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American Institute of Aeronautics and Astronautics

ENERGY EFFICIENCY AND POWER REQUIREMENTS IN HVAC APPLICATIONS

Essam E. Khalil F. ASME, AIAA, ASHRAE, ISIAQ

Professor of Mechanical Engineering, Cairo University, Egypt Khalile1@asme.org, tel.3356080, Fax 3362433

ABSTRACT The recent advances in air conditioning technologies and implementation had led to better performance, development and modifications to air flow pattern in air conditioned rooms’ design for ultimate comfort [1]. Extensive efforts are exerted to adequately predict the air velocity and turbulence intensity distributions in the room and to reduce the energy requirements and noise abatement that ultimately produce quite, energy efficient air conditioning systems with acceptable indoor air quality. The present work summarizes the Egyptian activities in manufacturing, installation, education, research and development. Air Conditioning and Refrigeration industry had flourished in Egypt since the beginning of twentieth century. Back in the fifties of last century, air-conditioned cinemas and theatres were built both at Cairo and Alexandria. Few individual attempts to institutionalize the private HVAC industry were started by, among others, ELTAHRY, and BARAKAT families. Koldair, a government owned manufacturer and contractor dominated the Egyptian market for manufacturing some small Direct expansion (Dx) units, cooling towers and air handling units in the sixties and seventies, Khalil [2],now newly established ,privately owned ,local manufacturers emerged during the past two decades. To design an optimum HVAC airside system that provides comfort and air quality in the air-conditioned spaces with efficient energy consumption is a great challenge. This paper evaluates recent progresses in HVAC airside design for the air-conditioned spaces. The present evaluation study defines the current status, future requirements, and expectations. It has been found that, the experimental investigations should be considered in the new trend of studies, not only to validate the numerical tools, but also to provide a complete database of the airflow characteristics in the air-conditioned spaces. Based on this analysis and the vast development of computers and associated software, artificial intelligent techniques will be a competitive candidate to the experimental and numerical techniques. Finally, research that relates the different designs of the HVAC systems and energy consumption should be more devoted to the optimization of airside design as our expected ultimate target would be to enhance the indoor comfort environment and air quality.

INTRODUCTION The Egyptian community in its path for rapid development is endeavouring to make all necessary and appropriate measures to enhance the efficiency of energy utilization. The energy production, transmission, distribution and utilization efficiency becomes a vital factor and measure of national development. Throughout the nation, energy resources are widely used and consumption rates are in general exceeding the International accepted values. Energy rationalization and audit exercises were developed and monitored by universities and research centres as well as the ministry of Energy through the past two decades with a definitive positive energy reduction and enhanced benefits. To enforce energy efficiency in building services technology, a comprehensive energy efficiency code for residential and commercial buildings is needed. Such a code should be capable of meeting the requirements of both low rise building and high rising buildings in urban, suburban and rural areas and for both the residential and commercial application codes. The following figures show the production of the various HVAC equipment in Egypt and some of the Arab World. These include, but not limited to, split units for residential and commercial applications, as well as fan sections and air handling units. Local manufacture of cooling towers and Dx-packaged units are indicated in table 1.

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0

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1965 1970 1975 1980 1985 1990 1995 2000 2005

Years

KW

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Figure 1: Progress of Locally Manufactured HVAC Units, Khalil [2]

PRODUCT CAPACITY RANGE

Air Handling Units Up to 1500000 m3/h

Condensing Units Up to 120 KW

Fan Sections Up to 150000 m3/h

Packaged/Split Unit Up to 70 KW

Window Units Up to 7 KW

Room Split Units Up to 15 KW

Cooling Towers UP to 700 KW

TABLE 1 Local Manufactured Air Conditioning Units, Khalil [2]

ENERGY EFFICIENCY IN BUILDINGS

Desire and need to develop and construct energy efficiency compliance guidelines are basically dependent on the structure of the market: suppliers/manufacturers as follows: 1. Energy-efficient buildings: This market is defined by new construction and retrofit of existing construction of buildings. Specific elements currently addressed include the building fabric (or envelope) and energy-efficiency of heating, ventilation and cooling equipment. 2. Building control systems design This market is defined as products and systems for building automation and building management. The total global building automation international market is estimated at USD 6 billion. 3. Indoor air quality This market consists of the production and installation of products and systems to provide ventilation of indoor air. The intent is to both provide healthier working conditions and to conserve the envelope of the building, with a minimum impact on the environment. The market suppliers for ventilation systems for indoor air consists of product manufacturers (responsible for the design, manufacture, and testing of products), installation and maintenance firms, and consulting engineers. 4. Indoor thermal environment This market is closely tied to the markets and the suppliers for energy-efficient buildings and indoor air quality. Both economical and comfort elements affect the indoor thermal environment. 5. Indoor acoustical environment

