Vertical temperature gradients in apartments with hydronic radiator heating Mats Dahlblom 1 , Birgitta Nordquist 1 , Petter Wallentén 2 , Lars-Erik Harderup 2 and Lars Jensen 1 . 1 Building Services, Department of Building and Environmental Technology, LTH, Lund University, Sweden 2 Building Physics, Department of Building and Environmental Technology, LTH, Lund University, Sweden Mats.dahlblom@hvac.lth.se Abstract. A vertical temperature stratification normally exists in rooms during the heating season in cold climates. An expression of the gradient in apartments heated by hydronic radiator heating systems with exhaust ventilation has earlier been developed assuming a dependency of the outdoor temperature. The ex- pression was used by a public real estate owner when re-calculating measured indoor temperature at 2.1 m above floor to 1.2 m above floor representing the occupancy zone and used for individual metering and billing of space heating cost. To validate the suggested expression temperature measurements have been made at four heights in living rooms in apartments built in the 70’s. The heights includes 0.0, 0.1, 1.1 and 1.7 m above floor. The theoretical expression has been compared to the full-scale measurements and in general the expression overestimates the vertical temperature gradient. The measured gradients are generally very low. The thermal comfort in the aspect of vertical temperature gradient is good for the studied period. Keywords: Vertical temperature gradient. Indoor temperature. Residential apartments. Hydronic heating system. 1 Introduction A vertical temperature stratification usually arise indoors. The pattern of this gradient depends during the heating season on the type of heating system, and the characteris- tic of the surrounding surfaces and the type of heat sources inside the room. The type of ventilation system will also influence the temperature distribution in the room. The vertical gradient is important for thermal comfort aspects, a too high temperature difference may negatively affect the thermal comfort experience. The gradient is also important in aspects of controlling the heating system. The feed forward control method used for hydronic heating system that has been applied for many years only account for the outdoor temperature. This may result in too high room temperatures and unnecessary energy use during for example sunny days. It