What is cassette Unit?

A cassette air conditioner is basically a type of split system, as it consists of two units; One is installed inside and the other outside. The difference with cassette-type air conditioners is that the indoor unit is installed on the ceiling.

Lighting in the places we live, and work is critical to our ability to work efficiently and safely. Plus, proper lighting conditions prevent eye strain, allowing you to work comfortably for long periods of time. This article describes proper lighting conditions and various lighting concepts during a conversation.

While light intensity is important to reduce eye strain, architects and designers must also consider color temperature. Temperature affects a person's alertness. Humans are more alert in midday blue light and more relaxed in the warm light morning and evening light.

We need to understand two main concepts when planning a building's lighting level:

·       lighting level

·       lighting power density.

light levels in buildings

Since we mainly work on our buildings, we need to understand the illuminance or the amount of light falling on the surface. In an office, we may want to understand the amount of light falling on our desks; However, in a gym or hallway, we may be more interested in the amount of light hitting the floor.

Illumination is measured in foot candles (FC) or lux.

1 FC is the amount of light that falls on a surface of 1 square foot when 1 lumen is shone from 1 foot away this equals 1 lumen per square foot.

1 lux is the amount of light that falls on a surface of 1 square meter when illuminated by 1 lumen from 1 meter away this equals 1 lumen per square meter.

10 lux is approximately 1 FC.

It should provide enough light to allow people to complete their tasks, but not so much light that tasks are difficult to see - too much light is just as bad as too little light. Detailed tasks like drafting require a lighter, while simple tasks like walking can be done in dim light.

Some Fundamentals on Home Electricals

We pay for our electricity charges in kilowatt-hours. In electrical engineering, the power of an item is expressed in watts (W) and it is related to the voltage [in volts (V)] and the current [in ampere (A)] as follows:

W = V × A

Thus, if we use a 15 A fuse with a current of 220 V, the fuse can stand up to a power of 220 × 15 = 3300 W (3.3 kW) only. In fact, we generally do not allow the total connected load per fuse to be more than 3 kW. Hence, in general, we use only 13 A–15 A fuse in each of the circuits in a building.

Note Capacities of electrical systems like inverters, and solar panels are expressed in kilowatts (kW) or kilovolt ampere (kVA).

Load Rating of Lighting Devices Used in Buildings

For lighting in the building, we may use

1.  Tungsten filament lamp of different wattage

2.  Fluorescent lamps of different wattages [These lamps consume only 20% of the current consumed by that the filament lamps for the same brightness. Nowadays, compact fluorescent lamps (CFLs) are also available that are to be fitted into the sockets like the old electric bulbs.]

3.  Flood light lamps

4.  Other special lamps

The brightness of a lamp is expressed in a unit called Lumen (lm). The relationship given in the Table below can be taken when we consider electric lighting.

Table: Relationship of wattage and lumen

The equivalence in wattage of filament lamps and fluorescent lamps for lighting is shown in the Table below

Table: Equivalence in wattage and lumen

(Note: The unit of electricity based on which we pay charges is a kilowatt hour (kWh). One 25 W lamp burning for 40 hours consumes only 1 kWh or one unit of electricity. Hence, it is not the lighting of a house that consumes much current, but it is the electric machines like refrigerators, air conditioners, ovens, etc. that consume more current (see Table below)

From the Table above, fluorescent lamps are much more economical to use than ordinary filament lamps. However, fluorescent lamps should not be used in enclosed fittings or exposed to water or rain and should not be used in dimming circuits.

Load Rating of Usual Household Appliances

The load (in watts) of the common household appliances we use is given in the Table below.

Lighting and Power Circuits

Electric supply in a building is to be made not only for general lighting but also for electrical equipment like refrigerators, air conditioners, etc. We will see that connections to various types of devices are made by different circuits known as the lighting circuit, power circuit, and fixed appliance circuits.

Lighting circuits

Low-wattage units like lights can be connected by two wires: one phase and the neutral. However, the most commonly used is the three-wire circuit system as shown in the Figure below. It is known as the loop-in method. It uses an earthed twin cable and a circuit breaker on the fuse protection device also.

Figure: Lighting circuit wiring diagram of the loop in method (N = Neutral, L = Live, E = Earth); 1. A consumer control unit (mains switchboard), 2. Ceiling rose, 3. One-way switch, 4. Lamp, 5. Two-way switch.)

