thermal performance and sustainability assessment of a health … · 2006-10-26 · thermal...
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Thermal Performance and Sustainability Assessment of a Health Building in a Maritime Climate – A Case Study in Sheffield, UK Dr. Haşim ALTAN, the University of Sheffield, School of Architecture, Building Energy Analysis Unit, the Arts Tower, Western Bank, Sheffield S10 2TN, United Kingdom Tel: +44 114 222 0375 / Fax: +44 114 279 8276 / E-mail: [email protected] Abstract Sustainability has acquired great importance due to the negative impact of various developments on the environment. Sustainable building is now a global issue and its life cycle influences the life cycles of the planet drastically. As a result, it is important to say that, in order to achieve better building performance and sustainability that could also help to reduce pollutions and improve the environment, sustainable building design and development is vital. This paper demonstrates how building monitoring and simulation analyses could be used in a rational and innovative way for better building performance and sustainability, and provides a case study that investigates the potential overheating periods and explores the possibility of minimising its impact by the control of daylighting and window shading. Keywords: Thermal Comfort, Building Performance, Sustainability, Building Simulation Analysis, Case Study Introduction Sustainability has acquired great importance due to the negative impact of various developments on the environment. Sustainable building is now a global issue and its life cycle influences the life cycles of the planet drastically. This being said, it is vital that sustainable building design and development is in the agenda for working towards better building performance and sustainability in the built environment and therefore help contribute to reducing pollutions and improving the environment.
Figure 1: Student Health Building and Simulation Model.
The University of Sheffield’s new Student Health Centre, which was completed in September 2004, has won two prizes at the annual Royal Institute of British Architects’ (RIBA) Yorkshire Awards 2005. This building was specially designed to be naturally ventilated and lit. Despite the fact that the building has a high-quality design and incorporated the use of environmentally friendly measures, there has been a number of complains from occupants about higher room temperatures, which relates to the cause of thermal discomfort. The quality of daylight is very important and the optimisation of window shading is equally necessary while maintaining thermal comfort within buildings. The following studies carried out for better building performance and sustainability, such as analyses involving building monitoring of internal conditions in specific rooms and examining overheating periods during summer season. Building Monitoring Post-occupancy monitoring has been undertaken to investigate the internal conditions in specific rooms and measuring overheating periods in the Student Health Building. The following floor plans are to give an idea about which rooms the temperatures were monitored with an indication to sensors’/loggers’ location and the building’s orientation (see figure 2).
Figure 2: Floor Plans and Rooms Monitored.
- Rooms monitored: Consulting Room Reception Staff Room Practice Manager
The following tables (see tables 1-4) consist of the data measured over a four weeks period at 20 minutes intervals during summer 2005, and the mean internal temperature and relative humidity recorded in six different rooms within this building. Additionally, the following figures (see figures 3-6) show the overall change recorded during these weeks on charts.
Table 1: Mean Internal Temperature and Relative Humidity Recorded During 14-22 Jul 05. Room Mean Internal Temperature (IT) (°C) Mean Relative Humidity (RH) (%)
C18 26.47 35.47C20 24.58 42.29C10 26.19 35.34C08 22.97 43.97
Reception 25.03 41.2B03 25.66 43.61
Figure 3: Mean Internal Temperature and Relative Humidity Recorded During 14-22 Jul 05.
0 10 20 30 40
C18
C20
C10
C08
Reception
B03
°C / %
50
Mean IT (°C) Mean RH (%)
Table 2: Mean Internal Temperature and Relative Humidity Recorded During 25 Jul-2 Aug 05.
Room Mean Internal Temperature (IT) (°C) Mean Relative Humidity (RH) (%)C18 21.87 44.23C20 21.53 52.95C10 23.59 41.31C08 20.2 52.89
Reception 22.97 46.55B03 23.42 48.01
Figure 4: Mean Internal Temperature and Relative Humidity Recorded During 25 Jul-2 Aug 05.
0 10 20 30 40 50 60
C18
C20
C10
C08
Reception
B03
°C / %
Mean IT (°C) Mean RH (%)
Table 3: Mean Internal Temperature and Relative Humidity Recorded During 9-17 Aug 05. Room Mean Internal Temperature (IT) (°C) Mean Relative Humidity (RH) (%)
C18 23.98 42.34C20 22.83 50.08C10 23.7 43.88C08 22.39 49.56
Reception 23.62 47.03B03 23.98 48.19
Figure 5: Mean Internal Temperature and Relative Humidity Recorded During 9-17 Aug 05.
