Heat recovery ventilation

Heat recovery (HR ) is a collective term for methods of rehabilitation of the thermal energy of the process exiting mass flow. In the simplest case, with relatively continuous heat transfer and recording, a heat exchanger is sufficient, otherwise a heat accumulator is additionally required, for example a regenerator as a short -term heat storage.

Goal of recovery is to minimize the primary energy demand. In addition to the energy industry needs ecological demands are met.

Survey

The process of recovery can be used for heating or cooling processes in gases, liquids or solids. Heat recovery systems can be according to their heat exchanger divided into:

  • Recuperative systems
  • Regenerative systems
  • Regenerators
  • Heat pumps
  • Combined circulation systems
  • Heat pipes
  • Rotors
  • Other

(*) Included leakage and / or co-rotation (. /. ) Missing reference scale

Rückwärm and moisture recovery

The recovery efficiency is the ratio of the transmitted temperature to the temperature difference of the input media and is identical to the temperature degree of exchange, efficiency and change degree. The recovery efficiency can refer to the hot and cold side. For the same heat capacity flow in the sensitive case, the values ​​of both recovery efficiencies are equal. The recovery in the above picture is for example a two-sided heat recovery (19 ° C - 0 ° C) / (24 ° C - 0 ° C) = (24 ° C - 5 ° C) / (24 ° C - 0 ° C) = 0.8 or 80 %. Analog is the moisture recovery of the transmitted absolute humidity to the maximum transferable absolute humidity.

Benefits of heat recovery

  • Reduce the connected load [kW ] for heating and cooling energy
  • Reduction of energy consumption [kWh ] for heating and cooling
  • Reduction or elimination of boiler, chiller, cooling tower, piping, mechanical equipment room, chimney, ...
  • Reducing capital and operating costs in other systems (eg heating, cooling )
  • Reduction of pollutant emissions
  • Reduction of the temperature difference (elimination or reduction of the reheater for comfortable supply air temp. )

Applications of heat recovery

  • Heat recovery for air exchange: Both air-conditioned buildings and passive houses and Minergie houses is used to control the temperature of the supply air to the energy content of the exhaust air. In the cold season, the air is heated and cooled in the warm season. As new buildings are built to protect against external noise and heat losses close, the use of ventilation systems with heat recovery in residential happens to sufficiently automatically dissipate moisture and prevent mildew from forming. Recirculation mode is not classified as a heat recovery. Heat recovery systems with multifunctional use are used as refrigerating system ( adiabatic machine) and can cool from the evaporative cooling of the exhaust air.
  • Heat recovery from waste water: The majority of the hot water consumption in the household is required for body care. When showering, find a flow of warm waste water and the decrease of cold water for heating the water instead of simultaneously. In one case, line - heat exchanger, the waste effluent is cooled and warmed up the inflowing cold water. The warmed cold water then continues to flow into the water heater and uses up to 35% less energy to be warmed up to 60 ˚ C. Normally, the temperature of the mixed wastewater from residential buildings is so low that the thermal energy contained in it can only be used with heat pumps (see wastewater heat recovery). Heat exchangers for locations where sufficient warm water accumulates (shower, bath tub) are still relatively uncommon, although they are currently economically. An interesting development are shower enclosures, shower trays and down pipe heat exchangers where the cold water is heated with the waste water. This cold water is preheated and can be used directly or fed into hot water heater. Conclusion: A significant reduction of the required energy consumption for hot water.
  • Heat recovery from industrial processes: In many industrial processes, high temperatures are necessary. During cooling of the products, but also of the heated ambient air or other gases, which are heated during the process, heat may be recovered. It is this heat at low temperature levels recuperatively (ie, that both fluids run in separate systems ) involved in the process or use it for heating purposes. Furthermore, one can convert the heat into electrical energy. Since waste heat usually obtained at a low temperature level, a conversion into electric energy is possible only with the help of most of the ORC process.
  • Heat recovery with an exothermic reaction: In some industrial processes involves the mass flow leaving the process in addition to the heat and combustible gases can provide more heat by the combustion. In a hot blast stoves of the provided for the blast furnace process " hot wind " is produced by recovering the heat and blast furnace gas from the combustion of blast furnace gas and natural gas supplied. With this technique it was possible to increase in the 19th century the " hot blast " up to temperatures of about 1300 ° C. Only by making some alloys was economically successful, such as ferro manganese, which at the time was important to the war ship, and ferrosilicon.
  • The use of exhaust gases from boilers ( " economizer " ) and power plants (combined heat and power) is not generally referred to as heat recovery.
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