Power circuits

Equipment (like refrigerators, and water pumps) of not very high wattage are connected to the three-wire system. These are called power circuits, as shown in the Figure below. Switches of the lighting circuits and sockets of power circuits are placed on the same switchboard.

Fixed appliance circuits

These are the circuits for individual units like an air conditioner with high wattage. These should be always earthed. It is interesting to examine how earthing of equipment adds to its safety. We have the relation V = IR, where V is the voltage in volts (V), I is the current in amperes (A), and R is the resistances in ohms (W). If there is any leakage of electricity, then because of earthing the resistance R becomes small and the amperes of current I become very large. This blows out

Figure: Power circuit wiring diagram: Ring main wiring (N = Neutral, L = Live, E = Earth); 1. The consumer control unit, 2. 15 A socket outlets in ring main, 3. 15 A spur socket outlet.)

the 15 A fuse we have put in the circuit at the switchboard. This switches off the current and the equipment remains safe. Note: The above explanation shows that it is very important that we should not put more than 15 A fuse in these circuits for home appliances. Only the main fuse connecting to the external supply is to be high, usually 100 A.

We can classify the masonry walls of a building into two types. The first type is the load-bearing walls of a building in which all the loads are carried down to the foundation through the walls. The second type of wall is the walls in reinforced concrete framed buildings or partition walls where the walls are designed as filler walls and not as load-bearing walls. In this article, we deal mainly with some of the causes of cracks in load-bearing walls. We also briefly discuss the filler walls.

Cracks in Load Bearing Walls

The main walls in buildings are usually 11/2 brick or one brick walls in thickness (Partition walls can be even half-brick walls.) The cracks in buildings (both in masonry and concrete works) are classified as follows according to the width of the cracks:

1. Less than 1 mm cracks are called thin cracks.

2. 1 mm to 2 mm cracks are medium cracks.

3. 2 mm to 4 mm cracks are wide cracks.

4. More than 4 mm cracks are very wide cracks.

Measurement of Cracks

When we see any crack in a structure, we show our interest in its size and try to find out whether it is an active (growing) crack or a passive (does not become bigger with time) crack. The size of a crack (or crack width) is measured by means of a crack gauge. There are different types of gauges. One type is shown in the Figure below. This type of crack gauge has different widths marked on it. We measure crack width by comparing the crack width with the different sizes marked in the scale and thus, find the size.

Crack gauge.

To find out whether it is an active or passive crack, we measure the crack with the passing of time by using the crack gauge or glass strip technique, as shown in the glass strip is pasted normally to the crack. It breaks if the crack is active.

Measurement of the progress of cracks (a) glass tell-tale for observing movements of cracks and (b) glass tell-tale for measuring movements of cracks.

Causes of Cracks

The first step in the treatment of cracks is to find their cause after which it is easy to treat the cause and then, repair the cracks.

Some of the reasons for the formation of a crack in a load-bearing wall can be one or more of the following reasons:

1. Defective rendering and plastering (shrinkage cracks)

2. Settlement of the foundation in a load-bearing wall or other settlement in the wall

3. Temperature effects

4. Local deformation at junctions of masonry with concrete members like concrete slabs bearing on masonry walls.

5. Cracks in half brick partition walls.

Some of these causes along with their remedies are briefly explained in the subsequent articles.

How to Repair Rising Dampness in walls of Ground Floors in Buildings Constructed without DPC? and How to Repair Efflorescence in Buildings?

Introduction

The plinth is the portion of the wall of a building immediately above ground level to the ground floor level. This height usually ranges from 45 cm to 100 cm. Nowadays, in building construction, we provide a beam at the lower or upper level of the plinth, called the plinth beam. It is usually 10 cm thick with at least 6 mm rods spaced at 10 cm at the top and the bottom and 6 mm stirrups at the rate of 23 cm. (This is in addition to the grade beam or ground beam we provide at the foundation level for isolated footings, under reamed piles, etc.)

