Gunter Gartler, Dagmar Jahnig, Gottfried Purkarthofer, Waldemar Wagner
AEE-INTEC, A-8200 Gleisdorf, Feldgasse 19, Austria
Phone: +43/3112/5886/64, Fax: +43/3112/5886/18, Email: g. gartler@aee. at

Long-term heat storage enables a major technical break-through for an effective year round use of solar thermal energy. Thermo-chemical processes as used in sorption storage systems give a new chance to store the heat with a high energy density and for extended periods. The project MODESTORE (Modular High Energy Density Sorption Heat Storage) is being supported by the European Commission since April 2003. The major objectives of this project are the monitoring of a first generation system installed in the past and the development of a second generation prototype. The main improvement is the integration of key components (evaporator/condenser and the reactor) into one single container. A modular design enables to operate in a wide variety of applications in the near future. Test runs of the installed first generation system have been done under controlled conditions to gain operation experience and to assure a detailed characterisation of the complete system. A control program was written in order to operate the storage in a reliable and automatic way. Detailed experimental data of all tests were obtained, analysed and evaluated. Furthermore a simulation model was developed. The validation of the simulation model was done comparing simulated and measured charging and discharging cycles. The model represents well the basic performance of the adsorption heat store. The newly developed second generation prototype will be engineered and extensively tested, analysed and evaluated under practical conditions to allow the finalisation of the product development and identification of the most attractive market.

Fig. 1 compares the room and the ambient air temperature in / at the four low-energy office buildings. The cumulative duration curves show how often the temperature exceeds a given limit. However, these curves cannot be used to evaluate the comfort since the comfort depends on the ambient air temperature. The indoor/outdoor temperature graphs, which are independent of the actual weather, evaluate the comfort.

— The room temperature in the Fraunhofer ISE building is too high. While the room temperature was slightly too high in 2002, the room temperature did not meet the comfort range during the summer 2003 (temporarily 3 — 4 K too warm).

— The Pollmeier (low heat gains) and the Lamparter building (earth-to-air heat exchanger) provided comfortable room temperatures in summer 2002. In 2003, the room temperature was 1 — 2 K too high.

The graphs take only working hours into account. The following statements s1 — 4 can be derived from an extensive data analysis based on these measurements and are discussed in this paper:

(s1) Self evident, if the weather (and the other boundary conditions) do not change, the thermal performance of a building remains also unchanged.

(s2) Obviously, if the weather changes, the thermal behaviour of a building (here: degree hours over 25°C) will change.

(s3) If the chronology of climate situations (here: periods of warm weather) changes, the thermal performance of a building will change.

(s4) In both years, the buildings did not meet the comfort criteria strictly. The increased failure to meet the comfort standard in 2003 can be explained by using smaller time constants t than in 2002. That means that the heat storage capacity was completely utilised due to the longer cycle periods of warm weather.

Fig. 1: Cumulative duration curves of room and ambient air temperatures and indoor- versus-outdoor graphs with comfort criteria according to DIN 1946.

A "summer day” is defined by a daily maximum temperature of 25 °C or higher. Furthermore, the frequency of room temperatures above 25 °C is often used as a simplified comfort criteria for passively cooled buildings. For these reasons, this temperature limit is used as a consistent standard for comparison. The graphs for Fraunhofer ISE, Pollmeier and Lamparter show generally the same behaviour: Each building exceeded 25 °C more often during the warm summer 2003 than during the typical summer 2002, which is characterised by the degree hours Dh in Table 1.

The difference of the degree hours approximately corresponds to the area between the 2002-line and the 2003-line for the ambient and the room air temperature in Fig. 1. The ratio of the two areas indicates how the building can compensate for high ambient air temperatures: The smaller the ratio, the less the ambient air temperature affects the room temperature. The Fraunhofer ISE building (98 %) has coped with the summer 2003 worse than the Pollmeier (52 %) or the Lamparter building (63 %). This characteristic building behaviour is discussed — together with the energy balance of the buildings — in detail in the results analysis.

The measured variables over the course of the trial are presented in Figure 5 and 6 The estimates of mean and standard deviation of the recorded data are summarised іг Table 3. The measured data show that indoor air temperature is not homogeneous and present moderate vertical and north-south gradient. The differences observed betweei them are always less than 1 °C. It has to be notice that the indoor air temperature dati could be influenced by the wall surface temperatures, because the air temperature data are close to a ‘resultant temperature’, which takes values in between the actual mean radiant and indoor air temperatures. The indoor air temperature considered for analysis i the average of the air temperature measured by the sensors located near the north and the south walls at 1.5 m height.

