The Effects of Aqueous Mixtures of Amphiphilic Molecules in Building Hydronic Heating Systems

Abstract

Since 1970, emissions associated with building space heating and cooling have been declining due to improved building and heating system efficiencies. However, space heating and cooling still account for approximately 20% of the UK’s CO2 emissions. Therefore, innovative solutions are required to reduce building energy consumption and carbon emissions. A potential technology that is often overlooked, both within industry and academia is hydronic central heating additives that modify the properties of the working fluid. There are several commercial central heating system additives which claim to reduce the energy consumption of buildings by improving heat transfer and heating efficiency, but their effects are often poorly understood. This thesis focuses on the energy saving opportunities that can be brought about by changes to working fluid properties inside a hydronic central heating system. Specifically, it characterises an energy saving additive (EndoTherm), which is a proprietary blend of alkyl polyglycosides (APGs). This includes determining the intrinsic fluid properties, defining phase boundaries, and quantifying their impacts on flow and heat transfer within heating system components. The magnitude of any energy saving opportunities was determined using a bespoke dynamic room and heating system model, which was developed in a MATLAB environment and validated against a real building. It was found that dosed EndoTherm had a relatively large impact on the equilibrium surface tension, heat capacity, thermal conductivity and steady flow viscosity of the working fluid compared to that expected from a simple mixture at the concentration of APGs. The uncertainty of the measured fluid properties was less than 1% of the measured values for 95% confidence intervals (80% for heat capacity). Nevertheless, the impacts of fluid property modifications on the flow and heat transfer characteristics in a bespoke test rig lay within the measurement uncertainty. The room and heating system model demonstrated fluid properties had a non-linear impact on the energy consumption of a room. These changes were attributed to variations in excess heating and heating system responsiveness (resulting in demand shifting). Under specific conditions, the daily energy consumption of a room could be reduced by ~10% for changes to working fluid heat capacity or flow rate, whilst reductions of up to 2% were observed for changes in fluid thermal conductivity. The thermal capacitance of the building fabric somewhat buffered the long term energy saving opportunities for idealised repeating scenarios. This resulted in long term energy saving opportunities of 3.5%, 3.0% and <1% for changes to working fluid heat capacity, flow rate and thermal conductivity respectively. However, the opportunities for energy savings through fluid property modifications achievable with dilute APGs were modest compared to case studies. For a single room, following the SAP heating profile without high frequency heating disturbances (<1 hr), a daily energy saving opportunity of up to 2.9% was identified, decreasing to 0.7% for an idealised repeating scenario. However, the energy saving opportunities may be larger when considering the impacts of the inherent heating disturbances in buildings, non-equilibrium fluid properties and variable heating profiles, which should be further studied.