Screen reader users, click here to load entire articleThis page uses JavaScript to progressively load the article content as a user scrolls. Screen reader users, click the load entire article button to bypass dynamically loaded article content. Volume 43, Issue 4, April 2011, Pages 805–813 Nonlinear multivariable control and performance analysis of an air-handling unit Received 26 September 2010, Revised 4 November 2010, Accepted 25 November 2010, Available online 3 December 2010To maintain satisfactory comfort conditions in buildings with low energy consumption and operation cost, control of air-conditioner units is required. In this paper, nonlinear control of an air-handling unit (AHU) is investigated and compared for two control approaches: gain scheduling and feedback linearization. A nonlinear multi input–multi output model (MIMO) of an air-handling unit (AHU) is considered. Both indoor temperature and relative humidity are controlled via manipulation of valve positions of air and cold water flow rates.

Using an observer to estimate state variables, a hybrid control system including regulation system for disturbance rejection and nonlinear control system for tracking objectives is designed. Achievement of tracking objectives is investigated for various desired commands of indoor temperature and relative humidity; including a sequence of steps and ramps-steps. According to results, more quick time responses with a bit more overshoot in tracking set-points/paths are achieved by using feedback linearization method (especially for temperature). However, valves position as input control signals are associated with less oscillation (and consequently less energy consumption) when the controller designed based on gain scheduling approach is used. Finally, it is shown through phase portrait of the system that the controller designed based on feedback linearization shows a robust performance in the presence of random uncertainty in model parameters.Keywords; ; ; ; ; Copyright © 2010 Elsevier B.V.

March 2008, Volume 1, Issue 1, pp 53–63Simulation and experimental analysis of a fresh air-handling unit with liquid desiccant sensible and latent heat recoveryResearch ArticleReceived: 20 November 2007Revised: 13 February 2008Accepted: 14 February 2008DOI: 10.1007/s12273-008-8210-0Cite this article as: Xie, X., Jiang, Y., Tang, Y. et al. Build. air conditioning unit with heat AbstractThis article introduces a liquid desiccant fresh air processor. cleaning a central air conditioning unitIts driving force is low-grade heat (heat obtained from 65 – 75°C hot water). 4 ton complete ac unitInside the processor, the air is dehumidified by the evaporative cooling energy of the indoor exhaust air. A four-stage structure is used to increase the efficiency of the combined sensible and latent heat recovery from the exhaust air.

A mathematical model of the fresh air processor was set up using Simulink®. A liquid desiccant fresh air processor was constructed and tested for outside air conditions of 29.1 – 33.6°C, 13.7 – 16.7g/kg humidity ratio, and supply air conditions of 23.6 – 24.2°C, 7.4 – 8.6g/kg humidity ratio. The average measured COPf was 1.6 (cold production divided by latent heat removed) for the range of conditions tested. The corresponding average COPsys of the system including the regenerator was 1.3 (cold production divided by heat input). The detailed operating parameters of each part of the test unit were also measured. The test data was compared with the simulated performance. The characteristic coefficients (such as the volumetric mass transfer coefficient of the air-water evaporative cooling module, etc.) in the mathematical model were modified to calibrate the model output to the measured data. The calibrated simulation model was used to investigate the control strategy of the fresh air processor.

The flow rate of the strong solution into the unit and the number of operation stages may be controlled separately or together to meet different indoor air requirements at different outdoor conditions. The hot water driven liquid desiccant air conditioning system was compared with a typical vapor compression system with an average COP of 4.5; the pump and fan power of the proposed system was 40% of the combined chiller, pump, and fan consumption. We achieved savings of over 30% of the power consumption compared with the traditional system under the designed outdoor air conditions. Volume 56, January 2013, Pages 150–159 Nonlinear dynamics, bifurcation and performance analysis of an air-handling unit: Disturbance rejection via feedback linearizationa b Received 10 August 2012, Revised 23 August 2012, Accepted 18 September 2012, Available online 26 September 2012Nowadays, dynamic analysis of air-conditioner units is essential to achieve satisfactory comfort conditions in buildings with low energy consumption and operation cost.

In this paper, a nonlinear multi input–multi output model (MIMO) of an air-handling unit (AHU) is considered. In the presence of realistic harmonic disturbances, nonlinear dynamics of AHU is investigated. The effect of various thermodynamics and geometrical parameters on limit cycles behaviour of the indoor temperature is investigated. It is observed that the indoor space volume plays as the bifurcation parameter of the system. Decreasing the indoor space volume leads to the occurrence of secondary Hopf (Neimark) bifurcation and consequently the unstable quasi-periodic solution of the indoor temperature. To overcome this problem, a multivariable control strategy based on feedback linearization approach is implemented, in which the air and cold water flow rates are the control inputs while the indoor temperature and relative humidity are the control outputs. It is shown that the designed controller guarantees the comfort indoor conditions by preventing the unstable quasi-periodic responses and improving the limit cycles behaviour.