Overheating in buildings: lessons from research

Overheating in buildings: lessons from researc

Briefing: Heat-wave-coping measures for housing

The effect of climate change is increasingly manifested through more frequent and more intense extreme weather events, including heat waves and flooding. This briefing demonstrates how internal temperatures in housing can be reduced during a heat wave period purely by passive means

Evaluation of thermal comfort in naturally ventilated school classrooms using CFD

This paper investigates the performance and control of natural ventilation during the heating season in order to avoid occupant discomfort. The current study examined different window configurations under a wide range of external temperatures and wind speeds using a CFD simulation tool. The results showed that thermally comfortable indoor conditions could be achieved in a UK classroom when external temperatures are as low as 8°C using high-level openable windows. At lower external temperatures, occupants are predicted to be thermally dissatisfied due to localised discomfort caused by draughts. The results from the CFD model also suggest that acceptable internal thermal conditions can be maintained with wind speeds up to 10m/s, for an external temperature of 10°C. The PMV results indicated that thermal comfort is achieved and is uniformly distributed within the classroom. This work will enable the UK’s Education Funding Agency to have a greater understanding of the effective control of windows to eliminate wintertime discomfort and avoid unnecessary heating for naturally ventilated spaces

The effect of refurbishment and trickle vents on airtightness: the case of a 1930s semi-detached house

As UK homes are insulated and draught proofed in an attempt to reduce wintertime heating demand they become more airtight. Any reduction in infiltration could have a detrimental effect on indoor air quality. Controllable background ventilation provided by trickle vents is one method of maintaining indoor air quality. A 1930s semi-detached 3-bedroom house was refurbished with double-glazed windows, trickle vents, doors and loft insulation. 167 blower door tests were carried out pre- and post-refurbishment between January and March 2017 to understand the repeatability of the test and quantify how trickle vents affect airtightness. The refurbishment reduced air leakage by 29% from 20.8 to 14.7m3/h/m2 at 50Pa (with all windows and trickle vents closed), but still in excess of the current UK regulations for new builds (10m3/h/m2 at 50Pa). Opening trickle vents provided limited additional ventilation, only increasing air change rate by 1.8m3/h/m2 with all vents open. The test was found to be repeatable with a standard error of 0.07m3/h/m2 at 50Pa with no relationship between the test result and wind speed or direction. The results lead to two important conclusions. Firstly, after refurbishing older homes of this type, infiltration rates are still well above recommendations for adequate indoor air quality. Secondly, the omission of trickle vents in older homes may not unduly diminish indoor air quality

Measuring and mitigating overheating risk in solid wall dwellings retrofitted with internal wall insulation

Upgrading the thermal insulation of UK houses to improve wintertime energy efficiency raises concerns about potential summertime overheating risk. To address these concerns, experiments were conducted in a pair of thermally matched, solid walled houses, located in the UK. One of the pair was retrofitted with internal wall insulation, while the other remained uninsulated; both houses were monitored for four weeks during the summer of 2015. Operative temperatures in the living room and main bedroom were observed to be higher in the internally insulated house in comparison to the uninsulated house. The houses were again monitored for a further three weeks with a simple overheating mitigation strategy applied consisting of night ventilation and shading using internal blinds. The data were normalised for variations in external weather conditions using a linear regression model, with the exponentially-weighted outdoor running mean air temperature as the predictor variable of indoor operative temperature. The results showed that the mitigation strategy was effective at reducing the internal temperature in the internally insulated house to a level similar to that observed in the uninsulated house. The marginal increase in overheating risk should not be considered a barrier to the uptake of IWI in this type of house and location, at this time. Shading devices and secure noise attenuating vents for existing dwellings may be needed as part of a package of refurbishment in the future. It could become a requirement within the Building Regulations [1] to reduce overheating risk when retrofitting existing homes

Ranking of interventions to reduce overheating in dwellings during heat waves [conference paper]

Extreme weather events, including heat waves, are predicted to increase in both frequency and severity over the coming decades. Low rates of house building and a growing population mean there is a need to plan for climate adaptation of existing dwellings. This research uses dynamic thermal simulation to model the effect of a series of passive heat wave mitigating interventions for UK dwellings. The interventions include a range of additions and modifications to solar shading, insulation and ventilation. Results are presented for 19th century end terraced and mid terraced houses. Simulations were performed for buildings with the front of the terrace facing both north and south, with two different occupancy profiles: occupation by a family, at work and school during the day and by an elderly couple, assumed to occupy the houses 24 hours a day. The simulations were performed for a 4-day heat wave, during which daily maximum temperatures exceeded 350C. The results show the effectiveness of interventions that reduce solar gains through the building fabric, such as external wall insulation and light coloured walls. These are particularly effective for the end terraced house, which has a much larger external wall area than the mid terraced house. Control of solar gains through the glazing, by use of shutters and fixed shading, are also effective interventions, particularly for south facing rooms. The addition of internal wall insulation can help to reduce overheating for rooms occupied only during the evening and overnight. However, it is shown to increase the overheating problem, when compared to the base case houses, for living rooms occupied during the daytime. When considering interventions to reduce overheating in dwellings, it is therefore critical to take into account the residents and their corresponding occupancy profiles as well as house construction type, location and orientation