optimised for the winter case. The influence of changing the direction of rotation will be analysed in further investigations in 2004.

0 10 20 30 40 60 60 70 80 80 100 of operation hours figure 4: cumulative frequency curves for ambient and room temperature 2002 and 2003 Figure 4 illustrates the comparison of the years 2002 and 2003 in an other way. The cumulative frequency curves are evaluated using 5 — minute-average temperature values only for the operation times of the plant. As room temperature the exhaust air temperature of the air conditioned room is used. For the times, where both rooms are used the temperature of mixed air streams is chosen. Figure 4 illustrate the percentage of temperature ranges within the operation time.

Looking at the ambient temperature of 2002 and 2003 it can be seen, that in 2003 at 25 % of the operation time the ambient air temperature was higher than 25 °C, whereas in 2002 this was the case for 11 % of the time only. Looking at the room temperature, in 2002 2.5 % of the operation time the limit of 27 °C was exceeded. In 2003 this was in 5 % of the operation time the case.

SHAPE * MERGEFORMAT

In /14/ it was evaluated that in Freiburg the average ambient air temperature during summer1 2002 was 1.5 K higher and during summer1 2003 5.2 K higher than in the Test Reference Year, which was used for simulation. Comparing the results with the promised 0 — 2 % operation time exceeding the temperature limit of 27 °C of the simulation study, the realised conditions are very satisfying.

1.3 electricity consumption

The total electricity consumption for the whole monitoring period was about 26649 kWh. This value is measured in total for all plant consumers by a central electric power meter.

	07 — 12/2001	01 — 12/ 2002	01 — 12/ 2003	Total
electricity consumption	6652	9577	10420	26649

table 3: electricity consumption 07/ 2001 — 12/ 2003

The electricity consumption is in general far higher than estimated. Three main reasons

were found to be responsible for the high consumption /15/.

• High stand-by electricity consumption, which varies between 0,2 and 0,5 kW. The higher value is caused by security functions which are active in winter. For the whole year this means a standby electricity consumption of approx. 2600 kWh.

• Fan efficiency was overestimated. The calculations done in the phase of plant design act on the assumption of a constant overall fan efficiency of 0.6 (hydraulic/electric). This assumption is right for high volume flows; in this case the efficiency can be even higher. But the volume flow is varying according to the room demand and is often quite low. In 2002 and 2003 the inlet volume flow is at more than 60 % of the operation time lower than 4000 m3/h. At 4000 m3/h the fan efficiency is about 0.45 and at 2000 m3/h for example only 0.25.

•

inlet volume now in m’/h/10 figure 5: el. consumption before and after changing air duct pressure control (minutely values)

Constant air duct pressure control caused at low volume flows higher air duct pressure than necessary for delivering the air. The higher pressure must be generated by increasing the frequency and therefore the electricity consumption. This control was changed in summer 2003. Now the demanded air duct pressure is implemented as a function of the volume flow. Figure 5 shows the results of the changed control. The electricity consumption per inlet volume flow decreased significantly.

The reasons found for the high electricity consumption are not caused by solar components of the system. This means that high stand-by consumption and constant air duct pressure control could in the same way be also a problem for conventional ventilation systems. For both the solar desiccant system as well as the conventional air handling unit there is a potential for optimisation in general.

Discussing the energetic performance one should compare the solar DEC plant with a reference system. The reference system must be a ventilation system serving the same rooms with the same comfort, therefore a compression chiller is needed. Calculating the reference system return air humidification and heat recovery is used to minimise the refrigerating capacity of the chiller. The COP of the chiller is assumed to be 4. For the reference system a nominal pressure drop of 727 Pa and for the solar DEC system a value of 1382 Pa was assumed. The higher nominal pressure drop of the solar DEC system is caused by the desiccant wheel, the second humidifier and the collector field. The duct pressure drops are the same.

figure 6: comparison of electricity consumption of a solar DEC plant and a compression chiller driven reference system

For calculating the electricity consumption the above mentioned findings concerning like stand-by consumption, volume flow dependent efficiency and air duct pressure control were considered in calculation. Therefore, in figure 6, the calculated electricity consumption of the solar DEC system is similar to measured values (cooling mode, 2002).

