Air conditioning for large multistory buildings

AIR CONDITIONING FOR LARGE MULTISTORY BUILDINGS,[object Object],PREPARED BY,[object Object],NOOR AZILA BINTI JAMARI,[object Object],LECTURER,[object Object],CIVIL ENGINEERING DEPARTMENT,[object Object]

Most large multistory buildings use highly centralized air conditioning equipment. The roof and basement are the usual choice for these central station systems. ,[object Object],The basement has the advantage of easy utility connections, noise isolation, not being valuable rental area and the fact that structural loads are not a problem.,[object Object],INTRODUCTION,[object Object]

The roof is the ideal location for fresh air intakes and heat rejection to the atmosphere.,[object Object],Cooling tower are noisy, produce very hot and humid exhaust air, so the best location for cooling rower is placed on the roof.,[object Object],SECTION OF A TYPICAL MULTISTORY BUILDING WITH A ROOFTOP CENTRAL STATION MECHANICAL SYSTEM,[object Object]

In most buildings, the mechanical equipment is shown to be on the roof. This section shows an all-air system served by a single central air handling unit on the roof.,[object Object],To avoid the large vertical ducts, separate air handling units can be placed on each floor and only water circulates vertically. This saves much energy because moving air great distances requires much power. ,[object Object],MECHANICAL EQUIPMENT IS STILL ON THE ROOF, EACH FLOOR HAS A SEPARATE AHU,[object Object]

The advantage of all-air system is complete control over air quality is possible. The disadvantage is that all-air systems are very bulky and a significant part of the building volume must be devoted to them. ,[object Object],There are 5 system in all-air system categories.,[object Object],i. Central Plants,[object Object], ii. Variable Air Volume (V.A.V),[object Object], iii. Terminal Reheat System,[object Object], iv. Multizone System,[object Object], v. Double Duct System ,[object Object],ALL-AIR SYSTEM,[object Object]

The central air conditioning system has the limitation of the same air quality being delivered throughout the building.,[object Object],If the structure is zoned or divided and compartmented into several different functions such as offices, workshops, canteen.,[object Object],The temperature of each element can be controlled with zoned thermostats.,[object Object],The fan precedes the chiller and reheater coils and blow air through the air-handling unit.,[object Object],Several ducts radiate from the unit to designated zones within the building. ,[object Object],CENTRAL PLANTS SYSTEM,[object Object]

CENTRAL PLANTS SYSTEM,[object Object]

This is a single duct system that can easily have many zones. A variable air volume control box is located wherever a duct enters a separate zone.,[object Object],A thermostat in each zone controls the air flow by operating a damper in the V.A.V control box. More cooling is required, more cool air is allowed to enter the zone. ,[object Object],ii. VARIABLE AIR VOLUME SYSTEMS,[object Object]

VAV system.,[object Object],Floor plan of a VAV system.,[object Object],VAV control box.,[object Object]

At the first the terminal reheat system looks just like the V.A.V system but in fact it is very different. ,[object Object],This system has terminal reheat boxes in which electric strip heaters or hot water coils reheat air previously cooled.,[object Object],All others zones will reheat the cold air to the desired temperature.,[object Object],iii. TERMINAL REHEAT SYSTEM,[object Object],Terminal reheat system.,[object Object]

In this system, every zone receives air at the required temperature through a separate duct.,[object Object],These ducts are supplied by a special multizone air handling unit that custom mixes hot and cold air for each zone. ,[object Object],This is accomplished by motorized dampers located in the air handling unit but controlled by thermostats in each zone. Depending on the temperature, the ratio of hot and cold air varies but the total amount of air is constant. ,[object Object],iv. MULTIZONE SYSTEM,[object Object]

The multizone unit is supplied with hot water, chilled water and a small amount of fresh air.,[object Object],Each multizone unit can handle about 8 zones.,[object Object],Because moderate air temperatures are created by mixing hot and cold air, this system also wasteful of energy.,[object Object],Disadvantage this system are costs relatively high while the thermal control is relatively poor.,[object Object]

Like the multizone system, the double duct system mixes hot and cold air to achieve the required air temperature.,[object Object],Instead of mixing the air at a central air handling unit, mixing boxes are dispersed throughout the building.,[object Object],The double duct system creates a high level of thermal comfort and allows for great zoning flexibility, it is very expensive, requires much building space and its wasteful of energy.,[object Object],v. DOUBLE DUCT SYSTEM,[object Object],Double duct system.,[object Object]

To reduce the size of the ducts, a high-velocity version of this system,[object Object],High-velocity air systems (6000 feet/minute) consume more fan power than normal velocity systems(2000 feet/minute).,[object Object],Because of these problem and because V.A.V system are a good alternative, dual duct systems are not used much anymore.,[object Object]

These system supply both airand water to each zone of a building.,[object Object],It greatly decreases the size of the equipment because of the immense heart-carrying capacity of water as opposed to air.,[object Object],Air is supplied mainly because of the need for ventilation.,[object Object],There are 2 system in air-water system categories.,[object Object],i. Induction System,[object Object], ii. Fan- coil with supplementary air,[object Object],But in this topic is cover induction system only,[object Object],AIR-WATER SYSTEM,[object Object]

A small quantity of high-velocity air is supplied to each zone to supply the required fresh air and to induce room air to circulate.,[object Object],Most induction terminal units are found under windows where they can effectively neutralize the heat gain. ,[object Object],As the high-velocity air shoots into the room it induces a large amount of room air to circulates.,[object Object],This combination of room air and fresh air, then passes over heating or cooling coils.,[object Object],INDUCTION SYSTEM,[object Object]

Local thermostats regulate the temperature by controlling the flow of either hot or cold water through the coils.,[object Object],It takes a lot of fan power to circulate air at high velocity throughout a building.,[object Object],Because of the high cost of energy and the expense of high-velocity ductwork, the use of induction systems is limited.,[object Object],Induction system. ,[object Object]

Induction system. ,[object Object],Induction unit with cooling or heating coils,[object Object]

These systems supply no air.,[object Object],There are 2 system in all-water system categories.,[object Object],i. Fan-coil System,[object Object], ii. Water Loop Heat Pump System,[object Object],But in this topic is cover Fan-coil system only.,[object Object],ALL-WATER SYSTEM,[object Object]

The fan-coil unit basically consists of a fan and a coil within water circulates. ,[object Object],The units are in the form of cabinets for placement under windows.,[object Object],The fan blows room air across coils containing either hot or cold water.,[object Object],Thermostatically controlled valves regulate the flow of water through the coils. ,[object Object],A 4 pipe system, which is has 2 pipes for hot water supply and return and another 2 pipes for cold water supply and return.,[object Object],FAN-COIL SYSTEM,[object Object]

Condensation on the cooling coils must be collected in a pan and drained away.,[object Object],When the fan-coil unit is on an outside wall, it is possible to have an outdoor air intake connected to the unit.,[object Object],A three-speed fan switch allows occupants of the zone to have some control over the temperature.,[object Object],Fan-coil units are most appropriate for air conditioning buildings with small zones (eg. Apartments, condominiums, motels, hotels, hospitals and schools).,[object Object],Fan coil units also located above windows, in small closets or in the dropped ceiling above a bathroom.,[object Object]

Fan Coil System.,[object Object],Schematic diagram of an under window FCU ( 4 pipe system).,[object Object]

FCU placed in a small closet.,[object Object],FCU placed above a dropped ceiling.,[object Object]

Air conditioning for large multistory buildings

Air conditioning for large multistory buildings

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