Scholarly article on topic 'Solar-active-houses – Analysis of the Building Concept based on Detailed Measurements'

Solar-active-houses – Analysis of the Building Concept based on Detailed Measurements Academic research paper on "Earth and related environmental sciences"

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{solar-active-house / "heat storage" / "hot water storage tank" / "high solar-thermal fraction"}

Abstract of research paper on Earth and related environmental sciences, author of scientific article — Wolfgang Kramer, Axel Oliva, Gerhard Stryi-Hipp, Sven Kobelt, Dominik Bestenlehner, et al.

Abstract Nine solar-active-houses are analyzed in detail within the project “HeizSolar”. In solar-active-houses, more than 50% of the total heat consumption for space heating and domestic hot water preparation is covered by solar thermal energy. The analysis reveals two different approaches to reach such high solar thermal fractions. A solar thermal fraction of 100% is feasible; however long- term heat storage is a major challenge.

Academic research paper on topic "Solar-active-houses – Analysis of the Building Concept based on Detailed Measurements"

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Energy Procedia 48 (2014) 895 - 903

SHC 2013, International Conference on Solar Heating and Cooling for Buildings and Industry

September 23-25, 2013, Freiburg, Germany

Solar-active-houses - analysis of the building concept based on

detailed measurements

Wolfgang Kramera, Axel Olivaa*, Gerhard Stryi-Hippa, Sven Kobeltb, Dominik Bestenlehnerb, Harald Drückb, Jürgen Bühlc, Georg Daschd

aFraunhofer-Institute for Solar Energy Systems ISE, Heidenhofstrasse 2, 79110 Freiburg, Germany bSolar- und Wärmetechnik Stuttgart, Pfaffenwaldring 6, 70550 Stuttgart, Germany cTechnical University of Ilmenau, Helmholtzring 1, 98693 Ilmenau, Germany aSonnenhaus Institut e. V., Achenfeldweg 1, 83259 Schleching, Germay

Abstract

Nine solar-active-houses are analyzed in detail within the project "HeizSolar". In solar-active-houses, more than 50 % of the total heat consumption for space heating and domestic hot water preparation is covered by solar thermal energy. The analysis reveals two different approaches to reach such high solar thermal fractions. A solar thermal fraction of 100 % is feasible; however long-term heat storage is a major challenge.

© 2014 TheAuthors.Published by ElsevierLtd.

Selectionandpeerreview bythe scientific conferencecommitteeofSHC 2013underresponsibilityofPSE AG Keywords: solar-active-house, heat storage, hot water storage tank, high solar-thermal fraction

Nomenclature

EFA effective floor area [m2] according to EnEV 2009 [5] HT' specific transmission heat loss coefficient [W/(m2^K)j Acoii,a aperture area of solar collector field [m2]

* Corresponding author. Tel.: +49 761 4588 5698; fax: +49 761 4588 9698 E-mail address: axel.oliva@ise.fraunhofer.de

1876-6102 © 2014 The Authors. Published by Elsevier Ltd.

Selection and peer review by the scientific conference committee of SHC 2013 under responsibility of PSE AG doi: 10.1016/j.egypro.2014.02.103

acou tilt angle of the collector field in [°]

Vstor volume of hot water storage tank [m3]

GcoU irradiation perpendicular to the collector plain [4] [kWh/m2]

Tamb,a average ambient temperature for one year according to [4]

QSH heat consumption/demand for space heating [kWh/m2EFA]

QDHW heat consumption/demand for domestic hot water preparation [kWh/m2EFA]

Qaux heat supply of auxiliary heating system [kWh/m2EFA]

fsoi,th solar thermal fraction [-]

1. Introduction and goals of the project "HeizSolar"

Due to the German government's aim to reduce greenhouse gas emission, there is an urgent need for low carbon dioxide emitting technology for heat supply systems in private households. The concept of the so called solar-active-houses (SAH) can make a significant contribution to this aim. Such houses are equipped with a large solar thermal system. The building envelope is thermally insulated at a high level and it is heated by a low temperature heating system. The solar thermal fraction of the total heat demand for space heating (SH) and domestic hot water preparation (DHW) is higher than 50 %.

