The main objective in terms of energy efficiency of a ventilation system with heat recovery is to reduce the primary energy consumption of the building. Hence, the ratio between between saved and consumed energy should be greater than one and depends on various parameters. Fresh air supply can be decreased because of shortcuts within the system and unbalanced air flows, possibly resulting in lower heat recovery rates and unwanted ventilation losses. On the other hand, the energy consumption is often increased due to inefficient fan components or high pressure drops of inadequate components or design. These parameters among others were measured at 20 centralized and 10 to 67 (depending on the measured parameter) decentralized devices in field tests, with the goal of providing an overview of the performance of state-of-the-art ventilation systems in residential buildings. Nearly all devices showed shortcomings at one or more parameters. The values for shortcuts, heat recovery rates, sensitivity to pressure differences between in and outside and specific fan power in most cases differed from values provided by the manufacturers.
Member States of the European Union are obliged to present a calculation method and certificate for the energy performance for buildings according to the guidelines 2002/91/EG und 2010/31/EU. In Luxembourg it is obligatory to add the real final energy consumption to the certificate after 3 years. The measured real final energy consumptions and the calculated ones were compared for 125 single-family homes and 105 multi-family homes with 870 dwellings in total. The mean calculated values for single-family homes were 74 % higher, the mean calculated values for multi-family homes 103 % higher than the actual measured data. The older the buildings, the higher the deviations, as the input parameters, which were partly assumed and partly predefined, diverge between calculations and reality. Sensitive parameters of interest are the indoor room temperature, the U-values, the used assessment for thermal bridges and the air exchange rate.
The idea of adapting the air supply rate to the actual demand in a building is not a new one. In commercial buildings it is already state-of-the-art to establish a demand controlled ventilation, where the level of air flow is based on sensors or time control. In residential buildings however, mechanical ventilation systems, whether centralized or decentralized, are in most cases operated in a constant modus, providing fresh air regardless if the fresh air is needed or not, even though the technology and the components needed for demand controlled ventilation exist and can be purchased at reasonable prices. In this article, results of field tests with a semi-centralized demand feedback-controlled ventilation system are shown and compared to outcomes with other demand controlled systems. The semi-centralized prototype includes decentralized fans per ventilation zone, making a room-wise ventilation possible and valves to balance the system hydraulically unnecessary. It is shown that each presented concept of demand controlled ventilation can save energy by decreasing the operational time or the mean air flow rate without compromising air quality. Concepts which make a zone-or even a room-wise control of air flow possible, showed the highest energy saving potential of up to two-thirds compared to a system operating at constant flow rates. In addition to the energy savings due to decreased operational time, the maintenance and filter costs are decreased while the user * Corresponding author Email address: alexander.merzkirch@uni.lu (Alexander Merzkirch)Preprint submitted to Building and Environment June 4, 2015 comfort is increased, as natural ventilation in spring, summer and autumn may easily be added when ∆T between inside and outside is small.
The public building stock of a country, consisting of schools, offices, accommodation facilities, single-and multi-family homes, accounts for a high consumption of electrical and heat energy. Therefore, this stock is often object to actions with the goal of lowering this energy usage by increasing the efficiency of those buildings. This is usually done by applying measures to the building envelope like insulation and/or new windows and by using more efficient HVAC technology. But often, in the initial state, the current energy consumption of such a stock is unknown or only known for single buildings. In this case, the calculation of energy and costs savings is either impossible or not exact. This paper shows a way to quantify and categorize the end-energy for heat use of the public building stock in Luxembourg, which consists of 1,744 Mio. m 2 gross area, while the information about this stock was incomplete in the first place.This analysis was done in cooperation with the national administration of public buildings.A certain amount of sample buildings was analyzed and then separated into three groups of low, normal and high end-energy use. The boundaries of these groups were chosen according to literature values, derived from European retrofit projects, which also served as the source for possible costs of renovations. This data was extrapolated to the whole stock. This information serves as a basis for future decisions concerning the retrofit of those buildings and makes a
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