SHAPE * MERGEFORMAT

5 4

3 2 1 0 -1 -2 -3

0 100 200 300 400 500

Time (Hour)

Figure 6: Measured data: Indoor air Ta. Heat fluxes through different walls.

The air temperature standard deviation is reduced from the outdoor 5 °C to the indoor

1.6 °C, outdoor the mean air temperature is 18.8 °C while indoor it increases around 1 °C. Mean air relativity humidity decreases indoor 5 % and it standard deviation is reduced from the outdoor 21.3 % to the indoor 6.3 %. Wall flux data show that ceiling heat flux is smaller comparing to the others walls, this is due to the ceiling sensor location on the vertical of the polystyrene beam. Also it has been observed that main wind direction is E-W.

The spectral analysis of the main outdoor variables allows to identify the frequency ranges over which the building are mainly excited.

The normalised cumulative spectra of two main variables affecting the system thermal performance are presented in Figure 7: the outdoor air temperature and the solar global horizontal radiation. The conclusions from their analysis are:

Outdoor temperature: 97% of the variance is concentrated over the frequency range [0, 1/10 h-1]. It exhibits a clear 24 h periodicity, as well as secondary spectral peaks (variance concentration) at 1/12 h-1 and 1/6 h-1 frequencies.

Solar radiation: 94% of the variance is concentrated over the frequency range [0, 1/11 h — 1]. As in the previous case, it exhibits a clear 24 h periodicity and a secondary spectral peak at 1/12 h-1 frequency.

The normalised cumulative spectra of indoor variables describing the building response: air temperature and heat fluxes through different surfaces are presented in Figure 7. This spectral analysis shows that the building acts as a low-pass filter. 97% of the variance of the indoor temperatures is distributed over the frequency range [0, 1/24 h1], it is 24 h harmonic and presents a secondary spectral peak at 1/12 h-1 frequency.

All the heat flux time series present a clear 24 h periodicity as well as spectral peaks at 1/12 h"1 and 1/6 h"1 frequencies. South, north and west walls heat flux present similar spectral density. 97% of their variance is concentrated over the frequency range [0,1/7 h-1]. While ceiling heat flux presents significant spectral power over the whole spectrum, 95% of the variance is concentrated over the frequency range [0, 1 h-1].

In order to have the correct value of the average day light factor the measurement should be made at cloudy conditions, so to realize the perfect anisotropy and uniformity of the sky; in alternative it is necessary to shadow the detector so to measure only the distributed component of the sun light.

The measurements have been performed at noon when the sun was at 0 azimuth on the horizon by means of luxmeters.

According the rules the measurements inside the building should be performed at 0.90 m above the floor, corresponding to our working plane height.

Figure 3. Points location for the illumination measurements Outside the measurements has been achieved on an horizontal plane near the building facing the whole sky dome and avoiding the direct sun component.

The measurements have been referred to an area Ap and the average lighting has been measured as the average weight on the total area.

The DF is defined as :

DF = Em / Ee = (XEi x Ap) / (Ee x At)

Ei indoor point of lighting measurement [lux] Ee Outdoor measurement lighting [lux]

Ap Area of measurement [m2]

At Total area [m2]

We can notice that the DF value, though halved after the insertion of PV modules, from 17.7 % to 8.9 %, is well beyond the minimum suggested, 3-5 %. It can be concluded that with the modules we have reached a greater control on the entering light. At the same moment the overheating and the glaring effects are largely reduced.

Friedrich Sick

Fachhochschule fur Technik und Wirtschaft FHTW Berlin, Treskowallee 8, 10318 Berlin
phone: 030-55134-258, fax 030-55134-199, email: F. Sick@FHTW-Berlin. de

Optimum daylighting of interior spaces is most effectively achieved by pure archi­tectural (or: structural) measures of which the most basic ones are the dimension­ing and positioning of daylight openings in the building envelope as well as geome^ try and surface characteristics of the considered space. Multidimensional regres­sion analyses with such parameters performed for a number of simple geometric cases show both their qualitative and their quantitative influence [Sic03]. The re­sults are presented graphically and in a programmed form using a simple software tool.

