JP6976586B2 - Air-conditioned indoor environment cleaning system - Google Patents

Description

The present invention relates to an air-conditioned indoor environment cleaning system.

Air conditioners and floor heating systems are becoming widespread as a means of heating and cooling to make the interior a comfortable space. As for floor heating, electric type and hot water type have been known for a long time, and in recent years, underfloor heating and cooling systems using underfloor space have become known. For example, an air pit having a hot air blower, an air flow path connected to the air pit and extending under the floor, and a hot air outlet opened in the floor and blowing air from the air flow path to the floor are provided. There is a floor heating system in which the air blown to the air pit is warmed by a warm air blower and passes through the air flow path to warm the underfloor and the floor surface, and is blown into the room from the warm air outlet to warm the room ( Patent Document 1).
In addition, among the means of purifying the indoor air to make the room comfortable, the technology of applying plaster that adsorbs odors and diatomaceous earth to the walls and ceiling is known as a means of using building materials for interiors. Has been done. In addition to building materials, air purifiers using filters such as HEPA filters are known. However, although filters such as HEPA filters of air purifiers can remove dust and fine particulate matter in the air, formaldehyde, VOCs (toluene, xylene, etc.), which are considered to be one of the causes of sick house syndrome, etc. The volatile organic compounds of formaldehyde could not be cleaned.

Japanese Unexamined Patent Publication No. 11-44435

If the air in the room is clean as well as the air conditioning in the room, a more comfortable living environment can be created. In particular, if volatile organic compounds can be purified, it will prevent sick house syndrome. However, with technologies that use plaster or diatomaceous earth as interior materials, there is a limit to the adsorption capacity that utilizes the material performance of plaster and diatomaceous earth, and adsorbs volatile organic compounds in excess of a predetermined amount. I couldn't get it. In addition, if additional equipment is installed in the room like an air purifier, the equipment must be installed in each room, and the utilization efficiency of the indoor space is reduced by the amount of the equipment, and the air in the entire room is purified. It was difficult to turn into.

The present invention has been made in view of the above-mentioned current situation, and an object of the present invention is to provide an air-conditioned indoor environment cleaning system capable of decomposing and cleaning volatile organic compounds.

The air-conditioned indoor environment cleaning system of the present invention is provided in a living room or behind the ceiling, and is provided with a heat exchanger that sucks and heats or cools the air in the living room, and is provided under the floor or behind the ceiling of the living room to exchange heat. A chamber box in which heated or cooled air is guided through a vessel, a duct in which one end is connected to the chamber box to guide the air heated or cooled by the heat exchanger, and air guided by the duct. An air-conditioned indoor environment cleaning system including an air outlet for discharging air into a living room, wherein an air filter is provided in at least one of the heat exchanger, the chamber box, the duct, and the outlet. A water-based coating agent containing tolumarin powder and cupric tartrate water and an additive that decomposes volatile organic compounds by the circulating energy of air or a temperature change was applied to the surface of the air filter. It is characterized by.

Further, the air-conditioned indoor environment cleaning system of the present invention is provided in a living room or behind the ceiling, and is provided with a heat exchanger that sucks and heats or cools the air in the living room, and is provided under the floor or behind the ceiling of the living room. A chamber box in which heated or cooled air is guided through a heat exchanger, a duct in which one end is connected to the chamber box to guide the air heated or cooled by the heat exchanger, and a duct guided by the duct. An air-conditioned indoor environment cleaning system including an outlet for discharging the air to a living room, in which a tourmaline is provided on the inner surface of at least one of the heat exchanger, the chamber box, the duct and the outlet. It is characterized by being coated with an aqueous coating agent containing powder and cupric tartrate water, and containing an additive that decomposes volatile organic compounds by circulating energy of air or a temperature change.

Further, the air-conditioned indoor environment cleaning system of the present invention is provided in a living room or behind the ceiling, and is provided with a heat exchanger that sucks air in the living room to heat or cool it, and is provided under the floor or behind the ceiling of the living room. A chamber box in which heated or cooled air is guided through a heat exchanger, a duct in which one end is connected to the chamber box and for guiding air heated or cooled by the heat exchanger, and a duct guided by the duct. An air-conditioned indoor environment cleaning system including an outlet for discharging the air to the living room, wherein the outlet is provided near the wall of the living room, and the air discharged from the outlet is provided. At least one of the surface of the wall receiving the air flow and the surface of the ceiling connected to the wall contains tolumarin powder and cupric tartrate water, and decomposes volatile organic compounds by circulating energy of air or temperature change. It is characterized in that an aqueous coating agent containing the additive is applied, or a calcium hydroxide-based paint containing the additive is applied.