Comparing only the electricity consumption of fans and pumps, as ca be seen in figure 6, the reference system needs less electricity. This is caused by lower pressure drops and less components. Calculating the electricity consumption for the reference system with compression chiller (COP = 4), the ambient and room conditions given in figure 1 were assumed. Part of the refrigerating capacity is covered by enthalpy recovery. The necessary heating capacity was neglected for the discussion.

As figure 6 clearly shows the electricity consumption of a reference system with compression chiller at the assumed conditions would be definitively higher. Of course it has to be taken into consideration that caused by the not optimised direction of rotation during the summer season in the last years, the assumed inlet air conditions could not be always realised with the solar DEC system.

1.4 Collector performance

The yearly air collector performance is characterised by total specific irradiation and the specific collector gains. For the evaluation of a system without any storage and irregular operation, the irradiation in times of operation is also important to know.

Therefore the efficiency, ■p, for this solar autonomous system is defined in two different ways.

П, оы = (1)

QIRR, total

n. = —Qolaa:— (2)

operation

IRR, operation

Equation (1) defines the efficiency by dividing the gained solar energy by the total irradiation. Equation (2) defines the efficiency by dividing the gained solar energy by the amount of irradiation within the times, where the plant was operating.

In table 4 these values are given for 2002 and 2003. The value of the total collector efficiency is quite low, because of the low amount of yearly plant running hours. The collector efficiency in operation times is ranging between 20 and 25 %. Taking into account, that the collector gains are only usable in the desiccant and the heating operation mode, this is an acceptable result.

	total irradiation [kWh/ m2]	Irradiation plant on [kWh/ m2]	total collector gain [kWh/ m2]	total collector efficiency	collector efficiency plant on
01 — 12/ 2002	1092	371	74	0.07	0.20
01 — 12/2003	1296	414	100.8	0.08	0.24

table 4: collector performance values

є

collector

32,4

(3)

solar ,2001—2003 P EL, coll

Interesting for primary energy aspects is the question of used ventilator electricity for "collecting” the solar gains. Therefore an electricity coefficient is defined by dividing the solar gains by the collector fan electricity consumption (equation 3). This was done for a period between July 2001 and end of April 2003. The electricity coefficient is about 32.4.

It is important to mention that the electricity consumption of the collector fan is also influenced by the pressure drop of the desiccant wheel. Its pressure drop is at least in the same range as the pressure drop of the whole collector array. Therefore it can be estimated that the electricity factor including primary energy consideration would be at least double as high if only the electricity consumption due to the solar collector pressure drop is considered.

In 2002 and 2003 nearly 19 % of the collector gains were used for heating purposes. In the heating case between 15 and 18 % of the necessary energy input could be covered by this solar input.

1.5 Cooling performance

The cooling energy is calculated by balancing the input air stream between ambient and input conditions. The driving energy input for the cooling case is solely covered by the solar air collector gains. Therefore the solar fraction for the cooling case is 100%.

The cooling process can be characterised by the "coefficient of performance”, COPthermai. This value points out the ratio of useful and invested energy.

COP _ Qcoolmg Vinlet P! hambient hinlet ) (4)

thermal (4)

solar, cooling solar, cooling

Table 5 shows the values of the cooling performance for the whole monitoring period. The thermal COP varies between 21 and 38 %. The difference between the average thermal COP value of 2002 and 2003 can be explained by different ambient conditions (cp. Figure 4) and by changed volume flow distribution of the inlet volume flow. total cooling energy plant [kWh] collector gains used for cooling [kWh] COP, thermal 01 — 12/ 2002 1263 6039 0.21 01 — 10/ 2003 3068 7996 0.38 table 5: cooling performance values

The thermal COP increases with increasing ambient temperature. This is caused by the greater temperature difference between ambient and room. Looking at the COP as function of the inlet volume flow, it was realised, that the COP increases with increasing volume flow. In 2003 the average inlet volume flow was higher than in 2002. This effect is caused by the specific configuration of the solar DEC plant. There are times where only a small inlet volume flow is needed. In case of high irradiation the energy given by the collector field is more than needed for regeneration.

A COP comparing the cooling capacity with the electricity consumption therefore required is not yet available on an annual basis. But looking at the assumed conditions of figure 1 and the results of figure 6 for a volume flow of 8000 m3/h the electricity related COP for the reference system would be about 1.5 and the one of the solar DEC system 5.2.