In all buildings, nowadays, we build a damp-proof course (DPC) to prevent dampness from going up the walls from the foundation due to the capillary action of groundwater. The damp-proof course can be on the plinth beam or on a beam built separately always above the ground level. If it is built separately, it should be at least 40 mm to 50 mm thick and should have 1:2:4 concrete with a waterproofing compound. Over this, we paint a thick layer of bitumen to prevent water from rising from the wall from the foundation. A much cheaper way for low-cost buildings is to put only a 1:3 cement mortar layer with bituminous paint (or a bituminous membrane placed over it) in a portion of the wall above the ground. This should be provided for all walls, i.e., external, and internal walls. Thus, DPC prevents water from rising from the wall from the foundation by capillary action. Even though in all the new buildings, nowadays, we place the DPC, in old buildings like old assembly halls, old church buildings, and old residences, these are absent. How we prevent moisture migration in these old buildings where DPC has not been provided is the major problem dealt with in this article.

Methods to Rectify Dampness

The following methods are usually recommended:

1. Construct a new DPC (Note: Conventional type consists of 40 mm to 50 mm thick cement concrete in the proportion of 1:2:4 with water-proofing compound.)

2. Pressure injection or gravity feeding of a suitable chemical solution within the plinth (Water soluble silicon solutions are commonly used.)

3. Pressure injection of resin mortar in boring holes

Construction of New DPC

For installing a DPC in an old building that has been built without DPC, we cut the mortar bed joint of two brick courses above ground level in stages of about one meter in length at a time. No two adjacent lengths should be repaired consecutively. A new DPC with a waterproofing compound can be inserted with the rebuilding of the removed brick course. This method is too slow and may lead to structural settlement and cracking of walls if the walls are weak. Hence, the methods described in the subsequent section are usually recommended.

Method of Injection of Chemicals (Silicon)

Another method of repair is the injection of chemicals as a liquid. The most common method used for placing DPC is based on injecting water-soluble silicon (which has the moisture-resisting property) into the brickwork, as shown in Figure below.

In this article, we will explain the repair process for Reinforced concrete beams and columns damaged by steel corrosion where the depth of the affected concrete has reached the reinforcement level. As the amount of steel rust exceeds that of the original steel, the concrete around the steel cracks. In some cases, the cover concrete may fall off. Corrosion can be caused by carbonation or chloride.

The following procedure is followed to repair these reinforced concrete members. The main difference between slabs from columns and beams is that for the latter, a more elaborate formwork must be used to place the concrete. Otherwise, we can place concrete with shotcrete

Repair of Cracks in Beams and Columns when Corrosion has Reached Reinforcement Level

Step 1: As these members carry heavy loads, first support the beam and column using supports to relieve part of its load. Then, remove the damaged concrete to expose the steel.

Step 2: Investigate the type of corrosion with phenolphthalein tests to determine whether the corrosion is due to carbonation or chloride effect. Also, determine the depth to which erosion has continued. If it's due to carbonation, it's worth fixing. But if it is due to chloride corrosion, the same corrosion can occur elsewhere if the concrete near the steel is not completely replaced. Here, we assume that carbonation is the only cause of corrosion.

Step 3: If the steel is completely corroded, remove 15mm to 25mm of concrete from the entire steel.

Step 4: Clean the concrete surface and steel surface thoroughly with water. A rust removal solution can also be used for steel. It dissolves the rust and adheres to the steel as a coating.

Step 5: When the steel is reduced by about 15% due to corrosion, place the necessary additional steel and bond it properly with the old steel or additional support. New steel can also be supported by spot welding to old steel. Place required shear reinforcements for beams and binders for columns.

Step 6: Apply proper bonding coat to the old concrete surface and steel surface.

Step 7: If necessary, attach the formwork to the column for concreting the removed area. For columns, it is easy to place formwork or self-compacting concrete for pouring concrete. For beams, it is more convenient to use expanded wire mesh

Step 8: Before the bond coat dries, compact the void space of the member with cement, sand, small coarse aggregate (10mm and below) and micro concrete with superplasticizer as required. Water-cement ratio should not exceed 0.5. In some cases, we may have to use self-compacting concrete. This is achieved by using concrete chemicals such as superplasticizers. For patch repairs or repairing small areas, we usually use simple polymer-modified cement mortar. For larger repairs, it is better if we use shotcrete to fill the removed area.

Step 9: Apply a 1:3 (finely sanded) coating within 48 hours of completing Step 8.

Step 10: Wet curing should be done for at least 7 days.

Step 11: After complete drying, a coat of waterproof paint is given to protect the member and match the surrounding surfaces. Note: In larger jobs, it is better to place concrete or mortar using shotcrete, also known as gunite.