air handling

Ventilation and

Air Handling

Csaba SzikraFaculty of Architecture

Department of Building Energetic and Services

Assignment of comfort ventilation systems is to serve fresh air to the indoors and the occupied area.

If the ventilation, system apart from serving necessary amount of fresh air, has additional assignment, according to the function the following systems can be identified:

Air cooling

Air heating

Humidifying

Dehumidifying

Air conditioning

Ventilation and Air HandlingClassification according to the function

Department of Building Energetics and ServicesH 1111 Budapest, Műegyetem rkp. 3.

The ventilation system also can be classified according to the environmental pressure in between the ventilated room and its surroundings.

Accordingly we can define:

depressive

compressive

balanced

Ventilation and Air HandlingClassification according to the pressure related to its surrounding


If the infiltration is undesired for ventilated area because the surrounding air quality is harmful compressive ventilation system can be applied. In this case the pressure of the ventilated area is increased by 20-30Pa. Typical applications are labs industrial clean areas, pharmaceutical production areas, operating theatres and boiler houses. Also this type of ventilation can be applied in restaurants where smell problem can be solved this way, which could path through from the kitchen to the serving areas. Other applications: Bath, hotel rooms etc.

In compressive ventilation systems there are two duct systems. One for the incoming air and one for the exhaust air, but in always fun is installed in the incoming duct. The exhaust duct can be neglected, in this case the air is leaving through the building envelop. The level of the over pressurizing is equal to the pressure loss of the exhaust duct. If there is no installed exhaust duct the system is called inlet ventilation. The inlet ventilation system apart from serving fresh air to the occupied area, can handle other functions like air heating and air cooling.



Fan

Inlet air

If the air quality of the ventilated place is harmful to the surrounding, depressive ventilation system could be applied. Typical applications: Baths, toilets, swimming pools, industrial areas, kitchen, laundries. The pressure of the ventilated area is 20-30Pa less than the pressure of the surrounding areas.

In depressive ventilation system there is an exhaust duct with an inbuilt fan. The entering air is coming through an inlet duct or a building shell. If there is installed inlet duct the pressure different of the ventilated area is equal to the pressure loss of the inlet duct. If there is no inbuilt inlet duct we call that system exhaust ventilation. The depressive and the exhaust ventilation system are not suitable for serving other functions like air heating and cooling.



Exhaust airFan

In balanced ventilation system there is no pressure different in-between the ventilated area and its surroundings. In this case for the incoming and also for the exhausting air there are separated duct with inbuilt fan. With balanced ventilation system all the other services can be handled. Also with a small modification of the incoming and exhausting air volume, this can be achieved by adjusting element, depressive and compressive ventilation system can be operated.



FanExhaust air

FanInlet air

In central ventilation system the incoming and the exhausting air join in one common area, which is always an air handling unit. For the air handling unit there are separated ducts, which are (Figure 4.):

Fresh air duct, with an air intake inlet at the external area,

Exhaust duct, with an ejection outlet also in the external area,

Inlet duct for serving the handled air to the ventilated area,

Outlet duct for the removal and delivering to the air handling unit of the used air.

One important aim of the air handling unit is to recover the energy content from the exhaust air to the fresh air.

Ventilation and Air HandlingCentral ventilation system


Air handling unit

Inlet air

outlet air

Ventilated area

Fresh air Exhaust air

Most of the cases the local ventilation system means air exhaust system. In the exhaust ventilation system there is only one exhaust duct for removal of the air from the ventilated area. In this case the inlet air enters to the ventilated area through the building envelop, or a cut-through on the external wall.

The incoming air volume depends on the air tightness of the building shells, openings or a size of the cut-through.

The air which enters in the building shell is unhandled. At winter it is cold at summer it is hot.

The energy content of the exhaust air is not recovered. Which energetically not an efficient case.

The pressure of the ventilated area is less than the surroundings area’s pressure.

The investment cost is low.