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This market is comprised of all commercial buildings; specifically, of work spaces, such as offices, and learning spaces, Figure 2: Split DX-Air Conditioners Production Figure 3: Fan Section Production Capacity, Khalil 2 by capacity. Khalil2

Figure 4: Air Handling Units Production, Khalil 2

such as schools, and other space where speech intelligibility or privacy are issues. Suppliers include manufacturers of equipment and components comprising the indoor environment and architectural and engineering design firms and consultants. 6. Indoor visual environment The market addressed by this segment includes all commercial indoor spaces, building components (window, room, and surfaces), and lighting sources where the major concern is human occupancy. Suppliers include manufacturers of equipment and components comprising the indoor space and architectural and lighting design firms and consultants.

Energy efficiency directives and measures objectives would be to promote the improvement of energy performance of buildings through cost-effective measures.These also include the convergence of building standards towards those of international states which already have ambitious levels relative to the national level. The proposed measures included the following main items: • Methodology for integrated energy performance standards

FAN SECTION PRODUCTION IN THE ARAB WORLD,UNITS,1998

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SPLIT UNITS PRODUCTION ,1998 , KW Cooling

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AIR HANDLING & FAN SECTIONS UNITS ORODUCTION , 1998

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• Application of these standards on new and existing buildings • Certification schemes for all buildings • Inspection and assessment of boilers/heating and cooling installations

Common methodologies for integrated minimum energy efficiency standards for one country should aim to: 1. Integrate insulation, heating, hot water, cooling, ventilation (incl. natural), built-in lighting, passive and renewable energy installations, indoor climate, building position and orientation and indoor climate. 2. Reflect active solar and Residential heat and electricity, Combined Heating and power (CHP ), daylighting. 3. Give flexibility to designers to meet energy reduction standards in the most cost-effective way 4. Be expressed in simple energy indicators 5. Are adopted by country for different categories of buildings taking into account climatic differences

AIR-CONDITIONED APPLICATIONS

To design an optimum HVAC airside system that provides comfort and air quality in the air-conditioned spaces with efficient energy consumption is a great challenge. Air conditioning identifies the conditioning of air for maintaining specific conditions of temperature, humidity, and minimal dust level inside an enclosed space. The conditions to be maintained are dictated by the need for which the conditioned space is intended and comfort of users. Comfort air conditioning is defined as “the process of treating air to control simultaneously its temperature, humidity, cleanliness, and distribution to meet the comfort requirements of the occupants of the conditioned space” [1]. Air conditioning, therefore, includes the entire heat exchange operation, as well as the regulation of velocity, thermal radiation and quality of air, as well as the removal of foreign particles and vapours [1]. Among the factors affecting HVAC developments and needs are: 1. Comfort levels 2. Air quality 3. Energy efficiency

Indeed, the humans spend great part of their life spans in the enveloped spaces, which can be artificially climatically conditioned. The air-conditioned applications vary according to the functionality and the sensitivity degree of the application. These applications can be divided into residential, commercial, and healthcare applications. The healthcare applications and some sort of the commercial applications have so critical influence on the human health.

LIFE CYCLE COST AND ENERGY EFFICIENCY PREAMBLE

Energy crisis in the early 1970s forced the development of energy conserving strategies in a variety of industries. Sustainability and energy efficiency continue to be strong issues in this time of limited resources. Therefore, the implementation of energy conserving strategies in the HVAC systems must be balanced with occupant comfort and health. Few guidelines gave specific recommendations about the energy saving in the HVAC systems, but these recommendations do not meet all requirements and design varieties. Indeed, in the hot and humid climate the outdoor conditions play important role in the energy consumption. Also the utilization strategies of the conditioned air in the conditioned space play an important role to save the energy consumption. An office building is considered in the present work . Load Characteristics Office buildings usually include both peripheral and interior zone spaces. These zones may be extensively subdivided. Peripheral zones have variable loads because of changing sun position and weather. These zone areas typically require heating in winter and cooling in summer. Interior space conditioning is often by systems that have variable air volume control for low or no-load conditions,ref. [3-8]. Most office buildings are occupied from approximately 8:00 a.m. to 6:00 p.m.; many are occupied by some personnel from as early as 5:30 a.m. to as late as 10:00 p.m. Occupancy varies considerably. In accounting or other sections where clerical work is done, the maximum density is approximately one person per 8 m2 of floor area. Where there are private offices, the density may be as little as one person per 20 m2. The lighting load in an office building constitutes a significant part of the total heat load. Lighting and normal equipment electrical loads average from 20 to 50 W/m2, but may be considerably higher, depending on the type of lighting and the amount of equipment. Buildings equipped with computer systems hardware and other electronic equipment can have electrical loads as high as 50 to 100 W/m2.

