Thesis Abstract

This study develops computer application in Visual basic computer programming language named Computer Application for Determination of Space Cooling Loads, to handle space cooling load estimate for air conditioning in developing country.

To make the developed program more friendly, basic equations relating to the problem are presented, number of tables commonly use and construction materials with their thermal properties are inbuilt in the program. Beside, this project uses number of assumptions proposed by ASHRAE for its calculation of heat gain and cooling load.

Finally space cooling load of an actual building in University of Nigeria Nsukka (i.e. 3rd year classroom in Mechanical Engineering Department) is computed using the developed program and the maximum space loads which are required for the space are 11432 watts sensible and 4120 watts latent.

Thesis Overview

INTRODUCTION

Cooling load calculations are carried out to estimate the required capacity of cooling systems, which can maintain the required conditions in the conditioned space. To estimate the required cooling capacity, one has to have information regarding the design indoor and outdoor conditions, specifications of the building, and specifications of the conditioned space (such as the occupancy, activity level, various appliances and equipment used etc.) and any special requirements of the particular application. For comfort applications, the required indoor conditions are fixed by the criterion of thermal comfort, while for industrial or commercial applications the required indoor conditions are fixed by the particular processes being performed or the products being stored. The design outdoor conditions are chosen based on design dry bulb and coincident wet bulb temperatures for peak summer or winter months for cooling and heating load calculations.

For estimating cooling loads, one has to consider the unsteady state processes, as the peak cooling load occurs during the day time and the outside conditions also vary significantly throughout the day due to solar radiation. In addition, all internal sources add on to the cooling loads and neglecting them would lead to underestimation of the required cooling capacity and the possibility of not being able to maintain the required indoor conditions. Thus cooling load calculations are inherently more complicated as it involves solving unsteady equations with unsteady boundary conditions and internal heat sources.

The total building cooling load consists of heat transferred through the building envelope (walls, roof, floor, windows, doors etc.) and heat generated by occupants, equipment, and lights. The load due to heat transfer through the envelope is regarded as external load, while all other loads are referred to as internal loads.

The percentage of external versus internal load varies with building type, site climate, and building design. The total cooling load on any building consists of both sensible as well as latent load components. The sensible load affects dry bulb temperature, while the latent load affects the moisture content of the conditioned space.

Buildings may be classified as externally loaded and internally loaded. In externally loaded buildings the cooling load on the building is mainly due to heat transfer between the surroundings and the internal conditioned space. Since the surrounding conditions are highly variable in any given day, the cooling load of an externally loaded building varies widely. In internally loaded buildings the cooling load is mainly due to internal heat generating sources such as occupants or appliances or processes. In general the heat generation due to internal heat sources may remain fairly constant, and since the heat transfer from the variable surroundings is much less compared to the internal heat sources, the cooling load of an internally loaded building remains fairly constant. Obviously from energy efficiency and economics points of view, the system design strategy for an externally loaded building should be different from an internally loaded building. Hence, prior knowledge of whether the building is externally loaded or internally loaded is essential for effective system design.

As mentioned before, the total cooling load on a building consists of external as well as internal loads. The external loads consist of heat transfer by conduction through the building walls, roof, floor, doors etc, heat transfer by radiation through fenestration such as windows and skylights. All these are sensible heat transfers. In addition to these the external load also consists of heat transfer due to infiltration, which consists of both sensible as well as latent components.

The heat transfer due to ventilation is not a load on the building but a load on the system. The various internal loads consist of sensible and latent heat transfer due to occupants, products, processes and appliances, sensible heat transfer due to lighting and other equipment. Figure 1.1 below shows various components that constitute the cooling load on a building.

Figure 1.1 Sources of cooling load

1.1 Building survey

Space characteristics and heat load sources. The very foundation of the heat load estimate depends upon very precise survey of the heat load components of the conditioned space. The complete drawings, mechanical and architectural, and field sketches and some time photographs of important aspects are part of good survey. The following physical aspects are worth considering:

1. Orientation of the building. This aspect defines the location of the conditioned space with respect to

• Compass points for sun and wind effects.
• The adjoining permanent structures for shading effects.

1. Use of conditioned space. It may be used for office, or hospital, or some shop, residence.
2. Physical dimension of spaces. Length, width and height are recorded.
3. Ceiling height. Floor-to-floor height or floor to ceiling height may be noted down.
4. Construction materials. The materials of construction used, thickness of walls and roofs, floors and partitions and their location in the building structure are noted.
5. Windows. Size and location of windows, the type of glass used and whether single or double double is to be noted. Also the type of shading on it must be noted.
6. People. The number of people, their duration of occupancy, their nature of work activity and any special features like concentration at any place in the conditioned space must be noted.
7. Lighting. The load in watts at peak, the nature of load incandescent, florescent must be noted.
8. Appliances. Location, rated wattage for the appliances must be considered.
9. Continuous and intermittent operation. Whether the plant has to operate every day of the season or only occasionally as in churches and ballrooms.

1.2 RESEARCH OBJECTIVES

Traditionally, load estimating for air conditioning systems is done either by manual calculation or judgmental estimation based on experience of the air conditioning practitioner. While manual calculation is laborious, estimate based on judgment is liable to error due to gigantic, complex and dynamic nature of present day architectural designs. Load estimating through computer automation is likely to make a positive impact in the dynamic nature of air conditioning applications.

The goals of this project are to:

• Develop a program that can easily calculate space-cooling load of a room.
• Develop a graphic user interface (GUI) – To make the programs that will be developed user-friendly type.
• Calculation of cooling load of an actual building in University of Nigeria Nsukka with the developed program.

 1.3 SCOPE

The work to be carried out can be summarized as follows:

• Develop the program that can calculate space cooling load of a room with computer programming language.

Develop a graphic user interface(GUI) – To make the programs that will be developed user-friendly type, GUI (graphic user interface) will be developed, So that any person with out knowing the detail of the program can run and have the cooling load of a space.