In small areas where there is no required continuous operation of the ventilation system, with wall mounted local fans, demand controlled ventilation can be achieved.

Ventilation and Air HandlingLocal ventilation – Exhaust system


As it was seen in local exhaust and inlet ventilation also there is only one duct for the incoming or leaving air. The only different is in stead of applying local fans one bigger size fan serving the ventilated areas. This ventilation system schema is mostly applied in exhaust ventilation system of multilevel buildings. The fan is installed in the main duct or at the end of the duct as a roof fan. Heat recovery system can not be applied, and also the demand control can not be achieved easily, so this system is not energy efficient. Application of this system is advantageous where there is no heat requirement and continuous operation is required

If demand control is required, there is possible to install motor controlled shuttle valve, which closes the airflow when there is no need for ventilation. In this case the electric motor of the fan has frequency converter, so the volume flow rate is adjustable.

Ventilation and Air HandlingCentral ventilation – Exhaust system


Roof fan: These types of fans are mounted at the end of the duct on masonry wall or on external metal frame. There two types of roof fans according to the direction of the ejecting air: horizontal and vertical Considering acoustic point of view, the vertical type is better, because the radiated noise distribution is higher at the top of the instrument.

Ventilation and Air HandlingFans


Duct fans: For smaller pressure head there is an axial bladed, for higher there are pressure head radial bladed. Axial bladed fans mostly are applied in smaller systems. Because of in bigger system needs bigger pressure, so in higher system always better o apply redial bladed fans. For smaller systems better to apply duct fan because there is no need for separated room for the ventilation. Disadvantages of the duct fans are the noise level, which emitted to the fan’s environment. Duct fan is suitable for exhaust, inlet and also for balanced ventilation system.

Ventilation and Air HandlingAir handling : Fresh air system


The aim of the central ventilation system is to serve fresh air to the ventilated area and to remove the contaminant source from the occupied rooms.

The balanced ventilation system with a central air handling unit has four ducts. For supplying the air there is a fresh air duct and inlet duct. The exhaust system is for removing the contaminated air which has to parts: before the air handling unit an outlet duct and after the air handling unit the exhaust duct.

The supply system and the exhaust system are connected by the heat recovery. The aim of the heat recovery is to gain the energy content of the exhausting air for the supply air. The heat recovery preheats the fresh air.

Exhaust airFresh air

Ventilated area

Outlet air

Inlet air

Air handling unitFan for exaust air

Faninlet air

Heatingcoil

Heat recovery Filter

Silencer

Silencer



The heating coil heats the air to the ambient room temperature. In smaller systems, meaning limited air volume, the heating coil is not necessary. In this case the heat recovery is the only heater in the system. Because the efficiency of the heat recovery is not 100%, additional heat load is necessary. That additional heat load is assured by the heating system.

The Supply and the Exhaust system are extended by silencer. The aim of the silencer is to reduce the noise level produced by the elements of the air handling unit. The crucial element of the equipment concerning acoustic problem is the fan of the supply and fan of the exhausting system. But other elements can produce also noise like duct, filter coil etc.


Ventilated area

Outlet air

Inlet air


Faninlet air

Heatingcoil


Silencer

Silencer



In comfort range, the necessary air volume estimation is based on the number of occupancies, moisture carbon dioxide and moisture source. Air volume estimation based on indoor air quality gives higher amount of flow rate. In this case all the internal contaminant sources are considered, like emission of volatile organic compounds and radon etc.

When the ventilation system is designed for night ventilation, the heat recovery is extended by a bypass duct. That is because during natural cooling there is no need for recovered heat.


Ventilated area

Outlet air

Inlet air


Faninlet air

Heatingcoil


Silencer

Silencer



When the ventilation system design is based on the occupancy requirements like fresh air for metabolism or based on assurance of the indoor air quality of based on moister removal produced by a human called comfort ventilation.

