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Proceedings of ISES Solar World Congress 2007: Solar Energy and Human Settlement

802

collectors in Neckarsulm (Fig. 4) and Crailsheim and a new

plant with 2 900 m² is under construction in Munich (2).

Fig. 4: Solar block heating in Neckarsulm, DE.

The first large-scale solar plant in Austria

– a small local

biomass-fired heating plant complemented with a solar

system - was built in Deutsch-Tschantschendorf in 1995.

Graz is now the large-scale solar city of Austria with the

first plant built in 2002 (Fig. 5) and two new plants, the

largest one with >5 000 m² connected to the district heating

network.

Fig. 5: Solar district heating plant in Graz, AT.

The most widely implemented application of large solar

heating systems in The Netherlands

is collective housing,

institutions and homes for the elderly. Most systems have

about 100 m² of solar collectors, but some are larger, for

example the “Brandaris” building in Amsterdam with 700

m² of rooftop mounted collectors. Two large-scale plants

are designed with seasonal storage, one is a recent plant

with 2 900 m² of solar collectors connected to an aquifer

storage in Schalkwijk. There are further a couple of

solar block heating plants in France

, Switzerland and

Poland

2.3 Other Applications

A couple of the large solar systems in the Netherlands and

Greece

are industrial heat applications, e.g. a plant with

2 400 m² of flat plate collectors on the Van Melle industry

in Breda, The Netherlands. The first large-scale solar

cooling plant - 2 700 m² of flat plate collectors providing

heat to two adsorption chillers (2h350 kW) – was installed

in Athens, Greece in 1998. At present there are also a

couple of recent large-scale solar cooling plants in Italy

and

Spain

, e.g. a plant with 1 500 m² of solar collectors for

industry cooling by Inditex in Spain.

Table 3 shows the largest solar cooling plants in Europe,

where the cooling capacity is about half that of the nominal

power of the collector array. The majority of solar

cooling plants are equipped with absorption machines

(LiBr), but the largest one is equipped with an adsorption

machine.

TABLE 3: SOLAR COOLING PLANTS IN EU

Plant,

Year in operation, Country

Coll.area

(m²)

Size

(kW

)

Sarantis, 1998, GR

2 700 1 980

Arteixo. A Coruña, 2003, ES

1 500 1 050

ParcBIT, 2001, ES 900 630

Consejeria educ. Toledo, 2004, ES

796 560

Paço d’Arcos/Oeiras, 2004, PT

674 470

Bolzano, 2007, IT

627 440

Bolzano, 2007, IT

572 400

El Oso Avila, 2003, ES

504 350

Bolzano, 2002, IT

442 310

3. DISCUSSION

The first large-scale demonstration plants date from 1979

and the oldest plant still in operation dates from 1984. This

proves that the collectors can operate for a much longer

time than 20 years, as new plants are equipped with

improved components. The rather poor development of the

number of plants shows, however, that there are a number

of barriers still to be tackled.

3 SOLAR COLLECTOR TECHNOLOGIES AND SYSTEMS

803

The large-scale approach is so far promoted by a small

group of consultants and contractors and there need to be

many more that carry the message and develop the

technologies. The investment costs and thereby the solar

heat costs are not yet considered to be low enough to

convince conservative thermal utilities and facility

managers. There is further a need to reduce the gap

between the actual status of existing technologies and

present knowledge about these technologies by potential

users. The most efficient way is probably through further

demonstration together with the development of suitable

contracting and third part financing models.

The European Solar Thermal Technology Platform (ESTTP)

has been formed to develop a vision and a strategy for solar

thermal in Europe. To acknowledge the importance of

large-scale systems, one of the working groups deals with

Solar District Heating (and Cooling). The vision for

large-scale systems will be developed in co-operation with

representatives for Euroheat & Power with the intention to

broaden the no of potential actors to promote, develop and

demonstrate large-scale applications. There is an interest

to increase the share of renewable energy in district heating

(and cooling) systems and a major advantage with solar

heat over other renewable heating alternatives is that is

available everywhere.

The working group will develop a comprehensive vision

based on identified barriers, foreseen technology developments

and possible progressive and conservative policy scenarios.