Further, in the air-conditioned indoor environment cleaning system of the present invention, it is preferable to provide a booster fan in the vicinity of the outlet, and the heat exchanger, the chamber box, the duct and the outlet are provided. In the case of a building having living rooms on a plurality of floors, it is preferable to prepare for the living rooms on each floor.

According to the air-conditioned indoor environment cleaning system of the present invention, volatile organic compounds can be decomposed and cleaned, and as a result, an air-conditioned indoor environment that can be used as a countermeasure against sick house syndrome and a heat shock with a small indoor temperature difference. A cleaning system can be provided.

It is a partial cut perspective view of one Embodiment of the air-conditioning type indoor environment cleaning system of this invention. It is a partial cut perspective view of another embodiment of the air-conditioning type indoor environment cleaning system of this invention.

Hereinafter, embodiments of the air-conditioned indoor environment cleaning system of the present invention will be specifically described with reference to the drawings.
The air-conditioned indoor environment cleaning system 10 of the embodiment of the present invention shown in the partially cut perspective view of FIG. 1 includes a heat exchanger 11, a chamber box 12, a duct 13, and an outlet 14.

The heat exchanger 11 is provided in the living room 1. The heat exchanger 11 is connected to, for example, a heat source 15 provided outdoors to exchange heat. The heat source 15 is, for example, a heat pump unit. The heat exchanger 11 has a built-in fan and sucks the air in the living room 1 to heat (in the case of heating) or cool (in the case of cooling), and adjust the humidity as necessary. Further, the air-conditioned indoor environment cleaning system 10 may be a system of only heating (heating) or a system of only cooling (cooling).

The chamber box 12 is generally provided under the floor directly below the heat exchanger 11. However, it is not limited to directly under the heat exchanger 11, and when the heat exchanger 21 is provided in the attic as in another embodiment shown in FIG. 2, the chamber box 22 exchanges heat. It can be installed behind the ceiling together with the vessel 21. The chamber box 12 of FIG. 1 is connected to the heat exchanger 11 and once collects the warm air heated by the heat exchanger 11 or the cooled cold air and distributes them to various places to improve the thermal efficiency of heating or cooling. There is.

Under the floor of the living room 1, one end of the duct 13 is connected to the chamber box 12, and the other end is open to the underfloor space. Warm or cold air is discharged from the chamber box 12 through the duct 13 and from the other end of the duct 13 into the underfloor space. The underfloor space is heated by the warm air discharged from the other end of the duct 13, or the underfloor space is cooled by the cold air. At the same time, the underfloor space is heated or cooled by radiation from the surface of the duct 13 between one end and the other end of the duct 13.
By heating or cooling the underfloor space, the floor surface is heated or cooled, and it also has the effect of floor heating or floor cooling.

An outlet 14 penetrating the underfloor and above the floor is provided preferably near the wall of the living room 1, and warm air or chilled air in the underfloor space is discharged to the living room 1 from the outlet 14. In the air-conditioned indoor environment cleaning system of the present embodiment, not only the floor heating or floor cooling described above, but also the indoor space is heated or cooled by hot air or cold air directly guided on the floor.
The air in the living room 1 is sucked into the heat exchanger 11, and heating or cooling is continued by circulating the air using the equipment of the air-conditioned indoor environment cleaning system.

The air-conditioned indoor environment cleaning system 10 of the present embodiment has an operation panel 16 on one surface of the wall 18, and a remote controller 17 is detachably attached.
Further, if necessary, a booster fan 19 can be provided in the vicinity of the outlet 14, or under the floor directly below the outlet 14 in the illustrated embodiment. The booster fan 19 is for increasing the air flow from the outlet 14.

The air-conditioned indoor environment cleaning system 10 of the present embodiment can be applied not only when the building is a one-story building, but also when the building has a plurality of floors, the heat exchanger 11 and the chamber box 12 are used. , Duct 13 and outlet 14 can be provided corresponding to the living room on each floor.

