Category Archives: BACKGROUND


Only a few works have been devoted to the matters of electro-adsorption interaction of SVHI screens with the residual gas [1-5]. At the same time, the F. F. Vol’kenshtein’s monograph [48] is devoted to electronic process on semiconductor surfaces where the results of the 40-year work of the author and his colleagues in the field of physics and chemistry of semiconductor surfaces are summarised. The semiconductor surface in the work cited above is considered from the positions of the interface between two phases. The interaction between gas molecules of the residual medium and free semiconductor electrons and holes occurs at this interface. As the majority of metals have an oxide film, then their surfaces in most cases are semiconductor surfaces. Among works devoted to the physics and chemistry of semiconductor surfaces, the most substantial are monographs by K. Haufe [49] and S. Morrison [50], F. F. Vol’kenshtein [48], A. V. Rzhanov [51]. It is necessary to note a great contribution of the V. S. Kohan’s school into the theory of interaction of active gases with metal films [52]. A very meaningful is the monograph of the Indian physicist K. L. Chopra [38]
devoted to the investigation of physical processes passing in thin films of metals, semiconductors and dielectrics.

By the present time, the main tendencies of further development of the superinsulation have been carried out in the following directions. First of all, studies devoted to the optimal installation of the superinsulation [53], the process of vacuuming of the cryogenic equipment superinsulation [54-57], investigations of gas permeability of the superinsulation [58, 59], the determination of diffusion coefficients of residual gases in the superinsulation [60], investigations of the kinetics of gas release of heat-insulating materials in vacuum [61], investigations on studying of the distribution law of residual gases in superinsulation layers [62], investigations on studying if the unsteady pressure field in the superinsulation [63], investigations of the properties of superinsulation materials [64, 65], investigations of heat and mass exchange in the superinsulation [66-68]. The work [69] has a high theoretical and practical value, Mikhalchenko with colleagues have detected therein a hundred-fold pressure ratio in the middle of the sample over its thickness and on the outer insulation layer with the temperature of 77K. In the work [70], it has been obtained that the pressure in the superinsulation grows proportionally to the squared insulation thickness. In addition, it has been detected that the pressure distribution over the insulation thickness in the steady mode has a parabolic nature.

In order to improve the conditions of superinsulation vacuuming, it has been proposed to perforate screens [71]. Barron [72] has come to a conclusion that if the perforated hole area equals to 10% of the screen area, then the rate of gas pumping-out from the insulation increases approximately by 1000 times. In the work [73], it has been shown that gas releases of screens can be absorbed inside the insulation, for example, by means of the use of glass — fibre paper with filaments from activated charcoal as a pad’s material. In the work [74], it has been determined that gas releases of screens can be absorbed inside the insulation, for example, by means of a low-temperature gas absorber.

Studies are known devoted to surface effects on a dimension-quantised screen — vacuum heat-insulation in the conditions of cryogenic temperatures and vacuum [75], influence of surface centres on the gas medium formation in HIC, selection of a metallised coating of the superinsulation, optimisation of the technology of manufacture of a metallised film with the account of electro-adsorption phenomena on the film surface: selection of the crystal size to be applied onto the polymer film substrate, values of the thickness of the metal spraying onto the film, management of the metallised film properties by the introduction of special alloying gases at the manufacture, etc.

Quite a few works have been devoted to operational methods and means of maintaining and monitoring of the optimal mode of the superinsulation functioning [76, 77].

The investigations devoted to surface effects on dimension-quantised films in the superinsulation, influence of the surface centres of superinsulation screens on the gas medium formation in HIC, selection of the metallised coating of superinsulation screens, optimisation of the technology of manufacture of a metallised film with the account of electro­adsorption phenomena on the film surface, selection of the crystal size to be applied onto the polymer film substrate, values of the thickness of the metal spraying onto the film, management of the metallised film properties by the introduction of special alloying gases at the manufacture, management of the value of the surface potential of superinsulation screens by means of connection of the superinsulation screen to an external potential, etc., are completely absent.

In addition, the matters of selection of the protective casing of the reservoir, introduction of an additional "dry" volume into the cryogenic reservoir design between the
casing and the additional moisture-insulating shell are completely missed. The shell can be made with an overflow moisture-impermeable valve. As to the matter of exclusion of a moisture film on the outer heat insulation surface, we are aware of only one work [78].

It is well-known that the film alloying by gas impurities can lead to the improvement of their properties [79]. The task of management of the film properties by their alloying with impurities was stated in a number of works [80].

A special attention will be paid to the management of properties of screens on the polymer basis by means of their modification by the ion implantation. By the present time, a sufficiently large volume of work on the investigation of kinetic phenomena in conducting organic films has been carried out [81-86].

The complexity and diversity of processes being observed in heat-insulating cavities cause a necessity of the conduction of additional emergent experiments with the use of newest measuring apparatus.

