JP7528345B1 - Hot and cold water type latent and sensible separation air conditioning system - Google Patents

Abstract

[Problem] To obtain a highly efficient air conditioning system that uses both an air-cooled chiller and a water-cooled chiller. [Solution] The system comprises a hot and cold water air conditioner (1) that supplies air for conditioning that has been heat exchanged with heat source water to a space to be conditioned, and a heat source device (3) that adjusts the temperature of the heat source water. The heat source device (3) comprises an air-cooled chiller and a water-cooled chiller. The system comprises a first air conditioning group (A) made up of hot and cold water air conditioners (1) that use the heat source water of the air-cooled chiller, and a second air conditioning group (B) made up of hot and cold water air conditioners (1) that use the heat source water of the water-cooled chiller. [Selected Figure] Figure 2

Description

This invention relates to a hot and cold water type latent/sensible separation air conditioning system.

Conventional hot and cold water air conditioning systems were generally of the central type, which sent heat source water from an air-cooled chiller to the air conditioner for air conditioning. There are two types of this type of air conditioning system: a two-pipe system that switches between the heat source water, cold water and hot water, for heating and cooling, and a four-pipe system that sends cold water and hot water at the same time, allowing for simultaneous heating and cooling.

JP 2016-85013 A

An air-cooled chiller alone has poor energy conversion efficiency because it uses air as a heat source, and there was concern that the heat exhaust in summer would induce the heat island effect, and that defrosting in winter would cause uneven air conditioning. Also, in air-conditioned areas that require a mix of cooling and heating operations, a two-pipe system would not be able to handle the situation, making them less comfortable, and a four-pipe system would result in excessive equipment and operating costs.

In order to solve the above problems, the present invention is most primarily characterized by comprising a hot and cold water air conditioner that exchanges heat between heat source water and air for air conditioning to supply the air for air conditioning to the space to be conditioned, a heat source device that adjusts the temperature of the heat source water, and a heat source water circuit that circulates the heat source water between the hot and cold water air conditioner and the heat source device, the heat source device comprising an air-cooled chiller that adjusts the temperature of the heat source water with an air-source heat pump for chiller, and a water-cooled chiller that adjusts the temperature of the heat source water with a water-source heat pump for chiller, a first air conditioning group composed of the hot and cold water air conditioners that exchange heat between the air for air conditioning and the heat source water of the air-cooled chiller to condition the space to be conditioned, and a second air conditioning group composed of the hot and cold water air conditioners that exchange heat between the air for air conditioning and the heat source water of the water-cooled chiller to condition the space to be conditioned.

According to the inventions of claims 1 and 2 , the ratio of the first air conditioning group of air-cooled chillers to the second air conditioning group of water-cooled chillers can be set according to outdoor air conditions such as regional temperature differences and heat utilization such as groundwater, thereby increasing the energy conversion efficiency of the heat source and suppressing exhaust heat problems and uneven air conditioning . In the case of low air conditioning load such as in intermediate seasons, the heat source device can be stopped and independent cooling and heating operation can be performed using only the air-cooled outdoor air conditioning unit, improving energy efficiency and comfort. No need for a four-pipe system, reducing equipment and operating costs. Further energy savings can be achieved by using the heat of the return air in the air source heat pump to exchange heat with the outdoor air and introduce the outdoor air.
According to the invention of claim 3, in low-rise areas, building wastewater or the like can be collected by its own weight and used as a heat source for the water-cooled chiller without using a pump, resulting in energy savings.

1 is a simplified diagram showing an example of installation of the present invention in a building. 1 is a simplified diagram showing the overall configuration of the present invention; FIG. 2 is a simplified explanatory diagram of a heat source device of a first air conditioning group. FIG. 4 is a simplified explanatory diagram of a heat source device of a second air conditioning group. FIG. 2 is a simplified explanatory diagram of a chilled/hot water type air conditioner and an air-cooled outdoor air conditioner. FIG. 1 is a simplified explanatory diagram of an outdoor air-source heat pump.

Figures 1 and 2 show an embodiment of the hot and cold water type latent/sensible separation air conditioning system of the present invention. This latent/sensible separation air conditioning system has a first air conditioning group A and a second air conditioning group B, with the first air conditioning group A installed in the upper to middle areas of a building such as a building, and the second air conditioning group B installed in the lower area of the building.

