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Bart Cremers
Year:
2019
Languages: English | Pages: 5 pp
Bibliographic info:
40th AIVC - 8th TightVent - 6th venticool Conference - Ghent, Belgium - 15-16 October 2019

The outdoor climate is changing and the airtightness and insulation levels of residential buildings are improving. During the warmer season this can lead to overheating problems, especially when the house is situated in urban areas. In order to reduce overheating problems, ventilative cooling can be used to keep the indoor conditions at a comfortable level. Natural ventilation is not always a feasible solution, for the risk of burglary, and when the outdoor temperatures are not suitable for cooling the house, for instance in urban heat islands. 
This document describes the monitored performance of a ventilation system in a nearly zero energy building in Modena, Italy. The house is ventilated with a balanced ventilation system in combination with a water/air heat exchanger in the supply air from the ventilation unit, hereafter named postconditioning system. The water in the exchanger comes from a heat pump, activated by a room thermostat that defines whether there is a request for cooling or heating. In summer, the system cools and dehumidifies the fresh air (postcooling) and in winter the system heats the fresh air (postheating). The resulting cooling and heating is the only conditioning means in the house, there is no other cooling or heating system installed in the house. 
The monitored performance is shown with example weeks in summer, autumn and winter. In these weeks the functional modes of balanced ventilation and postconditioning are shown, together with the resulting temperatures in the relevant air streams. The modes of indoor heat recovery, indoor heat extraction and outdoor heat rejection, in combination with postcooling or postheating, can clearly be observed. The overall performance during a 7 month period is shown in a correlation graph where extract, supply and postconditioned supply temperatures are given as a function of outdoor temperature.  
The postconditioning system does not only show the cooling effect in a sensible way (temperature decrease of supply air) but also in a latent way (humidity decrease of supply air). This is indicated by the monitored temperatures when the water temperature in the postconditioning system is dropping below the dew point of the fresh air in summer. The resulting condensation on the postconditioning exchanger decreases the absolute humidity of the fresh air, which adds to the comfort of the fresh air supply even further. 
The ventilative cooling as a result of indoor heat extraction, outdoor heat rejection, in combination with postcooling is discussed looking at the resulting extract air temperatures (indication of indoor temperatures). It is shown how the overheating problem in this house is reduced by the mechanical ventilation system, even when summer outdoor air temperature and humidity are higher than indoors. Both the hygiene in terms of guaranteed fresh air, and the comfortable supply air temperatures, make this ventilation system a comfortable, and energy efficient solution for all seasons of the year.