Evaluation of Indoor Microclimate in Low-energy Structures Regarding Applied Energy Sources, Building Materials and

Construction Systems

(1)ZUZANA MASTNA, (2)PETR MASTNY (1)FCE, Institute of Building Structures

Brno University of Technology Veveri 331, 602 00 Brno

(2)FEEC, Centre of Research and Utilization of Renewable Energy Sources Brno University of Technology

Technicka 10, 616 00 Brno CZECH REPUBLIC

(1)mastna.z@fce.vutbr.cz, (2)mastny@feec.vutbr.cz http://www.vutbr.cz

Abstract: - Since low-energy and passive objects have become a “standard” for newly built structures, there should be evaluated overall resulting indoor climate in such type of indoor environment. Not many studies evaluating indoor climate have been presented so far. Indoor climate evaluation has great importance mainly because low-energy and passive indoor climate is influenced by many different factors among which the most important are: applied constructions and building envelopes, quality and type of used building materials, air-proofness of building envelopes and applied energy systems. The paper focuses on a case study a low-energy building with specific used building materials and energy systems. There are presented results of measuring taken within this low-energy house. There is explained the evaluation of the most significant parameters of indoor climate resulting in stating solutions for optimization of indoor climate. Key-Words: - Indoor Microclimate, Forced Ventilation, Heat Pump, Low-energy Structures, Air-proofness 1 Introduction Energy savings are – regarding further education and interest in environmental issue – not only up-to-date scientific subject, but energy savings are also important part of energy policy of the Czech Republic and the European Union. Regarding this fact energy saving approach is one of the major issues within building sector of the European Union.

Presently the issue of low-energy buildings develops toward evaluation of already constructed buildings. Such development is a logical presumption of following evaluation of existing conceptions as it can bring optimization of used processes and solutions.

Indoor climate has major impact on human health. That is why it is essential to monitor and consequently evaluate indoor climate of low-energy (and passive) buildings which create specific microclimate.

Indoor climate is a specific part of environment which is formed by agencies representing energy and mass flows in between two environs. Microclimate is mainly influenced by building

constructions and by applied energy systems as well. The most important part of indoor climate is thermal-hygric microclimate which represents 30% of overall microclimate. Its fragmental components are: indoor air temperature (54%), indoor air humidity (23%) and speed of indoor air flow (23%) [1]. 2 Indoor Microclimate of Low-energy

Structures Low-energy buildings are characterized by specific heat demand reaching values at the maximum 50 kWh/m2a. Thus such building structures have to be designed regarding maximum energy savings.

To reach maximum energy savings within modern buildings there is a major constructional demand on air-proofness of building envelopes. The quality of air-proof envelopes influences the amount of total heat loss caused by infiltration. On the contrary air-proof constructions lead to higher indoor air humidity and can result in unsatisfactory indoor microclimate. Regarding indoor microclimate of poor quality there

Recent Researches in Environment, Energy Systems and Sustainability

ISBN: 978-1-61804-088-6 177

is often mentioned the occurrence of molds resulting into allergies and asthma. Occurrence of molds within building constructions is related to permanent high relative air humidity (long-term values above 60%). As it is shown in the Figure 1, the percentage of surviving microorganism is increasing with the indoor air relative humidity reaching values below 30% and above 60%.

Therefore another important parameter of indoor climate (together with thermal-hygric) which can be directly influenced by applied energy systems and building constructions is a toxic microclimate. The most monitored characteristic of toxic microclimate regarding low-energy houses is concentration of carbon dioxide - CO2. It is the most significant pollutant of indoor air. Carbon dioxide is produced by human breathing and its concentration is higher inside the building than in the outdoor air. Concentration of carbon dioxide is related to indoor air relative humidity: the higher relative humidity is, the higher is the concentration of CO2.

Hence very important issue within low-energy (and passive) structures is the ventilation of building. There can be recognized two types of ventilation: natural of forced ventilation.

Fig. 1 Percentage of surviving microorganisms in relation to relative air humidity [1] 3 Air-proofness and the Function of

Vapor Barrier As it is explained above, for the low-energy structures it is essential to reach high air-proofness of building envelopes. Since low-energy buildings are mostly constructed as prefabricated wooden constructions the function of air-proof layer has a vapor barrier usually designed as a vapor and air proof foil. The major importance regarding air-

proofness has the quality of labor with which the vapor barrier is built in the envelopes.

