Abstract: An impact resistant sectional door includes a plurality of interlockingly coupled extruded thermoplastic polymer elongated panels. An elongated panel edge includes a channel and an adjacent edge of an adjacent panel includes a protrusion. The protrusion nests in the channel. Each end cap is rotatingly coupled to an adjacent end cap by a door hinge. The roller is adapted to ride in a door track and to pivot about a rolling plane of the roller. An impact load applied to one or more elongated panels causes one or more of the elongated panels to elastically deform at a spring rate in response to the impact and one or more of the protrusions to slide away from one or more of the channels. The impact resistant sectional door remains substantially undamaged. A method for protecting a sectional door from an impacting force is also described.

Abstract: An impact resistant sectional door includes a plurality of interlockingly coupled extruded thermoplastic polymer elongated panels. An elongated panel edge includes a channel and an adjacent edge of an adjacent panel includes a protrusion. The protrusion nests in the channel. Each end cap is rotatingly coupled to an adjacent end cap by a door hinge. The roller is adapted to ride in a door track and to pivot about a rolling plane of the roller. An impact load applied to one or more elongated panels causes one or more of the elongated panels to elastically deform at a spring rate in response to the impact and one or more of the protrusions to slide away from one or more of the channels. The impact resistant sectional door remains substantially undamaged. A method for protecting a sectional door from an impacting force is also described.

Abstract: An absorption chiller having a protection system for preventing the chilled water in the evaporator tubes from freezing in the event the water flow through the tubes closes down while the machine is running. A sensor in the evaporator heat exchanger is arranged to detect when the water flow through the heat exchanger tubes closes down and signals the machine controller. The controller, in turn, shuts down the machine and opens a valve in a feed line to the evaporator to deliver a high temperature working fluid from another section of the machine to the evaporator to maintain the temperature in the evaporator above that at which the water in the tubes freezes.

Abstract: A feedforward control method for an absorption chiller includes determining the disturbance transfer function, determining the capacity valve transfer function, measuring the actual disturbance, and implementing the feedforward control function in a feedforward controller. The feedforward control function is represented by the ratio of the disturbance transfer function divided by the capacity valve transfer function. The disturbance transfer function and the capacity valve transfer function are measured by applying a known amplitude input perturbation to the disturbance or capacity valve and recording the resulting perturbation in the output leaving chilled water temp. The disturbance transfer function is then the ratio of the delta leaving chilled water temperature divided by the delta change in the disturbance. The capacity transfer function is the ratio of the delta leaving chilled water temperature divided by the delta change in the capacity valve.

Abstract: Data points are determined for an absorption chiller system which relate a position of the capacity valve to the heat input into the system. A continuous curve is determined which estimates the relationship between the position of the capacity valve and the heat input for all of the data points and all the points in between. The slope of this curve is the valve gain. The error for the system is defined as the difference between the setpoint and the leaving chilled water temperature. The leaving chilled water temperature of the system is measured to determine the actual error for the system, after which a linearizing gain derived as a function of the inverse of the valve gain is used in the system control algorithm to linearize the overall valve gain, thereby eliminating capacity valve hunting and producing an improved transient response.

Abstract: An over-concentration control system for use with an absorption machine of the type having either a single, double and triple effect cooling and heating cycle, which uses lithium bromide in solution with water as the operating liquid. The operating liquid being characterized by a concentration indicative of the quantity of lithium bromide dissolved in water, and by a phase diagram having a crystallization boundary that defines the combinations of concentration and temperature which correspond to a condition of saturation in the solution. A sensing means is provided at a predetermined location within the system which is responsive to the depth of said solution for generating a concentration signal indicative of the concentration of the liquid. A temperature sensor is also provided for generating a temperature signal indicative of the temperature of the liquid.