Energy Analysis of Selected Air Distribution System of Heating, Ventilation and Air Conditioning System: A Case Study of a Pharmaceutical Company

The higher energy consumption causes environmental degradation along with depletion of conventional energy resources. The share of energy consumption in buildings is increasing with urbanization and that ultimately requires effective measures for energy conservation. In buildings, HVAC (Heating Ventilation and Air Conditioning) systems require huge amount of energy. This paper estimates the effects of compression of duct insulation of an HVAC system onthe auxiliary power consumption and temperature of supplied air. A mathematical model is developed in EES (Engineering Equation Solver) to ascertain these effects. The simulation results show that the cooling loss due to the insulation compression is about 14%. By increasing the insulation thickness from 10-40mm at selected points, the heat gain is estimated to decrease from 4.29-2.46kW. In addition to that effects of compression of thermal insulation on GHG (Greenhouse Gas) emission are investigated to reduce from 4.2-2.3kg/ kW. Subsequently, the AC (Auxiliary Consumption) and temperature of the supplied air decrease by 5% and 0.4C, respectively.

has increased the energy consumption in various sectors throughout the world [1]. The building services are an energy intensive sector. The main service in a building application is HVAC system, which is designed to maintain and control the space condition to a comfortable and healthy indoor environment [2]. It is stated that around 40% of the US total energy consumption is in buildings, of which 60% is utilized in and industrial processes. Therefore, optimal design of duct is crucial for energy savings in these sectors which ultimately led to a lower environmental impact and energy costs. Numerous researchers have conducted energy and cost based analyses of different duct systems [8][9][10]. The energy consumption data of building shows that there is a great potential of energy savings through effective thermal protection. The effectiveness of thermal performance of an HVAC system reduces the fuel consumption and environmental pollution as well [9]. The economical and optimal thickness of insulation is a function of design, operation and economic parameters of air distribution system [11]. The economical and optimum insulation thickness considers the initial cost incurred on the insulation plus cost saved in terms of energy savings during the expected lifetime of system [12].
The concept of degree-time is mostly used to calculate the thickness of thermal insulation along with its material.
It is considered as simplest method mostly employed under static conditions. The economic analysis is carried out to determine the insulation thickness for different piping network used to transport oil in an industry. Their analysis was based on non-linear cost functions i.e. initial cost of material and annual energy savings. Rockwool and calcium silicate was used as insulation material, nominal size of piping was chosen between 0.1-0.273mm and working fluid was superheated steam, crude oil and 300 different distillates were considered along with constant convective heat transfer coefficient [13].The computer code is generated by Oztürk, and Karabay [14] to determine the optimum insulation thickness and size of the pipe.

PROBLEM STATEMENT
The function of duct in air distribution system is to transport specific amount of fresh outdoor air, return air, conditioned, supply and exhaust air to or from the conditioned space through space diffusion devices.In

SELECTED AIR DISTRIBUTON SYSTEM
The schematic view of selected air distribution system for the HVAC system under study is illustrated in Fig. 2. The branches of portion B supplies air to Zone-II. The cooling load of Zone-II is greater than Zone-I therefore, conditioned air is supplied with two branches in Zone-II and with one in Zone-I.
The design parameters of the duct are illustrated in Fig. 3 and Table 1 Tables   1-2 and Fig. 3, respectively [23].
The design and operating parameters of air distribution system are obtained from Novartis pharma Pvt. Ltd. with portable digital hygrometer, portable digital anemometer and pressure transducers as given in

ASSUMPTIONS
In order to evaluate the performance of the selected air distribution system, a mathematical model has been developed with the following simplified assumptions: (a) Steady state conditions are considered.
(b) Uniform heat gain occurs throughout the duct.
(c) Temperature of the surrounding of duct is assumed as T a =303K [23,24].

MODEL VALIDATION
The model is validated comparing the simulation results of heat gain with the measured quantities of heat gain, which is obtained from measured values of dry bulb temperature and relative humidity. The dry bulb temperature at the inlet and exit of the duct is measured with temperature gauge. The relative humidity is measured using a digital portable hygrometer. The enthalpy of is obtained using EES property function for mixture of air and water corresponding to measured value psychrometric properties. The measured psychometric properties are given in Table 3.  Table 3 in Equation (2) as shown in Fig. 4. The results show that the heat gain estimated from the developed mathematical model was around 4.29kW while that obtained from the measured values was around 4.52kW. This shows an average difference of less than 5.27% between the measured and model results.

RESULTS AND DISCUSSION
The effects of compression of thermal insulation on heat gain in different portions of SAD (Supply Air Duct), AC of HVAC system, GHG emission and supply air temperature are illustrated in Figs. 5-8.

Effect of Insulation Compression on AC of HVAC System
The effect of compression of thermal insulation at selected points of the duct on auxiliary power consumption of HVAC system is demonstrated in Fig. 6, which indicates that auxiliary power consumption decreases as insulation thickness increases. The HVAC system under study has the cooling capacity of 8.76 tons, whereas it is estimated by that nearly 0.65 kW of auxiliary power needed for one ton refrigeration.
Machine used as an HVAC system [18]. Correspondingly, the total AC of the system under study is around 5.7 kW and total heat gain by the conditioned air is estimated to be 4.29kW at insulation thickness of 10 mm. Thus, the AC corresponding to its cooling loss due to compression of thermal insulation is 0.80kW/ton capacity. The consumption decreases as the insulation thickness increases, the diminution is significant during initial rise in the thickness. The AC may reduce to 0.46kW at 40 mm thickness, which is around 5% of the total AC of HVAC system.

Effect of Insulation Compression on CO 2 Emission
The GHG (CO 2 ) emission varies inversely with insulation thickness as demonstrated in Fig. 7. The variation is more significant during initial rise in the thickness. The CO 2 emission reduces from 4.2-2.3kg/kW by increasing the insulation thickness from 10-40mm at point of compression.

CONCLUSIONS
Following results are concluded from this study: (iii) The energy loss due to heat gain in selected air distribution system could be decreased from 14-8% with optimum thickness i.e. around 6% of cooling load could be saved.
(iv) The AC due to cooling loss in the selected air distribution system can be reduced from 0.80-0.46kW.