As already mentioned, in the summer case the heat recovery wheel and the desiccant wheel should rotate in opposite directions /6/. This will be realised within the cooling season 2004. A significant increase of the heat recovery efficiency is expected. The results will be presented in future publications.

1.1 Experimental Set-up

Measurements were executed in the Visual Comfort Evaluation (VCE) set-up which consists of a 1:5 scale model of a 3.6 x 5.4 x 3 m3 office room with an artificial overcast sky, see [1]. The inner walls are matt black (RAL 9005) to exclude the influence of internal reflections on the effect of the contrast region. A hole in the long side of 0.3 x 0.6 m2 simulates the window. The wall next to the window is painted matt white (RAL 9010). All materials are positioned to the right side of the window, and if the materials were not high enough they were elevated using a piece of string, see figure 1.a.

All luminance measurements were performed with a Minolta LS-110. The top-angle is 1/3 degree. At a minimum distance of 1014 mm, the diameter of the measured spot is 4.8 mm. The measurements were taken at a height halfway between the top and the bottom of the window. On the right-hand side of the wall measurements were taken every 2.5 cm in the horizontal direction. Two measurements were taken in the transition region, and one in the window along the line given in figure 1.b.

Figure 1: Experimental set-up (a) and measurement points given in the vertical cross section (b)