A vision based on a “conservative policy scenario” will

probably result in a potential close to 2 PJ solar heat in

district heating systems in 2020 (3). A vision based on a

“progressive policy scenario” should show a much larger

potential.

4. ACKNOWLEDGMENTS

The author wants to acknowledge the Swedish Energy

Agency for financial support and colleagues in the Working

group for Solar District Heating within the European Solar

Thermal Technology Platform (ESTTP) and others for their

contributions.

5. REFERENCES

(1) J-O. Dalenbäck (2004). Large-scale Solar Heating

Systems – A Challenge for Europe. Proceedings

Gleisdorf Solar 2004, Austria.

(2) D. Mangold (2007). Seasonal Storage – A German

Success Story. Sun & Wind Energy

, 1/2007.

(3) S. Werner, Principal author (2006). Possibilities with

more District Heating in Europe. Ecoheatcool WP4

Euroheat & Power (www.euroheat.org).

STUDY ON THERMAL PERFORMANCE ANALYSIS METHOD OF DIRECT-GAIN

SOLAR DWELLINGS WITH FLOOR HEATING

B. Chen, J.J. Liu, Y.Y.Sun

Laboratory of Building Environment and New Energy Resources,

School of Civil and Hydraulic Engineering, Dalian University of Technology,

Dalian, Liaoning 116024, PR China

ABSTRACT

The new dwellings which have big window to wall ratio

(WWR) in the southern facade, can be considered as

direct-gain passive solar house. Although floor heating

system has been widely used in the new residential

buildings, few studies focus on the coupled effect of the

solar radiation and heat storage of the concrete slab on

indoor thermal environment during heating period. The

object of this study is presenting a thermal performance

analysis method about the new dwellings with a hybrid

system with floor heating and solar direct gain. In this

paper, in order to calculate the solar direct gain through

the window which is absorbed by the slab, a simulation is

performed for determining the cumulate irradiated

concrete slab area during heating period in Dalian,

northern China. Furthermore, the coupled effect of heat

storage and direct solar radiation on indoor thermal

environment is discussed using field survey and theory

analysis. A modified index taking into account heat

storage and solar radiation for the traditional calculation

method of heat load in direct gain solar dwellings with

floor heating system are described. The results are very

beneficial to improve indoor thermal comfort and reduce

energy demand of the buildings.

1. INTRODUCTION

In recent years, the large glass windows are gradually

adopted in newly-built residences with floor radiant heating

system. These kind of houses are favored by habitant,

because of less clothes and warmth like summer. But this

warmth indoor climate bring into much energy

consumption and heavy environment load. The room with

the large glass windows in the south wall is similar to direct

gain passive house, the heat absorbed by concrete slab

and other thermal mass is slowly released into indoor air

with long-wave radiation. And it’s known that the glass

baffle permeation of long-wave radiation , which can be

used to improve indoor thermal comfort, and get the

excellent energy-saving result. Some studies on the

suitable window-to-wall ratio have been studied[1]~[4].

The effect of thermal mass on indoor environment mainly

include: (1) the role of thermal mass on reducing peak

cooling loads[5]. (2) parameters affecting the performance

of thermal mass. (3)how to use passive solar wall to control

indoor air temperature swing caused by outdoor climate[6].

(4) the transient models of building internal thermal

mass[7]. (5) optimal building thermal mass control[8], etc.,

but few studies on the role of thermal mass in design have

been found.

In this paper, the direct heat gains by floor and thermal

storage volume by concrete slab are calculated, and the

analysis method of indoor thermal environment in the

residences with the large glass windows and floor radiant

heating system is mainly discussed. Field survey data are

used to analysis the role of solar radiation and thermal

storage on indoor thermal environment.

3 SOLAR COLLECTOR TECHNOLOGIES AND SYSTEMS

805

2. FIELD SURVEY

The field survey of the dwellings with floor heating system

has been performed in Dalian during Jan.2007, the results

show that the indoor air temperature difference

-10

-5

1 3 5 7 9 11 13 15 17 19 21 23

Time

Temperature/

indoor air temp. floor surface temp.

outdoor air temp.