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However, this method is expensive, so the suspended ceiling is often used as a return air plenum with the air drawn from the space to above the suspended ceiling through the lights. Miscellaneous allowances (for fan heat, duct heat pickup, duct leakage, and safety factors) should not exceed 12% of the total load. Building shape and orientation are often determined by the building site, but certain variations in these factors can produce increases of 10 to 15% in the refrigeration load. Shape and orientation should, therefore, be carefully analyzed in the early design stages. Figure 5 represent the quick estimation of the cooling load for the typical office buildings. Design Concepts The variety of functions and range of design criteria applicable to office buildings have allowed the use of almost every available air-conditioning system. While multi-storey structures are discussed here, the principles and criteria are similar for all sizes and shapes of office buildings . Attention to detail is extremely important, especially in modular buildings. Each piece of equipment, duct and pipe connections, and the like may be duplicated hundreds of times. Thus, seemingly minor design variations may substantially affect construction and operating costs. In initial design, each component must be analyzed not only as an entity, but also as part of an integrated system. This systems design approach is essential to achieve optimum results. However, owner-occupied buildings may require considerable design flexibility, because the owner will pay for all alterations. The speculative builder can generally charge alterations to tenants. When different tenants occupy different floors, or even parts of the same floor, the degree of design and operation complexity increases to ensure proper environmental comfort conditions to any single tenant, group of tenants, or all tenants at once. This problem is more acute if tenants have seasonal and variable overtime schedules. In small to medium-sized office buildings, air source heat pumps may be chosen. In larger buildings, internal source heat pump systems (water-to-water) are feasible with most types of air conditioning systems. Heat removed from core areas is either rejected to a cooling tower or perimeter circuits. The internal source heat pump can be supplemented by a boiler on extremely cold days or over extended periods of limited occupancy. Removed excess heat may also be stored in hot water tanks. Suspended ceiling return air plenums eliminate sheet metal return air ductwork to reduce floor to-floor height requirements. However, suspended ceiling plenums may increase the difficulty of proper air balancing throughout the building. Where large central units supply multiple floors, shaft space requirements depend on the number of fan rooms. In such cases, one mechanical equipment room usually furnishes air requirements for 8 to 20 floors (above and below for intermediate levels), with an average of 12 floors.

Figure 5: Office buildings; calculated based on quick estimation1

Special Considerations

Office building areas with special ventilation and cooling requirements include elevator machine rooms, electrical and telephone closets, electrical switchgear, plumbing rooms, refrigeration rooms, and mechanical equipment rooms. The high heat loads in some of these rooms may require air conditioning units for spot cooling. In larger buildings having intermediate elevator, mechanical, and electrical machine rooms, it is desirable to have these rooms on the same level or possibly on two levels. The relation between the HVAC system various cost analyses is indicated by Figure 7 that considered owning cost, operating cost and repairing and maintenance cost.

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Owning Costs Analysis Major decisions affecting annual owning and operating costs for the life of the building must generally be made prior to the completion of contract drawings and specifications. To achieve the best performance and economics, comparisons between alternative approaches to handle engineering requirements pertaining to each project must be made in the early stages of architectural design. Oversimplified estimates can lead to substantial errors in evaluating the system. A thorough understanding of the installation costs and accessory requirements must be established. A reasonable estimate of the cost of components may be derived from cost records of recent installations of comparable design or from quotations submitted by manufacturers and contractors.

Figure 6: Building Configuration Figure7: General Procedure of Analysis1

Operating Costs Analysis Operating costs result from the actual operation of the system. They include fuel and electrical costs, wages, supplies, water, material, and maintenance parts and services. ASHRAE Handbook, Fundamentals 2001 outlines how fuel and electrical requirements are estimated. Note that total energy consumption can not generally be multiplied by a per unit energy cost to arrive at annual utility cost. The total cost of electrical energy is usually a combination of several components: energy consumption charges, fuel adjustment charges, special allowances or other adjustments, and demand charges. The actual level of demand represents the peak energy use averaged over a specific period, usually 15, 30, or 60 minutes accordingly; high electrical loads of only a few minutes’ duration may never be recorded at the full instantaneous value. Alternatively, peak demand is recorded as the average of several consecutive short periods (i.e., 5 min out of each hour). The particular method of demand metering and billing is important when load shedding or shifting devices are considered. The portion of the total bill attributed to demand may vary widely, from 0% to as high as 70%.