0 10 20 30 40 50 60
C18
C20
C10
C08
Reception
B03
°C / %
Mean IT (°C) Mean RH (%)
Table 4: Mean Internal Temperature and Relative Humidity Recorded During 17-24 Aug 05.
Room Mean Internal Temperature (IT) Mean Relative Humidity (RH) (%)C18 26.42 36.47C20 24.38 45.35C10 25.55 37.98C08 23.01 47.41
Reception 24.52 42.82B03 24.61 47
Figure 6: Mean Internal Temperature and Relative Humidity Recorded During 17-24 Aug 05.
0 10 20 30 40 5
C18
C20
C10
C08
Reception
B03
°C / %
0
Mean IT (°C) Mean RH (%)
The thermal comfort of a human being is dependant on the thermal balance of the body, which is in turn dependant on parameters such as; air temperature, mean radiant temperature, relative air velocity, relative humidity. As regards the Student Heath Building, the following figures (see figures 7-
10) show the overheating periods recorded on a weekly bases in specific rooms during summer 2005. As it can be seen clearly on below graphs; there have been significant overheating periods and therefore the occupants, especially in rooms C18 and C10, have experienced thermal discomfort.
Figure 7: Overheating Periods in Consulting Room C18 During 14-22 Jul 05.
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
14/07/2005 15/07/2005 16/07/2005 17/07/2005 18/07/2005 19/07/2005 20/07/2005 21/07/2005 22/07/2005
°C
Ext Max Internal Temperature Ext Min Comfort Max Comfort Min
- Overheating period.
Figure 8: Overheating Period in Consulting Room C10 During 14-22 Jul 05.
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
14/07/2005 15/07/2005 16/07/2005 17/07/2005 18/07/2005 19/07/2005 20/07/2005 21/07/2005 22/07/2005
°C
Ext Max Internal Temperature Ext Min Comfort Max Comfort Min
Comfort Zone
Comfort Zone
- Overheating period. Please note that the minimum and maximum external temperatures (Ext Min and Ext Max) used on these graphs are obtained from the nearest Met Office available in the area and the internal temperature used is the average for each day recorded by sensors/loggers during summer 2005. In
addition, the ‘Comfort Zone’ is defined according to the CIBSE Concise Handbook’s recommended values for each specific space within this building (i.e. office space, consulting room, etc.).
Figure 9: Overheating Period in Consulting Room C18 During 17-24 Aug 05.
0.0
5.0
10.0
15.0
20.0
25.0
30.0
17/08/2005 18/08/2005 19/08/2005 20/08/2005 21/08/2005 22/08/2005 23/08/2005 24/08/2005
°C
Ext Max Internal Temperature Ext Min Comfort Max Comfort Min
- Overheating period.
Figure 10: Overheating Period in Consulting Room C10 During 17-24 Aug 05.
0.0
5.0
10.0
15.0
20.0
25.0
30.0
17/08/2005 18/08/2005 19/08/2005 20/08/2005 21/08/2005 22/08/2005 23/08/2005 24/08/2005
°C
Ext Max Internal Temperature Ext Min Comfort Max Comfort Min
- Overheating period.
Comfort Zone
Comfort Zone
It is clear that close attention will have to be paid to the way the natural ventilation is provided and the use of daylighting within this building in order to avoid such problems with thermal comfort. The temperature within the building has the greatest influence on thermal comfort. It is important that there
is neither under nor over heating. As a result, heat gains from occupants, computers, lights, etc. need to be calculated carefully as they can provide a considerable heat load, which could again affect thermal comfort. Building Performance and Simulation Analysis The study in this part consist of Thermal and Lighting Analysis, and Design Modifications carried out by computer simulations (using Ecotect and Radiance) to establish the thermal discomfort levels, the quality of natural lighting and the optimisation of window shadings. Furthermore, the results of these computer simulations can be used for comparison with the post-occupancy monitoring findings and would therefore also help to develop certain operating strategies. Thermal Analysis The following analyses are compiled to show the thermal discomfort levels in degree hours provided on yearly bases in specific rooms in this building. In these calculations, both example rooms used (see figure 11 and 12) are neither air-conditioned nor heated, however are occupied, and therefore perform discomfort calculations showing the amount of time the internal temperature of these rooms spend outside the specified comfort conditions for each month.
