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Categorization and comparison of air-conditioning systems from a technology and performance perspective--case study of an industrial installation.


Separating buildings in thermal zones helps in choosing the air-conditioning system which will be used for their air treatment. An air-conditioning installation is at least trying to regulate the temperature or the ventilation of a space. So, the basic categorization of air-conditioning systems can be done by the criteria of the way and means used to achieve the desired conditions of inner climate in an air-conditioned space. The aim of this paper is to compare four of the most commonly installed/used air-conditioning systems.

The systems referred in this paper are meant to be installed in an industrial facility in the region of Alexandroupolis, in Greece. Consequently, the final conclusions are drawn from the study which was conducted for that building. The complexity of industrial buildings, such as the one examined, is the complexity and variation of spaces. Different kinds of spaces require different kinds of air conditioning and ventilation. For example, production space, where there are many working people as well as machines, is an overburdened environment. Thus, its demands for cooling loads and air renewal are very high.

There are certain stages that must be followed when conducting an air-conditioning study. The first and most basic stage is to calculate the building cooling loads. By doing so, the space specificities and the cooling requirements of each space can be understood. The method used in this study is the ASHRAE Radiant Time Series (RTS) method. The next stage is to perform the necessary studies for each system installed. A brief reference to these studies is made in the main paper ("Case Study--Utilized Application in an Industrial Facility").


As mentioned above, this paper is based on an air-conditioning study for an industrial facility (Vrellas 2009). This study is the planning process in theoretical level as far as concerning the practical application and calculations required for a study from beginning to completion. Some information was taken from two other similar diploma dissertations, with the titles "Air-Conditioning and Ventilation Study of an Industrial Facility" (Seretoudi 2005) and "Heating Study of an Industrial Facility" (Kiriakou 2008). From the latter, valuable information was taken about the way air-conditioning and heating systems operate.

Regarding the theoretical approach of this paper, a number of technical books and manuals were used. For the categorization of the air-conditioning systems made in this paper, the most vital sources were the two volumes for heating and air conditioning written by Sellountos (2002). These two volumes explain much about air conditioning and heating and are an analytical tool for understanding how these systems can be put into categories. The next most vital sources were ASHRAE Handbook--Fundamentals (2001) and ASHRAE Handbook--HVAC Systems and Equipment (2008), which gave much information about system functioning. Some other technical books are those written by Lefas (1992) and Recknagel and Spenger (1980). Their main object is to explain the function of fans, air ducts, air-conditioning units, orifices, and other fundamental elements of air conditioning. Another technical book is that of the air distribution as a basic factor of convenience in air conditioning, written by Daskalopoulos (2004).

The information about the variable refrigerant volume (VRV) system and the energy saving was mainly taken from articles written by two mechanical engineers. The first is 'VRV system: The solution for energy saving' written by Pauleas (2007) and it explains the most basic advantages of this air-conditioning system. The second is 'Air-conditioning systems and energy saving' written by Papakostas (2005) and it makes a brief reference on the ways of energy saving and how the VRV system can be used for this purpose.

Furthermore, certain software was used when conducting the air-conditioning study to give the measurements and the vital data for drawing the conclusions of this paper. The software used was Adapt Manager and Auto fine of the 4M Company. The technical data about the orifices were taken by the Aerogrammi Company (2008).


Categorization of air-conditioning systems is done according to three basic criteria:

1. The level of air treatment

2. The heat transfer conductor

3. The equipment location and the application scope

Categorization of Air-Conditioning Systems by the Air-Treatment Level

Air-conditioning systems, according to the level of treatment provided in the air, can be divided into

a. Ventilation systems which ensure the air renewal in a space.

b. Partial air-conditioning systems which, apart from the air renewal, provide a partial treatment that includes cleaning and heating the air.

c. Complete air-conditioning systems which ensure temperature preservation and humidity of an enclosed space within defined limits and include provisions for cleaning, heating, cooling, humidification, dehumidification, and air renewal.

