PARTES DE UN SISTEMA EÓLICO

With regard to the function and useful life of the con- tact fills, the fresh water should be of drinking quality and have a pH of between 5.0 and 8.0.

Solenoid valve

Overflow run off

Drain line Filter

Pump Min. water level Max. water level

Nozzles Inlet

Chamber Droplet separator

formed which later evaporate so that condensation will not occur in downstream components. Electric power is required for producing steam. The steam humidifier nor- mally also requires water treatment.

Summary

Air humidification can take place either by supp- lying steam to the air by means of a steam humi- difier or by letting the air come in contact with the surface of a liquid so that the water evapora- tes, so-called evaporative humidification. Evapo- rative humidifiers are available in two designs: contact humidifiers and nozzle humidifiers. Contact humidifiers

In contact humidifiers, water evaporates from wet, unheated humidifier fills. What drives the process is the difference in steam pressure be- tween the air near the surface of the water and the free air stream. The energy for evaporation is taken from the air. The temperature of the air then drops 2.5 °C per gram humidification.

The function of the contact fill is to form a large contact surface between the air and water. The material in the fills is aluminium, which has been hygroscopically treated to give it a wetting surface, or micro glass.

The surfaces are designed with a structure that steers the water toward the upstream side in

order to balance the condition that the air presses the water downstream. The function of the con- tact fill is to form a large contact surface between the air and water.

Steam humidifiers

In steam humidifier, steam is supplied to the air via so-called steam lances positioned in (the duct) the air stream. It is important that the air is not saturated with steam which would otherwise give rise to condensation in the ducts and cause hygienic problems. It is also important to provide sufficient distance from the steam lances to the nearest component in the system. Condensation will otherwise form on the component.

Nozzle humidifiers

Nozzle humidifiers have a chamber with a number of nozzles that spray fine jets of water upstream toward a dewatering fill. A robust pump generates a relatively high pressure in the nozzles that provides thin jets which break apart into droplets.

The most important reason why an air treatment system is controlled is to create a comfortable indoor climate. The room temperature and the extent to which a room is ventilated, i.e. a measure of the air change rate in the room, are the factors that affect indoor climate the most. Because of this must the air temperatur and air flow from the air handling unit be controlled.

Since we always want to minimize the amount of energy consumed by the air treatment system, the con- trol system must be designed to manage this task. It is also necessary to protect and maintain the air treat- ment system. This is why the controls have to be equip- ped with monitors and alarms.

In order to understand the content of the pages that fol- low, it will be of benefit to be familiar with the basics on how the components of an air handling unit are control- led and regulated.

To show this, we shall make use of a block diagram, which shows a closed-loop system, i.e. a system with feedback.

Some form of disturbance have an effect on the control object. A sensor (actual value sensor) reads the regula- ted quantity, such as temperature, transmitted from the system being controlled. This value, the actual value, is the value that comes from the component just now. The actual value is transmitted to a point of comparison in the system. A signal reprenting the required value be also comes to this point. If the sig- nals do not agree, an error signal is transmitted ahead to the controller which controls to the correct value.

How can we now translate this to describe what occurs in an air handling unit?

The variable to be controlled in this example is the temperature and the component to be controlled is the air heater. Temperature sensor GT1 (the actual value sensor) reads the temperature in the air just now (the actual value). The actual value is transmitted to con- troller RC1 which knows the set point, controls to the correct temperature and transmits a control signal to the valve actuator (SV1) which either opens or closes the hot water valve.

• General particulars on control • Dynamic properties/Time delay

In control systems

• Various types of controllers/control principles – PID control – Cascade control – On-off control – Multi-step control • Temperature control • Air flow/pressure control • Anti-frosting protection • Outdoor air compensation • Night-time heating • Night-time cooling

• CO2 compensation

• Alarms

• Communication

The chapter deals with the following

Actuating signal

Set point signal

Actual value signal

+

-

Actual value sensor

Controller Item being

controlled Disturbance Measurement signal Controlled variable ST1 GT5 SV1 CP1 TF1 PREMISES GT1 RC1 M M

To make it easier to see the how long it takes before the temperature changes, the system’s dead time, after the heating output has been increased; we dis- locate the curves in the chart. The figure below also shows the time constant which corresponds to how long it takes to reach 63% of the final value.

If we take a short time constant the process will be quick, however in most air treatment applications we want the process to be slow.