Category Archives: BACKGROUND


In works [6,7], on the grounds of thermodynamic description of non-equilibrium systems with the use of phase space formalism and the multi-dimensional fundamental equation at the availability of diffusion, the processes of chemical instability generating fluctuations in a macroscopic system including the vacuum cavity of a cryogenic reservoir with the superinsulation inside it have been explained. In addition, the macroscopic system consists of a large number of particles N ^ ■*> and occupies the macroscopic volume V^ ■*> at finite density N /V. Moreover, an external influence is directed to the system — in the form of low-magnitude fluctuations of the diffusive flow with the donor gas and water vapour concentration changing in composition. In work [6], small and intermediate magnitudes of fluctuations have been considered, which most effectively deflect the system from the unstable state.

This review covers the consideration and analysis of the data being accumulated by the present time on passing of electro-sorption processes in screen-vacuum heat insulation (superinsulation) layers of big cryogenic reservoirs.

Periodic variations of the concentration of the effusion flow in the link with electro-sorption processes lead to the appearance of chemical pseudowaves. In a diffusion system with chemical reactions, information is transmitted at an infinitely high speed, as such a system related to the parabolic type. Therefore no delay periods are observed between the rate of change of the concentration parameters of effusion values and the variation of thermodynamic parameters in the thermodynamic open macrosystem being investigated. The influence of chemical pseudowaves on the
cryogen product volatility as well as on reduction of the safety degree of thermally controlled objects have been analysed.

At the investigation of a non-adequate process, the variations of volatility in identical cryogenic reservoirs during purposeful reduction of the hydrogen concentration in a clearly expressed hydrogen residual atmosphere the following effects have been detected [6,7]:

1. Effect of effusion induced hydrogen instability of the superinsulation (EIHIS)


2. Effect of effusion induced heat conduction instability of the superinsulation in cryogenic and vacuum facilities (EIHCIS) [6, 7],

3. Effect of multiplication of the amount of desorbed hydrogen molecules in respect to the magnitude of inflowing humid air molecules in the superinsulation of cryo-vacuum objects (MADHM) [6, 7].

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].

As a rule, in the process of operation of big cryovacuum objects, when the heat insulation routine maintenance intervals are exceeded, a process of daily fluctuations of the residual pressure and volatility of the cryogenic liquid arises. The cryogenic reservoirs in question of the RS-1400/1.0 type (hydrogen, nitrogen, oxygen) [10] had an insignificant atmospheric effusion leak being within the tolerance by magnitude. Variations of the residual pressure and volatility of the cryogenic liquid occur in such heat-insulating cavities (HIC) with expressed symbate nature in respect to the variations of the atmospheric leak effusion component.

However for the residual pressure variations, the multiplication mode of desorption processes is characteristic as compared with the calculated effusion flow. The influence on the residual HIC atmosphere by a selective chemical hydrogen absorber based on palladinised manganese dioxide [30,31,34] has allowed to reduce the cryogenic liquid volatility from 1100 kg/day to 390 kg/day [6]. The oscillatory process of the volatility has stopped. The oscillatory process of the residual pressure occurred with the monotonously decreasing correlation coefficient (the variation of the residual medium pressure — the relative humidity) as the hydrogen was pumped out from its maximal value of 0.95 to negative values. After pumping out of the calculated amount of residual hydrogen, the correlation coefficient has changed its sign and has been monotonously increased by modulus up to the value of

0. 95. The process of reduction of the correlation coefficient has been symbate in respect to the process of hydrogen removal from HIC. The change of sign of the correlation coefficient occurred at the moment when the whole calculated amount of hydrogen had been removed from HIC [6]. Such behaviour of the correlation coefficient has caused an idea of the electronically stimulated adsorption-desorption process of acceptor or donor gas depending upon the Fermi level of the metallised screen surface. Two hypotheses have been considered:

1. Adsorption-desorption process thermostimulated in micropores.

2. Electronically stimulated adsorption-desorption process of acceptor or donor gas (depending upon the Fermi level) by the inflow of ionised oxygen and water vapour.