In any air-conditioning system there can be noticed (Figure 1)

* The air imported to the space (air input--ventilation)

* The air extracted from the space (air output--back ventilation)

* Part of the bleed air/refund, returned in the enclosed space (recirculation)

* The air discharged into the environment

* The air imported from the surrounding environment (fresh outdoor air)

Categorization of Air-Conditioning Systems by the Heat Transfer Conductor

On the basis of the ways and means the final comfort conditions are achieved in the air-conditioned space, four categories of air-conditioning systems can be distinguished:

a. Air Conditioning Using Only Air

In these systems, the conditioned air is produced in the central air-conditioning unit (CAU) and is transported through the network of ducts to air-conditioned rooms. In the CAU, the outside air is drawn from the outer environment and is mixed in the mixing chamber with a portion of the air which returns from the building (recirculation air) and filtered. The next step is the air treatment (e.g., heating, cooling, humidification, dehumidification, depending on the desired conditions.) Eventually the air is driven through a fan and distribution ducts to various rooms. Cooling or heating of the air is achieved with water in the CAU by the air/water exchangers (cooling/heating elements).

b. Air-Conditioning Systems Using Only Water

In these systems the control of the air conditions is done by the air circulation space through appropriate terminals (fan coil units [FCUs]), which use hot or cold water. The FCUs are located in certain areas of the building. Coldwater production takes place in chillers (water cooled or air cooled). Hot water is supplied by boilers. FCUs include a heating or cooling element and a fan used to force the air circulation. Central conditioned air is supplied to areas or zones of the building. This air is recirculated, thus, fresh outside air supply should be treated with a separate way.

c. Air-Conditioning Systems Using Air and Water


In these systems there is a provision of conditioned air and cold or warm water to appropriate terminals, which are located in certain areas of the building. It is therefore necessary to install a network of vents and a water pipe network. In many cases, air flow takes place outside the terminals (e.g. FCUs) with an independent air duct network. These systems combine the features and advantages of both above systems: using only air and only water.

d. Air-Conditioning Units Using Refrigerant and Air

* Split Type Units: The units of this type dominate the market in the area of local HVAC. The vast spread of air conditioning in recent years can be attributed to a type of air-conditioning unit called the heat pump. The heat pump is an air-conditioning system that can be used both for cooling and heating. Its operating principle is that it has the ability to reverse the process of transferring heat from one place to another. Heat pumps are much more energy efficient than other air-conditioning systems. The heat pump can be applied in homes and offices, offering reduced requirements in domestic fuel consumption for heating from 30% to 50%. For air conditioning, cooling or heating of independent or selected rooms in homes, offices, etc., heat pumps are an ideal solution, both in terms of efficacy and low cost.

* Variations of the variable-airflow system: The feature of this system is that the air enters the air-conditioned rooms with constant temperature, but the supply fluctuates depending on the variation of the load of each space. The change in air flow is achieved with air configuration and distribution terminals, which are controlled by a thermostat. The change of supply is usually combined with a variable flow fan or a bypass fan. The fan air supply is regulated by controlling static pressure.

* The refrigerant-air air-conditioning system (VRV): In this system the terminal units operate cooling fluid instead of warm or cold water. Consequently, the terminal units are refrigerant-air exchangers. Each outdoor unit can be connected to a number of indoor units which can be of any type such as flooring, ceiling, wall, etc., and can accept outer fresh air. The outdoor unit, depending on its type, can provide either only heating or only cooling or both simultaneously. In cases of partial load, the power of outdoor unit is adjusted using a frequency converter (inverter) to save energy.

This new system ushered in a new generation of multi-straddling systems, VRV variable volume coolant, where the indoor unit-heat pump can be connected to multiple indoor units through a centralized network of cooling pipes (Figure 2). The most sophisticated VRV systems of current generation have the ability to connect up to 16 indoor units to 1 outdoor unit, with linear control performance through inverter compressors 10%-100% and the ability to extend main pipe up to 100 meters (328 feet) for each indoor unit, with a maximum external-internal unit height difference of 15 meters (50 feet) between indoor units. It can also operate in extreme external environmental conditions from -15[degrees]C (5[degrees]F) when heating to 45[degrees]C (113[degrees]F) when cooling.