Read More 10.07.2015   Sonar-Collecttors The design of the Solar Window As an answer to the search for truly building integrated solar energy systems, an experimental design was proposed, which combines all useable forms of solar energy into one system; active and passive heating, PV electricity and daylight. The concept also aims at visually exposing the system in a novel and attractive way. The key for this challenge was simply to use a window as the glazing for a solar collector. By using hybrid absorbers and pivoted reflectors behind the window, a multifunctional and responding building skin is achieved. The basic concept of building integration is hence changed from the notion of the solar energy system being part of the building envelope, to the idea of the building envelope being part of the solar energy system. The system consists of three main components: the window, the hybrid absorber and the reflector, see figure 1. The combination is intended to give synergy effects by ascribing the components multiple functions redactor screens in open mode redactor screens mode insulation PV/T hybrid absorbar _ Figure 1: Description of the Solar Window in open and closed mode The hybrid absorber is fixed in an angle of 20° to the horizontal plane. A 2 mm thick aluminium absorber has PV cells laminated on the upper side. The thickness reduces movements due to temperature differences, which otherwise puts the PV cells at risk of cracking. Water pipes are attached to the bottom for distributing active solar gains and for cooling the PV cells and the cavity between the window surface and the reflectors. Building integrated, they also serve as supporting structure for the absorbers and the reflectors, and as the pivot for the reflectors. EPS insulation around the pipes also makes endings for the rotation of the reflectors, and connects the insulation of the reflectors into a continuous convection shield. The reflector screens are primarily intended for concentrating the solar radiation onto the hybrid absorber. Thus, the need for expensive absorber and PV cell area is reduced, as it is largely replaced by substantially cheaper reflecting material. The resulting distance between the fixed absorbers thus makes it possible to achieve transparency between them when the reflectors are of little use. Hence, daylight may filter through the structure, which also gives passive thermal gains. For passive solar house designs with use of large south facing window areas, risks of overheating and thermal losses are common. The reflectors are intended to reduce these problems, by serving as internal sunshades during daytime and as internal insulation during night time. The reflecting geometry is a two-dimensional parabolic curve, with the optical axis tilted by 15° from the horizontal plane, see figure 2. It has a geometrical concentration factor, i. e. the ratio between the glazed opening and the absorber area, of 2.45. The curve is extruded horizontally as a trough, and the reflector is constructed as a sandwich composition with a 35 mm EPS core between the reflective film on the concave side and a birch veneer on the convex side. The window serves as the climate shield and as the solar radiation transmitter for the system. After the solar radiation is transmitted through the window, it is distributed as daylight, passive or active heating, or as PV electricity, in proportions depending on the handling between the closed or open modes. For maximal input for the PV/T absorber through a vertical surface, the transmittance through the window needs to be maximized. Therefore, a highly transparent glass with anti-reflective coating is used. Due to the over-heating precautions by the solar shading and the cooling effect of the absorber, a higher transmittance of the glazing can be tolerated. Read More 10.07.2015   Sonar-Collecttors MAXIMUM FLUID POWER CONDITION The volume flow for maximum fluid power (MFP) is found when dPf /dV = 0: A[(KpVm — K_Vn)v]= 0 (m + 1)KpVMFp -(n + 1)KLVMFP = 0 The flow at maximum fluid power is then given by: Vm (6) The pressure potential at maximum fluid power follows when substituting Eq. (1) in Eq. (5): (pp )mFP = "(m+1) KLV|V|FPn (7) This relatively simple relationship depends on the exponents m and n only. In practice the power law relationship between pp and V would, for the appropriate values of Kp and of m, approximate the real relationship only in a limited region, but the point where Kp and m are calculated may be adjusted iteratively. The same applies to KL and n. In time-dependent analyses, a quasi-steady state condition is assumed during the time that the optimum is sought. In practical terms this implies that the turbine configuration (for example the rotor blade setting angles) can be adjusted much faster than plant operating conditions change. The assumption is that during this interval a fixed relationship between the pressure potential and the volume flow exists, or Kp and m are constant, and so are KL and n. (9) The MFP flow rate is then 1/V3 of the maximum flow rate that occurs when pt = 0. Also, when m = 0 (pp = constant) and n = 2, Eq. (8) reduces to: ‘ ‘ (2-0) = 2 = 3 ( pt pp, (2 +1) TP JMFP (10) In the special case when m = 0 