Wealth Creation

The Renewable Energy Centre is located in a relatively affluent part of the United Kingdom. However, the relocation of an expanding company to Kings Langley will provide opportunities for work and provide alternative career possibilities outside the magnet of London, obviating the need to commute. The new facilities will assist RES in expanding their operations worldwide and the creation of wealth inherent in this expansion.

Transference of the content and the experience gained from the design, installation, commissioning and testing of the energy systems to those in the construction, renewable and property industries and businesses in the UK will foster the growth and development of them. The professional and commercial exploitation of design strategies, installation design and new products resulting from the project will also assist development of them.

Life Chances

The main social benefit locally will be the provision of an efficient and stimulating workplace. However, the decision to operate the new head office as a visitors’ centre and information resource, allowing those of all levels of interest to learn about the technologies and issues involved in creating low and zero net energy work settings, provides an invaluable national facility. The web site allows access to this data and information world

Clean and Green

Bringing back to life a derelict building rather than building new is a considerable benefit in terms of land utilisation, use of resources and improving the amenity of the area. The construction work was undertaken on the basis of minimising waste and using materials and components with low embodied energy from readily available resources.

In order to minimise the need for energy, a judicious combination of active systems (mechanical ventilation, artificial cooling, heating and lighting, building management systems) and passive systems (solar heating, natural ventilation and lighting, solar shading, a well insulated building envelope incorporating thermal mass) was developed.

The buildings are exposed to considerable external noise from passing trains to the west and the motorway to the south. To cut out the disturbance from noise inside the buildings, the outward facing facades had to be sealed. This, together with the relatively high levels of heat generated by modern office use, requires the building to be artificially cooled in summer months. The cooling source is water drawn from aquifers located in the chalk below the building. This strategy avoids the heavy energy consumption and potential polluting effects of refrigeration plant normally used for air conditioning. The cool water is used to drop the temperature of air being fed into the building and/or is circulated through convectors within the office space, cooling the air within it.

Heat is supplied from the biomass boiler (or gas boiler until such time the biomass plant is installed) and from the PVT array, either direct or via the seasonal ground heat store. Hot water from these sources is used in a similar way as the chilled water for cooling. Electricity is generated from the PVT array and the wind turbine.

Windows can be opened in facades and roofs facing away, or sheltered from, the motorway and the railway, to ventilate the building in temperate conditions. Exposed
windows are shaded from the sun by fixed glass or aluminium screens and by deciduous tree planting, thereby reducing unwanted solar gains and the need for cooling. The building is well insulated and sealed.

Predicted energy use and energy supply is shown in the table below. The current monitoring programme will show whether these predictions are born out in reality.


Space heating

Building annual loads (2500m2 building gross area)

115 MWh


PV/T direct contribution

3.2 MWh*

15 MWh

Heat collected into storage

24 MWh

Pumping load/heat lost from storage

-4.5 MWh

-12 MWh

Wind Turbine

250 MWh

Miscanthus: peak expected production (60odt/year)

160 MWh

Net contribution



187 MWh

Potential electrical export



Potential surplus miscanthus for heat export

102 MWh

*With 48 m2of PV

Estimated energy balance for the site:

A building management system (BMS) controls and optimises all the energy systems, including opening and closing the roof lights. It also records all monitored results from the various energy systems before passing the results to a site in Denmark for uploading onto the website.

RES actively encourages staff to use public transport, bicycles and car sharing for travel between home and office.

About 5ha of the 7.5ha site are given over to miscanthus cultivation. In addition there is a car park and a 5 aside football pitch. The remainder of the land is planted with indigenous species of trees, shrubs and grasses. Wild life is encouraged by the re-creation of natural habitats.