Air-Conditioning Systems Categorized by the Equipment Location and the Application Scope

The most widely used categorization for air-conditioning systems is based on criteria of size and scale, that is, correlation of the heat unit (heat engine) location with the air-conditioned space and scope of the system. In terms of the location of the apparatus in the air-conditioned space and scope of the system, the following two main categories of air-conditioning systems can be distinguished:

a. Local Air-Conditioning Systems

Air-conditioning systems which are designed to condition a space (or a part thereof) from within a location or adjacent to it are known as local systems. The main feature of local air-conditioning units is that they can be placed in any room, without the need for a central system. So, they can be easily installed in spaces in which the initial construction had not been prepared. These systems are mainly placed in urban houses. The technical term for them is split type air-conditioning units, because they consist of an outdoor and indoor unit.

b. Central Air-Conditioning System

Air-conditioning systems which are designed to treat various areas of a building from a central location and have identified components for the distribution of air conditioning in rooms are known as central systems. In central air-conditioning systems the central engine room (boiler room, cooling room, and heat exchanger) is located relatively far from the air-conditioned spaces. The terminal units located at each room are connected to the main engine through appropriate conduits (ducts or piping for hot-cold water or refrigerant).


A central air-conditioning installation is comprised of

* The central unit of thermal processing, which can process air, water, or refrigerant fluid

* The pipeline inlet or exhaust heat (pipes or ducts)

* The local units for processing, regulating air flow and diffusion, receiving heat from the space, and some units collecting and removing the 'polluted' air

* The automations and the control systems which are necessary for adjusting the unit according to the needs of each space

Air-Conditioning System Criteria of Choice

Choosing the right air-conditioning installation according to space needs is a topic that concerns many engineers who want to have the "perfect" air-conditioning system for their building. An air-conditioning system cannot be "perfect" by itself. It is the space in which it will be installed that will make it perfect, thus ideal for use. A good analysis of the term space needs would lead to the perception of the "perfect" air-conditioning system. As mentioned above, a basic space need is the air-treatment level. There are cases of facilities that require high air treatment, like laboratories or medical facilities. In such cases there are basic needs for air cleaning, humidification/dehumidification, and many air renewals. In this demanding category we can include hospitals that require all the above in a large scale and with a low noise level. Large scale means the need for a central air-conditioning system. Although hospitals have large spaces for installations, there are private clinics that lack spaces. So, in this case, another important factor is the device dimensions that the system requires for its operation.

Table 1 is a brief categorization of the certain air-conditioning systems examined in this paper. Split type units are suitable for local applications such as houses and offices; they can confront relatively small cooling loads; most of them cannot renew the air, so they offer partial air treatment. Their purchase cost is relatively small, while their operating cost can differ according to use and technology. VRV systems are suitable for small separated spaces, like offices, malls, hotels, etc. It can offer partial and total air treatment, because if we want air renewal an additional device is required (Pavleas 2007). Its purchasing cost is relatively small and it is ideal for confronting partial loads. FCUs offer partial air treatment because they cannot renew the air by themselves. Their function is like that ofa common radiator. Their difference is that they circulate cold water instead of hot water and they work with fans. So, they can not confront partial loads. CAUs guarantee total air treatment, but they need the necessary air duct network in order to lead the treated air inside the building. They can confront large cooling loads, thus they are suitable for large facilities that need central air conditioning.


The following application study is regarding an industrial facility located in Alexandroupolis. The building examined consists of three levels:

The basement, where there are the production space, 249.4 [m.sup.2] (816.93 [ft.sup.2]), the warehouse of raw materials, and the boiler room, along with the cooling room.

The ground floor, where there are the assembly space, 285.6 [m.sup.2] (935 [ft.sup.2]), and the area of 135.9 [m.sup.2] (442.91 [ft.sup.2]) for finished products.

The first floor which houses the sales room, 20.4 [m.sup.2] (65.62 [ft.sup.2]); the accounting room, 19.7 [m.sup.2] (62.34 [ft.sup.2]); the secretary's office, 24.2 [m.sup.2] (78.74 [ft.sup.2]); the manager's office, 30.4 [m.sup.2] (98.43 [ft.sup.2]); the conference room, 52.5 [m.sup.2] (170.6 [ft.sup.2]); and the exhibition room, 69.3 [m.sup.2] (226.38 [ft.sup.2]), with a hall of 25.1 [m.sup.2] (82.02 [ft.sup.2]); and the essential WCs. WCs also exist in the other two levels.

