Façade renovations of dwellings for high comfort with low temperature heating

Abstract

Especially in colder climates, like The Netherlands, a large quantity of non-renewable energy is used for space heating by burning natural gas. To meet climate goals, natural gas should be replaced with renewable sources. Reducing the total energy demand for space heating and lowering the design water temperature in a heating system enable more renewable energy production alternatives for space heating. So high temperature heating (HTH) systems need to be replaced with low temperature (LTH) alternatives to get dwellings through the energy transition.

Despite the indisputable advantages of LTH, it also comes with risks. One risk is that heating elements need to become exceedingly large to ensure sufficient heating capacities. Insufficient capacities may adversely affect indoor thermal comfort. To mitigate this effect, extra measures should be taken in the façade, ground floor and roof to reduce infiltration and increase insulation. In order to introduce these measures a renovation should be carried out. This study will focus on façade renovations.

For the assessment of comfort levels when changing to LTH, this research presents a case study into a typical Dutch terraced dwelling. This case study was carried out through simulations in TRNSYS 17. This is a validated program simulating energy flows in transient systems. Although TRNSYS 17 has built-in comfort calculation options, these were not deemed sufficiently transparent in their workings for this study. Furthermore, calculations of view-factors, mean radiant temperatures (MRT) and the predicted mean vote (PMV) showed deviations from standards NEN-EN ISO 7726 and 7730. Therefore a workaround is presented which calculates comfort levels closer in line with standards.

Two façade options were investigated for 1 HTH and 3 LTH systems. The HTH model was calibrated to match measured air and surface temperatures of a test dwelling. LTH was then simulated while keeping the current radiators, which showed that diminished capacities significantly reduce comfort and façade renovations cannot realistically mitigate this. This option is not possible when changing to LTH in dwellings in general. Then a system with specialized LTH radiators was investigated, with capacities determined through ISSO 51. This still showed a high peak of discomfort at current insulation levels. Comfort levels were improved significantly after a renovation to match the new ‘Target Values’ (‘Streefwaarden’) for insulation and an ‘excellent’ qualification for infiltration reduction. Finally, underfloor heating was investigated, resulting in enhanced comfort levels both with current and updated insulations levels. In all cases, a renovation has a positive effect on comfort levels and reduces heat transfers.