The air-conditioned indoor environment cleaning system 10 shown in FIG. 1 is an example in which the heat exchanger 11 is provided in the living room and the chamber box 12 is provided under the floor. , Heat exchangers and chamber boxes can also be installed in the roof.

An air-conditioned indoor environment cleaning system 20 according to another embodiment of the present invention, in which a heat exchanger and a chamber box are provided in the attic, is shown in FIG. 2 with a partially cut perspective view. The air-conditioned indoor environment cleaning system 20 of FIG. 2 includes a heat exchanger 21, a chamber box 22, a duct 23, and an outlet 24. The air-conditioned indoor environment cleaning system 20 of the present embodiment shown in FIG. 2 is an example in which the heat exchanger 21 and the chamber box 22 are provided in the attic.

The heat exchanger 21 is connected to a heat source (not shown) provided outdoors to exchange heat. The heat exchanger 21 has a built-in fan and sucks the air in the living room 2 to heat (in the case of heating) or cool (in the case of cooling), and adjust the humidity as necessary. Further, the air-conditioned indoor environment cleaning system 20 may be a heating (heating) only system or a cooling (cooling) system.

The chamber box 22 is provided connected to the heat exchanger 21 at the attic. The chamber box 22 once collects warm air heated by the heat exchanger 21 or cooled cold air and distributes them to various places to improve the thermal efficiency of heating or cooling.

Behind the ceiling, one end of the duct 23 is connected to the chamber box 22 and the other end is connected to the diffuser 25 attached to the outlet 24. The outlet 24 is an opening penetrating the attic and the ceiling. The warm or cold air heat exchanged by the heat exchanger 21 is discharged from the chamber box 22 through the duct 23, through the diffuser 25, and from the outlet 24 to the living room 2. In the air-conditioned indoor environment cleaning system of the present embodiment, the indoor space is heated or cooled by hot air or cold air directly guided to the living room 2.
The air in the living room 2 is sucked into the heat exchanger 21, and heating or cooling is continued by circulating the air using the equipment of the air-conditioned indoor environment cleaning system.

The air-conditioned indoor environment cleaning system 20 of the present embodiment has an operation panel 26 on one surface of the wall 28, and a remote controller 27 is detachably attached.
Further, if necessary, a booster fan (not shown) can be provided in the diffuser 25. The booster fan is for increasing the air flow from the outlet 24.

The air-conditioned indoor environment cleaning system 20 of the present embodiment can be applied not only when the building is a one-story building, but also when the building has a plurality of floors, the heat exchanger 11 and the chamber box 12 are used. , Duct 13 and outlet 14 can be provided corresponding to the living room on each floor.
Further, the systems may be combined so that the living room on the first floor is the air-conditioned indoor environment cleaning system 10 shown in FIG. 1 and the living room on the second floor is the air-conditioned indoor environment cleaning system 20 shown in FIG. ..

The air-conditioned indoor environment cleaning system 10 of the present invention shown in FIG. 1 is for purifying the air in the living room 1.
(1) An aqueous coating agent for air purification is applied to at least one of the air filters provided or may be provided in the heat exchanger 11, the chamber box 12, the duct 13, and the outlet 14. To form a coating film,
(2) An aqueous coating agent for air purification is applied to the inner surface of at least one of the heat exchanger 11, the chamber box 12, the duct 13, and the outlet 14 to form a coating film, and (3). ) On at least one of the surface of the wall 18 that receives the air flow of the air discharged from the outlet 14 and the surface of the ceiling connected to the wall 18, at least one selected from the pyroelectric powder and the piezoelectric powder, and a metal. A water-based coating agent containing an additive contained in water is applied to at least one selected from a complex, a metal powder and a metal ion, or a calcium hydroxide-based paint containing the additive is applied.
Of these, it has at least one structure.

The air-conditioned indoor environment cleaning system 20 of the present invention shown in FIG. 2 is used to purify the air in the living room 2.
(4) An aqueous coating agent for air purification is applied to at least one of the air filters provided or may be provided in the heat exchanger 21, the chamber box 22, the duct 23, and the outlet 24. To form a coating film,
(5) An aqueous coating agent for air purification is applied to the inner surface of at least one of the heat exchanger 21, the chamber box 22, the duct 23, and the outlet 24 to form a coating film, and (6). ) On at least one of the surface of the wall 28 that receives the air flow of air discharged from the outlet 24 and the surface of the ceiling connected to the wall 28, at least one selected from the pyroelectric powder and the piezoelectric powder, and a metal. A water-based coating agent containing an additive contained in water is applied to at least one selected from a complex, a metal powder and a metal ion, or a calcium hydroxide-based paint containing the additive is applied.
Of these, it has at least one structure.

