Adaptive comfort technology for temperature control in balanced ventilation systems

This study describes the implementation of adaptive comfort technology in balanced ventilation units, with and without postconditioning. From monitored projects, examples are given how the indoor temperature setpoint varies in time. Data is given how the bypass and the postconditioning react to changing indoor temperature setpoint, and how they influence the fresh air supply temperature, and ultimately influence the indoor temperature to comfortable levels.

Keywords: Balanced ventilation, smart ventilation, postconditioning, passive cooling, adaptive comfort technology

Introduction

Adaptive comfort is regarded as a way to express the comfort of residents in a building. It reflects the fact that the temperature where people feel comfortable is not fixed during the year, but it changes with the seasonal variation in outdoor temperature.

The adaptive comfort model is mostly used to assess the comfort range of people, given a range of indoor temperatures during the year. Yet, it is rarely used to set temperature setpoints in balanced ventilation systems.

Figure 1 is a simplified graphical representation how the temperature setpoint would vary during the year with a fixed temperature profile and an adaptive temperature profile. In case of the adaptive temperature profile, outside the heating season the temperature setpoint is gradually increased to higher levels when outdoor temperatures rise. During the heating season, however, the temperature setpoint remains constant.

The use of the adaptive temperature profile serves three goals:

1.    It avoids discomfort in summer when indoor temperatures remain at winter levels. Indoor temperatures should ideally be no more than 5°C below outdoor levels.

2.    Van Marken Lichtenbelt (2022) has indicated that an adaptive temperature profile prevents the body from ‘thermal boredom’ and increases the resistance of residents to heat waves.

3.    An adaptive temperature profile reduces unnecessary cooling energy and costs.

Figure 1. Schematic principle of fixed and adaptive temperature profile.

Adaptive comfort technology in balanced ventilation systems without postconditioning

Balanced ventilation systems bring filtered, fresh air into a building and extract stale air out of the building. The primary function is to refresh the indoor spaces for a healthy living and working environment. The secondary function of balanced ventilation systems is to bring in the fresh air in an energy efficient way and with comfortable supply air temperatures. Energy is transferred between the outgoing stale air and the incoming fresh air. When energy recovery is not needed, the recovery is temporarily reduced or switched off.

Figure 2 illustrates the basic principle of the control of a balanced ventilation system. The black sloping line is the indication of the indoor temperature setpoint, measured in the unit in the extract air. For low outdoor temperature, heat recovery is used. When outdoor temperatures are above a certain threshold, bypass can be activated to bring passive cooling to the house, but only when extract temperatures are higher than the temperature setpoint. When outdoor temperatures are above extract temperature, the bypass is deactivated again allowing cold recovery to supply fresh air while keeping most heat outside.

Figure 2. Schematic working principle for ventilation system without postconditioning.

The extract temperature setpoint is the control parameter that decides how often the bypass is activated for passive cooling. For low setpoint, the bypass is activated more frequently than for a higher setpoint. The default temperature profile NORMAL increases the extract temperature setpoint with running mean outdoor temperature (Figure 3). The end user has the possibility to change from the temperature profile NORMAL to temperature profiles COOL or WARM. This shifts the temperature setpoint below and above the default profile, respectively. In all three profiles, the temperature setpoint changes with the average outdoor temperature, but the ‘cooler’ the profile, the more frequently the bypass will be used for passive cooling.

Figure 3. Adaptive temperature control in ventilation system without postconditioning

The monitored result for a balanced ventilation system without postconditioning in a house in Switzerland is given in Figure 4. The graph shows the measured temperatures (measured in the unit) from January to July 2022. The outdoor temperature (light green) and the running mean outdoor temperature (dark green) are gradually rising from winter to summer. The adaptive temperature setpoint (grey) increases therefore in this period from 21.5°C to 24°C. The extract temperature (yellow) is also rising in this period from 22.5°C to 25°C. In January, February and March the heat recovery is maintaining a comfortable supply temperature (red) which is just below the extract temperature. From April on, the bypass activation for passive cooling is allowed because the heating season has ended. Please note that when the outdoor is warmer than the extract, the bypass does not activate, to keep the heat outside of the house.