Fig. 1: Temperature comparison of indoor air and floor

surface of rooms facing south and north. (Real line:

room facing south; Dashed: room facing north).

between rooms facing south and north in sunny day is

about 3ć(see Fig. 1), and the indoor air temperature of the

room facing south in fine day is 3ć higher than the one in

cloudy day (see Fig. 2). Although actual operation heat flux

was only about 1/4 of design value, serious indoor overheat

appeared (overheat degree is about 7~10ć). The overheat

-10

-5

1 3 5 7 9 11131517192123

Time

Temperature/

indoor air temp. floor surface temp.

outdoor air temp. outdoor air temp.

Fig. 2: Temperature comparison of indoor air and floor

surface in clear day and cloudy day, respectively.

(Real line: clear day; Dashed: cloudy day).

bring into some health problems and uncomfortable

because of high air temperature and low relative humidity.

In the traditional design of floor heating system, the effect

of solar radiation is ignored, but in fact, the efficiently

using solar radiation can improve indoor thermal comfort

and save more energy resource.

3. ANALYSIS OF AFFECTING FACTORS

From the field survey data , room facing south is almost

overheat in fine day. In order to distinguish the reasons,

heat balance relationship of room is drawn in Fig.3. In

practice, heat supply Q

of floor heating system is

determined based on design parameters specified in design

criteria, namely, heating load Q

is computed based on

indoor/ outdoor design temperature.

According to the heat

balance at the inner surface of the building

envelope of the conditioned space, an equation is

established in the following form:

Q+Q'=Q

˄1˅

Where Qüheat supply, W/h;

Q'ü solar radiative energy, W/h;

heat loss through exterior envelope, W/h;

üthermal

storage volume of floor and ceiling

slab , W/h;

ü convective heat transfer, W/h;

downward

heat transfer (heat loss), W/h.

In actual floor heating system design, heat released from

floor only includes radiative, convective heat transfer and

downward heat loss, solar heat gain and the effect of heat

charge/discharge from slab(thermal mass) are not taken into

account, but these factors should lead to overheat problem

in floor heating room.

From above analysis, it has been seen that the role of solar

radiative heat gain and heat charge/discharge on indoor

thermal environment of direct gain room with floor heating

can contribute to reducing design heat supply. As shown in

Fig. 4, because of characteristic of heat charge/discharge of

inner thermal mass in floor heating room, indoor air

temperature is obviously greater than that in other heating

Proceedings of ISES Solar World Congress 2007: Solar Energy and Human Settlement

806

Fig. 3: Heat balance in a conditioned space.

methods, even if in the same heat supply. Therefore, effect

of solar radiative heat gain and heat charge/discharge must

consider in investigation of indoor climate of room with

floor heating, in order to achieve reasonable design heat

supply and optimal operative mode.

(a) floor heating (b) radiator heating

Fig. 4: Comparison of heat exchange process in different

heating methods.

4. INDOOR THERMAL ENVIRONMENT ANALYSIS

The effects of inner thermal mass of room with

slab-on-grade radiant floor heating system on indoor

climate are mainly as follow:

(1) The rise of indoor air temperature is slower than that in

other heating methods during the initial stages of floor

heating system operation due to thermal storage.

(2) When the outdoor temperature is higher than the

outdoor design temperature, the actual heat supply will be

greater than design heat supply if no reasonable operation

control, which leads to overheat, and additional heat .

accumulation in slab. Sometimes, this overheat hart to shift

even open the windows, but also waste energy.

(3) For rooms facing south in the newly built residence, the

ratio of the window and the wall is greater than the

specified value in design criteria, so that the moor solar

rediative heat gain in floor increase heat storage volume. of

slab, accordingly, actual heat supply increase.

4.1ʳ Calculation Solar Radiative Heat Gain in Concrete

Slab during the Heating Period

In this paper, take a room facing south with a size of

4.8m×5.4m×3m as an example, some representative

window to wall ratios are used to simulate, such as 0.53,

0.5, 0.8, 0.46, 0.44, 0.40, 0.35 and 0.3. Part of the solar heat

gain admitted into the conditioned space through window is

absorbed by floor, this part of heat gain depend on change

of sunlit floor area, it is given as

= A

× S

× α ˄2˅

Where, A

is the sunlit area of floor, m

; a is the absorbance,

equals 0.7; S

is the solar radiation transmitted through the

window glass, which can be given by S

= H

btv

× τ

˄W/m

˅,

in which H

btv

is the solar intensity irradiated on the outdoor

glass facing south , W/m

. τ

is transmittance of the

window glass. Transmittance at different time can be

obtained from appendix B2 in Ref.[9].

