Using Thermostats for Indoor Climate Control in Office Buildings: The Effect on Thermal Comfort

Georgios Kontes, Georgios Giannakis, Philip Horn, Simone Steiger, Dimitrios Rovas
2017 Energies  
Thermostats are widely used in temperature regulation of indoor spaces and have a direct impact on energy use and occupant thermal comfort. Existing guidelines make recommendations for properly selecting set points to reduce energy use, but there is little or no information regarding the actual achieved thermal comfort of the occupants. While dry-bulb air temperature measured at the thermostat location is sometimes a good proxy, there is less understanding of whether thermal comfort targets are
more » ... comfort targets are actually met. In this direction, we have defined an experimental simulation protocol involving two office buildings; the buildings have contrasting geometrical and construction characteristics, as well as different building services systems for meeting heating and cooling demands. A parametric analysis is performed for combinations of controlled variables and boundary conditions. In all cases, occupant thermal comfort is estimated using the Fanger index, as defined in ISO 7730. The results of the parametric study suggest that simple bounds on the dry-bulb air temperature are not sufficient to ensure comfort, and in many cases, more detailed considerations taking into account building characteristics, as well as the types of building heating and cooling services are required. The implication is that the calculation or estimation of detailed comfort indices, or even the use of personalised comfort models, is key towards a more human-centric approach to building design and operation. estimating thermal comfort will alter the operational constraints [5,6] and can influence design and operational decisions. Over-relaxing comfort, while positive from an energetic perspective, can lead to dissatisfied users and incur indirect costs related to productivity loss [7, 8] . Estimation of thermal sensation has been the subject of active research for many years, and the knowledge acquired has been incorporated into national and international standards [9] [10] [11] . Research on building energy management systems and model-based control [12] [13] [14] [15] [16] [17] hints at the need for proper comfort estimation; a similar view is shared by the industry [18] . Nevertheless, the use of thermostats for temperature regulation remains the current state of practice in most buildings. The thermostats ensure that temperature is maintained within a band around a target set point (e.g., 22 • C ± 2 • C), with the implicit assumption being that within that range, comfort is guaranteed. In practice, this happens mainly due to increased capital and commissioning costs, since calculating complex thermal sensation indices usually requires the installation of additional sensors. Changing the set point or increasing the dead band can lead to significant energy savings [4, [19] [20] [21] [22] , but i is also evident from field experiments in spaces with dry-bulb temperature control that users tend to act upon the controllable elements of a building-such as windows, blinds, lights and thermostats-in response to their feeling of thermal discomfort, with potentially detrimental effects to energy performance [23] [24] [25] . A significant effort has been undertaken within the IEA-EBC Annex 66 project [26] , towards analysing and modelling occupant behaviour in buildings, as well as quantifying the impact of users' behaviour in actual energy consumption. A review of the findings of Annex 66 can be found in [27] . There, the DNAS (Drivers, Needs, Actions, Systems) framework is presented, capturing four key aspects in the human-building environment interaction:
doi:10.3390/en10091368 fatcat:tseatzivqbd55mwtb5ldyshx2q