Different simulations were made to estimate the optical and thermal properties of the system. The forward ray-tracer ASAP [2] was used for the former and the latter were calculated with the explicit finite differences program HEAT2 [3].

The chosen nomenclature for the irradiances can be found in Figure 2. The system was tested with two different slopes в (the angle between the system’s surface and the horizontal), for в = 90°, the panes are positioned vertically, and with в = 30°, so that Idir on a summer noon would be perpendicular to the surface at WQrzburg latitude. In both cases the daylighting element was facing south (azimuth y = 0°).

Optical properties

A reflective layer was assumed to be deposited on the focusing line of the glass bars (see Fig. 1) in order to send the direct radiation back outside. First simulations showed that starting from solar altitudes as of about 40° for a solar azimuth Ys of 0, the transmission of the direct radiation grows as a result of multiple reflections on the back of the reflective layer (see Fig.3).

Fig. 3 Multiple reflections on the back of the reflective layer for solar altitudse as > 40°,

solar azimuth ys = 0°.

In order to avoid this problem and still keep the glare to a minimum, the back of the reflective layer was assumed to be black. This resulted in a higher absorptance but suppressed the high transmittance of the system for direct radiation. The results can be seen in Figures 4a and 4b, which also show the high transmittance for the diffuse radiation.

Fig. 4 Optical properties with the back of the reflective layer painted black for direct (left)
and diffuse radiation (right) at different altitudes and azimuth = 0°(south).

In a next step the optical properties of the system with the reflective layer painted black on the rear were calculated for all the solar angles occurring on a south fagade. Then the test reference year (TRY 05) for WQrzburg [4], which includes the direct radiation on a normal plane (Idir) and the diffuse radiation on the south fagade (Idiff) for every hour in a year starting January 1 at 0:00h, was applied to these data in order to obtain the transmittance, reflectance, and absorptance over a year for direct and diffuse radiation.

Figure 5 shows that for the direct radiation the transmission rarely rises above 20%. This is important in order to reduce glare problems. As one can see, during summer a large part of the radiation is absorbed mainly by the black side. This will lead to the glass bars heating up, which will in turn emit thermal radiation into the room. As we will show later, this effect is not dramatic as there is still the low-e coated glass pane behind the bars and thus the main part of the heat radiation will be blocked.

Fig. 5 Optical data of the system for direct radiation plotted over the hours of a year

(starting January 1, 0:00h).

The same simulation was carried out for the diffuse radiation (Fig.6). It is clearly visible that the transmission is high throughout the year, thus supplying the room with sufficient daylight.

The reference case of SIEEB corresponds to the preliminary design of the building with optimized envelope. The characteristics of building envelope includes the low e-values of windows, walls and roof. For energy simulation, the whole building is divided into 28 thermal zones according to location and function of each zone. In each zone, different categories of spaces were considered in respect of their use in the building, e. g. office, laboratory/meeting room, atrium, corridor and underground space (box). Among these, the offices, laboratories and atrium are conditioned spaces and, the corridors and underground space (box) are non-conditioned spaces. The HVAC systems, four-pipe induction unit (FPIU), were simulated for providing thermal comfort conditions inside each zone by primary air distribution. The internal loads and the set points of thermal comfort conditions for each category of space corresponding to Reference Case are shown in Table 2.

As per the requirement and functioning of the building, the schedule for the occupancy and lighting is considered from 8 AM to 10 PM (functioning hours of the building) as 100% throughout the year. This is defined according to the occupation hours of Tsinghua University. However the schedule for equipment is considered from 8 AM to 5 PM as 100% and from 5 PM to 10 PM as 40% of the total equipment load.

Table 2. Reference case — Loads and thermal comfort conditions

The HVAC systems are considered to be off during mid seasons (16 March — 14 May and 16 September-31 October) of the year. The climatic data used for simulations is based on test reference year (TRY) for Beijing climate. The results of simulations are presented below:

Figure 3 shows the annual energy demand for cooling, heating and lighting & equipments in percentage of total energy demand. It can be seen that the energy demand for air­conditioning has a very high contribution in total energy loads. Cooling demand dominates the building energy loads (40%) and the heating demand is relatively lower (18%).

It can also be observed that the internal loads (lighting and equipments) are very important and have accounted for about 42% of total energy demand. The monthly energy demand for cooling, heating and lighting & equipments are shown in figure 4. The peak loads for cooling, heating and lighting & equip. in SIEEB are 963, 357 and 230 kW respectively.

