Memoria Investigaciones en Ingeniería, núm. 26 (2024). pp. 2-37

https://doi.org/10.36561/ING.26.2

ISSN 2301-1092 • ISSN (en línea) 2301-1106 – Universidad de Montevideo, Uruguay

Este es un artículo de acceso abierto distribuido bajo los términos de una licencia de uso y distribución CC BY 4.0. Para ver una

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Memoria Investigaciones en Ingeniería, núm. 26 (2024). pp. 2-37

https://doi.org/10.36561/ING.26.2

ISSN 2301-1092 • ISSN (en línea) 2301-1106 – Universidad de Montevideo, Uruguay

Este es un artículo de acceso abierto distribuido bajo los términos de una licencia de uso y distribución CC BY 4.0.

Para ver una copia de esta licencia visite https://creativecommons.org/licenses/by/4.0/

Revitalizing Comfort: Designing an Energy–Efficient HVAC System for the

University Auditorium

Comodidad revitalizante: Diseño de un Sistema HVAC Energéticamente Eficiente

para el Auditorio Universitario

Revitalizando o Conforto: Projeto de um Sistema HVAC com Eficiência Energética

para o Auditório Universitário

Abdul Samad Khan

(*), Muhammad Ehtesham ul Haque

, Adeel Ahmed Khan

Syed Izhar ul haque

, Syed Obaidullah

, Muhammad Umer Khan

Recibido: 29/07/2023 Aceptado: 13/04/2024

Summary. - Nowadays, thermal comfort is becoming a major problem for people due to increasing global warming

and climatic changes, but it can be resolved by the concept of Heating, Ventilation, and Air Conditioning (HVAC)

systems. The purpose of HVAC is to provide occupants with a comfort zone so that they can feel comfortable according

to their thermal comfort. The core objective of this study is to design and propose an HVAC system as per actual

design conditions for the University Auditorium located in Karachi, Pakistan. A direct Expansion (DX – Type) system

is installed in the Auditorium that has exceeded the lifespan of twenty years, refrigerant R-22 which is currently being

used has been obsolete due to its high GWP (Global Warming Potential) and ODP (Ozone Depletion Potential) values

which are 1810 and 0.05 respectively. To achieve the objective of this study, two approaches are employed. Cooling

Load Temperature Difference (CLTD) method & Hourly Analysis Program (HAP) software. The cooling load

calculated from the CLTD method is 202 kW equivalent to 57.5 Ton of Refrigeration (TR). On the other side, the

cooling load calculated from HAP software is 192.8 kW equivalent to 55 TR. By considering the calculated cooling

load for the University Auditorium, two different HVAC systems are proposed, based on Water cooled and Air-cooled

Vapor Compression Cycle. After this study, engineers will be able to design an HVAC system for any facility as per

design conditions. Also, they can propose different cost-effective and energy-efficient HVAC systems for that

particular space.

Keywords: HVAC; Auditorium; Duct sizing; Cooling load; Piping.

(*) Corresponding Author

Lecturer, Department of Mechanical Engineering, NED University of Engineering and Technology (Pakistan), abdulsamadkhan@neduet.edu.pk,

ORCID iD: https://orcid.org/0009-0005-5449-635X

Assistant Professor. Department of Mechanical Engineering, NED University of Engineering and Technology (Pakistan),,

mehaque@neduet.edu.pk, ORCID iD: https://orcid.org/0000-0001-8751-348X

Assistant Professor. Department of Mechanical Engineering, NED University of Engineering and Technology (Pakistan),

adeelahmedk@neduet.edu.pk, ORCID iD: https://orcid.org/0009-0004-6790-8176

Senior Undergraduate Student. Department of Mechanical Engineering, NED University of Engineering and Technology (Pakistan),

izharmumshad97@hotmail.com, ORCID iD: https://orcid.org/0009-0002-5693-5879

Senior Undergraduate Student. Department of Mechanical Engineering, NED University of Engineering and Technology (Pakistan),

syedobaid2121@gmail.com, ORCID iD: https://orcid.org/0009-0000-0168-6196

Senior Undergraduate Student. Department of Mechanical Engineering, NED University of Engineering and Technology (Pakistan),

engineerumerkhan@gmail.com, ORCID iD: https://orcid.org/0009-0001-7173-6395

A. Samad Khan, M. Ehtesham ul Haque, A. Ahmed Khan, S. Izhar ul haque, S. Obaidullah, M. Umer Khan

Memoria Investigaciones en Ingeniería, núm. 26 (2024). pp. 2-37

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ISSN 2301-1092 • ISSN (en línea) 2301-1106 – Universidad de Montevideo, Uruguay 3