Maintenance Costs Analysis The quality of maintenance and maintenance supervision can be a major factor in the energy cost of a building. ASHRAE Handbook, Applications [19999] covers the maintenance, maintainability, and reliability of systems, refs. [10-23]. Dohrmann and Alereza 1986 24 obtained maintenance costs and HVAC system information from 342 buildings located in 35 states in the United States. The 1983 costs in U.S. dollars, based on data collected showed a mean HVAC system maintenance cost of 32¢ per square foot per year, with a median cost of 24 ¢/ft2 per year. The age of the building has a statistically significant but minor effect on HVAC maintenance costs. When analyzed by geographic location, the data revealed that location does not significantly affect maintenance costs. Analysis also indicated that building size is not statistically significant in explaining cost variation. The type of maintenance program or service agency, which the building management contracts for, can also have a significant effect on total HVAC maintenance costs. While extensive thorough routine and preventive maintenance programs cost more to administer, they usually produce benefits such as extended equipment life, improved reliability, and less system downtime.

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Case Study Details Data were been collected on various equipment list prices from international and local manufacturers for the equipment required to air condition the present 5 floors commercial building, each floor is being of area of 2500 m2 . The following analysis covers the use of the following systems: Option Description

1 System with Air Cooled Chillers 2 x 400 TR (TR= ton Refrigeration = 3.5 kW). 2 System with Air Cooled Chillers 4 x 200 TR. 3 System with Water Cooled Chillers 2 x 400 TR. 4 System with Water Cooled Chillers 4 x 200 TR. 5 System with Packaged water-cooled DX units and Cooling towers.

RESULTS AND DISCUSSIONS

The cost of the cooling equipment (chillers or packaged units) contributes to about 35 to 81% of the total initial equipment cost for the various options, Figures (8-17). The lowest being that for option 3 (Water Cooled 2 x 400 TR). The maintenance cost is usually calculated in accordance with the ASHRAE formula as stated earlier with appropriate correction for data validation and inflation rates. The relative influence of the maintenance cost does not exceed 9%. The effect of the operating cost of the various systems for Options 1 to 4 is of the same order of magnitude. It is apparent that the water-cooled packaged units are competing options. The total cost for Option 5 is the lowest as its value is 1,188,539 LE (LE is Egyptian Pound = 0.16 US $) for 15 years life span. The cost is nearly 50% of Option 4. Tabulated data obtained from the previous calculations are shown in Figures (8 – 17) for the various options. The cost estimates under Option 4 indicated the highest total annual cost, for water cooled 4x200 TR Chillers and related systems. The initial capital cost was estimated as 6,874,443 LE, giving 8593.1 LE/TR as an average. It is worth noting that the chillers alone contribute to 43.35% of the total initial cost as shown in Figure 14. On the other hand for the same system but 2x400 TR water cooled chillers, 5,850,843 LE and the chillers contribute to 35.90% which is the lowest percentage among the first four options (chillers Options). For these options the corresponding minimum imported items’ cost is 43.09% of the total cost (chillers + building management and control). These options utilize chilled water systems with central compressors and condensing plant whether water or air-cooled.

RECOMMENDATIONS Recommendations are based on the above analyses and the data collected with the prevailing prices, energy, water and maintenance costs at January 2003 in Egypt [2]. It is apparent that water-cooled packaged units are of superior performance in terms of energy consumption and initial costs. Care should be taken when designing such systems to properly consider the outdoor summer climatic conditions and particularly those of the relative humidity and dry bulb temperatures when cooling towers options are considered. Building management systems are highly recommended to monitor, control and to save energy with high durable performance. Water treatment of chilled water and condenser-cooling water systems are found crucial to guarantee long life and good reliable performance.

