Two pipes or four pipes fan coil units

Fan Coil Unit is one of the most practical air conditioning equipment that includes one or more fans (Fan) and coil (Air), air filter (Air Filter), drain tray (Drain Tray), and control system. Fan coil passes through coils containing hot water (in winter) and coils containing cold water (in summer) to provide heating and cooling in the environment and circulates hot or cold air inside the building.
Fan coils are used in all seasons to provide heating and cooling needed for residential, office, hotel, and general spaces that need separate temperature regulation.
Fan coils are classified according to their appearance and installation location in the desired location, including ground, wall, ceiling, cast, and channel types.

Click to view brands, models, and different types, find out the price, and buy fan coil units.

Also, fan coils are divided into two categories based on the number of inlets and return pipes in their water distribution system:

1. Two-Pipe Fan Coil Unit
2. Four-Pipe Fan Coil Unit

In the following, each of the two-pipe and four-pipe fan coils will be introduced and the specifications, mode of operation, advantages, and disadvantages of each will be explained in detail.

Two-Pipe Fan Coil Unit

In a two-pipe fan coil, there is only one inlet pipe (HWS / CWS: Hot / Chilled Water Supply) and one return pipe (HWR / CWR: Hot / Chilled Water Return) for water flow, which is connected to a chiller or heating boiler. Available in the package / central engine room and provide heating or cooling of the building.
The two-pipe fan coil system consists of a fan and a water coil. This coil is connected to two inlets and return pipes of the water flow. A cold or hot water coil operates.
The two-pipe fan coil requires a status sensor, which is usually a temperature sensor and is installed on the water inlet to the system to determine how the system works (heating or cooling).

What is the performance of the Two-Pipe Fan Coil Unit?

If two-pipe fan coils are used, the building uses a central chiller to cool the water in the cooling cycle and a heating boiler to heating the water in the heating cycle. Due to the presence of an inlet pipe and a water return pipe, there is only one water cycle in the building's cooling or heating piping system. As a result, the two-pipe fan coil starts working in the building based on the seasonal weather conditions and provides only either heating or cooling, so that if the system is set for heating, it is possible to use the cooling feature at the same time. Does not exist and vice versa. Therefore, the occupants of the building may have to endure temperature fluctuations every year in spring and autumn. The activity of the fan coil in heating or cooling mode is determined by a thermostat installed in the building spaces.
The fan used in a double-tube fan coil has three speeds; low, medium, and high speed, which is adjusted to transfer different amounts of airflow in CFM (fan coil aeration volume in cubic meters per minute).

The exact structure of the two-pipe fan coil can be seen in the image below.

Advantages of two-pipe fan coil

• Excellent performance for residential apartments and hotels
• Less expensive installation compared to a four-pipe fan coil
• Reasonable energy efficiency
• simple design

Disadvantages of two-pipe fan coil

• Impossibility of providing heating and cooling at the same time
• It has to be manually changed from heating mode to cooling mode and vice versa, and this is not only inconvenient but also time-consuming.
• Seasonal fluctuations in temperature may cause inconvenience to residents.

The expected useful life of a two-pipe fan coil is 30 to 35 years. During this time, fan motors or control valve actuators may need to be replaced; however, all equipment is easily accessible through the front panel, and the components used in its structure are generally common and easily accessible.
Two-pipe fan coils have been used for decades and these fan coils are known as a simple and reliable system. Advances in motor technology (eg DC motors), fan speed changes plus the possibility of pumping hot or cold water at variable speeds, and burner and boiler combustion technologies reduce energy consumption at the desired temperature by fan coils. It has become a two-pipe.

Four-Pipe Fan Coil Unit

Usually in spring and autumn, when the temperature is mild, the inside of the building on the south side, which is exposed to sunlight (especially in buildings with glass facades or large windows), the temperature may rise and need cooling. To be felt. At the same time, residents on the opposite side of the building, the so-called behind the sun (north side), may feel the need for heating. In such circumstances, in large and public buildings such as hotels, hospitals, important national centers, luxury residential and office buildings, etc., the use of four-pipe fan coils has an advantage and justification. Each of the four-pipe fan coils, despite having two coils and the possibility of providing cooling and heating at any time, is only able to provide one of the cooling or heating functions.