The experimental set up

The test building is located in the outskirts of Milano. At the first floor there are two test rooms having the same volume, the same exposure of the windowed facade and the same internal loads. The rooms are equipped with radiant panels formed of small pipes, installed into the ceiling in test room 1 and into the walls in test room 2. The pipes are made of polypropylene and have an external diameter of 3.35 mm and a thickness of 0.5 mm.

The experimental system layout is shown in Figure 1. It consists of two water loops: a rooms loop, containing the radiant panels and removing heat from the building, and a ground loop, containing the earth-to-water heat exchangers and discharging heat into the ground. Thermal interaction between the loops is achieved through a counter current flow heat exchanger. Each loop is provided with a pump.

The ground heat exchanger consists of 10 vertical steel pipes 6 m deep connected in parallel. The pipes are arranged in two parallel lines in a rectangular pattern. The distance between adjacent tubes is 1.5 m. Each element consists of two concentric tubes so that warm water coming from the building flows down through the hollow space between the outer and the inner tube and flows back into the inner tube. A layer of insulating material
covering the internal tube prevents heat transfer between the descending and the ascending fluid.

A monitoring system collects data with a time step of 10 minutes. The following quantities are measured:

— in the test rooms: air temperature, mean radiant temperature, radiant panels surface temperature, air humidity

— in the rooms loop: water temperatures at the inlet and the outlet of the radiant panels

— in the ground loop: water temperatures at the inlet and the outlet of the earth-to-water heat exchanger

— in the ground: temperatures at different depths (1.5, 3, 4.5 and 6 m) in the perturbed and in the unperturbed zones

— meteorological quantities, i. e. outdoor air temperature and humidity, wind speed, global horizontal solar radiation

The water mass flow rates are measured with variable area flow-meters by manual reading. Power consumption of the pumps is measured through electricity meters.

Mont-Cenis Academy building in Herne-Sodingen

The greenhouse structure includes two linear, three-storey wings that are arranged in two rows along a central axis. Inner spaces under glass are landscaped with water and greenery, creating a large-scaling winter garden. In the winter it works in tandem with the concrete and gravel floors to collect solar energy, while acting as a thermal buffer-zone. In summer PV modules integrated with glass roof act as shade-system device protecting against overheating and from too much light. The parts of the fagade can be opened to ventilate the greenhouse through natural cross ventilation.

fig.7 the semitransparent roof — and elevation PV system

The PV semitransparent system, applied in roof surface and integrated with glass area, don’t disturb natural lighting, but in some places limit visual contact with the surrounding from winter garden. Increased number of photovoltaic modules, integrated for example on the fagade’s areas, would generate more electrical power, but quality of inner physical environment would be much lower (light and shadow contrast, visual barrier). The only disadvantage of this envelope concept is worse conditions of daylight access in buildings inside (fig.7).


The architecture of the building may be defined by selecting its features that include: urban matters (especially building’s closest surroundings), its function with sort of utility process in the interior, structure and aesthetics.

The real and potential impact of PV modules’ usage on the inner space environment may have its response in some of these features, causing architectural consequences.


Table 1 Glazing types studied.

Clear DG Low-e DG AR Low-e DG

First pane (outside)

Clear 4mm

Clear 4mm

Clear 4mm

Second pane (inside)

Clear 4mm

SnO2 4mm

SnO2+AR 4mm

Three different types of glazings with various U-values and transmittances are studied in this paper: one "standard” clear double-glazed window (clear DG), one low-e coated double-glazed window (Low-e DG) and one low-e plus AR-coated double-glazed window (AR Low-e DG), Table 1.

