Stanley Kurvers, Eric van den Ham and Joe Leyten are affiliated to Delft University of Technology, Faculty of Architecture, The Netherlands. Arjen Raue is affiliated to Utrecht University, The Netherlands. Sarah Juricic is affiliated to Centre d'Etudes Techniques de Lyon, France.
Robust Climate Design Combines Energy
Efficiency with Occupant Health and
Comfort
S.R. Kurvers A.K. Raue E.R. van den Ham
J.L. Leyten S.M.M. Juricic
ABSTRACT
Often, when designing and operating buildings, the goal is to achieve low energy consumption as well as a healthy and comfortable indoor environment. Studies in the US and The Netherlands show a large discrepancy between the predicted and the actual energy consumption of buildings. Some buildings perform better than predicted, while other buildings perform (much) worse. Other studies show that the level of occupant satisfaction is often much lower than was anticipated during the design. It is hypothesised that, in daily practice, certain building typologies are more “robust” in terms of indoor climate design and energy performance. If we could determine the building characteristics that make a building robust, we would be able to use this knowledge for “best practices” during the design.
To test the robustness hypotheses, a preliminary study was carried out using two databases: one Dutch database that consists of predicted and actual energy use, and the European Hope database that consists of health and comfort symptoms. Both databases include building characteristics too. In this study, the buildings were divided into nine typologies. The results show that the buildings with a combination of building characteristics denoted as “climate oriented” had the lowest energy use as well as the lowest Building Symptom Index, whereas the building type “climate ignoring” showed higher risks of high energy use as well as a higher Building Symptom Index.
INTRODUCTION
In an ideal design process, Project Definition includes performance targets for the indoor environment, sustainability and energy consumption of a building. Although code compliance is often accepted for business as usual performance, a variety of guidelines and standards are used to define more outstanding performance. Especially if ‘green’ building certification such as LEED or BREEAM is pursued, the project will explicitly have to comply with more ambitious performance criteria for thermal comfort, indoor air quality, visual and acoustic comfort, energy use, carbon emissions and numerous others.
It should be noted that most green building certifications are based on theoretical performance, as predicted during design stages. This raises the question: how good are our green buildings in practice? Extra money and effort is invested in meeting the often very ambitious performance schemes, so does it work out? Long term overall performance – e.g. 5 or 10 years after project completion – is rarely published. However, some discrete performance aspects have been thoroughly evaluated in scientific publications. This paper discusses the results of some of these and puts them in perspective.
ENERGY PERFORMANCE IN PRACTICE
Some studies compare actual energy performance to predicted performance during design. Figure 1 shows a random test of 73 building in the Netherlands [Van den Ham, 2009]. Results indicate that, although buildings with a lower predicted Energy Performance Coefficient generally perform better, results vary widely, with exceptions up to 2- or 5-fold excess.
Figure 1 Predicted energy consumption (X-axis) in relation to actual energy consumption (Y-axis) [van den Ham, 2004]
In a study from the United States [Turner, 2008] on the effect of LEED certification on energy performance, the predicted energy performance is compared to the actual energy consumption in operation. Here too, modeled energy consumption predicts average energy consumption in operation well, but the actual energy performance of separate buildings varies considerably.
In Figure 2, buildings above the sloped line perform better than predicted. Meanwhile, just as many buildings perform worse, in some cases considerably worse.
There is clearly room for improvement, in the first place for more reliable modeling, but also for better understanding of the mechanisms behind the wide variety in energy performance between actual buildings. It is not unthinkable that some building features and factors that correlate with increased energy consumption may also correlate with reduced occupant satisfaction with the indoor environment.
THERMAL COMFORT IN PRACTICE
Numerous studies have investigated the occupants’ satisfaction with the thermal environment in their building. One such study, of comfort and health of 34,000 occupants in 215 buildings in the United States, Canada and Finland [Huizenga, 2006], shows that 42% of the occupants were dissatisfied with their thermal environment (figure 3) and that a mere 11% of the buildings achieved 80% satisfied occupants, as required in ASHRAE standard 55 (figure 4). Results for perceived dissatisfaction with air quality are comparable: about one third of the population was not satisfied.
Figure 3 Distribution of thermal satisfaction votes of all occupants in 215 buildings. 42% of the occupants are dissatisfied (vote -1, -2 and -3) [Huizenga, 2006].