The water-based coating agent for air purification applied to the inner surface and walls of air filters and equipment is composed of at least one selected from pyroelectric powder and piezoelectric powder as additives, and metal complexes, metal powders and metal ions. It includes at least one selected. The water-based coating agent contains this additive in water.

As a result of diligent research as a novel additive capable of decomposing volatile organic compounds without the need for a photocatalytic material, the present inventors have conducted intensive studies and found that at least one selected from pyroelectric powder and piezoelectric powder and a metal complex. , Metal powder and at least one selected from metal ions have been found to be effective as a photocatalyst, and have led to the present invention. The additive of the present invention can be coated on the air filter or the inner surface of the equipment of the air-conditioning type indoor environment cleaning system 10, for example, added to calcium hydroxide-based paint, coated on the surface of calcium hydroxide-based paint, or a wallpaper. By using it as an adhesive, it can exert a catalytic effect to decompose VOC gas and the like and convert it into _{water and CO 2.}

The action and effect of the above-mentioned additive of the present invention have not always been elucidated in principle and theory, but it is considered by the inference of the present inventors to have the following action and effect. At least one selected from the pyroelectric powder and the piezoelectric powder in the additive generates an electric charge due to the air circulation energy in the house or the temperature change in the living room, and this electric charge is the metal complex contained in the additive. Pyroelectric powder or piezoelectric powder conducts to at least one selected from metal powder and metal ions, and holes are formed in the pyroelectric powder or piezoelectric powder to be positively charged, and the holes in the pyroelectric powder or piezoelectric powder are around. It takes an electron from the OH ⁻ ion of water and generates an OH radical. On the other hand, electrons conducted in at least one selected from metal complexes, metal powders and metal ions react with oxygen in the air to generate superoxides. It is considered that VOC gas and the like can be decomposed by the oxidizing power of these OH radicals and superoxides.

The effect of the present invention is that, as described later, according to the experiments of the present inventors, a plate coated with an aqueous coating agent containing the additive of the present invention on the surface is housed in a closed container, and formaldehyde is placed in the closed container. When it was introduced and the temperature was raised, it was _{confirmed that the formaldehyde concentration decreased and the CO 2} concentration increased.

Hereinafter, each component of the additive contained in the aqueous coating agent will be described.
(Pyroelectric powder and piezoelectric powder)
A pyroelectric body is a substance that receives heat energy to generate an electric charge, and a piezoelectric body is a substance that receives a pressure to generate an electric charge. Pyroelectric bodies are generally included in piezoelectric bodies because they have a piezoelectric effect. Therefore, in the present invention, it is not necessary to strictly distinguish between the pyroelectric body and the piezoelectric body.

Typical examples of the pyroelectric body and the piezoelectric body include barium titanate, lead zirconate titanate, potassium niobate, and bismuth sodium titanate, but the materials are not limited to these materials and have piezoelectricity. Anything may be used, and for example, piezoelectric polymer material powder, metal powder, silicon carbide powder, silicon powder, tourmaline, quartz, or the like may be used. In addition, two or more of these materials can be used in combination.

The pyroelectric body and the piezoelectric body are used in the form of powder in the present invention. By making it into a fine powder, the dispersibility in water is improved. The average particle size of the powder can be about 3 μm or less. If the average particle size exceeds about 3 μm, the color of each powder affects the calcium hydroxide-based paint and coating agent, which is not preferable. The lower limit is not particularly limited, but the manufacturing cost increases as the fineness becomes finer, so that the lower limit can be set to about 0.5 μm or more. In the examples described later, those having an average particle size of 3 μm were used.

In the additive of the present invention, the blending amount of the pyroelectric powder and the piezoelectric powder with respect to water is not particularly limited. A formulation in which the pyroelectric powder and the piezoelectric powder are sufficiently dispersed in water and have the effect of decomposing volatile organic compounds when the additive of the present invention is used as a calcium hydroxide-based paint, an adhesive or a coating agent. Can be a quantity.