The soft, ARCHSCI, has been used for simulating hourly

change of sunlit floor area during heating period, hourly

average sunlit areas are calculated statistically based on 8

kinds of window to wall ratio, the results are shown in Fig. 5.

According to the sunlit area computed above, the direct

heat gain absorbed by concrete slab has been calculated, as

shown in Fig. 6. Take window to wall ratio 0.53 an

example, the hourly average direct heat gain of the floor is

28W~1491W from 6:00 to 16:00. The corresponding solar

heat gain absorbed by the floor equivalently increased as

much as 0.02~1.15 times of the additional heat supply

while heat supply is 50W/m

in continuous heating.

23ć

18ć

3 SOLAR COLLECTOR TECHNOLOGIES AND SYSTEMS

807

300

600

900

1200

1500

8:00 10:00 12:00 14:00 16:00

Ti me

Direct Heat Gain/

WWR0.53 WWR0.50 WW R0.48 WWR0.46

WWR0.44 WWR0.4 WWR0.35 WWR0.3

Fig.5: Hourly change of average floor sunlit area with

different window to wall ratios.

200

400

600

800

1000

1200

1400

1600

8:00 10:00 12:00 14:00 16:00

Ti me

Direct Heat Gain/

WWR0.53 WWR0.50 WWR0.44

WWR0.4 WWR0.35 WWR0.3

Fig. 6: The hourly change of average solar radiative heat

gain absorbed by concrete slab with different

window to wall ratios.

4.2 Analysis of Indoor Climate on Coupled Solar

Radiation and Heat Charge/Discharge of Thermal

Mass

Thermal network model of the room has been established

according to thermal balance principle, the ceiling and floor

was considered as a thermal mass only, a computing

program was adopted to computing. Under intermitted

heating condition in which one day was considered as a

period, heat charge/discharge of thermal mass, indoor air

temperature, surface temperature of floor and ceiling were

computed, which results were shown in Fig. 7. The

operation mode is determined based on that of field

measurement residence , namely from 2:00 to 8:00 and

from 14:00 to 20:00 were heating period, rest of which was

unheated. From Fig.7, as heating begins, concrete slab

began to charge, thermal storage volume gradually goes

down; when stop heating, indoor air temperature almost has

no change, because of effect of heat discharge of inner

thermal mass. Compared with traditional room heated by

radiator, indoor air temperature swing is small(about 2ć),

load-shift is obvious.

-2000

-1500

-1000

-500

500

1000

1500

2000

2500

2:00

4:00

6:00

8:00

10:00

12:00

14:00

16:00

18:00

20:00

22:00

0:00

2:00

Time

Heat/kJ

Temperature/

floor charge and discharge ceiling charge and dischage

heat supply solar radiation received by floo

floor surface temp. indoor temp.

ceiling temp.

Fig. 7: The effect of solar radiation.

In unheated period (from 8:00 to 14:00), due to the effect of

solar radiation, concrete slab is not discharging only as

heating period, it begins charge from 10:00, total thermal

storage volume goes on. Indoor temperature is about 2ć

higher than that without solar radiation, while ceiling was

charging all over the periods.

5. ADAPTIVE COMPUTING METHODS OF HEAT

SUPPLY

Because of the effect of heat charge/discharge characteristic

of inner thermal mass, transient heat supply is not equal to

transient heat load. The computing results shows, in cloudy

day, while it was heating, about 70% of the heat supply was

stored, the envelope temperature went on, indoor

temperature field is uniform than other heating manner.

