recirculation

Buildings account for approximately 40 % of energy use in the European Union, as well as in the United States. In light of the European Energy performance of buildings directive, efforts are underway to reduce this energy use by targeting zero or nearly zero energy buildings. In such low energy buildings in cold climates, ventilation to ensure suitable indoor air quality is responsible for half or more of their energy use. The use of heat recovery and demand-controlled ventilation are potential solutions to reduce ventilation-related energy consumption.

Tracer gas measurements are an unparalleled means of measuring air recirculation, leakage, and air flow rates in air handling systems [1-5]. However, such measurements are subject to significant measurement uncertainty in field conditions. A common problem is imperfect mixing of tracer gas.

The International Space Station (ISS) is the biggest multinational space program ever with 16 countries involved. Since November 2000 the station is permanently occupied with a crew of 3 astronauts. Till 2006 the station will be further assembled and the crew will be increased to 7 astronauts. To maintain a comfortable and safe environment under micro gravity conditions in a completely sealed space habitat advanced ventilation technology had to be developed to maintain air temperature, air humidity and air velocity as well as contaminant concentrations well below required levels.

The effect on ventilation effectiveness parameters of the recirculation of air is investigated. The results of work with respect to air change effectiveness parameters is explained and extended to the effect of recirculation on the contaminant removal effectiveness parameter of local air quality index. It is demonstrated, first with respect to a simple system with one supply and exhaust and then by extension to a system with multiple exhausts, that it is possible to calculate the effect of recirculation by means of a simple algebraic expression.

When it is required to predict the local mean age of air, the calculations are often carried out assuming that there is no recirculation that is that all of the supply air is fresh. However, local mean age values will be greater than in the fresh air case when some of the exhaust air is recirculated. This paper examines and discusses the effect of recirculation and shows that, for many systems the increase in local mean age due to recirculation can be calculated by means of an elementary analysis that leads to a simple algebraic expression.

The thermal performance of the underground airpipe air conditioning system constructed at the Non-Conventional Energy Research Institute, Ghosi has been studied. The heat exchanger is used in recirculation mode to aircondition eight rooms in a guest house at the Institute. The temperature and relative humidity of a conditioned and non-conditioned room are measured every two hours. The cooling potential of the system is estimated. It is observed that reasonably good thermal comfort conditions can be created in the building with such a system.