Abstract
Thermal bridges in building walls are usually caused by mortar joints between insulated building blocks and by the presence of concrete columns and beams within the building envelope. These bridges create an easy path for heat transmission and therefore increase air-conditioning loads. In this study, the effects of mortar joints only on cooling and heating loads in a typical two-story villa in Riyadh are investigated using whole building energy analysis. All loads found in the villa, which broadly include ventilation, transmission, solar and internal loads, are considered with schedules based on local lifestyles. The thermal bridging effect of mortar joints is simulated by reducing wall thermal resistance by a percentage that depends on the bridges to wall area ratio (TB area ratio or Amj/Atot) and the nominal thermal insulation thickness (Lins). These percentage reductions are obtained from a correlation developed by using a rigorous 2D dynamic model of heat transmission through walls with mortar joints. The reduction in thermal resistance is achieved through minor reductions in insulation thickness, thereby keeping the thermal mass of the wall essentially unchanged. Results indicate that yearly and monthly cooling loads increase almost linearly with the thermal bridge to wall area ratio. The increase in the villa’s yearly loads varies from about 3% for Amj/Atot = 0.02 to about 11% for Amj/Atot = 0.08. The monthly increase is not uniform over the year and reaches a maximum in August, where it ranges from 5% for Amj/Atot = 0.02 to 15% for Amj/Atot = 0.08. In winter, results show that yearly heating loads are generally very small compared to cooling loads and that heating is only needed in December, January and February, starting from late night to late morning. Monthly heating loads increase with the thermal bridge area ratio; however, the variation is not as linear as observed in cooling loads. The present results highlight the importance of reducing or eliminating thermal bridging effects resulting from mortar joints in walls by maintaining the continuity of the insulation layer in order to reduce energy consumption in air-conditioned buildings.
Highlights
Thermal bridges in the outer walls of buildings are typically caused by mortar joints between insulated building blocks and by concrete structural elements, such as columns, beams and slabs
The thermal bridging effect resulting from mortar joints is simulated, in the present whole building analysis, by reducing the wall thermal resistance (R-value) by a percentage that corresponds to the bridge to wall area ratio and the nominal thickness of the insulation layer
The effects of thermal bridges in insulated building walls on the yearly, monthly and daily cooling and heating loads in a typical villa in Riyadh were investigated by using a commercial whole building energy simulation computer package (HAP)
Summary
Thermal bridges in the outer walls of buildings are typically caused by mortar joints between insulated building blocks and by concrete structural elements, such as columns, beams and slabs. These bridges create an easy path for heat transfer across the building envelope and usually result in increased heating and cooling loads in buildings. The main difficulty in modeling thermal bridges stems from the fact that they create signifiScuastnaitnatbwilitoy -2d01i6m, 8e, 5n6s0ional (2D) effects on heat transmission across building walls in th2eocf a21se of mortar joints and three-dimensional (3D) effects in the case of concrete structural elements. Tuhsiensge wlohaodles bruoiladdinlyg ienncelrugdyeavnaelnytsiilsa.tTiohnesleoalodasd,ssoblraoradlolyadinsc,liundternal loads v(leingthiltast,iopneolopaldes,,esqoulairplmoaednst,,ienttce.r,nwalitlhoatdysp(ilcigahl tssc,hpeedopullee,sebqausipemd eonnt,leotc.a,lwliiftehsttyypleicsa)lasnchdeodfulceosurse heat trbaansesdmoisnslioocnalthlirfeosutyglhest)haendviollfac’osuernsve ehleoaptetr,awnsitmhisthsieonlatthtreorubgehinthgetvhiellad’os menivnealnopt elo, wadithunthdeelratRteiryadh ambiebnetincgonthdeitdioonmsi.nant load under Riyadh ambient conditions
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