The concept of the study conducted was the air conditioning and the ventilation of the building and the proposal of alternative air-conditioning solutions.

Two solutions of air conditioning were proposed for each of the two kinds of spaces having completely different needs in ventilation and air conditioning. Firstly, the air conditioning of the offices (the first floor) was accomplished either with floor FCUs (for cooling and heating) or with multizone air-conditioning variable-refrigerant-volume system (VRV) respectively. Meanwhile, the air conditioning of the production space (the basement) and the assembly and finished products spaces (ground floor) was accomplished either with two air duct systems with two CAUs or with ceiling FCUs (cooling only) with an independent ventilation system, respectively. In summarizing the above the cases examined are

Case A--Office Spaces:

A1, cooling-heating with floor FCUs ("Air-Conditioning Systems Using Only Water")

A2, cooling-heating with VRV system ("Air-Conditioning Units Using Refrigerant and Air")

Case B--Production, Assembly, Finished Products Spaces:

B1, Ceiling FCUs and independent air duct network (Ventilation) ("Air-Conditioning Systems Using Air and Water")

B2, Air duct network with CAUs ("Air-Conditioning Systems Using Only Water")

In the study conducted, all air-conditioning systems referred above were used ("Categorization of Air-Conditioning Systems by the Heat Transfer Conductor"). Particularly, "Air-Conditioning Systems Using Only Air" is the B2 case, "Air-Conditioning Systems Using Only Water" is the A1 case, "Air-Conditioning Systems Using Air and Water" is the B1 case and "Air-Conditioning Units Using Refrigerant and Air" is the A2 case. In this paper all systems used are central air-conditioning systems.

Furthermore, the following studies were performed (after the calculation of the building cooling loads).

For case A1:

Cooling Studies

* Calculation of pipes in order to choose the chiller, the circulator and the expansion tank for the floor FCUs

Heating Studies

* Calculation of thermal losses in order to choose the boiler, the burner, the fuel tank and the chimney

* Calculation of two pipe system installation in order to choose the circulator and the expansion tank

For case A2:

* Calculation of VRV installation. At this point, certain emphasis should be given to the fact that the VRV system can operate both cooling and heating. Subsequently, the comparison cannot be made unless the case of heating for the floor FCUs is confronted. So, two more studies can be noticed for case A1 regarding heating of the offices.

For case B1:

* Calculation of ceiling FCUs installation

* Calculation of air duct network for space ventilation

For case B2:

* Psychometric calculation in order to choose the CAU

* Calculation of air duct network

The case of heating for the production, assembly and finished products spaces was not confronted. To confront the case of heating for these spaces separate thermal losses calculations should be made. Furthermore, due to the fact that in Case B1 ventilation cannot be supported by the FCUs, an additional air duct network study must be conducted so that all factors are taken into account when comparing the two systems.

The cost of all necessary components for each installation was estimated with the completion of each individual study (cooling loads calculation, psychrometry, air ducts and orifices calculation, pipes calculation for the FCUs, VRV calculation). The final comparison of air-conditioning alternative forms was accomplished with conclusions that had been taking into account the comparative advantages and disadvantages of each case.


All alternative cases of air conditioning proposed in this study had the same calculation basis. Thus, the cooling loads calculation was made at the beginning of the study and had been the same for each of the compared cases (Vrellas 2009).

Case A--Office Spaces

In Case A, if we count on economic results and performance criteria, the choice for cooling and heating respective spaces through the VRV-system solution seems much more preferable than the floor FCUs solution.

* Purchase Cost: After conducting a market research (Vrellas 2009), it can be noted that VRV system has lower purchase cost (three times less) than the floor FCUs installation (Table 2).

