GLAZED BALCONIES AND SUN SPACES ENERGY SAVERS OR ENERGY WASTERS? Olaf B. Jørgensen and Ole J. Hendriksen Esbensen Consulting Engineers Ltd., Vesterbrogade 124 B, DK-1620 Copenhagen V, Denmark, Tel.: +45 33 26 73 00, Fax.: +45 33 26 73 01, e-mail: o.b.joergensen@esbensen.dk, o.j.hendriksen@esbensen.dk Abstract This paper analyses different designs of glazed balconies in order to determine if glazed balconies will always offer energy savings or if they might lead to increased energy consumptions. There is a potential risk as glazed balconies are often used in connection to small apartments which might make the tenants heat the balconies. If the balconies are not designed for heating, the energy consumption might increase dramatically in stead of giving energy savings. The analyses are carried out for various glazing types, orientations and patterns of occupancy. The studies indicate that increases of the energy consumption of up to 200% are possible when using improper designs. By using correct solutions, energy savings of up to 28% are possible even when heating the balconies to 20 C throughout the year and up to 40% when the balconies are not heated. Based on the analyses, two different principal designs are defined and recommended for future applications. These designs are also demonstrated in three demonstration projects in Denmark and Germany. 1. INTRODUCTION From previous R&D projects concerning glazed balconies and sun spaces it is often recognised that the expected energy savings are not achieved when the tenants have moved in and the buildings are in use. In many cases the energy consumption is actually increased. The reason for this is typically that the glazed rooms have not been designed with sufficient respect to typical variations of use. To ensure that the intended energy savings are obtained, this study has focused on optimising the design of glazed balconies with respect to energy savings and comfort conditions. The designs shall be sturdy against unintended use of glazed balconies. Parts of the research and design development has been included in the work of IEA SHCP Task 20, Subtask B Development of Improved/Advanced Renovation Concepts and Subtask F Improvement of Solar Renovation Concepts. During 1996-1999, numerous studies of different design proposals with glazing and insulating the balconies have been carried out as part of the design optimisation. Besides the facade design, different typical user scenarios have been analysed. The studies have especially focussed on the risk of introducing an increase of the energy demand as the tenants in real use situations might heat the balconies. Focus has also been put on ensuring a comfortable thermal indoor climate. Finally, also combinations with different ventilation systems have been studied The design has been developed in a close collaboration between Esbensen and different architects, facade contractors and housing companies. During the design development valuable advice and recommendations has been given by our colleagues from the IEA SHCP Task 20 and different ongoing EU projects in which we are involved. Important or critical elements have been tested in mockups. full scale prototypes have been used to visualise the design proposals for the clients and the occupants. The different design solutions have been tested/demonstrated in Danish and German demonstration projects, all including 1-2 years of detailed monitoring. 2. APPROACH AND ANALYSIS METHODS The issue of unintended heating of glazed balconies has been raised during the design process of several renovation projects involving glazed balconies. In these design studies different parameter studies were carried out in order to reach energy savings by a proper combinations of glazing areas, glazing types, insulation and air tightness of glazed balconies. During the design process it was clarified, that the expected energy savings of an improper design could turn to an increased energy use if the balconies were heated by the occupants. It was therefore crucial to test each balcony design in order to analyse the sensitivity of heating the balconies. The analysis was done by performing thermal simulations of different designs in combination with different patterns of occupancy. Simulations of heat flows, temperature conditions, etc. for a whole year have been carried out with the thermal simulation program "tsbi3". This program is developed for analysis and design of building elements and system components as well as simulation of the dynamic performance of a building under realistic use and operation. Outdoor climate data from the Danish Test Reference Year, "TRY", have been used for the simulations. Furthermore, successive design reviews and evaluations were carried out to improve the design of glazed balconies. In some cases full scale mock-ups of critical elements were carried out. Finally, intensive monitoring of energy consumption and thermal comfort has been carried out, is ongoing or will take place in three different demonstration buildings.