Figure 11: Annual Thermal Discomfort Period in Degree Hours in Room C18.
Table 5: Thermal Discomfort Period in Room C18. TOO HOT TOO COOL TOTAL MONTH (Hrs) (Hrs) (Hrs) Jan 0 184 184 Feb 0 160 160 Mar 0 176 176 Apr 0 108 108 May 0 143 143 Jun 15 125 140 Jul 48 48 96 Aug 48 48 96 Sep 4 57 61 Oct 0 150 150 Nov 0 176 176 Dec 0 161 161 TOTAL 115 1536 1651 Occupancy: Weekdays 09-17 / Weekends 00-00 (1 Person) Comfort: Adaptive - Free Running (± 1.75) Comfort Band Temperature: 22-26 (°C) Air Change Rates: Air Infiltration: 0.50 / Wind Sensitivity: 0.25
Figure 12: Annual Thermal Discomfort Period in Degree Hours in Room C10.
Table 6: Thermal Discomfort Period in Room C10. TOO HOT TOO COOL TOTAL MONTH (Hrs) (Hrs) (Hrs) Jan 0 184 184 Feb 0 160 160 Mar 0 176 176 Apr 0 109 109 May 0 146 146 Jun 15 128 143 Jul 47 49 96 Aug 48 48 96 Sep 4 58 62 Oct 0 155 155 Nov 0 176 176 Dec 0 162 162 TOTAL 114 1551 1665 Occupancy: Weekdays 09-17 / Weekends 00-00 (2 Person) Comfort: Adaptive - Free Running (± 1.75) Comfort Band Temperature: 22-26 (°C) Air Change Rates: Air Infiltration: 0.50 / Wind Sensitivity: 0.25
In above tables/charts, Degree Hour discomfort values simply weight each hour of discomfort by the number of degrees outside the comfort band. Thus, both charts for these two specific rooms selected as examples, picks a significant thermal discomfort during summer season, which also explains why the monitoring findings for summer 2005 have shown significant overheating periods. As a result, this indicates that there are some weaknesses in both the design strategies as well as operational methods used and therefore, it is again clear that close attention will have to be paid to the alternative strategies for natural ventilation and the control of daylighting and window shading within this building in order to avoid such problems with thermal comfort. Lighting Analysis The quality of daylight is very important and it generally recognised that a Daylight Factor (DF – the relationship between the amount of natural light available at a location within a building compared to the amount available at the same time outside the building) of 2% is appropriate for the room to be perceived as being ‘naturally lit’.
For this part of the study, the simulation studies carried out were aimed at establishing the daylight factors in consulting rooms, as there were certain design issues with the design of windows; both related to the use of daylighting and the privacy within these rooms. The following two consulting rooms are selected as examples. These analyses have been considered under overcast sky conditions, as the daylight factors calculated under these conditions would provide more appropriate values for further evaluation in these rooms (considering the worst case scenario) (see figure 13 and 14).
Figure 13: Daylight Factors in Consulting Room C10:
on the Vertical Surfaces
on the Working Plane
Figure 14: Daylight Factors in Consulting Room C08:
on the Vertical Surfaces
on the Working Plane
This is also further demonstrated in the Radiance simulations shown in figures 15 and 16, see below:
Figure 15: Overcast Sky Conditions Radiance Simulations in Consulting Room C10:
Vertical Section
Horizontal Section
Figure 16: Overcast Sky Conditions Radiance Simulations in Consulting Room C08:
Vertical Section
Horizontal Section
The results have clearly shown that the Daylight Factors (DFs) on the surfaces within these consulting rooms (C10 and C08), are above 2% indicating that the rooms will appear well lit. Although the results have presented sufficient daylighting in these rooms, in practice due to privacy, window blinds are mainly used and therefore artificial lighting is mostly in operation. This collides with the initial design principles (energy efficiency/environmentally friendly measures) and therefore is being compromised in practice, which also explains why Design Modifications are considered in this case study (see the following section).