The minimum requirement on the volume flow rate of the comfort ventilation is 20m3/h,person

If the aim of the ventilation system is to serve the minimum fresh air for the occupants, there is no recirculation in the air handling unit.


Ventilated area

Outlet air

Inlet air


Faninlet air

Heatingcoil


Silencer

Silencer

Ventilation and Air HandlingAir handling : Air heating


In air heating system the temperature of the inlet air is higher than the ambient air temperature. The additional temperature different covers the heat loss of the heated space.

The energy requirement of the air heating system has to parts. First the air is heated to the ambient temperature, second it is overheated. It means that the heat requirement of the air handling unit is higher than in the simple ventilations system without air heating. The heat load different and the overheating cover partly or totally the heat loss through the building envelop. The entering overheated air cools under to the ambient room temperature.

Recirculation box


Air handling unit

Ventilated areaInlet air

Outlet air

SilencerFilterHeat recovery Heatingcoil

Faninlet air

SilencerFan for exaust air

Ventilation and Air HandlingAir handling : Air heating


The schema of the central heating system is extended by a recirculation box and its . The necessary fresh air depends on the number of occupancies, but the heat loss on the external temperature. This means the required fresh air and inlet air have different dependencies.

When the external temperature is low and there is no occupancies most of the air flow is re-circulated. Energetically the recirculation is more efficient than the heat recovery. Only the required fresh air is passing through the air handling unit.

The temperature of the inlet air is 15-30°C higher than the ambient temperature. That is because the higher ambient temperature has no as bad effect as the colder one on thermal comfort of the occupant.

Recirculation box


Air handling unit


Outlet air

SilencerFilterHeat recovery Heatingcoil

Faninlet air


Ventilation and Air HandlingAir handling : Air cooling


The air cooling system is along with serving the necessary fresh air for the occupancies in addition partly or even totally removing the internal and external heat gain of the building..

Sizing of the air cooling system is based on the removal of the heat gains. In bigger public buildings the central air handling unit is only serving the necessary fresh air, the additional cooling load locally enters the cooling place.

The air cooling system is similar to the air heating system. The cooling media is chilled water. If the surface temperature of the cooling coil is lower than the due point temperature, which depends on the ambient temperature and relative humidity, on the surface of the coil water starts condensating. (for instance t=20°C, RH=50% →tdue point=9.3°C). In this case apart from removal of the heat from the air the latent heat is removed and the moisture content of the entering air also becomes lower.


Outlet air

Silencer

Air handling unit


Heat recovery Recirculation box

Heatingcoil

Filter Faninlet air

Silencer

Fan for exaust air

Coolingcoil

Ventilation and Air HandlingAir handling : Air cooling


In general case the inlet air temperature is 5-10°C lower than the ambient room temperature. In special cases when the air distribution system is made good mixing in a residential area the temperature different could be even higher. If the temperature different is too high compare to an ambient air temperature and the air velocity is too high it cases rheumatic disease. By the air distribution system and the air volume the air velocity and the temperature different should be kept as low as it possible to avoid comfort problems.

The balanced air cooling system with a central air handling unit has four ducts. For supplying the air there is a fresh air duct and inlet duct. The exhaust system is for removing the increased temperature air which has to parts: before the air handling unit an outlet duct and after the air handling unit the exhaust duct.


Outlet air

Silencer

Air handling unit



Heatingcoil

Filter Faninlet air

Silencer

Fan for exaust air

Coolingcoil

Ventilation and Air HandlingAir handling : Dehumidifying


The aim of the dehumidifying system is to keep the relative humidity and the moisture content of the internal are below the required level. In this process the water content of the air is reduced.

Application for comfort range: In the internal area, high relative humidity damaging for the building construction. The building elements like windows walls and other elements absorbs moisture from the air. High moisture content causes lifetime reduction, geometric torsion of the timber building element, and causes corrosion on the metal building elements. Dehumidifier system removes the unnecessary humidity from the air.

Typical application in household and public building is to remove the evaporated water from the surface of the swimming pools.