The urgency of investigations on the development of a fundamentally new superinsulation is in the present time dictated by the beginning of intensive works on the development of ecologically clean transport on hydrogen in all developed countries.

Energy, Economy and Ecology Analysis

All levels of society should be sensitive to the environmental issues. The ecological parameters must be taken into consideration as a part of the external costs. But these costs someone has to pay. The sustainable development has to balance power supply and demand respecting both economical and ecological criteria. However, it will be very difficult to secure energy at low cost, with high rates of economy growth and acceptable pollution levels. Having this in mind, renewable energy resources could play a dominant role in the 21st century alone and in combination with other ecologically acceptable fuels.

The price of fossil fuels (coal, oil, natural gas) does not represent their true cost to the society. Besides many factors the ecological impost also has to be included in cost of fossil fuel. The impost consists of:

— Repayment of environment contaminators according to the emission of CO2, SO2, NOx,

— Repayments according to the burden of the environment-communal or dangerous waste,

— Repayments for the environment contamination caused by traffic — motor vehicles.

The example of solar energy utilization project described here shows savings of

thermal energy in the system of space heating and domestic hot water preparation. A yearly value of solar contribution at level of 70 % is expected. The solar contribution in electricity supply of the house is around 50%. Also a temporary excess of electricity produced in PV generator can be delivered to the network. The reduction of the emission of the CO2 at the rate of 6500 kg per year is expected.

The house is also equipped with rain-water collection system, saving almost 55% of overall sanitary domestic water demands.

2. Conclusions

The pilot project "Solar roof Spansko-Zagreb" shown here presents production of both thermal energy and electricity in the family house. In this work the possibility of energy savings in the system of space heating and domestic hot water preparation is presented in the case when solar energy is used, and electricity production from solar energy is shown. On the other side, almost ideal supplementation of the city gas as an additional fuel with solar energy, especially in the reduction of harmful gases emission is shown. The significance of this pilot project is in the usage of renewable energy resources, which are capable to ensure large enough amounts of energy for both economic growth and sustainable development for the well of future generation.

Simulation of buildings insulated according to passive house criteria and reference user behaviour

It is possible to reach high accordance of the measured and simulated room air temperatures, when very detailed input data is available. Little differences i. e. in the user behaviour can alter the results significantly because the heat demand of the building is very small (ref. Table 1). An increase of the room set temperature from 20°C to 25°C increases, for example, the space heating energy demand by over 50% (with all other parameters fixed).

For detailed simulations and comparisons the user behaviour taken from standards is not sufficient. Even user profiles evaluated from questionnaires are sometimes not accurate enough (this is especially true for the ventilation by windows). Figure 2 shows the examples for the daily distribution of persons in the apartment and the electricity demand other than HVAC system chosen in this study.

Figure 2 Average daily distribution of persons in the apartment (left) and electricity
demand other than HVAC-system (right) (Streicher et al. 2004).

Control strategy with fuzzy & conventional approach

The three operations, measurement, decision and action, are always present in every type of control. Measured are ambient conditions, in our case the internal illumination, global and reflected solar radiation and the current position of the roller blind. On the basis of the measurements, the controller decides what to do to follow the desired (set point) inside illumination. As a result of the controller’s decision, the system must take an action. This is in our case accomplished with the suitable alternation of the roller blind position. Variable
solar radiation is called a disturbance in the process, because it causes the deviation of the controlled inside illumination from the set point value. Because of the external disturbances, such as changeable solar radiation, the automatic process control for the window geometry alternation is justified. The illumination algorithm was designed and developed progressively during the research procedure. The design of the light control loop was based on experimentation. The first set of measurements was used to examine the relation between the outside solar radiation and the inside daylight illumination with different surfaces of the window and in changeable weather conditions. After getting the experience in this sphere the control algorithm was developed and improved progressively with the aid of experiments. The control algorithm is created in the IdR BLOCK environment, where placing and interconnecting various blocks define the control scheme. To each block a subprogram, which performs the necessary operation of input data, is assigned. Blocks are grouped into block groups, called loops, and they are framed into control algorithm. The proper functioning of the control algorithm is of essential importance for the adequate adjustment and velocity of alternations of the roller blind with regard to external disturbances, i. e. solar radiation changes. The assessment of the control algorithm is subjective. We observed, how the alternation of the window geometry — roller blind positioning — influences the internal lighting and luminous efficacy with respect to the given solar radiation.

fuzzy sets on proper domain. The first input is set point inside illumination and the second is the difference between the inside illumination and the set point illumination

For adaptable window geometry fuzzy logic [7,8,9] is a system advantage in controlling, because of the fuzzy controllers’ ability of non­linear mapping between the ambient conditions and the corresponding roller blind position. In fuzzy systems the advantage of reduced complexity is taken into account and it is achieved with subjective estimation of the used information. The principle, which derives directly from human reasoning, is based on a linguistic model, which is expressed with a set of conditional rules, IF-THEN statements. We want the movable shading device to be alternating, as if it was adapted manually to the internal demands and external conditions. We have to find a linguistic model for the optical process as a basis for the fuzzy controller, expressed with a set of fuzzy rules. With the determination of IF-THEN statements and fuzzy sets the input and output relations for each fuzzy controller are determined. The inputs are in our case on-line measured external and internal conditions and the output is an appropriate roller blind position. The designer must select appropriate fuzzy sets with membership functions for all input and output variables (Fig 2).