The first air conditioning group A and the second air conditioning group B are equipped with a hot and cold water air conditioner 1, an air-cooled outdoor air conditioner 2, a heat source device 3, a heat source water circuit 4, and a control device 5. These hot and cold water air conditioners 1, air-cooled outdoor air conditioners 2, and conditioned spaces such as outdoors and indoors are connected by ducts 6 (shown simplified with thick lines) so that conditioned air (outdoor air, return air, supply air, exhaust air) flows.

As shown in Figures 3 and 4, the heat source device 3 includes an air-cooled chiller 12 that adjusts the temperature by cooling or heating the heat source water using a chiller air heat source heat pump 11, and a water-cooled chiller 22 that adjusts the temperature by cooling or heating the heat source water using a chiller water heat source heat pump 21.

The first air conditioning group A is composed of hot and cold water air conditioners 1 that condition the conditioned space by exchanging heat between the conditioned air and the heat source water of an air-cooled chiller 12, and the second air conditioning group B is composed of hot and cold water air conditioners 1 that condition the conditioned space by exchanging heat between the conditioned air and the heat source water of a water-cooled chiller 22.

The air-cooled chiller 12 is equipped with a chiller air source heat pump 11 that exchanges heat with the circulating refrigerant using heat from outside air, a radiator fan 14 that passes outside air (heat source air) through the heat source air heat exchanger 13 of the air source heat pump 11 to exchange heat, and a casing 15 that houses these.

The air-source heat pump 11 is composed of a heat source air heat exchanger 13, a heat source water heat exchanger 16, a compressor 17, an expansion valve 18, a four-way valve 19, and a refrigerant piping circuit 20, and repeats the process of compression, condensation, expansion, and evaporation for the circulating refrigerant, absorbing heat in the refrigerant evaporation process and releasing heat in the refrigerant condensation process for the air and heat source water that exchange heat with this refrigerant.

The heat source air heat exchanger 13 has a group of heat transfer tubes (not shown) inserted into a group of plate fins, and exchanges heat between the air and the refrigerant flowing through the group of heat transfer tubes. The heat source water heat exchanger 16 has a heat transfer plate (not shown) that separates the heat source water and the refrigerant flowing inside, and exchanges heat between the heat source water and the refrigerant through this heat transfer plate. The air-cooled chiller 12 is installed on the roof of a building, etc.

The heat source device 3 of the water-cooled chiller 22 is equipped with a heat storage tank 23 and a protective water heat exchanger 24. The water-cooled chiller 22 is equipped with a chiller water heat source heat pump 21 and a casing 26 that houses it, and exchanges heat between the circulating refrigerant of the water heat source heat pump 21 and the heat storage water of the heat storage tank 23 via the circulating water that flows between the protective water heat exchanger 24 and the heat storage water heat exchanger 25. The heat storage water is derived from building wastewater, sewage, river water, groundwater, etc.

The water heat source heat pump 21 is composed of a water heat exchanger 25 for heat storage water, a water heat exchanger 27 for heat source water, a compressor 28, an expansion valve 29, a four-way valve 30, and a refrigerant piping circuit 31, and repeats the process of compression, condensation, expansion, and evaporation for the circulating refrigerant, absorbing heat in the refrigerant evaporation process and releasing heat in the refrigerant condensation process for the heat source water and circulating water that exchange heat with this refrigerant. The water heat exchangers 25 and 27 are configured in the same way as the water heat exchanger 16 for heat source water of the air-cooled chiller 12.

The circulating water flowing between the heat storage water heat exchanger 25 and the protective water heat exchanger 24 exchanges heat with the heat storage water in the heat storage tank 23 in the protective water heat exchanger 24, and exchanges heat with the circulating refrigerant in the heat storage water heat exchanger 25. The heat storage water that has flowed through the protective water heat exchanger 24 is discharged to the outside.

As shown in FIG. 5, the hot and cold water air conditioner 1 is equipped with a hot and cold water coil 35 that exchanges heat with the air for conditioning using heat source water (hot or cold water) flowing inside, a water volume control valve 36 that adjusts the heat exchange capacity (capacity to cool or heat the air for conditioning) of the hot and cold water coil 35 by increasing or decreasing the flow rate of the heat source water, an air supply fan 37 that supplies the air for conditioning to the space to be air-conditioned, and a casing 38 that houses these. The hot and cold water coil 35 has a similar configuration to the heat source air heat exchanger 13 of the air-cooled chiller 12, and heat source water flows inside. The hot and cold water air conditioner 1 cools or heats the air for conditioning and supplies it to the space to be air-conditioned to condition it.

