In this paper we proposed and tested a new methodology of studying the kinetics of water vapour sorption/desorption under operating conditions typical for isobaric stages of sorption heat pumps. The measurements have been carried out on pellets of composite sorbent SWS-1L (CaCl2 in silica KSK) placed on a metal plate. Temperature of the plate was changed as it takes place in real sorption heat pumps, while the vapour pressure over the sorbent was maintained almost constant (saturation pressures corresponding to the evaporator temperature of 5 degrees C and 10 degrees C and the condenser temperature of 30 degrees C and 35 degrees C). Near-exponential behaviour of water uptake on time was found for most of the experimental runs. Characteristic time T of isobaric adsorption (desorption) was measured for one layer of loose grains having a size between 1.4 mm and 1.6 mm for different heating/cooling scenarios and boundary conditions of an adsorption heat pump. Maximum specific power estimated from the iota-values can exceed 1.0 kW/kg of dry adsorbent, that gives proof to the idea of compact adsorption units for energy transformation with loose SWS grains. (C) 2008 Elsevier Ltd. All rights reserved.