Figure 4 Distribution of thermal satisfaction score of 215 buildings. Guidelines are based on 80% of occupants satisfied. Only 11% of the buildings in this study achieve this target value [Huizenga, 2006]. The assumption that requiring a narrow temperature bandwidth will result in improved thermal comfort is reflected in international standard ISO 7730 and European standard EN 15251. These standards define three levels of thermal comfort: class I, II and III, where class I has the narrowest acceptable temperature bandwidth. These compare to classes A, B and C in ASHRAE standard 55. It can be expected that energy consumption will increase with a more narrow bandwidth, as more cooling and heating corrections are needed to stay within tighter temperature limits.
Does this extra energy actually result in more comfort? This was studied in [Arens, 2010], where three databases were used: ASHRAE RP884 with 45 office buildings, the SCATS database with 26 office buildings of several types in five European countries, and the Berkeley City Centre (BCC), a modern, naturally ventilated office building in California. Table 1 shows that the three comfort classes were perceived quite similarly by the occupants, despite that observed temperatures were within tighter limits. In general, differences were either nonexistent or not statistically significant. As no other studies were found that prove the opposite, it can be concluded that class A is less desirable than class B as more energy is required and the outcome is not better. As class C is on the edge of 80% acceptance, class B is the most realistic design target.
Table 1. Results from the ASHRAE RP-88 database. Percentage acceptance in practice for the three theoretical indoor climate classes [Arens, 2010].
THE ROBUSTNESS HYPOTHESIS
Consultants explain the discrepancies between predicted and actual energy, health and comfort in several ways. Aberrations may be the result of poor commissioning, changes in building use, undesired occupant interventions, or cost cuts during design or operation. Our own investigations in a large number of buildings showed that certain building types tend to have a higher and less predictable energy consumption than others. There are indictors that lately, in certain types of buildings with a high environmental ambition, where energy reduction is paramount, a high tech approach based on mechanical services is preferred over a low tech approach based on architectural means. These high tech concepts seem to ignore external conditions, e.g. by implementing fully glazed facades and low thermal mass. Meanwhile, other parts of the design seem to ignore the individual occupant, for instance by providing large open work areas and no operable windows.
In [Leyten, 2006,], the hypothesis is raised that buildings with certain feature sets are more likely to meet the desired energy and comfort levels than others. These successful buildings are characterized as more ‘robust’. The level of ‘robustness’ is the result of numerous design and maintenance factors. Some examples of robustness affecting factors are:
Lack of individual control. Lack of occupant control over the indoor environment decreases robustness and increases the probability that the actual situation differs from the desired situation. Examples are:
- Occupants experience a lack of means to adjust the indoor climate to their comfort temperature and to variations over time of their desired temperature.
- Occupants experience a lack of means to compensate for uncomfortable temperatures as a result of control system errors.
Occupant considerations and tradeoffs. Effective influence of occupants on their indoor climate helps them compensate for poor conditions, especially if the occupants are offered means to trade off positive and negative effects of their interventions [Leyten, 2006]. E.g. increased air velocity as a result of open windows or ceiling fans can be experienced as draught, but also as a nice breeze on a warm day. Open windows can cause extra noise, meanwhile they can be a very effective means to obtain thermal comfort and air quality. Occupants have their own considerations and can manage these tradeoffs by themselves, e.g. by opening windows only when they go out for lunch.
Active versus passive design. Buildings with mechanical cooling are more sensitive to unexpected energy consumption patterns [van den Ham, 2009] and discomfort [Leyten, 2006].
Sensitivity to deviations from design assumptions. Some complex technical services are sensitive to, sometimes small, deviations from design assumptions. For example: in induction units, it is important that features including capacity, air velocity, temperature, nozzle shape and inlet are carefully selected in accordance with size and shape of a room, window positioning, heat sources et cetera. Apparently small changes during construction or operation can result in considerably different air flow patterns, therefore discomfort.
Maintenance requirements. Some designs require more maintenance than others. In practice, diligence tends to decrease during a building’s life cycle, as intensive maintenance is a popular target for budget cuts. These cost reductions often seem harmless as negative effects only become apparent over time.
Combined heating and ventilation. If ventilation and heating are one system, technical failures have double effect. E.g. in an all air system, a broken fan belt will result in poor air quality as well as in thermal discomfort. Buildings with separate ventilation and heating systems are less sensitive to this effect [Leyten, 2006].
Lack of transparency to occupants. It should be clear to occupants what will happen if they operate thermostats and other controls. Therefore, controls must be intuitive and easy to operate.
Lack of transparency to service staff. Some building have such complicated systems that service engineers have trouble finding out how they are intended to operate. This often results in shortcuts and workarounds, not using a system’s full potential to deliver comfort and efficiency.
PRELIMINARY TESTING OF THE ROBUSTNESS HYPOTHESIS
As mentioned, the robustness hypothesis is based on decades of experience in numerous buildings. To be able to test the hypothesis, extensive research in a large number of buildings is required, using a well-defined protocol. Until such a project can be carried out, some insights can be derived from a preliminary study using two existing databases [van den Ham, 2009 and Bluyssen, 2011].