While it stopped, the heat released into the indoor air

mainly come from inner thermal mass, and because of long

wave radiation, heat loss from glasses was greatly

decreased, restrain the fluctuation of indoor temperature. In

sunny day, because of solar radiation, while it was

discharging, heat discharge was only 16.6% of that while it

was cloudy, more heat was stored. So, the effect of solar

radiation and heat discharge inner thermal mass is equal to

an addition to equivalent heat supply. The equivalent heat

Proceedings of ISES Solar World Congress 2007: Solar Energy and Human Settlement

808

supply can be described as follow:

equivalent heat supply

Ĭahbhchdesign heat supply

where a is ratio of thermal storage volume to heat supply; b

is ratio of heat released to heat storage; c is a coefficient

considering solar radiation. So, take Dalian city, China as

an example, according to new energy saving standard of

civil building, in china, the value of a, b, c , as shown in

Table 1.

TABLE 1: RECOMMEND COEFFICIENT VALUE

(DALIAN, CHINA)

a b c

0.45 0.9 1.0~1.3

If design heat supply was computed with the new method,

in cloudy, 58.7% of that can be reduced; in sunny, 76.3% of

that can be reduced, energy saving effect was very evidence,

and indoor comfort can be improved too.

6. CONCLUSIONS

The thermal environment evaluation methods of direct-gain

rooms with floor heating was studied in this paper, some

points are as follow:

(1) The effect of the solar radiation and thermal storage

characteristics on indoor thermal environment should be

considered during design period of floor heating.

(2) From computing hourly change of sunlit floor area, can

achieve more accurate solar radiative heat gain absorbed by

floor.

(3) The equivalent heat supply taken into account the effect

of solar radiation and heat charge/discharge of inner

thermal mass has been proposed, can make design heat

supply more reasonable.

7. REFERENCES

(1) Long Enshen, Fu Xiangzhao, “Effect of Area Ratio of

Window to Wall on Cooling and Heating Energy

Consumption Index and Energy Efficient Rate for

Residential Buildings”, HV&AC, 2007, 37(2 ): 46-49.

(2) Wang Liping, Wong Nyuk Hien, Li Shuo, “Facade

Design Optimization for Naturally Ventilated

Residential Buildings in Singapore”, Energy and

Buildings, 2007, 39 (8): 954-961.

(3) T. Miyazaki, A. Akisawa, T. Kashiwagi, “Energy

Savings of Office Buildings by the Use of

Semi-transparent Solar Cells for Windows”, Renewable

Energy, 2005, 30 (3): 281-304.

(4) Mehlika N, Inanici F, Nur D, “Thermal Performance

Optimization of Building Aspect Ratio and South

Window Size in Five Cities Having Different Climatic

Characteristics of Turkey”, Building and Environment,

2000, 35 (1): 41-52.

(5) Beat Lehmann, Viktor Dorer a, Markus Koschenz,

“Application Range of Thermally Activated Building

Systems Tabs”, Energy and Buildings, 2007,39 (5):

593-598.

(6) L. Zalewski, M. Chantant a, S. Lassue b, B. Duthoit b,

“Experimental Thermal Study of A Solar Wall of

Composite Type”, Energy and Buildings, 1997, 25 (1):

7-18.

(7) Wang Shengwei, Xu Xinhua, “Parameter Estimation of

Internal Thermal Mass of Building Dynamic Models

Using Genetic Algorithm”, Energy Conversion and

Management, 2006, 47 (13-14):1927-1941.

(8) Gregor P. Henze, Jens Pfafferott, Sebastian Herkel,

Clemens Felsmann, “Impact of Adaptive Comfort

Criteria and Heat Waves on Optimal Building Thermal

Mass Control”, Energy and Buildings, 2007, 39 (2):

221-235.

(9) Li Yuanzhe, “Passive Solar House Design Handbook”,

1993.

TECHNICAL POTENTIAL OF SOLAR THERMAL DRIVEN OPEN CYCLE

ABSORPTION PROCESSES FOR INDUSTRIAL

AND COMFORT AIR CONDITIONING

Roland Heinzen, Michael Krause, Ulrike Jordan, Klaus Vajen

Kassel University, Institute for Thermal Energy Technology

34109 Kassel, Germany

heinzen@uni-kassel.de

ABSTRACT

The open absorption process is basically an air drying pro-

cess. Applications for this process can be found in the

sector of industrial and comfort air conditioning. In this

investigation seven categories of applications are described

and characterized concerning their specific requests for

temperature and humidity.