The input and output numerical values must belong to appropriate membership functions, which are correlated and combined with the aid of logical fuzzy in IF-THEN statements. With the aid of the linguistic terms the measured values are described as sets of ordered pairs: numerical values and degrees of memberships to fuzzy subsets. The correlation, non-linear mapping between two inputs and one output, is graphically represented with a specific 3D shape as shown in Fig. 3. The actual numerical output value, the current position of the roller blind, is located on the 3D shape. The output values depend on the inputs, measured condition values and on the designed fuzzy model.

The control algorithm is defined as cascade control (Fig 4). Fuzzy controller is used as the main controller while PID is the auxiliary one.

Heat Supply systems

Compared to a conventional house, a high performance house has a very small heating demand (ca. 15 kWh/m2a), a micro peak heating capacity (typically under 10 W/m2) and shortened heating period (i. e. November — March in the moderate EU climatic area). The limit temperature for heating demand achieves 12 °C. This defines a new set of requirements for domestic technical systems. The heat production plant can be small and inexpensive, as also the heat distribution system. The very slow rate of heat loss means that the timing of the heat supply can be very relaxed. However, the auxiliary heat supply must shut down very quickly, e. g. when the sun shines, to avoid overheating and comfort problems.

To produce the needed remaining heat, 31 % of the projects rely on a small heat pump,

10 % burn biomass — primarily wood pellets and 14 % are connected to district heating.

size of the solar area to the net heated floor area [m2/m*]

0.6 —————————

■ solar DHW systems □ solar combi systems

■ solar air systems ■ solar electricity

average solar DHW : 0.05 m2 solar collector area per

Figure 4 Use of solar energy systems in the analyzed projects — size of the systems in relation to the gross area of the solar system to the net heated floor area of the building

The remaining 37 % of the houses have a fossil heating system (fossil fuel fired). Some projects have a combined heat and power system, increasing the overall efficiency. Most of the heat supply systems are combined with a solar thermal system to produce domestic hot water. In total, 67 % of all buildings use active solar supply for hot water production and 22 % for combined space and domestic water heating. 35 % of all buildings have a photovoltaic system to produce electricity. Figure 4 illustrates the ratio of solar thermal collector gross area to the net heated floor area of the building. This ratio averages 0.05 m2 collector area per m2 net heated floor area. For the PV-Systems the mean value is about 0.13 m2 module area per m2 net heated floor area.

Ventilation loss must be decreased while assuring best indoor air quality. In 68 % of the investigated buildings a mechanical ventilation system with heat recovery is installed. In some buildings (about 28 %) the mechanical ventilation is combined with an earth-to-air

heat exchanger (eta-hx). An eta-hx in high performance housing is a part of the strategy to increase the degree of ambient or renewable energy use. Its benefits in order of importance are:

• prevent freezing in the air-to-air heat exchangers of heat recovery systems,

• increase the temperature of the supply air,

• improve indoor comfort in summer by cooling the supply air.

The relative importance of these three functions varies with the general building concept and the climate. In the demonstration buildings with an eta-hx, the mean value for the specific surface area of the eta-hx per volume of air flow was 0.14 m2/m3h.

The benefit supplying air tempered by the eta-hx does, however, reduce the efficiency of the heat recovery from the heat exchanger. In some passive-houses the supply air is further heated, up to 50 °С, eliminating the need for radiators in all but perhaps the bath room. The mechanical ventilation rate in the buildings is usually designed to supply between 0.4 and 0.5 room volumes per hour.

Another method to reduce ventilation heating demand is by using an exhaust ventilation system. Fresh air can be preheated by solar air collectors ( in 11 % of the projects) or by using a sunspace (13% of the projects).

heat losses transmission

гдо, т2К ♦detached A semi detached ■ row • apartment

heat losses ventilation [W/m2k]

Figure 5 Transmission and ventilation losses of the analyzed buildings (related to facade area)

With this new ventilation strategies the specific ventilation losses can be reduced in the average to 0.30 W/rnF K, which is lower than the transmission losses. Figure 5 shows the relation between transmission and ventilation losses for the projects.