Insufficient quality of vapor barrier can result in many characteristics degrading entire low-energy structure:

• Degrading thermal insulation o In case the vapor and air-proof barrier

does not work properly then the diffusion flow transferring air humidity can condensate within the thermal insulation layer. Since the insulation material is mostly mineral (air-leaking and liquid-absorbing) the condensation of air humidity is allowed (under specific thermal-hygric conditions) and the mineral insulation degrades.

• Increasing thermal loss of the building structure o Together with degrading thermal

insulation layer in the building envelopes there appear increasing thermal loss of the building structure (humid mineral insulation loses thermal-insulation function).

• Decreasing indoor air relative humidity o Since the diffusion flow can transfer

through building envelopes, a particular amount of indoor air humidity leaves indoor climate and relative indoor air humidity thereby decreases. As it is shown in the Figure 1 and Figure 2 even low relative air humidity causes unsatisfactory microclimate (since there is a high percentage of surviving microorganism and the human mucous membranes of upper airways get dry and that can result in allergies and asthma as well).

• Insufficient operation of systems of forced ventilation o The systems of forced ventilation are

often used in the low-energy buildings. Such units work as over-pressure or under-pressure systems. In structures with poor air-proof envelopes these systems cannot operate as they should. Resulting indoor microclimate is therefore hardly sustainable.

• Decreasing persistence and stability of wooden bearing constructions o In case the diffusion flow can transfer

through the envelopes it is obvious that air humidity reaches even the bearing wooden construction. Consequently the wooden frames can lose its persistence

Recent Researches in Environment, Energy Systems and Sustainability

ISBN: 978-1-61804-088-6 178

and stability because wooden constructions cannot be exposed to a long-term high humidity with values above 20%.

Fig. 2 Basal corpuscles of upper airways A) in optimal condition B) dried [1] 4 Energy Systems in Low-energy

Building Structures To ensure quality indoor microclimate of low-energy buildings there are at present used two typical energy systems:

• Hot water systems o Warm water systems are the simplest

regarding operation, regulation and investment costs. Such systems cannot ensure ventilation of building, this means that the occupants have to ventilate naturally and frequently.

• Systems of forced ventilation and hot air heating o Such systems belong to air systems – air

is used to ensure both ventilation and heating. The principle of operation of system with forced ventilation and heating is shown in Figure 3.

• Electrical convector heating systems o Application of electrical convector

heaters depends on the type of constructions – for the light constructions it is very advantageous system with low operation costs contrary to heavy constructions where such system is - regarding operation - very expensive. The main reason is the construction accumulation which is very low with light constructions and very high with the heavy construction systems.

• Heat pump in cooperation with solar collectors

o There appeared a new conception of using heat pumps and solar systems in low-energy houses – combined system in which heat pump cooperates with solar system. This cooperation works on a simple principal – when the temperature in the suggested combined system falls under the temperature of bivalence, the solar collector activates and the thermal energy obtained from the solar system is used for increasing temperature at the heat pump input.

c2 –circulation and fresh air, e1ZR – incoming air transferred through underground collector, i1 – waste air from toilet, bathroom and kitchen, c1 – circulation air, i2 – outgoing waste air after recuperation, RC – venting and heating unit, IZT – integrated heat accumulator, ZR – underground collector, S – solar collectors

Fig. 3 Scheme of system with forced ventilation and hot air heating in connection with solar system and underground collector [6] 5 Building Materials and its Influence

on Indoor Climate Type of designed constructions and building materials is decisive for the resulting indoor climate of low-energy and passive buildings. There can be recognized two different construction systems:

• Heavy Construction systems, • Light construction systems.

Heavy construction systems are represented

mainly by masonry, concrete and lime-sand constructions. Heavy constructions have very good acoustic parameters and are typical with accumulation. Accumulation – as the ability to absorb thermal energy and humidity – is an attribute that must be considered in quality building design. The response of heavy constructions on changing temperatures outside building are slow – all temperature extremes from outdoor environment

Recent Researches in Environment, Energy Systems and Sustainability

ISBN: 978-1-61804-088-6 179

reflect in the indoor climate with approximately 10-12 hour delay.

Since heavy constructions also absorb indoor humidity, its lowering is usually necessary (heavy constructions of low-energy and passive buildings usually generate high relative indoor air humidity – therefore the application of forced heating and ventilation is in such type of construction positive.