Figure 4. SIEEB (Reference case) — Monthly Energy Demand

Kudel’kina Evgeniya Viktorovna, Russian Federal Nuclear Center — All-Russian Research Institute of Experimental Physics (RFNC-VNIIEF)

Gusev Alexander Leonidovich, Russian Federal Nuclear Center — All-Russian Research Institute of Experimental Physics (RFNC-VNIIEF)

Turhan Nedjat Veziroglu, Clean Energy Research Institute University of Miami Michael Douglas Hampton, University of Central Florida

1. Introduction

Emergency conditions in big cryostats in the circumstances of their long-term operation have been discussed in this review. Emergency conditions in cryostats arise at the appearance of considerable heat flows into a cryoagent, which much more exceed the certificate flows and come in over heat bridges and through heat insulation [1-3]. During a long-term operation of big cryostats, especially in the end of the routine maintenance interval, residual hydrogen gets accumulated in heat-insulating cavities. Hydrogen, as a rule, appears as a result of inter-lattice hydrogen diffusion from thick and warm cryostat casing walls into the vacuum cavity. The residual medium of other gases is mainly formed due to the atmospheric air inflow through microloosenesses. Big cryostats always contain microloosenesses. In the beginning of the cryostat operation, they are, as a rule, insignificant, and then grow due to the processes in welds approaching by magnitude to the maximal permissible value.

The most spread strategies of the cryostat superinsulation operation are built on strictly determined heat insulation routine maintenance intervals. At this stage of cryogenic engineering development, designers, as a rule, determine the routine maintenance interval as one year. However such attitude leads to considerable operational and energy costs. It would be more expedient to build the planning strategy of the routine maintenance interval with the account of changes in the cryostat design condition. In a number of works [4, 5], a possibility is postulated to predict the beginning of the extreme cryostat operation period as well as to plan the optimal duration of routine maintenance intervals. At the same time, as the operational practice has shown, when the routine maintenance interval in cryostat superinsulation is exceeded under certain conditions, some phenomena impeding the normal cryostat operation may appear. However the conduction of extreme planned experiments on full-scale big cryostats has allowed to prove the possibility of management of these effects in order to eliminate a negative effect and obtain a positive effect in case when it is impossible to conduct an emergency superinsulation routine maintenance. In addition, the analysis of these phenomena has permitted to build models, which can be useful at the development of fundamentally new versions of superinsulation embodiments. These processes can be completely stopped and eliminate their extreme danger.

The proposed review covers discussions and analysis of the data being accumulated by the present time on proceeding of electro-sorption processes in screen-vacuum heat insulation (SVHI) layers of big cryogenic reservoirs and cryogenic pipelines [6-7]. Their

influence on the cryogenic products volatility as well as on the safety reduction of thermostatically controlled objects has been demonstrated.

A special attentions has been paid to the field effect, the Bardeen-Brettain-Shockley gas-water cycle, the electro-adsorption effect, metastable states of superinsulation surface, kinetics and dynamics of the residual atmosphere of very big cryogenic reservoirs with insignificant effusion leaks, the cryogenic liquid volatility, the determination of the heat inflows to a cryogenic liquid in the conditions of ambient parameter changes. For the first time, the following recently discovered phenomena in big cryogenic reservoir superinsulation have been described in the references being reviewed [6-9]:

an effect of effusion induced hydrogen superinsulation instability, an effect of effusion induced heat-conductive superinsulation instability in cryogenic-vacuum objects, an effect of multiplication of the number of desorbing hydrogen molecules in respect to the inflowing moist air molecule magnitude.

The effects in heat insulation can be controlled. In order to create new heat insulation samples with a high exergy efficiency and a high safety degree, new heat-insulating structures and designs should be developed [8, 9].

The main tendencies of further superinsulation development have been determined. A fundamentally new approach to the superinsulation designing and calculation has been demonstrated, which, apart from radiation and convection heat conduction mechanisms, takes account of convection component composition variations. In addition, the convection component variations occur due to the change of residual water composition and concentration as a result of the electro-sorption process. The electro-sorption process arises at the availability of clearly expressed hydrogen residual atmosphere on superinsulation heat screens with water concentration changes in the air inflowing through microloosenesses into the heat insulation cavity [6, 7].

