Alternate control methods for adsorption heat pumps

•Adsorption system performance at off-design conditions deteriorates with standard controls.•Specific adsorption and bed temperature based controls evaluated.•Alternate controls more suitable for transient source temperature.•Autonomous, off-grid operation with alternate control methods presented. Adsorption heat pumps are often driven by heat sources with variable temperatures. They are typically optimized for operation at design conditions by suitably fixing the cycle time. Cycle time affects cooling duty, COP, and specific cooling capacity of an adsorption system. Although using fixed cycle time is the common approach, it can lead to poor system performance at off-design conditions. Two alternate control methods are investigated here. The first method, adsorbent control, uses the concentration of refrigerant within the bed as the control variable to determine switching from adsorption to desorption. The second method uses the temperature of the adsorbent bed as the control variable. These methods are compared with the fixed cycle time approach and it is found that alternate methods improve COP by 5-50% when the source temperature decreases from the design value. They are also better suited to maintain constant cooling power at higher source temperatures. A thermal switch concept that enables heat pump operation without using electricity is proposed, thus advancing the development of a fully autonomous, off-grid adsorption heat pump.