Occupant-responsive integrated ventilation and heating solutions with excellent comfort for new and renovated dwellings

Improving the energy efficiency of buildings is a necessary step towards a low-carbon society. In the Danish residential sector, increasingly ambitious building standards are leading to the spread of new and retrofitted dwellings built on the same model: heavy facades with high levels of insulation, hydronic underfloor heating embedded in a concrete slab, and mechanical ventilation with heat recovery, often partly or fully automated.

This model is becoming standard practice in most new development projects; however, little is known about the way occupants experience and use such dwellings – and in particular the new technical installations. Research works in several countries have demonstrated that low-energy dwellings consume on average more energy than predicted.

Moreover, post-occupancy evaluations highlighted a number of issues related to the technical installations in such dwellings with negative consequences on occupant satisfaction. The first objective of this project was to understand the advantages and shortcomings of heating and mechanical ventilation systems in low-energy homes, seen from the point of view of occupants.

To do so, occupant comfort and satisfaction in dwellings were approached with an interdisciplinary toolset. A field study consisting of a survey and semi-structured interviews permitted to gather insights on occupants’ preferences, opinions and behaviours. The interviews were carried out in collaboration with social scientists.

The second objective was to contribute to the development of solutions to the issues highlighted in the field study. This was first done by identifying some personal and contextual factors that impacted occupant satisfaction and should be taken into consideration in building design and operation. Finally, a data-driven tool to automatically detect faults and inefficiencies on heating installations was built and demonstrated on a test apartment.

The field study revealed that, while indoor environmental quality was overall considered satisfactory, the technical installations could become a source of dissatisfaction for occupants. They were overall perceived as complex and opaque, as occupants lacked technical information and guidance to understand and operate them.

Moreover, in all investigated dwelling types, both new and retrofitted, the technical installations suffered from malfunctions when occupants moved in, which affected comfort and in some cases energy use, and which were difficult for occupants to diagnose. When no manual control options were available, some occupants found workarounds and alternative control strategies, for example by fully disconnecting ventilation systems.

When examining occupant interaction with technical installations in case studies in different building types and locations around the world, a number of non-physical factors showed an influence on occupant satisfaction with these installations. Occupants’ understanding of the technology and their perceived control over the indoor environment were key to their acceptance of technical installations, which in turn influenced the proper operation of these systems.

Occupants’ perception of indoor environment quality in homes was correlated to their perception of the usability of technical installations. When focusing on occupants’ acceptance of remote thermostat control for demand response, previous thermostat use habits were found to be the main factor impacting the success of such strategies, before thermal discomfort.

These factors – occupants’ technical knowledge, perceived control, interface usability and previous habits – influence the performance of technical installations in buildings but are rarely considered when designing these systems and their control logic. Finally, it was demonstrated that data that is already being collected in many buildings could be used to detect faulty or inefficient heating operation.

By simply collecting indoor air temperature and heating setpoint data, one could distinguish several ways in which occupants used underfloor heating and identify households who had difficulties operating it. By complementing this dataset with data from the heat meter and the circulation pump, a grey-box model of the heating installation was built, which permitted to detect excessive water temperatures and flowrates in the underfloor heating loops and to suggest operational improvement scenarios.

More work is needed to improve the reliability of this method, but it has potential to be integrated into a fault detection tool to assist occupants or operators in improving the operational efficiency of residential heating systems. Summing up, technical installations in low-energy dwellings can become a source of dissatisfaction for occupants, because they suffer from faults that are not systematically corrected before move-in, and because their complexity and opacity makes it difficult for occupants to operate them and diagnose issues.

These shortcomings could be solved with (1) an increased effort on user-friendliness, communication and technical guidance around these systems and their control logic, (2) more systematic commissioning and post-occupancy evaluations, and (3) an increased use of data collected in dwellings to automatically detect faults and inefficiencies and inform building occupants and operators.