3. BUILDINGS BEFORE RENOVATION The demonstration buildings are covering a wide range of the renovation potential of North European residential multi storey buildings. The first building (The Yellow House) is a typical multi storey apartment building of 1900. Many of such buildings are currently going through extensive renovation as part of urban renewal activities in Denmark. The second building (Østerbo) is a typical Danish brick work building of the 50 s, with existing open balconies. The third building (Engelsby) of 1966 represents a type of buildings (tower blocks) which have been constructed in a very high number in many European countries. These tower blocks are often equipped with open balconies. 3.1 The Yellow House, Aalborg, Denmark The aim of this project has been to demonstrate an innovative energy conscious solar based building renovation which shall reduce the energy demand for space heating, ventilation, hot water and electricity by up to 60%. Various types of solar energy utilisation are exploited to achieve a major reduction of the energy demand. The project has served as the Danish demonstration project in the IEA SH&CP Task 20: Solar Energy in Building Renovation. The Yellow House is located in Aalborg and was built in 1900. It is four stories high and consists of 8 apartments. The orientation of the building facades is South-North. The South facade faces a backyard. The North facade faces a street. The heat transfer coefficients of the main construction elements before renovation are shown in table 1. The architects of the building renovation were Jacob Blegvad Architects. The energy design was developed by Esbensen Consulting Engineers Ltd. Figure 2 The Yellow House seen from the backyard before renovation. Aalborg, Denmark. 3.2 Østerbo, Vejle, Denmark This project will demonstrate an exemplar European energy conscious building renovation. The project focuses on the implementation of the latest and most promising solar techniques developed in several ongoing international research projects, in which the design team is already involved. Energy savings of 50% are expected. The key objectives of the project are: - A new flexible facade concept - Substantial energy savings - Innovative passive and active solar energy components - Integrated energy design The project has received support from the EU THERMIE program, project FLEXREN. The buildings are constructed in the early 1950 s and consist of 104 apartments with a total area of 7700 m 2. The buildings are situated in an open area. The exterior walls are massive brick walls or non insulated cavity brick walls. The heat transfer coefficients of the main construction elements are shown in table 1. The architects of the building renovation were Plan 1 Architects. The energy design was developed by Esbensen Consulting Engineers Ltd. Figure 1 The Yellow House seen from the street before renovation. Aalborg, Denmark. Figure 3 Typical block of Østerbo before renovation. Vejle, Denmark.
3.3 Engelsby, Flensburg, Germany The buildings are of a size and form which is typical for a lot of housing areas from the 60'es and 70'es. A special problem for these kind of areas is their image. The buildings are in great need of renovation due to a high energy demand for space heating as well as a very poor indoor climate (Sick Building Syndrome) which makes the apartments less attractive for the rental market. Thus, the building owner (the housing company BIG Heimbau AG), the Municipality of Flensburg and the local government of Schleswig-Holstein decided to help to try to improve the local area. The buildings are constructed in 1966. External walls consist of 24 cm sand-lime brick with an exterior facade cladding of eternite plates and an internal surface of gypsum boards. Only the two lower floors of the buildings are insulated (50 mm). This insulation however, has collapsed. The heat transfer coefficients of the main construction elements are shown in table 1. An important element in the design process has been to work with the different innovative technical measures at a very early stage of the planning process to make these elements fully integrated in the final building design. Energy savings of up to 60% are expected. The project has received support from the EU THERMIE program as part of the SHINE project The architects of the building renovation were Stærmose & Isager Architects. The energy design was developed by Esbensen Consulting Engineers Ltd. U-values W/m 2 K 3.1 The Yellow House 3.2 Østerbo 3.3 Engelsby External walls 1.45 1.00 1.35 Internal walls 1.70 2.00 2.00 Ceiling 0.76 0.30 0.60 Floor 0.76 0.35 2.6 Windows 6.0 3.0 3.0 Table 1 U-values of the main construction elements of the three demonstration buildings before renovation. 4. DESIGN SCENARIOS In order to optimise the design of the glazed balconies, the influence of numerous single parameters have been studied. The most important/influential of these parameters proved to be 1) Glazing types and sizes, 2) Orientation and 3) Use of balcony : 4.1 Glazing types and sizes Four glazing types were modelled. U-value, light transmittance, and g-value are shown in brackets: Single glazing, no frames and sealing (6.0, 0.91, 0.87) Single glazing, standard framing (6.0, 0.91, 0.87) Double glazing, standard framing (2.9, 0.82, 0.76) Low-e glazing (1.1, 0.79, 0.59) 4.2 Orientation Three orientations and balcony types were modelled: East, inside the facade South, inside and outside the facade West, outside the facade Figure 4 Photo of one of the Engelsby tower blocks before renovation. Flensburg, Germany. Figure 5 Floor plan Engelsby. 4.3 Use of balcony 11 scenarios of the use of the balconies were modelled: Heating of the balconies 24 hours per day during the heating season No heating of the balconies Heating in weekends (3 variations) Heating on week days (3 variations) Heating all week (3 variations)