Fan for exaust air

Air handling unit


Outlet air

SilencerFaninlet air

FilterCoolingcoil

Heatingcoil

Recirculation box

Heat recovery

Silencer

Ventilation and Air HandlingAir handling : Central dehumidifying with fresh air service


The fresh air ventilation system and air heating system are working as a dehumidifier system when the external temperature is below the internal ambient temperature. That is because warming up the air drying it at the same time. In several cases the air heating and ventilation system are enough to solve dehumidification problems in the ventilated area.

This schema of the dehumidifying system is similar to the air cooling system. But in a case of air drying the surface temperature of the cooling coil is below the due point temperature of the air.

The heating coil heats the air temperature back to the ambient room temperature.


Fan for exaust air

Air handling unit


Outlet air


FilterCoolingcoil

Heatingcoil

Recirculation box

Heat recovery

Silencer

Ventilation and Air HandlingAir handling : Central dehumidifying without fresh air service


If in apart from drying service of the fresh air is not necessary this schema could be applied


Outlet air


Air handling unit


FilterHeatingcoil

Coolingcoil

Ventilation and Air HandlingAir handling : Local dehumidifying equipments


The local air drying system has a similar structure than the central air drying without fresh air supply. But the equipment contains in one covering box all the necessary elements including heating and cooling.



The humid air of the swimming pool enters to the equipment at the evaporator thought the cooled surface. In the evaporator the moisture condensates and the air cools down. At the other side of the equipment the air passing through the condenser. By the hot surface of the condenser the air is heated. The dry and warm air leaves the equipments and enters back to the swimming pool.

In order to achieve efficient system, additional heat exchanger is built for heating the water of the swimming pool, which uses the additionally loaded energy by the compressor.

The heat exchanger also make the cooling cycle more efficient.

In the equipment there is an inbuilt fan which is responsible for the air circulation.



The air drying equipment should be placed close to the area where dehumidification is required. In case of swimming pool it is placed at align of the water of under the ceiling. It is possible to place the equipment also at the other side of the wall.

The condensate always goes back to the swimming pool.

In a case of smaller swimming pools (household range) 2kW electric power is sufficient of removing 5l water in one our. That 2 kW electric energy because of closed air and cooling cycle heats the air and the water of the swimming pool.

The equipment can be extended by and electric battery or heating coil which is serving the necessary heat load to the area.

Ventilation and Air HandlingAir handling : Central air conditioning


Air conditioning is the system in which the equipment handles the temperature the humidity and the pressure of the internal place. The air conditioning system distributes and collects the air of the internal place, removes the polluted air and handles the indoor air qualityrequirements.

Central air conditioning system is applied in residential buildings, public and office buildings but also essential applications are industrial and agricultural applications.

If the air conditioning system design is based on the requirements of the occupancy it called comfort air conditioning. If the air conditioning system designs for industrial or agriculturalcases it called industrial air conditioning.

Heatingcoil (after heating)

Humidifyer


Outlet air


Air handling unit



Coolingcoil

Heatingcoil

Filter Faninlet air

Silencer

Ventilation and Air HandlingAir handling : Types of humidifiers


Stream generating pan: This type consists of an enclosed water tank, which is connected to the main air duct. High-temperature water coils or direct-fired gas or electrical elements heat the water in the tank. The tank water vaporizes, and the moisture is entrained into the air stream as it passes over the tank.

Steam jet: Steam generated from an external source positioned close to the unit is injected into the air-stream. It is essential that the steam supply is uncontaminated and odorless.

Air Washer: It consists of a chamber incorporating a water spray system, a collection tank, and an eliminator section. The air, in passing through the chamber, comes into intimate contact with the water, mass transfer of moisture into the air-stream occurs.

Heatingcoil (after heating)

Humidifyer


Outlet air


Air handling unit



Coolingcoil

Heatingcoil

Filter Faninlet air

Silencer

air handling

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