As shown in Figures 5 and 6, the air-cooled outdoor air-conditioning unit 2 includes an outdoor air-source heat pump 41 that uses the heat of the return air to exchange heat with the outdoor air, an outdoor air-conditioning compressor 47 that constitutes part of the air-source heat pump 41 and adjusts the heat exchange capacity (the capacity to cool or heat the air for air conditioning) of the air-cooled outdoor air-conditioning unit 2 by increasing or decreasing the output of the air-source heat pump 41, a humidifier 51 that humidifies the outdoor air and adjusts the humidity of the outdoor air by increasing or decreasing the amount of humidification, an outdoor air fan 42 that supplies the outdoor air taken in from outside to the hot and cold water air conditioner 1, an exhaust fan 43 that exhausts the return air taken in from the conditioned space to the outdoors, and a casing 44 that houses these.

The air heat source heat pump 41 is composed of an outdoor air heat exchanger 45, an exhaust air heat exchanger 46, an outdoor air conditioning compressor 47, an expansion valve 48, a four-way valve 49, and a refrigerant piping circuit 50, and repeats the processes of compression, condensation, expansion, and evaporation for the circulating refrigerant, absorbing heat in the refrigerant evaporation process and releasing heat in the refrigerant condensation process for the air that exchanges heat with this refrigerant, and the four-way valve 49 switches between cooling and heating operation (cooling and heating of air for air conditioning). The outdoor air heat exchanger 45 and the exhaust air heat exchanger 46 are configured in the same way as the heat source air heat exchanger 13 of the air-cooled chiller 12.

Outside air from outdoors is supplied to the hot and cold water air conditioner 1 via the air-cooled outdoor air conditioner 2. The hot and cold water air conditioner 1 takes in outside air from the air-cooled outdoor air conditioner 2 and air (return air) from the conditioned space, and supplies it to the conditioned space. A portion of the return air is taken in from the conditioned space by the air-cooled outdoor air conditioner 2 and exhausted to the outdoors. The airflow direction of the conditioned air is illustrated by thick dotted arrows. In the illustrated example, the humidifier 51 is a steam type that humidifies air with steam, but it may be an evaporation type or other type.

As shown in FIG. 2, the heat source water circuit 4 includes a forward path 55 and a return path 56 that are made up of water pipes, and a water pump 57 that circulates heat source water through these paths. The heat source water circulates between the heat source device 3 and the hot and cold water coil 35 of the hot and cold water air conditioner 1.

The outward path 55 is provided so that the heat source water is diverted from the heat source device 3 to the hot and cold water coil 35 of the hot and cold water air conditioner 1, and then reaches the return path 56 where it merges and mixes. The return path 56 is provided so that the heat source water that has flowed through the hot and cold water coil 35 of the hot and cold water air conditioner 1 reaches the heat source device 3.

If the heat source water temperature is outside the set water temperature range, the operation of the heat source device 3 is started to cool or heat the water to adjust the temperature to within the set water temperature range. Examples of the temperature range of the heat source water are 7 to 12°C for cold water and 40 to 45°C for hot water, but other temperature ranges are also possible.

As shown in FIG. 5, the control device 5 includes a remote control 61, an outdoor air conditioner cooling control unit 62, an air conditioner cooling control unit 63, an outdoor air conditioner heating control unit 64, an air conditioner heating control unit 65, and an air supply fan control unit 66. The remote control 61 includes switches, input buttons for various settings, a display unit, etc., and has the function of setting the set temperature and set humidity of the conditioned space (return air) and the air conditioning mode of cooling or heating, as well as starting and stopping the air conditioning operation and adjusting the temperature and humidity via the control device 5.

When the conditioned space is outside the set temperature and humidity ranges, the control device 5 controls the operation of the water volume control valve 36, the outdoor conditioning compressor 47, the humidifier 51, and the supply air fan 37 in conjunction with each other to condition the conditioned space to the set temperature and humidity, and when the conditioned space is within the set temperature range, it closes the water volume control valve 36 to stop the flow of heat source water, and controls the operation of the outdoor conditioning compressor 47 and the humidifier 51 to condition the conditioned space to the set temperature and humidity. The control device 5 is composed of a microprocessor, various sensors, and other control devices.