Possible system configurations of an open absorption sys-

tem are presented for each application category. As the

main result a graph is derived from the collected and

calculated data which helps to design an open absorption

system and to choose the design for the absorber

component and the type of liquid desiccant which matches

the requirements of the application in question.

1. INTRODUCTION

Many applications in the industrial and comfort air condi-

tioning sector require hygienic clean, dry and cooled or

heated air. So far electrically driven vapour compression

machines, electrical heaters or fossile fired burners are ap-

plied to produce dry and cooled or heated air. The wide use

and high primary energy consumption of these

conventional technologies result in ecological and

sometimes even economical drawbacks. The solar driven

open absorption process with aqueous salt solutions

represents a promising alternative in cases where

dehumidification is necessary.

The system evolving from the open absorption process is

referred as a liquid desiccant system (LDS). Solar thermal

driven liquid desiccant systems have many potential

advantages and can provide a promising alternative to

conventional vapor compression systems:

 LDS is driven by low temperature heat e.g. solar,

district heating, waste heat and therefore avoids peak

electricity demand during the air conditioning season

[Lowenstein 1998].

 The supply of solar energy and the demand for cooling

and dehumidification are usually in phase [Henning

2003].

 LDS results in drier ductwork to prevent mold and

bacterial growth [Bland 2002].

 Desiccants can remove contaminants from air streams

to improve indoor air quality.

 LDS have the potential to become more economic than

solid desiccant and vapour compression technologies

[Lowenstein 1998].

Figure 1 shows a schematic of the liquid desiccant air dry-

ing process in the dashed area. It presents possible driving

heat sources (left), the coupling to different cooling techno-

logies (center right) and possible applications where LDS

can be technically viable and economically and ecolo-

gically useful (right).

Proceedings of ISES Solar World Congress 2007: Solar Energy and Human Settlement

810

In the absorber component of a LDS a hygroscopic aqueous

salt solution e.g. lithium chloride (LiCl), calcium chloride

(CaCl

), etc. is brought in contact with a humid air stream. The

moisture is absorbed by the salt solution. The absorption of

moisture causes the release of evaporation heat, so that both,

the air stream and the salt solution are heated in this process.

The air leaves the absorber with a lower humidity ratio while

the salt concentration of the liquid desiccant decreases.

Depending on the application a cooling process is coupled

to the LDS. For this a direct or indirect evaporative cooler

[Lävemann 2005], an absorption cooling machine

[Simader 2005] or a vapour compression machine [Al-Jaa-

fari (2003)] can be coupled to the process. The cooling pro-

cess can be added either in serial to the dehumidification

stage [Steimle 1998] or simultaneously [Saman 2002]. For

a simulataneous cooling process it is necessary to have a

cooling fluid cycle within the absorber. These absorbers are

referred to as internally cooled absorbers while absorbers

without the cooling cycle are referred to as adiabatic ab-

sorbers. LDS coupled with cooling processes can be used

for [Lowenstein 1998]:

 comfort air conditioning in offices, public and res-

idential buildings

 warehouses and production halls for preservation and

archiving purposes

 condensation protection to prevent mould and rust

destruction from equipment

 production processes e.g. in the food production,

pharmaceutic production, semi-conductor production,

rubber industry, confectioneries

The air stream from the absorber can be used directly for:

 high efficiency heat recovery and indirect air heating in

low energy buildings [Kerskes 2004]

 low temperature drying of agricultural goods and

industrial products (“gentle drying”) [Rane 2005]

 high efficiency heat recovery and humidity control for

indoor swimming pools and greenhouses [Waldenmaier

1998]

The aqueous salt solution needs to be regenerated after ab-

sorbing moisture. Similar to the absorber the salt solution in

the regenerator is exposed again to an air stream. Either the

desiccant or the air stream are heated by a low temperature

heat source e.g. solar thermal air or liquid collectors,

combined heat and power plants or waste and process heat.

The regeneration temperature depends on the type of salt

solution, the desired concentration and on the heat source.