and n = 2, Eq. (6) reduces to: VMFP _ 0.5 f pp ^ V 3KL J The turbine pressure drop as fraction of the pressure potential at maximum fluid power is found by subtracting the system loss from the pressure potential: pt = pp — KLVn ь^^ f Pi 1 = (n-m) pp Jmfp" ( +1) (8) Note that when m = -1, then V = 0 and pp is infinite; the power law is unrealistic at very small flows. Kp(m +1)" KL (n + 1)y n-m SHAPE * MERGEFORMAT The MFP condition occurs at pt/pp = 2/3 only in the special case when m = 0 (i. e. constant pressure potential) and n = 2. When n = 2 and m Ф 0, then pt/ppfor maximum fluid power exceeds 2/3 when m is negative (i. e. pressure potential decreases with volume flow). Read More 10.07.2015   Sonar-Collecttors Components and System Description The main components of the system are: solar collectors, thermal storage tank, auxiliary heater, single-effect absorption chiller, and building. The flow diagram of the system is given in Figure 1. relief valve Figure 1. Solar-assisted absorption cooling system. The system is modeled using a TRNSYS simulation program [5]. The weather data of Assab is extracted from the result of experiment, while the weather data of Nicosia is extracted from Meteonorm [6]. Solar collectors The characteristics of two types of solar collectors, evacuated tube, ESC and double­glazed, DGC solar collectors are given in table 1. Table 1. Characteristics of the collectors used in the simulation No. Description ESC DGC 1 Fluid specific heat (kJ/kg K) 4.190 4.190 2 Tested flow rate (kg/h m2) 50.000 50.000 3 Intercept inefficiency 0.878 0.760 4 Efficiency slope (kJ/h m2 K) 5.148 15.690 5 Efficiency curvature 0.000 0.000 6 Incident angle modifier 0.200 0.100 Storage tank Two storage tanks with a volume of 2m3 and 1.5m3 are selected for the two systems, which include evacuated tube collectors and double-glazed flat plate collectors, respectively. Auxiliary heater An auxiliary heater is used to add energy to the system whenever the energy delivered from the solar energy is not enough to overcome the energy required. The heater has a maximum capacity of 25 kW. Absorption chiller The full description of the single-effect absorption chiller and its diagram is given in many literature studies and therefore excluded here. Building The model uses TYPE 19 (Transfer Function method). The model calculates energy loads based only upon the net gains or losses from the space. The loads are considered independent of the heating or cooling equipment operation. The user specifies the set temperature for heating or cooling. The program determines the energy necessary to keep the room at the set points. The details of the building are: Assab is located on Latitude 13.07°N, longitude 42.63°E and altitude 10m and Nicosia is located on Latitude 35.15°N, longitude 33.35, and Altitude 5 m. The building has a floor area of 92 m2, doors area of 13.3 m2and windows area of 4.78m2. Each wall is constructed of 0.24m common break and 0.02 m cement plaster. The floor consists of selected soil, stone and concrete coating (0.20m each) and cement tile (0.02m) and the roof consists of corrugated sheet metal (0.002m), stud and cheap wood ceiling (0.04 m). The doors are made of wood with 0.03 m thickness and the windows are made of 0.006m clear single-glass. Insulation with different thickness is added to the walls, roof and floor and the doors and the windows have overhung and wing walls. The thermal properties of the building materials are taken from [7] and [8]. The heat transfer through the floor of this particular building is calculated by the technique used in Thermal Performance of Building-Heat Transfer via the Ground-Calculation Manual [9]. Read More 10.07.2015   Sonar-Collecttors Tools for advanced design studies The highest degree in flexibility and precision offer open architecture tools. As the source code of the program modules which reflect the model components is open in these tools, the source can be modified or self written components may be added because of individual requirements. For example, advanced models for thermally driven chiller cycles /7/ could be integrated into the programme library of the simulation environment. The time step in the system simulation is in general adjustable, enabling thereby the user to implement and test more sophisticated control strategies in the modelled system. A detailed energy flow study including the part-load behaviour is possible with simulation tools of this type. As a disadvantage in the use of these open simulation platforms it should be mentioned that the setup of a desired system model requires much more effort compared to the programs, presented in the previous sections. Beside the development of the system model and of the energetic and economic performance evaluation strategy, the testing of the model can be considerably time consuming. Three types of these tools will be mentioned here, although more software tools may have the potential to be used for thermal system simulation. A worldwide well known computing software is Matlab, developed in 1984. This technical computing environment can be coupled with the graphical modular simulation surface Simulink. Several tool boxes for different research topics can