When the heat source water is cold water and the air conditioning mode is cooling, the outdoor air conditioner cooling control unit 62 performs one of the following operations: outdoor air conditioner cooling operation in which the air-cooled outdoor air conditioner 2 cools the outdoor air with sensible heat and supplies the air at the set temperature when the outdoor air temperature exceeds the set temperature and the outdoor air humidity is equal to or lower than the set humidity, outdoor air conditioner cooling blowing operation in which the air-cooled outdoor air conditioner 2 supplies the outdoor air without adjusting the temperature and humidity when the outdoor air temperature is equal to or lower than the set temperature and the outdoor air humidity is equal to or lower than the set humidity, and outdoor air conditioner cooling dehumidification operation in which the air-cooled outdoor air conditioner 2 cools and dehumidifies the outdoor air and supplies the air at the dew point temperature of the set specific enthalpy when the outdoor air humidity exceeds the set humidity. The set specific enthalpy is calculated from the set temperature and the set humidity.

When the heat source water is cold water and the air conditioning mode is cooling, the air conditioner cooling control unit 63 performs one of the following operations: air conditioner cooling operation in which the cold/hot water air conditioner 1 cools the air for conditioning with sensible heat to bring the conditioned space to the set temperature when the return air temperature exceeds the set temperature and the return air humidity is equal to or lower than the set humidity, air conditioner cooling fan operation in which the cold/hot water air conditioner 1 supplies air for conditioning without adjusting the temperature and humidity when the return air temperature is equal to or lower than the set temperature and the return air humidity is equal to or lower than the set humidity, and air conditioner cooling dehumidification operation in which the cold/hot water air conditioner 1 cools and dehumidifies the air for conditioning and supplies it at the dew point temperature of the set specific enthalpy when the return air humidity exceeds the set humidity.

When the heat source water is hot water and the air conditioning mode is heating, the outdoor air conditioner heating control unit 64 performs one of the following operations: outdoor air conditioner heating operation in which the air-cooled outdoor air conditioner 2 heats the outdoor air and supplies it at the set temperature when the outdoor air temperature is below the set temperature and the outdoor air humidity is equal to or higher than the set humidity, outdoor air conditioner heating and humidifying operation in which the humidifier 51 humidifies the outdoor air and supplies it at the set humidity when the outdoor air temperature is equal to or higher than the set temperature and the outdoor air humidity is equal to or higher than the set humidity, outdoor air conditioner heating and blowing operation in which the air-cooled outdoor air conditioner 2 supplies the outdoor air without adjusting its temperature and humidity when the outdoor air temperature is equal to or higher than the set temperature and the outdoor air humidity is equal to or higher than the set humidity, and outdoor air conditioner heating and humidifying operation in which the air-cooled outdoor air conditioner 2 and humidifier 51 heat and humidify the outdoor air and supply it at the set temperature and humidity when the outdoor air temperature is below the set temperature and the outdoor air humidity is less than the set humidity.

When the heat source water is hot water and the air conditioning mode is heating, the air conditioner heating control unit 65 performs either an air conditioner heating operation in which the hot and cold water air conditioner 1 heats the air for air conditioning to bring the conditioned space to the set temperature when the return air temperature is below the set temperature, or an air conditioner heating fan operation in which the hot and cold water air conditioner 1 supplies air for air conditioning without adjusting the temperature and humidity when the return air temperature is above the set temperature.

The supply air fan control unit 66 controls the amount of heat in the supply air per hour by increasing or decreasing the supply air volume of the supply air fan 37, thereby suppressing the difference between the return air temperature (the temperature of the conditioned space) and the set temperature. This makes it possible to perform comfortable air conditioning with little deviation or temperature unevenness between the temperature of the conditioned space and the set temperature by suppressing overshoots and undershoots in the amount of heat in the supply air of the supply air fan 37, even during intermediate periods when the air conditioning load is less than the minimum air conditioning capacity of the chilled/hot water air conditioner 1 or the air-cooled outdoor air conditioner 2.

