Originally from Mexico, Olivia Guerra-Santin received a degree in Architecture from the UAEMex and a MSc in Urban Environmental Management from Wageningen University. In 2010, she obtained her PhD at the OTB Institute for Housing and Mobility Studies at TU Delft. Since then, Guerra-Santin worked as research associate at the Welsh School of Architecture in Cardiff University, and as postdoc researcher at the Faculty of Industrial Design of TU Delft and The Hague University of Applied Sciences. From 2016 to 2018, Guerra-Santin worked as consultant and project manager of H2020 projects on smart cities. She was appointed assistant professor in the Department of the Built Environment at Eindhoven University of Technology (TU/e) in 2019. 

With her research, Guerra-Santin aims to design and evaluate energy-efficient and healthy environments. Her expertise involves user-centred and data-driven research methods, building monitoring and performance evaluation, and the use of Living Labs for socio-technical research. Guerra-Santin’s topics of interest include building management and control, occupant behaviour, and building performance.

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BUILD UP (BUP): Can you define building performance assessment, and describe what the benefits are?

OLIVIA GUERRA-SANTIN (OG-S): Building performance assessment could be defined as the process followed to determine whether a building has reached the energy targets anticipated during the planning and design phases. This process can start from the design stage of the building, although it is often focused on the pre- and post-occupancy phases. 

Post-Occupancy Evaluation (POE) consists of several activities carried out after the delivery of the building. These can include building monitoring (with environmental sensors and energy meters), energy audits, and thermal comfort and satisfaction assessment through the use of diverse quantitative and qualitative methods. Occupants' behaviour itself (how people interact with the building and building systems) can also be the focus of the POE. POE is necessary because the actual performance of the building can only be measured after the occupants have moved in. Energy performance assessment can be carried out before occupancy, but it then focuses only on the efficiency of the installations and the performance of the building envelope, not on energy consumption. There are many methods to assess performance before occupancy (also used during construction such as air permeability tests, tracer gas tests, co-heating tests, etc.) that can tell a lot about how the individual elements of the building perform (including the building envelope) but cannot tell us how much energy will be used since energy consumption also depends on occupants typologies, intensity of use of the systems, the needs and preferences and behaviour of the occupants and the effectiveness of the building management. In my opinion, building performance assessment must include some type of POE.

In general, the benefits of the energy performance assessment can be seen in the increased energy efficiency of buildings, higher levels of comfort for the occupants, lower energy costs, and increased trust in low-carbon technologies. However, the specific benefits are varied and depend on the party carrying out the evaluation. The assessment results can be used to 1) improve the building’ performance either through fine-tuning of the installations, or through feedback to occupants and building managers; 2) to verify the building’s performance for compliance, performance contracts or certifications (usually intended to brand buildings as ‘green’); and 3) to learn from the process to improve future projects.

“The specific benefits of the energy performance assessment are varied and depend on the party carrying out the evaluation”

It is important to make a distinction between the theoretical and actual performance of buildings. Theoretical performance (obtained from EPCs, labels, most commercial certifications) are based on design values, intentions, and assumptions regarding building occupancy. Theoretical performance should only be taken as the baseline to assess performance. This is against what we compare the actual (measured, monitored) performance. However, a difference between the theoretical and actual performance does not always indicate that there is a fault either with the building envelope and systems or with the occupant's behaviour. There can often be performance gaps that have been created by the (wrong) assumptions made about the use of the building. This is why, next to POE, it is good practice to also do a design review, but these are not normally carried out. 

BUP: To what extent is building performance assessment used in the building sector? Can it be implemented in all types of buildings? If so, what are the different goals?

OG-S: Building performance assessment can take various forms in the building sector. Performance assessments (either focused only on energy or also on other performance aspects, such as indoor environment and comfort) can be carried out in some parts of the building, during a specific phase (e.g., commissioning), and with a specific goal. These are still dependent on the specific building regulations and policies in the country, although there are currently efforts to homogenise performance assessment tools and certifications. For example, in the UK an air permeability test (before occupancy) is required in new buildings, while in the Netherlands energy monitoring (after occupancy) is required to prove the energy neutrality of (rental) zero-energy dwellings. The performance assessment is often used to support or to comply with a specific regulation. However, performance assessments for the most part, are still mostly based on theoretical or simulated performance, and more often than not, they only focus on energy performance. Furthermore, most aspects of building performance assessment are still only carried on a theoretical level, for example energy labels and EPCs (Energy Performance Certificates) are often based on building simulations or other types of calculations that rely on assumptions or design values. Nevertheless, these are still considered important aspects of building performance assessment. 

Performance assessment can in theory be carried out in all types of buildings. The regulations and compliance dictate the differences in what is actually monitored in practice. Building regulations and performance certificates already include renovated buildings. These regulations and certificates are also different for domestic and non-domestic buildings. For example, all new domestic buildings require an EPC, while energy labels for existing buildings are necessary when the property changes ownership. Although energy labels are intended to inform the buyer about the energy efficiency of their future home, they are used more for compliance (to sell the house) rather than to give useful information to the buyer. For non-domestic buildings it is quite a different story, especially for rental properties, since (commercial) energy certifications can be very useful for the potential tenant to estimate their future energy bills and employees’ comfort, apart from giving extra ‘green points’ to both the renting company and the building owner. 

 “Although energy labels are intended to inform the buyer about the energy efficiency of their future home, they are used more for compliance (to sell the house) rather than to give useful information to the buyer”

This situation is probably related to the fact that in non-domestic buildings, other factors such as branding and energy costs are important for the owners, but also because of the presence of a facilities manager in the building, which offers the possibility to use the information provided by the assessment to improve the performance of the building.