Resumen. - Hoy en día, el confort térmico se está convirtiendo en un gran problema para las personas debido al

aumento del calentamiento global y los cambios climáticos, pero puede ser resuelto por el concepto de sistemas de

Calefacción, Ventilación y Aire Acondicionado (HVAC). El objetivo de HVAC es proporcionar a los ocupantes una

zona de confort para que puedan sentirse cómodos de acuerdo con su confort térmico. El objetivo central de este

estudio es diseñar y proponer un sistema HVAC según las condiciones de diseño reales para el Auditorio Universitario

ubicado en Karachi, Pakistán. En el Auditorio se encuentra instalado un sistema de Expansión Directa (Tipo DX) que

ha superado la vida útil de veinte años, el refrigerante R-22 que se utiliza actualmente ha quedado obsoleto por su

alto GWP (Global Warming Potential) y ODP (Ozone Depletion Potencial) valores que son 1810 y 0.05

respectivamente. Para lograr el objetivo de este estudio, se emplean dos enfoques. Método de diferencia de

temperatura de carga de enfriamiento (CLTD) y software de programa de análisis por hora (HAP). La carga de

refrigeración calculada a partir del método CLTD es de 202 kW equivalente a 57,5 Toneladas de Refrigeración (TR).

Por otro lado, la carga de refrigeración calculada a partir del software HAP es de 192,8 kW equivalente a 55 TR. Al

considerar la carga de enfriamiento calculada para el Auditorio Universitario, se proponen dos sistemas HVAC

diferentes, basados en el ciclo de compresión de vapor enfriado por agua y enfriado por aire. Después de este estudio,

los ingenieros podrán diseñar un sistema HVAC para cualquier instalación según las condiciones de diseño. Además,

pueden proponer diferentes sistemas HVAC rentables y energéticamente eficientes para ese espacio en particular.

Palabras clave: HVAC; Auditorio; Dimensionamiento de ductos; Carga de enfriamiento; Piping.

Resumo. - Hoje em dia, o conforto térmico está a tornar-se um grande problema para as pessoas devido ao aumento

do aquecimento global e às alterações climáticas, mas pode ser resolvido pelo conceito de sistemas de Aquecimento,

Ventilação e Ar Condicionado (HVAC). O objetivo do HVAC é proporcionar aos ocupantes uma zona de conforto

para que se sintam confortáveis de acordo com o seu conforto térmico. O objetivo principal deste estudo é projetar e

propor um sistema HVAC de acordo com as condições reais de projeto para o Auditório Universitário localizado em

Karachi, Paquistão. No Auditório está instalado um sistema de Expansão Direta (Tipo DX) que ultrapassou sua vida

útil de vinte anos. O refrigerante R-22 atualmente utilizado tornou-se obsoleto devido ao seu alto GWP (Potencial de

Aquecimento Global) e ODP (Depleção de Ozônio). Potencial) valores que são 1810 e 0,05 respectivamente. Para

atingir o objetivo deste estudo, duas abordagens são utilizadas. Método de diferença de temperatura de carga de

resfriamento (CLTD) e software de programa de análise horária (HAP). A carga de resfriamento calculada a partir

do método CLTD é de 202 kW equivalente a 57,5 toneladas de refrigeração (TR). Por outro lado, a carga de

refrigeração calculada a partir do software HAP é de 192,8 kW equivalente a 55 TR. Ao considerar a carga de

refrigeração calculada para o Auditório Universitário, são propostos dois sistemas HVAC diferentes, baseados no

ciclo de compressão de vapor refrigerado a água e arrefecido a ar. Após este estudo, os engenheiros serão capazes

de projetar um sistema HVAC para qualquer instalação com base nas condições de projeto. Além disso, eles podem

propor diferentes sistemas HVAC econômicos e energeticamente eficientes para esse espaço específico.