Of course, the superiority of the VRV system does not stop here but continues with the low operating cost of the system as shown in the following paragraphs:

* Saving energy required for heat transfer: Extensive research done in Japan on central air-conditioning systems in office buildings showed that 48% of energy consumption is due to air conditioning. From this figure 28% is wasted in the energy transfer of air-conditioned areas, and only 20% is designated for the actual production of the required heating or cooling through air-conditioning devices. A conventional system with chiller and FCUs uses water as heat transfer conductor and has capacity of around 5kcal/kg. On the contrary, the VRV system uses refrigerant R-410A that can transfer 49kcal/kg, that is, it transfers 10 times greater energy than water. Furthermore, the conventional system uses pumps, fan-coils and CAUs for energy transmission. The VRV system uses the same energy with the external compressor units for transporting the coolant into the internal units. It has no pumps or other installations, thus there are no losses created from pipes and air ducts. In doing so, it saves energy in the range of 15%-20% compared to the other conventional systems (Pavleas 2007).

* Avoiding excess heating or cooling: The traditional cooler system has few control levels. For example, a cooler installation of 100 refrigeration tons (RT) usually has 4-8 operating levels. Each time the system requires an increase or decrease in its performance, a big level change of at least 12.5 RT must be done. The VRV system uses high-tech inverter compressors to alter its performance in an analog manner and always according to the desired cooling or heating load. On the contrary to the classic system, the VRV system of 100 RT (consisting of 12 modules) has 252 operating levels, which render its function entirely proportionate as it can respond to load variations of 0.4 RT. Furthermore, the function of traditional internal FCUs is based on the ON/OFF fan or the three way valve. However, VRV units use electronically controlled proportional valves regulating the quantity of the coolant and have three temperature sensors (one for the return of the air and two on the inlet and outlet of the coolant temperature). A microprocessor in the indoor unit calculates the exact performance level related to the load fluctuations. With the analog performance control achieved by the VRV system, space overheating or overcooling is avoided, thus energy is saved (Papakostas 2005).

* High efficiency on partial loads: VRV system allows each building zone to be air conditioned independently, consuming energy only for the rooms in which the unit is functioning. For example, if in an office building a single office should be air conditioned, the VRV system will only operate the indoor unit of this office and the corresponding outdoor unit connected with it, even adjusting performance proportionally according to the load at the site. In this case, the conventional chiller system with fan coils would be energy consuming as it would require the entire installation to function. Thanks to the advanced inverter technology and the use of two compressors per outdoor unit (module), the VRV system has proven to be an air-conditioning system with the lowest power consumption by achieving one of the highest efficiency operating levels range from 20% to 80% of total load demand. For the case of a building that needs air conditioning most of the year, the VRV system excels by far the traditional chiller system (Pavleas 2007).

In Table 3 there is a simple example comparing the behavior of the two systems when they deal with a partial load. The example takes into account a cooling performance of 100 RT (352 kW) and 12 VRV modules of corresponding performance.

So this simple example reveals that the VRV system (when is charged with 50% of the load) compared to the traditional chiller system achieves significant energy saving of around 44%. In fact, the saving achieved by the VRV system is greater, if the linear system response and the direct heat transfer to indoor units are taken into consideration, compared to that of the chiller system, where the FCUs have limited operating levels and greater inertia of the extensive hydraulic network.

* Air renewal with energy saving: In conventional water systems the renewal of air and ventilation is achieved by simple fans, or in some cases massive air-air exchangers are used to recover some of the sensible heat from the discharged air to the incoming fresh air.

* Central control, energy management, and rapid return: VRV systems have central control and energy management systems that can be easily operated by a computer. Thus, they offer greater flexibility, additional control capabilities, and even greater energy saving. The VRV system clearly offers rapid money return to the owner, compared to the traditional systems, due to

** lower operating cost by 40%-50% compared with the traditional cooler system,

** lower maintenance cost due to simpler installation and electronic self-diagnostic fault (no extensive hydraulic systems, pumps, tanks, valves, accessories, and so on), and

** saving of useful spaces, as there are no requirements for extensive engine rooms as in conventional systems.

Table 4 makes a brief comparison of floor FCUs versus the VRV system. The VRV system is superior to floor FCUs in every comparison criteria. The only criteria where the floor FCUs system is better than the VRV is the operating cost for maximum cooling load. In the other criteria (purchase cost, maintenance cost, energy saving, technical criteria, and system life time) the VRV system is preferable for installation than the other system.