The four-pipe fan coil includes a fan, cold water cooling coil, hot water heating coil, etc. The four-pipe fan coil circulates the ventilated air inside the building by circulating air on the coils. Four-tube fan coils are designed in such a way that they can perform dehumidification of air due to the possibility of providing simultaneous cooling and heating of air; However, the amount of dehumidification may be limited due to the increase in cold inlet water temperature.

As mentioned before, the four-pipe fan coil has two separate hot and cold water coils, and each coil has its water inlet and returns pipes:

1.  HWS: Hot Water Supply
2.  HWR: Hot Water Return
3.  CWS: Chilled Water Supply
4. CWR: Chilled Water Return

Therefore, in a four-pipe fan coil, there are two inlet and return pipes, and due to the existence of such facilities in the fan coil system, the ability to provide simultaneous heating and cooling is provided, and this type of fan coil can be provided simultaneously at any time. Provide heating or cooling in the building around the clock. The activity of four-pipe fan coils in heating and cooling mode is completely independent, so they can cool part of the building and heat another part at any time.
Unlike two-pipe fan coils, four-pipe fan coils do not require a status change sensor due to the simultaneous availability of hot and cold water.
A four-pipe fan coil can also have a cold water coil and an electric or gas heaoil. As long as the cooling and heating are independent, the fan coil has a four-pipe structure.

What is the performance of the Four-Pipe Fan Coil Unit?

When using a four-pipe fan coil, like a two-pipe fan coil, the building uses a chiller to cool the water in the cooling cycle and a heating boiler to heating the water in the heating cycle. So there are two separate water cycles in the building; one for heating and the other for cooling. In this case, a separate four-pipe fan coil provides the required heating and cooling. The thermostat installed in the building spaces determines whether the heating cycor thecle coil is used in the desired space.
The fan used in the four-pipe coil fan also has three speeds; low, medium, and high speed, which are adjusted to transfer different amounts of airflow in CFM (fan coil aeration volume in cubic meters per minute).

Start-up process in a four-pipe fan coil

The thermostat activates heating or cooling as follows.
The thermostat of the control valve opens the water to the heating or cooling coil and turns on the fan so that the airflow circulates on the heating or cooling coil.
The four-pipe fan coil starts its heating or cooling activity at any time of the day or year based on the set temperature of the thermostat.

The exact structure of a four-pipe fan coil can be seen in the image below.

Advantages of four-pipe fan coil

• Always the availability of hot and cold water and the ability to provide heating and cooling simultaneously by different fan coils in the building
• Possibility to personalize Fan coil activity for the building so that some rooms are cool and others are warm.
• Performance flexibility in a building with diverse heating and cooling needs
• No need to change the position manually
• Easier operation and lower operating costs due to higher efficiency

Disadvantages of four-pipe fan coil

• More expensive installation compared to a two-pipe fan coil
• Double the number of valves, coils, controllers, and piping required from the building engine room to the coil of each four-pipe fan coil
• Calibration is necessary to maintain energy efficiency

Double the probability of leakage in pipes in the long run due to more plumbing

You can also read the article FAN COIL UNIT SELECTION TIPS for more information.

For which buildings is a four-pipe fan coil suitable?

All buildings have unique conditions and the choice of air conditioning system for them must be carefully evaluated in terms of quantity and quality. In many cases, a four-pipe fan coil is a right choice; In other cases, this is not the case. Units in which the possibility of installing a four-pipe fan coil should be seriously considered have the following features:

• Large units such as university campuses, large and luxury residential complexes, large hotels, medical centers, and ...
• Units that most of the spaces have a high latent heat ratio (buildings with high population density such as residential or office buildings)
• Units with minimal occupied space that need cooling in winter (an all-air system with an economizer is more suitable for comfortable conditions of units with crowded design)
• Units that require separate room temperature control.

Final speech

The specialized collection (Damatajhiz) (the first and most reliable authority in the country in the field of building facilities equipment and all air conditioning devices), offers you all kinds of sand filters and hundreds of other products, guaranteeing the originality of the product, valid warranty, and reasonable price. In addition, if you have any questions about choosing and comparing the brands of this product, you can get free advice from the heating equipment experts.

In Iran, the first and most famous specialized group in the field of building installation equipment, air conditioners, and all equipment for swimming pools, saunas, and jacuzzis since 2004, DamaTajhiz is a specialized group. Refer to the time of this group. For more information, you can get advice from the DamaTajhiz Engineering and Production Company experts by calling 021-88822550.

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