Light construction systems are represented mainly by various frame constructions (wooden, metal) with high percentage of insulations. Therefore such systems are advantageous for low-energy and passive houses for their high thermal standard. Light constructions have minimal accumulation – which means that the response on outdoor temperature extremes is short – approximately 1-3 hours.

Since light constructions do not accumulate thermal energy there can be conveniently applied electrical convector heaters with are in such constructions used effectively.

Since light constructions do not accumulate indoor humidity and the construction do not contain built-in humidity they keep indoor air relative humidity at average values, in such type of construction it is not advantageous to design hot air heating since it lowers indoor air humidity to very low values (see study case below). 6 Low-energy Single Family House –

“Kubis” Family house „Kubis“ (Fig. 4) is designed as a low-energy prefabricated wooden house with the principals of low-energy building: the south facade has most glass areas for reaching maximum thermal gains – but also using shading system for keeping temperature extremes under control, the north facade has only minimal glass areas. Regarding heating system there is designed forced ventilation and hot air heating and solar collectors (primary pre-heating hot service water) – for the operating scheme see Fig. 5.

There have been monitored the most significant parameters of indoor microclimate (thermal-hygric and toxic) such as: indoor and outdoor air temperatures, indoor and outdoor air relative humidity and concentrations of carbon dioxide.

There have been monitored both winter (heating) period and summer period. Obtained results from the measuring showed important information about application of forced ventilation and hot air heating unit. It is essential to compare heating and summer period, because during heating period the forced ventilation and hot air heating unit has been operating, during summer period it has been out of

order and the building has been ventilated naturally (the influence of the unit excluded).

Fig. 4 Single family house Kubis

RC - venting and heating unit, IZT – integrated heat accumulator, Solar – solar collectors, TUV – hot service water [6]

Fig. 5 Operation scheme of energy system in single family house Kubis 6.1 Evaluation of Measured Dates during

Heating Period Regarding most significant parameters during the heating period of thermal-hygric and toxic microclimate then the family house Kubis does not create optimal microclimate.

Indoor air relative humidity values are in between 25 – 35%, average value is 28% which is beneath the minimum set by the standard 6/2003 (Ministry of Health) – see Graph 1.

Average increase of daily temperature is 3°C which comply with the limit Δt ≤ 5°C, but in Graph 1 there can be seen that average indoor air temperature is 23.75°C, the limit interval is 20°C ≤ ti ≤ 24°C, during measuring 43% of all measured values of indoor air temperature were above the maximum limit therefore the indoor climate of family house „Kubis“ is not thermally satisfactory stable – see Graph 1.

Average value of concentration of carbon dioxide is 0.051% which does not exceed the maximum health-damaging limit 1.5% - see Graph 2.

Recent Researches in Environment, Energy Systems and Sustainability

ISBN: 978-1-61804-088-6 180

6.2 Evaluation of Measured Dates during Summer Period

Regarding most significant parameters during the summer period of thermal-hygric and toxic microclimate then the family house Kubis keeps optimal microclimate.

Indoor air relative humidity values are in between 36 – 58%, average value is 45% which is the optimal level set by the standard 6/2003 (Ministry of Health) – see Graph 4.

Average increase of daily temperature is 2.21°C which comply with the limit Δt ≤ 5°C, but in Graph 3 there can be seen that average indoor air temperature is 25.55°C, the limit interval is 22°C ≤ ti ≤ 26°C, during measuring 34% of all measured values of indoor air temperature were above the maximum limit therefore the indoor climate of family house Kubis during summer period is more thermally stable than during heating period – see Graph 3.

Average value of concentration of carbon dioxide is 0.07% which does not exceed the maximum health-damaging limit 1.5% - see Graph 5 7 Conclusion Contemporary demands on low costs of heating within modern building structures result in major interest in low-energy civil constructions. This point of view is typical for investors. Regarding low-energy buildings there are many more issues that have to be solved by engineers who design building structures. Most of the decisive parameters and technical issues are related to:

• High quality of constructional design and details

• High thermo-insulation standard • Quality indoor microclimate • Suitable energy systems • Air-proofness of building envelopes • High quality of labor in situ

Since for many of the technical issues mentioned

above are responsible various specialized engineers, it is essential to ensure that the specialists share and respect their knowledge mutually. As simple as it seems that might be probably the most complicating factor within the design of low-energy building structures. Definitely this is the point that cannot be underestimated.