be purchased for Simulink, one of them is the tool box CARNOT /8/, developed at the Aachen University of applied sciences, which provides components for heating systems and solar thermal collector systems. Additional components for cooling equipment may be added using the standard Simulink procedure for the implementation of self written code (C-language). Primarily designed for solar thermal and HVAC systems with their controllers, the simulation environment ColSim (Collector Simulation) provides improved numeric algorithms in the program’s solver to allow precise simulation also in small time steps down to a few seconds, a requirement especially in the development of control algorithms /9/. ColSim uses the plug flow model in tracing the mass flow through a hydraulic network. This approach allows a mass flow and energy balance in every time step, representing one of the main features in ColSim’s error detection routine. Currently, the platform Linux is used. The programme is available for free, and due to several users in different projects, the number of available system component models grows continuously. Public domain software is used for the graphical design of a desired system as well as in the visualisation of online results. TRNSYS /10/, commercially available since 1975, disposes of a large set of models for standard hydraulic components, solar collectors and other HVAC equipment. The subroutines, containing a certain component of the hydraulic system, are called ‘types’ in TRNSYS. The arrangement of the required types into a hydraulic system to be simulated is called simulation ‘deck’. While the hydraulic system may be composed and configurated using either the graphical surface or a text editor provided with TRNSYS, a special building editor (PREBID) is used to specify a desired building, in order to allow the calculation of heating / cooling loads in TRNSYS. To give an example for the application of TRNSYS, an additional type for a desiccant cooling system was developed at Fraunhofer ISE. This type contains the models for a desiccant wheel, heat recovery unit, humidifier, heat exchanger, fan and the like. In combination with a control and operation type for the desiccant cooling system, this type can be implemented into the hydraulic scheme of a TRNSYS deck. TRNSYS simulations using these additional components of a desiccant cooling system were applied in the design phase of the first solar autonomous air-conditioning system in Germany /11/. TRNSYS was also used in the simulation of the solar assisted cooling system of the new federal environment agency building in Dessau, Germany /12/. In this application, an adsorption chiller will be implemented for chilled water supply in order to cool mainly computer rooms. Cooling is required due to the high internal loads throughout the year, but in the cold season, the cooling load can be covered by direct evaporative cooling via the cooling tower. Beside a parametric study investigating different solar collector areas and storage sizes, the most promising system configuration was intensively studied by varying control parameters and the type of the solar thermal collector. For the adsorption chiller, cooling tower and for the system control, self written types were applied in the simulation calculations. 3 Summary Solar assisted air-conditioning is a growing application and provides the attractive opportunity in saving primary energy and peak-power demand in electricity. To date, most of the existing plants (approx. 50 installations in Europe) have been installed in the frame of demonstration and research projects and thus with very high effort during system design and planning. Actually, a lack of knowledge and experience in design and planning on the commercial side has to be overcome by measures to support the planning of the systems. Rules, guidelines and tools have been created for this reason in the course of numerous projects, with the capability in assisting the planning of a solar air-conditioning system on different levels. A selection of this measures was briefly discussed in this paper. The application of these or similar planning support measures is useful, since the integration of a renewable energy system with the property of fluctuating energy supply complicates the appropriate design and configuration of the system. Fundamental design errors may be avoided and the achievement of target values, e. g. of primary energy savings, can be ensured. Read More Календарь Апрель 2024 Пн Вт Ср Чт Пт Сб Вс 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30   Рубрики 1 BIOFUELS A Look Back at the U. S. Department of Energy’s Aquatic Species Program: Biodiesel from Algae A. Worrall ABOUT THE AUTHOR ACCELERATOR DRIVEN SUBCRITICAL REACTORS ADVANCED BIOFUELS Advanced Biofuels and Bioproducts Advanced separation techniques for nuclear fuel reprocessing and radioactive waste treatment ADVANCES IN Advances in Biochemical Engineering/Biotechnology Advances in Biofuels Advances in Biorefineries Alcoholic Fuels Algae Energy All alternative energy Alternative transportation An Indispensable Truth An Introduction to Nuclear Materials AN INTRODUCTION. TO THE ENGINEERING. OF FAST NUCLEAR REACTORS ANNEX