The Climatic Design Consult (CDC) database was used to study how certain building features relate to predicted and actual energy consumption. The European Hope database was used to study relations between building features and health and comfort [Bluyssen, 2011]. The databases include technical features of the buildings, such as mechanical services and façade setup. Based on these features, nine typologies or ‘design profiles’ were defined. Criteria for these typologies included special attention for energy efficiency in design or operation, occupant control options and whether climatic and meteorological circumstances were considered in the design. Table 3 shows the nine typologies.
The main objective of the preliminary study was to reveal how (combinations of) building features relate to energy consumption and perceived health and comfort. Figure 5 shows the actual energy consumption in relation to the chosen typologies. The table indicates that typology 5 (‘Climate Oriented’, e.g. natural ventilation, operable windows and extensive use of thermal mass) consumes, in practice, less energy than typology 4 (‘Climate Ignoring’, i.e. mechanical ventilation, active cooling, little use of thermal mass) and typology 6 (‘Climate Ignoring’ / ‘User Oriented’).
Table 2. Building typologies (design profiles) based on energy, occupant and indoor climate features [Juricic, 2012].
Figure 6 shows that also the difference between calculated and actual energy consumption strongly depends on the chosen typology, and that typology 5 (‘Climate Oriented’) results in a more predictable energy use than the other typologies.
Figure 6 Energy use deviation of the distinct design profiles [Juricic, 2012].
Figure 7 shows the relation between the typologies and Building Symptom Index (BSI). The BSI is the average number of building related health symptoms per building. In this case, BSI5 is used: the five most typical building related symptoms. Therefore, the BSI5 value ranges from 0 to 5. In figure 7, ‘climate ignoring’ typologies 4, 6 and 9 have the highest BSI scores, whereas ‘climate oriented’ typologies 5 and 7 have the lowest BSI, so the lowest prevalence of the five most typical symptoms.
An interesting result is that, when figures 5, 6 and 7 are compared, typologies 4 and 6 have poor scores for energy as well as health, and typology 5 performs well on both energy and health. This indicates that low energy consumption and high occupant satisfaction with the indoor environment can go well together, as a result of a right set of design decisions, so in a robust climate design!
CONCLUSIONS
Energy consumption and comfort in buildings in operation is often different from design intentions and predictions. Some building typologies tend to behave like predicted, whereas other typologies tend to diverge significantly. It is proposed that this difference in predictability is, at least partially, caused by a difference in robustness of the building typology. This robustness hypothesis has not yet been tested in full, however a preliminary study, where a limited number of buildings were classified in nine typologies, shows different outcomes for (predictability of) energy and indoor environmental performance. Moreover, this preliminary study indicates that in some typologies, good energy and good indoor environment performance can go well together.
These are encouraging results that justify further research. As this preliminary research was based on two databases, one for energy and one for occupant satisfaction, it is even more important that further research is carried out in a group of buildings where energy and occupant perception are monitored in the same building and at the same time.
REFERENCES
1. Ham, E.R. van den, Nobel, K.C.J., Schatgraven in de bestaande gebouwenvoorraad, Pilot kantoren en scholen, Climatic Design Consult 1002.32, 26 October 2009, (Novem report).
2. Turner, C., Frankel, M., Energy Performance of LEED® for New Construction Buildings, NBI-report for the US
Green Building Council, 2008.
3. Huizenga, C., Abbaszadeh, S., Zagreus, L., Arens, E.A., Air Quality and Thermal Comfort in Office Buildings: Results of a Large Indoor Environmental Quality Survey, Proceedings of Healthy Buildings 2006, Lisbon, Vol. III, 393-397.
4. Arens, et. al., “Are ‘class A’ temperature requirements realistic or desirable?”, Building and Environment, No 45 (2010), pp. 4-10.
5. Leyten J.L., Kurvers, S.R., Robustness of buildings and HVAC systems as a hypothetical construct explaining differences in building related health and comfort symptoms and complaint rates, Energy and Buildings, June 2006.
6. Bluyssen, Aries and van Dommelen, Comfort of workers in office building projects: the European, HOPE project, 2011, Building and Environment, vol 46 issue 1.
7. Juricic, S.M.M. , Van den Ham E.R, Kurvers, S.R., Robustness of a building - Relationship between building characteristics and energy use and health and comfort perception, Proceedings of 7th Windsor Conference: The changing context of comfort in an unpredictable world Cumberland Lodge, Windsor, UK, 12-15 April 2012.