Figure 4. Monitored temperatures for ventilation system without postconditioning.

Adaptive comfort technology in balanced ventilation systems with postconditioning

For balanced ventilation systems with postconditioning, Figure 5 shows the basic principle of control. The ventilation system supplies fresh air in an energy efficient way by first attempting to use heat recovery (saving on central heating system) in the heating season and cold recovery (saving on central cooling system) in the cooling season. In the intermediate season and the cooling season, the fresh air supply (green line) is kept comfortably cool by possible activation of the bypass, as explained in the previous chapter.

Figure 5. Schematic working principle of ventilation system with postconditioning.

Postconditioning is used to actively heat the ventilation air (in heating season) and actively cool the ventilation air (in cooling season) with the goal of maintaining a comfortable indoor temperature. The postheating and postcooling produces the energy needed to maintain the indoor temperature. Therefore, balanced ventilation systems with postcondition can really bring the indoor temperature to comfortable levels (as long as the specifications of the unit are sufficient for the thermal loads of the house). This technology is described in more detail by Cremers (2022).

Figure 6 shows the result of the implemented adaptive temperature profile for a balanced ventilation system with postconditioning in a house in Italy. The graph shows the measured temperatures (measured in the unit) from January to July 2022. The outdoor temperature (green) is gradually rising from −1°C in winter to 34°C in summer. The adaptive temperature setpoint (black) therefore increases in this period from 22°C to 26°C. The extract temperature (yellow) is also rising in this period from 23°C to 26°C (diurnal variation originates from nighttime relaxation of setpoint).

The supply temperature of the fresh air (red) shows that in January, February and March postheating is used for maintaining a comfortable indoor climate. From the end of March, the bypass activation is allowed and it is sufficient to keep the extract temperature close to the adaptive temperature setpoint. From the end of May onwards, the heat transmission and solar gains are higher than the passive cooling with bypass can bring, so that the control switches to postcooling. Even in this period the extract temperature is close to the setpoint indicating that the postcooling output is sufficient in this low energy house.

Figure 6. Monitored temperatures for a balanced ventilation system with postconditioning. Gaps in the chart are due to periods during which data transmission had failed.

Discussion and conclusions

For balanced ventilation without postconditioning, the adaptive temperature setpoint results in slightly lower comfort temperatures when outdoor temperatures are in the range of 10‑17°C, and slightly higher comfort temperatures when outdoor temperatures are in the range of 17-23°C, when people are adapted to higher temperatures.

The result of adaptive temperature setpoint gets even more pronounced when postconditioning is used. In the algorithms of balanced ventilation systems with postconditioning, the temperature setpoint is kept fixed during the heating season. However, in the intermediate and cooling seasons, the setpoint is increasing with average outdoor temperature.

The resulting effect is that the comfort for residents is still good, but without too much (unnecessary) effort for the cooling system. Therefore, the cooling output stays within bounds which has benefits for a sustainable environment and for the costs for cooling for the residents. Moreover, the sound impact of the cooling system stays within bounds. In the long run, the variation in indoor temperatures also makes the human body more resistant to the impact of heat waves, as suggested by Van Marken Lichtenbelt (2022).

While the adaptive temperature setpoint generally offers advantages over a fixed setpoint, some occupants may prefer a fixed temperature. Therefore, the adaptive setpoint is the default option, but users can switch to a fixed setpoint if desired.

References

Cremers, B. E. (2022). The monitored performance of the combination of balanced ventilation with post-conditioning by an air-to-air heat pump. Proceedings of the 42nd AIVC Conference. Rotterdam, The Netherlands.

Van Marken Lichtenbelt, W., Pallubinsky, H., & Kramer, R. (2022). Creating health and resilience by a dynamic indoor climate. REHVA 14th HVAC World Congress. Rotterdam, The Netherlands.