Palavras-chave: AVAC; Público; Dimensionamento de dutos; Carga de resfriamento; Tubulação.

Nomenclature:

A Area

ACH Air Changes per Hour

 Cooling Load Temperature Difference Adjusted

D Diameter

E Efficiency

 Ballast Factor

 Utilization Factor

g Acceleration due to gravity

 Inside Relative Humidity

 Head Loss

 Mixed air enthalpy

 Outside air enthalpy

 Recirculated air enthalpy

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l Length

 Equivalent Length

 Mixed air flowrate

 Outdoor air flowrate

 Recirculated air flowrate

N No. of Occupant

󰇗 Heat Gain

󰇗 Latent Heat Gain by Infiltration

󰇗 Sensible Heat Gain by Infiltration

󰇗 Latent Heat Gain

󰇗 Sensible Heat Gain

󰇗 Latent Heat Gain by Ventilation

󰇗 Sensible Heat Gain by Ventilation

 Temperature below the floor of the Auditorium

 Outside average temperature

 Inside design temperature

 Mixed air temperature

 Outside design temperature

 Supply air temperature

R Thermal Resistance

 Area Outdoor Air rate

 People's Outdoor Air rate

U Thermal Transmittance

V Volume

v Velocity

󰇗 Infiltration Air Flowrate

󰇗 Minimum Outdoor Air Flowrate

󰇗 Outside Air Flowrate

󰇗 Recirculation Air Flowrate

󰇗 Ventilation Air Flowrate

W Wattage

 Inside Humidity Ratio

 Outside Humidity Ratio

Greek Symbols:

ρ Density

 Pressure drop

 Relative Humidity

 Heat gain through wall or roof, at calculation hour 

 Time

 Time interval

 Sol-air temperature at time   

 Constant indoor room temperature

 Conduction transfer function coefficients

Subscripts:

a adjacent space

adj adjusted

 average

 inside

il infiltration latent

is infiltration sensible

M mixed

m minimum outdoor air

n summation index (each summation has as many terms as there are non-negligible values

of coefficients)

 outside

P people

R recirculated

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r recirculation

S supply

vl ventilation latent

vs ventilation sensible

Acronyms

AHU Air Handling Unit

ASHRAE American Society of Heating, Refrigeration & Air Conditioning Engineers

CLF Cooling Load Factor

CLTD Cooling Load Temperature Difference

DX Direct Expansion

EER Energy Efficiency Ratio

GWP Global Warming Potential

HAP Hourly Analysis Program

HFC Hydrofluorocarbons

HVAC Heating Ventilation and Air Conditioning

IAQ Indoor Air Quality

LHG Latent Heat Gain

ODP Ozone Depletion Potential

PET Polyethylene terephthalate

SCL Solar Cooling Load Factor

SEER Seasonal Energy Efficiency Ratio

SHG Sensible Heat Gain

TFM Transfer Function Method

TR Ton of Refrigeration

VCC Vapor Compression Cycle

1. Introduction. - Nowadays, global warming become one of the major issues. If temperature, pressure, and relative

humidity in the ambient atmospheric conditions are observed, there is an uncomfortable situation for the people. There

are many regions in the World where outside ambient conditions are too hot and humid. So, in this situation, people

can’t perform daily life activities and tasks due to their lower thermal comfort. Due to the environmental changes, the

term “climate” comes into play [1]. Pakistan, the country in this World is now tolerating the summer season extending

from April to November. At the global scale, it is significantly observed there was a greater number of hot days as

compared to cold days over the past decade which is evident the frequency of hot and humid days is higher. Also, from

the study conducted by the Pakistan Meteorological Department, a significant increase in heatwave days is observed

which is now a major issue for Pakistan especially the occupants living in different cities due to thermal comfort zones

[2].

Without people's thermal comfort, the occupants can’t feel comfortable, and they can’t perform daily activities. By

considering the mentioned situation and conditions related to human comfort, especially in hot climatic conditions,

scientists developed the concept of an HVAC system which is the most important requirement for people.

The concept of thermal comfort is a state of mind, the essential parameter for the occupant’s comfort zone that provides

satisfaction to the occupant so that one can perform his tasks in a comfortable environment [3-5]. The comfort zone

for an occupant is predicted by relative humidity, air velocity, air & radiant temperatures, clothing insulation, and

metabolic rate [6], it can be defined by a range of operative temperatures that will provide acceptable thermal

conditions for a person's state of mind [7].

