Air conditioning and method of dehumidifier control

An air conditioner comprising a dehumidifier having a plurality of coil portions, coolant supply means and coolant flow control means controlling coolant flow from the coolant supply means and through the coil portions selectively in a stage of a progression of stages of coil portions constituting the active size of the dehumidifier, each stage being of appropriate size to service a respective segment of a total range of sensible and latent cooling loads in a space to be conditioned by said air conditioner, from the peak load to the minimum part load at which the system is required to operate,

• a system control means comprising a sensor which senses magnitude of the sensible load, selects the dehumidifier stage which is compatible with said load and causes coolant control means to control an appropriate rate of coolant flow through the coil portions of said selected stage,
• an air flow fan, means directing air flow from the fan through at least said coil portions containing said coolant flow,
• control logic which, as load reduces through a segment of said load range, causes the velocity of said coolant flow to be reduced progressively through said selected dehumidifier stage until a minimum load condition of said stage is sensed at which point, if load continues to reduce, said control means causes at least one portion of said dehumidifier to be substantially isolated from the coolant flow circuit and thereby deactivated such that the next smaller size of dehumidifier stage is established and said control means causes the flow velocity of said coolant through said next smaller size dehumidifier stage to be increased sufficiently to maintain the same sensible cooling capacity as that of the larger dehumidifier stage immediately before the change-over of the stages, but an increased latent cooling capacity due to the interface temperature of said next smaller stage which carries said increased velocity of coolant flow being colder than that of said larger stage which carried the lower velocity of coolant flow.

An air conditioner comprising a dehumidifier having a plurality of coil portions, coolant supply means and coolant flow control means controlling coolant flow from the coolant supply means and through the coil portions selectively in a stage of a progression of stages of coil portions constituting the active size of the dehumidifier, each stage being of appropriate size to service a respective segment of a total range of sensible and latent cooling loads in a space to be conditioned by said air conditioner, from the peak load to the minimum part load at which the system is required to operate,

• a system control means comprising a sensor which senses magnitude of the sensible load, selects the dehumidifier stage which is compatible with said load and causes coolant control means to control an appropriate rate of coolant flow through the coil portions of said selected stage,
• an air flow fan, means directing air flow from the fan through at least said coil portions containing said coolant flow,
• control logic which, as load reduces through a segment of said load range, causes coolant flow velocity to be reduced in at least one portion o.+-.said selected dehumidifier size stage and increase in one at least other portion of said selected dehumidifier stage which forms also portion of the next smaller stage, in such manner as to provide a gradual transition from one stage to the next whilst maintaining at all times a high velocity of coolant flow in at least one portion of each active stage, and as the load continues to reduce the size of the dehumidifier and the coolant flow are caused by the system control means to progress smoothly through the progression of decreasing dehumidifier stages until the minimum size stage only remains active at which point said system control means preferably maintains air flow volume constant and progressively increases the proportion of outside air.

An air conditioner comprising a dehumidifier,

• said dehumidifier comprising a plurality of coil portions, and means interconnecting the coil portions into a plurality of coolant circuits cooled by circulation of coolant,
• coolant supply means, conduits connecting the dehumidifier and coolant supply means in a coolant circuit, an air flow fan, means coupling the air flow fan and the dehumidifier such that the fan, in operation, selectively causes air flow through the coil portions, at least one sensor downstream of the dehumidifier,
• coolant control means selectively controlling flow of coolant from the supply means through the coil portions, and coupling means coupling said flow control means to the sensor in such a way that at peak load conditions, all coil portions receive coolant flow and as load diminishes from peak conditions through a top range of the part load conditions, coolant flow through at least one of the coil portions is restricted by said flow control means thereby reducing heat transfer in that portion, until the minimum of the said top range of load is reached, at which stage on a further reduction in load said flow control means causes another portion of the coil to be largely isolated from said coolant circuit whilst the coolant flow through the remaining coil portions is increased to maintain the required total cooling capacity, sufficiently to allow for the increased proportion of outside air in the case of a variable air volume system, but with an increase in the ratio of latent cooling to sensible cooling to that required to maintain comfort resulting from the higher heat transfer coefficient on the coolant side due to the higher coolant flow rate which produces a lower temperature at the coil surface, with further reduction in load the process being repeated until the minimum of the next range of load is reached, at which stage a second portion of the coil is isolated from said coolant supply means whilst again the flow through the remaining portions of the coil is increased to maintain the required total cooling capacity but again with the required increase in the ratio of latent cooling to sensible cooling, which is equivalent to the required reduction in the sensible heat ratio;
• the process proceeding through in appropriate number of stages with sufficient overlap between stages to ensure control stability until the required minimum range of part load operation is reached, at which stage only one remaining portion of the coil receives coolant from the coolant supply means by way of the flow control means until the minimum of said minimum range of load is reached at which stage the supply air is progressively increased until the outside air conditions are appropriate for untempered air only to be supplied in the manner of a simple ventilation system.

An air conditioner for conditioning a conditioned space comprising a dehumidifier, said dehumidifier comprising a plurality of coil portions,

• coolant supply means, conduits connecting the dehumidifier and coolant supply means in a coolant circuit, an air flow fan, air flow dampers, means coupling the air floW and the dehumidifier such that the fan, in operation, causes air flow through one at least of the coil portions, at least one sensor downstream of the dehumidifier,
• valves selectively controlling flow of coolant from the supply means through the coil portions, said valves including an electrically operated modulating valve, valve coupling means coupling the valves to the sensor in such a way, that, as load diminishes from peak conditions to part load conditions, coolant flow through a coil portion is restricted by a said valve thereby reducing heat transfer surface of the dehumidifier, but coolant flow through the remainder of the coil portions remains sufficient to maintain dehumidification,
• a further sensor associated with said air flow fan, and air flow speed control means,
• said further sensor being an air flow sensor, a logic circuit, and means so interconnecting said logic circuit, air flow sensor and air flow speed control means that, if air flow speed reduces to an insufficient ventilation velocity pursuant to load reduction, air flow speed is again increased by a preset signal from the control system which, is operative to reset the supply air thermostat to a higher temperature thus decreasing the enthalpy difference across the coil condition curve and causing the air flow dampers associated with said conditioned space to move to more open positions and thus to increase the volume flow rate of the fan to result in an effective ventilation for that space.