Besides these parameters, also the insulation level of the North facing parts, the air change rate and the daylight levels have been analysed. These parameters proved to have less variations with respect to the heating demand and the potential energy savings compared to the above listed parameters and therefore the results from these studies are not included in this paper. 5. RESULTS FROM PARAMETER STUDIES A basic study of the influence of the glazing area on the energy savings was carried out for three different glazing types. In this study, the reference apartment has massive brick walls (U = 1.45 W/m²K) and the windows are single glazed (U = 6.0 W/m²K). The influence on the potential annual energy savings for space heating is shown in figure 6. Figure 6 shows, that the glazing area has only a slight influence on the potential energy savings. With U-values around 1.1W/m²K the savings are almost independent of the glazing area. Annual Savings [kwh/m²] 60 50 40 30 20 10 0 0% 10% 20% 30% 40% 50% 60% 70% 80% Net Glazing Ratio [%] U = 1.1 U = 1.35 U = 1.6 Figure 6 Annual savings in heating demand for three different glazing types and sizes (variation of the net glazing ratio ~ percentage of facade area). Further studies have especially focussed on the risk of introducing an increase of the energy demand as the tenants might heat the balconies. The main results of the studies are shown in table 2, 3 and 4. Besides, the overall thermal comfort conditions have been analysed for the glazed balconies. Selected results are shown in figure 7. Glazing type Unheated balcony Heated balcony [kwh] [kwh/m²] [%] [kwh] [kwh/m²] [%] 1 2497 49 27 10922 192-220 2 2622 52 23 6264 110-83 3 2078 41 39 2446 43 28 4 2360 46 31 3724 65-9 5 2683 53 22 7735 136-126 Table 2 Expected annual energy demands and relative savings for space heating for different types of glazed balconies. Results for an apartment with outside balcony facing west (type 2): 1: All glass with insulation of existing wall between balcony and living room 2: 1 layer of glass, uninsulated parapet 3: Highly insulating glass (U = 1.1 W/m²K), insulated parapet 4: Conventional double glazing, insulated parapet 5: Conventional double glazing, uninsulated parapet Glazing type Unheated balcony Heated balcony [kwh] [kwh/m²] [%] [kwh] [kwh/m²] [%] 1 4668 70 24 8503 118-39 2 4838 73 21 6542 91-7 3 4388 66 28 4675 65 24 4 4566 69 25 5294 73 13 5 4919 74 20 7184 100-18 Table 3 Expected annual energy demands for space heating and relative savings for different types of glazed balconies. Results for an apartment with inside balcony facing south (type 5). Same glazing types as listed in table 2
Heating demand [kwh/year] Apartment South, Outside balcony Single glazing, uninsulated parapet Apartment South, Inside balcony Low-e gas filled double glazing, insulated parapet Before renovation 7592 6114 After renovation Unheated balcony 2759 2451 Heated balcony All heating season 11704 3535 Parts of heating season 9am 6pm 2pm 10pm 6pm 10pm 9am 6pm 2pm 10pm 6pm 10pm Week days 5177 5408 4571 2670 2732 2665 Weekend 3813 3922 3459 2554 2579 2547 All days 6133 6475 5325 2736 2831 2740 Table 4 Expected annual energy demands for space heating before renovation and after renovation for different time schedules, when the two types of balconies (South facing outside and South facing inside ) are heated. Hours > 24 C Hours > 22 C Hours > 20 C Hours > 18 C 1 layer of glass with noninsulated parapet Double glazing with noninsulated parapet Double glazing with insulated parapet Gas filled low-e double glazing with insulated parapet Hours > 15 C Hours < 12 C 0 10 20 30 40 50 60 70 80 Percentage Figure 7 Thermal comfort expressed by the relative period of occupancy exceeding certain operative temperatures and the relative period of occupancy with operative temperatures below 12ºC. From table 2, 3, and 4 it is seen that it is important to design glazed balconies that are sturdy against unintended use such as heating by electrical heaters or similar equipment. The studies have been made for various heating scenarios and the tendency is similar but of course less significant if the balconies are only heated in shorter periods. The parameter studies show, that the largest energy savings for an unheated balcony in all cases are obtained by using low-e and gas-filled double glazings. Hereafter follows conventional double glazing and insulated parapet, then all glass with insulation of existing parapet between balcony and living room, single glazing and insulated parapet and finally conventional double glazing with uninsulated parapet. If the glazed balcony is heated to 20ºC in the heating season, only inside balconies with insulated parapets and either low-e glazing or conventional double glazing will provide savings. All other balcony types will introduce an increase of the heating demand of up to more than 200%. The relatively large glazing areas in glazed balconies can lead to overheating at the balcony or in the adjacent rooms. This can be prevented by excessive venting via openable windows in the balcony. The overheating occurs in short periods during summer as shown in figure 6.
