heat recovery

Besides the hygienic aspect, also the aspect of energy saving of heating residential buildings is very important. This is only possible by mechanical ventilation with heat recovery. This paper describes a part of the large variety of systems, which are nowadays available on themarket. The main difference of these systems are: * single room unit/decentral unit and * central unit for one dwelling or a single family building.

This paper investigates quantitatively the energy conservation achieved by balanced ventilation with heat recovery and upstream ground heat exchanger. The investigations were conducted on an occupied single-family house equipped with such a balanced ventilation system. The heat recovery unit of this system consists of a plate-type heatexchanger with a downstream small air-to-air heat pump. In addition this house is equipped with a ground heat exchanger.

A heat recovery system reclaims heat from outgoing stale air, supplying it to incoming fresh air. The energy benefit is greatest if it supplies all the fresh air to the house and none enters via uncontrolled openings, hence ventilation heat recovery (VWR). A sunspace (or conservatory) attached to a dwelling will almost always be at some temperature above ambient. Heat losses by conduction through the adjacent building fabric and ventilation losses via cracks will be reduced.

The house dust mite inhabits bedding and soft furnishings in homes. It is implicated as a major cause of allergic asthma. Maintenance of indoor humidity below a level of 7 g/kg inhibits the growth of the mite population. A pilot survey was carried out by EA Technology in cooperation with the Building Research Establishment to investigate the effect of mechanical ventilation with heat recovery (MVHR) both on indoor humidity and mite abundances.

A prototype of a low cost, low energy office building was built using a new Finnish component system building technology. Thanks to the energy efficient windows, the thermal insulation of the building envelope and the demand-controlled variable outdoor air flow HVAC system with heat recovery and energy-storing structures, the need for heating and cooling energy has been reduced to such a level that a low energy office can be cooled with outdoor air and with the aid of a heat recovery device. The building is kept warm with the support of its own operations almost throughout the year.

In well insulated buildings the ventilation heat is sometimes higher than the heat losses by transmission. For a air change rate of 0,8 per hour the specific heat flux must be calculated with 25 w/m², so heat recovery can save some energy. In all considerations the saving in the heating system must be compared with the additional energy for the fans, because this energy is of a higher quality. To optimize the heat recovery system, the different designs of the heat exchanger, the annual running hours and the annual hours for heat recovery must be taken into account.

The greenhouse effect is one of those topics in environmental politics which are currently worldwide at stake. There are several national concepts aiming at the diminution of CO2-emission in order to lessen the greenhouse effect. One of these concepts is the CO2-reduction programme of the Federal Republic of Germany. With this resolution, passed on November 7th, 1990, Germany's Federal Government aims high: national carbondioxide emission is to be cut back by 25 per cent by the year 2005.

For more than 20 years, energy recovery systems have been operated successfully in European countries in comfort and industrial ventilation systems in order to reduce the heating and cooling capacity as well as to reduce the annual energy consumption for the treatment of supply air. By 1991 the total heating capacity of all installed energy recovery systems in Europe was about 60.000 MW and the equivalent of the annual energy savings was about 10 million tons of oil.

The new building and HVAC technology was used when an EBES multistorey residential building was built in Helsinki. In the EBES system the building structures are used as an installation space for the heating, piping, ventilation and electrical systems. Building structures are also used as a storage for heating and cooling energy. The main objectives of the overall EBES system are to improve the indoor air quality and energy economy and at the same time to improve the quality of the construction process and reduce costs.