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The Barbour Guides are intended to provide a short introduction to, or overview of, a given subject area. They should

not be viewed in any way as being complete or comprehensive. Barbour recommends further reading, starting with

the references listed in the Guide and other information held within the Barbour services.

HEAT RECOVERY

GUIDANCE

Typical heat recovery devices include: Run-around coils Thermal wheels Cross flow heat exchangers Plate heat exchangers Recuperator Heat pipe RegeneratorTechnical considerations to take into account when selecting heat recovery devices include: Heat recovery efficiency (sensible and total) Airflow arrangement Fouling (filters should be placed in both supply and exhaust air streams) Corrosion (particularly in process applications) Cross-contamination Condensation and freeze-up Pressure drop Face velocity Construction materials (suitability for temperatures, pressures, contaminants) Maintenance (in particular cleaning of surfaces) ControlsHeat recovery should be considered at an early design stage as system layouts will need totake into account heat recovery requirements, e.g. proximity of supply and exhaust airstreams.

Check that when integrating heat recovery systems into the design of air conditioning andventilation systems, that there is sufficient energy being rejected to justify the addedcomplications and running costs.

Temperature conditions across the whole season should be taken into account whenassessing viability.

Infiltration has a significant impact on the viability of air to air heat recovery.

Check that the required temperature and humidity is maintained without adding or removingmore heat than necessary.

Consider the application, space available and required air quality when selecting heatrecovery systems, e.g. run-around coil, thermal wheel, plate heat exchanger, heat pipes, heatpump, generator, etc.

When selecting a suitable heat recovery system, consider the quality and condition of theexhaust air to assess likely contaminant load and composition, moisture content, etc.

Consider whether latent heat transfer is required as well as sensible.

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Consider whether cross-contamination between air streams is acceptable for the application.Assess the risk of cross-contamination between exhaust and supply air streams by bothcarryover and leakage.

Allow for the additional resistance of heat exchange devices within the air stream when sizingfans (and pumps for wet heat recovery devices) as this can be substantial. The extra fanpower required should be taken into account when assessing system economics.

The efficiency (effectiveness) of the heat recovery device can be used as a measure of theheat recovered. Typical efficiencies are: Thermal wheels - 65-85% (depending on media construction in the thermal wheel) Recuperators/plate heat exchangers - 50-80% Run-around coils - 45-65% (depending on number and spacing of coil rows and

temperatures)

In applications involving thermal wheels, cross-contamination from exhaust air stream tosupply air stream is possible.

Supply and extract ducts need to be adjacent to incorporate a thermal wheel.

There will be a risk of cross-contamination if mechanical damage occurs with a plate heatexchanger.

Consider the option of pre-heating incoming air via atria, conservatories and open roof spacesor by using waste heat from air-cooled condensers, from, for example, industrial refrigerationsystems and computer rooms.

Provide condensate drains where required.

Frost protection should be provided for run-around coils.

Provide modulation control to prevent over heating in warm weather.

Allow sufficient space for installation, access and maintenance. Thermal wheel installationscan be very large indeed.

Consider whole life costs and relative merits of different heat recovery system types.

REFERENCE DOCUMENTS

The following documents provide further guidance:

BS EN 308: 1997 Heat exchangers - test procedures for establishing the performance of airto air and flue gases heat recovery devicesBS EN 378-4: 2000 Refrigerating systems and heat pumps - safety and environmentalrequirements - operation, maintenance, repair and recoveryBS EN 13141-7: 2004 Ventilation for buildings performance testing of components/productsfor residential ventilation performance testing of a mechanical supply and exhaustventilation units (including heat recovery) for mechanical ventilation systems intended forsingle family dwellings Air Infiltration and Ventilation Centre, Technical Note 45 Air-to-air heat recovery in ventilation1994BRE Report 416 Air-conditioning systems in buildings using air cycle technology - design andapplication guide 2001BSRIA Technical Note 83/4 Heat recovery and heat pumps in buildings guide for buyersand specifiers 1983BSRIA Technical Note 86/11 Selection of air-to-air heat recovery systems 1986CIBSE Guide B Heating, ventilating, air conditioning and refrigeration 2005

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