The solar thermal heat generating system consists of a large collector area and a high-capacity thermal water storage tank. A well-conceived building concept allows for high passive solar gains. The thermal collectors are steeply tilted. They are mounted onto the roof or the façade. In more sophisticated applications the collector area is integrated into the roof or the façade.

The major goals of the research project "HeizSolar" are:

• Prove the SAH concept

• Identify optimization potentials

• Create a validated scientific dynamic simulation tool

• Provide a methodology for the comparison with other low CO2-emission heat supply concepts

• Establish deeper knowledge about solar-active-houses on the level of planners/installers

The concept of solar-active-houses is systematically analyzed and evaluated for the first time. In total, nine buildings are monitored. The monitoring data is used to prove the concept, to identify optimization potentials and to validate dynamic simulation models. This paper presents the results of the monitoring for three selected examples of SAH.

2. Data acquisition

2.1. Locations of the monitored solar-active-houses

Six typical single-family houses (SFH) and three multi-family houses (MFH) are monitored. The locations are shown in Figure 1. A large variety of types of houses and climatic conditions in Germany are covered by the analysis. However, it is obvious, that the majority of houses are located in the south, where climatic conditions are favorable for the SAH concept. The characteristics of three selected houses and the results of the monitoring are shown in Table 1. The concept of heat supply has been described in detail for all houses in [1].

Figure 1 : Location of the monitored houses

2.2. Measuring concept

The measuring concept developed for the SAH allows for detailed and precise monitoring of each building. Special attention is paid to the hydraulic circuits. Heat meters are placed in all hydraulic circuits in order to be able to calculate the energy balance of the complete heat supply system. Thermal energy storage plays a major role in this type of system. Therefore, a very detailed measurement of the temperature profile inside the thermal water storage tank is performed. Temperature sensors are mounted at different levels of the tank in order to derive information about its thermal charge level and thermal stratification. The solar irradiation is measured perpendicular to the solar collector plane for the determination of the solar input to the collector. Power consumption of all electric components of the heat supply system is monitored as well. In cases, where a PV system is installed, electric power generation is also logged. Pressure gauges are installed for recording the conditions of operation, which is particularly interesting during the summer period with excess solar heat generation and, possibly, stagnation with the production of steam. For the calculation of primary energy consumption, the quantity of wood consumed by the auxiliary heating system is determined. A more detailed description of the measuring concept can be found in [1]. Figure 2 shows a typical installation scheme for a solar-active-house.

2.3. Determination of heat losses and the charge level of the thermal heat storage

The heat storage tank is a very crucial component of the investigated heat supply system. The heat capacity of the storage system, the way of charging and discharging and its heat losses are important concerning the performance of the entire solar thermal heat supply system. However, direct in situ measurement of heat losses of the storage tank is not possible. Therefore, three different methods for the determination of these losses were developed and cross-validated. These methods are described in [2].

3. Analysis

3.1. Performance indicator

The solar thermal fraction fsoith is an important performance indicator of a solar thermal system. It is defined by eq. (1) and eq. (2). All necessary data is measured by heat meters. Qaux is the heat supplied by the auxiliary heating system to the hot water storage tank or directly to the heating circuit. QSH and QDHW represent the heat consumption for SH and DHW.

useful solar gains Qsolme , _Q

■DHW

Qsol ,use QsH + QdHW - Qaux

It is important to mention, that the widely spread definition offsoiih,=Qso/(Qsoi+Qaia) is not used for this analysis. Qsoi+Qaux is the total heat provided by the collector and the auxiliary heating device. This sum corresponds to the total amount of heat consumed including all heat losses. The problem of using such a definition, especially in SAH, is due to the fact that a large part of the heat losses are attributed to the storage tank. However, increasing storage tank losses lead to higher solar thermal gains, in particular during summer time, when these losses are completely compensated by solar thermal gains. The result of this would be an increasing solar thermal fraction. Thus, worse thermal insulation would lead to a higher solar thermal fraction which is in contradiction to the intention of such a performance figure.