At present the low-energy buildings issue developed towards evaluation of already existing buildings. There has to be monitored indoor microclimate of realized buildings since there de facto appears the final outcome resulting from

cooperation and coexistence of building materials, building constructions and applied energy systems. There has to be defined relationships between different parts of the energy systems and the building structures. Such issue should be in engineering practice increasingly in demand. Heavy and light building constructions create and keep different indoor climate of buildings and its characteristics must be considered when designing proper energy system.

The paper focuses on a case study where a low-energy single family house has been monitored. This building is designed as a typical low-energy structure and includes in its design all common design elements such as – compact shape of the building, south facing glassed facade as a passive solar system, minimal glassed areas facing north, solar collectors as active solar system combined with a unit of forced ventilation and hot air heating, high standards of building envelopes regarding high thermo-insulating parameters and constructional details. Within single family house Kubis there have been monitored both heating and summer period. Measuring proved that indoor climate in the Kubis building structure is poor during heating period and on the contrary the indoor climate in this building is optimal during summer period. The point is that during heating period there is in operation the unit of forced ventilation and hot air heating, while during summer period this unit is out of order and the house is ventilated naturally. Regarding measured values, obtained parameters and knowledge it can be mentioned that:

• Energy systems have to cooperate with building structures - forced heating and hot air heating unit works in overpressure or underpressure mode – all building envelopes have to be air-proofed so that the unit can work properly – since house Kubis is heated by the forced heating and hot air heating unit with recuperation of waste air the required air-proofness of all envelopes have to be n50< 1.0 h-1 (see Table 1). Envelopes in the Kubis structure have been measured to have air-proofness n50 = 1.3 h-1. It is obvious that the unit cannot work properly in single family house Kubis

• Final indoor microclimate in low-energy structures has to maintain optimal – as the measured parameters proved, indoor air humidity during heating periods gets very low in Kubis house, the hot air heating unit has to solve this problem and there should be designed additional humidification of incoming air since there is no other chance to keep optimal indoor climate.

Recent Researches in Environment, Energy Systems and Sustainability

ISBN: 978-1-61804-088-6 181

It can be stated that integrated energy systems within low energy structures have to respect the constructional design of the building and vice versa.

Cooperation of both constructions and energy systems is eminently essential.

Relative air humidity and air temperature

-4

-2

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

14:5

418

:54

22:5

42:

546:

5410

:54

14:5

418

:54

22:5

42:

546:

5410

:54

14:5

418

:54

22:5

42:

546:

5410

:54

14:5

418

:54

22:5

42:

546:

5410

:54

14:5

418

:54

22:5

42:

546:

5410

:54

14:5

418

:54

22:5

42:

546:

5410

:54

14:5

418

:54

22:5

42:

546:

54

1.3.2007 2.3.2007 3.3.2007 4.3.2007 5.3.2007 6.3.2007 7.3.2007 8.3.2007

date

tem

pera

ture

[°C]

/rela

tive

hum

idit

20

30

40

50

60

70

80

90

100

110indoor air temperature outdoor air temperature

outdoor air relative humidity indoor air relative humidity

Graph 1 Indoor and outdoor air temperature and relative air humidity during heating period

Concentration of indoor CO2

0,04

0,045

0,05

0,055

0,06

0,065

0,07

0,075

14:5

418

:54

22:5

42:

546:

5410

:54

14:5

418

:54

22:5

42:

546:

5410

:54

14:5

418

:54

22:5

42:

546:

5410

:54

14:5

418

:54

22:5

42:

546:

5410

:54

14:5

418

:54

22:5

42:

546:

5410

:54

14:5

418

:54

22:5

42:

546:

5410

:54

14:5

4

18:5

422

:54

2:54

6:54

1.3.2007 2.3.2007 3.3.2007 4.3.2007 5.3.2007 6.3.2007 7.3.2007 8.3.2007

date

conc

entra

tion

of C

O2 [

%]

Graph 2 Concentration of CO2 during heating period

Recent Researches in Environment, Energy Systems and Sustainability

ISBN: 978-1-61804-088-6 182

Graph 3 Indoor and outdoor air temperature during summer period

Graph 4 Relative indoor air humidity during summer period

Graph 5 Concentration of CO2 during summer period

Classification of building structure

Historical structures

Common new built structures

Low-energy structures with forced heating

Low-energy structures with heat recuperation

Passive structures with heat recuperation

Specific heat demand for heating > 300 kWh/(m2a) <140

kWh/(m2a) < 50 kWh/(m2a) < 50 kWh/(m2a) < 15 kWh/(m2a)

