Performance of a natural ventilation system with heat recovery in UK classrooms: An experimental study

Abstract

This paper presents the ventilation performance of a Passive Ventilation System with Heat Recovery (PVHR) based on in-situ monitoring in a primary school in London. The study involves long-term (15month) monitoring of temperature, relative humidity and Carbon dioxide (CO 2 ) concentrations in both the classrooms and the outdoor environment. In addition, short term (1&2 week) observational monitoring was performed in two classrooms at ventilation system level and classroom level, during both the heating and non-heating seasons. Temperatures and air velocities were measured within the PVHR system while instances of window opening and the number of students were noted in daily diaries. Air permeability and infiltration measurements were performed to characterise the spaces.Time-varying ventilation rates were estimated through a form of continuity equation considering CO 2 generation rates by occupants. Preliminary results show that the operation of the ventilation system is more sensitive to changes in wind speed and direction than to buoyancy. When negative pressure was observed on the classrooms" facades the ventilation system was supplying two to three times more air in comparison to instances when positive pressures were observed. The assessment of the ventilation performance of such natural ventilation systems depending solely on wind and buoyancy is complicated as they are dynamic systems that constantly balancing with the surrounding conditions, and the operation is highly correlated to the airtightness of the building"s envelope. Highlights: CO 2 concentrations in classrooms with passive ventilation systems (PVHR) were satisfactory  Airtightness significantly affects the performance of the passive ventilation system  Passive ventilation system appears more sensitive to wind changes than to buoyancy ACCEPTED MANUSCRIPT A C C E P T E D M A N U S C R I P T 2  Human behaviour such as window opening can significantly boost the ventilation rate of the PVHR system 1 Introduction According to the Climate Change Act (2008), the UK government is committed to tackling climate change by reducing greenhouse gas emissions for the year 2050 by at least 80% from the 1990 baseline (DECC 2008). Space Heating, Ventilation and Air-Conditioning (HVAC) account about two thirds of the total non-industrial energy use (Deuble and de Dear 2012, Lomabrd et al., 2008, Khan et al., 2008) from which 30-50% is related to ventilation and infiltration and about 40% accounts for heating. A reduction in the energy required to heat and ventilate buildings will contribute to a significant reduction of greenhouse gas emissions. Natural ventilation strategies consume negligible amount of energy by utilizing natural driving forces of wind and buoyancy (temperature differences between the indoor and outdoor environment-stack effect) can provide a viable alternative to energy consumption for mechanical air-conditioning systems and a fundamental method towards energy efficient design of buildings (Calautit and Hughes 2014, Khan et al., 2008). Sev...

19th-century thermosiphon ventilation and its potential for heat recovery in buildings today

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Experimental Evidence of the Coupling between the Energy Charge–Discharge and Natural Ventilation in a Full-Scale Passive Building

“…The experimental study of only the natural ventilation process has achieved and continues to be of high interest in different countries, despite the high instrumentation and equipment costs. In most cases, when it is performed, the experimental study mostly concerns the airflow characteristics of the building rather than its coupling with the thermal characteristics [16][17][18][19][20]. Caciolo et al [16] also focused on the airflow rate characteristics for a single-sided natural ventilation strategy by placing various hot-wire anemometers at the openings.…”

“…However, studies that aimed to obtain experimental evidence on coupling heat and mass transfer have generally implemented global instrumentation of the building [18][19][20][21][22][23].…”

Using exhaust air heat for residential buildings with warm attics

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