Theoretical models for the appearance of effusion induced hydrogen and heat conduction instabilities of the superinsulation have been proposed for the first time in this review. Thermodynamic description of these new effects has been carried out with the use of analytical thermodynamics mechanisms. On the grounds of variational description of heat and mass transfer processes for a heterogeneous system in the continuum approximation and with the account of electro-sorption processes according to the hydrogen-water cycle of Bardeen-Brettain-Shockley, a formulation of the mathematical model of molecular heat and mass exchange in superinsulation has been derived.

A fundamentally new approach to the superinsulation construction and calculation, which, apart from radiation and convection heat conduction mechanisms, takes account of the convection component variation mechanism. In addition, the convection component variations occur due to the change of residual water composition and concentration as a result of the electro-sorption process. The electro-sorption process arises at the availability of clearly expressed hydrogen residual atmosphere on superinsulation heat screens with water concentration changes in the air inflowing through microloosenesses into the heat insulation cavity.

David Lloyd Jones, Studio E Architects

The Renewable Energy Centre at Kings Langley in the UK is the new headquarters and visitors’ centre for Renewable Energy Systems Ltd, a company whose business is developing wind farms on a global basis. The original buildings on the site housed chickens to provide eggs for the nearby Ovaltine malt drink plant. These buildings, derelict for 10 years, have now been converted and extended to provide for the office and visitors’ centre accommodation. A sustainable approach was taken, particularly in respect to energy supply and use. The design was based on the comprehensive application of passive and active solar measures and is believed to be the first commercial net zero carbon dioxide emissions building in the UK. The project was completed in December 2003 and the energy systems, weather and internal comfort are being monitored over a 2 year period. An Ec Framework 5 grant contributed to the cost of a hybrid PV thermal array, a seasonal heat store, the space heating and the associated mechanical and electrical systems.

The domestic hot water was set to the standard value for the NOVEM reference house being 10.2 GJ/day (for all 4 houses). This was translated into a water volume of 134 litre/day to be heated from 15 to 65 oC. Five times a day one fifth of the daily water consumption was drawn off (7, 8, 13, 18 and 19 hour).

The heating of hot water is preferent to the space cooling of the house. So the storage of the solar system is first heated up to around 70 oC before cooling of the house takes place (or can even take place with a single effect system). The waste heat of the condenser/absorber is not being used to preheat the domestic hot water. This would make the system too complicated.

Sorption System

For cooling in summer the sorption system is driven by the solar system with temperatures below 100 oC. In winter the sorption system can be driven by the auxiliary heater at higher temperatures (the higher the generator temperature the higher the power of the sorption machine and the better the price/performance ratio). We presume a generator temperature of 150 oC in winter, however this will complicate the system design (i. e direct firing).

The sorption system is characterised by the heat transfer values of the evaporator, generator and condenser/absorber according to the zero order model. The following values were used as default:

• Evaporator heat transfer: 200 W/K

• Condenser/absorber heat transfer: 400 W/K

• Generator heat transfer: 200 W/K

This set of heat transfer values delivers 5.5 kW of condenser/absorber power at a generator temperature of 150 oC, a condenser/absorber temperature of 50 oC and an evaporator temperature of 10 oC. The generator power is in this case 3.6 kW and the evaporator power is 1.9 kW. So the cooling COP is 0.53 and the heating COP is 1.53. Of course these values depend strongly on the generator, condenser/absorber and evaporator temperatures, however the condenser/absorber power at these temperatures was used to characterize the system in the following figures. For example a condenser/absorber power of 2.75 kW represents a sorption system with 100 W/K evaporator heat transfer, 200 W/K condenser/absorber heat transfer and 100 W/K generator heat transfer.

Solar system

A typical selective flat plate collector with the following characteristics was used:

no = 0.797 [] Efficiency at zero temperature difference

U = 4.22 [W/m2K] Constant part of heat loss factor

Ut = 0.00504 [W/m2K2] Temperature dependent part of heat loss factor

The collector area was in most simulations 8 m2 while the sensible heat storage was kept at

300 litre. These are standard values for a solar combi system with standard flat plate

collectors in The Netherlands. With lower collector area the contribution to the space heating

becomes negligible. With these dimensions the heat surplus in summer is rather big,

because in summer 2 m2 of collector area would be sufficient for hot water.

In stead of standard flat plate collectors also high efficiency evacuated tube collectors (for example Sydney type) can be used. In that case around 30 to 40% smaller collector areas are possible with the same contribution to space heating, hot water and cooling.