When air conditioning operation is started with the remote control 61, the air-cooled outdoor air conditioner 2 cools or heats the outside air to the set temperature of the conditioned space, and the air-cooled outdoor air conditioner 2 and humidifier 51 dehumidify or humidify the outside air to the set humidity of the conditioned space, and supply it to the hot and cold water air conditioner 1. The hot and cold water air conditioner 1 cools or heats the air for air conditioning (outside air and return air) to bring the temperature of the conditioned space closer to the set temperature. When the air conditioning load decreases, the supply air volume of the supply air fan 37 is controlled to finely adjust the temperature of the conditioned space. In this way, the hot and cold water air conditioner 1 and the air-cooled outdoor air conditioner 2 can be linked and controlled by a single remote control 61 to perform air conditioning, simplifying operation and reducing equipment costs and labor.

The present invention is not limited to the above-mentioned embodiment. For example, the ratio of the first air conditioning group of air-cooled chillers to the second air conditioning group of water-cooled chillers can be changed, the first air conditioning group A and the second air conditioning group B can be arranged in the upside-down areas from the example shown in the figure, or the areas can be subdivided and installed alternately. Furthermore, a latent/sensible separation air conditioning system can be configured with only one of the first air conditioning group A and the second air conditioning group B, and the number of chilled/hot water air conditioners 1 and air-cooled outdoor air conditioners 2 can be increased or decreased. In addition, the chilled/hot water air conditioner 1 does not have to be an integrated unit of the chilled/hot water coil 35 and the supply air fan 37, but can be a separate type in which the chilled/hot water coil 35 and the supply air fan 37 are separate units connected by a duct, and the combination and installation location can be changed freely.

1: hot and cold water type air conditioner 2: air-cooled outdoor air conditioner 3: heat source device 4: heat source water circuit 5: control device 11: air source heat pump for chiller 12: air-cooled chiller 21: water source heat pump for chiller 22: water-cooled chiller 35: hot and cold water coil 36: water volume control valve 41: air source heat pump for outdoor air conditioning 47: outdoor air conditioning compressor 51: humidifier 62: outdoor air conditioning cooling control unit 63: air conditioner cooling control unit 64: outdoor air conditioning heating control unit 65: air conditioner heating control unit A: first air conditioning group B: second air conditioning group

Claims (3)

