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Abstract. In designing an energy-efficient HVAC system, several factors being to play an important role. Among several others, the performance of cooling coil which is embodied through its configuration, directly influence the perfor-mance of HVAC systems and should be considered to be crucial. This paper investigates and recommends design improvements of cooling coil geometry contributes for a central cooling system by using a simulation-optimisation ap-proach. An actual central cooling plant of a commercial building in the hot and dry climate condition is used for experimentation and data collection. An algo-rithm was created in a transient system simulation program to predict the best design. Available experimental results were compared to predicted results to va-lidate the model. Then different models of several new designs for cooling coil were constructed to evaluate the potential of design improvements. Afterwards, the computer model was used to predict how changes in cooling coil geometry would affect the building environment conditions and the energy consumption of the HVAC components. 35162
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Keywords: Cooling coil, Design Optimization, Energy Saving, Comfort enhancement.
1 Introduction The increasing consumption of energy in buildings on heating, ventilating and air-conditioning (HVAC) systems has initiated a great deal of research aiming at energy savings. With the consolidation of the demand for human comfort, HVAC systems have become an unavoidable asset, accounting for almost 50% energy consumed in building and around 10-20% of total energy consumption in developed countries (Pe-rez-Lombard et al. 2008) Because building cooling load varies with the time of the day, an HVAC system must be complemented with an optimum design scheme to reduce the energy consumption by keeping the process variables to their required set-point efficiently in order to maintain comfort under any load conditions. One of the effective ways of achieving energy efficiency is to design cooling coil configurations properly that has motivated us to propose a design procedure which significantly lead to an overall reduction in HVAC energy consumption. Therefore, it is not surprising that the design of energy efficient HVAC components is receiving a lot of attention. (Jabardo et al. 2006) presented results from an investigation carried out with commer-cial air coils of 12.7 mm of tube diameter. They tested coils with different fin pitch and tube rows in order to determine their effect over the thermal performance. (Sekhar and Tan 2009) investigated the performance of an oversized coil at different conditions during the operation stage.the results showed that the humidifying perfor-mance of the oversized coil at the reduced loads during normal operation can be con-siderably enhanced by changing the effective surface area of the coil through a simple mainpulation of the effective number of rows. (Cai et al. 2004) derived a model for a cooling coil based on energyconservation and heat transfer principles.
Catalogue fit-tings of published coil data and experiments on a centralized HVAC pilot plant were conducted and the results showed that the model can achieve good and accurate esti-mation over the entire operating ranges and thus the model can be used to handle real time information.However, no work has been mentioned to optimize the cooling coil geometry by using combined simulation of building dynamic behaviour with a de-tailed operational data of a real tested central HVAC system. The objective of this paper is to minimize the energy consumption of building cooling system by using the design improvements of cooling coil geometry contri-butes while satisfying human comfort and system dynamics. For this purpose, a real-world commercial building, located in a hot and dry climate region, together with its central cooling plant (CCP) is used for experimentation and data collection. The exist-ing central cooling plant was tested continuously to obtain the operation parameters of system components under different conditions. In order to take into account the nonli-near, time varying and building-dependent dynamics of the CCP, a transient simula-tion software package, TRNSYS 16, is used to predict the CCP energy usage. The cooling coil model was developed and coded within the TRNSYS environment.On the basis of the TRNSYS codes and using the real test data, a simulation module for the central cooling plant is developed and embedded in the software. An optimization algorithm which uses an iterative redesign procedureis developed and implemented in the cooling coil module in order to calculate and select its optimum configuration.The simulation results are compared with the monitored data in order to analyze the per-formance and feasibility of the proposed method. To show the effect of proposed approach, the comfort condition index, predicted mean vote (PMV), is studied. 2 Methodology 2.1 Cooling Coil Model The central cooling plant which is installed in the building consist of one water cooled chiller, one cooling tower, one air handling unit (AHU), two chilled water pumps and two condenser water pumps.In this section, a mathematical model is developed for the cooling coil of AHU in order to truly simulate the effects of its operation on the whole system performance: where Qcc is the cooling coil capacity, Fs is the cooling coil core surface area parameter, Aa is face area of the coil, Nr is the number of rows in the cooling coil and Uo and DTm are respectively the overall heat transfer coefficient based on outside surface area of the cooling coil and log-mean temperature difference of the cooling coil and are determined as: ,11iro fohAhU+=η (