The energy simulation tool ParaSol v2 was used to simulate the monthly average direct and total solar energy transmittance (Ts0| and g-value) as well as the annual energy demand. The solar transmittance, Tsol is the transmittance of the glazing for the entire solar spectrum. ParaSol simulates the monthly average value of Tsol, taking into consideration the actual climate and solar angles. The g-value (total solar energy transmittance) is the solar transmittance plus the absorbed heat in the window panes emitted to the inside. Consideration of potential overheating problems was done by looking at the number of overheating hours. ParaSol simulates a room module with only one wall and one window that abuts to the outside climate. The other three walls, floor and ceiling abuts to other rooms with the same indoor temperature i. e. adiabatic walls. ParaSol is a freeware developed by The Division of Energy and Building Design, Lund University (Bulow-Hube H. and Wall M). It is available at (http://www. parasol. se).

Each glazing type was studied in three different Nordic climates: Copenhagen (DK), Stockholm (SWE) and Helsinki (FIN). The Parasol simulations were also done for all 4 major directions (N, E, S, W) and the average was then taken from these four simulations. The ParaSol simulations were used to evaluate the potential of energy savings by using AR — coating on a low-e DG.

The room size investigated was 20 m2 (L x W x H = 5.0 m x 4.0 m x 2.7 m) and can be regarded as a typical living room. The temperature set point was 20°C for heating. No consideration of the cooling demand was done in this paper, since air-conditioning is not common in residential buildings in Scandinavia. The ventilation rate was set to a constant value of 0.6 ach. The internal heat load was 5 W/m2 both day and night. The glass area was assumed to be 70% of the window area, or approximately 2.1 m2. See Table 2.

Table 2 Input data used in the simulations of the room.

0.4 W/m2K 5 x 4 x 2.7 m 2.31 x 1.3 m 2.88/2.61 W/m2K 1.85/1.90 W/m2K 1.85/1.90 W/m2K 0.6 ach 5 W/m2

Exterior wall U-value

Room size L x W x H

Window measurement incl. frame

Clear DG U-value excl. frame / incl. frame

Low-e DG U-value excl. frame / incl. frame

AR Low-e DG U-value excl. frame / incl. frame

Ventilation (00-24)

Internal heating load (00-24)

To simulate the daylight availability we used Rayfront v1.04. Rayfront is a user interface to the lighting simulation software Radiance which is the industry standard raytracing engine for physically correct lighting simulations.

The Rayfront simulations were performed to obtain the daylight factor, which is a measure of the ratio between the interior illuminance and the exterior illuminance from an unobstructed overcast sky, see equation 1. The daylight factor was calculated 0.8 m above the floor level. Since the daylight factor is independent of orientation and latitude, it was only studied for one location (Stockholm) and one orientation. The simulations were made for the standard CIE overcast sky with the reference illuminance value of 13826.73 lux (default value in Rayfront) for the 21st of June.

The daylight factor is defined as:


DF = *100% Eq.1


Ei= daylight illuminance on indoor working plane

Eo= simultaneous outdoor daylight illuminance on a horizontal plane from an obstructed hemisphere of overcast sky

In Rayfront the transmittance of the window is given by the transmissivity parameter. The transmissivity is calculated from the light transmittance of the window according to the following formulas:

The total light transmittance of the window with two panes (index 1 and 2) was obtained from:


1 — Rsi* Ris2

T =


0.8402528435 + 0.00725223 * Tvis2 — 0.9166530661

Where index 1 and 2 refer to the transmittance T and reflectance R of the two panes. The transmissivity was then calculated from the light transmittance in Eq.2:


Equation 3 was found in the Radiance manual. The equation recalculates the light transmittance to transmissivity because Radiance uses the transmissivity parameter instead of the transmittance.

The properties of the different panes with and without coatings are described in Table 3.

Clear 4mm SnO2 4mm SnO2+AR 4mm



















Table 3 Optical data for the individual glass types studied.

*Values from (Hammarberg, 2002).

Table 4 Visual input data for the glazing types studied.

Clear DG

Low-e DG

AR Low-e DG














Figure 1 The annual heating demand, as an average value for all four directions, for each window and climate.