Case B--Production, Assembly, Finished Products Spaces

In Case B, the purchase costs of the two compared systems (for cooling production, assembly, and finished products spaces, though heating was not considered) were similar for both installations. Subsequently, the choice was based on technical and convenience criteria.

* Purchase Cost: The purchase costs, after conducting a market search (Vrellas 2009), for the B1 Case (ceiling FCUs with independent ventilation system) and for the B2 Case (air duct in conjunction with CAUs) are similar, as shown (Table 5). Thus, the decision of choosing the best system for this case cannot be made by using this criterion.

* Energy Consumption:

** For B1 case: 11x FCU CWS 15, 15x FCU CWS 13, 9x FCU CWS 06, 1 x chiller of 196 kW, 4x Fyrogenis fans: SF 355, SF 560, SF 500, SF 710. Total installed cooling power = 196 kW (669 kBtu).

** For B2 case: CAU1 of 67.9 kW (50% air recirculation), CAU2 of 46.3 kW (35% air recircula tion), 1xchiller of 131 kW, 2x Fyrogenis fans: SF 560, SF 500. Total installed cooling power = 131 kW (447 kBtu) (Vrellas 2009).

* Air duct network lifetime: It should be noted that the air duct network lifetime in both cases is finite due to debris transport and deposition from the inner and outer environment on the surface of the air ducts. These dust debris cause subsequent reduction of the air duct cross section and increase the pressure drop of the network. Thus, this changes all the data calculations.

* Technical criteria: In the case of ceiling FCUs installation, the most important thing is the accurate application of study, because of the independent ventilation system. There must not be large losses in the air output and changes in the prevailing conditions of the comfort zone. As a result, a smaller number of openings for air flow were placed to avoid air bundle conflict between the air duct network fans and the FCUs. T2 and OK (Table 6 and 7) are the two different orifice types selected (Aerogrammi 2008). This situation resulted in increased air supply at the orifices, which led to faster airflow speed (Table 6) and higher noise levels (Table 7) in the B1 case. Consequently, based on these technical and convenience criteria the best choice is installation B2.

Table 8 makes a brief comparison of Ceiling FCUs with independent ventilation versus air duct network with CAU system. The air duct network with CAU surpasses the ceiling FCUs system in nearly all comparison criteria. More specifically, the air duct network in conjunction with CAU is slightly better regarding the purchase cost and the maintenance cost. This system is much better regarding all technical criteria, because it makes less noise and creates better convenience zones. Its operating costs as well its energy saving prove to be better for large cooling loads. The life time of both systems proves to be the same due to the fact that both systems have air ducts, thus debris make their life to be finite after a long period of use.


Industrial facilities are characterized by much space specificity. Each facility consists of many different spaces which have their own needs for air conditioning, depending on their operation and use. In the study conducted, it is clearly understood that office spaces have different demands on cooling loads from those of production, assembly, finished goods, etc. In spaces with many people, machinery, devices, and lighting, there are increased demands for cooling load and ventilation. Another factor that affects the cooling loads demands are the building materials of each industrial facility, which are likely to vary from space to space. This leads to the conclusion that thermal conductivity changes, and thus recalculation of the heat losses and cooling loads is required. The differences of each space such as workshops, dressing rooms, offices, production rooms, as well as the disparity in size, as large windows, and different heights do not allow us to conduct a single study that involves all parts of the facility. Because of the variations presented in both constructional and operational facility level, each part should be studied individually. However, the cooling loads calculation is at the beginning before any other air-conditioning study. From the above it is clearly concluded that each system is not suitable for every space and this derives from a combination of certain criteria.

The concept of this study is how to choose the most suitable air-conditioning system for each space. In Case A for the office premises, a solution was given through economic and energy criteria in favor of a VRV-system installation over a floor FCUs installation. In Case B for production, assembly, and finished goods premises, technical and convenience criteria gave the most appropriate solution of a CAU with an air duct network. Subsequently, for the air conditioning (cooling-heating) of this industrial facility the combination of Case A2 and Case B2 is proposed. More specifically, the final installation would be VRV system for an office area and air duct network in conjunction with air-conditioning units for production, assembly, and finished goods spaces. While for Case A strictly economic and energy efficiency criteria were followed, for Case B technical and convenience criteria helped in choosing the most suitable air-conditioning system.