Most of the apartment and row buildings have transmission losses less than 0.4 W/rnF K (facade area) and ventilation losses lower than 0.6 W/rnFK (net heated floor area). These buildings are very efficient (passive-houses) and have heat recovery systems with earth-to air heat exchangers. The higher transmission and ventilation losses of the semi-detached buildings with less efficient building designs and exhaust air systems are also evident if the graph.

Indoor Surfaces Reflectance

In order to analyse the impact of the surfaces reflectance, daylight factors were monitored from 10.00 to 17.00 under overcast sky in two different cases. The relative difference between daylight factors observed in the test module and in a first scale model (cf. Figure 1.a), showing larger differences of surfaces reflectance (cf. Table 1, Scale model 1), were used to assess this impact. A subsequent improvement of the scale model by the way of a closer match of the surfaces reflectance (cf. Table 1, Scale model 2) was used in an attempt to reduce the divergence between the two kinds of daylight factors. To avoid any bias due to the sky luminance distribution, all models were placed next to the test module (cf. Figure 1.b); measurements in the model and the test room were carried out simultaneously.

Scale Model Location

The scale model location was considered as one possible main source of error, through the impact of different sky view factors and external reflected components : it was carefully analyzed by placing scale models close to the test module, but at different distance from the later (cf. Figure1.b). Work plane illuminances were monitored from 14.00 to 16.00 under clear sky, enhancing the contribution of the external reflected component, their relative divergence being compared. The scale model was placed first in another module, located only a few meters away from the test module, the corresponding window plane
being fully coplanar; the model was moved next to the test module in order to make it benefit from identical sky view factor and external reflected component. Scale model 2 was used in this case, to avoid any bias due to the surface reflectance; measurements in the model and the test room were carried out simultaneously.

Samples description

A set of glasses with geometrical obstruction, not commercial at the moment, was characterized to evaluate the luminous performance and the influence on the visual comfort for users. Obstructions and decor have different geometries and colours and reduce both the light transmittance and the view through the glazing.

The demand of decorated glass increases and the market provides multiple choices as concerns both, the production technologies (silk screen printing, acid etching, etc.) and the type of decorations (geometrical patterns, colours, shapes and drawings, etc.).

The glazing components characterized in this work are laminated glass panes (safety products) 30 x 30 cm2 in size. The decors seen in figure 1 are sublimated on a plastic interlayer and laminated between two glass panes (3 mm float glass).

This innovative system preserves the decor from aging and scratching and allows to use this decorated glass in applications usually avoided in the case of single glass panes. This particular safety glass can be used to decorate the facades of buildings, partition elements in public rooms, or shop windows and doors; it can be also utilized in interior design such as shower boxes, stairs, parapets, shelves, and so on.

The decor design has really no limits, since the technology adopted allows to print on glass every type of pattern and picture (i. e. points, lines, rainbows, water effect, rock effect, photographs, etc.).

Figure 1. Details of samples 6, 12 and 13

Normal Hemispherical Transmittance

Figure 2. Normal hemispherical transmittance of the selected samples

The three samples analyzed in this work features only geometric patterns (with different shapes, colors and dimensions) due to the difficulty to determine the visual properties of the artistic decors. Sample number 12, figure 1 on the left, has rectangular black obstruction on clear glass. The dimensions of the rectangles vary with the same pitch on the x and y axis. Sample number 13, on the right, has rectangular white obstructions on clear glass, but the texture varies along the two axis. Sample number 6, across the other samples in the picture, is the only sample with color. Its decor looks like a random distribution of blue rain drops on the clear glass.

Development of a High Energy Density Sorption Storage System

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.

Monitoring: Room Temperatures

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.




и 28

I 26





« ,,1 d v



16-12 -8 -4

4 8 12 16 20 24

28 32 36 40



ambient air temperature [°C]

-16 -12 -8 -4 0 4 8 12 16 20 24 28 32 36 40

ambient air temperature [°C]

(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.

Table 1: Degree hours over 25 °C in the summers of 2002 and 2003.



Fraunhofer ISE







Dhoutdoor air








Dhindoor air








Experimental data 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.


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.

Table 3: Mean and standard deviation of the recorded data.


Standard deviation

Outdoor air temperature (°C)



Outdoor air relativity humidity (%)



Wind velocity (m/s)



Global horizontal solar flux (W/m2)



Diffuse solar flux (W/m2)



Air Ta near southwall 50 cm height (°C)



Air Ta near southwall 150 cm height (°C)



Air Ta near southwall 250 cm height (°C)



Air Ta near northwall 150 cm height (°C)



Indoor air relativity humidity (%)



Heat flux south wall (W/m2K)



Heat flux north wall (W/m2K)



Heat flux west wall (W/m2K)



Heat flux ceiling (W/m2K)



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].