III. AHWR. Bhabha Atomic Research Centre, India ATOMIC ACCIDENTS BACKGROUND Bioenergy Bioenergy — Realizing the Potential Bioenergy from Wood BIOENERGY. RESEARCH:. ADVANCES AND. APPLICATIONS BIOETHANOL BIOFUEL'S ENGINEERING PROCESS TECHNOLOGY BIOFUELS BIOFUELS 1 Biofuels and Bioenergy Biofuels for Road Transport Biofuels from Agricultural Wastes and Byproducts BIOFUELS FROM ALGAE Biofuels Refining and Performance BIOGAS BIOGAS 1 BIOMASS — DETECTION, PRODUCTION AND USAGE Biomass and Biofuels from Microalgae Biomass Conversion Biomass Gasification and Pyrolysis BIOMASS NOW — CULTIVATION AND UTILIZATION BIOMASS NOW — SUSTAINABLE GROWTH AND USE Biomass Recalcitrance Biomasses identities Biotechnological Applications of Hemicellulosic Derived Sugars: State-of-the-Art Biotechnological Applications of Microalgae Biotechnology. for Fuels and Chemicals Cellulosic Energy Cropping Systems Comprehensive nuclear materials DESIGN FEATURES TO ACHIEVE. DEFENCE IN DEPTH IN SMALL AND. MEDIUM SIZED REACTORS Design of Reactor Containment Systems for Nuclear Power Plants ENERGY Energy Efficiency ENERGY SERVICES IN THE HINDU KUSH HIMALAYAN REGION Energy Storage Estimating Loss-of-Coolant Accident (LOCA) Frequencies Through the Elicitation Process EUROSUN 2008 EuroSun2004 EuroSun2008-10 EuroSun2008-11 EuroSun2008-13 EuroSun2008-2 EuroSun2008-3 EuroSun2008-4 EuroSun2008-5 EuroSun2008-7 EuroSun2008-9 EXAMPLES OF REACTIVITY-CONTROL SYSTEMS Exploitation des creurs REP Fast Breeder Reactor Programs: History and Status Fast Reactor Safety. (Nuclear science. and technology) Fertilization Frequency Response Testing. in Nuclear Reactors Fuels and Chemicals. from Biomass Gebaudetypologie Bayern Geothermal Energy GREEN BIORENEWABLE. BIOCOMPOSITES Handbook Nuclear Terms Handbook of biofuels production Handbook of Small Modular Nuclear Reactors Hydrogen — Fuel Cells Hydropower IAEA RADIATION TECHNOLOGY SERIES No Infrastructure and methodologies for the. justification of nuclear power programmes Innovative Biofibers from Renewable Resources Integral design concepts of advanced water cooled reactors Introduction to Nuclear Power Liquid Biofuels: Emergence, Development and LIQUID, GASEOUS AND SOLID BIOFUELS — CONVERSION TECHNIQUES Management von Biogas-Projekten Materials' ageing and degradation in. light water reactors Microbes and biochemistry of gas fermentation Modern Power Station Practice Natural circulation data and methods for advanced water cooled nuclear power plant designs Natural gas Neutron Scattering Applications and Techniques Nuclear and Radiochemistry Nuclear Back-end and Transmutation Technology for Waste Disposal NUCLEAR CHEMICAL ENGINEERING NUCLEAR ELECTRIC POWER Nuclear energy Nuclear Power and the Environment Nuclear power plant life management processes: Guidelines and practices for heavy water reactors NUCLEAR POWER PLANTS NUCLEAR POWER the PUBLIC Nuclear Reactor Design NUCLEAR REACTOR ENGINEERING Nuclear Reactors 1 NUCLEAR REACTORS 2 Others Particle Image Velocimetry (PIV) Passive Safety Systems and Natural Circulation in Water Cooled Nuclear Power Plants PHYSICS OF. HIGH-TEMPERATURE. REACTORS POWER Pretreatment Techniques for Biofuels and Biorefineries Principles of Fusion Energy PROCESS SYNTHESIS. FOR FUEL ETHANOL. PRODUCTION Production of Biofuels and Chemicals with Ionic Liquids Progress, Challenges, and Opportunities for. Converting U. S. and Russian Research Reactors Pumping Pyrolysis Radioactive waste management and contaminated site clean-up Recycling of Biomass Ashes Renewable Energy Products Rudiger Meiswinkel, Julian Meyer, Jurgen Schnell Second Generation Biofuels and Biomass Small modular reactors (SMRs) the case of Russia solar energy Solar Thermal and. Biomass Energy Sonar-Collecttors SonSolar Springer Series in Materials Science Study on Neutron Spectrum of Pulsed Neutron Reactor Sustainable Biotechnology Switchgrass Technologies for Converting Biomass to Useful Energy The Asian Biomass Handbook The Experimental Analyze Of The Solar Energy Collector The Future of Nuclear Power Thermal biomass. conversion and utilization —. Biomass information. system Thoria-based Nuclear Fuels Type of Membrane Contactor Suitable for CO2-O2 Exchanges in Culture Broth Vereinfachtes Verfahren WAS INTENTIONALLY LEFT BLANK Why We Need Nuclear Power wind power WORKSHOP ON NUCLEAR REACTION DATA AND. NUCLEAR REACTORS:. PHYSICS, DESIGN AND SAFETY Автономное энергообеспечение Альтерантивная энергия Альтернативные источники энергии и энергосбережение Без рубрики Биотопливо Ветровая энергия Ветрогенераторы, солнечные батареи и другие полезные конструк­ции Возобновляемые источники энергии ВОПРОСЫ ТЕОРИИ. И ИННОВАЦИОННЫХ РЕШЕНИЙ. ПРИ ИСПОЛЬЗОВАНИИ. ГЕЛИОЭНЕРГЕТИЧЕСКИХ СИСТЕМ ГЕЛИОЭНЕРГЕТИКА Другая энергия Зарядные станции Источники питания Источники энергии ИСУ Концентраторы солнечного излучения КРЕМНИЕВЫЕ СОЛНЕЧНЫЕ БАТАРЕИ Получение кремниевых пластин для солнечной энергетики Применение солнечной энергии Разное Солнечная электроэнергия Солнечная энергия Солнечная энергия — использование Солнечные батареи Солнечные коллекторы Солнечный ДОМ ТОНКОПЛЕНОЧНЫЕ. СОЛНЕЧНЫЕ ЭЛЕМЕНТЫ. НА ОСНОВЕ КРЕМНИЯ ФОТОЭЛЕКТРИЧЕСКОЕ. ПРЕОБРАЗОВАНИЕ. 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