An HVAC system is mainly responsible for maintaining the desired IAQ by supplying adequate and acceptable fresh

air [8, 9]. HVAC systems need to be much more efficient as it consumes around 60% of the building’s total energy

consumption [10]. In Pakistan, it is observed that the systems which are installed for human comfort are not designed

on standard conditions. Either the system is overdesigned in that it produces too much cooling effect and is not

economically feasible or the system is under designed so that the occupants are not thermally comfortable [11].

Heat gain is the heat generated by material or equipment in space. HVAC system performance depends on the heat

generated by several pieces of equipment. Heat gain ultimately depends on several factors such as room orientation

relative to solar radiation, electric devices or appliances, wall and roof materials, and the number of occupants present

in a space [12].

Nowadays, due to increasing heat-generating sources and hot & humid climatic conditions, the need for an air

conditioning system is a must. On a domestic level, air conditioning requirement is fulfilled by split air conditioners

[13] but in large buildings, offices, or auditoriums, these are not feasible due to insufficient supply of air flowrate. So,

to resolve this issue, the HVAC system plays an important role to supply adequate fresh air and maintain IAQ within

A. Samad Khan, M. Ehtesham ul Haque, A. Ahmed Khan, S. Izhar ul haque, S. Obaidullah, M. Umer Khan

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the facility. Researchers and designers introduced some software to make energy-efficient systems. But the problem

with this software is it doesn’t completely fit the real-time data and the real-time data is something else that is different

from the built-in values of the software. This is the reason why when researchers design a particular system that is only

based on software and no manual method is used, there must be an error [14].

There are several ways to determine the cooling load of space. Some methods such as CLTD, CLF, SCL, and HAP

(Transfer Function) are being used for cooling load calculation. Each of these methods possesses a different and unique

methodological approach for calculating space cooling load. CLTD and HAP methods will be discussed in this paper

[15].

CLTD is widely used for manual cooling load calculation, as proposed by ASHRAE. This method is used to calculate

space cooling loads in which heat-dissipating devices are present. It is also used to calculate the load due to heat

dissipation from the walls, windows, and roofs in the space [16]. For walls and roofs, CLTD uses the concept of heat

transfer temperature difference but for internal load and windows, it uses CLF [17]. The tabulated CLTD and CLF data

were calculated using the transfer function method, which yielded cooling loads for standard environmental conditions

and zone types. The cooling loads for each component are then summed to obtain the total zone cooling load [18]. The

cooling load of an auditorium space is determined using the CLTD/CLF method, developed as a manual calculation

technique relying on tabulated CLTD and CLF values. These tabulated data were derived using the transfer function

method, providing cooling load estimates for typical environmental conditions and zone types. These loads were

subsequently standardized for easy hourly calculation by designers through normalization. Total zone cooling load is

computed by summing the cooling loads of individual components.

HAP is a powerful computer-based tool developed by Carrier Corporation, designed for consulting engineers, HVAC

contractors, facility engineers, and other professionals involved in the design and analysis of commercial building

HVAC systems. The HAP uses the ASHRAE Transfer Function Method (TFM) for system load calculations and

detailed 8,760 hour-by-hour simulation techniques for energy analysis. The TFM uses transfer functions to model

transient heat transfer equations [19].

The two major functions of HAP are:

1. Estimating load and designing systems

2. Performing Energy and Cost analysis

The HAP software uses a specific built-in program called the “HAP System Design Load” program to calculate, design,

and size the HVAC system. The following are some features of this program:

 Calculates design cooling and heating loads for spaces, zones, and coils in the HVAC system.

 Determines required airflow rates for spaces, zones, and the system.

 Sizes cooling and heating coils.

 Sizes air circulation fans.

 Sizes chillers and boilers.