Design Modifications Covering the lower half of the window area with a non-transparent material (such as painted MDF board) in Consulting Rooms: The Design Modification studies carried out in these consulting rooms by covering the lower half of the window area to find out if the rooms will still be well lit. Although the quality of natural light entered in this specific room (consulting room C10 is used as an example for this paper) was decreased by having a non-transparent cover, this consulting room appeared to be well lit. This is further demonstrated with the Daylight Factors on the working plane within this room, which is still above 2%, indicating that the room will appear well lit. The following figures (see figures 17 and 18) show the overall change; between before and after covering the lower half of the window area, and provides the DFs obtained throughout these analyses.
Figure 17: Daylight Factors in Consulting Room C10 – Before and After Covering Half of the Window Area:
Before
After
This is also verified in the Radiance Simulations as shown below:
Figure 18: Radiance in Consulting Room C10 – Before and After Covering Half of the Window Area:
Before
After
The results of this Design Modification undertaken will support the use of daylighting (one of the initial design principles of energy efficiency/environmentally friendly measures) within the Student Health Building and also provide alternative solution to the privacy issue experienced in these consulting rooms in practice. In this paper, only one alternative design modification is suggested, however there are other solutions that could be also considered which would also be equally feasible in daily practice.
Conclusions This paper has demonstrated evidently the benefits of using such improved strategies in refurbishment stages; however also stressed the importance of using such techniques for sustainable building design and development to forecast the dynamic response and performance of buildings. To make effective use of building simulation, it is vital that designers and developers adopt some common-sense practices, to overcome various problems that can easily be avoided at the early stages of the design, such as those issues experienced in this study. In addition, with both building monitoring surveys and the integration of computer simulations, a better overall understanding of the impacts of overheating periods, thermal comfort levels, adequate daylighting and window shadings on the overall performance can be obtained. This overall understanding has resulted in modifications to the design, which further inputs the building performance. Post-occupancy monitoring has shown that there are significant periods of overheating during summer season, especially in the east-facing rooms. This is also assisted by the building performance and simulation studies undertaken and the results has also presented that there are potential discomfort levels during summer months (June, July and August) in these specific rooms in the Student Health Building. With regards to the design modification studies; it was very important to pay attention to both key factors in order to come up with alternative solutions such as exercised in this study, although other approaches could also be equally applicable (other than covering part of the window with MDF board - some different solar transmittances and solar heat gain coefficients could be explored by adding external shading devices, internal blinds, changing the type of glass, etc.). In this case study, decisions were made by taking into consideration the use of daylighting (for building energy efficiency) as well as the privacy (for patient care) within the consulting rooms. It was suggested that the consulting rooms were simulated with the lower half of the window covered with a non-transparent material. The results have indicated that although the daylight factors would decrease there was sufficient light to still allow the rooms to be adequately day lit, which expresses the whole purpose of this paper how an example of a good practice can be achieved. References Augenbroe, G. and Winkelmann, F., 1991, Integration of Simulation into the Building Design Process, Building Simulation ‘91 Conference, August 20-22, 1991, Sophia-Antipolis, Nice, France, Page(s) 367-374, International Building Performance Simulation Association (IBPSA). Augenbroe, G. 1992, Integrated Building Performance Evaluation in the Early Design Stages, Building & Environment, Volume 27, Number 2, Page(s) 149-61. BRE (Building Research Establishment), 1995, Designing Buildings for Daylight. Professional Studies in British Architectural Practice. BR 288. BRE, UK. British Standards, 1992, BS 8206-2 Lighting for Buildings – Part 2: Code of Practice for Daylighting, BSI, UK. CIBSE (Chartered Institute of Building Services Engineering), 1998, Energy Efficiency in Buildings, CIBSE Publication, UK. CIBSE (Chartered Institute of Building Services Engineering), 1999, Environmental Design: CIBSE Guide A, CIBSE Publication, UK. CIBSE (Chartered Institute of Building Services Engineering), 2001, CIBSE Concise Handbook, CIBSE Publication, UK. Clarke, J. A. and Janak, M., 1998, Simulating the Thermal Effects of Daylight-Controlled Lighting, Building Performance (BEPAC UK), Issue 1, Spring 1998, UK. DETR (Department of the Environment, Transport and the Regions), 2000, Building a Better Quality of Life, The Stationary Office, UK. ECOTEC: http://www.squ1.com/ecotect/ecotect.html RADIANCE: http://radsite.lbl.gov/radiance/home.html THERMIE, 1994, Daylighting in Buildings, PUCD-OPET, UK. Waltz, J. P., et al, 2000, Computerized Building Energy Simulation Handbook, The Fairmont Press, USA.