Initial approach: the dual mode concept

The typical active design approach when considering A/C buildings is the most compact and massive type, with minimum opening and sealed to avoid excessive convective gains. The typical passive design approach when considering houses in tropical regions is a building with many openings on the North and South walls for natural ventilation, lightweight and completely shaded to avoid solar heat gains. This houses designed for full cross ventilation was quite successful in achieving relative comfort as long as the residential densities were low. With the growth of suburban densities, the air velocity is reduced to such an extent that it no longer produces the desired relief. Furthermore, this type of construction does not seem to cope with noise problems, privacy necessities and thermal comfort for different activities.

From traditional knowledge, low mass materials such as wood construction are considered appropriate for free running operation in hot humid climates as their indoor temperature drops rapidly in the evening, when the winds usually subside. High-mass buildings cool down more slowly during the night, which causes discomfort during sleep.

The dual mode project has demonstrated that ventilated high mass buildings can have lower indoor maximum temperature than low-mass buildings. High mass buildings on a 24- hour period can have more discomfort in cumulative degree hours of discomfort but on a daytime basis only have far more advantages. And also, if at night time there is ventilation (natural or ceiling fans), the indoor night temperature in high mass buildings is very close to those in low mass buildings. The conclusion is that for free running operation, if there is assisted ventilation at night, high mass buildings can be more comfortable during most of the time than low mass ones.

For a conditioned operation, a high mass building can be more energy efficient during a 24 hour period. If insulated, a low mass building can also have high performance. During daytime as well, high mass is far more efficient. However, for nighttime use only, the accumulated heat of the high mass structure almost triples the energy requirements for high mass buildings. This could be reduced by an "economy-cycle” — (night air flush) operation of the A/C system.

In summary, compared to the base case, an optimized all free running house will improve up to 19% the levels of thermal comfort. However, it will be unsuitable for air conditioning operation. An optimized fully conditioned house will improve up to 35%, but will have high levels of thermal discomfort if a free running operation is used. All the dual mode cases (1­

5) had superior performance for both conditioned and free running operation modes. If a dual mode operation (5 use patterns) is being used, the following savings are possible, compared to the base case:

1) TOC o "1-5" h z 51% improvement in thermal comfort and 87% reduction in cooling loads

2) 17% improvement thermal comfort and 78% reduction in cooling loads

3) 38% improvement in thermal comfort and 66% reduction in cooling loads

4) 31% improvement in thermal comfort and 98% reduction in cooling loads

5) 40% improvement in thermal comfort and 89% reduction in cooling loads

System validation and performance test

solid building without heatin g or cooling, Jan. 4th


Figure 3: Display of results from the validation of the building model with BESTEST

light weight build ing without heatin g or cool­ing, Jan. 4th

The validation primarily includes the model of the building as well as some special plant components. The internationally accepted testing procedure BESTEST is applied to the building model. Fig 3 shows results from the room-temperature calculation of a freely oscil­lating room built first using both light materials and then using a solid style of construction. Results from Lacasa (bold red line) are comparable to the results from well-known soft­ware-tools like TRNSYS, DOE2 or TAS. Models for all components were validated by measurement data from test stations as well as data from real constructions.



Lacasa has up to now been successfully used as a supportive planning tool in 9 projects for the renovation and improvement in energy use in public buildings. Two of the most complex projects included the Humbold-University of Berlin with 10 buildings and an area of 135.000 m2, plus an educational institute in Schwelm with a heated area of 135.000 m2.

Lacasa was used to determine the reduction of operational costs and to evaluate different renovation concepts.

6 Summary


Lacasa has introduced a new standard for the practical and intuition-based simulation of building systems and components. The system meets both practical planning engineering demands as well as scientific requirements. Ennox®-Systemoptimierung GmbH (www. ennox. com) has been

established as a result of this project, whose Managing Director was the Project Leader at the Solar Institute in Julich. With the establishment of the company, the know-how, conti­nuity and further development of the software in conjunction with the Solar Institute in Julich is assured.

