Abstract
Exposed heavyweight constructions with a high specific heat capacity can dampen and delay transient heat flows in buildings. This paper explores the dynamic effects of various construction assemblies and explores the effect of different temperature control strategies in relation to the thermal mass. The thermal inertia of a building not only affects the pace of heating up a thermal zone, but also the temperature set-back that can be attained with an intermittent heating regime, and thus the setpoints of control regimes. Based on a simulation study, it is demonstrated that the impact of the thermal mass on the heating demand of dwellings is rather limited in a temperate climate. Lightweight timber frame construction can display an annual heating energy demand of up to 6.6% higher compared to a heavy mass concrete and limestone construction in case of fixed thermostat setpoints. If a different control strategy with a highly intermittent thermostat schedule is implemented, the energy use of the lightweight construction can conversely have a lower heating energy expenditure, with a reduction of up to -4.5%. Modelling assumptions on the HVAC system capacity, the timing of the start-up moment of intermittent heating and the type of thermostat control – either based on air temperature or operative temperature – can have a significant influence on the simulation outcomes. Depending on the modelling assumptions and temperature control strategies implemented, the detailed dynamic simulations display that heavy mass buildings will not necessarily yield a lower heating demand as would be predicted by simplified monthly quasi-steady state calculations. In general, it is advocated that a better understanding of control strategies and resulting comfort sensations is required in building design and performance simulation.
Highlights
Improving the energy performance of buildings has become a major societal challenge due to economic, political and ecological motives
In a building which exhibits less thermal inertia, gains might lead to a rise in indoor surface and air temperature, which results in higher transmission and ventilation losses, a slightly elevated heating energy demand later on, compared to a heavy mass equivalent
The thermal inertia effect causes a delay in heating up the building, but in a similar fashion slows down the temperature decay during the night
Summary
Improving the energy performance of buildings has become a major societal challenge due to economic, political and ecological motives. During a hot summer day, a high thermal inertia of the construction can result in slower warming up of the thermal mass inside the building envelope and a reduced overheating risk. Thermal mass is often believed to have a positive effect on reducing heating energy demand. The exposed thermal mass of a construction can store heat gains from the sun or from internal gains and release the stored energy later, reducing the additional heat input required . In a building which exhibits less thermal inertia, gains might lead to a rise in indoor surface and air temperature, which results in higher transmission and ventilation losses, a slightly elevated heating energy demand later on, compared to a heavy mass equivalent
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