The system comprises a hot and cold water type air conditioner (1) that exchanges heat between heat source water and air for air conditioning to supply the air for air conditioning to a space to be conditioned, a heat source device (3) that adjusts the temperature of the heat source water, and a heat source water circuit (4) that circulates the heat source water between the hot and cold water type air conditioner (1) and the heat source device (3),
the heat source device (3) comprises an air-cooled chiller (12) that adjusts the temperature of the heat source water with a chiller air-source heat pump (11), and a water-cooled chiller (22) that adjusts the temperature of the heat source water with a chiller water-source heat pump (21);
a first air conditioning group (A) composed of the chilled/hot water air conditioner (1) that conditions the conditioned space by heat exchange of the air for conditioning with the heat source water of the air-cooled chiller (12), and a second air conditioning group (B) composed of the chilled/hot water air conditioner (1) that conditions the conditioned space by heat exchange of the air for conditioning with the heat source water of the water-cooled chiller (22) ,
The system includes the chilled/hot water air conditioner (1) that takes in outside air and return air as the air for conditioning and supplies the air to the conditioned space, and an air-cooled outdoor air conditioner (2) that supplies the outside air to the chilled/hot water air conditioner (1) and exhausts the return air to the outdoors,
The cold/hot water type air conditioner (1) includes a cold/hot water coil (35) for exchanging heat with the air for conditioning using the heat source water, which is cold water or hot water, circulating inside the cold/hot water coil (35), and a water amount control valve (36) for adjusting the heat exchange capacity of the cold/hot water coil (35) by increasing or decreasing the amount of the heat source water circulating inside the cold/hot water coil (35).
The air-cooled outdoor air-conditioning unit (2) includes an outdoor air-conditioning air-source heat pump (41) that utilizes heat of the return air to exchange heat with the outdoor air, an outdoor air-conditioning compressor (47) that constitutes a part of the outdoor air-conditioning air-source heat pump (41) and adjusts the heat exchange capacity of the air-cooled outdoor air-conditioning unit (2) by increasing or decreasing the output of the outdoor air-conditioning air-source heat pump (41), and a humidifier (51) that humidifies the outdoor air and adjusts the humidity of the outdoor air by increasing or decreasing the amount of humidification,
a control device (5) that, when the conditioned space is outside a set temperature and set humidity range, controls the operation of the water volume control valve (36), the outdoor air conditioning compressor (47), and the humidifier (51) to condition the conditioned space to the set temperature and set humidity, and, when the conditioned space is within the set temperature range, closes the water volume control valve (36) and controls the operation of the outdoor air conditioning compressor (47) and the humidifier (51) to condition the conditioned space to the set temperature and set humidity . The control device (5)
When the heat source water is cold water,
an outdoor air conditioner cooling operation in which, when the outdoor air temperature exceeds the set temperature and the outdoor air humidity is equal to or lower than the set humidity, the outdoor air is cooled by sensible heat using the air-cooled outdoor air conditioner (2) and supplied at the set temperature;
an outdoor air conditioner cooling blowing operation in which the outdoor air is supplied without temperature and humidity adjustment by the air-cooled outdoor air conditioner (2) when the outdoor air temperature is equal to or lower than the set temperature and humidity and the outdoor air humidity is equal to or lower than the set humidity;
In a range where the outdoor air humidity exceeds the set humidity, the outdoor air conditioner (2) cools and dehumidifies the outdoor air and supplies the air at a dew point temperature of a set specific enthalpy.
An outdoor air-conditioning unit cooling control unit (62) that performs any one of the above operations;
When the heat source water is cold water,
an air conditioner cooling operation in which, when the return air temperature exceeds the set temperature and the return air humidity is equal to or lower than the set humidity, the air for air conditioning is cooled by sensible heat using the hot and cold water air conditioner (1) to bring the conditioned space to the set temperature;
an air conditioner cooling blowing operation in which the air for air conditioning is supplied by the hot and cold water air conditioner (1) without adjusting the temperature and humidity when the return air temperature is equal to or lower than the set temperature and humidity and the return air humidity is equal to or lower than the set humidity;
an air conditioner cooling and dehumidifying operation in which, when the return air humidity exceeds the set humidity, the air for air conditioning is cooled and dehumidified by the hot and cold water air conditioner (1) and air is supplied at the dew point temperature of the set specific enthalpy;
An air conditioner cooling control unit (63) that performs any one of the above operations;
When the heat source water is hot water,
an outdoor air conditioner heating operation in which, when the outdoor air temperature is lower than the set temperature and the outdoor air humidity is equal to or higher than the set humidity, the outdoor air is heated by the air-cooled outdoor air conditioner (2) and supplied at the set temperature;
an outdoor air conditioner heating and humidifying operation in which the outdoor air is humidified by the humidifier (51) and supplied at the set humidity when the outdoor air temperature is equal to or higher than the set temperature and the outdoor air humidity is lower than the set humidity;
an outdoor air conditioner heating and blowing operation in which the outdoor air is supplied without temperature and humidity adjustment by the air-cooled outdoor air conditioner (2) when the outdoor air temperature is equal to or higher than the set temperature and humidity and the outdoor air humidity is equal to or higher than the set humidity;
an outdoor air conditioner heating and humidifying operation in which, when the outdoor air temperature is lower than the set temperature and the outdoor air humidity is lower than the set humidity, the outdoor air is heated and humidified by the air-cooled outdoor air conditioner (2) and the humidifier (51) and supplied at the set temperature and the set humidity;
An outdoor air-conditioning unit heating control unit (64) that performs any one of the above operations;
When the heat source water is hot water,
When the return air temperature is in a range below the set temperature, the cooling/hot water type air conditioner (1) heats the air for air conditioning to bring the temperature of the conditioned space to the set temperature.
When the return air temperature is in a range equal to or higher than the set temperature, the hot and cold water type air conditioner (1) supplies the air for air conditioning without adjusting the temperature and humidity of the air conditioner.
An air conditioner heating control unit (65) that performs any one of the above operations;
The hot and cold water type latent and viscous water separation ventilation and air conditioning system according to claim 1 . 3. The hot and cold water type latent/sensible separation air conditioning system according to claim 1 or 2, wherein the first air conditioning group (A) is installed in an upper to middle floor area of a building, and the second air conditioning group (B) is installed in a lower floor area of the building .

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