(Metal complex, metal powder and metal ion)
Charges generated from the pyroelectric body and the piezoelectric body are transmitted to the metal complex, the metal powder, and the metal ion to generate holes in the pyroelectric body and the piezoelectric body. Further, in the metal powder, the electric charge received from the pyroelectric body or the piezoelectric body reacts with oxygen in the air to generate superoxide.

Examples of the metal complex, the metal powder and the metal ion include a copper complex, a copper powder or a copper ion. Copper has good conductivity and has an antibacterial effect. Therefore, by including the metal complex, copper powder or copper ion in the additive of the present invention, it has not only the above-mentioned effect of generating holes but also the effect of preventing the generation of mold. Therefore, it is useful for improving the health of the resident of the house by using the system containing the additive of the present invention. Further, the material of the metal complex, copper powder or copper ion is cheaper than that of platinum or the like. In addition, a plurality of metal complexes, copper powder and copper ions can be included in the additive of the present invention. Examples of the water containing the metal complex include cupric tartrate water.

In the additive of the present invention, the blending amount of the metal complex, the metal powder and the metal ion with respect to water is not particularly limited. It can be appropriately determined according to the amounts of the pyroelectric powder and the piezoelectric powder described above.

(Other ingredients)
The additive of the present invention may contain at least one selected from the above-mentioned pyroelectric powder and piezoelectric powder, and at least one component selected from metal complexes, metal powders and metal ions. For example, it can contain a retainer or a dispersant for uniformly holding the piezoelectric element in water. As the retainer or dispersant, for example, zeolite, silicon oxide or the like can be used. Further, depending on the application, a binder, an adhesive or the like can be included in the additive of the present invention.

[Production method]
The additive of the present invention can be produced by containing each of the above-mentioned components in water.

In the air-conditioned indoor environment cleaning systems 10 and 20 of the present embodiment, a coating film of the water-based coating agent is formed on the surface by applying the water-based coating agent containing the above-mentioned additive to the inner surface of the air filter or the device. This coating film has the effect of decomposing VOC gas and the like in the air by the circulating energy of the air and purifying the air. In other words, it is applied to the inner surface of the air filter or equipment as a more effective place to receive the circulating energy of air.

Further, in the air-conditioned indoor environment cleaning systems 10 and 20 of the present embodiment, a coating film of a water-based coating agent containing the above-mentioned additives is applied to the inner surface of the air filter or the device of the air-conditioned indoor environment cleaning systems 10 and 20. Not limited to what is formed, the above-mentioned can be applied to the surface of the wall near the outlet that receives the airflow from the outlets 14 and 24, the surface of the ceiling connected to the wall, or both the surface of the wall and the surface of the ceiling. A coating film of a water-based coating agent containing an additive may be formed, or the wall and / or ceiling in the vicinity of the outlets 14 and 24 may be a finishing material containing the water-based coating agent containing the above-mentioned additive. .. Then, even with a slight flow velocity from the air outlets 14 and 24, the wall in the vicinity of the air outlet contributed to air purification and was applied to the equipment of the air-conditioned indoor environment cleaning systems 10 and 20. Combined with the air purification by, the living rooms 1 and 2 can be further purified. Further, by providing the booster fans 19 at the outlets 14 and 24, the airflow from the outlets can be increased, and the living rooms 1 and 2 can be further cleaned.

The blending amount when the additive of the present invention is added to the water-based coating agent or the calcium hydroxide-based paint can be appropriately determined according to these uses. In one example, considering the decomposing effect of volatile organic compounds, the amount of pyroelectric powder and piezoelectric powder should be about 1 g to 3 g per square meter when applied to the surface of wallpaper or calcium hydroxide paint. The blending amount can be adjusted.

The effect of the air-conditioned indoor environment cleaning system of the present invention will be clarified by experimental data.
An additive for an interior material containing 100 g of tourmaline powder in 1000 cc of cupric tartrate water (800 ppm) was prepared. This interior material additive 630 cm ³ was added to 500 g of a calcium hydroxide-based paint and kneaded to obtain a coating material. This coating material was applied to a base paper and attached to an aluminum plate (thickness of 3 mm) as a test piece. The dimensions of the test piece were 165 mm × 165 mm × 3 mm.