Finally, this paper aims to be used as a guide for future studies in industrial air-conditioning systems and to provide basic methods for comparing different air-conditioning systems. Its target audience is new engineers and other industrial HVAC stakeholders that face the problem of choosing the appropriate system for each case. V


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ASHRAE. 2008. ASHRAE Handbook--HVAC Systems and Equipment. Atlanta: ASHRAE.

Daskalopoulos, D. 2004. The air distribution as a basic factor of convenience in air conditioning.

Kiriakou, G. 2008. Heating study of an industrial facility. Diploma thesis, Department of Production and Management Engineering, Democritus University of Thrace--Thrace, Greece.

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Papakostas, T.K. 2005. Air-conditioning systems and energy saving.

Pavleas, T. 2007. VRV system: The solution for energy saving.

Recknagel, H., and E. Spenger. 1980. Heating--Air Conditioning, Giourdas Publications.

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4M. 2009. Adapt Manager, Auto fine.

Vrellas G. Charisis is a production and management engineer of Democritus University of Thrace. Karakatsanis S. Theoklitos is an assistant professor of Democritus University of Thrace (D.U.Th.), Greece.
Table 1. Categorization of Certain Air-Conditioning Systems

AC System       Air      Heat Conductor   Application
             Treatment                       Scope

Split Type    Partial     Refrigerant        Local

VRV           Partial     Refrigerant      Local and
             and Total                      Central

FCU           Partial        Water          Central

Fans          Partial         Air            Local

Air Ducts     Partial         Air           Central

CAU            Total      Refrigerant/      Central

Air Ducts      Total     Air for Ducts      Central
with CAUs                 Refrigerant/
                         Water for the
                          Central Unit

Table 2. Purchase cost for Case A
(1 Euro = 1,22 US Dollars)

Purchase Cost             [euro]     $

Floor FCUs Installation   30.350   37.021
VRV System                11.660   14.223

Table 3. Electric Consumption of the FCUs and the VRV System

Electricity           Operating at             Operating at
Consumption            100% of the              50% of the
                     Load (= 352 kW)          Load (= 176 kW)

Chiller            135 kW (Coefficient      70 kW (Coefficient
                  of Performance = 2.6)    of Performance= 2.5)
Primary and               12 kW                    12 kW
  Circuit Pumps
FCUs (Total)              147kW                    82 kW
VRV                140 kW (Coefficient      46 kW (Coefficient
                  of Performance = 2.52)   of Performance = 3.9)

Table 4. Comparison of Floor FCUs and VRV system

                     Floor FCUs      VRV

Purchase Cost                      [check]
Operating Cost                     [check] *
Maintenance cost                   [check]
Energy Saving                      [check]
Technical Criteria                 [check]
Life Time                          [check]

* VRV is better only for partial load.

Table 5. Purchase cost for Case B
(1 Euro = 1.22 US Dollars)

Purchase Cost               [euro]       $

Ceiling FCUs Installation   53.800    65.593
Air Duct Network            68.700    83.760
Installation B1 (Total)     122.500   149.353
Installation B2             121.500   148.134

Table 6. Air Flow Speed at the Orifices for Both Cases (m/s)

Case   Type   Orifice A   Orifice B   Orifice C

B1      T2      0.58        0.52        0.65
B2      OK      0.08        0.01        0.03

Table 7. Noise Levels at the Orifices for Both Cases (dBA)

Case   Type   Orifice A   Orifice B   Orifice C

B1      T2      37.63       32.9        50.35
B2      OK      24.23        <20         <20

Table 8. Comparison of Ceiling FCUs with Independent
Ventilation System and Air Duct Network with CAU

                          Ceiling         Air Duct
                     FCUs--Ventilation   network-CAU

Purchase Cost                              [check]
Operating Cost                             [check]
Maintenance Cost                           [check]
Energy Saving                              [check]
Technical Criteria                         [check]
Life Time
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Author:Charisis, Vrellas G.; Theoklitos, Karakatsanis S.
Publication:ASHRAE Transactions
Article Type:Report
Geographic Code:4EUGR
Date:Jul 1, 2013
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