Innovative Commercial Buildings in Upper Austria

Christiane Egger, O. O. Energiesparverband Christine Ohlinger, O. O. Energiesparverband LandstraRe 45, 4020 Linz T: +43-732-7720-14380, F: -14383 E: office@esv. or. at. I: www. esv. or. at

Based on the regional energy strategy and implemented by O. O. Energiesparverband, the regional energy agency of Upper Austria, a commercial buildings programme was launched. The new programme is based on the successful previous buildings programmes which led to a 30% energy reduction in 95% of all new one-family houses since 1993.

The commercial building programme features especially low energy and passive house commercial buildings and includes a number of support activities ranging from energy and auditing services, information and awareness raising activities and a regional third party financing programme to special supports for industry & companies and a regional R&D programme.


The basis of all programmes is the Upper Austrian energy strategy and action plan. It started in 1994, when the first Energy Plan was passed which defined concrete goals to reduce fossil fuel consumption by increasing both energy efficiency (EE) and the use of renewable energy sources (RES) by the year 2000. A comprehensive energy action plan was developed and implemented, which led to the significant market development of RES:

• increase of RES from 25% in 1993 to more than 30% in the year 2002

• reduction of energy consumption in new single-family buildings by more than 30% since 1993

• in total, renewable energy sources provide or secure employment for 15,000 people.

In the year 2000, the Upper Austrian Government passed the "Energy 21" strategy, continuing the strategy of the successful first energy plan (1994-2000) into the 21st century. Concrete goals were defined to be reached by 2010, including for example:

• doubling biomass and solar thermal installations

• increasing energy efficiency by 1 % annually

Again the new energy strategy combines a clear political commitment and targets with the implementation of a detailed action plan. O. O. Energiesparverband is responsible for the implementation of most of the measures included in the action plan. One central activity within the energy strategy and action plan is the new commercial buildings programme.

Figure 1: Scheme of the compact unit . Control strategy

Usually a storage tank with 250 litre covers the hot water demand of at least one day. So it is necessary to heat it up only once a day. This is the basic assumption of the control strategy: The heat source with a better relation of thermal energy gain to electric consumption is the first choice, in this case the solar collector. Fortunately, there is some knowledge on the availability of solar energy. The expectation of solar gains is high in the morning, lower in the afternoon an zero at night. So it would be good to heat up the storage with the heat-pump in the late afternoon. The hot water consumption in the evening and in the morning will cool down the lower part of the storage and allow a maximum of solar gains.

But as an other complication also the heat-pump has a relatively low power and needs several hours to heat up the storage. It is necessary to have more knowledge of the temperature profile in the storage.

The control strategy was developed in computer simulations with MATLAB Carnot [1]. In the simulations, it has been shown that three temperature sensors are sufficient for the knowledge of the temperature profile. The strategy defines a time at which the storage has to be at set point temperature (e. g. 5 p. m.). The 1.5 kW heat-pump may rise the temperature in the storage with a rate of approx. 5 K/h. A temperature ramp is calculated
and compared to the average of the 3 storage temperature sensors (see figure 2). On a day with no solar gains the average temperature will cross the ramp early and the heat — pump will start to heat the storage. With high solar gains the average temperature will always be above the ramp.

When the temperature at the top sensor drops below the set-pint the heat-pump and eventually the electric heating are switched on immediately.

—no solar gain —low solar gain —A— high solar gain profile

Figure 2: Temperature profile of the control strategy and actual average temperature in the storage tank for different solar gains.

In the computer simulations the control strategy has a solar fraction between 40 and 50 %, depending on the hot water demand (5 m2 flat plate collector, weather data Wuerzburg, 200 litre per day at 45 °C).


The strategy was tested on the test rig under different conditions. The first tests were carried out with a prototype of the compact unit. The control program was running under MATLAB on a normal PC and the compact unit was controlled with an IO-card.