On the other hand, heat losses of the storage tank may contribute to the heating of the house, if the tank is located inside the house's insulated envelope. However, this effect is smaller than the previous one, because the heating period is shorter than the non-heating period in summer. On top of that the mean temperature of the storage tank is lower during the heating period. Therefore, definition (1) is a rather conservative approach.

cold hot water water

(p— pressure □— temperature, direct ^— temperature, strap-on

^ Solar irradiation

IW electric energy IQ heat energy (Pa pump

thermostat-controlled valve

manually operated valve motor-operated valve

solar collector array 68 m:

Figure 2: Schematic drawing of a typical data acquisition installation with sensor types and positions

Figure 3: Heat balance and charge level of the thermal storage tank of the SAH in Munich (MUN)

3.2. Typical one year cycle

Figure 3 shows a typical one year cycle of a SAH. In phase 1, the charge level (grey line) of the thermal energy storage is reduced during the winter heating period. However, solar thermal gains are still important.

When the charge level has reached a minimum, auxiliary heating is necessary (phase 2). In phase 3, solar gains exceed the heat demand. The buffer storage is charged to its maximum value. It is remarkable, that it takes only two months until the buffer storage is charged. This phase is followed by phase 4, when solar excess heat cannot be used for further charging the storage tank. In order to avoid excessive thermal stress in the installation, excess heat has to be discharged by circulating the heat transfer fluid between storage tank and collector field during night time (Qsolcool). Another possibility to get rid of the excess heat is heating of a swimming pool, for example.

Figure 4 shows the results of a 100% solar heated house. At first glance, the graph looks quite similar to the previous one. However, due to the very large thermal storage tank, the discharge phase lasts until the end of January. Similar to the previous case is the fact that recharging the buffer storage only takes 2 months. During 6 months in summer time no more heat can be stored in the storage tank. Excess heat can be discharged by night time cooling of the system.

An important finding is that in both cases shown solar gains during winter time play an important role. On the other hand, even with large storage volume, one cannot see seasonal storage of heat. The storage tank is rapidly charged to the maximum value within only 2 months. However, the storage is not able to make use of the solar heat produced for 5-6 months during summer time.

■Qdhw+ QSH

■■I

discharge of storage until jan 2012

heating

significant solar yield during heating periode

1.00 0.75 0.50 0.25 0

<V <y -v> v>

o & & o O O <V-

<<§> ^ # ^ ^ ^ cf & ^ <f ^ ^

Figure 4: Heat balance and charge level of the thermal storage tank of the SAH in Kappelrodeck (KAP)

This result leads to the idea of a concept with highly efficient use of solar irradiation in winter when heating is required without the use of any extra-large thermal storage. Such a concept is realized in the house in Rottenburg (ROT) (figure 5). The very steeply tilted collectors (75°) are mounted in the façade, in order to use the winter sun to a maximum extent. The storage volume is only 1.9 m3. The results of this house are shown in figure 5. The most important difference compared to the previously shown results is the very evenly distributed solar gains throughout the year. Solar gain values in the winter period are almost as high as in the summer period. There is no need for cooling during the summer period at all.

However, the solar thermal fraction in this case is only 51%. This is due to the relatively poor insulation of the building compared to the previous ones. It is also obvious that the maximum usable collector area of such a concept is limited by the available surface area of the façade and it is also prone to shading problems.

From intermediate operation of the auxiliary heating system in April and October one can conclude that a larger storage tank could improve solar thermal fraction. This and other potentials of optimization have to be proved by detailed simulation.

3.3. Summary of results and characteristics of the mentioned houses

Table 1 gives an overview of some of the investigated SAH. The houses are presented with their main characteristics as well as their measured heat consumption and solar thermal fraction for the year 2012 [3].

Figure 5: Heat balance and charge level of the thermal storage tank of the of the SAH in Rottenburg (ROT)

All nine monitored SAH do reach a solar-thermal fraction fsoi,h of more than 50 %. However, when comparing the performance of different SAH based on this performance number, one has to take into account different boundary conditions (i.e. different climatic conditions and different numbers of residents).

It turns out that the house occupants have quite a significant influence on the solar thermal fraction. Especially in the case where a manually fed wood stove is used, the consumption of fuel depends very much on the attitude of the occupant. Their acceptance of slight deviations from comfortable temperature conditions plays an important role in whether the 100% solar fraction is reached or not.