For solar thermal driven LDS an economical useful

regeneration temperature ranges from 50 °C to 80 °C. Heat

from fossile or waste heat sources may be used at higher

values depending on the temperature available. Re-

generators working on higher temperatures are constructed

as 1½ – 2 stage boilers with multiple heat recovery stages

[Lowenstein 1992], while regenerators working on a lower

temperature level are often constructed similarly to the

absorber. Like for the absorber internally heated or

adiabatic regenerators can be used.

LDS allow additionally a lossfree chemical heat storage by

utilizing the concentration shift of the aqueous salt solution.

Especially in combination with exclusively solar driven

Fig. 1: Liquid desiccant air drying process: from source to application.

3 SOLAR COLLECTOR TECHNOLOGIES AND SYSTEMS

811

LDS, this storage capability can be utilized to bridge day

periods with insufficient radiation in comfort or industrial

air conditioning applications, to run drying processes at

night time or as a seasonal storage for heating purposes in

low energy buildings.

2. TECHNICAL APPLICATIONS FOR LIQUID DESIC-

CANT SYSTEMS

It can be distinguished between seven different application

categories which are characterized in the following sections.

2.1 Comfort Air Conditioning

The classic application for LDS is comfort air conditioning

in domestic and commercial buildings. Example applica-

tions are: shopping centres, offices and administration

buildings, etc. This application type is characterized by a

strong demand for humidity control because of either

outside weather conditions or high internal latent loads. The

space temperature and humidity requirements are regulated

after international or national standards (ISO 7730,

DIN 1946, ASHRAE 55) and depend generally on the

outside conditions and on the activity level of the persons

within the room. In the German standard DIN 1946 the

comfort zone is defined in the range of 22°C to 26°C for

the room temperature and from 30% to 65% for the relative

humidity level.

2.2 Warehousing, Preservation and Archiving

Warehouses are no typical applications for dehumidification

control. However, there are some exceptions: wine depots,

paper depots, textile and yarn depots, etc. The product

quality is highly sensible to latent loads as it either rottens

or degenerates. A relative humidity level has to be kept

between 30 % and 50 % at a highly varying application

depending storing temperature between 5 °C and 30 °C [Bland

2002]. For conservation of historical buildings, art works,

books, in museums and galleries it is recommended to keep

also a humidity range between 30 % and 50 % at room

temperatures between 14 °C and 22 °C [DIN ISO 11799].

2.3 Condensation Protection

Dehumidification is an essential method to ensure

condensation protection and value conservation of equip-

ment. Condensation will appear in processes with uninsu-

lated pipes, pumps and tanks which are traversed by cold

water and cause the formation of mould and rust. Example

applications are breweries, steam power stations, water-

works, etc. [Socher 1993] states that mould can be avoided

below a relative humidity of 70%. Rust can be essentially

reduced below a relative humidity of 50%. Below 35% r.h.

the formation of rust can be completely avoided.

2.4 Air Conditioning for Industrial Processes

Some examples where dry air is needed in industrial pro-

cesses are the following: lacquering in the automobile in-

dustry, cement fabrication, drug production in the pharma

industry, etc. The specific requirements for temperature and

humidity differ strongly with the application. Extreme low

relative humidities below 30% have to be kept in some

drug production and packaging processes, while the

humidity requirements are restricted for lacquering only to

60% r. H. [Oelsen 2001].

2.5 Gentle Drying

“Gentle“ drying can be used for heat sensible products and

substances. This is especially the case for medical plants,

food products (fruits, vegetables, corn, fish) and flowers.

These products have to be dried below a temperature of

60°C to keep the substance or shape, in some cases even

below 45°C. The relative humidity should be kept in all

cases below 40 %.

[Conrad 1996] studied the prototype of a solar sorption

storage system for drying medical plants under Slovenian

climate. The system worked as a dehumidifier and heat

recovery system during night and times of insufficient irra-

diation. During sufficient irradiation the dryer was fed by

hot air from a solar air collector.

2.6 Heat Recovery and Humidity Control for Indoor

Swimming Pools and Greenhouses

Indoor swimming pools and greenhouses have a very high

energy consumption due to very high internal latent loads

which are removed in general by fresh air exchange. Sensible

heat recovery is mostly realized in these systems but a major

Труды Всемирного конгресса Международного общества солнечной энергии - 2007. Том 2

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