| MVHR Luxembourg Setpoint tempearture, (oC) overheating). The tests reported in this article employed air temperature sensors (outdoor; supply after recovery; supply after conditioning; extract; and exhaust), humidities (outdoor; supply after recovery; extract; and exhaust), measurements of both the supply and extract air streams (flowrate; fan speed; fan duty), and electrical consumption. All parameters were recorded over one year (18 July 2021 to 17 July 2022) every five minutes and summarised in hourly averages for further analysis. The Modena house, in a humid subtropical climate zone, was built in 2017 and consists of three floors with total floor area of 270m2. The insulation is within passive house limits, with a U-value of 0.132W.m-2.K-1 for the walls and 0.123W.m-2.K-1 for the roof. There are no other heating or cooling units used, other than the technology described in this article. The house in Luxembourg, an oceanic climate that is typically 1K to 2K cooler than London, was built in 1981 and renovated in 2020, with a total floor area of 185m2. Typical U-values for this house are 0.14W.m-2.K-1 for the walls and 0.20W.m-2.K-1 for the roof. No other heating systems are used aside from the system under test. A recent review3 undertaken by Spiekman et al has indicated that occupants have been shown to find it challenging to determine the optimal operation mode. In the normal operation of these systems, the various operational modes are automatically chosen by the control algorithm, based on the actual and the desired conditions. During the cooler periods of the year, the temperature of the incoming outdoor air is initially raised by the heat recovery (avoided heating in Figure 2). If the adaptive controller requires a higher temperature, the coil will act in heating mode (supplied from the air-toair heat pump) and will further increase the temperature of the supply air (active heating in Figure 2). -5 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 30 20 10 -10 -10 10 15 20 10 20 30 40 Outdoor temperature (oC) Modena, Italy 30.0 25.0 20.0 15.0 10.0 25 Prevailing mean ambient temperature, pma, (C) Figure 4: Desired indoor temperature as a function of the prevailing mean ambient temperature pma for the house in Luxembourg 15-09-21 14-09-21 13-09-21 12-09-21 11-09-21 10-09-21 9-09-21 8-09-21 7-09-21 6-09-21 1-09-21 0.0 5-09-21 5.0 4-09-21 Figure 3: Cooling effect of the system before and after activation of active cooling. Lines indicate temperatures of outdoor air (green); supply air after active cooling (red); extract air (yellow); and setpoint for extract (black) 3-09-21 Temperature (oC) 35.0 A change in temperature profile setting on 21 February 2022 raised setpoint by about 0.5K 5 0 40.0 Normal profile after 21-2-22 Normal profile before 21-2-22 0 Figure 2: Schematic representation of the working principle. Black line: temperature of indoor air; green line: temperature of supply air (possibly after active conditioning) 0 2-09-21 CPD PROGRAMME When temperatures outside are warmer than inside, the heat exchanger reduces the temperature of the incoming outdoor air to approach the cooler indoor air temperature (avoided cooling in Figure 2 ). If there is a need for further cooling, the coil (supplied from the air-to-air heat pump) will operate in cooling mode, providing both cooling and, potentially, dehumidification (active cooling in Figure 2). During the periods of the year with mild temperatures, heat recovery automatically reduces as the temperatures inside and outside approach each other, or totally shuts off, with the adaptive controller activating a bypass in order to bring in cooler air. This period is shown as ventilative cooling in Figure 2. The cooling effect of the installation on the indoor climate in summer can be demonstrated by the example period shown in Figure 3 (in Modena). During the first five days, the ventilation system including recovery was operational, but the active cooling had been switched off. The supply temperature during the day was brought to the indoor level (effect of cold recovery), but the extract temperature remained at a high level, with extract temperatures up to 30C. During nights, the bypass was activated to bring in the cool outdoor air, with the resulting supply air temperature being close to the outdoor air temperature. After five days (6 September 2021), the active cooling was put into use. The heat pump brought the supply air to approximately 15C. The cooling effect on the indoor climate can be seen during the course of a couple of days, with a gradual decrease in extract temperatures. After four or five days, the extract temperature had reached the desired setpoint of 26C and remained at that level. Extract temperatures for Modena ranged from 22C (winter) to 27C (summer) and 20C (winter) to 25C (summer) for Luxembourg. In Italy, both 32 November 2022 www.cibsejournal.com CIBSE Nov 22 pp31-34 CPD 207 Zehnder Supp.indd 32 21/10/2022 17:06