Some previous case studies were performed by different researchers for cooling load calculation of particular facilities

by different methods and there is a significant result variation after validation by researchers which leads to an

inappropriate design of the HVAC system. ALameen awad Alameen et al. [20] performed a study related to the

designing of an Air Conditioning System for a Sports Hall, with a capacity of 1000 occupants in Sudan by using CLTD

and HAP methods. The results obtained from CLTD and HAP were 116 TR and 103 TR respectively, with a percentage

error of 13%. Khakre et al. [21] conducted a study for cooling load calculation that incorporates the CLTD method for

an evaporative cooling system. The cooling load obtained from the CLTD method was 42.35 TR and from the HAP

program, it was 38.6 TR, contributing an error of 9% which is not allowed to design an accurate HVAC system. These

variations of calculated cooling load from two different methods make it impossible to design an accurate HVAC

system.

Based on cooling load calculation, all previous research studies are focused on designing of HVAC system for any

facility by using the CLTD method and HAP software. The purpose of this research study is to design and propose

different possible HVAC systems for the University Auditorium. A Central Air Conditioning system is already

installed in the Auditorium which is DX – type system. An HVAC system that is currently being operated has exceeded

the lifespan of twenty years and Refrigerant R-22 (Chloro-Difluoro-Methane) is currently being used and has been

obsolete due to high GWP and ODP values. In the existing HVAC system, R-22 enters AHU and cools the air without

the need for secondary refrigerant but it’s a danger zone for occupants if the refrigerant piping leaks for some reason,

it will directly be mixed with cool air and goes into the space where potential health hazards for occupants will be

taken place. So, R-22 (Freon) is not suitable for the cause rather it will be harmful to the occupants. To the knowledge

of the authors, no study is available that proposed new HVAC systems with the refrigerant R-410 (A) for the University

Auditorium. R-410 (A) is a zeotropic and its ODP is zero due to the absence of chlorine. Although it has a higher GWP

than R-22 due to its higher SEER rating, and by reducing the power consumption of the system, it is overall more

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environmentally friendlier than R-22. The novelty of this research work is to fill this research gap. In this paper, the

cooling load of the University Auditorium is calculated via the CLTD method and HAP software. The calculated

cooling load is then used to select new equipment like Chillers for both proposed systems which are water-cooled and

air-cooled. Other equipment like AHU, cooling towers, and pumps are also selected for both systems as per available

data and calculations.

2. The University Auditorium. - The analysis involves the designing of an HVAC system for the University

Auditorium located in Karachi. The Auditorium contains electrical equipment and devices that are dissipating

continuous heat for which proper temperature control is necessary and IAQ must be maintained. The audience or

working staff can’t feel comfortable in such an environment when there is no proper control of inside dry bulb

temperature and relative humidity due to occupants present at that particular time. DX – Type system has already been

installed in the Auditorium and this system provides both air-conditioning as well as ventilation through a ducting

network in which refrigerant directly enters AHU and cools the air without the need for any secondary refrigerant. This

system has exceeded the lifespan of twenty years with the usage of R-22 which is now obsolete due to its high GWP

and ODP values which are 1810 and 0.05 respectively. Montreal and Kyoto Protocols introduced HFCs for the

replacement of chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) because of the low ODP of

HCFCs [22]. However, the qualifying criteria for the selection of refrigerant is not only based on ODP but the potential

alternative refrigerant has been selected based on a high energetic performance and GWP [23, 24]. Table I represents

the specification of components installed in the HVAC system of the University Auditorium.

Table I. Existing HVAC system of the University Auditorium

The occupancy schedule is taken as 6 hours (from 0800 hours to peak time of 1400 hours). The geographical location

of the Auditorium is as: Latitude is 24.9 °N, Longitude is 67.1 °E and Elevation is 51 meters. The orientation of all

four walls of the Auditorium in a cardinal direction is shown in Figure I.

Components

Specifications

Compressor

Company: Carlyle Carrier

Type: Open-Drive Reciprocating

Model: 5H66

Condenser

Shell & Tube Type

Evaporator

DX - Type

Expansion device

Thermal Expansion Valve

Air Handling Unit

 Size: 400 x 300 x 175 cm

 Coil Area: 300 x 170 cm

Cooling Tower

Induced draft Counter Flow

Refrigeration cycle

Vapor Compression

Refrigerant

R-22 (Chloro-Difluoro Methane)

Other capacities

 Compressor: 75 hp

 AHU fan: 15 hp

 Cooling tower pump: 1.5 hp

 Condenser water pump: 9.8 hp