The effect of a rotary heat exchanger in room-based ventilation on indoor humidity in existing apartments in temperate climates

Abstract

Document VersionPeer reviewed version Link back to DTU Orbit Citation (APA): Smith, K. M., & Svendsen, S. (2016). The effect of a rotary heat exchanger in room-based ventilation on indoor humidity in existing apartments in temperate climates. Energy and Buildings, 116, 349-361. DOI: 10.1016/j.enbuild.2015.12 AbstractThe investigation constructed and simulated moisture balance equations for single-room ventilation with a non-hygroscopic rotary heat exchanger. Based on literature, the study assumed that all condensed moisture in the exhaust subsequently evaporated into the supply. Simulations evaluated the potential for moisture issues and compared results with recuperative heat recovery and whole-dwelling ventilation systems. To assess the sensitivity of results, the simulations used three moisture production schedules to represent possible conditions based on literature. The study also analyzed the sensitivity to influential parameters, such as infiltration rate, heat recovery, and indoor temperature. With a typical moisture production schedule, the rotary heat exchanger recovered excessive moisture from kitchens and bathrooms, which provided a mold risk. The rotary heat exchanger was only suitable for single-room ventilation of dry rooms, such as living rooms and bedrooms. The sensitivity analysis concluded that varying heat recovery or indoor temperature could limit indoor relative humidity in dry rooms when a moderate risk was present. The rotary heat exchanger also elevated the minimum relative humidity in each room, which could help to avoid negative health impacts. A discussion emphasized the potential benefits of selecting heat recovery to match the individual needs of each room. KeywordsDecentralized ventilation; single-room ventilation; room-based ventilation; rotary heat exchanger; moisture issues; mold risk; renovated buildings; energy retrofit; temperate climate. 2 Highlights• The simulated rotary heat exchanger provided moisture concerns in several rooms.• The rotary heat exchanger was only suitable for ventilation of so-called dry rooms.• Varying heat recovery or temperature can limit indoor relative humidity in dry rooms.• Single-room ventilation allows selection of heat recovery to match the needs of rooms. Nomenclature

Annual Performance of Sensible and Total Heat Recovery in Ventilation Systems: Humidity Control Constraints for European Climates

“…Considering a HR device and the mixing process, xMA = (xR mOA + xRA mCA)/mMA (6) this can be expressed as:…”

“…In particular, when dehumidification by cooling processes is needed, heat recovery can be counter effective, because of the subsequent need for cooling the fresh air to the dew point conditions. This effect can be emphasized by heat recovery systems able to recover latent and sensible heat, as shown by Smith and Svendsen [6], who investigated three different scenarios of moisture production and simulated the annual humidity level profile when heat recovery was used, disclosing occurrences of excessive humidity because of excessive recovery. Some studies in the literature also compared the performance of system configurations equipped with either sensible or latent heat recovery devices [7][8][9] or the impact of frost-protection methods on the energy recovery [10].…”

Solar control solutions for reducing overheating risks in retrofitted Danish apartment buildings from the period 1850- 1900 – A simulation-based study

“…The moisture production from typical activities occurring in the apartment was set to 2.6·10 -4 kg/s in the bathroom and 1.10·10 -4 kg/s in the kitchen [14], and it follows the occupancy schedules for these two rooms.…”

Natural Ventilation Effectiveness of Round Wall-Mounted Vent Caps in Residential Kitchens

“…The results indicated that the ventilations of a kitchen greatly affect the exposure level, because the particle dispersion is sensitive to the air distribution. Smith and Svendsen [7] established moisture balance equations for a single-room ventilation with a non-hygroscopic rotary heat exchanger, and showed that the rotary heat exchanger recovered excessive moisture from kitchens and bathrooms, which reduced the risk of mold. Pinto and Viegas [8] examined the effect of combined natural and mechanical ventilation in a kitchen on the exhaust of the appliance's combustion products.…”

“…Mechanical ventilation (by the operation of a hood or an exhaust fan) [4][5][6][7][8][9][10][11][12][13][14] or natural ventilation (e.g., opening the kitchen window) [15][16][17][18][19] can usually be employed to control kitchen air quality. The contrasting needs for thermal comfort and indoor air quality management by ventilation should be taken into consideration [20].…”