Reservoirs of Heat: A Defining Characteristic of High Thermal Mass Earth-Sheltered Buildings

Stable internal air temperatures are a defining characteristic of high thermal mass buildings, a tenet consistent with subterranean and earth-sheltered buildings. This paper introduces independent, evidence-based research from two earth-sheltered projects (18 buildings) providing empirical data in support of the premise that, ‘high thermal mass buildings should be the building form of choice in reducing heating/cooling loads together with concomitant greenhouse gas emissions’. The phenomenon responsible for stabilizing internal air temperatures in high thermal mass buildings is referred to by this author as a ‘residual heat reservoir’. This is the presence of a body of heat energy retained within the superstructure, sufficient to sustain habitable internal air temperatures, with low to no heating loads. In the first of two earth-sheltered projects, ‘Hoddins Way’ (Lincolnshire, 2009) [1] nine offices, the residual heat reservoir was identified, measured, and quantified. The recorded average internal air temperature was 22.2 C, experiencing an annual temperature variance of eight degrees centigrade (±4 °C) with an exceptionally low supplementary heating load of 9.1 KWh/m2/year. The second project is ‘Howgate Close’ (Nottinghamshire, 2022) [2] nine dwellings, same design principles with an improved construction specification, to optimize the reservoir of heat. After 10 months of occupation, average internal air temperature is circa 22 C (±2 °C) achieved with no heating load. Viewing high thermal mass buildings as reservoirs of heat energy with an active thermal core, assists in understanding how to usefully employ heavy building materials, allied with super-insulated and passive solar techniques for a more environmentally responsible form of development.