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Façade-integrated ventilation units with heat recovery - energy efficiency and indoor air quality

This contribution reports on investigations about the performance of decentralised ventilation units with heat recovery. Such units can be easily installed in individual rooms and therefore offer an interesting alternative to central ventilation units. Nevertheless these units exhibit some problems. Experimental examinations of two commercial decentralised units showed that the real effectiveness of heat recovery was always below 50 % and that considerable leakage between the air ducts can result in poor indoor air quality.

A heat and mass transfer analysis of cross-flow air-to-air total heat exchangers made of moisture-permeable paper

This paper presents an analysis of air-to-air total heat exchangers (heat and mass transfer) built up using moisture permeable paper (but impermeable to air molecules). Performance of 6 such total heat exchangers made of different types of paper were tested, in order to know their air leakage ratio and their energy saving ratio. An analysis is presented about the effect of leakage on energy recovery efficiency.

Advantageousness comparison of air ventilation systems

This study is an analysis of the advantages of two ventilation systems (exhaust mechanical ventilation, balanced mechanical ventilation with heat recovery) using the Negative Index approach, which is affected by life cycle cost and environmental impact. The balanced system appears to be a better choice (less environmental impact, better indoor air quality) even if its life cycle cost is higher.

Exhaust air heat recovery in buildings

The market evolution of domestic exhaust air heat pumps since 1979 in Sweden is described. Some information is also given about the German market. Technologies of different exhaust air heat pumps systems are shown and results of several monitoring projects in Sweden are summarized : they show for houses built in the 1980's an electricity consumption of 90 to 130 kWh/m2/year (including domestic hot water and household electricity), depending on the thermal characteristics of the building envelope. The energy savings thanks to the exhaust air heat pump are about 30%.

Heat recovery in building envelopes.

Postulates that figures for the energy load of a building affected by infiltration may be too high because the simple formula used does not account for heat recovery within the building envelope. In the study, sensible heat transfer was simulated with the used of CFD in typical envelopes. The results confirmed a possible overprediction of energy load up to 95% at low leakage rates.

Air toxics in a new Australian dwelling over an 8-month period.

Outlines a 'healthy house' design for suburban Australia. The design incorporated a tight building envelope and a ducted mechanical ventilation (and heat recovery) system, providing a minimum ventilation rate of 0.35 air changes per hour. Partial filtration and dehumidification of the air was also included. Low-VOC building materials were chosen. Total volatile organic compound (TVOC) concentrations were approximately 4,000 microgrammes per m3 just after construction, decreasing by a double-exponential model to 300 microgrammes per m3 by eight months, which is good.

Super-efficient mechanical ventilation.

A novel ventilation system has been installed in buildings constructed for the New Campus of the University of Nottingham. Super-efficient mechanical ventilation has been used as part of an integrated environmental strategy and operates with fan input powers below 0.5 W. l-1.  s-1 of airflow. The complete plant was assembled from innovative low-pressure components and has exceptional performance. A key element of the design is that components of the system are bypassed when not in use. At the heart of the system is a low-velocity, high efficiency thermal wheel.

Designing for air to air heat and moisture exchange in HVAC applications.

Air-to-air heat and moisture exchange between exhaust and supply airflows can substantially reduce HVAC costs. This paper outlines the design considerations that should be included when selecting a type of exchanger and shows how the performance of each recovery device can be determined. Energy wheels, which transfers both heat and water vapor, are given special consideration. The HV AC design for heat and moisture exchanger sizing is presented as a least life-cycle cost design problem.

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