Two test pieces were prepared, and a formaldehyde reduction test was conducted in accordance with JSTM H 5001 (a test method for reducing indoor air pollution concentration by a small chamber method). In this test, the volume of the small chamber is 20 L, the sample load factor is 2.2 m ² / m ³ , and the 100 μg / m ³ concentration of formaldehyde is continuously supplied into the small chamber at 167 mL / min using a seal box. , Air was collected at the outlet of the small chamber 1 day, 3 days, and 7 days after the start of the test. In addition, air collected 1 hour, 3 hours, 7 hours, and 24 hours after the formaldehyde supply was stopped (air flow stopped) at the outlet of the small chamber.

Formaldehyde feed in small chamber one day after the test started, formaldehyde concentration in a small chamber inlet concentration of formaldehyde small chamber outlet is 108μg / m ³ was 27 [mu] g / m ^3.
As for the formaldehyde supply to the small chamber 3 days after the start of the test, the formaldehyde supply concentration at the entrance of the small chamber was 106 μg / m ³ and the formaldehyde concentration at the exit of the small chamber was 47 μg / m ³ .
The formaldehyde supply to the small chamber 7 days after the start of the test was that the formaldehyde supply concentration at the entrance of the small chamber was 109 μg / m ³ and the formaldehyde concentration at the exit of the small chamber was 53 μg / m ³ .
From the above results, it was found that the formaldehyde concentration was reduced by the test piece.

An additive for an interior material containing 100 g of tourmaline powder in 1000 cc of cupric tartrate water (800 ppm) was prepared. This interior material additive 630 cm ³ was added to 500 g of a calcium hydroxide-based paint and kneaded to obtain a coating material.

This coating material was applied twice to each of six 30 cm square refractory boards and dried. The dried refractory board was attached to each of the six inner surfaces of a closed rectangular parallelepiped container and fixed to form a test piece.

A formalin container with an open lid was placed inside the test piece, and the closed container of the test piece was sealed. Then, it was heated to bring the temperature inside the specimen to 40 ° C. The formaldehyde concentration and the carbon dioxide concentration in the specimen were measured every 3 hours while maintaining the temperature of 40 ° C. using a Kitagawa gas detector.

As a result, the initial value of formaldehyde concentration was 30 ppm, 10 ppm after 3 hours, 5 ppm after 6 hours, and a trace amount after 9 hours.
The initial value of carbon dioxide concentration was 1000 ppm, 1400 ppm after 3 hours, 1600 ppm after 6 hours, and 2000 ppm after 9 hours.
After stopping the heating of the specimen and leaving it for 10 days, the formaldehyde concentration was 0 ppm and the carbon dioxide concentration was 500 ppm.

From the above results, it was found that the carbon dioxide concentration increases as the formaldehyde decreases. It is considered that this is because the formaldehyde absorbed in the coating material was decomposed by the additive for the interior material.

Although the embodiment of the present invention has been described above with reference to the drawings and examples, the air-conditioned indoor environment cleaning system of the present invention is not limited to the embodiments and examples shown in the drawings, and the gist of the present invention is used. It is possible to make many transformations as long as it does not deviate from. For example, the outlet is not limited to the case where it is provided on the floor surface shown in FIG. 1 or the case where it is provided on the ceiling surface shown in FIG. 2, and may be provided on a wall surface.

10, 20 Air-conditioned indoor environment cleaning system 11, 21 Heat exchanger 12, 22 Chamber box 13, 23 Duct 14, 24 Outlet 15, 25 Heat source 16, 26 Operation panel 17, 27 Remote control 18, 28 Wall 19 Booster fan

Claims (4)

A water-based coating agent containing tolumarin powder and cupric tartrate water and an additive that decomposes at least one volatile organic compound selected from formaldehyde, toluene and xylene by the circulating energy of air or temperature change is applied. An air filter characterized by being made. The air filter according to claim 1, which is provided in at least one of a heat exchanger, a chamber box, a duct, and an outlet. An air conditioning system coated with a water-based coating agent containing tourmaline powder and cupric tartrate water and containing an additive that decomposes volatile organic compounds by circulating energy of air or temperature change. The air conditioning system according to claim 3, wherein the water-based coating agent is applied to at least one inner surface of a heat exchanger, a chamber box, a duct, and an outlet.

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