4. Conclusions

A monitoring campaign on nine different solar-active-houses has been conducted. The feasibility of the concept of SAH (Solar-Active-Houses) has been proved. For the examined period, all SAH achieved a solar thermal fraction fso,th of more than 50 %, thus, reducing the auxiliary heating demand significantly and correspondingly the primary energy consumption and the CO2 emissions are lowered.

Basically, two different approaches for reaching high solar thermal fractions could be observed. The more common concept relies on maximizing the collector surface in combination with a large thermal storage volume. The second approach focuses on the maximum use of winter solar irradiation by tilting the collectors very steeply. At the same time, storage volume is minimized.

In either concept the use of solar gains during the heating period is vital for achieving high solar fractions. This is due to the fact that seasonal heat storage with thermal water storage is hardly possible in the monitored houses, even with large storage volumes .

A well-insulated building envelope is a primary condition for achieving high solar fraction. The occupants' attitude and behavior play an important role as well.

Table 1: selection of monitored SAH

position, federal state, number of residents acronym* EFA | Ht' | A„ii,a (ao) | Vso

auxiiiiary heating system(mode of operation); system of ventiiation

Period

[kWh/m2]

[°C] [kWh/m2] [kWh/m2] [kWh/m2]

fsol.th

Jan-Dec Jan'12-Dec'12

Rottenburg, Baden-Württemberg, 5 residents

231,5 m2 | 0,34 W/(m2K) | 30,0 m2 (75°) | 1,9 m3

pellet stove (manual); heat recovery with ground heat exchanger

8,9 10,7

43,9 27,7

12,5 11,0

0,70 0,51

Jan-Dec Jan'12-Dec'12

Kappelrodeck, Baden-Württemberg, 2 residents

300,1 m2 I 0,16 W/(m2K) | 101,0 m2 (35°/65°) | 42,8 m3 no auxiliary heating system; heat recovery

1.177 1.244

8,9 22,9 11,3 11,4

1,00 1,00

Jan-Dec Jan'12-Dec'12

Munich, Bavaria, 6 residents

549,1 m2 | 0,28 W/(m2K) | 62,0 m2 (44°) | 14,9 m3 Firewood gasification boiler (manual); heat-recovery

1.187 1.328

8,9 35,9 7,3 15,5

12,5 5,7

0,60 0,79

5. Outlook

During the course of the current project further detailed investigations will be performed in order to complete the data acquisition. Special attention will be paid to the identification of optimization potential. The bases for the optimization process are detailed dynamic simulation models, which will be established and calibrated using the collected data.

Another work package deals with a method for the comparison of the SAH-concept with other low CO2-emission heat supply concepts.

The further development of the project "HeizSolar" can be followed on: www.diesolarheizung.info. Acknowledgements

The project "HeizSolar" is funded by the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (Bundesministerium für Umwelt, Naturschutz und Reaktorsicherheit BMU). The authors are thankful for the support and take full responsibility for the content of this publication.

References

[1] Oliva, A. et. Al., solar-active-house - research on a promising technology, 5th European solar thermal energy conference ESTEC, Marseille, 2011

[2] Oliva, A. et al., Messdatenbasierte Modellbildung für typische SolarAktivHäuser, 23. OTTI Symposium Thermische Solarenergie, Bad Staffelstein, Ostbayerisches Technologie-Transfer-Institut e. V. (OTTI), ISBN 978-3-943891-10-2, Regensburg, 2013, p. 262

[3] Kobelt, S. et al., Messtechnische Analyse von neun SolarAktivHäusern, 23. OTTI Symposium Thermische Solarenergie, Bad Staffelstein, Ostbayerisches Technologie-Transfer-Institut e. V. (OTTI), ISBN 978-3-943891-10-2, Regensburg, 2013, p. 256

[4] DIN Deutsches Institut für Normung e.V.: DIN V 4108-6:2003-06, Wärmeschutz und Energie-Einsparung in Gebäuden, Teil 6: Berechnung des Jahresheizwärme- und des Jahresheizenergiebedarfs. Beuth Verlag GmbH, Berlin, 2003.

[5] EnEV 2009 - Energieeinsparverordnung für Gebäude, Verordnung über energiesparenden Wärmeschutz und energiesparende Anlagentechnik bei Gebäuden (Energieeinsparverordnung - EnEV 2009), http://www.enev-online.org/enev_2009_volltext/index.htm