In two demonstration projects (Østerbo and Engelsby) the results from the risk analyses of energy and comfort conditions made the clients decide for the advanced glazed balconies rather than the traditional ones. 6. BUILDINGS AFTER RENOVATION The three demonstration projects in which the optimised glazed balconies are implemented also include a number of other innovative energy elements. These are: 6.1 The Yellow House: Glazed balconies and glazed facades Ventilated solar walls Window integrated Venetian blinds Demand controlled ventilation Roof integrated solar collectors Facade integrated PV panels Figure 9 Vertical cross section of the advanced glazed balcony in The Yellow House. Figure 8 The Yellow House, South facade, after renovation. Aalborg, Denmark. Photo: Jens V. Nielsen. 6.2 Østerbo: Glazed balconies Unventilated solar walls with transparent insulation Ventilated solar walls Preheating of inlet air via radiator Demand controlled ventilation Figure 10 Typical glazed balcony in an outside application. Østerbo, Vejle, DK. Photo: Plan 1 Architects.
6.3 Engelsby: Glazed balconies Ventilated solar walls Solar collectors for DHW Demand controlled ventilation Glazed staircases Apartments for disabled heating the balcony. This risk is avoided when using gas filled low-e double glazings and insulating the parapet of the balcony. From the analysis, two principal designs are recommended: A) For the balconies that are placed inside the facade, the design with energy glazing and insulation of the external parapet is recommended as this design will be very sturdy against unintended use such as heating because of the high insulation level and because heating the balcony will still offer significant energy savings for space heating and ventilation. B) For the balconies that are placed outside the facade, the design with the very open glazing is recommended as this design will also be very sturdy against unintended use as heating of the balcony will be very difficult due to the very open design. Technically, these balconies would also benefit from the highly insulated solution but because of the large glazing areas such a design might be too expensive. Figure 11 Engelsby tower block after renovation. Flensburg, Germany. Photo: Stærmose & Isager Architects. The expected energy demands for space heating before renovation, for a standard renovation and for the actual renovation are shown in table 5 below. Annual energy demand for space heating [kwh/m² per year] The Yellow House Østerbo Engelsby Before ren. 132 118 165 Standard ren. ~ 92 105 - After ren. 53 60 66 Table 5 Expected energy demands for space heating before renovation, for a standard renovation and for the actual renovation for the three demonstration projects. The expected results for The Yellow House and Engelsby have been presented more in detail at previous Eurosun conferences. Besides, the monitored results from The Yellow House and Engelsby are presented in separate papers at the Eurosun 2000 conference. 7. CONCLUSIONS 7.1 Energy From the analyses it is seen that the risk of increasing the energy demand when using poorly insulated glazed balconies is high due to the risk of unintended use such as 7.2 Thermal comfort Regarding the thermal conditions, at the balcony and in the apartments it is expected that the thermal conditions will be very attractive for the recommended design (insulated parapets and highly insulating glazings) as the temperatures in the balcony during the heating season will be very pleasant and that overheating during summer is avoided by opening the balcony. From the reactions from The Yellow House and Engelsby it is known that the tenants are very pleased by the new advanced glazed balconies. 7.3 Daylight As a result of the reduced amount of daylight in the rooms next to the balconies, and especially in the East facing glazed balconies, it is recommended to make a design that will increase the daylight level. In this case the best solution was to actually add a new window in the West facing exterior wall of this room. As the daylight level even before the renovation was quite poor in this room, this was considered a very attractive solution by the building owner as well as the tenants. 7.4 Moisture and relative humidity From the monitored data in The Yellow House and Engelsby it is seen that the relative humidity on the balconies and in the apartments will be decreased significantly. It should however, be noted that these apartments are also provided with a demand controlled moisture regulated exhaust air ventilation system which is of course the main reason for the decreased moisture content of the indoor air. However, the glazed balcony will also lead to an effective drying out of the moisture damaged facades and concrete slabs at the balconies.
