heat recovery

The monitoring of a demand controlled heat recovery ventilation system with ground heat exchange in a zero-energy building in Groenlo, The Netherlands, revealed interesting practical insights.

As building insulation level increases, the coupling of ventilation systems with building enveloppe airtightness becomes an important issue in order to improve buildings energy performances. A building ventilation model can be built on a set of resistances and generators in order to handle infiltration, natural ventilation as well as fan driven air flows. The model is able to assess the indoor air humidity level and the building energy balance.

Infiltration has traditionally been assumed to contribute to the energy load of a building by an amount equal to the product of the infiltration flow rate and the enthalpy difference between inside and outside. Application of such a simple formula may produce an unreasonably high contribution because of heat recovery within the building envelope. Previous laboratory and simulation research has indicated that such heat transfer between the infiltrating air and walls may be substantial.

This paper is based on the first Belgian case study developed in the frame of theIEA-ECBCS annex 48 project.

In cold and moderate climates, improvements in building shell insulation and air-tightness imply a shiftin heating loads from transmission and infiltration towards ventilation. Heat recovery from the ventilation airflow plays an increasingly important role in minimising energy needs. Such heat recovery systems rely on the input of electric power (to drive fans, heat pumps, etc.) in order to recover thermal energy. Since electricity input is relatively small compared to the amounts of thermal energy recovered, such systems are efficient from an energy viewpoint.

Balanced ventilation systems with heat recovery and earth to air heat exchangers are interestingtechniques, which can reduce heating and cooling demand of buildings, and improve internal thermal comfort. A numerical study is carried out to evaluate the impact of these two systems on the energy consumption and thermal comfort of a single family house. The impact on the CO2 emission is also given.

Major ventilation developments covering systems, measurements and design methods have taken place over the last 25 years. Our understanding about the impact of ventilation on the indoor environment and energy use has also evolved. This paper outlines these developments. Many future challenges are considered including minimum ventilation rates, energy efficient cooling, cost effective heat recovery and the development of calculation techniques.

For retrofitting of existing dwellings MVHR is seldom applied, despite the potential in energy saving and improving thermal comfort and indoor air quality. Major barriers and limitations for application are lack of space, especially for the supply ducts and the MVHR units as well as the complexity of execution. Also initial costs are an important barrier. Limiting supply ducts could be beneficial for application in single family dwellings. In a study some configurations with simplified air supply with MVHR in single family dwellings have been investigated.

Problems of heat and mass transfer optimization in the plate cross-flow heat exchangers, usedin air conditioning systems for energy recovery from exhaust air, are discussed. The mainpeculiarity of the investigated unit is the possibility of realization of heat transfer withinexhaust air canals in the dry heat exchange conditions or in the conditions of coupled heatand mass transfer with occurrence of vapour condensation on the whole or on a part of theheat exchange surface of the matrix in the form of dew or frost.

This paper shows how air-to-air heat and energy system design problems can be formulated for a simple HVAC configuration and solved for the least life-cycle cost system while still retaining a small payback period. Mathematical expressions and design tables are presented to facilitate the design process. The design process is illustrated for the city of Chicago where both large heating and cooling loads occur in HVAC applications. The example design problem presented shows that