Figure 8: Initial Cost Analysis of Option 1 Figure 9: Various Costs Analysis of Option 1

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Figure 10: Initial Cost Analysis of Option 2 Figure11: Various Costs Analysis of Option 2

Figure 12: Initial Cost Analysis of Option 3 Figure 13: Various Costs Analysis of Option 3

Figure 14: Initial Cost Analysis of Option 4 Figure 15: Various Costs Analysis of Option 4

Figure 16: Initial Cost Analysis of Option 5 Figure 17: Various Costs Analysis of Option 5

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REFERENCES

[1] ASHRAE Handbook, Fundamentals 2001, ASHRAE, Atlanta, USA. [2] Khalil, E. E., 2003, Technical Assessment of Water-Cooled vs Air-Cooled Systems in Air-Conditioned Commercial

Buildings Applications in Egypt, Cairo University, Egypt, 2003. [3] Liu, J., Aizawa, Y., and Yoshino, H., 2002, Experimental and numerical study on simultaneous temperature and

humidity distributions, ROOMVENT 2002, pp 169-172. [4] Naydenov, K., Pitchurov, G., Langkilde, G., and Melikov, A. K., 2002, Performance of displacement ventilation in

practice, ROOMVENT 2002, pp 483-486. [5] Jacobsen, T. S., Hansen, R., Mathiesen, E., Nielsen, P. V., and Topp, C., 2002, Design method and evaluation of

thermal comfort for mixing and displacement ventilation, ROOMVENT 2002, pp 209-212. [6] Kameel, R., and Khalil, E. E., 2001, Numerical computations of the fluid flow and heat transfer in air-conditioned

spaces, NHTC2001-20084, 35th National Heat Transfer Conference, Anaheim, California. [7] Khalil, E. E., 2000, Computer aided design for comfort in healthy air conditioned spaces, Proceedings of Healthy

Buildings 2000, Vol. 2, pp461-466. [8] Nakamura, Y., and Fujikawa, A., 2002, Evaluation of thermal comfort and energy conservation of an ecological village

office, ROOMVENT 2002, pp 413-416. [9] ASHRAE, Applications, 1999, ASHRAE, Atlanta. [10] Lee, T. G., De Biasio, D., and Santini, A., 1996, Health and the built environment: Indoor air quality, Vital Signs

Curriculum Materials Project, Health and the Built Environment, The University of Calgary, 1996. [11] Rea, W J., 1992, Chemical sensitivity, volume 1. Boca Raton: Lewis Publishers, 1992. [12] ASHRAE standards 55-1981, ASHRAE, Atlanta. [13] Holmberg, S., and Einberg, G., 2002, Flow behaviour in a ventilated room – measurements and simulations,

ROOMVENT 2002, pp197-200. [14] Corgnati, S. P., Fracastoro, G. V., and Perino, M., 2002, Influence of cooling strategies on the air flow pattern in an

office with mixing ventilation, ROOMVENT 2002, pp165-168. [15] Cho, Y. and Awbi, H. B., 2002, Effect of heat source location in a room on the ventilation performance, ROOMVENT

2002, pp445-448. [16] Liu, Y., and Moser, A., 2002, Airborne particle concentration control for an operating room, ROOMVENT 2002,

pp229-232. [17] Kameel, R., and Khalil, E. E., 2002, Prediction of flow, turbulence, heat-transfer and air humidity patterns in operating

theatres, ROOMVENT 2002, pp 69-72. [18] Kameel, R., and Khalil, E. E., 2003, The prediction of airflow regimes in surgical operating theatres: a comparison of

different turbulence models, 41st aerospace sciences meeting and exhibit, Reno, Nevada, AIAA-2003-0859, 2003. [19] Kameel, R. and Khalil, E.E., 2004, Time-Dependent and Three-Dimensional Computational Fluid Dynamics Model,

2nd BSME/ASME International Conference on Thermal Engineering, Bangladesh. [20] Kosonen, R., 2002, Displacement ventilation for room air moisture control in hot and humid climate, ROOMVENT

2002, pp 241-244. [21] Leite, B. C. C., and Tribess, A., Analysis of underfloor air distribution system: Thermal comfort and energy

consumption, ROOMVENT 2002, page 245-248. [22] Collignan, B., Couturier, S., and Akoua, A. A., 2002, Evaluation of ventilation system efficiency using CFD analysis,

ROOMVENT 2002, pp 77-80. [23] Somarathne, S., Kolokotroni, M., and Seymour, M., 2002, A single tool to assess the heat and airflows within an

enclosure: preliminary test, ROOMVENT 2002, pp 85-88. [24] Dohrmann, D. R., and T. Alereza, 1986, Analysis of survey data on HVAC maintenance costs. ASHRAE Transactions

92(2A): pp 550-65.