7.5 Noise From the demonstration projects no experiences about noise problems have been observed yet. Because of the noise insulation which have been carried out, no noise problems are expected as this part of the design is identical to well known standard designs for avoiding noise from steps. 7.6 Total concept The specific numbers and expected savings in this paper relates specific sites and buildings. However, the tendency of the results from these three very different building types is quite similar. For that reason, the results can be considered to be valid and useful for architect and engineers when designing energy conscious designs for glazed balconies in Denmark and in similar European climates (e.g. b, DE, IRL, NL, S, UK, etc.). Two of these demonstration projects have received solar awards. In 1998, The Yellow House received the Danish Solar Award and in 1999 the Engelsby project was awarded a first price in a mess competition ( Solar 99 ) for exemplar solar energy projects in Germany. The concept development and the implementation, demonstration and evaluation of the concept documents that it is possible to design cost-effective and architecturally attractive advanced glazed balconies for building renovation which provides significant energy savings, increased thermal and visual comfort, improved air quality and an effective protection against degradation of the building envelope. When designed correct glazed balconies will be energy savers and not potential energy wasters! 8. ACKNOWLEDGEMENTS This project has been supported financially by many parties: The EU DG XVII THERMIE Programme, the Local Government of Schleswig-Holstein, the Danish Ministry of Housing and the Danish Ministry of Energy and Environment. Furthermore, valuable advice and guidance has been received from the participants in the IEA SHC Task 20 project as well as the participants in the EU THERMIE SHINE project. REFERENCES Herde A. de, Nihoul A. (1997). Improved Solar Renovation Concepts. Technical Report of STB IEA SHC Task 20 Solar Energy in Building Renovation. Haller A. (1999). Solar Renovation Concepts and Systems. Technical Report of STF IEA SHC Task 20 Solar Energy in Building Renovation. Johnsen K., Grau K. (1994). tsbi3, Users Manual. Danish Building Research Institute. Andersen B. et al (1982) Vejrdata for VVS og Energi. Dansk referenceår TRY. SBI- rapport 135, Statens Byggeforskningsinstitut. English summary. Stærmose & Isager K/S, Birch & Krogboe A/S, Esbensen A/S (2000). Pilotprojekt Flensborg-Engelsby. Projekt 173 By- og Boligministeriet Projekt Renovering Housing Company Østerbo, Esbensen Consulting Engineers Ltd., Fraunhofer Institute for Solar Energy Systems (1998). Flexible Facade System for Energy Conscious Renovation of European houses (FLEXREN). Project proposal and contract No. BU/0204/98/DK/DE. Coordinator Housing Company Østerbo Jaure, S. et al (1996) Solar Housing through Innovation for Natural Environment (SHINE). THERMIE Project proposal and contract No. BU/1051/96. Co-ordinator Serge Jaure, ArchiMEDES, Granges, France Jørgensen O. B. (1996) Integration of solar energy in future renovation of multi storey housing The Yellow House. EuroSun 96, Freiburg, Germany. Jørgensen, O.B., (1998) Solar renovation project Engelsby, EuroSun98, Slovenia. Jørgensen O.B., Nielsen T. L. (2000). Monitored results from The Yellow House. Paper at Eurosun 2000. Jørgensen O.B., Nielsen T. L. (2000). Monitored results from Engelsby. Paper at Eurosun 2000.