Heating and cooling of buildings may be done by water based radiant systems, where pipes areembedded in the concrete slabs between each storey. Hundreds of buildings with such systems arenow being constructed or are in operation in Europe.Because these types of systems are using the building mass for heating and cooling it is oftenquestioned how the systems should be controlled and operated. The present paper presents aparametric study of different control and operation concepts for both cooling (summer) and heating(winter) periods. The study is based on dynamic computer simulations for two climate zones,Wrzburg in Germany and Venice in Italy.The results show that this type of system will not only provide sufficient cooling in summer, but alsocomfortable conditions in winter. It is sufficient to operate the system during the night and use a deadbandbetween 21 C and 23 C room operative temperature. Supply water temperature controlaccording to outside temperature conditions will provide acceptable indoor conditions and low energyconsumption.