BUP: What is the link between building performance assessment and the energy performance of buildings?

OG-S: The energy performance of a building is an important part of the building performance assessment. However, building performance in practice is often only focused on energy performance assessment. This is for several reasons. Firstly, energy performance can be directly reflected in costs. Secondly, because EPC’s and commercial certificates often have a very strong focus on energy performance. A third reason is because it is relatively easy to estimate the energy performance (i.e., based on energy consumption) than indoor environmental performance. The wide availability of energy smart-metering has made this possible. Although some building systems already include the monitoring of some indoor parameters for their control (e.g., temperature, CO2 concentration, etc.), data collection and management is still intrusive and involves privacy issues.

BUP: Can you describe what the role of occupant behaviour is on building design and energy performance of buildings, and give some examples of different types of behaviour (and their impact on building performance)? 

OG-S: There are two main interrelated reasons why occupants' behaviour plays an important role in the design and performance of buildings. Energy consumption not only depends on how efficient installations are, or how airtight the building envelope is. Occupant-related activities and choices such as temperature settings, natural ventilation patterns (opening windows) use of appliances and even occupancy itself (how many people are in the buildings and when) all have an effect on energy demand. They affect indoor environment parameters (CO2 levels, RH, temperature), and increasing the intensity of use of the installations. These behaviours have been until recently only considered during the design phase of buildings through assumptions (e.g., in building simulations or EPCs), for example by defining a standard or average temperature setting, air changes per hour, litres of hot water use, etc. These assumptions are often far from reality as they do not consider the wide variety of needs and preference of building occupants and are very often not explicit in the design process. This last aspect is particularly important in energy performance assessment, if we do not know what assumptions regarding the users were made, it is difficult to determine how good or bad the performance of the building is when we compare the actual energy consumption with the design values. 

For example, in domestic buildings, we see differences in energy consumption and indoor environmental quality because of the differences in occupants’ behaviour. In one home, occupants might have the thermostat setting on 21 degrees, and might have the habit of ventilating the rooms daily (through opening windows), even in the winter for a few hours and they might also sleep with a window open. Another household in the same building could prefer to keep the thermostat on 24 degrees and keep all but one window closed, or only ventilate through windows in the summer. These behaviours, we find, come from the needs and preferences of the users, such as age, health condition, daily activities and even country of origin. Some behaviour can change over time, but other will not. If the buildings’ design does not allow the occupants to accommodate their indoor environment to their needs and preferences, they become dissatisfied and might try to restore their comfort by other means (e.g., getting an extra heating source, unplugging the ventilation system, etc), which might also have consequences both for energy efficiency and for the indoor environment. 

 “If we do not know what assumptions regarding the users were made, it is difficult to determine how good or bad the performance of the building is when we compare the actual energy consumption with the design values”

This point has become clear in recent years in building performance assessment, but there is still a long way to go in the consideration of occupants in the design of buildings, so-called user-centric design.

BUP: How can the subjective aspects of evaluating buildings´ occupants be overcome? 

OG-S: In my opinion we should not try to overcome these subjective aspects, but to work with them. Subjective aspects of building performance would be those ‘needs and preferences’ mentioned before. Indeed, these might be subjective and depend on the specific building user, but that does not make them wrong or irrelevant. 
We see now that user-centric design has become more important in the building industry and within building research. However, at the same time we often hear from researchers and practitioners trying to reduce the influence of people in the buildings by reducing their means for control. 

We often see reduced control in office buildings, of course in this case, the interaction of many different people within the system makes it sometimes the only possible solution. However, this lack of control (e.g., windows that cannot be opened, automatically controlled blinds, centrally controlled thermostats) can also increase the percentage of people dissatisfied with their environment. In domestic buildings, these trends for less user control are seen in very low energy projects, in which the range of temperature settings in the thermostat (due to a low-temperature system) and the number of windows that can be opened (because of the presence of an efficient ventilation system) are limited. What we see in homes, even in rental ones, is that people make modifications to the systems to take control back, which as mentioned before, could potentially increase energy consumption (and costs) and decrease indoor quality.

Considering the subjective aspects is important during the design of buildings. What is also important is to be realistic on occupant-related design parameters so that when we assess the performance of buildings, we can avoid the ‘performance gap’ created by these unrealistic expectations. 

BUP: Could you highlight a specific example of evaluating occupants´ behaviour in residential buildings? What are the lessons learned?

OG-S: Within a project on the renovation of the building stock in the Netherlands, we monitored a number of renovated flats in the rental sector. In this project we wanted to know more about the causes of occupants’ behaviour and how it affects building performance. What we saw is that people struggle with the use of new home systems (e.g., heat recovery ventilation and low-temperature heating). The struggles are related to the lack of feedback from the systems to the people (e.g., they do not know if fresh air is coming in, or if the heating is working), and also to the lack of information and understanding of how the systems work.

We also found that within the building, people had very different preferences in relation to temperature and fresh air; some occupants preferred a relatively low temperature in their homes (especially in the bedrooms), while others were barely warm on the highest possible setting and thus relied on extra heaters. In the same way, some occupants kept the windows constantly open, especially in the bedroom, throughout the year, while others kept the windows mostly shut. We also saw a lack of trust in the mechanical ventilation system. Most residents kept the system in the lowest setting, which is only advised in the absence of people. 

In this case, we could say that some behaviours were wrong, and we aim to change them. However, by investigating further, we saw that some behaviours came from real needs and preferences of people, for example, the residents with the thermostat on the highest setting and extra heater came originally from a warmer country, the resident that kept windows open was allergic to dust, and the resident that kept the ventilation system on the lowest setting did so because of the noise. We can see that you cannot change these behaviours, but that we need to design buildings that allow people to have the indoor environment that is right for them.