The hot water demand was varied from 100 to 300 litres per day. The control strategy works well with a hot water consumption up to 200 litres. At higher values the losses and thermal conduction in the storage may force the heat-pump to heat the storage more than once a day and the solar gains are reduced. The control strategy is not very sensitive to variations of the taping profile unless the daily consumption is not more than 200 to 220 litres.

In summer 2002 the first compact unit was installed in a passive house. The house has a surface of 180 m2 and a heating demand of 14.1 kWh/(m2y) (PHPP result [2]). A 3 m2 vacuum tube collector (type Vitosol 200) is installed. The consumption is relatively low with less than 100 litres per day. The solar fraction in 2003 was about 53 %.

Figure 3 shows the temperatures in the storage during a day with moderate solar gain.


—■— Solar Collector —Storage Top —A— Storage Centre —V— Storage Bottom

—— Heat-pump

Collector pump


Figure 3: Temperatures in the storage an solar collector over a 2-day period.


The test rig results and the first data from field tests show a good behaviour of the system. For the compact unit with a small heat-pump it is a very convenient solution since heat — pump and solar collector have a better performance if they are allowed to work on the lower cold part of the storage tank.

The control strategy may be a solution for a simple solar system with a relatively small storage tank if a solar fraction of about 50 % is accepted.

The strategy may also be applied in standard systems with a bivalent storage tank (two separated heat exchangers). In this case the strategy may help to reduce the charging of the storage with the backup heating in the morning when the expectation of solar gains is still high. For a backup heat source with a higher power the knowledge of the temperature profile in the storage is less important. The two sensors which usually installed are sufficient.


Indoor Thermal Climate

The indoor thermal climate conditions are primarily depended on the internal heating load from people, equipment, artificial light and the sun. The indoor thermal climate is regulated by ventilation and night cooling of the building by using the internal mass of the library, e. g. concrete floor and books.

For reducing the internal heat load as much as possible and thus reducing the numbers of hours the fans needs to assist the natural ventilation, integrated blinds are used in the facade windows and the artificial lighting is subdued/shut off after the level of daylight.

The indoor thermal climate has been simulated with the thermal simulation program BSim2002 (BuildingSimulation 2002), which is a computer based calculation program for simulation and analysis of the indoor climate and energy consumption in buildings. By constructing a
detailed mathematical model of the structure, it is possible to simulate a large number of indoor climate and energy parameters. This is done taking into consideration the dynamic interaction between the outdoor climate and miscellaneous design of structures, installations and running situations.

4.1 The model

Based upon the construction details derived from among others the daylight simulations and the natural ventilation system the following building model was made in BSim2002 that corresponds close to the actual conditions.

Figure 12. BSim2002 model of Albertslund Library with skylights and all fins. Seen from northeast.

The library is divided into 4 sections, children’s section (south), north section, east section and a west section that is closed and has its own mechanical ventilation system with cooling. The west section is the administrative area for the library, while the rest of the library is public.

The most important elements in this simulation are the ventilation system, the internal mass from all the books and the internal heating load from the artificial lighting system due to high demand of lighting level on the bookshelves and wishes for the artificial light by the architects.

4.2 Natural Ventilation system

The ventilation system is a natural ventilation system with fan assistance. The minimum temperature of the intake air is 18 °C and the amount of fresh air is regulated by the CO2 level during the heating season and by the indoor temperature outside the heating season. There is no cooling coil in the ventilation system. The air change is set to a maximum of 1 h-1 during the heating season and 5 h"1 outside heating season. The high rate of air change, 5 h, during the summer is kept by the assisting fans. The low rate of air change during the heating season and the fact that it is controlled by the level of CO2 decreases the energy demand for space heating and ventilation. During summertime, when needed, night cooling is initiated and with fan assistance if needed. The internal mass from all the books acts as a good buffer and has been taken into account in the simulations.