Required air-proofness (n50) > 7 h-1 < 4,5 h-1 < 1,5 h-1 < 1,0 h-1 < 0,6 h-1

Table 1 Required air-proofness of building structures regarding thermal-technical standard of the building [2] Acknowledgements The conclusions presented in this paper were supported by specific research project No. FAST-S-11-64/1435 – Optimization of the

design of modern wooden structures in terms of construction physics. The research was performed in Center for Research and Utilization of Renewable Energy Sources

Recent Researches in Environment, Energy Systems and Sustainability

ISBN: 978-1-61804-088-6 183

(CRURES). Authors gratefully acknowledge financial support from European Regional Development Fund under project No. CZ.1.05/2.1.00/01.0014. References: [1] Jokl, M., Prof., Ing., DrSc., Theory of Indoor

Microclimate, reissue - Editorship ČVUT, Prague, 1993, 261 pages, 177 pictures, ISBN 80-01-00481-3

[2] Composite authors, Indoor Microclimate of Buildings, first printing, EXPO DATA Ltd, Brno, 2001, 126 pages, ISBN 80-7293-023-0

[3] Mastny, P.; Matousek, A. Increase of Efficiency of Energy System with Heat Pump Using Solar Radiation. Energy and Environment Proceeding of the RES'07, Arcachon, France, October 14 16, 2007: ISBN: 9789606766091

[4] Patkova, Z., Forced Ventilation and Heating of Wooden Prefabricated Houses and its Influence on Indoor Climate. Heating and Installations 3/2009, pages 46 – 49, May 2009, ISSN 1211-0906

[5] Patkova, Z., Microclimate of Low-energy Houses and Building Services. Treatise on dissertation thesis, Brno University of Technology, 2004

[6] Atrea, s.r.o., graphs and schemes by the producer of forced ventilation unit

[7] Ioan Sarbu, Energy Efficiency of Low Tenperature Central Heating System, Advances in Energy Planning, Environmental Education and Renewable Energy Sources, WSEAS Conference Proceedings, May 2010, pp. 30-35, ISSN: 1790-5095

[8] Kyncl, J., Some Remarks on Electric Heating System Design, Proceedings of the 9th International Scientific Conference EPE 2008, Brno, Czech Republic, pp. 393-396, ISBN: 978-80-214-3650-3

[9] Mastny, P., Batora, B., Increases in Power Efficiency of Renewable Power Sources, Proceedings of the 3rd WSEAS International Conference on Renewable Energy Sources 2009, University of La Laguna, Tenerife, Spain, pp. 374-378, ISBN: 978-960-474-093-2

[10] Mastny, P., Machacek, J., System for Measuring and Collecting Data - Results of Measuring on Combined System -, WSEAS Applied Informatics & Communications, 2008, pp. 192-197, ISSN 1790-5117

[11] Mastny, P., Mastna, Z., Designing Energy Systems for Low Energy Buildings with the

Support of Knowledge Technologies. In Proceedings of the 11th International Scientific Conference Electric Power Engineering 2010, Brno University of Technology, Czech Republic, BUT FEEC DEPE, 2010, pp. 385-389, ISBN: 978-80-214-4094-4

[12] Catalin Badea, Corneliu Bob, Liana Iures, Waste Materials Used For Building Construction, Advances in Energy Planning, Environmental Education and Renewable Energy Sources, May 2010, pp. 54-59, ISSN: 1790-5095

[13] Radil, L., Mastny, P., Simulation Cycle of Heat Pump by the Help of Wolfram Mathematica, Proceedings of the 11th International Scientific Conference EPE 2010, Brno, Czech Republic, pp. 375-377, ISBN: 978-80-214-4094-4

[14] Corneliu Bob, Tamas Dencsak, Liana Bob, Sustainability of buildings, Advances in Energy Planning, Environmental Education and Renewable Energy Sources, WSEAS Conference Proceedings, pp. 69-74, May 2010, ISSN: 1790-5095

Recent Researches in Environment, Energy Systems and Sustainability

ISBN: 978-1-61804-088-6 184